

Wave Energy Dissipation by Permeable and Impermeable Submerged Breakwaters


Pages :
26352645


Authors :
Yonguk Ryu,
Dongsoo Hur,
Sungboo Park,
Ho Hwan Chun,
Kwang Hyo Jung,
The purpose of this study was to investigate the effect of the porosity of a submerged breakwater on wave fields, including snapshots of the wave, velocity profiles of the water over the structure, and the kinetic energy of the wave. Twodimensional experiments were conducted for submerged trapezoidal breakwaters with impermeable and permeable layers in a twodimensional wave tank. The flow fields obtained by the particle image velocimetry (PIV) technique are presented to understand the flow characteristics due to the waves’ interactions with the submerged impermeable and permeable breakwaters, and these characteristics showed that the vertical velocity dominant flow occurred under the crest of the wave. In addition, the kinetic energies were compared for different porosities and wave conditions. The comparisons of the wave flow fields and kinetic energy distributions showed that the different pattern of the dissipated kinetic energy was dependent on the porosity. The dissipation of kinetic energy also was observed to increase as the wave period increased. The comparisons indicated that greater amounts of energy were dissipated for longer wave periods.





A Novel ExplicitImplicit Coupled Solution Method of SWE for Longterm River Meandering Process Induced by Dambreak


Pages :
26472660


Authors :
XiaoGang Zheng,
Jaan Hui Pu,
Ridong Chen,
Xingnian Liu,
Songdong Shao,
Large amount of sediment deposits in the reservoir area can cause dam break, which not only leads to an immeasurable loss to the society, but also the sediments from the reservoir can be transported to generate further problems in the downstream catchment. This study aims to investigate the shorttolong term sediment transport and channel meandering process under such a situation. A coupled explicitimplicit technique based on the EulerLagrangian method (ELM) is used to solve the hydrodynamic equations, in which both the small and large time steps are used separately for the fluid and sediment marching. The main feature of the model is the use of the CharacteristicBased Split (CBS) method for the local time step iteration to correct the ELM traced lines. Based on the solved flow field, a standard Total Variation Diminishing (TVD) finite volume scheme is applied to solve the sediment transportation equation. The proposed model is first validated by a benchmark dambreak water flow experiment to validate the efficiency and accuracy of ELM modelling capability. Then an idealized engineering dambreak flow is used to investigate the longterm downstream channel meandering process with nonuniform sediment transport. The results showed that both the hydrodynamic and morphologic features have been well predicted by the proposed coupled model.





Numerical Predictions of Pressure Fluctuations in a Model Pump Turbine with Small Guide Vane Opening based on Partial Averaged Navier Stokes Approach


Pages :
26612669


Authors :
J. T. Liu,
Yulin Wu,
Yong Li,
Comparing with conventional hydraulic turbine (e.g. Francis turbine), pump turbine shows significant unstable characteristics because its design is a compromise between a pump and a turbine. In present paper, unsteady flow and pressure fluctuations within a model pump turbine are numerically studied through Partial Averaged Navier Stokes (PANS) approach. The PANS approach is fulfilled through modification of RNG kε turbulence model in a commercial CFD code. Pump turbine operating at different conditions with guide vanes opening angle 6° is simulated. Results revealed that the predictions of performance and relative peaktopeak amplitude by PANS approach agree well with the experimental data. Velocity, vortex and turbulent kinetic energy at the inlet of runner are very large near the pressure surface and the blade leading edge, leading to high pressure fluctuations within the vaneless area otablef pump turbine. The maximum amplitude of pressure fluctuation occurs when the pump turbines run at runaway point. The primary dominant frequency of pressure fluctuation is the runner blade passing frequency in the vaneless space. The above high pressure fluctuations should be avoided during the design of pump turbines especially those operating at highhead condition.





Influence of Size and Location of a Thin Baffle on Natural Convection in a Vertical Annular Enclosure


Pages :
26712684


Authors :
M. Sankar,
B. V. Pushpa,
B. M. R. Prasanna,
Y. Do,
This article reports the numerical study of natural convection in a differentially heated cylindrical annular enclosure with a thin baffle attached to inner wall. The inner and outer walls of the annulus are respectively maintained at higher and lower temperatures, whereas the top and bottom walls are thermally insulated. Using an implicit finite difference technique, the effects of baffle size and location on natural convection has been investigated for different Rayleigh numbers and radius ratios by fixing the Prandtl number at 0.707. Through the detailed numerical simulations, we have successfully captured the important effects of baffle size and location on the flow pattern and heat transfer rate. It has been found that the size and location of baffle modify the flow pattern and heat transfer rate in a completely different conducts. The numerical results corroborates that the average heat transfer rate increases with the Rayleigh number, radius ratio, baffle position; but decreases with baffle length. Further, it has been observed that it is possible to enhance or suppress the flow circulation and heat transfer rates by a proper choice of baffle size and location, and Rayleigh number.





Evaluation Study of PressureStrain Correlation Models in Compressible Flow


Pages :
26852693


Authors :
Aicha Hanafi,
H. Khlifi,
This paper is devoted to the secondorder closure for compressible turbulent flows with special attention paid to modeling the pressurestrain correlation appearing in the Reynolds stress equation. This term appears as the main one responsible for the changes of the turbulence structures that arise from structural compressibility effects. The structure of the gradient Mach number is similar to that of turbulence, therefore this parameter may be appropriate to study the changes in turbulence structures that arise from structural compressibility effects. Thus, the incompressible model (LRR) of the pressurestrain correlation and its corrected form by using the turbulent Mach number, fail to correctly evaluate the compressibility effects at high shear flow. An extension of the widely used incompressible model (LRR) on compressible homogeneous shear flow is the major aim of the present work. From this extension the standard coefficients Ci became a function of the compressibility parameters (the turbulent Mach number and the gradient Mach number). Application of the model on compressible homogeneous shear flow by considering various initial conditions shows reasonable agreement with the DNS results of Sarkar. The ability of the models to predict the equilibrium states for the flow in cases A1 and A4 from DNS results of Sarkar is examined, the results appear to be very encouraging. Thus, both parameters Mt and Mg should be used to model significant structural compressibility effects at highspeed shear flow.





