فهرست مطالب
 Volume:9 Issue: 4, 2016
 تاریخ انتشار: 1395/03/30
 تعداد عناوین: 50


Pages 15591568The purpose of this paper is to develop an approximate method for the evaluation of the normal force acting on a flexible plate normal to the wind flow and the deformation of the plate. A theoretical modelling is firstly proposed to predict the relationship between the normal drag coefficient of a rigid curvedplate and the configuration of the plate with the aid of a series of numerical analyses of structure and fluid dynamics. Then, based on the theoretical modelling, an approximate method for the evaluation of the normal force acting on the plate and the deformation of the plate is constructed using only the iteration of structure mechanics analysis, instead of conventional complex iterations of fluidstructure coupling analysis. Simulation tests for 3D flexible plates with different lengths and different material moduli are conducted. Also a comparative simulation test of a 3D flexible plate used in a previous experiment is performed to further confirm the validity and accuracy of the approximate method. Numerical results obtained from the approximate method agree well with those obtained from the fluid dynamics analysis as well as the results of the previous wind tunnel experiment.Keywords: Wind flow, Flexible plate, Fluid, structure interaction, Normal force, Approximate method

Pages 15691577Fluid flow around and heat transfer from a rectangular flat plane with constant uniform heat flux in laminar pulsating flows is studied, and compared with our experimental data. Quantitatively accurate, secondorder schemes for time, space, momentum and energy are employed, and fine meshes are adopted. The numerical results agree well with experimental data. Results found that the heat transfer enhancement is caused by the relative low temperature gradient in the thermal boundary layer, and by the lower surface temperature in pulsating flows. In addition, the heat transfer resistance is much lower during reverse flow period than that during forward flow period. The flow reversal period is about 180 degree behind the pulsating pressure waves. Besides, spectrum results of the simulated averaged surface temperature showed that the temperature fluctuates in multiplepeaked modes when the amplitude of the imposed pulsations is larger, whereas the temperature fluctuates in a singlepeaked mode when the amplitude of the imposed pulsation is small.Keywords: Pulsating flow, Heat transfer enhancement, Computational fluid dynamics

Pages 15791590A multidimensional virtual characteristicbased scheme (MVCB) by the aid of artificial compressibility is developed for convective fluxes in laminar and turbulent incompressible flows. The proper combinations of compatibility equations are determined to obtain primitive variables on cell interfaces. The Reynolds averaged NavierStokes equations joined with SpalartAllmaras turbulent model are solved by finite volumes. This scheme is applied to the flows between parallel plates, over backwardfacing step, and in square liddriven cavity at a wide range of Reynolds numbers. A FORTRAN 90 code has been written and all the results have come out from this code. Several comparisons confirm the scheme ability in accurate simulation of flows without need to any artificial viscosity in laminar and turbulent regimes.Keywords: Navier, Stokes equations, Reynolds averaging, Spalart, Allmaras model, multi, dimensional characteristics, artificial compressibility, Finite volume method

Pages 15911601A numerical study is carried out for a free convection flow past a continuously moving semiinfinite vertical cylinder in the presence of porous medium. The governing boundary layer equations are converted into a nondimensional form and then they are solved by an eﬃcient, accurate and unconditionally stable implicit finite difference scheme of CrankNicolson method. Stability and convergence of the finite difference scheme are established. The velocity, temperature and concentration profiles have been presented for various parameters such as Prandtl number, Schmidt number, thermal Grashof number, mass Grashof number and permeability of the porous medium. The local as well as average skinfriction, Nusselt number and Sherwood number are also shown graphically. It is observed that the increase in the permeability parameter leads to increase in velocity profile, local as well as average shear stress, Nusselt number and Sherwood number but leads to decrease in temperature and concentration profiles. The results of temperature and concentration profiles are compared with available result in literature and are found to be in good agreement.Keywords: Vertical cylinder, Natural convection, Heat, mass transfer, Porous medium, Finite difference

Pages 16031614The interplay between stratification and shear in lakes controls the vertical mixing, which is the most important mechanism affecting the transport of heat, salt, momentum and suspended and dissolved substances. This study attempts to quantify and characterize the turbulence from direct measurements conducted in a reservoir. A 3D numerical model is used to investigate the water column hydrodynamics for the duration of measurements and the performance of various turbulence models used in the CFD model are investigated via simulation of mixing in the reservoir. The drawdown curves produced by the turbulence models are formulized through linear equations. Although, use of different turbulence models do not have significant effects on the flow hydrodynamics away from the intake structure; significant effects especially on turbulence kinetic energy production are observed at the orifice. Therefore, for simulation of withdrawal flow, either use of shear stress transport (SST) komega models solving equations all the way to the wall or kepsilon models with the nonequilibrium wall function is recommended to account for the changes in the pressure gradient. In this study, the methods using quantified turbulent characteristics of the flow to reformulate the Stokes settling velocity to be applied in turbulent flows are also investigated. An approach to predict setting velocity in turbulent flows that utilizes acoustic Doppler instruments for quantification of turbulent characteristics is presented. Modification of the Stokes settling velocity with the nondimensionalized turbulent kinetic energy production profiles lead better results than other turbulence characteristics (buoyancy flux and by Richardson number flux) widely used in characterizing turbulent mixing.Keywords: Vertical mixing, Stratified reservoirs, Turbulent mixing, Turbulence models, Settling velocities

Pages 16151625This paper deals with peristaltic transport of PhanThienTanner fluid in an asymmetric channel induced by sinusoidal peristaltic waves traveling down the flexible walls of the channel. The flow is investigated in a wave frame of reference moving with the velocity of the waveby using the long wavelength and low Reynolds number approximations.The nonlinear governing equations are solved employing a perturbation method by choosing We as the perturbation parameter. The expressions for velocity, stream function and pressure gradient are obtained. The features of the flow characteristics are analyzed through graphs and the obtained results are discussed in detail. It is noticed that the peristaltic pumping gets reduced due to an increase in the phase difference of the traveling waves. It is also observed that the size of the trapping bolus is a decreasing function of the permeability parameter and the Weissenberg number. Furthermore, the results obtained for the flow characteristics reveal many interesting behaviors that warrant further study on the nonNewtonian fluid phenomena, especially the Peristaltic flow phenomena.Keywords: Trapping phenomena, Peristaltic transport, Phan, thien, tanner fluid, Porous medium, Asymmetric channel

