Recent Volume
Vol12 , No 1 (in press)
Laminar Forced Convection and Entropy Generation of ZnO-Ethylene Glycol Nanofluid Flow through Square Microchannel with using Two-Phase Eulerian-Eulerian Model
Pages : 1-10
Authors : C. Uysal,  K. Arslan,  H. Kurt, 
In this paper, convective heat transfer and entropy generation of ZnO-EG nanofluid flow through a square microchannel are numerically investigated. Flow is modelled by using Eulerian-Eulerian two phase flow model. Nanoparticle volume fraction of ZnO-EG nanofluid ranged between %1.0 and %4.0. As a result, it is found that the convective heat transfer coefficient of flow increased from 9718.15 W/m2K to 23010.79 W/m2K when 4.0% ZnO nanoparticle addition to pure EG at Re=100. Total entropy generation of ZnO-EG nanofluid decreases with increase in nanoparticle volume fraction of ZnO-EG nanofluid. It is also observed that the Bejan number decreases with increase in nanoparticle volume fraction of ZnO-EG nanofluid.
   PDF XML

Flow Control in a Cavity with Tiny-Obstacles on the Walls for Mixing Enhancement Part I: Flow Physics
Pages : 11-23
Authors : B. Maneshian,  K. Javadi,  M. Taeibi-Rahni, 
This paper seeks to make a study on flow control in two-dimensional square cavities having obstacles on their walls. The goal of using these passive controllers is to enhance mixing in an enclosed space. Lattice Boltzmann method is used to simulate the problem. Results are presented for various Reynolds numbers, 400≤Re≤4000 and different arrangements of tiny-obstacles with different heights. To give a perspective on the physics of this problem, time evolution of the flow is studied at Re = 1000. Then, the flow structure is studied for different Reynolds numbers. Findings show that the interaction of the main vortex with the tiny-obstacles inserted on the wall cavity changes the flow pattern at higher Reynolds numbers totally which is of high importance for mixing, such that the main primary vortex turns into a scooplike vortex along the upper wall. Also, merging the two bottom corner vortices forms a main secondary vortex which fills the cavity. Results show that obstacles heights and the gap between the upper wall and the upper obstacle are key parameters from flow control and mixing viewpoint. Also, the number of tiny-obstacles can be considered as another tool in this regard. The spaces between the obstacles don’t have much influence on the flow behavior. Obstacles with δ≤2% don’t change the flow field and can’t be considered as a flow control tool.
   PDF XML

Numerical Flow Simulation and Cavitation Prediction in a Centrifugal Pump using an SST-SAS Turbulence Model
Pages : 25-39
Authors : M. Ennouri,  H. Kanfoudi,  A. Bel Hadj Taher,  R. Zgolli, 
The paper handles the subject of the modelling and simulation of the flow inside a centrifugal pump through non-cavitating and cavitating conditions. Operating under cavitation state is so perilous to a pump and can considerably reduce its lifetime service. Hence, to provide highly reliable pumps, it is essential to comprehend the inner flow of pumps. The investigated centrifugal pump comprises five backward curved-bladed impeller running at 900 rpm. The modelling process started with an unsteady numerical analysis under non-cavitating conditions to validate the numerical model and the solver comparing with the available testing data. Due to high Reynolds numbers, turbulence effects have been taken into account by unsteady RANS methods using an SST-SAS turbulence model. The obtained pump performances were numerically compared with the experimental ones, and the outcome shows an acceptable agreement between both. The temporal distribution of the internal flow parameters such as pressure and velocity was then studied. Furthermore, basic investigations of cavitating flow around 3D NACA66-MOD profile using a recently developed and validate cavitation model was established. The verification of the numerical simulation validity was based on comparing calculated and experimental results and presented good agreement. Finally, a 3D simulation of the inception of the cavitating pocket inside the centrifugal pump is performed to analyze the impact of the cavitation in the decrease of the head and efficiency.
   PDF XML

