

Evaluation of Optimum Modes and Conditions of Cavitation and Acoustic Absorption Intensification for Increasing Efficiency of Gas Mixtures Separation


Pages :
12351246


Authors :
R. N. Golykh,
The paper presents theoretical studies of absorption gas mixture separation under ultrasonic vibrations influence, which provides cavitation and acoustic process intensification. The theoretical studies based on consecutive consideration of this process beginning with single cavitation bubble dynamic which generates shockwave for increasing interface “gasliquid” and ending with determining absorption productivity providing required concentration of target gas mixture component. In result of the studies, it is evaluated, that cavitation and acoustic intensification increase interface “gasliquid” up to 3 times with amplitude of oscillations of solid surface 1…2 μm. From the data about surface increasing the analysis of the gas absorption process in the liquid film was performed. For this analysis, the model of gas absorption taking into account surface increasing under acoustic cavitation influence was developed. The model of absorption allows to obtain that the absorption productivity under ultrasonic vibrations influence is increased up to 2 times and more. The obtained results can be used for development of highefficiency absorption apparatus that is supplemented by ultrasonic influence sources.





Numerical Study of Flow Past Two Transversely Oscillating Triangular Cylinders in Tandem at Low Reynolds Number


Pages :
12471260


Authors :
Q. Zhai,
H. K. Wang,
G. L. Yu,
Flow past two tandem triangular cylinders forced to oscillate transversely in a uniform flow, is numerically investigated at a Reynolds number Re = 100. The incompressible NavierStokes equations in ArbitraryLagrangianEulerian formulation are solved by fourstep fractional finite element method. The two cylinders are oscillated in phase and their motions are limited to low amplitudes with a wide frequency range. This study focuses on two typical spacings between the two cylinders, corresponding to vortex suppression (VS) regime and vortex formation (VF) regime respectively for flow past two stationary cylinders. Numerical results show that the response characteristics of two cylinders are significantly affected by the spacing, oscillation amplitude and frequency. For the VS spacing, both cylinders have a wider lockon region, especially at relatively larger amplitude and higher frequency; the downstream wake patterns are mainly 2S and a combination of 2S* and 2S. However, for the VF spacing, the lockon frequency range of the cylinders is even slightly narrower than that of a single oscillating cylinder; the wake field is more complex since it may comprises 2S, P+S and 2S* structures at some higher frequencies. Additionally, the hydrodynamic forces are also discussed in terms of mean and root mean square quantities, and reveal large differences between oscillating and stationary cylinders.





Curvature Effects on the Electromagnetic Force, Efficiency, and Heat Transfer of a Weak Low Profile MagnetoHydrodynamic Blanket Propulsion System


Pages :
12611270


Authors :
M. A. Feizi Chekab,
P. Ghadimi,
The present study concerns the numerical assessment of the effects of longitudinal and lateral curvature of a flexible low profile magnetohydrodynamic blanket on its thrust, performance, and heat transfer. To this end, after validating the solver with the analytical solution of the Hartman problem, negative and positive curvatures are taken into consideration in lateral and longitudinal directions on the blanket and electromagnetic and velocity fields, temperature distributions, force density fields and profiles are extracted and compared to the flat MHD blanket. It is demonstrated that negative curvatures increase the thrust force and temperature of the blanket and the reverse occurs for the positive curvatures. It is also shown that the longitudinal curvature affects the blanket thrust by 2.5% up to 5.2%, its efficiency by nearly 6% and the temperature change from 25 up to 28%. On the other hand, for the lateral curvatures, the overall thrust produced by the blanket is affected by about 6% to +6%, the efficiency is affected by 10% to 25% and temperature change is affected by 2 to 6%.