Pages 16271639In this paper, effects of nonequilibrium condensation on deviation angle and performance losses of wet stages of steam turbines are investigated. The AUSMvan Leer hybrid scheme is used to solve the twophase turbulent transonic steam flow around a turbine rotor tip section. The dominant solver of the computational domain is the nondiffusive AUSM scheme (1993), while a smooth transition from AUSM in regions with large gradients (e.g. in and around condensation and aerodynamicshocks) to the diffusive scheme by van Leer (1979) guarantees a robust hybrid scheme throughout the domain. The steam is assumed to obey nonequilibrium thermodynamic model, in which abrupt formation of liquid droplets produces a condensation shock. To validate the results, the experimental data by Bakhtar et al. (1995) has been used. It is observed that as a result of condensation, the aerothermodymics of the flow field changes. For example for supersonic wet case with back pressure Pb=30 kPa, the deviation angle and total pressure loss coefficient change by 65% and 200%, respectively, with respect to that in dry case.Keywords: Condensation shock, Deviation angle, Performance loss, Steam turbine

Pages 16411644This paper considers the classical problem of the steady boundary layer flow past a semiinfinite flat plate first considered by Blasius in 1908 with generalized surface slip velocity. Numerical solutions are obtained by solving the nonlinear similarity equation using the bvp4c function from MATLAB for several values of the slip parameters.Keywords: Blasius problem, Generalized slip velocity, Numerical results

Pages 16451654In this paper, we have investigated the onset of double diffusive convection (DDC) in a couple stress fluid saturated rotating anisotropic porous layer in the presence of Soret and Dufour effects using linear stability analyses which is based on the usual normal mode technique. The onset criteria for both stationary and oscillatory modes obtained analytically. The effects of the Taylor number, mechanical anisotropy parameter, Darcy Prandtl number, solute Rayleigh number, normalized porosity parameter, Soret and Dufour parameters on the stationary and oscillatory convections shown graphically. The effects of couple stresses are quite significant for large values of the nondimensional parameter and delay the onset of convection. Taylor number has stabilizing effect on double diffusive convection, Dufour number has stabilizing effect in stationary mode while destabilizing in oscillatory mode. The negative Soret parameter stabilizes the system and positive Soret parameter destabilizes the system in the stationary convection, while in the oscillatory convection the negative Soret coefficient destabilize the system and positive Soret coefficient stabilizes the system.Keywords: Couple stress fluid, Rotation, Anisotropy, Soret parameter, Dufour parameter, Double, diffusive convection (DDC)

Pages 16551665A numerical study of oscillatory magnetohydrodynamic (MHD) natural convection of liquid metal between vertical coaxial cylinders is carried out. The motivation of this study is to determine the value of the critical Rayleigh number, Racr for two orientations of the magnetic field and different values of the Hartmann number (Harand Haz) and aspect ratios A. The inner and outer cylinders are maintained at uniform temperatures, while the horizontal top and bottom walls are thermally insulated. The governing equations are numerically solved using a finite volume method. Comparisons with previous results were performed and found to be in excellent agreement. The numerical results for various governing parameters of the problem are discussed in terms of streamlines, isotherms and Nusselt number in the annuli. The time evolution of velocity, temperature, streamlines and Nusselt number with Racr, Har, Haz, and A is quite interesting. We can control the flow stability and heat transfer rate in varying the aspect ratio, intensity and direction of the magnetic field.Keywords: MHD, Numerical modeling, Liquid metal, Natural convection, Hydrodynamic stability, Cylindrical annulus

Pages 16671678This article presents the nonlinear free convection boundary layer flow and heat transfer of an incompressible Tangent Hyperbolic nonNewtonian fluid from a vertical porous plate with velocity slip and thermal jump effects. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a secondorder accurate implicit finitedifference Keller Box technique. The numerical code is validated with previous studies. The influence of a number of emerging nondimensional parameters, namely the Weissenberg number (We), the power law index (n), Velocity slip (Sf), Thermal jump (ST), Prandtl number (Pr) and dimensionless tangential coordinate ( ) on velocity and temperature evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate and local skin friction are also investigated. Validation with earlier Newtonian studies is presented and excellent correlation achieved. It is found that velocity, skin friction and heat transfer rate (Nusselt number) is increased with increasing Weissenberg number (We), whereas the temperature is decreased. Increasing power law index (n) enhances velocity and heat transfer rate but decreases temperature and skin friction. An increase in Thermal jump (ST) is observed to decrease velocity, temperature, local skin friction and Nusselt number. Increasing Velocity slip (Sf) is observed to increase velocity and heat transfer rate but decreases temperature and local skin friction. An increasing Prandtl number, (Pr), is found to decrease both velocity and temperature. The study is relevant to chemical materials processing applications.Keywords: Non, newtonian tangent hyperbolic fluid, Boundary layer flow, Weissenberg number, Power law index, Velocity slip, Thermal jump, Skin friction, Nusselt number

Pages 16791694A numerical investigation is carried out to investigate the fluid flow field and heat transfer characteristics of two dimensional laminar incompressible jet flows. Simulations are performed for a single vertical slot jet on a block mounted on the bottom wall and the top wall is confined by a parallel wall surface. The present study reveals the vital impact of the Aspect Ratio (AR) and Reynolds number (Re) on the fluid flow and heat transfer characteristics over a wide range. It is observed that the presence of a solid block in the channel increases the overall unsteadiness in the flow. The correlation between the Reynolds numbers and reattachment length is suggested, for all Aspect Ratios (ARs). The horizontal velocity profile at various downstream locations for all ARs is employed to find out the location where the flow gets fully developed. The primary peak value of the Nusselt number (Nu) occurs at the stagnation point, and the secondary peak is at a downstream location. The average Nusselt number increases with the increase of Reynolds number and decreases with the increase of the distance between the jet and the block. The heat transfer correlations between the Reynolds number and Nusselt number are analyzed for constant wall temperature boundary conditions.Keywords: Impinging jet, Reynolds number, Aspect Ratio, Nusselt Number, Vortex center, Coefficient of friction