Experimental Investigation of the In-Cylinder Tumble Motion inside GDI Cylinder at Different Planes under Steady-State Condition using Stereoscopic-PIV
Pages : 41-49
Authors : Mohammed El Adawy,  M. R. Heikal,  A. Rashid A. Aziz, 
This paper describes an experimental study aimed at the characterization of the steady-state tumble motion in the cylinder of an engine using stereoscopic particle image velocimetry (Stereo-PIV). More specifically, a pent-roof four valves gasoline direct injection (GDI) engine head was mounted on a modified FEV steady-state flow rig for applying Stereo-PIV at different measurement vertical tumble planes at mid cylinder, mid injector and mid valve. The flow field was described by the distribution of the ensemble average flow patterns for 1000 pairs of images for every case, vorticity contours, turbulent kinetic energy and tumble ratio. The results revealed that the higher velocities acquired at the mid valve plane improved the turbulent kinetic energy and tumble ratio compared to the other planes. There was a good level of agreement between direct and indirect methods used for calculating the tumble ratio.
   PDF XML

Study of Pulsatile Flow in Common Carotid Artery with Different Stenosis' Shapes within Various Wall Conditions
Pages : 51-59
Authors : P. Bayat,  M. R. Tavakoli, 
Recently, due to the development of CFD techniques, many attempts have been made to simulate the initiation and progression of atherosclerosis. In recent works, various curves have been suggested to model the stenosis shape. However, little effort has been made to study the importance of the stenosis shape on the flow behavior. In this study, four types of stenosis with asteroid, Gaussian, semi-circle, and sinusoidal shapes were simulated in order to study the effect of the stenosis shape on flow behavior and diagnosis parameters. Shear stress and flow behavior were investigated in the common carotid artery with stenosis severities of 30%, 40%, and 50%. Flow was assumed to be unsteady and the inlet to be a pulsatile flow. Two cases of Newtonian and non-Newtonian fluids were simulated. The no-slip and permeable boundary conditions were imposed on the outer walls. To examine the effect of the location of stenosis, modeling was conducted at various locations. The results showed that the maximum shear stress occurs in the Gaussian stenosis at the opening of the stenosis. Semi-circle, sinus, and asteroid shapes had the next largest shear stress values. Additionally, the location of stenosis had a negligible effect on the maximum shear stress. However, flow resistance increased with increasing the stenosis’s distance from the beginning of the artery. This study indicates that stenosis shape highly affects the flow characteristics, and stenosis severity is not the only parameter that is important. Hence, the stenosis shape should be considered when simulating atherosclerosis.
   PDF XML

Intake Flow Interference Analysis of Combination Intake Port in Diesel Engine
Pages : 61-67
Authors : D. W. Jia,  X. W. Deng,  J. L. Lei, 
In order to analyze the intake flow characteristics of a four-valve direct injection(DI) diesel engine, the experiments and numerical simulations were conducted to investigate the flow coefficient, swirl ratio and intake flow interference of the following 4 combinations of intake ports: (1) helical (left) and tangential (right), abbreviation ; (2) tangential (left) and helical (right); (3) helical (left) and helical (right); and (4) tangential (left) and tangential (right).Results show that the relative flow coefficient and swirl ratio could be directly reflect the interference of combined intake port, and when the ratio was close to 1, which showed that intake port had less interference ;and when the ratio was close to 0, which showed that the interference was serious. The relative flow coefficient of the 4 combinations of intake ports has little difference, but the relative swirl ration had significant difference in the whole valve lift range. And there had little interference between adjacent intake ports, but the swirl was strongly formed in cylinder at the maximum valve lift.
   PDF XML

Experimental Study on the Friction Drag Reduction of Superhydrophobic Surfaces in Closed Channel Flow
Pages : 69-76
Authors : M. Monfared,  M. A. Alidoostan,  B. Saranjam, 
Due to the importance of copper and its alloys in marine applications, the main objective of this research is to provide a simple, effective and low cost manufacturing approach to fabricate a superhydrophobic riblet copper surface with high drag reduction capability in laminar and turbulent flow regimes. Therefore, the riblets are produced by wire cut technique on the copper substrate and then by using a wet chemical method, a superhydrophobic coating is produced on the riblet surface. A pressure drop measurement system consists; pump, closed channel flow with a fabricated surfaces on the lower wall, connections and pressure drop transmitter is employed to measure the pressure drop in the close channel flow, for Reynolds number from 300 to 2769, in order to evaluate the ability of the fabricated surface to reduce the friction drag. The experimental results revealed that combining the abilities of the riblet and superhydrophobic surfaces increases the surface’s ability to reduce friction drag. In addition, the riblet surface and superhydrophobic riblet surface on average decreased the friction drag by 10.33% and 42.65% correspondingly in water flow ranging from laminar to turbulent flow regime. Finally, according to the experimental results, the drag reduction performance of riblet surface is improved from 18.9% to 56.9% after superhydrophobic coating.
   PDF XML

