Journal Of Applied Fluid Mechanics
Volume:9 Issue: 5, Sep-Oct 2016

This paper presents an experimental investigation of the aerodynamic and thermal characteristics of a round jet of hot air, injected through a nozzle into a parallel air flow, simulating a hot streak. Experiments were performed by imposing the same total pressure, established by means of a five-hole probe, for the mainstream and the jet at nozzle exit. Time-averaged temperatures at different points over planes downstream of the nozzle exit section were measured by thermocouple rakes. Experimental data, presented in a non-dimensional form, provide a representation not correlated to individual maximum jet temperature and Reynolds number, in the respective fields of variation. The attenuation of the hot jet strength is reported as a function of the normalized axial coordinate for the various operating conditions considered. Results obtained for the hot jet discharged into a parallel flow are compared with data obtained for the hot jet spreading into stagnant air.

Computational fluid dynamics (CFD) study was done on the propeller design of a micro aerial vehicle (quadrotor-typed) to optimize its aerodynamic performance via Shear Stress Transport K-Omega (SST k-ω) turbulence model. The quadrotor model used was WL-V303 Seeker. The design process started with airfoils selection and followed by the evaluation of drone model in hovering and cruising conditions. To sustain a 400g payload, by Momentum Theory an ideal thrust of 5.4 N should be generated by each rotor of the quadrotor and this resulted in an induced velocity of 7.4 m/s on the propeller during hovering phase, equivalent to Reynolds number of 10403 at 75% of the propeller blade radius. There were 6 propellers investigated at this Reynolds number. Sokolov airfoil which produced the largest lift-to-drag ratio was selected for full drone installation to be compared with the original model (benchmark). The CFD results showed that the Sokolov propeller generated 0.76 N of thrust more than the benchmark propeller at 7750 rpm. Despite generating higher thrust, higher drag was also experienced by the drone installed with Sokolov propellers. This resulted in lower lift-to-drag ratio than the benchmark propellers. It was also discovered that the aerodynamic performance of the drone could be further improved by changing the rotating direction of each rotor. Without making changes on the structural design, the drone performance increased by 39.58% in terms of lift-to-drag ratio by using this method.

The onset of convection in a porous medium saturated by a dielectric nanofluid with vertical AC electric field is investigated. The flux of volume fraction of a nanoparticle with the effect of thermophoresis is taken to be zero on the boundaries and the eigenvalue problem is solved using the Galerkin method. The model used for nanofluid incorporates the combined effect of Brownian diffusion, thermophoresis and electrophoresis, while for porous medium Darcy model is employed. The results show that increase in the AC electric RayleighDarcy number, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh-Darcy number are to hasten the onset of convection. The size of convection cells does not depend on nanofluid parameters, but decreases with increasing the AC electric Rayleigh-Darcy number. The non-existence of oscillatory convection is also obtained. Keywords:

Currently, research on the aerodynamic lift of vehicle windshield wipers is confined to the steady results, and there are very few test results. In the face of this truth, a wind tunnel test is conducted by using the Multipoint Film Force Test System (MFF). In this test, the aerodynamic lift of four kinds of wiper is measured at different wind speeds and different rotation angles. And then, relevant steady-state numerical simulations are accomplished and the mechanism of the aerodynamic lift is analyzed. Furthermore, combined with dynamic meshing and user-defined functions (UDF), transient aerodynamic characteristics of wipers are obtained through numerical simulations. It is found that the aerodynamic lift takes great effect on the stability of wipers, and there is maximum value of the lift near a certain wind speed and rotation angle. The lift force when wipers are rotating with the free stream is less than steady, and the force when rotating against the free stream is greater than steady.

In this study, stability of unsteady mixed convection in a horizontal annulus between two concentric cylinders was investigated numerically. The surfaces of the cylinders were considered to be at fixed temperatures and it was assumed that the hot inner cylinder is rotating at a constant angular velocity. The buoyancy forces were formulated utilizing the Boussinesq approximation. The governing equations of fluid flow and heat transfer in the annulus were solved with a finite element method for different values of the geometric (radius ratio) and transport parameters (Rayleigh number and Reynolds number). Development of the convective flow and heat transfer was expressed by the average Nusselt number for the outer cylinder. The results show that, for a narrow gap annulus, convective flow induces flow bifurcation and becomes unstable for high values of the Rayleigh number. Flow becomes more unstable with an increase in the Reynolds number. For a wide gap annulus, flow is stable for all values of the Rayleigh number if the rotation effects are small. On the other hand, convective flow becomes unstable for the modest and high values of the Ra number with an increase in the Re number.