Investigation of Magneto Hydrodynamic Natural Convection Flows in a 3D Rectangular EnclosurePages 16951708The article deals with magnetic field of free convective flows in cavities similar to those used in artificial growth of single crystals from melts (horizontal Bridgman configurations) and having aspect ratios an equal to 4. The combined effect of wall electrical conductivity and vertical direction of the magnetic field on the buoyancy induced flow of mercury was investigated numerically. The validation of the numerical method was achieved by comparison with both experimental and analytical data found in the literature. The plotted results for variation of velocity, temperature and Nusselt number in terms of the Hartmann number Ha and Rayleigh number Ra showed a considerable decrease in convection intensity as the magnetic field is increased, especially for values of Gr situated around 107. The calculations also showed that the vertically directed magnetic field (perpendicular to the xz plane) is the most effective in controlling the flow and hence the speed of growth of the crystal. Also, wall electrical conductivity enhances damping by changing the distribution of the induced electric current to one which augments the magnitude of the Lorentz force.Keywords: Natural convection, Magnetic field, Cavity, Liquid metal, finite, volume, Lorentz force, tridimensional

Pages 17091720In the present study, the onset of DarcyBrinkman double diffusive convection in a Maxwell fluidsaturated anisotropic porous layer is studied analytically using stability analysis. The linear stability analysis is based on normal technique. The modified DarcyBrinkmam Maxwell model is used for the momentum equation. The Rayleigh number for stationary, oscillatory and finite amplitude convection is obtained analytically. The effect of the stress relaxation parameter, solute Rayleigh number, Darcy number, DarcyPrandtl number, Lewis number, mechanical and thermal anisotropy parameters, and normal porosity parameter on the stationary, oscillatory and finite amplitude convection is shown graphically. The nonlinear theory is based on the truncated representation of the Fourier series method and is used to find the heat and mass transfer. The transient behavior of the Nusselt and Sherwood numbers is obtained by solving the finite amplitude equations using the RungeKutta method.Keywords: Double diffusive convection, Darcy brinkman Maxwell model, Porous layer, Anisotropy, Heat, mass transfer

Pages 17211730The peristaltic flow of a copper water fluid investigate the effects of entropy and magnetic field in an endoscope is studied. The mathematical formulation is presented, the resulting equations are solved exactly. The obtained expressions for pressure gradient, pressure rise, temperature, velocity phenomenon entropy generation number and Bejan number are described through graphs for various pertinent parameters. The streamlines are drawn for some physical quantities to discuss the trapping phenomenon.Keywords: MHD, Peristaltic flow, Copper nanoparticle, Endoscope, Entropy generation

Pages 17311743The problem of convection in a ﬂuid with temperature dependent viscosity and imposed shear ﬂow, driven by pressure gradients and by a top moving wall, is studied for the case of poorly thermal conducting horizontal walls. Analytical expressions accounting for temperature dependent viscosity effects were obtained for the critical Rayleigh number and frequency of oscillation under a shallow water approximation for Poiseuille, Couette and returning primary ﬂows. The results of this investigation contirbute and extend previous ﬁndings showing that the onset of convection can be achieved at smaller critical Rayleigh and wavenumbers. The results include approximations of weak and strong shear ﬂows along with conditions for rigidrigid and rigidfree boundaries. It was found that the imposed shear ﬂow does not inﬂuence the critical wavenumber but it does increases the critical Rayleigh number. In this case convection sets in as oscillatory.Keywords: Temperature dependent viscosity, Shallow water approximation, Returning ow

Pages 17451751The purpose of present investigation is to deal with gjitter forces of a time varing gravity field on unsteady hydromagnetic flow past a horizontal flat plate in the presence of a transverse magnetic field and the flow at the entrance also oscillates because of an applied pressue gradient. This problem deals with mixed convection driven by a combination of gjitter and oscillating pressure gradient under the influence of an applied magnetic field. Analysis of this type find applications in space fluid system design and interpreting the experimental measurements in microgravity flow and heat transfer system.Keywords: MHD flow, G, jitter forces, Critical Grashof number, Forced convection

Pages 17531762The present study deals with the FalknerSkan flow of rate type nonNewtonian fluid. Expressions of an OldroydB fluid in the presence of mixed convection and thermal radiation are used in the development of relevant equations. The resulting partial differential equations are reduced into the ordinary differential equations employing appropriate transformations. Expressions of flow and heat transfer are constructed. Convergence of derived nonsimilar series solutions is guaranteed. Impact of various parameters involved in the flow and heat transfer results is plotted and examined.Keywords: Oldroyd, B fluid, Mixed convection, Thermal radiation, Falkner, Skan flow

Pages 17631775The problem of darcian natural convection in inclined square cavity partially ﬁlled between the central square hole ﬁlled with ﬂuid and inside a square porous cavity ﬁlled with nanoﬂuid is numerically studied using the ﬁnite element method. The left vertical wall is maintained at a constant hot temperature Th and the right vertical wall is maintained at a constant cold temperature Tc, while the horizontal walls are adiabatic. The governing equations are obtained by applying the Darcy model and Boussinesq approximation. COMSOLs ﬁnite element method is used to solve the nondimensional governing equations together with the speciﬁed boundary conditions. The governing parameters of this study are the Rayleigh number (103 ≤ Ra ≤ 107), the Darcy number (10−5 ≤ Da ≤ 10−3), the ﬂuid layer thickness (0.4 ≤ S ≤ 0.8) and the inclination angle of the cavity (0◦ ≤ ω ≤ 6 0◦). The results for the values of the governing parameters in terms of the streamlines, isotherms and average Nusselt number will be presented. The convection is shown to be inhibited by the presence of the hole insert. The thermal property of the insert and the size have opposite inﬂuence on the convection. The results have possible applications in heatremoval and heatstorage ﬂuidsaturated porous systems.Keywords: Natural convection, Square cavity, Nanouid, Interface, Darcy model