Numerical Simulation of Diffuser of a Gas Turbine using the Actuator Disc Model
Pages : 77-84
Authors : S. Sadasivan,  S. K. Arumugam,  M. Aggarwal, 
An analysis of the exhaust diffuser section of a gas turbine is presented by incorporating the reduced order mathematical model “actuator disc concept” that represents the last stage of the turbine. The actuator disc model is one of the simplified numerical methods for analyzing the aerodynamic performance of axial turbine stage. In which, the rotor and the stator of the turbine stages are modeled as zero thickness discs with a specified blade speed and zero speed respectively. Finite volume based commercial CFD package ANSYS FLUENT was employed for the numerical investigation of the applicability of the proposed simplified model. The compressible Navier-Stoke equations along with k- turbulent model were solved in the computational domain by incorporating suitable boundary conditions. The implementation of actuator disc boundary conditions is described in detail. The numerical results obtained from the proposed model are in good agreement with the experimental data available in the literature. The effect of casing angle on the performance of diffuser is presented.
   PDF XML

Double-Diffusive Convection in an Oldroyd-B fluid Layer-Stability of Bifurcating Equilibrium Solutions
Pages : 85-94
Authors : K. R. Raghunatha,  I. S. Shivakumara, 
The nonlinear stability of stationary and oscillatory double-diffusive convection in an Oldroyd-B fluid layer is investigated using a perturbation method. The cubic Landau equations are derived and based on which the stability of stationary and oscillatory bifurcating solutions in the neighborhood of their critical values is discussed. The boundary between stationary and oscillatory convection demarcated by identifying a codimension-two points in the viscoelastic parameters plane. The bifurcating solution is found to be subcritical depending on the choices of physical parameters. Heat and mass transport are estimated in terms of Nusselt numbers. The effect of Prandtl number is observed only in the case of oscillatory motions and increase in its value is to decrease the heat and mass transfer. Besides, increasing relaxation and retardation parameters is to decrease and increase the amount of heat and mass transfer, respectively in the stationary case, while these parameters found to exhibit an opposing kind of behavior in the case of oscillatory motions.
   PDF XML

Numerical Analysis of Homogeneous and Stratified Turbulence under Horizontal Shear via Lagrangian Stochastic Model: Richardson Number Effect
Pages : 95-102
Authors : L. Thamri,  T. Naffouti,  M. Bouzaiane, 
The present investigation is carried out to reveal Richardson number (Ri) effects on an homogeneous and stratified turbulence under horizontal shear. The problem is simulated via Lagrangian Stochastic model (LSM). Hence, the method of Runge Kutta with fourth order is adopted for the numerical integration of three differential systems under non linear initial conditions of Jacobitz (2002) and Jacobitz et al. (1998). This study is performed for Ri ranging from 0.2 to 3.0. It has been found that computational results by the adopted model (LSM) gave same findings than that of preceding works. It has been shown a global tendency of different parameters governing the problem to equilibrium asymptotic states for various values of Ri. The comparative study between the computations of the present LSM and direct numerical simulation of Jacobitz demonstrates a good agreement for both methods for the ratios of; potential energy Kθ/E and kinetic energy K/E toward the total energy E and the principal component of anisotropy b12 It has been found that Ri is the most important parameter affecting the thermal and dynamic fields of the flow. Hence, increase Ri conduct to increase the uniform stable stratification and decrease for the uniform mean shear S. It can be concluded that Ri is a main non-dimensional parameter which enable us to understand physical phenomenons produced inside stratified shear flows.
   PDF XML