In this study, the main objective is to develop a one dimensional model to predict design and off design performance of an operational axial flow compressor by considering the whole gas turbine assembly. The design and off-design performance of a single stage axial compressor are predicted through 1D and 3D modeling. In one dimensional model the mass, momentum and energy conservation equations and ideal gas equation of state are solved in mean line at three axial stations including rotor inlet, rotor outlet and stator outlet. The total to total efficiency and pressure ratio are forecasted using the compressor geometry, inlet stagnation temperature and stagnation pressure, the mass flow rate and the rotational speed of the rotor, and the available empirical correlation predicting the losses. By changing the mass flow rate while the rotational speed is fixed, characteristic curves of the compressor are obtained. The 3D modeling is accomplished with CFD method to verify one dimensional code at non-running line conditions. By defining the threedimensional geometry of the compressor and the boundary conditions coinciding with one dimensional model for the numerical solver, axial compressor behavior is predicted for various mass flow rates in different rotational speeds. Experimental data are obtained from tests of the axial compressor of a gas turbine engine in Sharif University gas turbine laboratory and consequently the running line is attained. As a result, the two important extremities of compressor performance including surge and choking conditions are obtained through 1D and 3D modeling. Moreover, by comparing the results of one-dimensional and three-dimensional models with experimental results, good agreement is observed. The maximum differences of pressure ratio and isentropic efficiency of one dimensional modeling with experimental results are 2.1 and 3.4 percent, respectively.

Two different channel entrance designs, code named Valley First (VF) and Peak First (PF), were experimentally visualized by means of smoke-wire visualization technique to observe their effects towards the streamwise counter-rotating vortices generated. The spanwise wavelength of the vortices was pre-set by modifying the leading edge. The investigation was carried out on the laminar boundary-layer flow in a rectangular channel with one-sided wavy surface that has amplitude a and wavelength λ of 7.5 mm and 76 mm, respectively. The vortices in the channel with VF design preserve farther downstream than those on the PF design, which might be caused by the large favorable pressure gradient between the entrance flat plate and the first peak location. The counter-rotating vortices could still be observed at non-dimensionalized streamwise distance χ (= x/λ) = 2.47 for Reynolds number Re (= UH/ν) = 9900 in channel with VF design. For lower Re, the vortices could preserve further downstream. In contrast, in channel with PF design, the structures were only visible clearly up to approximately χ = 1.32 for Re = 4700 and χ = 0.39 for Re = 5200.

A quasi two-dimensional numerical study is performed to analyze the thermo-magneto-convective transport of liquid metal around a square cylinder in a square duct subjected to a strong externally imposed axial magnetic field. The channel bottom wall is considered heated while the top wall is maintained at the free stream temperature keeping the cylinder adiabatic. The Reynolds and Hartmann numbers are kept in the range 0 Re 6000  and 0 Ha 2160  . The flow dynamics in the aforementioned range of parameters reveals the existence of four different regimes out of which the first three ones are similar to the classical non-MHD 2-D cylinder wakes while the fourth one is characterized by the vortices evolved from the duct side walls due to the boundary layer separation which strongly disturbs the Kármán vortex street. The flow dynamics and heat transfer rate from the heated channel wall are observed to depend on the imposed magnetic field strength. With increasing magnetic field, the flow becomes stabilized resulting in a degradation in the forced convection heat transfer. A special case at a very high Reynolds number 4 3 10Re  with Ha = 2160 is also considered to show the development of a Kelvin–Helmholtz-type instability that substantially affects the heat transfer rate.

Heat transfer, fluid flow and entropy generation due to buoyancy forces in a 2-D enclosure equipped with a conductive baffle and containing Al2O3nanofluid is carried out using different conductivities of baffle and different concentrations of nanoparticles. The bottom wall is subjected to constant hot temperature. The right and left vertical walls are maintained at lower temperature and the top wall is insulated. The finite volume method is used to solve the governing equations and calculations were performed for Rayleigh number from 103 to 106, thermal conductivity ratio from 0.01 to 100 and volume fraction of nanoparticles from 0 to 0.2. An increase in mean Nusselt number and a decrease of the total entropy generation were found with the increase of volume fraction of nanoparticles for the whole range of Rayleigh number.