UpperConvected Maxwell Fluid Flow with Variable ThermoPhysical Properties over a Melting Surface Situated in Hot Environment Subject to Thermal StratificationPages 17771790An upperconvected Maxwell (UCM) fluid flow over a melting surface situated in hot environment is studied. The influence of melting heat transfer and thermal stratification are properly accounted for by modifying the classical boundary condition of temperature to account for both. It is assumed that the ratio of inertia forces to viscous forces is high enough for boundary layer approximation to be valid. The corresponding influence of exponentially space dependent internal heat generation on viscosity and thermal conductivity of UCM is properly considered. The dynamic viscosity and thermal conductivity of UCM are temperature dependent. Classical temperature dependent viscosity and thermal conductivity models are modified to suit the case of both melting heat transfer and ther mal stratification. The governing nonlinear partial differential equations describing the problem are reduced to a system of nonlinear ordinary differential equations using similarity transformations and completed the solution numerically using the RungeKutta method along with shooting technique (RK4SM). The numerical procedure is validated by comparing the solutions of RK4SM with that of MATLAB based bvp4c. The results reveal that increase in stratification parameter corresponds to decrease in the heat energy entering into the fluid domain from freestream and this significantly reduces the overall temperature and temperature gradient of UCM fluid as it flows over a melting surface. The transverse velocity, longitudinal velocity and temperature of UCM are increasing func tion of temperature dependent viscous and thermal conductivity parameters. At a constant value of melting parameter, the local skinfriction coefficient and heat transfer rate increases with an increase in Deborah number.

Study of Flow Patterns in Radial and Back Swept Turbine Rotor under Design and OffDesign ConditionsPages 17911798Paper details the numerical investigation of flow patterns in a conventional radial turbine compared with a back swept design for same application. The blade geometry of a designed turbine from a 25kW micro gas turbine was used as a baseline. A back swept blade was subsequently designed for the rotor, which departed from the conventional radial inlet blade angle to incorporate up to 25° inlet blade angle. A comparative numerical analysis between the two geometries is presented. While operating at lower than optimum velocity ratios (U/C), the 25° back swept blade offers significant increases in efficiency. In turbocharger since the turbine typically experiences lower than optimum velocity ratios, this improvement in the efficiency at offdesign condition could significantly improve turbocharger performance. The numerical predictions show offdesign performance gains of the order of 4.61% can be achieved, while maintaining design point efficiency.Keywords: Gas turbine impeller, Numerical simulation

Pages 17991806A linear stability analysis is carried out to discuss the effects of horizontal magnetic field and horizontal rotation on thermal instability problem of a couplestress fluid through a Brinkman porous medium. After employing normal mode method on the dimensionless linearized perturbation equations, it is noted that for the stationary state, Taylor number A T promotes stabilization, whereas medium porosityhastens the onset of convection. The medium permeability P , magnetic field Q , couplestress and DarcyBrinkman parameter A D play dual role in determining the stability/instability of the system under certain restrictions. Also, the sufficient conditions responsible for the nonexistence of overstability are gained and the principle of exchange of stabilities holds good for a magnetorotary system.Keywords: Couple, stress fluid, Magnetic field, Rotation, Brinkman porous medium

Pages 18071817The unsteady laminar incompressible flow and heat transfer characteristics of an electrically conducting micropolar fluid in a porous channel with expanding or contracting walls is investigated. The relevant partial differential equations have been reduced to ordinary ones. The reduced system of ordinary differential equations (ODEs) has been solved numerically by lowerupper (LU) triangular factorization or Gaussian elimination and successive over relaxation (SOR) method. The effects of some physical parameters such as magnetic parameter, micropolar parameters, wall expansion ratio, permeability Reynolds number and Prandtl number on the velocity, microrotation, temperature and the shear and couple stresses are discussed.Keywords: Magnetohydrodynamics (MHD), Expanding or contracting walls, Porous channel, Wall expansion ratio, Quasi, linearization

Effect of Heat Transfer on Oscillatory Flow of Blood through a Permeable CapillaryPages 18191827Of concern in the paper is a study on heat transfer in the unsteady magnetohydrodynamic (MHD) flow of blood through a porous segment of a capillary subject to the action of an external magnetic field. Nonlinear thermal radiation and velocity slip condition are taken into account. The timedependent permeability and suction velocity are considered. The governing nonlinear patial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then solved numerically using CrankNicolson scheme. The computational results are presented in graphical/tabular form and thereby some theoretical predictions are made with respect to the hemodynamical flow of blood in a hyperthermal state under the action of a magnetic field. Effects of different parameters are adequately discussed. The results clearly indicate that the flow is appreciably influenced by slip velocity and also by the value of the Grashof number. It is also observed that the thermal boundary layer thickness enhances with increase of thermal radiation.

Pages 18291837This paper presents a numerical study with pressurebased finite volume method for prediction of noncavitating and time dependent cavitating flow on hydrofoil. The phenomenon of cavitation is modeled through a mixture model. For the numerical simulation of cavitating flow, a bubble dynamics cavitation model is used to investigate the unsteady behavior of cavitating flow and describe the generation and evaporation of vapor phase. The noncavitating study focuses on choosing mesh size and the influence of the turbulence model. Three turbulence models such as SpalartAllmaras, Shear Stress Turbulence (SST) kω model and ReNormalization Group (RNG) kε model with enhanced wall treatment are used to capture the turbulent boundary layer on the hydrofoil surface. The cavitating study presents an unsteady behavior of the partial cavity attached to the foil at different time steps for σ=0.8. Moreover, this study focuses on cavitation inception, the shape and general behavior of sheet cavitation, lift and drag forces for different cavitation numbers. Finally, the flow pattern and hydrodynamic characteristics are also studied at different angles of attack.Keywords: Cavitation, CAV2003 hydrofoil, Finite volume method, Turbulence model, Unsteady flow