Investigations of Combustion Performance in LPP Combustor


Pages :
12711282


Authors :
Y. W. Yan,
Y. P. Liu,
J. H. Li,
W. Cai,
A Lean Premixed Prevaporized (LPP) lowemission combustor which is applied with the combustion technology of staged lean fuel is developed. To study the cold flow dynamics and the combustion performance of the LPP combustor, both experimental tests using the Particle Image Velocimetry (PIV) to quantify the flow dynamics and numerical simulation using the Fluent software are conducted respectively. To investigate the emissions of the LPP combustor, four kinds of inlet conditions (viz. 7%, 30%, 85% and 100% F∞ (Thrust Force)) were conducted using numerical simulation. Numerical results are in good agreement with the experimental data. Results show that:1) a Primary recirculation zone (PRZ), a Corner recirculation zone (CRZ) and a Lip recirculation zone (LRZ) exist in the LPP combustor, and the velocity gradients between pilot swirling flow and primary swirling flow have contributed to the exchanges of mass, momentum and energy. 2) With the decrease of thrust force, NO mass fraction, CO2 mass fraction and total pressure losses at the exit of LPP combustor fall gradually. 3) Thermal NO formation rate closely relate to the zone area where gas temperature overruns 1900K and the maximum temperature in LPP combustor. 4) The combustion performance of the LPP combustor proposed in this paper is very well, and through comparative analysis with four kins of typical gas tubine combustor, the NO emission is very low and is equivalent to the CAEP6 43.87%.





Particle and Gas Flow Modeling of Wallimpinging Diesel Spray under Ultrahigh Fuel Injection Pressures


Pages :
12831291


Authors :
P. Ghadimi,
M. Yousefifard,
H. Nowruzi,
Advanced models of spray breakup and droplet collision are implemented in OpenFOAM code for comparing the flatwall impinging and free fuel sprays under ultrahigh pressure direct injection diesel engines. The nonevaporating spray and ambient gas flow characteristics are analyzed by a combination of Eulerian and Lagrangian methods for continuous and dispersed phase, respectively. Various injection pressures and two different impinging distances are used. Reynolds Averaged Navier Stokes (RANS) equations are solved using standard kε turbulence model. Computational domain and grid size are determined based on a mesh study. Numerical results are validated by published experimental data for free and wallimpinging sprays. The robustness and accuracy of the proposed scheme are confirmed by comparing the main characteristics of spray and surrounding gas against published experimental data. To accomplish this, spray shape, penetration and gas velocity vectors are compared with experimental data and insightful understanding of the spray characteristics are provided. In comparison with free spray, tip penetration has been limited in impinging sprays. Turbulent flow in impinging sprays leads to more induced air motion. Also, impinging spray leads to more pushedout gas velocity. The obtained results indicate that the numerical findings are generally in good agreement with experimental data in case of ultrahigh injection pressures and microhole injectors.





Instability of MHD Flow in the Duct with Electrically Perfectly Conducting Walls


Pages :
12931304


Authors :
S. Dong,
L. S. Liu,
X. M. Ye,
The stability problem of conducting fluid flow in a square duct with perfectly conducting walls is investigated. A homogeneous and constant static magnetic field is applied along the vertical direction of the flow. Nonmodal linear stability analysis is performed on this problem for the first time and the effect of the imposed magnetic field is also taken into account. The amplification and distribution of primary optimal perturbations are obtained by solving iteratively the direct and adjoint governing equations with respect of perturbations. Four modes of perturbations with different symmetries in the space are investigated. Computational results show that, the MHD duct flow is stable at either small or large Hartmann number, but unstable at moderate one. The primary optimal perturbations are in the form of streamwise vortices, which are located inside the thin sidewall layers parallel to the magnetic field. The size of the vortices is decreased with the growing of Hartmann number Ha, meanwhile the amplification of the perturbations is reduced due to the magnetic damping effect. The Hartmann layer perpendicular to the magnetic field seems to be irrelevant to the stability of the MHD duct flow. The most unstable perturbation is in the form of Mode I, which having corotating vortices at opposite sidewalls and the vortices tend to enhance each other.