Investigation on Aerodynamic Behaviour of a SUV Car Model with Vortex Generators at Different Yaw Conditions
Pages : 103-117
Authors : G. Shankar,  G. Devaradjane,  S. Sunil, 
The present work discusses the aerodynamic behaviour of a typical SUV car model mounted with three vortex generators (VGs) similar to the shape of a right-angled triangle in four different yaw angle configurations, the results of which have been quantitatively assessed in the sub-sonic wind tunnel and by using realizable (k- ε) model. The VG positioned in the middle is kept in the fixed state while the yaw position of VGs on either side has been modified and its significance is presented in this article. The pressure distribution data along the central plane of the car model for all the cases have been obtained by using 32 channel digital pressure scanner that is connected with the pressure tapings prepared in the symmetrical plane of the car model. Simultaneously two separate cantilever type load cell setup is used in this work to measure the magnitude of drag and lift force with measuring sensitivity of about 0.01N. From the experiments, it is determined that the car model with outer VGs heading the rear windshield and central plane possess the maximum drag and lift coefficient reduction rate of about 4.35% and 3.23% respectively compared to car model without VGs. In addition to these findings it is also determined that the vehicle model with VGs positioned perpendicular to the wind stream direction exhibited strong drag magnitude than that of the vehicle without VGs. This increased drag can be utilized for rapid deceleration of vehicle motion (Aerodynamic braking) particularly at the instance of vehicle is running at high speed conditions. The realizable (k- ε) model estimated the drag and lift coefficient closer to that of wind tunnel results and exhibited a maximum error deviation of 2.38%. Further, realizable (k- ε) model predicted the existence of the magnitude of velocity gradient, intensity of turbulent kinetic energy variation and streamlined pattern of velocity gradient around the vehicle with VGs compared to the case of vehicle model without VGs at its rear end.
   PDF XML

Computational Fluid Dynamic Simulation of Dispersed Oil-Water Flow with New Drop Coalescence Model
Pages : 119-126
Authors : A. A. Amooey,  Elham Omidbakhsh Amiri, 
The three-dimensional oil-water flow in horizontal pipe has been investigated by introducing population balance equation (PBE). The water fraction of inlet flow and mixture velocity varies from 46% to 60% and from1.25 m/s to 3m/s, respectively. The multiple size groups model has been applied to the non-uniform drop size distribution in oil-water flow. The drop coalescence models have a clear efficacy on the prediction capability of the PBE. In this work, drop coalescence model for oil-water is modified and used for predicting the phase distribution of dispersed oil - water in horizontal pipe. Population balance with modified Coulaloglou’s frequency model is used. The attention of the modification is on the presence of droplets that reduce the free space for droplet motion and cause an enhancement in the collision frequency. The phase distribution profile from numerical results is presented and discussed. Acceptable agreement with the experimental data is achieved by using the modified coalescence model. Also, at 46% water fraction and mixture velocity equal as 3 m/s, model with population balance with modified Coulaloglou is 4% and 1% better than Luo’s model and Coulaloglou’s model, respectively.
   PDF XML

Flow Control of Non-Newtonain Fluid using Riga Plate: Reiner-Phillipoff and Powell-Eyring Viscosity Models
Pages : 127-133
Authors : A. Ahmad, 
This article investigates the controlling effects of electromagnetic field generated by Riga plate on the boundary layer flow of non-Newtonian fluid. Two classical viscosity models of non-Newtonian fluids namely; Powell-Eyring and Reiner-Phillipoff fluid models have been considered to study the different behaviors of non-Newtonian fluid flow. Numerical solution of the problem in the presence of strong suction is obtained using the nonlinear shooting method. The results are studied in terms of modified Hartmann number, non-Newtonian fluid parameters and the Bingham number. Linear regression is performed on the numerical results to present the correlation expression for the skin friction.
   PDF XML

Effects on Heat Transfer and Radial Temperature Profile of Non-Isoviscous Vibrational Flow with Varying Reynolds Number
Pages : 135-144
Authors : S. K. Mishra,  H. Chandra,  A. Arora, 
A valid CFD model is employed to show the impact on heat transfer of one-dimensional laminar non-isoviscous flow through pipe subjected to forced transverse vibration. Through transverse vibration, which produces the chaotic fluid motion and swirling effects, adequate radial mixing across the tube can be achieved which leads to the great addition in heat transfer. Thermal boundary layer developed more quickly and thus, temperature profile developed wilder than steady flow under the effect of vibration in both radial and axial direction, considerably for low Reynolds Number; as Reynolds number increases that effectively reduced. In this study, these impacts are quantitatively exhibited for Newtonian and shear-thinning liquid at various Reynolds numbers; and found that application of superimposed vibrational flow limited to considerably for small: Reynolds number and flow behavior index of shear thinning fluids.
   PDF XML