Investigation of the Rotor Wake of Horizontal Axis Wind Turbine under Yawed Condition


Pages :
26952705


Authors :
B. Noura,
I. Dobrev,
R. Kerfah,
F. Massouh,
S. Khelladi,
The wake and the lack of existing velocity behind the wind turbine affect the energy production and the mechanical integrity of wind turbines downstream in the wind farms. This paper presents an investigation of the unsteady flow around a wind turbine under yawed condition. The simulations and experimental measures are made for the yaw angle rotor 30° and 0°. The wind velocity is 9.3 m/s and the rotation velocity rotor of the wind turbine in 1300, 1500 and 1800 rpm. The wind turbine rotor which is modeled is of a commercial wind turbine i.e. Rutland 503. The approach Improved Delayed Detached Eddy Simulation (IDDES) based on the SST turbulence model is used in the modeling of the flow. The solutions are obtained by using the solver which uses finite volume method. The particle image velocimetry (PIV) method is used in wind tunnel measurements in the experimental laboratory of the ENSAM ParisTech. The yawed downstream wake of the rotor is compared with that obtained by the experimental measurements. The results illustrate perfectly the development of the near and far wake of the rotor operation. It is observed that the upstream wind turbine yawed will have a positive impact on the power of the downstream turbine due the distance reduction of the downstream wake of the wind turbine. However the power losses are important for yawed wind turbine when compared with the wind turbine without yaw. The improved understanding of the unsteady environmental of the Horizontal Axis wind Turbine allows optimizing wind turbine structures and the number of wind turbines in wind farms.





A SemiAnalytical Solution for a Porous Channel Flow of a NonNewtonian Fluid


Pages :
27072716


Authors :
P. Vimala,
P. Blessie Omega,
A theoretical study of steady laminar twodimensional flow of a nonNewtonian fluid in a parallel porous channel with variable permeable walls is carried out. Solution by Differential Transform Method (DTM) is obtained and the flow behavior is studied. The nonNewtonian fluid considered for the study is couple stress fluid. Thus, in addition to the effects of inertia and permeabilities on the flow, the couple stress effects are also analyzed. Results are presented and comparisons are made between the behaviour of Newtonian and nonNewtonian fluids.





CFD Modeling of Wing and Body of an AUV for Estimation of Hydrodynamic Coefficients


Pages :
27172729


Authors :
N.M Nouri,
K. Mostafapour,
S. H. Hassanpour,
Coefficients or hydrodynamic derivatives of autonomous underwater vehicles (AUVs) play a key role in their design and maneuverability. Using a suitable method to estimate these coefficients serves as a time efficient approach to raise the achievable precision in the design and control of AUVs. This paper estimates hydrodynamic derivatives of an AUV using computational fluid dynamics (CFD) for the wings and body. CFD modeling was performed to simulate captive model tests including straight line and planar motion mechanism (PMM). In such runs, the process was implemented separately for the wing and body. Experimental tests for the same AUV in the water tunnel were carried out for CFD validation. Comparing the numerical results to the experimental data, it was shown that the modeling method is able to estimate these coefficients at reasonable accuracy. The proposed modeling method was proved to be efficient in estimating hydrodynamic derivatives and hence can reduce associated computational costs with the process of detail design of AUVs.





Large Eddy Simulation of the FlowField around Road Vehicle Subjected to Pitching Motion


Pages :
27312741


Authors :
Z. Q. Gu,
T. M. Huang,
Z. Chen,
Y. Q. Zong,
W. Zeng,
In order to study the aerodynamic responses of a vehicle pitching around its front wheel axle, large eddy simulation (LES) is used to investigate the flowfield around road vehicle. The numerical method is validated by 1/3scale wind tunnel model on steady state. The LES results keep good agreement with the wind tunnel data. Furthermore, LES is applied to simulate the sinusoidalpitching motion of vehicle body with frequency 10Hz. It can be found that the aerodynamic force coefficient and flow field changed periodically when the vehicle body takes periodically motion, whose results are completely different from the quasisteady simulation results. When vehicle body suddenly changes direction, the hysteresis effects of the flow is clearly shown through investigating the transient flow field, aerodynamics force coefficient and pressure coefficient. The hysteresis effects of the transient flow field is also studied by vortices visualization technical, and the transient flow field from space and time is further understood.





Experimental Investigation of the Free Surface Effect on the Conical TaylorCouette Flow System


Pages :
27432751


Authors :
F. Yahi,
Y. Hamnoune,
A. Bouabdallah,
S. Lecheheb,
F. Mokhtari,
The aim of this work is to highlight the critical thresholds corresponding to the onset of different instabilities considered in the flow between two vertical coaxial cones with and without free surface. The inner cone is rotating and the outer one is maintained at rest. Both cones have the same apex angle Φ =12° giving a constant annular gap δ =d/R1max. The height of the fluid column is H=155mm and It can be progressively decreased for each studied case of the flow system. Two kinds of configurations are studied, small and large gap. The working fluid is assumed as Newtonian and having constant properties like density and viscosity within the range of the required experimental conditions. By means of visualization technique of the flow we have been able to show the different transition modes occurring in the conical flow system according to the aspect ratio and then the induced action of the free surface which introduces a delay in the onset of different instability modes. The obtained results in term of features and stability of the flow are compared to those of Wimmer and NouiMehidi.





Effect of Impeller Clearance and Liquid Level on Critical Impeller Speed in an Agitated Vessel using Different Axial and Radial Impellers


Pages :
27532761


Authors :
Chitra Devarajulu,
Muruganandam Loganathan,
The effect of impeller clearance and liquid level on the critical impeller speed (Njs) for various radial and axial flow impellers in 0.29 m ID agitated vessel has been studied. Five types of radial impellers: Rushton turbine (RT), Straight blade (SB), Curved blade (CB), Curved blade with disc (CBWD) and R130 impeller and four types of axial impellers: Rushton turbine 45o angle (RT 45), Pitched blade (PBT), A320 and HE3 impeller were used. Tap water and resin particle of 0.506 mm were used as liquid and solid phases, respectively. The impeller clearance to vessel diameter (T) was varied between 0.17 and 0.41. The liquid level (H) was also varied as H/T=0.5, H/T=0.75 and H/T=1. The R130 impeller and A320 impeller was found to be more efficient among radial and axial impellers respectively. A new expression for Zwietering constant ‘S’ was developed to predict critical impeller speed, considering impeller clearance and liquid level for all the impellers. The results obtained here show that the ‘S’ values increase with increase in clearance, and decrease with liquid level for all impellers and it also depends on the type of impeller.





Stability Analysis of Twin Axial Groove Hybrid Journal Bearing


Pages :
27632768


Authors :
V. K. Dwivedi,
Satish Chand,
K. N. Pandey,
Stability of rigid rotor supported on hybrid journal bearing with twin axial groove has been investigated using stiffness and damping coefficients of the bearings. In this paper the stability analysis of twin axial groove bearing is determined in different fluid flow regime. Non linear journal centre trajectories are drawn for small amplitude oscillations of the journal centre about its steady state position. It was observed that turbulence decreases 10 to 12 percent the stability margin of twin grooved journal bearings.