Pages 18391850In this paper, two new analytical models have been developed to calculate twophase slug flow pressure drop in microchannels through a sudden contraction. Even though many studies have been reported on twophase flow in microchannels, considerable discrepancies still exist, mainly due to the difficulties in experimental setup and measurements. Numerical simulations were performed to support the new analytical models and to explore in more detail the physics of the flow in microchannels with a sudden contraction. Both analytical and numerical results were compared to the available experimental data and other empirical correlations. Results show that models, which were developed based on the slug and semislug assumptions, agree well with experiments in microchannels. Moreover, in contrast to the previous empirical correlations which were tuned for a specific geometry, the new analytical models are capable of taking geometrical parameters as well as flow conditions into account.Keywords: Slug flow, Microchannels, Two, phase flow, Sudden, area change

Pages 18511863Anumericalmodelisimplementedtodescribeﬂuiddynamicprocessesassociatedwithmidlatitude smallscale (10 km) upper ocean fronts by using modiﬁed state of the art computational ﬂuid dynamics tools. A periodic system was simulated using three different turbulent closures: 1) URANSReynolds Stress Model (RSM, seven equation turbulence model), 2) LESStandard Smagorinsky (SS,algebraicmodel),and3)LESModiﬁedSmagorinsky,introducingacorrectionfornonisotropic grids (MS). The results show the front developing instabilities and generating submesoscale structures after four days of simulation. A strongly unstable shear ﬂow is found to be conﬁned within the mixed layer with a high Rossby number (Ro > 1) and high vertical velocity zones. The positive (negative) vertical velocity magnitude is found to be approximately O(10−3) m/s(O(10−2) m/s), one (two) order(s) of magnitude larger than the vertical velocity outside the submesoscale structures, where the magnitude is stable at O(10−4) m/s. The latter value is consistent with previous numerical and experimental studies that use coarser grid sizes and therefore do not explicitly calculate the small scale structures. The nonlinear ﬂow introduced by the submesoscale dynamics within the mixed layer and the nonisotropic grid used in the calculations generates a disparity between the predicted horizontal wavenumber spectra computed using the RSM model with respect to the linear eddy viscosity model SS. The MS approach improves SS predictions. This improvement is more signiﬁcant below the mixed layer in the absence of ﬂow nonlinearities. The horizontal spectra predicted with the RSM model ﬁts a slope of−3 for large scale structures and a slope between−2 and−5/3 for turbulent structures smaller than 300 m. This work contributes to the investigation of thephysicalandmethodologicalaspectsforthedetailedmodellingandunderstandingofsmallscale structures in ocean turbulence.Keywords: Submesoscale, Ocean vertical mixing, Turbulence, Geophysical uid dynamics

Pages 18651875A numerical simulation method is employed to investigate the effect of the steady multiple plasma body forces on the flow field of stalled NACA 0015 airfoil. The plasma body forces created by multiple Dielectric Barrier Discharge (DBD) actuators are modeled with a phenomenological plasma method coupled with 2dimensional compressible turbulent flow equations. The body force distribution is assumed to vary linearly in the triangular region around the actuator. The equations are solved using adualtimeimplicit finite volume method on unstructured grids. In this paper, the responses of the separated flow field to the effects of single and multiple DBD actuators over the broad range of angles of attack ( 9−30 ) are studied. The effects of the actuators positions on the flow field are also investigated. It is shown that the DBD have a significant effect on flow separation control in low Reynolds number aerodynamics.Keywords: Flow Control, Dielectric Barrier Discharge, Numerical Simulation, Multiple Plasma Body Forces, Low Reynolds Number Flow

Pages 18771886Investigation of unsteady MHD natural convection flow through a fluidsaturated porous medium of a viscous, incompressible, electricallyconducting and opticallythin radiating fluid past an impulsively moving semiinfinite vertical plate with convective surface boundary condition is carried out. With the aim to replicate practical situations, the heat transfer and thermal expansion coefficients are chosen to be constant and a new set of nondimensional quantities and parameters are introduced to represent the governing equations along with initial and boundary conditions in dimensionless form. Solution of the initial boundaryvalue problem (IBVP) is obtained by an efficient implicit finitedifference scheme of the CrankNicolson type which is one of the most popular schemes to solve IBVPs. The numerical values of fluid velocity and fluid temperature are depicted graphically whereas those of the shear stress at the wall, wall temperature and the wall heat transfer are presented in tabular form for various values of the pertinent flow parameters. A comparison with previously published papers is made for validation of the numerical code and the results are found to be in good agreement.Keywords: Unsteady MHD natural convection flow, Convective surface boundary condition, Porous medium, Optically thin fluid, Non, similar solution

Pages 18871896Taylor Couette flow (TCF) is an important template for studying various mechanisms of the laminarturbulent transition of rotating fluid in enclosed cavity. It is also relevant to engineering applications like bearings, fluid mixing and filtration. Furthermore, this flow system is of potential importance for development of bioseparators employing Taylor vortices for enhancement of mass transfer. The fluid flowing in the annular gap between two rotating cylinders has been used as paradigm for the hydrodynamic stability theory and the transition to turbulence. In this paper, the fluid in an annulus between short concentric cylinders is investigated numerically for a three dimensional viscous and incompressible flow. The inner cylinder rotates freely about a vertical axis through its centre while the outer cylinder is held stationary and oscillating radially. The main purpose is to examine the effect of a pulsatile motion of the outer cylinder on the onset of Taylor vortices in the vicinity of the threshold of transition, i.e., from the laminar Couette flow to the occurrence of Taylor vortex flow. The numerical results obtained here show significant topological changes on the Taylor vortices. In addition, the active control deeply affects the occurrence of the first instability. It is established that the appearance of the Taylor vortex flow is then substantially delayed with respect to the classical case; flow without control.Keywords: CFD simulation, Pulsating motion, Finite geometry, Active control, Taylor, vortex flow