Experimental and Computational Simulation of an Open Terrain Wind Flow around a Setback Building using Hybrid Turbulence Models
Pages : 145-154
Authors : K. B. Rajasekarababu,  G. Vinayagamurthy, 
In recent days, building aerodynamics has gained more attention to urban planners, architects, and wind engineers in understanding the wind flow behaviors around tall buildings. CFD (Computational Fluid Dynamics) simulations are the major tool regularly carried out to assess the wind flow pattern around the buildings to demonstrate the atmospheric and wind tunnel environment in accordance with the turbulence parameters. One of the most challenging tasks is to evaluate a turbulence model which precisely represents atmospheric turbulence flow using computation resources. This study is intended to analyze the precision and numerical stability of open terrain wind flow around a setback building with sharp edges of aspect ratio of 1:5. Hybrid turbulence models using Delayed Detached Eddy Simulation (DDES) and Improved Delayed Detached Eddy Simulation (IDDES) are employed with (Y+) wall treatment in combination with roughness parameters. From the numerical simulation, the size of re-circulation zones in addition to wake separation zones in a three-dimensional plane are determined to assess the flow characteristics of the building at 00 wind incidence. The mean pressure coefficients (CP mean) are validated against the results obtained from Boundary Layer Wind Tunnel (BLWT) experiments carried out at CSIR-Structural Engineering Research Centre, Chennai.
   PDF XML

Numerical and Experimental Study to Predict the Entrance Length in Pipe Flows
Pages : 155-164
Authors : H. Düz, 
Here, a steady, incompressible and isothermal flow in the inlet region of a circular pipe were numerically and experimentally studied to predict the entrance length. The region in the upstream of fully developed pipe flow is referred to as the developing flow region, the effects of which on flow parameters are referred to as entrance effects. Entrance length shows the length of the developing flow region. The analysis of entrance flow is difficult and complicated as there are many parameters such as different pipe inserts affecting it. Earlier empirical results on the entrance region are inconclusive and inconsistent. Initially, an experimental study was performed with pipes of different roughness to validate the numerical results. Reynolds numbers used in the experiment ranged from 3000 to 25000. The entrance flow was numerically simulated in parallel to experimental pipe flows. Numerical results obtained were compared with those of the experimental study and of previous ones. Numerical and empirical data showed good agreement. Based on the numerical results, a well-defined numerical correlation was developed and proposed for the prediction of entrance lengths.
   PDF XML

Numerical Investigations on a Small-Scale Air-Slide Conveyor
Pages : 165-173
Authors : J. Xiang,  T. H. New, 
This study reports upon numerical investigations on a small-scale air-slide conveyor (ASC) model that is based on a full-scale industrial ASC currently in operation. For validation of the ASC model and prediction of details of cement flow distribution on time-basis, both steady-state and transient simulations are performed. Simulation results demonstrate the development of cement flow phenomenon and predict critical flow features in the system, which will be useful for predicting corresponding behavior in the full-scale industrial ASC. Mass balance is achieved and potential optimization technique is supported by simulation data. Both steady-state converged solution and results on time-basis are discussed. This study demonstrates the validity of ASC model design and paves the way for using similar numerical tools for future particle-laden flow studies. Lastly, it also offers design and optimization insights into such industrial ASC systems.
   PDF XML

On Wake Analysis of Flow Past Rotating Downstream Cylinder using Hilbert-Huang Transformation
Pages : 175-186
Authors : M. Neeraj Paul,  S. Tiwari, 
Two-dimensional numerical simulations have been carried out on flow past two inline circular cylinders with rotating downstream cylinder. Computations are performed for fixed Reynolds number equal to 150 such that the resulting flow field remains laminar and two-dimensional. The inter-cylinder spacing has been chosen equal to 5d ('d' being diameter of cylinder) such that the wake flow is predominantly unsteady. Rotational speed of the downstream cylinder has been varied to investigate its effect on transition in characteristics of temporal wake. This has been achieved by performing Hilbert-Huang transformation (HHT) on time series signals of drag and lift coefficients for the rotating cylinder. Unsteady periodic, unsteady non-periodic and steady transitions in flow behavior have been observed with an increase of rotational speed. Results are presented in the form of vorticity contours, Hilbert spectra and marginal spectra. Degree of stationarity of the signals as measure of nonlinearity has also been quantified. Comparisons are drawn against results from Fourier analysis and it has been shown that HHT is better suited to capture inter-wave and intra-wave modulations indicating nonlinear interactions in the wake.
   PDF XML