Effect of SideWalls on FlappingWing PowerGeneration: an Experimental Study


Pages :
27692779


Authors :
Ferhat Karakas,
Idil Fenercioglu,
Effect of constrained flow is investigated experimentally for a flapping foil powergenerator. The flow structures around and in the near wake of a flat plate placed between two side walls are captured via PIV technique with simultaneous direct force measurements in uniform flow at Re = 10 000. The rectangular flat plate oscillates with periodic nonsinusoidal pitching and plunging motions about its 0.44 chord position with stroke reversal times (TR) of 0.1 (rapid reversal) to 0.5 (sinusoidal reversal), phase angles of = 90° and 110°, plunge amplitude of 1.05 chords and pitch amplitude of 73° at a constant reduced frequency of k = 0.8. The nondimensional distances between the side walls and the oscillating flat plate are dw = 0.1, 0.5 and 1.0. Airfoil rotation speed dictates the strength, evolution and timing of shedding of leading and trailing edge vortices; as the stroke reversal time is decreased, earlier shedding of stronger vortices are observed. Increasing the phase angle between the pitching and plunging motions decreases the power generation efficiency for all cases. The highest power extraction coefficient is acquired for the nonsinusoidal case of TR = 0.4 in free flow. Optimum choice of sidewall distance improves power generation of flapping foils compared to free flow performance, up to 6.52% increase in efficiency is observed for the nonsinusoidal case TR = 0.4 with dw = 0.5, with remarkable enhancements for the sinusoidal case; 27.85% increase is observed with dw = 0.5 and 43.50% increase with dw = 1.0 where both cases outperform the highest power generation efficiency of the finite flat plate with nonsinusoidal flapping motion.





Applying Different Strategies within OpenFOAM to Investigate the Effects of Breakup and Collision Model on the Spray and inCylinder Gas Mixture Attribute


Pages :
27812790


Authors :
P. Ghadimi,
Mahdi Yousefifard,
Hashem Nowruzi,
In the current study, a 3D numerical simulation of twophase flow has been conducted in a direct injection CI engine using the EularianLagrangian approach and a new breakup model. The newly modified breakup scheme has been implemented for simulating the ultrahigh pressure diesel injection. The effects of droplet breakup and collision model on the spray and incylinder gas characteristics have been examined using the open source code OpenFOAM. Spray penetration and cone angle are investigated as spray properties and surrounding gas motion are studied by incylinder gas velocity and pressure distribution for nonevaporating conditions. In addition, vapor penetration of the evaporating spray is presented to study the effects of current scheme on the evaporating condition. The continuous field is described by RANS equations and dynamics of the dispersed droplet is modeled by Lagrangian tracking scheme. Results of the proposed modified KHRT model are compared against other default methods in OpenFOAM and favorable agreement is achieved. Robustness and accuracy of different breakup schemes and collision models are also verified using the published experimental data. It is demonstrated that the proposed breakup scheme and Nordin collision model display very accurate results in the case of ultrahigh pressure injection.





Effects of Variable Viscosity on PowerLaw Fluids over a Permeable Moving Surface with Slip Velocity in the Presence of Heat Generation and Suction


Pages :
27912801


Authors :
Kannan Thangavelu,
M. B. K. Moorthy,
In this paper, a numerical investigation on the effects of variable viscosity, slip velocity and heat generation or absorption on powerlaw fluids with heat and mass transfer over a moving permeable surface is carried out. The transformation of the governing boundary layer equations into ordinary differential equations has been performed by applying similarity transformations. The transformed governing equations are numerically solved by using MATLAB BVP solver bvp4c. The obtained results are presented graphically and discussed for various values of the viscosity parameter, the slip parameter, the heat generation or absorption parameter, the Eckert number and Lewis number. The result shows that, the variable viscosity parameter , it is confirmed that the local skinfriction coefficient decreases while heat and mass transfer rates increases. The heat and mass transfer rates increases rapidly on increasing the Prandtl number. The rate of mass transfer is rapidly increased when the Lewis number increased.





Flow of a Second Grade Fluid through Constricted Tube using Integral Method


Pages :
28032812


Authors :
A M Siddiqui,
N. Z. Khan,
Muhammad Afzal Rana,
Tahira Haroon,
The steady flow of a second grade fluid through constricted tube for mild stenosis is modeled and analyzed theoretically. The governing equations are simplified by implying an orderofmagnitude analysis. Based on Karman Pohlhausen procedure polynomial solution for velocity profile is presented. Expressions for pressure gradient, shear stress, separation and reattachment points are also calculated. The effects of nondimensional parameters emerging in the model on the velocity profile, shear stress, pressure gradient are discussed and depicted graphically. The effect of nonNewtonian parameter on velocity profile, wall shear stress and pressure gradient is also analyzed. It is found that the Reynolds number strongly effect the wall shear stress, separation and reattachment points.





Mathematical Model of a Constructal Coanda Effect Nozzle


Pages :
28132822


Authors :
Michele Trancossi,
Jill Stewart,
Maharshi Subash,
Diego Angeli,
This paper analyses the ACHEON Coanda effect nozzle for aircraft propulsion, based on the dynamic equilibrium of two jet streams. The ACHEON concept, and, in particular, the HOMER nozzle, which is its main component, are presented, together with the literature milestones from which the idea originally stems. A subsystem analysis inspired by the principles of Constructal Theory is presented for the current architecture. A mathematical model of a 2D case of the system is developed, focusing on the combined effect of the mixing of the two streams and the Coanda adhesion over a convex surface. A validation of the model is also reported, based on 2D CFD analyses, under the hypothesis of incompressible flow. Results highlight that, in spite of its relative simplicity, the model produces accurate results.





Conjugate Effect of Joule Heating and Unsteady MHD Natural Convection in a Differentially Heated Skewed Porous Cavity Saturated by Cuwater Nanofluid


Pages :
28232836


Authors :
Omid Ghaffarpasand,
Conjugate effect of Joule heating and Lorentz force in a differentially skewed porous liddriven cavity saturated by Cuwater nanofluid have been examined numerically. A coordinate transformation is utilized to transform the physical domain to the computational domain in an orthogonal coordinate. The DarcyBrinkmanForchheimer model with Boussinesq approximation is adopted and the developed mathematical model is solved by finite volume method based on SIMPLE algorithm. The influence of porous medium permeability (Darcy number), Joule heating (Eckert number), nanoparticle volume fraction, as well as inclination angle of skewed cavity on fluid flow and heat transfer characteristics are studied. The entropy generation and Bejan number also evaluated to examine thermodynamic optimization of the MHD mixed convection in porous media. The results have been presented in terms of streamlines, average Nusselt number, entropy generation, and Bejan number for a wide range of key parameters.