Synthetic Separation Control Using Vortex Generator and Slot Jet in a High Load Compressor Cascade


Pages :
13051318


Authors :
J. Hu,
R. Wang,
P. Wu,
F. Li,
The compressor cascade performance is significantly restricted by the secondary flow mainly presented as the trailing edge separation and corner stall. This paper develops a synthetic flow control approach in a high turning cascade using the vortex generator and slot jet approach. Numerical simulations were conducted to assess the flow control benefits and illustrate the flow control mechanisms. Four configurations, the baseline, the two individual approaches and the synthetic approach, were simulated to compare the separation control effects. The simulations show that all the three configurations achieve considerable improvements of the cascade performance and the cascade sensitivity to incidence angle is greatly decreased. The synthetic approach improves the most among them which is almost the superposition of the two individual ones. In the synthetic approach, the trailing vortex induced by the vortex generator suppresses the end wall cross flow and deflects the passage vortex, and then prevents the production of corner stall; at the same time, the slot jet speeds up the trailing edge separation caused by the cascade high camber. Owing to the combination of the two aspects, the synthetic approach restricts the developments of secondary flow and vortices in the cascade, and improves the outflow uniformity. The synthetic approach nicely utilizes the advantages of the two individual approach while avoids the shortages by the complementation, so it can achieve more powerful flow control effects. At the end, vortices models are established to illustrate the secondary flow structure and the flow control mechanisms.





Optimization of a Diver Propulsion Vehicle Hydrodynamics Parameter and its’ Shape Improvement by CFD Method for Improving Underwater Speed Record


Pages :
13191328


Authors :
M. R. Sadeghizadeh,
B. Saranjam,
R. Kamali,
The hydrodynamic shape of high speed diver propulsion vehicle (DPV) is very important to its performance. One of the basic optimization steps is minimizing DPV drag force to reduce power required. In the present paper, the research has been started by optimization process with a basic design and it would be gradually improved to achieve favorable hydrodynamic characteristics according to diver size and his required volume. The main target is minimizing lift and drag force as objective function. Moreover, this optimization scenario is applicable and it has been followed on the real DPV prototype. The prototype has been constructed and tested in towing tank for results validation. The 3D geometry of a real diver has been created by image processing and software modeling. According to this model the first basic geometry had been designed and then it has been exported to CFD code for steadystate computational analysis. The SSTKω turbulence model has been selected in the solution to compute hydrodynamic forces. So the position of propulsion system and the shape of vehicle have been improved by repetition process. Output results show that the drag values will be significantly reduced with shape improvement about 51 percent in design speed.





Numerical Simulation with a DES Approach for a HighSpeed Train Subjected to the Crosswind


Pages :
13291342


Authors :
J. Zhang,
K. He,
X. Xiong,
J. Wang,
G. Gao,
A Detached Eddy Simulation (DES) method based on the SST kω turbulence model was used to investigate the instantaneous and timeaveraged flow characteristics around the train with a slender body and high Reynolds number subjected to strong crosswinds. The evolution trends of multiscale coherent vortex structures in the leeward side were studied. These pressure oscillation characteristics of monitoring points on the train surfaces were discussed. Timeaveraged pressure and aerodynamic loads on each part of the train were analyzed inhere. Also, the overturning moment coefficients were compared with the experimental data. The results show that the flow fields around the train present significant unsteady characteristics. Lots of vortex structures with different intensities, spatial geometrical scales, accompanied by a time change, appear in the leeward side of the train, in the wake of the tail car and below the bottom of the train. The oscillation characteristics of the flow field around the train directly affect the pressure change on the train surfaces, thereby affecting the aerodynamic loads of the train. The loads of each car fluctuate around some certain mean values, while the positive peak values can be higher than the mean ones by up to 34%. The load contributions of different parts to the total of the train are also obtained. According to it, to improve the crosswind stability of the highspeed train, much more attention should be paid on the aerodynamic shape design of the streamlined head and cross section. In addition, this work shows that the DES approach can give a better prediction of vortex structures in the wake compared with the RANS solution.