The rapid depletion of conventional fuel and fluctuation of Diesel price in the global market have promoted research for alternative fuels for Diesel engine. Among the different alternative fuels, vegetable oil having fuel properties similar to Diesel has an acceptable engine performance. Vegetable oils are producing less CO2 emissions to the atmosphere because of their agricultural origin and less carbon content compared to mineral Diesel. It also reduces import of petroleum products. In the present investigation, an experimental study is carried out on an I.C.E laboratory in single cylinder, four-stroke VCR, direct injection Diesel engine to analyze the performance and emission characteristics of pure Diesel and Jatropha oil-Diesel blended fuels with various blend ratios. The measurements are recorded for the compression ratio 16, 17 and 18 with varying load from idle to rated load of 5.2 kW. Comparative results are given at constant engine speed, variable compression ratio and different engine BMEP for baseline Diesel and Jatropha oil-Diesel blended fuels revealing the effect of Diesel and Jatropha-Diesel blended fuels’ combustion on engine performance and exhaust emissions. The results show that for same blend, performance of the engine is improved considerably with the increase in CR. Thermal efficiency, exhaust gas temperature and emission parameters such as NOX, HC and CO at CR 18 with blends containing up to 30% (by volume) Jatropha oil is comparable to that of diesel fuel. So, blends containing up to 30% (by volume) Jatropha oil at CR 18 can be honestly used as an alternative fuel without any engine modification.

This paper presents the unsteady magnetohydrodynamic (MHD) flow of a generalized Burger's fluid between two parallel side walls perpendicular to a plate. The flow is generated from rest at time 0 t induced by sawtooth pulses stress applied to the bottom plate. The solutions obtained by means of the Laplace and the Fourier cosine and sine transforms in this order are presented as a sum between the corresponding Newtonian and non-Newtonian contributions. We investigate the effect of magnetic field and permeability on the fluid motion by a numerical procedure for the inverse Laplace transform, namely Stehfest's algorithm. Moreover, the influence of side walls on the fluid motion, the effect of pulse period, magnetic and porosity parameters and material parameters is presented by graphical illustrations.

This paper deals with the momentum, heat and mass transfer behaviour of MHD nanofluid flow embedded with conducting dust particles past an inclined permeable stretching sheet in presence of radiation, nonuniform heat source/sink, volume fraction of nano particles, volume fraction of dust particles and chemical reaction. We have considered Cu-water nanofluid embedding with conducting dust particles. The governing partial differential equations of the flow, heat and mass transfer are transformed into nonlinear ordinary differential equations by using similarity transformation and solved numerically using Runge-Kuttabased shooting technique. The effects of non-dimensional governing parameters on velocity, temperature and concentration profiles are discussed with the support of graphs. Also, skin friction coefficient, Nusselt and Sherwood numbers are discussed and presented through tables. Under some special conditions present results have good agreement with the existed results. It is observed a raise in the heat transfer rate due to increase in the fluid particle interaction parameter. It is also observed that an increase in chemical reaction parameter enhances the mass transfer rate of the dusty nanofluid.

In this paper, we have considered the blood flow in a curved channel with abnormal development of stenosis in an axis-symmetric manner. The constitutive equations for incompressible and steady non-Newtonian tangent hyperbolic fluid have been modeled under the mild stenosis case. A perturbation technique and homotopy perturbation technique have been used to obtain analytical solutions for the wall shear stress, resistance impedance to flow, wall shear stress at the stenosis throat and velocity profile. The obtained results have been discussed for different tapered arteries i.e., diverging tapering, converging tapering, non-tapered arteries with the help of different parameters of interest and found that tapering dominant the curvature of the curved channel.

The paper presents the numerical simulation on combustion of methane and biogas mixtures in the swirl burner can-Type of gas turbine combustion chamber. The study deals with the impact of mass fraction of carbon dioxide for biogas on emissions of noxious compounds during combustion. The investigations were done for four different fuels: pure methane (100% CH4), three biogases (90%CH4%CO2, 75%CH4%CO2 and 70%CH4%CO2), with the constant value of equivalence ratio (  = 0.95). The numerical results show that a low content of carbon dioxide in methane-air mixture leads to a better flame stability through an increase of the volume of the recirculation zone. The numerical analysis has shown that the biogas fuel allows a reduction of about 33% on the NO emissions and about 10% on the CO emissions and carbon dioxide contained in the fuel leads to the lowering of the flame temperature, whose effect reduces NO emissions. The results of the investigation clearly demonstrate that it is possible to use such fuels in combustion systems with swirl burners.

In this paper, to study the incompressible fully developed flow of a non-Newtonian fourth grade fluid in a flat channel under an externally applied magnetic field, an appropriate analysis has been performed considering the slip condition on the walls. The governing equations, Ohm’s law, continuity and momentum for this problem are reduced to a nonlinear ordinary form. The nonlinear equation with robin mixed boundary condition is solved with collocation (CM) and least square (LSM) methods. The effects of parameters such as non-Newtonian, magnetic field and slip parameters on dimensionless velocity profiles will be discussed. In the end, the results could bring us to this conclusion that collocation and least square methods can be used for solving nonlinear differential equations with robin mixed condition.