Capillary Rise of Magnetohydrodynamics Liquid into Deformable Porous Material


Pages :
28372843


Authors :
Javed Siddique,
Abdul Kara,
We have developed a mathematical model for capillary rise of magnetohydrodynamic fluids. The liquid starts to imbibe because of capillary suction in an undeformed and initially dry spongelike porous material. The driving force in our model is a pressure gradient across the evolving porous material that induces a stress gradient which in turn causes deformation that is characterized by a variable solid fraction. The problem is formulated as a non–linear moving boundary problem which we solve using the method of lines approach after transforming to a fixed computational domain. The summary of our finding includes a notable reduction in capillary rise and a decrease in solid deformation due to magnetic effects.





Inﬂuence of Magnetic Field on Fingering Instability in a Porous Medium with CrossDiffusion Effect: a Thermal Nonequilibrium Approach


Pages :
28452853


Authors :
Atul Kumar Srivastava,
B. S. Bhadauria,
The purpose of this paper is to investigate the thermal instability problem under the inﬂuence of three diffusing components on ﬂuid saturated horizontal porous media under local thermal nonequilibrium effect. These three components are vertical magnetic ﬁeld, solute and heat. We considered an electrically conducting two components ﬂuid and anisotropic porous medium. The physical system is heated and salted from above. Flow in the porous medium is characterized by Darcy model, whereas the ﬂuid and solid phases are not in local thermodynamic equilibrium (LTNE). Linear stability analysis is used to calculate critical DarcyRayleigh number and corresponding wave number for onset of stationary convection. The study is based on mainly four controlling parameters, DarcyChandrasekhar number (Q), dimensionless interphase heat transfer coefﬁcient (H), Soret (Sr) and Dufour (Du) crossdiffusion parameters, among several. We illustrated the effects of these parameters on thermal instability and found parameters may have stabilizing or destabilizing effects, thus may advance or delay the onset of convection. Various comparative studies are also presented between different cases and conditions, such as for anisotropic and isotropic cases, crossdiffusion and without crossdiffusion cases and for different values of Sr and Du.





Effect of Radial Magnetic Field on Free Convective Flow over Ramped Velocity Moving Vertical Cylinder with Ramped Type Temperature and Concentration


Pages :
28552864


Authors :
V. Vanita,
Anand Kumar,
A numerical study has been performed to analyze the effect of radial magnetic ﬁeld on free convective ﬂow of an electrically conducting and viscous incompressible ﬂuid over the ramped moving vertical cylinder with ramped type temperature and concentration considered at the surface of vertical cylinder. The governing partial differential equations which describe the ﬂow formation have been solved numerically by using implicit ﬁnite difference method of CrankNicolson type. The simulation results of the considered model have been shown graphically. One of the interesting result of our analysis is that the local as well as average skinfriction, Nusselt number and Sherwood number have increasing tendency in time interval (0,1), thereafter these quantities decrease. We have also compared the case of ramped type boundary conditions with that of constant boundary conditions with help of table. The advantage of taking ramped type boundary conditions is that initial heat transfer rate and mass transfer rate are minimum in this case.





Phenomenological Features of Turbulent Hydrodynamics in Sparsely Vegetated Open Channel Flow


Pages :
28652875


Authors :
Soumen Maji,
Debasish Pal,
Prashanth Reddy Hanmaiahgari,
Jaan Hui Pu,
The present study investigates the turbulent hydrodynamics in an open channel ﬂow with an emergent and sparse vegetation patch placed in the middle of the channel. The dimensions of the rigid vegetation patch are 81 cm long and 24 cm wide and it is prepared by a 7× 10 array of uniform acrylic cylinders by maintaining 9 cm and 4 cm spacing between centers of two consecutive cylinders along streamwise and lateral directions respectively. From the leading edge of the patch, the observed nature of time averaged ﬂow velocities along streamwise, lateral and vertical directions is not consistent up to half length of the patch; however the velocity proﬁles develop a uniform behavior after that length. In the interior of the patch, the magnitude of vertical normal stress is small in comparison to the magnitudes of streamwise and lateral normal stresses. The magnitude of Reynolds shear stress proﬁles decreases with increasing downstream length from the leading edge of the vegetation patch and the trend continues even in the wake region downstream of the trailing edge. The increased magnitude of turbulent kinetic energy proﬁles is noticed from leading edge up to a certain length inside the patch; however its value decreases with further increasing downstream distance. A new mathematical model is proposed to predict time averaged streamwise velocity inside the sparse vegetation patch and the proposed model shows good agreement with the experimental data.





Chemical Reaction Effects on an Unsteady MHD Mixed Convective and Radiative Boundary Layer Flow over a Circular Cylinder


Pages :
28772885


Authors :
T. Poornima,
P. Sreenivasulu,
N. Bhaskar Reddy,
A mathematical model is presented for an optically dense fluid past an isothermal circular cylinder with chemical reaction taking place in it. A constant, static, magnetic field is applied transverse to the cylinder surface. The cylinder surface is maintained at a constant temperature. New variables are introduced to transform the complex geometry into a simple shape and the boundary layer conservation equations, which are parabolic in nature, are normalized into nonsimilar form and then solved numerically with the welltested, efficient, implicit, CrankNicolson finite difference scheme. Numerical computations are made and the effects of the various material parameters on the velocity, temperature and concentration as well as the surface skin friction and surface heat and mass transfer rates are illustrated graphs and tables. Increasing magnetohydrodynamic body force parameter (M) is found to decelerate the flow but enhance temperatures. Thermal radiation is seen to reduce both velocity and temperature in the boundary layer. Local Nusselt number is also found to be enhanced with increasing radiation parameter.





Effect of Perpendicular Magnetic Field on Chaos in a Rotating Cavity Heated from Side


Pages :
28872897


Authors :
R. Prasad,
A. K. Singh,
This paper presents chaotic behavior due to an applied perpendicular magnetic field on a rotating cavity heated from side using the theory of dynamical system. The solution to the nonlinear problem is obtained by using a truncated Galerkin method to find a set of ordinary differential equation for the time evolution of the Galerkin amplitudes. The system of differential equations is solved by using the fourthorder Runge Kutta method. Below a certain critical value of the scaled Rayleigh number the unique motionless conduction solution is obtained. At slightly supercritical values of scaled Rayleigh numbers transition to chaotic solutions occurs via a Hopf bifurcation. The chaotic behaviour can be obtained faster for decreasing Hartmann number as well as increasing scaled Rayleigh number. Also variation in Nusselt number increases with increasing scaled Rayleigh number and decreasing Hartmann number.