Drag Reduction of Non-Circular Cylinder at Subcritical Reynolds Numbers
Pages : 187-194
Authors : V. Suresh,  P. S. Premkumar,  C. Senthilkumar, 
Experimental and numerical investigation of fore body geometrical effects on drag and flow-field of non-circular cylinder ( D-shaped bluff body) were conducted in the subcritical flow regime at Reynolds number in the range of 1 x 105 ≤ Re ≤ 1.8 x 105. To shield the non circular cylinder ( D-shaped model ) front surface from the positive pressure of the unsteady vortex generation in the near wake, circular disk of various geometries were attached upstream of the non-circular cylinder base model. The fore body makes the streamlines that separate from its edges to attach smoothly onto the front face shoulders of the main body, thereby converting the bluff body into an equivalent streamlined body to result in low drag. The diameter of the fore body (b1) ranges from 0.25 to 0.75 times the hydraulic diameter of base model ( b2 ) and the gap ratio ( g/ b2 ),was in the range from 0.25 to 1.75 b2. The experimental and numerical investigations show that by using a circular disk as fore body with a width ratio b1/b2 of 0.75 and a gap ratio of g/ b2 = 0.75 results in a configuration having percentage drag reduction of about 67 % and 65 % respectively.
   PDF XML

Experimental Investigation and ANN Prediction on the Underbody Drag Minimization in Truck Model using DC Pulsed DBD Plasma Actuator as an Active Flow Control Device
Pages : 195-205
Authors : A. Sangeet Sahaya Jeyangel,  J. Jancirani, 
Copious researches have been accomplished in the realm of automotive aerodynamics leading to the reduction of drag in cars, trucks and buses. The overwhelming results have further spearheaded the present work in emphasizing the underbody drag minimization of distribution trucks using plasma actuator as an active flow control technique. Four different types of plasma actuators also called Active Side Skirt were experimentally evaluated on the scale down model of truck in a subsonic wind tunnel along with five different voltages ranging from 12 kV to 28 kV. The plasma actuator was positioned on the sides of the truck vertically as four individual units covering the front tyres and rear tyres. The results exhibit that the plasma actuator with a larger insulated electrode and with an electrode overlap distance had a good drag reduction rate of 8% at higher velocity (28 kV).The plasma generated by the Active Side Skirt induces an ionic wind along the stream wise direction keeping the flow attached throughout thereby helping in a reduced drag. An artificial neural network was developed using the data from the experimental analysis with Voltage, Velocity, Top width, Bottom width and Overlap distance as input parameter for training the network, further coefficient of drag taken as output parameter. A total of two hidden layers and seven neurons was used for the prediction. The test data that was not used for training, correlated with the ANN predicted value furthermore with the experimental values.
   PDF XML

Numerical and Experimental Investigation of the Flow over a Car Prototype for the Shell Eco Marathon
Pages : 207-218
Authors : F. Arpino,  G. Cortellessa,  A. Frattolillo,  F. Iannetta,  M. Scungio, 
The Eco-Marathon is a challenge organized by Shell in which student teams compete in designing energy-efficient vehicles. The event spark debate about the future of mobility and inspire engineers to push the boundaries of fuel efficiency. The aim of the present work consists of the numerical and experimental investigation of the aerodynamic performance of a Shell Eco Marathon prototype designed by a group of students of the University of Cassino, Italy. The car design has been provided by means of detailed 3D CFD modelling with Comsol Multiphysics®. The numerical tool has been validated against experiments conducted at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino. In particular, a scale model of the car has been investigated in an open chamber wind tunnel by means of the Particle Image Velocimetry (PIV) technique, for different free stream velocities within the range 11 – 23 m/s. Measurements have been associated to a proper uncertainty analysis. The experimental data has been compared to numerical results obtained employing different turbulence models and the validated numerical tool has been applied to the simulation of the full-scale car model, allowing to analyse the wake flow structures, and estimate the overall drag coefficient.
   PDF XML