In coaxial laser cladding, the quality and property of deposition products are greatly influenced by the powder flow, which is responsible to transport additive materials to the deposition point on a substrate precisely. The metallic powder flow in coaxial laser cladding is simulated by a numerical model based on the gas-solid flow theory. The characteristics of powder concentration distribution between coaxial nozzle and deposition point for a kind of nickel based alloy powder are studied by the proposed model. The relationship between the process parameters and powder flow characteristics, such as focus distance from the nozzle exit and maximum powder concentration, is analyzed to optimize the powder feeding process. In addition, the influence of substrate with different surface shapes on the powder flow is investigated. The results can be used as a guideline for the location of the substrate and the selection of proper processing parameters for coaxial laser cladding.

One of the most important problems in reducing the emissions of diesel engines is to exchange between the oxides of nitrogen and soot emissions. Fuel multiple injection and air injection into combustion chamber are among the most powerful tools to concurrent reduction of these two emissions. In this research, the effect of multiple injection and air injection on combustion and emission parameters has been studied by AVL fire computational fluid dynamic software. Six states of base and modified combustion chamber have been studied in two different injection patterns including 90 (25) 10 and 75 (25) 25 mods. Results show that concurrent applying of both multiple injection and air injection methods has resulted in simultaneous reduction of oxide nitrogen and soot pollutants and a negligible loss is seen in the operational parameters of engine. Compression between six studied cases show that the 90 (25) 10 mode of injection with modified combustion chamber is the optimum mode by decreasing of soot and oxides of nitrogen emissions about 29% and 20% respectively and 6% indicated power loss in compression to the base combustion chamber and single injection mode. The obtained results from the computational fluid dynamic code have been compared with the existing results in the technical literature and show acceptable behavior.

This study introduces a finite element method using a higher-order interpolation function for effective simulations of wave transformation. Finite element methods with a higher-order interpolation function usually employ a Lagrangian interpolation function that gives accurate solutions with a lesser number of elements compared to lower order interpolation function. At the same time, it takes a lot of time to get a solution because the size of the local matrix increases resulting in the increase of band width of a global matrix as the order of the interpolation function increases. Mass lumping can reduce computation time by making the local matrix a diagonal form. However, the efficiency is not satisfactory because it requires more elements to get results. In this study, the Legendre cardinal interpolation function, a modified Lagrangian interpolation function, is used for efficient calculation. Diagonal matrix generation by applying direct numerical integration to the Legendre cardinal interpolation function like conducting mass lumping can reduce calculation time with favorable accuracy. Numerical simulations of regular, irregular and solitary waves using the Boussinesq equations through applying the interpolation approaches are carried out to compare the higher-order finite element models on wave transformation and examine the efficiency of calculation.

The nanoparticle migration effects on mixed convection of alumina/water nanofluid in a vertical microchannel in the presence of heat source/sink with asymmetric wall heating are theoretically investigated. The modified two-component heterogeneous model is employed for the nanofluid in the hypothesis that the Brownian motion and the thermophoresis are the only significant bases of nanoparticle migration. Because of low dimensional structures in microchannels, a linear slip condition is considered at the surfaces, which appropriately represents the non-equilibrium region near the interface. Considering hydrodynamically and thermally fully developed flow, the basic partial differential equations including the continuity, momentum, energy, and nanoparticle fraction have been reduced to two-point ordinary boundary value differential equations before they have been solved numerically. The scale analysis of governing equations has shown that the buoyancy effects due to the temperature distribution is insignificant, however, the buoyancy effects due to the concentration distribution of nanoparticles have considerable effects on the flow and heat transfer characteristics of nanofluids. It is also revealed that the imposed thermal asymmetry would change the direction of nanoparticle migration and distorts the symmetry of the velocity, temperature and nanoparticle concentration profiles. Moreover, the best performance of the system is achieved under one-sided heating and a greater slip velocity at the walls.

This research study was aimed to develop a new concept design of a very low head (VLH) turbine using advanced optimization methodologies. A potentially local site was chosen for the turbine and based on its local conditions, such as the water head level of