Hydrodynamics of an Extinct Amphibian


Pages :
28992903


Authors :
B. W. Skews,
The Paleozoic amphibia known as Diplocaulus, of the order Nectridia, are characterized by long tabular horns similar in planform to the wings of a modern jet airliner. Previous research on the hydrodynamics of the head were established from wind tunnel tests but with a ﬁxed body position placed at zero incidence. The current paper examines the hydrodynamics and stability if both the head and body change incidence, in order to obtain an improved understanding of the overall hydrodynamics. It is found that the conditions would result in unstable motion indicating a high level of maneuverability. Under certain conditions of head and body orientation the situation is one of static equilibrium, assuming the drag is countered by the thrust produced by the tail. Assumptions are made regarding the densities of the body and head in order to determine buoyancy effects.





Parametric Study and Optimization of Ceiling Fan Blades for Improved Aerodynamic Performance


Pages :
29052916


Authors :
Ehsan Adeeb,
Adnan Maqsood,
Ammar Mushtaq,
Chang Hyun Sohn,
This paper includes parametric study and optimization of nonlinear ceiling fan blades by combining the techniques of Design of Experiments (DOE), Response Surface Methods (RSM) and Computational Fluid Dynamics (CFD). Specifically, the nonlinear (elliptical) planform shape of ceiling fan blade is investigated in conjunction with blade tip width, root and tip angle of attack. Sixteen cases are designed for three blade ceiling fan using two level full factorial model. The flow field is modeled using ReynoldsAveragedNavierStokes approach. The performance variables used to formulate a multiobjective optimization problem are volumetric flow rate, torque and energy efficiency. Response Surface Method is used to generate the optimized design for nonlinear ceiling fan blade profile. The results reveal that the interactions between the design variables play a significant role in determining the performance. It is concluded that the nonlinear forward sweep has a moderate effect on response parameters.





Comparison of Five TwoEquation Turbulence Models for Calculation of Flow in 90° Curved Rectangular Ducts


Pages :
29172931


Authors :
Kun Ma,
Huanxin Lai,
This paper presents a comparative study of five most widely used twoequation turbulence models in predicting the developing flows in two 90° curved rectangular ducts. These include the standard kε model, the shear stress transport kω model, and three lowReynolds number kε models by Jones and Launder, Launder and Sharma, and Nagano and Hishida, respectively. The computational time for convergent solutions, streamwise and secondary velocities, pressure distributions as well as the Reynoldsaveraged turbulence quantities resolved by these models are compared and validated against available experimental data. The purpose of this paper are to provide a detailed comparative verification for applying the five most widely used twoequation turbulence models to predicting curved rectangular duct flows, which are a kind of proto type flows in fluids engineering, and to provide a reference for the selection of turbulence models in predicting such flows in industrial applications.





Performance Enhancement of a LowPressure Ratio Centrifugal Compressor Stage with a Rotating Vaneless Diffuser by Impeller Disk Extended Shrouds


Pages :
29332947


Authors :
S. Seralathan,
D. G. Roy Chowdhury,
Numerical simulations have been carried out to examine the performance and flow parameters of forced rotating vaneless diffuser obtained by the extension of impeller disks of a lowpressure ratio shrouded type centrifugal compressor stage with diffuser diameter ratio 1.40. Four different levels of shroud extensions (i.e., impeller disks alone) forming the rotating vaneless diffusers are analyzed at four different flow coefficients. The extension of impeller disks alone by 40% of impeller exit diameter leads to a fully forced rotating vaneless diffuser thereby replacing the existing stationary vaneless diffuser. The comparative studies are performed using the same impeller with a stationary vaneless diffuser also having a diffuser diameter ratio of 1.40. Static pressure rise in ES40 is found to be higher than SVD by around 9.84% at design flow coefficient and also at above offdesign flow rates. Energy coefficient is highest for ES40, followed by ES30 compared to SVD. For ES40, the static pressure recovery coefficient also is higher compared to SVD. The efficiency of ES40 is lesser by around 5.40% to 3.43% compared to SVD, at design as well as at above offdesign flow coefficients. The stagnation pressure losses for ES40 drastically reduced compared to SVD. The comparison of stagnation pressure contours and absolute velocity contours near the hub and shroud walls of ES40 and SVD configurations shows that the rotating diffuser walls as in ES40 causes further addition of energy to the fluid. This adds up the kinetic energy level of the fluid which due to better diffusion, results in gain of static pressure rise. Moreover, there is a net increase in stagnation pressure distribution at the exit of diffuser due to rotating vaneless diffuser. Also, the presence of a fully rotating vaneless diffuser (ES40) smooth out the distorted entry flow profiles, thereby improving the performance of the centrifugal compressor stage.





Variational Approach of Marangoni Mixed Convection Boundary Layer Flow with Pade Technique


Pages :
29492955


Authors :
Murat Gubes,
Galip Oturanc,
In this paper, Variational Iteration method with combining Pade approximation (Modified Variational Iteration MethodMVIM) is performed to Marangoni convection flow over the surface with buoyancy effects which is occurred gravity and external pressure. After the appropriate transformation of equations, we get the dimensionless form to solve numerically with modified variational iteration method. We compare the our results with wellknown asymptotic expansion method used by Zhang Yan and Zheng Liancun and also compare with Fourth order Runge Kutta solution which are presented in tables. Very efficient and accurate results are obtained with presented method.





Contribution to the Experimental and Numerical Dynamic Study of a Turbulent Jet Issued from Lobed Diffuser


Pages :
29572967


Authors :
A. Bennia,
L. Loukarfi,
A. Khelil,
S. Mohamadi,
M. Braikia,
H. Naji,
In the present work, we are interested to the experimental and numerical study of the free turbulent lobed jet, used in residential heating and air conditioning. The objective of our study is the improvement of the diffusion performance of the ventilation driving air flow, in the occupancy zone. The experiments have been conducted in a room where the dimensions enables a better execution in the conditions of free and hot vertical jet at unfavorable pushing forces. The installation contains a hot air blowing diffuser oriented from top to bottom. The velocities of the flow were measured by a multifunctional thermoanemometer. The probe is supported by a stem guided vertically and horizontally in order to sweep a maximum space. Experimentally, we measured the axial and radial velocity field. The dynamics field analysis, show that in the potential core region, the dynamic profiles are more spread at the principal plane and this is due to the widening of the lobes’ opening. While, in the transition zone and in the region where the flow is fully developed, these profiles are not influenced by the type of plane and then the jet will be similar to the circular one. Numerically, we used the commercial software Fluent. The obtained numerical results with turbulence method, (RNG kε), were in good accordance with the experimental one.