Numerical Study of Water/Al2O3 Nanofluid Forced Convection in a Rotating Hydrophilic and Hydrophobic Microchannel
Pages : 219-231
Authors : A. Sohankar,  M. Riahi,  E. Shirani, 
In this work, water and water/Al2O3 nanofluid forced convection are studied numerically through a rotating U-shaped microchannel. The hydrophilic (no-slip flow) and hydrophobic (with slip length of 5 μm) conditions are used on the microchannel walls. Simulations are provided for various nanoparticle volume concentrations (ϕ=0-5%), and rotational speeds (ω =0-300 rad/s) and Reynolds numbers (Re=200-1000) to study their effects on the pressure drop, heat transfer, and thermal performance coefficient. A modified thermal performance criterion is suggested to include the variations of the working fluid properties relative to the reference case. It is observed that the existence of the nanoparticles in the base fluid provides considerable improvement on the heat transfer. The nanofluid flow also improves the thermal performance coefficient for volume concentrations of ϕ=0.5% and 2%, while it reduces for ϕ=5%. Although the thermal performance coefficient of the nanofluid flow at ϕ=5% decreases due to high pressure drop, but it is recommended to use water/Al2O3 at ϕ=5% as working fluid due to its high heat transfer enhancement (about 40%).
   PDF XML

The Influence of Surface Tension on Oblique Wave Scattering by a Rectangular Trench
Pages : 233-241
Authors : َA. Sasmal,  S. Paul,  S. De, 
The diffraction of obliquely incident wave by a symmetric rectangular submarine trench with the effect of surface tension at the free surface is investigated using two dimensional linearized potential theory. The reflection and transmission coefficients are computed numerically using appropriate multiterm Galerkin approximations involving ultraspherical Gegenbauer polynomials. These coefficients are represented graphically against the wave number in a number of figures. The theoretical observations are validated computationally. The derived result will coincide analytically and graphically with the results already present in the literature neglecting the effect of surface tension, which confirms the correctness of the result presented here. We observed the zero reflection phenomenon in the graphical representation. It is also noted that the values of reflection coefficient decreases as the surface tension increases. We conclude that realistic changes in surface tension on the free surface have a significant effect on the present study.
   PDF XML

Modeling Frictional Characteristics of Water Flowing Through Microchannel
Pages : 243-255
Authors : P. C. Jayadevan,  R. Siddharth,  Pradeep M. Kamath, 
The present study aims at modeling the real random rough surface of a microchannel with structured rough channel of known geometric parameters. The surface of the microchannel is created by sinusoidal function using MATLAB code and 2D simulation of the model is carried out with commercial software ANSYS Fluent. The height of the channel is varied from 100 to 250 µm and length of the channel is 12.5 mm. The range of Reynolds number selected for analysis is 100 to 500 with water as the fluid medium. The roughness height is selected within the range of actual manufacturing roughness level of microchannels. The results show that channel geometry has significant influence on flow characteristics. A new non-dimensional roughness parameter β, is proposed to represent the dependence of friction factor on geometric parameters in the laminar region. A correlation for flow friction is developed as a function of roughness parameter and Reynolds number.
   PDF XML

Study on Effects of Prandtl Number on Cross Buoyancy Flow past a Square Cylinder using OpenFOAM
Pages : 257-269
Authors : S. Tanweer,  A. Dewan,  S. Sanghi, 
The influence of Prandtl number on laminar, unsteady flow past a heated square cylinder placed in a free-stream has been studied computationally. The flow has been investigated for 0.02 < Pr < 100 at Re = 100 and Ri = 1. Effects of Prandtl number in unsteady mixed convection flow have been reported for the first time in the present study. The finite-volume based open source code OpenFOAM was used for the numerical simulations. An efficient algorithm (PIMPLE) has been used for the pressure-velocity coupling. Streamlines, isotherms, vorticity production and force coefficients have been studied in detail. The role of buoyancy on the baroclinic production has been discussed. Variation of lift coefficient with Pr was found to be quite interesting. The mean lift coefficient was found to be negative at low values of Pr but surprisingly it became positive at very high values of Pr.
   PDF XML

Double-Diffusive Bioconvection in a Suspension of Gyrotactic Microorganisms Saturated by Nanofluid
Pages : 271-280
Authors : S. Saini,  Y. D. Sharma, 
This paper focuses on analytical and numerical investigation of double-diffusive bioconvection in a porous media saturated by nanofluid using the modified mass flux condition. Normal mode technique is employed to solve the governing equations of the Brinkman-Darcy model. The Galerkin weighted residual method (single-term and six-term) is used to obtain numerical solution of the mathematical model. It is found that due to the presence of gyrotactic microorganisms, Rayleigh number is decreased substantially which shows that convection sets in earlier as compared to nanofluid without microorganisms and this destabilizing effect is more predominant for faster swimming microorganisms. modified Darcy number number, Soret parameter, and porosity postpone the onset of the bioconvection, whereas nanoparticle Rayleigh number, bioconvection Rayleigh number, nanoparticle Lewis number, Dufour parameter, Péclet number, and Lewis number pre-pone the onset of bioconvection under certain conditions.
   PDF XML