Aerodynamic Design and Performance Assessment of a CentripetalFlow Fan


Pages :
13431353


Authors :
Y. Song,
X. Sug,
D. Huang,
Z. Zheng,
In this paper, the aerodynamic and mechanical design of a centripetalflow fan has been undertaken at a particular thermal environment in which the working fluid behaves as an ideal gas. A preliminary design (onedimensional analysis) study was conducted at first, based on which threedimensional modeling and optimization were subsequently applied to the design of the centripetalflow fan. The aerodynamic performance of the designed fan and its operating characteristics in different working conditions were assessed by means of numerical simulations. Our results suggest that isentropic efficiency and pressure ratio of the centripetalflow fan at design operating conditions can reach 81.14% and 1.0833, respectively, which satisfy the requirements for fans in commercial and industrial applications. From the fan performance curves, it is found that as the mass flow rate increases, the efficiency of the fan operating at the designed rotational speed first increases and then decreases. There exists an optimal mass flow rate which leads to the maximum efficiency of the fan. Similarly, the fan pressure ratio first increases as the mass flow rate increases, attains a maximum value and then decreases as the mass flow rate further increases. At offdesign rotational speeds, although the fan characteristic curves show the same tendency as those observed at the design condition. Moreover, the fan characteristic curve becomes steeper with an increased rotational speed, which means that the variations of isentropic efficiency and pressure ratio with change in mass flow rate become much greater. The results of our present study confirm the feasibility of using the centripetalflow fan for various industrial applications.





Hydrodynamic Modelling of CoalBiomass Mixture in a Bubbling Fluidized Bed Reactor


Pages :
13551362


Authors :
M. Verma,
C. Loha,
A. N. Sinha,
M. Kumar,
A. Saikia,
P. Chatterjee,
Biomass is a renewable and sustainable energy source. Cofiring of biomass with coal will increase the renewable energy share by decreasing the coal consumption. In the present paper, hydrodynamic behaviour of coal and biomass mixture is investigated in a fluidized bed reactor. A Computational Fluid Dynamic (CFD) model is developed and the hydrodynamic behaviour of gas and solid is investigated in detail. The CFD model is based on EulerianEulerian multiphase modelling approach where the solid phase properties are obtained by applying the Kinetic Theory of Granular Flow (KTGF). Six different weight percentages of coal and biomass (100:0, 95:5, 90:10, 80:20, 70:30 and 50:50) are used for the present study. The hydrodynamic behaviour is analyzed in terms of the important hydrodynamic parameters like bed pressure drop, bed expansion ratio, particle volume fraction distribution and velocity distribution. The numerical model is also validated by comparing some of the numerical results with our own experimental data generated in a laboratory scale bubbling fluidized bed reactor.





On the Mechanism of Drag Reduction in FullyDeveloped Turbulent Channel Flow with a Streamwise Microfeatured Superhydrophobic Wall


Pages :
13631374


Authors :
M. SaadatBakhsh,
N. M. Nouri,
H. Norouzi,
The superhydrophobic drag reduction changes the structures of turbulent flow. However, the underlying mechanism is not clear. The aim of this study is to determine the alternations of turbulent flow due to applying a streamwise microfeatured superhydrophobic wall. Large eddy simulations are performed to explore the effect of microfeatures on nearwall behaviors. The results indicate that the outward motion of the lifted lowspeed streaks is restricted to the lower wall layers, and the region of maximum production of streamwise vorticities is shifted toward the microfeatured wall. The quadrant analysis of Reynolds stress shows that there is a stronger increase in outward motion of highspeed fluid and inward motion of lowspeed fluid than ejection and sweep.