Effect of Bottom Wall Heating on the Turbulent Fluid Flow in an Asymmetric Rectangular Diffuser: an Experimental Study


Pages :
29692979


Authors :
Somnath Bhattacharjee,
Arindam Mandal,
Rabin Debnath,
Snehamoy Majumder,
Debasish Roy,
Turbulent fluid flow and heat transfer in an asymmetric diffuser are important in the context of the power plant engineering such as gas turbine, aircraft propulsion systems, hydraulic turbine equipment etc. In the present study, an experimental investigation on the forced convective heat transfer considering turbulent air flow in an asymmetric rectangular diffuser duct has been done. The experimental setup considered for the analysis consists of a diffuser at different bottom wall temperatures and inlet conditions. The air enters into the diffuser at a room temperature and flows steadily under turbulent conditions undergoing thermal boundary layer development within the diffuser. Efforts have been focused to determine the effects of bottom wall heating on the recirculation bubble strength, thermal boundary layer, velocity fields, temperature profiles etc. The distribution of the local average Nusselt number and skin friction factor in the whole flow fields have been critically examined to identify the significance of bottom wall heating effects on the overall heat transfer rates.





Numerical Simulation of Steady Supercavitating Flows


Pages :
29812992


Authors :
Ali Jafarian,
AhmadReza Pishevar,
In this research, the Supercavitation phenomenon in compressible liquid flows is simulated. The onefluid method based on a new exact twophase Riemann solver is used for modeling. The cavitation is considered as an isothermal process and a consistent equation of state with the physical behavior of the water is used. High speed flow of water over a cylinder and a projectile are simulated and the results are compared with the previous numerical and experimental results. The cavitation bubble profile in both cases agrees well with the previous experimental results reported in the literature. As the result shows, coupling the twophase Riemann solver with the considered EOS prepares a robust method for simulating the compressible fluid flow with cavitation which can undertake the whole physical behavior of water in a supercavitation process. Furthermore, the influence of the cavitator head and the flow speed on the supercavitation bubble is explored. The results show that cavitators with sharper head results in a smaller supercavitating bubble. Increasing the flow speed beyond a specific limit does not have any significant effect on the cavitation bubble and slightly increases the bubble size.





Effect of Advance Ratio and Blade Planform on the Propeller Performance of a High Altitude Airship


Pages :
29933000


Authors :
Zhenchen Liu,
Peiqing Liu,
Qiulin Qu,
Tianxiang Hu,
Experimental investigations on the influences of Reynolds number, blade planform and advance ratio on the aerodynamic performance are carried. Different from conventional aircraft propellers, the HAA propellers are characterized by low Reynolds number, large thrust requirement and low advance ratio. At the moment, the theoretical guidance and industrial experience in designing such propellers are still lacked. In the present study, the influence of Reynolds number is firstly studied via tests of a propeller at different rotational speeds. It is found that, for the propeller with airfoil S1223, the influence of Reynolds number is negligible as Re0.7 > 1.2 × 105 ( ). The tests regarding the influences of blade planform and advance ratio on propeller performance are carried in the condition of Re0.7 ≥ 1.5 × 105. The results show that, when advance ratio is below 0.8, the blade with narrow tip is favorable to the propulsive efficiency. Hence, it is suggested that the blade with narrow tip should be adopted by the large thrust and small advance ratio HAA propellers. For HAA propellers with advance ratio greater than 0.8, the propulsive efficiency can be benefitted by increasing the blade tip width. Hence, the blade with wide tip is more suitable in this application.





Combination between the Inclinations of the Enclosure and the Magnetic Field Orientation on the Oscillatory Natural Convection


Pages :
30013011


Authors :
A. Atia,
S. Bouabdallah,
B. Ghernaout,
In this paper, we study the combination between the inclinations of the enclosure and the magnetic field orientation on the oscillatory natural convection. For this, a cylindrical enclosure filled with electrically conducting fluid, has an aspect ratio equal to 2, and subjected to a vertical temperature gradient and different uniform magnetic field orientations were considered. The finite volume method is used to discretize the equations of continuity, momentum and energy. Our computer program based on the SIMPLER Algorithm has a good agreement with available experimental and numerical results. The timedependent flow and temperature field are presented in oscillatory state, for different cases: inclination of the cylinder, under the effect of magnetic field in different orientations (δ = 0°, 30°, 45° and 90°) and the combination between them. The results are presented at various inclinations of the cylinder (φ = 0°, 30° and 45°), and the Hartmann numbers Ha ≤ 50. The stability diagrams of the dependence between the complicated situations with the value of the critical Grashof number Grcr and corresponding frequency Frcr, are established according to the numerical results of this investigation. The combination between the studied state has a significant effect on the stabilization of the convective flow, and shows that the best stabilization of oscillatory natural convection is obtained at the inclination of the cylinder φ = 30°, and the applied of radial magnetic field (δ = 0°).





Numerical Investigation of the Effect of Corner Radius on Forced Oscillating Square Cylinder


Pages :
30133022


Authors :
Sajjad Miran,
Chang Hyun Sohn,
The purpose of this work is to numerically visualize the flow past forced oscillating square cylinder and investigate the effect of corner radius on flow induced forces. The finite volume code was applied to simulate the two dimensional flow past forced oscillating square cylinder with different radius to diameter ratios, (R/D = 0 referring to a square cylinder with sharp edges and R/D = 0.5 as a circular cylinder). The near wake of a square section cylinder with an increment of R/D = 0.1 was studied as the body undergoes a complete oscillatory cycle at lockin condition, F = fe / fs = 1 (where fe is the excitation frequency and fs is the vortex shedding frequency for the stationary cylinder). The computational model was validated for flow past oscillating cylinder with R/D = 0.5 at frequency ratios F = 0.5, 1.0 and 1.50, using as the lockin and lockout limits and the results shown good agreement. It was observed that computed value of Strouhal Number is nearly same for both stationary and oscillation case and a similar trend was observed, as R/D ratio increases. However, the results obtained from oscillation cylinder cases show the significant increase in root mean square value of lift coefficient (CL,RMS) and mean drag coefficient (CD) as compared to the stationary cylinder. Finally, It was found that the percentage increase of CL,RMS is higher than CD in force oscillating condition for R/D = 0, whereas both values decreases with the increase of R/D.





Study of Free Surface Flows in Rectangular Channel over Rough Beds


Pages :
30233031


Authors :
S. H. Talbi,
A. Soualmia,
L. Cassan,
L. Masbernat,
This paper presents the results of an experimental and numerical study of fully developed flow in a straight rectangular open channel over rough beds. Conical ribs were placed on the flume bottom to simulate different bed roughness conditions. Acoustic Doppler Velocimetry (ADV) measurements were made to obtain the velocity components profiles as well as the Reynolds stress profiles, at various locations. The experimental results are validated by simulations using an algebraic stress model. These investigations could be useful for researches in the field of sediment transport, bank protection, etc.