Effect of the Heating Block Position on Natural Convection in a Three-Dimensional Cavity Filled with Nanofluids
Pages : 281-291
Authors : M. Sannad,  B. Abourida,  L. Belarche,  H. Doghmi,  M. Ouzaouit, 
This paper consists on a three-dimensional numerical approach of natural convection in a cavity containing the nanofluid. The cavity contains an isothermal heating block in the middle of the bottom (case BH) and the top (case TH) walls and kept at a hot temperature TH. The right and the left vertical walls of the cavity are kept at a cold temperature Tc. The study's parameters are: the volume fraction Ф varying between 0 and 0.03, and the Rayleigh number . The considered nanofluid is water + Cu. The results illustrate that the Rayleigh number Ra and the volume fraction Ф have a positive effect and they also improve the heat transfer. Interesting results have also been found while comparing the two considered configurations.
   PDF XML

Bluff Body Drag Control using Synthetic Jet
Pages : 293-302
Authors : P. Gil, 
The paper presents the results of an experimental investigation wherein the bullet form drag force as a function of oscillating actuator frequency, various voltage and for different orifice/slot configuration are studied. In order to perform the experiment, an axisymmetric bullet shape model with ellipsoidal nose was used in wind tunnel. The synthetic jet actuator was used to flow control at sharp cut end. The experiment was conducted in a wind tunnel with a working diameter of 1000 mm and a maximum velocity of 45 m/s. The measurements were carried out for the Reynolds number from 88000 to 352000 and for relatively large Strouhal numbers up to St = 4.5 based on model external diameter and free stream velocity. While synthetic jet was switched on, drag coefficient has been reduced by -6% and increased by +22% in relation to the case with the synthetic jet was switched off. The synthetic jet has more impact for relatively low free stream velocity and for single axisymmetric orifice.
   PDF XML

CFD Analysis of Aerodynamic Drag Effects on Vacuum Tube Trains
Pages : 303-309
Authors : S. A. Gillani,  V. P. Panikulam,  S. Sadasivan,  Z. Yaoping, 
Aerodynamic aspects of train shapes suitable for Vacuum Tube Train System are investigated in this paper. Three feasible geometries for the vacuum tube train system have been considered and modelled in three dimensions and have been computationally studied using the commercial software Ansys Fluent. Aerodynamic drag loads on these geometries have been calculated under different tube pressures and speeds of the train, which provide insight on various operating parameters that need to be considered while designing the vacuum tube train system. The present computational research shows that, the suitable vacuum pressure, and different shapes of head and tail of the train have significantly effects the drag force of the vacuum train in the tunnel. Overall, the elliptical train shape with a height to base ratio of 2:1 is more efficient for aerodynamic drag reduction of the vacuum tube train at the vacuum tube pressure of 1013.25 Pa.
   PDF XML

Numerical Simulation of Tidal Bore Bono at Kampar River
Pages : 311-318
Authors : A. C. Bayu,  S. R. Pudjaprasetya,  U. J. Wisha,  S. Husrin, 
A tidal bore is a natural phenomenon usually occur in bays with large tidal waves. Sometimes this large tidal inflow are channeled deep into a river. In Indonesia, this natural phenomenon is found in the Kampar River, which is known as the tidal bore Bono. Sometimes, these tidal bore phenomena disappear, as happened to the Mascaret, tidal bore on the River Seine France. Through an understanding of the formation of tidal bore mechanism, there is hope that the tidal bore Bono in Kampar River can be preserved. In this paper, the occurrence of tidal bore Bono is simulated using the non-hydrostatic Saint-Venant equation under a staggered grid formulation. To test the accuracy of the implementation, several scenarios of hydraulic jumps were simulated first. The numerical results have shown to quantitatively confirm the analytical formula of bore height and velocity, two parameters that are important to characterize a bore wave. Further, by adopting a model that incorporates the non-hydrostatic pressure, our simulation shows the appearance of an undular bore accompanying the shock front. Finally, by using tidal current data measured along Kampar River estuary, our simulation that employs the actual river topography can show the appearance of tidal bore Bono. Our simulations were shown to be in fair agreement with the measurement.
   PDF XML