Instability and fl w transitionof a vortex ring impinging on a wall were investigated by means of large-eddy simulation for two vortex core thicknesses correspondingto thin and thick vortex rings. Variousfundamentalmechanismsdictatingthefl w behaviours, suchas evolutionof vortical structures,instabilityandbreakdownof vortex rings,developmentof modalenergies, andtransition from laminar to turbulent state, have been studied systematically. Analysis of the enstrophy of wrappingvortices andturbulentkineticenergy (TKE) infl w fiel indicatesthattheformationand evolutionof wrappingvorticesareclosely associated withthefl w transitiontoturbulentstate. Itis foundthatthetemporaldevelopmentofwrappingvorticesandthegrowthrateofaxial fl wgenerated aroundthecircumferenceof thecoreregionforthethinringarefasterthanthoseforthethickring. Theazimuthalinstabilitiesof primaryandsecondaryvortex ringsareanalysed andthedevelopment of modalenergies reveals thefl w transitiontoturbulentstate. The law of energy decay follows a characteristick−5/3 law,indicatingthatthevorticalfl w hasbecometurbulent. Theresultsobtained inthisstudyprovide physical insightintotheunderstandingof theinstability mechanismsrelevant tothevorticalfl w evolution.

The recirculations are essential in river engineering because they form silting zones and favour the development of specific fauna and flora. This paper deals with the behaviour of the recirculation zones occurring downstream the sudden expansion of an open channel. An Acoustic Doppler Velocimeter is used to measure the flow details. The mean flow property such as the length of the recirculation, the average velocity field and velocity gradient are obtained. Then the self-similarity of the velocity profile is retrieved . The numerical simulation for the similar conditions are preformed with the CFD software STAR CCM. When compared with the experiments, the two approaches correspond well in terms of length of recirculation zone and also regarding details such as the velocity gradient profiles. Finally, the eddy viscosity concept is tested and the turbulent viscosity coefficient are obtained along the streamwise axis for all flows.

Current trends in engine design indicate the necessity to take advantage of the highest rates of heat transfer associated with nucleate boiling, mostly at high engine loads. When used in conjunction with advanced thermal management strategies, subcooled boiling may take place at very low velocities, for which little information is available, and in ducts with small cross-sectional area, so that undesired effects of the relative sizes of ducts and bubbles may appear. In this paper, experiments on subcooled boiling flow at low velocities and engine-like temperature conditions were conducted with a usual engine coolant. A high-speed photographic camera was used to collect images of the detachedvaporbubbles,andthemicroscopiccharacteristicsoftheheatingsurfaceweredetermined. Experimentalresultsforthemeanvaluesshowacceptableagreementwiththeresultsofamechanisticradiusmodel,whenassumingthatdepartureandlift-ofradiusarerelatedthroughtheflowboiling suppression factor. Additionally, the results obtained are compatible with the sizes of the nucleation sites estimated from the surface characterization. The results obtained for the size distribution are consistent with those found in the literature.

In this paper, applications of a numerical model on simulation of two and three-dimensional flows are presented. This model solves Navier-Stokes equations using finite volume method and large eddy simulation (LES) in a collocated mesh. Artificial compressibility method with dual time stepping is used to solve the time dependent equations. Also a modified m omentum i nterpolation method (MIM) based on the unsteady flows is deployed to overcome the non-physical pressure oscillation. Capability of the presented numerical code for flow simulation, is assessed by application for twodimensional square and three-dimensional lid-driven cavity flows. Numerical results of cavity flow presents very good agreement with the numerical and experimental data of other existent researches.

In this paper, the effect of inclination angle and magnetic field in a two-dimensional porous cavity filled with Cu-water nanofluid has been studied numerically. The equations are framed using the Darcy-Brinkman-Forchheimer model. The control volume technique is used to solve the governing equations and SIMPLE algorithm is employed for the momentum equations. Comparison test was done with previous available literatures and the results are found to be in good agreement. The results are presented for different values of inclination angle (0o≤γ≤180o),Hartmannnumber(0≤ Ha≤100),Darcynumber (10−5≤Da≤10−1)andsolidvolumefraction(0%≤ϕ≤5%)whilethe porosity ε, Rayleigh number Ra and Prandtl number Pr are fixed at 0.6, 106 and 6.2, respectively. It is found that the influence of solid volume fraction is strongly affected by the presence of strong magnetic field and the inclination angle 90o in the porous medium.