Pages 18971905This paper is concerned with the peristaltic transport of an incompressible nonNewtonian fluid in an elastic tube. Here the flow is due to three different peristaltic waves and two different types of elastic tube. The constitution of blood suggests a nonNewtonian fluid model and it demands the applicability of yield stress fluid model. Among the available yield stress fluid models for blood, the nonNewtonian Casson fluid is preferred. The Casson fluid model describes the flow characteristics of blood accurately at low shear rates and when it flows through small blood vessels. Long wavelength approximation is used to linearize the governing equations. The effect of peristalsis and nonNewtonian nature of blood on velocity, plug flow velocity, wall shear stress and the flux flow rate are derived. The flux is determined as a function of inlet, outlet, external pressures, yield stress, amplitude ratio, and the elastic properties of the tube. Furthermore, it is observed that, the yield stress, peristaltic wave, and the elastic parameters have strong effects on the flux of the nonNewtonian fluid, namely, blood. One of the important observation is that the flux is more when the tension relation is an exponential curve rather than that of a fifth degree polynomial. Further, in the absence of peristalsis and when the yield stress tends to zero our results agree with the results of Rubinow and Keller (1972). This study has significance in understanding peristaltic transport of blood in small blood vessels of living organisms.Keywords: Casson fluid, Peristaltic blood flow, Fluid flux, Amplitude ratio, Wall shear stress, Yield stress, Elastic tube

Pages 19071914This research deals with experimental work on solid suspension and dispersion in stirred tank reactors that operate with complex fluids. Only suspended speed (Njs) throughout the vessel was characterized using GammaRay Densitometry. The outcomes of this study help to understand solid suspension mechanisms involving changes the rheology of the fluid and provide engineering data for designing stirred tanks. All experiments were based on classic radial and axial flow impellers, i.e., Rushton Turbine (RT) and Pitched Blade Turbine in down pumping mode (PBTD). Three different liquids (water, waterࣀ, and water㰀) were employed in several concentrations. The CMC solution introduced as a pseudo plastic fluid and PAA solution was applied as a Herschel Bulkley fluid. The rheological properties of these fluids were characterized separately. According to the findings, the critical impeller speeds for solid suspension for nonNewtonian fluids were more eminent than those for water. Experiments were performed to characterize the effects of solid loading, impeller clearance and viscosity on Njs. Also the PSO method is employed to find suitable parameters of Zwietering's correlation for prediction of Njs in Non Newtonian fluids.Keywords: Liquid, Solid, Stirred tank, Gamma, ray densitometry, non, Newtonian fluids, Just Suspended Speed, PSO

Pages 19151925In the present work, the effect of magnetic field on double diffusive natural convection in a cubic cavity filled with a binary mixture is numerically studied using the finite volume method. Two vertical walls are maintained at different temperatures and concentrations. The study is focused on the determination of the entropy generation due to heat and mass transfer, fluid friction and magnetic effect. The influence of the magnetic field on the threedimensional flow, temperature and concentration fields, entropy generation and heat and mass transfer are revealed. The main important result of this study is that the increase of Hartmann number damped the flow and homogenized the entropy generation distribution in the entire cavity.Keywords: Entropy generation, Magneto convection, Heat, mass transfer

Pages 19271936This work numerically investigates the natural convection in an arch enclosure filled with Al2O3water based nanofluid. The left side wall of the enclosure is maintained at a higher temperature than that of right side wall while the remaining walls are kept adiabatic. Twodimensional steadystate governing equations are solved using the finite volume method (FVM). The present work is conducted to state the effects of pertinent parameters such as nanoparticles volume faction () = 0 to 9%, curvature ratio (CR) = 1 to 1.5 and Rayleigh number (Ra) = 104 to 106 on fluid flow and temperature distribution. The numerical results are presented in the form of streamlines, isotherms, local and average Nusselt number. It is observed from the investigation that the variables are exhibiting a significant impact on the heat transfer. The heat transfer rate is enhanced with the increment in the volume fraction of the nanoparticles up to 5% and after that it is decreased gradually. The heat transfer rate is increased with the increase of curvature ratio and it is significantly higher at CR = 1.5. As per the expectation, the heat transfer is increased along with the increment in Rayleigh number. A good agreement is found between the present work and experimental & numerical results from the literature.Keywords: Natural convection, Arch enclosure, Nanofluid, Curvature ratio, Nusselt number

Pages 19371944In this paper the problem of unsteady nanofluid flow over a stretching sheet subject to couple stress effects is presented. Most previous studies have assumed that the nanoparticle volume fraction at the boundary surface may be actively controlled. However, a realistic boundary condition for the nanoparticle volume fraction model is that the nanoparticle flux at the boundary be set to zero. This paper differs from previous studies in that we assume there is no active control of the nanoparticle volume fraction at boundary. The spectral relaxation method has been used to solve the governing equations, moreover the results were further confirmed by using the quasilinearization method. The qualitative and quantitative effects of the dimensionless parameters in the problem such as the couple stress parameter, the Prandtl number, the Brownian motion parameter, the thermophoresis parameter, the Lewis number on the fluid behavior are determined.Keywords: Nanofluid, Couple stress, Stretching surface, Vanishing nanoparticle flux, Spectral relaxation method

Pages 19451953In a tunnel fire, the production of smoke and toxic gases remains the principal prejudicial factors to users. The heat is not considered as a major direct danger to users since temperatures up to man level do not reach tenable situations that after a relatively long time except near the fire source. However, the temperatures under ceiling can exceed the thresholds conditions and can thus cause structural collapse of infrastructure. This paper presents a numerical analysis of smoke hazard in tunnel fires with different aspect ratio by large eddy simulation. Results show that the CO concentration increases as the aspect ratio decreases and decreases with the longitudinal ventilation velocity. CFD predicted maximum smoke temperatures are compared to the calculated values using the model of Li et al. and then compared with those given by the empirical equation proposed by kurioka et al. A reasonable good agreement has been obtained. The backlayering length decreases as the ventilation velocity increases and this decrease fell into good exponential decay. The dimensionless interface height and the region of bad visibility increases with the aspect ratio of the tunnel crosssectional geometry.Keywords: Tunnel fire, Smoke hazard, CO concentration, Maximum smoke temperature, Aspect ratio, CFD