Numerical Simulation of Coolant Temperature Rise by Copper Metal foam Insert in Watercooled AirKerosene Combustion Gas Heated Cooling Channel


Pages :
30333043


Authors :
J. B. Ralphin Rose,
S. K. George,
K. Rashid,
In the present article, the application of copper metal foam in the cooling channels of a water cooled airkerosene combustion gas heated test bench model that partially recreates a section of liquid rocket motor cooling system is numerically simulated. It helps to study the influence of copper metal foam inserts on coolant temperature rise, pressure and velocity. In the first case, the problem of conjugate heat transfer from the test bench to the coolant without copper metal foam is analyzed using coupled CFD analysis in ANSYS work bench. Subsequently, a second microanalysis is conducted by introducing a single cell of heated copper foam into the coolant using the results obtained from the first case. This microanalysis is repeated for different flow velocity magnitudes of the coolant inlet flows. The results show positive contribution in the overall temperature rise of the coolant. Additionally, the microanalysis also shows that, as the velocity of coolant increases the overall temperature rise of the coolant decreases and the results are presented here graphically.





Far Field Evolution of Momentum Driven and Scalar Dominated Flow Field


Pages :
30453051


Authors :
V. Ilangovan,
To capture the effect of initial conditions in far field evolution of momentum driven and scalar dominated flow field, Witze scaling has been used for collapsing vector and scalar data to attain asymptotic state at selfpreserving region of the jet. It incorporates the initial mass, momentum, energy to capture the effect of heating level on both near and far field development of strongly heated coaxial turbulent round air jets entering into quiescent ambient. This paper compares the effectiveness of potential core length and jet effective diameter as the length scales to collapse both mean and fluctuating components of velocity vector and temperature scalar. Similarity considerations with Witze length scale using the initial momentum flux and buoyancy flux gives a good collapse at all levels of heating.





Effects of Flexible Splitter Plate in the Wake of a Cylindrical Body


Pages :
30533059


Authors :
S. Teksin,
S. Yayla,
In the wake of the bluff bodies rigid splitter plates are known to control vortex shedding. In this study, the problem of flexible splitter plate in the wake of circular cylinder was investigated using Particle Image Velocimetry (PIV) experimentally. In this case; the splitter plate which has a certain amount of modulus of elasticity freely deforms along its length because of the fluid forces on plate. The diameter of cylinder, D was 60 mm while the Reynolds number based on the cylinder diameter is kept constant as 2500, the characteristics length of the control element, L was tested for four different cases that the values of L/D were 0, 1.25, 2.25, 2.5 in the investigation. As a consequence, turbulent kinetic energy, TKE, velocity vector field <V>, vortex<>, Reynolds stress <u′v′>, root mean square of streamwise and transverse velocities, <urms>/U, <vrms>/U were analyzed. It is found that the variable parameter of L/D affects the flow structures and also noted that it decreased maximum level of all characteristic values.





On the Effect of Aspect Ratio of Open Heated Channel Including an Active Obstacle upon the Turbulent Characteristics of a Thermal Plume: Experimental Analysis


Pages :
30613071


Authors :
Taoufik Naffouti,
Jamil Zinoubi,
Rejeb Ben Maad,
This paper reports an experimental investigation of aspect ratio effect of open vertical channel on turbulent characteristics of a thermal plume. The physical configuration is constituted essentially by a prallelepipedic channel and an obstacle of a rectangular section. The thermal plume is generated by a rectangular obstacle heated uniformly at the upper surface. This active source is placed at the entry of a vertical channel open at the ends. The symmetrical heating of channel walls by joule effect and by thermal radiation emitted by the plume, causes the appearance of a thermosiphon flow which interacts with this one. To investigate the flow fluctuations, an anemometer at constant current (CCA) is used. The results carried out with air (Pr = 0.71) are performed for Rayleigh number equal to 0.63 107 over a wide range of aspect ratio 1.25 ≤ A ≤ 30. Effects of this pertinent parameter are displayed upon thermal and dynamic turbulent fields. Using Taylor hypothesis, time and length scales of turbulent thermal field are studied. It is found that the turbulent characteristics of the flow are significantly influenced by the variation of aspect ratio. An optimum aspect ratio of channel characterized by a strong homogenization of turbulence of the flow is observed. The fine analysis of temperature fluctuations spectra shows the evolution of the vortices in energy cascade owing to the strong effect of thermosiphon flow which favours the vortex stretching.





Effect of Horizontal AC Electric Field on the Stability of Natural Convection in a Vertical Dielectric Fluid Layer


Pages :
30733086


Authors :
B. M. Shankar,
J. Kumar,
I. S. Shivakumara,
S. B. Naveen Kumar,
The stability of buoyancydriven parallel shear flow of a dielectric fluid confined between differentially heated vertical plates is investigated under the influence of a uniform horizontal AC electric field. The resulting generalized eigenvalue problem is solved numerically using Chebyshev collocation method with wave speed as the eigenvalue. The critical Grashof number Gc, the critical wave number αc and the critical wave speed cc are computed for wide ranges of AC electric Rayleigh number Rea and the Prandtl number Pr. Based on these parameters, the stability characteristics of the system are discussed in detail. It is found that the AC electric Rayleigh number is to instill instability on convective flow against both stationary and travellingwave mode disturbances. Nonetheless, the value of Prandtl number at which the transition from stationary to travellingwave mode takes place is found to be independent of AC electric Rayleigh number. The streamlines and isotherms presented demonstrate the development of complex dynamics at the critical state.





Vortex Interaction and RollUp in Unsteady Flow past Tandem Airfoils


Pages :
30873100


Authors :
H. Aziz,
R. Mukherjee,
A discrete vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady ﬂow past two airfoils in conﬁguration. The unsteady wakes of the airfoils are modeled by discrete vortices and timestepping is used to predict the individual wake shapes. The coupled ﬂow is solved using a combined zeronormal ﬂow boundary condition and Kelvin condition which result in (2N + 2)X(2N + 2) equations. Results are presented showing the eﬀect of airfoilairfoil and airfoilwake interaction on the aerodynamic characteristics of the conﬁguration. The eﬀect of relative velocity, rate of pitching and phaselag are studied on airfoil performance and wake shape is predicted.