This article examines the implementation of CFD technology in the design of the industrial liquid fuel powered swirl flame burner. The coupling between the flow field and the combustion model is based on the eddy dissipation model. The choice of the LES (Large Eddy Simulation) turbulence model over standard RANS (Reynolds Averaged Navier-Stokes) offers a possibility to improve the quality of the combustion-flow field interaction. The Wall Adapting Local Eddy-Viscosity (WALE) sub-grid model was used. The reaction chemistry is a simple infinitely fast one step global irreversible reaction. The computational model was setup with the Ansys-CFX software. Through the detailed measurements of industrial size burner, it was possible to determine the natural operational state of the burner according to the type of fuel used. For the inlet conditions, axial and radial velocity components were calculated from known physical characteristics of both the fuel and air input, with the initial tangential velocity of the fuel assumed as18% of the initial axial fuel velocity. Different swirl number (S) values were studied. Addition of a surplus (in comparison to conventional flame stabilization) of tangential air velocity component (W), the rotational component increases itself with a considerably high magnitude, contributing to the overall flame stabilization. The level of S especially influences the turbulent energy, its dissipation rate and turbulent (Reynolds) stresses. In the case of high swirl number values (S > 0,65) it is possible to divide the flow field in three principle areas: mixing area (fuel-air), where exothermal reactions are taking place, central recirculation area and outer recirculation area, which primarily contains the flow of burnt flue gases. The described model was used to determine the flow and chemical behavior, whereas the liquid atomization was accounted for by LISA (Linear Instability Sheet Atomization) model incorporating also the cavitation within injection boundary condition. The boundary conditions were determined based on the data from the experimental hot water system. Depending on system requirements, especially with continuous physical processes as well as the results of experimental measurements, the paper reports on determination of the mixing field and its intensity in the turbulent flow, the description of heat release and interaction of turbulent flow field and chemical kinetics in the case of confined swirling flames.

In this study, the numerical investigation of boundary layer flow over a moving plate in a nanofluid with viscous dissipation and constant wall temperature is considered. The governing non-linear partial differential equations are first transformed into a system of ordinary differential equations using a similarity transformation. The transformed equations are then solved numerically using the Keller-box method. Numerical solutions are obtained for the Nusselt number, Sherwood number and the skin friction coefficient as well as the concentration and temperature profiles. The features of the flow and heat transfer characteristics for various values of the Prandtl number, plate velocity parameter, Brownian motion and thermopherosis parameters, Eckert number and Lewis number are analyzed and discussed. It is found that the presence of viscous dissipation reduces the range of the plate velocity parameter for which the solution exists. The increase of both Brownian motion and thermophoresis parameters results to the decrease of the Nusselt number, while the Sherwood number increases with the increase of the thermophoresis parameter.

In this study, the effect of Hall current on the criterion for the onset of MHD convection in a porous medium layer saturated by a nanofluid is investigated. The model used for nanofluid combines the effect of Brownian motion and thermophoresis, while for a porous medium Brinkman model is used. A physically more realistic boundary condition than the previous ones on the nanoparticle volume fraction is considered i.e. the nanoparticle flux is assumed to be zero rather than prescribing the nanoparticle volume fraction on the boundaries. Using linear stability theory, the exact analytical expression for critical Rayleigh Darcy number is obtained in terms of various non-dimensional parameters. Results indicate that the magnetic field, Hall current, porous medium and nanoparticles significantly influence the stability characteristics of the system. The increase in the Hall current parameter, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh Darcy number is to hasten the onset of convection while the magnetic Darcy number, the porosity parameter and the Darcy number has stabilized on the onset of convection.

Free convective flow of a Jeffrey fluid in a vertical deformable porous stratum is investigated. It is assumed that heat is generated within the fluid by both viscous and Darcy dissipations. The velocity, displacement and the temperature distributions are evaluated using a perturbation method valid for small values of buoyancy parameter N . The effects of Jeffrey parameter, f  and s  on the flow velocity and solid displacement are discussed in detail. In the absence of Jeffrey parameter, deformable porous parameters and the pressure gradient, all the results reduce to the corresponding results of Rudraiah et al. (1977). Higher skin friction is observed for a given buoyancy force for a non-Newtonian Jeffrey fluid when compared with Newtonian fluid. On comparing deformable and undeformable porous layers of present work and Rudraiah et al. (1977), we conclude that the skin friction gets reduced when the porous material is a deformable one. It is noticed that the effect of increasing Jeffrey parameter is to increase the skin friction in the deformable porous stratum.

In this paper, formation and development of one of the most dominant vortex structures, namely, counterrotating vortex pair (CVP) which is seen in the jet in crossflow are investigated numerically. Influences of the inclination angles between the nozzle(s) and channel on the CVP are presented for three inclination angles, =30, 60 and 90 at velocity ratio, R=2.0. Effects of the number of the nozzles on the evolution of CVP is analyzed by considering the single and three side-by-side positioned circular nozzles. In addition to the CVP, some secondary vortices are also reported by considered relatively a narrow channel because their existence cannot be showed in wider channel. Simulations reveal that higher the inclination angle the more jet penetration into the channel in all directions and increasing the inclination angle causes larger CVPs in size. Although the flow structure of the CVP formed in the single and three side-by-side nozzles are similar their evolution is quite different.