Aerodynamic Study of Two Opposing Moving Trains in a Tunnel Based on Different Nose Contours


Pages :
13751386


Authors :
W. H. Li,
T. H. Liu,
J. Zhang,
Z. W. Chen,
X. D. Chen,
T. Z. Xie,
It is well known that the train nose shape has significant influence on the aerodynamic characteristics. This study explores the influence of four kinds of nose shapes (fusiform, flatbroad, bulgebroad, ellipsoidal) on the aerodynamic performance of two opposing highspeed trains passing by each other through a tunnel at 250 km/h. The method of three dimensional, compressible, unsteady Reynoldsaveraged NavierStokes equations and RNG kε double equation turbulence model was carried out to simulate the whole process of two trains passing by each other inside a tunnel. Then the pressure variations on tunnel wall and train surface are compared with previous fullscale test to validate the numerical method adopted in this paper. The assessment characteristics, such as transient pressure and aerodynamic loading, are analyzed to investigate the influence of nose shape on these assessment parameters. It is revealed that aerodynamic performance of trains which have longitudinal nose profile line B (fusiform, flatbroad shape) is relatively better when passing by each other in a tunnel. The results can be used as a guideline for highspeed train nose shape design.





Modified Model for Binary Nanofluid Convection with Initial Constant Nanoparticle Volume Fraction


Pages :
13871395


Authors :
J. Sharma,
U. Gupta,
V. Sharma,
A modified model considering effects of density as well as conductivity of nanoparticles is used to investigate the instability of a binary nanofluid layer. It is assumed that volume fraction of nanoparticles is small and remains constant at the initial state which leads to very interesting and useful results. The perturbed equations so found are analyzed using normal modes and weighted residual method. It is found that oscillatory motions are not possible and instability is invariably through stationary mode. After solving the problem analytically, numerical solutions are found for metallic (aluminium, copper, silver, iron) and nonmetallic (alumina, silica, titanium oxide, copper oxide) nanoparticles using the software Mathematica. The effects of size of nanoparticles, difference in solute concentration, volume fraction of nanoparticles, difference in temperature, conductivity and density of nanoparticles are studied on the onset of convection. The increase in density of nanoparticles destabilizes the fluid layer system where as increase in conductivity stabilizes the same. Lower density of aluminium makes it more stable than other nanoparticles in spite of having its lower conductivity. Metals are largely more stable than nonmetals.





Prediction of Cavitation Performance of Radial Flow Pumps


Pages :
13971408


Authors :
M. Kaya,
E. Ayder,
Cavitation is a major problem in pump design and operation because this phenomenon may lead to various types of instabilities, including hydraulic performance loss and catastrophic damage to the pump material caused by bubble collapse. Therefore, it is critical to predict the cavitation performance of the pump in the design phase itself. The motivation of this study is to develop a systematic methodology to calculate the cavitation performance of radial flow pumps. In the first step of the present work, a cavitating nozzle flow case for which the bubble dynamic behavior is accurately resolved in literature is studied numerically. Subsequently, the capabilities of three cavitation models, implemented in the commercial code Fluent, are evaluated for three radial flow pumps designed at specific speeds ns = 10.4, 22.4, and 34.4. The numerical results are validated with global quantities based on net positive suction head (NPSH) measurements. The results led to the determination of reasonably accurate NPSH values for the defined range of specific speeds.





Determination of the Modes and the Conditions of Ultrasonic Spraying Providing Specified Productivity and Dispersed Characteristics of the Aerosol


Pages :
14091419


Authors :
V. N. Khmelev,
A. V. Shalunov,
R. N. Golykh,
V. A. Nesterov,
R. S. Dorovskikh,
A. V. Shalunova,
For the spraying of liquids and the coating process at hightech productions the method of ultrasonic spraying in a layer having a number of advantages such as low energy capacity, high productivity, finedispersity of obtained aerosol and the absence of spraying agent, is used. However the main problem of ultrasonic spraying application is the absence of the reliable dependences of spraying characteristics (drop diameter and spraying productivity) on the liquid properties (viscosity, surface tension), modes (frequency and vibration amplitude of spraying surface) and conditions (the thickness of liquid layer) of the ultrasonic action. In order to determine these dependences it is proposed the model based on cavitation and wave theory of the drop formation, which allows obtain for the first time theoretical ground of the existence of optimum thickness layer, at which free surface of liquid is acted upon by maximum energy providing drop detachment. The model analysis lets show advisability of the application of vibration frequency of more than 100 kHz for the drop generation with the size of 10 μm and less with the productivity of no less than 0.2 ml/s. Obtained results are proved by the experimental studies, which allow their use for the formulation of the technical requirements to the ultrasonic sprayers at the realization of different technological processes.