Asymptotic Approach to the Generalized Brinkman’s Equation with PressureDependent Viscosity and Drag Coefﬁcient


Pages :
31013107


Authors :
Igor Pažanin,
Marcone Pereira,
Francisco Javier SuarezGrau,
In this paper we investigate the ﬂuid ﬂow through a thin (or long) channel ﬁlled with a ﬂuid saturated porous medium. We are motivated by some important applications of the porous medium ﬂow in which the viscosity of ﬂuids can change signiﬁcantly with pressure. In view of that, we consider the generalized Brinkman’s equation which takes into account the exponential dependence of the viscosity and the drag coefﬁcient on the pressure. We propose an approach using the concept of the transformed pressure combined with the asymptotic analysis with respect to the thickness of the channel. As a result, we derive the asymptotic solution in the explicit form and compare it with the solution of the standard Brinkman’s model with constant viscosity. To our knowledge, such analysis cannot be found in the existing literature and, thus, we believe that the provided result could improve the known engineering practice.





Modeling WindDriven Circulation and Chlorophyll Concentration in Lake Valencia


Pages :
31093115


Authors :
Maira A. ValeraLópez,
Juan GuevaraJordan,
Reinaldo García,
Ivan Saavedra,
José Rafael León,
The goal of this research is to describe circulations patterns and chlorophyll concentration in Lake Valencia. The hydrodynamics of episodic events are simulated with a shallowwater model, coupled with an advectiondiffusion equation. This model uses a MacCormackTVD numerical scheme to solve the continuity and momentum equations simultaneously while the advectiondiffusion equations determine the time dependent pollution dispersion, in particular the chlorophyll concentration. An analysis of chlorophyll concentration is completely developed and validated with satellite images of Lake Valencia. Although the use of shallow water models is a fairly standard in the study of lake circulation and chlorophyll concentration, its application to Lake Valencia is new. Therefore, the circulation and chlorophyll patterns developed in this numerical study represent an original contribution.





Onset of Convection in Porous Medium Saturated by Viscoelastic Nanoﬂuid: More Realistic Result


Pages :
31173125


Authors :
A. Srivastava,
B. S. Bhadauria,
The present paper deals with the linear thermal instability analysis of viscoelastic nanoﬂuid saturated porous layer. We consider a set of new boundary conditions for the nanoparticle fraction, which is physically more realistic. The new boundary condition is based on the assumption that the nanoparticle fraction adjusts itself so that the nanoparticle ﬂux is zero on the boundaries. We use OldroydB type viscoelastic ﬂuid that incorporates the effects of Brownian motion and thermophoresis. Expressions for stationary and oscillatory modes of convection have been obtained in terms of the Rayleigh number, which are found to be functions of various parameters. The numerical results have been presented through graphs.





Unsteady Magnetohydrodynamic Flow of Second Grade Fluid due to Uniform Accelerating Plate


Pages :
31273133


Authors :
A. Khan,
Gul Zaman,
New exact solutions for unsteady magnetohydrodynamic (MHD) ﬂows of a generalized secondgrade ﬂuid due to uniform accelerating plate are derived. The generalized secondgrade ﬂuid saturates the porous space. Fractional derivative is used in the governing equation. The analytical expressions for velocity and shear stress ﬁelds are obtained by using Laplace transform technique for the fractional calculus. The obtained solutions are expressed in series form in terms of Fox Hfunctions. Similar solutions for ordinary secondgrade ﬂuid passing through a porous space are also recovered. Moreover, several ﬁgures are sketched for the pertinent parameters to analyze the characteristics of velocity ﬁeld and shear stress.





Simulation of Fingering Phenomena in Fluid Flow through Fracture Porous Media with Inclination and Gravitational Effect


Pages :
31353145


Authors :
H. S. Patel,
R. Meher,
Here we have studied the fingering phenomena in fluid flow through fracture porous media with inclination and gravitational effect and investigate the applicability of Adomian decomposition method to the nonlinear partial differential equation arising in this phenomena and prove the convergence of Adomian decomposition scheme, which leads to an abstract result and an analytical approximate solution to the equation. Finally developed a simulation result of saturation of wetting phase with and without considering the inclination effect for some interesting choices of parametric data value and studied the recovery rate of the oil reservoir with dimensionless time.





An analysis on Free Convection Cooling of a 3×3 Heater Array in Rectangular Enclosure using CuEGWater Nanofluid


Pages :
31473157


Authors :
Abimanyu Purusothaman,
Venkatachalam Divya,
Nagarajan Nithyadevi,
H. F. Öztop,
This paper deals with the study of natural convection cooling of a discrete heater array in CuEGwater nanofluid filled rectangular enclosure. A 3 × 3 array of nonprotruding heat sources is embedded on one of the vertical walls of the enclosure while the top horizontal and opposite vertical walls are assumed to be isothermally cold. The remaining portions in which the heaters are mounted and all other walls are insulated. The above setup is modeled into a system of partial differential equations which are solved numerically using finite volume method based on the SemiImplicit Method for Pressure Linked Equation (SIMPLE) algorithm and power law scheme. The wide range of parameters for computation are the aspect ratio of the enclosure, the mixture proportion of Ethylene glycolwater, the solid volume fraction of the nanoparticle along with two different thermal conductivity models. It is observed that the proper choice of the computation parameters and thermal conductivity models could be able to maximize the heat transfer rate from the heater array. Also, the results obtained in this study will provide new guidelines in the field of electronic equipment cooling.





Influence of Transverse Magnetic Field on Microchannel Heat Sink Performance


Pages :
31593166


Authors :
K. Narrein,
Sivasankaran Sivanandam,
Poobalan Ganesan,
The aim of the present numerical investigation is to analyze the effects of transverse magnetic field on heat transfer and fluid flow characteristics in a rectangular microchannel heat sink (MCHS). The effects of Hartmann number, channel aspect ratio, total channel height and total channel width on heat transfer and fluid flow characteristics are widely investigated. The governing equations for threedimensional steady, laminar flow and conjugate heat transfer of a microchannel are solved using the finite volume method. The obtained results are discussed with various combinations of pertinent parameters involved in the study. The results reveal that magnetic field can enhance the thermal performance of the MCHS but it is accompanied with a slight increase in pressure drop.





Characterization of Swirling Flows in a Partly Open Cylinder


Pages :
31673176


Authors :
Malika Imoula,
R. Saci,
B. Benkoussas,
Renée Gatignol,
A partly open vertical diskcylinder system, with an annular top lid, is used to model numerically the characteristics of axisymmetric swirling flows with stagnation and associated flows reversal; commonly referred to as vortex breakdown. The flows are driven by the bottom disk uniform rotation and controlled by the competition between the noslip and stressfree surface conditions applied at the top. Depending on the radial extent of the free surface, distinct regions of toroidal, corner and onaxis vortex type flows were identified and mapped into a state diagram then discussed. In addition, the impact of the cavity aspect ratio on the onset conditions of stagnation and breakdown was highlighted. Moreover, the study explored the influence of a diffusion driven meridian circulation, induced by the sidewall differential rotation, which is revealed to constitute an effective non intrusive kinematic means of flow control.