Blending of fossil fuels with alcohols is one of the most impressive strategies for emission control and enhancement of fuel efficiency. Accordingly, in the current paper, the effects of blend of Heavy Fuel Oil (HFO) with bioalcohols are numerically studied on the non-reacting spray characteristics. Three different fuels are considered by mixture of HFO with 20% of n-Butanol, Ethanol, and Methanol and compared against Pure HFO. For this purpose, the microscopic and macroscopic spray characteristics of the blended fuels are evaluated through the investigation of spray penetration, cone angle, spray volume, and Sauter Mean Diameter (SMD). Moreover, for detailed understanding of the spray characteristics, the non-dimensional numbers of Weber and Ohnesorge, and liquid spray morphology are analyzed. Also, the study of Histogram of density and droplet diameter is conducted. Eulerian-Lagrangian multiphase scheme is used for simulation of air-fuel interaction in OpenFOAM CFD toolbox. Lagrangian Particle Tracking method is utilized for fuel droplet tracking in Lagrangian scheme. A hybrid breakup model of KH-RT and standard model of k-ε in RANS is used respectively for breakup and turbulence modeling. The obtained numerical results are validated against existing experimental data with suitable accordance. Based on the computational results, longer spray penetration length, larger spray cone angle and greater spray volume are achieved for the blended fuels. It was also concluded that HFO-Ethanol improves the macroscopic characteristics compared to two other blended fuels, albeit the effect is very minimal. In addition, lower SMD value is obtained for the blended fuels compared to pure HFO.

The paper presents a new method for in site discharge estimation in pressured pipes. The method consists in using the water hammer equations solved with the method of characteristics with an unsteady friction factor model. The differential pressure head variation measured during a complete valve closure is used to derive the initial flow rate, similarly to the pressure-time (Gibson) method. The method is validated with a numerical experiment, and tested with experimental laboratory measurements. The results show that the proposed method can reduce the discharge estimation error by 0.6% compared to the standard pressure-time (Gibson) method for the flow rate investigation.

A correlation-based transition model has been developed by Langtry and Menter for modern computational fluid dynamics codes, which is widely used for transition prediction in the field of turbomachinery and aircraft. Langtry’s transition model could simulate bypass, laminar separation and streamwsie Tollmien– Schlichting wave transition. Even so, this model has no ability to predict the transition due to crossflow instabilities in three dimensional boundary layer. In this paper, a new correlation-based transport equation for the transition due to crossflow instabilities has been established based on the experiment data and self-similar equations. The new transport equation is introduced to describe the crosswise displacement thickness Reynolds number growth in boundary layer. This new equation is added to Langtry’s intermittency factor equation to improve the ability of predicting transition. Finally, coupling of these transport equations and Shear Stress Transport (SST) turbulence model completes the new improved transition turbulence model. Comparisons of predictions using the new model with wind tunnel experiments of NLF (2)-0415 infinite swept wing and 6:1 inclined prolate spheroid validate the predictive qualities of the new correlation based transport equation.

This paper is focused on the study of heat and mass transfer characteristics of an unsteady MHD boundary layer flow through porous medium over a stretching sheet in the presence of thermo-diffusion and diffusionthermo effects with thermophoresis, thermal radiation and non-uniform heat source/sink. The transformed conservation equations are solved numerically subject to the boundary conditions using an optimized, extensively validated, variational finite element analysis. The numerical code is validated with previous studies on special cases of the problem. The influence of important non-dimensional parameters, namely suction parameter (), magnetic parameter (M), unsteadiness parameter (α), Soret parameter (Sr), Dufour parameter (Du) thermophoretic parameter (), space dependent (A1) and temperature dependent parameters (B1) and radiation parameter(An) on the velocity, temperature and concentration fields as well as the skinfriction coefficient, Nusselt number and Sherwood number are examined in detail and the results are shown graphically and in tabular form to know the physical importance of the problem. It is found that the imposition of wall fluid suction (>0) in the flow problem has the effect of depreciating the velocity, temperature and concentration boundary layer thicknesses at every finite value of η. This deceleration in momentum, thermal and concentration profiles is because of the fact that suction is taken away the warm fluid from the surface of the stretching sheet.

In this paper, the problem of nanofluid flow and heat transfer due to the impulsive motion of a semi-infinite vertical plate in its own plane in the presence of magnetic field is analyzed by the implicit finite-difference numerical method. A range of nanofluids containing nanoparticles of aluminium oxide, copper, titanium oxide and silver with nanoparticle volume fraction range less than or equal to 0.04 are considered. The Tiwari-Das nanofluid model is employed. The velocity and temperature profiles as well as the skin friction coefficient and Nusselt number are examined for different parameters such as nanoparticle volume fraction, nanofluid type, magnetic parameter and thermal Grashof number. The present simulations are relevant to magnetic nanomaterials thermal flow processing in the chemical and metallurgical industries.