Oscillating Motion of an OldroydB Fluid with Fractional Derivatives in a Circular Cylinder


Pages :
14211426


Authors :
N. Raza,
E. U. Haq,
M. M. Rashidi,
A. U. Awan,
M. Abdullah,
The velocity field and tangential shear stress for unsteady flow of an OldroydB fluid with Caputo fractional derivatives through an infinite long cylinder are evaluated. The fluid in the infinitely long cylinder is initially at rest and at t = 0+, due to shear, the fluid starts to oscillate longitudinally. We have solved the fractional model with the tool of Laplace and finite Hankel transformations. The solutions are in series form and are written in generalized Gfunction to avoid the entanglement. In limiting cases, the solutions of ordinary OldroydB fluid, Maxwell fluid with fractional as well as ordinary and Newtonian fluid are derived. Finally, behavior of different physical parameters on fluid is illustrated by graphs.





Massline Visualization of DoubleDiffusive Natural Convection inside a Cavity Filled with Nanofluid Subjected to Heat Flux and Transverse Magnetic Field


Pages :
14271440


Authors :
O. Ghaffarpasand,
In the present work, massline visualization technique as an innovative method is utilized to deepen our insights into the problem of doublediffusive natural convection of nanofluids. The effects of inclination angle and strength of the external magnetic field on one side and heat flux coefficient on the other side on the masslines, isoconcentrations, isotherms, heat and mass transfer are fairly studied and discussed. The governing equations together with appropriate boundary conditions are solved numerically using a finite difference method in a square liddrive cavity filled with Cuwater nanofluid. Four pertinent parameters are studied these; the orientation angle of the magnetic field (λ = 0◦ − 270◦), Hartman number (Ha = 0 − 100), heat flux coefficient (ε= 1 − 200), and nanoparticle volume fraction (ϕ = 0 − 10%). Results indicate that the orientation and strength of applied magnetic field can be considered as the key parameters in controlling doublediffusive natural convection. It is also found that the existence of metallic nanoparticles in the presence of magnetic field can play different roles in the heat and mass transfer variations. Meanwhile, high amount of heat flux injected through the cavity has an aiding effect on the convective current of mass within the cavity. Results also indicate that nanofluid has relatively smaller massline circulation loops than pure fluid.





Dynamic Simulation in Guide Vane Opening Process of a PumpTurbine in Pump Mode


Pages :
14411449


Authors :
L. Han,
H. J. Wang,
Y. H. Gao,
D. Y. Li,
R. Z. Gong,
X. Z. Wei,
During the process of switching conditions in pumpturbine, unstable ﬂow would take place and seriously impact on the stability and safety. This paper deals with the guide vanes’ moving process in pump mode through unsteady numerical simulations. Dynamic mesh methodology is used for simulations in which GVO (Guide Vane Opening) from 9mm to 26mm. Simulation results approve that, there are many complex vortex structures and ﬂow blockages phenomena under small GVO condition. Through the mathematical method of Fast Fourier Transform (FFT) and ShortTime Fourier Transform (STFT), the dominant pressure ﬂuctuation frequencies are from runner blade passing frequency (BPF) and its harmonic frequency, as well as some other low frequencies are from unsteady ﬂow states. Furthermore, the ﬂow states are more unstable and complex under small guide vanes moving process. Compared with ﬁxed GVO position, the ﬂow states are more unstable and complex under guide vanes moving process, while the amplitude of main frequencies becomes higher.





Simulation of Imbibition Phenomena in Fluid Flow through Fractured Heterogeneous Porous Media with Different Porous Materials


Pages :
14511460


Authors :
H. S. Patel,
R. Meher,
In this paper, the counter – current imbibition phenomenon in a fractured heterogeneous porous media is studied with the consideration of different types of porous materials like volcanic sand and fine sand and Adomian decomposition method is applied to find the saturation of wetting phase and the recovery rate of the reservoir. A simulation result is developed to study the saturation of wetting phase in volcanic as well as in fine sand with the recovery rate of the oil reservoir with the choices of some interesting parametric value. This problem has a great importance in the oil recovery process.





