فهرست مطالب

Applied Fluid Mechanics - Volume:9 Issue: 4, 2016
  • Volume:9 Issue: 4, 2016
  • تاریخ انتشار: 1395/03/30
  • تعداد عناوین: 50
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  • Jun, Feng Hu, Wen, Xue Wang Pages 1559-1568
    The 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 curved-plate 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 fluid-structure 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
  • Guoneng Li, Youqu Zheng, Huawen Yang, Yousheng Xu Pages 1569-1577
    Fluid 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, second-order 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 multiple-peaked modes when the amplitude of the imposed pulsations is larger, whereas the temperature fluctuates in a single-peaked mode when the amplitude of the imposed pulsation is small.
    Keywords: Pulsating flow, Heat transfer enhancement, Computational fluid dynamics
  • Seyed Esmail Razavi, Masoud Hanifi* Pages 1579-1590
    A multi-dimensional virtual characteristic-based 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 Navier-Stokes equations joined with Spalart-Allmaras turbulent model are solved by finite volumes. This scheme is applied to the flows between parallel plates, over backward-facing step, and in square lid-driven 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
  • Loganathan Parasuram*, Balakrishnan Eswari Pages 1591-1601
    A numerical study is carried out for a free convection flow past a continuously moving semi-infinite 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 Crank-Nicolson 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 skin-friction, 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
  • Sebnem Elci *, Huseyin Burak EkmekCi Pages 1603-1614
    The 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) k-omega 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
  • Kuppalapalle Vajravelu, S. Sreenadh, P. Lakshminarayana, G. Sucharitha, M.M. Rashidi* Pages 1615-1625
    This paper deals with peristaltic transport of Phan-Thien-Tanner 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
  • Hamed Bagheri Esfe, M.J. Kermani *, Majid Saffar Avval Pages 1627-1639
    In this paper, effects of non-equilibrium condensation on deviation angle and performance losses of wet stages of steam turbines are investigated. The AUSM-van Leer hybrid scheme is used to solve the two-phase turbulent transonic steam flow around a turbine rotor tip section. The dominant solver of the computational domain is the non-diffusive AUSM scheme (1993), while a smooth transition from AUSM in regions with large gradients (e.g. in and around condensation- and aerodynamic-shocks) 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
  • Teodor Grosan, Cornelia Revnic, Ioan Pop* Pages 1641-1644
    This paper considers the classical problem of the steady boundary layer flow past a semi-infinite 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
  • S. N. Gaikwad *, Shravan Kamble Pages 1645-1654
    In 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 non-dimensional 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)
  • Fateh Mebarek, Oudina *, Rachid BessaIh Pages 1655-1665
    A 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
  • V. Ramachandra Prasad, Shaik Gaffar*, O. Anwar Beg Pages 1667-1678
    This article presents the nonlinear free convection boundary layer flow and heat transfer of an incompressible Tangent Hyperbolic non-Newtonian 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 second-order accurate implicit finite-difference Keller Box technique. The numerical code is validated with previous studies. The influence of a number of emerging non-dimensional 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
  • Marimuthu Muthukannan, P. Rajeshkanna, S. Jeyakumar, Ankit Bajpai Pages 1679-1694
    A 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 3-D Rectangular Enclosure
    K. N. Mohamed, S. Benissad, F. Berrahil, K. Talbi Pages 1695-1708
    The 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 x-z 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
  • S. N. Gaikwad*, V. Javaji Pages 1709-1720
    In the present study, the onset of Darcy-Brinkman double diffusive convection in a Maxwell fluid-saturated anisotropic porous layer is studied analytically using stability analysis. The linear stability analysis is based on normal technique. The modified Darcy-Brinkmam 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, Darcy-Prandtl 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 Runge-Kutta method.
    Keywords: Double diffusive convection, Darcy brinkman Maxwell model, Porous layer, Anisotropy, Heat, mass transfer
  • N.S. Akbar, M. Raza *, R. Ellahi Pages 1721-1730
    The 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
  • Ildebrando PÉrez, Reyes* Pages 1731-1743
    The 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 rigid-rigid and rigid-free 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
  • S.K. Ghosh*, Sanatan Das, R. N. Jana, Ayan Ghosh Pages 1745-1751
    The purpose of present investigation is to deal with g-jitter 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 g-jitter 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
  • Muhammad Bilal Ashraf *, T. Hayat, H. Alsulami Pages 1753-1762
    The present study deals with the Falkner-Skan flow of rate type non-Newtonian fluid. Expressions of an Oldroyd-B 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
  • Ammar Alsabery, Habibis Saleh*, Ishak Hashim, S. H. Hussain Pages 1763-1775
    The 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. COMSOL’s finite element method is used to solve the non-dimensional 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 heat-removal and heat-storage fluid-saturated porous systems.