Pages 19551962The effect of cubic temperature profiles on the onset ferroconvection in a Brinkman porous medium in presence of a uniform vertical magnetic field is studied. The lower and upper boundaries are taken to be rigidisothermal and ferromagnetic. The RayleighRitz method with Chebyshev polynomials of the second kind as trial functions is employed to extract the critical stability parameters numerically. The results indicate that the stability of ferroconvection is significantly affected by cubic temperature profiles and the mechanism for suppressing or augmenting the same is discussed in detail. It is observed that the effect of Darcy number , Da magnetic number 1 M and nonlinearity of the fluid magnetization parameter 3 M is to hasten, while an increase in the ratio of viscosity parameter and Biot numberBi is to delay the onset of ferroconvection in a Brinkman porous medium. Further, increase in , Bi 1, M 3 M and decrease in , Dais to decrease the size of the convection cells.Keywords: Ferrofluid, Cubic temperature profiles, Ferro convection in Brinkman porous medium, RayleighRitz technique

Pages 19631968This study focuses on drag prediction in the nearwake of a circular cylinder by use of mean velocity profiles and discusses the closest location where a wake survey would yield an accurate result. Although the investigation considers both the mean and fluctuating velocities, the main focus is on the mean momentum deficit which should be handled properly beyond a critical distance. Digital Particle Image Velocimetry (DPIV) experiments are performed in a Reynolds number range of 100 to 1250. Wake characteristics such as vortex formation length (L) and wake width (t) are determined and their relations to drag prediction are presented. Drag coefficients determined by momentum deficit formula are found to be in good agreement with experimental and numerical literature data in present Reynolds number regime.Keywords: Circular cylinder, Drag prediction, DPIV, Momentum deficit

Pages 19691975In this article, we have studied the combined effects of Newtonian and Joule heating in twodimensional flow of Williamson fluid over the stretching surface. Mathematical analysis is presented in the presence of viscous dissipation. The governing partial differential equations are reduced into the ordinary differential equations by appropriate transformations. Both series and numerical solutions are constructed. Graphical results for the velocity and temperature fields are displayed and discussed for various sundry parameters. Numerical values of local skin friction coefficient and the local Nusselt number are tabulated and analyzed.Keywords: Heat transfer, Joule heating, Williamson fluid, Newtonian heating

Pages 19771989Two dimensional steadyhydromagnetic boundary layer ﬂow of aviscous, incompressible, and electrically conducting nanoﬂuid past a stretching sheet with Newtonian heating, in the presence of viscous and Joule dissipations is studied. The transport equations include the combined effects of Brownian motion and thermophoresis. The governing nonlinear partial differential equations are transformedtoasetofnonlinearordinarydifferentialequationswhicharethensolvedusingSpectral Relaxation Method (SRM) and the results are validated by comparison with numerical approximations obtained using the Matlab inbuilt boundary value problem solver bvp4c, and with existing results available in literature. Numerical values of ﬂuid velocity, ﬂuid temperature and species concentrationaredisplayedgraphicallyversusboundarylayercoordinateforvariousvaluesofpertinent ﬂow parameters whereas those of skin friction, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent ﬂow parameters. Such nanoﬂuid ﬂows are useful in many applications in heat transfer, including microelectronics, fuel cells, pharmaceutical processes, and hybridpowered engines, engine cooling/vehicle thermal management, domestic refrigerator, chiller, heat exchanger, in grinding, machiningand in boiler ﬂuegas temperature reduction.Keywords: Magnetohydrodynamics, Nanouid, Newtonian heating, Joule dissipations, Viscous dissipation

Pages 19911996An analytical model of a thermal anemometer sensor is developed. A thermal anemometer microsensor utilizing doped polycrystalline silicon is created. A liquid flow meter prototype based on a thermal anemometer microsensor is designed. Results of the flow meter testing are presented.Keywords: Thermal flow sensor, Heat mass transfer, Liquid flow meter, MEMS

Pages 19972007In the present study an unsteady mixed convection boundary layer ﬂow of an electrically conducting ﬂuid over an stretching permeable sheet in the presence of transverse magnetic ﬁeld, thermal radiation and nonuniform heat source/sink effects is investigated. The unsteadiness in the ﬂow and temperature ﬁelds is due to the timedependent nature of the stretching velocity and the surface temperature. Both opposing and assisting ﬂows are considered. The dimensionless governing ordinary nonlinear differential equations are solved numerically by applying shooting method using RungeKuttaFehlbergmethod. Theeffectsofunsteadinessparameter,buoyancyparameter,thermal radiation, Eckert number, Prandtl number and nonuniform heat source/sink parameter on the ﬂow and heat transfer characteristics are thoroughly examined. Comparisons of the present results with previously published results for the steady case are found to be excellent.Keywords: Boundary layer ow, Stretching sheet, Magnetohydrodynamic, Thermal radiation, Mixed convection, Heat transfer

Pages 20092023This paper presents numerical study of an ovalsail, a bluffbody equipped with a grid all along the span. Suction based ﬂow control is applied to this body that is developed for wind assisted ship propulsion. First,achoiceofnumericalturbulencemodelisdiscussedthroughresultsofanovalsail without suction. Three turbulence models are applied: the Rij SSG, the Rij EBRSM and the v2f model. Then, computations are performed for the ovalsail ﬁtted with suction grid. These last simulations are carried out with the lowReynoldsnumber Rij EBRSM turbulence model. The inﬂuence of the grid geometry on the ovalsail aerodynamic performances is highlighted. All simulations are carriedoutforthesailsetatzeroincidence. TheReynoldsnumberbasedonthefreestreamvelocity and the proﬁle chord is Re = 5105. Results are compared to available experimental data.Keywords: Flow control, Oval, sail, Turbulence, Numerical study, URANS, Suction