Aerodynamically Efficient Rotor Design for Hovering Agricultural Unmanned Helicopter


Pages :
14611474


Authors :
B. A. Haider,
C. H. Sohn,
Y. S. Won,
Y. M. Koo,
Unmanned aerial vehicles, especially agricultural unmanned helicopters (AUH), are nowadays extensively used in precision agriculture. AUHs have recently become responsible for spraying fertilizers and pesticides for crop yields. The strong downward rotating flow produced by the main rotor helps very uniform crop spraying which determines that how important is the aerodynamics of rotor blade in AUH. In this work, the aerodynamic performance of AUH rotor blades is evaluated and an efficient blade is obtained by numerically investigating the influence of design variables on the aerodynamics of rotor blades. The design variables consist of airfoil shape, pitch settings, and twist angle. The limited power available in hover and aerodynamic requirements (lift and drag) are the aerodynamic constraints. This analysis only considers the hovering flight condition at a constant rotational speed. The aerodynamically efficient rotor blade which is based on gradually varying and linearly twisted airfoil shapes, show a significant improvement in hover performance with relatively uniform blade loading. After testing, the optimum blade can be used as the main rotor in the AUH to perform precision farming.





A Novel Method for Defining the Leeward Edge of the Planar Jet in Crossflow


Pages :
14751486


Authors :
K. Zhao,
X. Yang,
P. N. Okolo,
Z. Wu,
W. Zhang,
G. J. Bennett,
To avoid the complexity of the edge definition by the half width, a new approach to defining the leeward edge of the planar jet in crossflow is introduced in this paper. Particle Image Velocimetry (PIV) experiments were performed to measure different flow regimes within the single jet and the dual jets configurations in crossflow. Based on the experimental data acquired, a series of velocity profiles were extracted from the flow field. In each profile, a velocity threshold was given to distinguish the regions sheltered and the regions not sheltered by the planar jet. The boundary of these regions was accordingly recognized as the leeward edge. Furthermore, fitting of the edge was carried out using a second order polynomial so as to enable a mathematical expression of the leeward edge. An application of the proposed approach towards the flow induced noise reduction using a planar jet is also discussed in this paper. In addition, the PIV frame assembly algorithm used in this study is reported.





On Dispersion in Oscillatory Annular Flow Driven Jointly by Pressure Pulsation and Wall Oscillation


Pages :
14871500


Authors :
A. Kumar Roy,
A. K. Saha,
S. Debnath,
Longitudinal dispersion of solute released in an unsteady flow between two coaxial cylinders is reexamined in the presence of first order chemical kinetics in the bulk flow. The flow unsteadiness is caused by the oscillation of the outer tube around its axis as well as by a periodic pressure gradient. Unlike some previous works, the gap width of the annular tube is used as the typical length scale which is physically meaningful to a greater extent. In order to employ the method of moment, a finite difference implicit scheme has been adopted to solve the Aris integral moment equations arising from the unsteady convective diffusion equation for all time periods. The individual and combined effects of different velocity components resulting from steady and timedependent parts of the driving forces are examined and they are identified based on their functionality. In any flow situation, wall factor is found to have a larger contribution in velocity as well as in dispersion compared to the pressure factor. The behaviour of dispersion coefficient with the variation of radius ratio, bulk flow reaction parameter, and frequency parameters have been examined. Dispersion coefficient is found to diminish with the increase of the reactionrate in the bulk flow, whereas the effect of the radius ratio on the dispersion coefficient is fixed by the form of the velocity distribution. The axial distributions of mean concentration are approximated using Hermite polynomial representation from the first four central moments for a range of different reactionrate parameters. It has been found that, irrespective of the flow situation, the peak of the concentration distribution decreases with the increase in reaction rate parameter.