    Keywords: Natural convection, Square cavity, Nanouid, Interface, Darcy model
  • Upper-Convected Maxwell Fluid Flow with Variable Thermo-Physical Properties over a Melting Surface Situated in Hot Environment Subject to Thermal Stratification
    Adeola John Omowaye, Isaac Lare Animasaun Pages 1777-1790
    An upper-convected 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 non-linear 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 Runge-Kutta 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 skin-friction coefficient and heat transfer rate increases with an increase in Deborah number.
  • Samip Shah*, Salim Channiwala, Digvijay Kulshreshtha, Gaurang Chaudhari Pages 1791-1798
    Paper 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
  • K. Chaudhary*, Vijendra Singh, S. Sharma Pages 1799-1806
    A linear stability analysis is carried out to discuss the effects of horizontal magnetic field and horizontal rotation on thermal instability problem of a couple-stress 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 porosityhastens the onset of convection. The medium permeability P , magnetic field Q , couple-stress and Darcy-Brinkman parameter A D play dual role in determining the stability/instability of the system under certain restrictions. Also, the sufficient conditions responsible for the non-existence of overstability are gained and the principle of exchange of stabilities holds good for a magneto-rotary system.
    Keywords: Couple, stress fluid, Magnetic field, Rotation, Brinkman porous medium
  • Yasmin Asia, Ali Kashif, Ashraf Muhammad* Pages 1807-1817
    The 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 lower-upper (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 Capillary
    Aniruddha Sinha Pages 1819-1827
    Of 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 time-dependent permeability and suction velocity are considered. The governing non-linear patial differential equations are transformed into a system of coupled non-linear ordinary differential equations using similarity transformations and then solved numerically using Crank-Nicolson 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.
  • Nure., Mostafa, M.M. Karim* Manirul Alam Sarker Pages 1829-1837
    This paper presents a numerical study with pressure-based 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 non-cavitating study focuses on choosing mesh size and the influence of the turbulence model. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence (SST) k-ω model and Re-Normalization Group (RNG) k-ε 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
  • A. Mehdizadeh Momen, S.A. Sherif*, William Lear Pages 1839-1850
    In this paper, two new analytical models have been developed to calculate two-phase slug flow pressure drop in microchannels through a sudden contraction. Even though many studies have been reported on two-phase 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 semi-slug 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
  • Pablo Cornejo*, Hector Sep, Uacute, Lveda Pages 1851-1863
    Anumericalmodelisimplementedtodescribefluiddynamicprocessesassociatedwithmid-latitude small-scale (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) LES-Standard Smagorinsky (SS,algebraicmodel),and3)LES-ModifiedSmagorinsky,introducingacorrectionfornon-isotropic grids (MS). The results show the front developing instabilities and generating sub-mesoscale 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 sub-mesoscale 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 sub-mesoscale dynamics within the mixed layer and the non-isotropic grid used in the calculations generates a disparity between the predicted horizontal wave-number 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
  • Roohallah Khoshkhoo, Alireza Jahangirian* Pages 1865-1875
    A 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 adual-timeimplicit 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
  • Gauri Seth*, Subharthi Sarkar, A.J. Chamkha Pages 1877-1886
    Investigation of unsteady MHD natural convection flow through a fluid-saturated porous medium of a viscous, incompressible, electrically-conducting and optically-thin radiating fluid past an impulsively moving semi-infinite 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 non-dimensional 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 finite-difference scheme of the Crank-Nicolson 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
  • Adel Lalaoua*, A. Bouabdallah Pages 1887-1896
    Taylor- 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 bio-separators 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
  • Kuppalapalle Vajravelu, S. Sreenadh, P. Devaki Devaki, K. V. Prasad* Pages 1897-1905
    This paper is concerned with the peristaltic transport of an incompressible non-Newtonian 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 non-Newtonian fluid model and it demands the applicability of yield stress fluid model. Among the available yield stress fluid models for blood, the non-Newtonian 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 non-Newtonian 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 non-Newtonian 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
  • Roozbeh Mollaabbasi*, Javad Mohebbi Najmabad Pages 1907-1914
    This 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 Gamma-Ray 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 (PBT-D). 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
  • Chemseddine Maatki, Walid Hassen, Lioua Kolsi *, Naif Alshammari, Mohamed Naceur Borjini, Habib Ben Aissia Pages 1915-1925
    In 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 three-dimensional 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
  • Manoj Kumar Triveni *, Dipak Sen, Rajsekhar Panua Pages 1927-1936
    This work numerically investigates the natural convection in an arch enclosure filled with Al2O3-water 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. Two-dimensional steady-state 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
  • Faiz Awad*, N. A. H. Haroun, Precious Sibanda, Melusi Khumalo Pages 1937-1944
    In 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 quasi-linearization 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
  • S. Gannouni *, R. Ben Maad Pages 1945-1953
    In 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 cross-sectional geometry.