Boundary Layer Flow and Heat Transfer over a Permeable Exponentially Stretching/Shrinking Sheet with Generalized Slip VelocityPages 20252036In this paper, the steady laminar boundary layer flow and heat transfer over a permeable exponentially stretching/shrinking sheet with generalized slip velocity is studied. The flow and heat transfer induced by stretching/shrinking sheets are important in the study of extrusion processes and is a subject of considerable interest in the contemporary literature. Appropriate similarity variables are used to transform the governing nonlinear partial differential equations to a system of nonlinear ordinary (similarity) differential equations. The transformed equations are then solved numerically using the bvp4c function in MATLAB. Dual (upper and lower branch) solutions are found for a certain range of the suction and stretching/shrinking parameters. Stability analysis is performed to determine which solutions are stable and physically realizable and which are not stable. The effects of suction parameter, stretching/shrinking parameter, velocity slip parameter, critical shear rate and Prandtl number on the skin friction and heat transfer coefficients as well as the velocity and temperature profiles are presented and discussed in detail. It is found that the introduction of the generalized slip boundary condition resulted in the reduction of the local skin friction coefficient and local Nusselt number. Finally, it is concluded from the stability analysis that the first (upper branch) solution is stable while the second (lower branch) solution is not stable.Keywords: Boundary layer, Heat transfer, General slip, Stretching, shrinking, Numerical solution, Dual solutions, Stability analysis

Pages 20372051Diffusionthermo and thermal radiation effects on an unsteady magnetohydrodynamic (MHD) free convective flow past a moving infinite vertical plate with the variable temperature and concentration in the presence of transverse applied magnetic field embedded in a porous medium have been analyzed. The flow is governed due to the impulsive as well as accelerated motion of the plate. The governing equations have been solved by employing the Laplace transform technique. The influences of the pertinent parameters on the velocity field, temperature distribution, concentration of the fluid, shear stress, rate of heat and mass transfers at the plate have been presented either graphically or in tabular form.Keywords: Magnetohydrodynamic (MHD) flow, Impulsive, accelerated motion, Radiation, Diffusion porous medium

Pages 20532062This study investigated the effects of temperature on the wave soldering of printed circuit boards (PCBs) using threedimensional finite volume analysis. A computational solder pot model consisting of a sixblade rotational propeller was developed and meshed using tetrahedral elements. The leaded molten solder (Sn63Pb37) distribution and PCB wetting profile were determined using the volume of fluid technique in the fluid flow solver, FLUENT. In this study, the effects of five different molten solder temperatures (456 K, 473 K, 523 K, 583 K, and 643 K) on the wave soldering of a 70 mm × 146 mm PCB were considered. The effects of temperature on wetting area, wetting profile, velocity vector, and full wetting time were likewise investigated. Molten solder temperature significantly affected the wetting time and distribution of PCBs. The molten solder temperature at 523 K demonstrated desirable wetting distribution and yielded a stable fountain profile and was therefore considered the best temperature in this study. The simulation results were substantiated by the experimental results.Keywords: Wave soldering, Wetting area, Volume of fluid (VOF), Finite volume method, Printed circuit board (PCB)

Pages 20632071The present work is proposed a numerical parametric study of heat and mass transfer in a rotating vertical cylinder during the solidification of a binary metallic alloy. The aim of this paper is to present an enthalpy formulation based on the fixed grid methodology for the numerical solution of convectivediffusion during the phase change in the case of the steady crucible rotation. The extended Darcy model including the time derivative and Coriolis terms was applied as momentum equation. It was found that the buoyancy driven flow and solute distribution can be affected significantly by the rotating cylinder. The problem is governed by the NavierStokes equations coupled with the conservation laws of energy and solute. The resulting system was discretized by the control volume method and solved by the SIMPLER algorithm proposed by Patankar. A computer code was developed and validated by comparison with previous studies. It can be observed that the forced convection introduced by rotation, dramatically changes the flow and solute distribution at the interface (liquidmushy zone). The effect of Reynolds number on the Nusselt number, flow and solute distribution is presented and discussed.Keywords: Vertical Solidification, Finite Volume method, Numerical analysis, Heat, mass transfer, Phase Change, Bridgman Growth

Pages 20732081Total Variation Diminishing (TVD) schemes are low dissipative and high resolution schemes but bounded by stability criterion CFLKeywords: TVD scheme, Shock tube problem, Explicit scheme, Efficient scheme, 1D Euler equation

Pages 20832095Using the YangShih low Reynolds kε turbulence model, the mean flow field of a turbulent offset jet issuing from a long circular pipe was numerically investigated. The experimental results were used to verify the numerical results such as decay rate of streamwise velocity, locus of maximum streamwise velocity, jet half width in the wall normal and lateral directions, and jet velocity profiles. The present study focused attention on the influence of nozzle geometry on the evolution of a 3D incompressible turbulent offset jet. Circular, squareshaped, and rectangular nozzles were considered here. A comparison between the mean flow characteristics of offset jets issuing from circular and squareshaped nozzles, which had equal area and mean exit velocity, were made numerically. Moreover, the effect of aspect ratio of rectangular nozzles on the main features of the flow was investigated. It was shown that the spread rate, flow entrainment, and mixing rate of an offset jet issuing from circular nozzle are lower than squareshaped one. In addition, it was demonstrated that the aspect ratio of the rectangular nozzles only affects the mean flow field of the offset jet in the near field (up to 15 times greater than equivalent diameter of the nozzles). Furthermore, other parameters including the wall shear stress, flow entrainment and the length of potential core were also investigated.Keywords: 3D offset jet, Numerical simulation, Aspect ratio, Rectangular nozzle, Circular nozzle

Pages 20972103The problem of laminar radiation and viscous dissipation effects on laminar boundary layer flow over a vertical plate with a convective surface boundary condition is studied using different types of nanoparticles. The general governing partial differential equations are transformed into a set of two nonlinear ordinary differential equations using unique similarity transformation. Numerical solutions of the similarity equations are obtained using the NachtsheimSwigert Shooting iteration technique along with the fourth order Runga Kutta method. Two different types of nanoparticles copper water nanofluid and alumina water nanofluid are studied. The effects of radiation and viscous dissipation on the heat transfer characteristics are discussed in detail. It is observed that as Radiation parameter increases, temperature decreases for copper water and alumina water nanofluid and the heat transfer coefficient of nanofluids increases with the increase of convective heat transfer parameter for copper water and alumina water nanofluids.Keywords: Laminar boundary layer, Nanofluids, Radiation, Viscous dissipation