    Keywords: Tunnel fire, Smoke hazard, CO concentration, Maximum smoke temperature, Aspect ratio, CFD
  • Dr. Nanjundappa C. E., I. S. Shivakumara, R. Arunkumar Pages 1955-1962
    The 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 Rayleigh-Ritz 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
  • Onur Son*, Oksan Cetiner Pages 1963-1968
    This study focuses on drag prediction in the near-wake 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
  • T. Hayat, Anum Shafiq *, Asif Farooq, H. Alsulami, Sabir Shehzad Pages 1969-1975
    In this article, we have studied the combined effects of Newtonian and Joule heating in two-dimensional 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
  • Bhupesh Kumar Mahatha, Raj Nandkeolyar*, Goutam Kumar Mahato, Precious Sibanda Pages 1977-1989
    Two 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 in-built 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 hybrid-powered 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
  • Oleg Sazhin* Pages 1991-1996
    An 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
  • Dulal Pal* Pages 1997-2007
    In 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 non-uniform heat source/sink effects is investigated. The unsteadiness in the flow and temperature fields is due to the time-dependent nature of the stretching velocity and the surface temperature. Both opposing and assisting flows are considered. The dimensionless governing ordinary non-linear differential equations are solved numerically by applying shooting method using Runge-Kutta-Fehlbergmethod. Theeffectsofunsteadinessparameter,buoyancyparameter,thermal radiation, Eckert number, Prandtl number and non-uniform 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
  • Ouahiba Guerri *, Erwan Liberge, Aziz Hamdouni Pages 2009-2023
    This paper presents numerical study of an oval-sail, a bluff-body 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,achoiceofnumericalturbulencemodelisdiscussedthroughresultsofanoval-sail without suction. Three turbulence models are applied: the Rij SSG, the Rij EBRSM and the v2f model. Then, computations are performed for the oval-sail fitted with suction grid. These last simulations are carried out with the low-Reynolds-number Rij EBRSM turbulence model. The influence of the grid geometry on the oval-sail 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 Velocity
    Ezad Hafidzuddin, Roslinda Nazar *, Norihan Arifin, Ioan Pop Pages 2025-2036
    In 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
  • Bhaskar Ch. Sarkar, R. N. Jana, Sanatan Das Pages 2037-2051
    Diffusion-thermo 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
  • M.S. Abdul Aziz*, M.Z. Abdullah, C.Y. Khor, F. Che Ani, N.H. Adam Pages 2053-2062
    This study investigated the effects of temperature on the wave soldering of printed circuit boards (PCBs) using three-dimensional finite volume analysis. A computational solder pot model consisting of a six-blade 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)
  • S. Nouri *, P. Spiterri, A. Ghezal Pages 2063-2071
    The 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 convective-diffusion 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 Navier-Stokes 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 (liquid-mushy 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
  • Noor Fatima Siddiqui *, Mukkarum Hussain, Mahmood Baig Pages 2073-2081
    Total Variation Diminishing (TVD) schemes are low dissipative and high resolution schemes but bounded by stability criterion CFL
    Keywords: TVD scheme, Shock tube problem, Explicit scheme, Efficient scheme, 1D Euler equation
  • Negar Mohammad Aliha, Hossein Afshin *, Bijan Farhanieh Pages 2083-2095
    Using the Yang-Shih low Reynolds k-ε 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, square-shaped, and rectangular nozzles were considered here. A comparison between the mean flow characteristics of offset jets issuing from circular and square-shaped 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 square-shaped 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
  • K. Gangadhar Pages 2097-2103
    The 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 Nachtsheim-Swigert 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