In this study, pressure drop for oil–water flow in horizontal pipes is represented by using artificial neural network (ANN). Results were compared with Al-Wahaibi correlation and Two-fluid model. This research has used a multilayer feed forward network with Levenberg Marquardt back propagation training for prediction of pressure drop. Original data were divided into two parts where 80% of data was used as training data and remaining 20% of data was used for testing. In this method inputs are oil superficial velocity, water superficial velocity, ratio of density, ratio of viscosity, diameter of pipe and roughness of the pipe wall. The number of neurons is set on four. The feasibility of ANN, Al-Wahaibi correlation and Two-fluid model has been tested against 11 pressure drop data sources. The average absolute percent error of Al-Wahaibi correlation and two-fluid model are 12.73 and 15.84 while this average for the same systems using neural network is only 6.36.so the ANN is in good agreement with experimental data.

In this study, an impeller and volute of a centrifugal pump were designed and numerically analyzed in order to improve the pump efficiency. Before design, experimental and theoretical studies were performed on a centrifugal water pump taken as Model Pump (MP). Design parameters were taken as 100 m3/h for volume flow rate, 18m for head and 1480 rpm for rotating speed. After the inspection of the flow field in the MP, some geometrical modifications such as impeller inlet and outlet diameters, blade inlet and exit angles, blade wrap angle, blade thickness, blade inletand exit widthswere realized to design a new pump. Numerical analyses were performed for 8 different volume flow rates overlapping with experimental operation points by Ansys-Fluent Software. In numerical studies, k-ε turbulence model and standard wall function were utilized. The experimental and computational results were compared with the model pump. According to the analysis results at design flow rate, hydraulic torque value is decreased from 56.62 Nm to 51.05 Nm, while hydraulic efficiency is increased from 55.98% to 63.09%. In addition, in order to see the roughness effect and increase the pump efficiency, the wetted surfaces of the impeller and volute were coated with a polyurethane dye material. Later, performance curves of the coated and uncoated pumps were experimentally obtained which showed that the shaft power of the pump for the coated case was decreased around 10% and the hydraulic efficiency of the pump was increased approximately 18%. According to the economic analysis by basic payback period of the polyurethane coating is less than one year and the internal income ratio for ten-year life-cycle period is around %114.

In this work, a numerical study of two dimensional laminar incompressible flow around the flexible oscillating NACA0012 airfoil is performed using the open source code OpenFOAM. Oscillatory motion types including pitching and flapping is considered. Reynolds number for these motions is assumed fixed at 12000. One of the important issues that must be considered in designing air structures, in particular the aircraft wing, is the interaction between the air and the elastic aircraft wings that is known as the Aeroelastic phenomenon. For this purpose, the effect of airfoil flexibility and flow induced vibration in these motion types is investigated and compared with the case of rigid airfoil. It is observed that the flexibility in both types of motions causes improvement of the thrust which is boosted with increasing the frequency. Contrary to thrust, the significant improvement of lift is only achievable in high frequencies. It was also found that the effect of flexibility on the flapping motion is higher than the pitching motion. For flow control on the airfoil, Dielectric Barrier Discharge plasma actuator is used in the trailing edge of a flexible airfoil, and its effect on the flexible airfoil is also investigated.

This study presents a numerical analysis on the effects of Soret, variable thermal conductivity, viscous-Ohmic dissipation, non-uniform heat sources, on steady two-dimensional hydromagnetic mixed convective heat and mass transfer flow of a micropolar fluid over a stretching sheet embedded in a non-Darcian porous medium with thermal radiation and chemical reaction. The governing differential equations are transformed into a set of non-linear coupled ordinary differential equations which are then solved numerically by using the fifthorder Runge-Kutta-Fehlberg method with shooting technique. Numerical solutions are obtained for the velocity, angular velocity, temperature and concentration profiles for various parametric values, and then results are presented graphically as well as skin-friction coefficient, and also local Nusselt number and local Sherwood number for different physical parameters are shown graphically and in tabular form. A critical analysis with earlier published papers was done, and the results were found to be in accordance with each other.

Numerical investigation for heat transfer with steady MHD natural convection cooling of a localized heat source at the bottom wall of an enclosure filled with nanofluids subjected to changeable thermal boundary conditions at the sidewalls has been studied in the a presence of inclined magnetic field. Finite difference method was employed to solve the dimensionless governing equations of the problem. The effects of governing parameters, namely, Hartmann number, solid volume fraction, the different values of the heat source length and the different locations of the heat source on the streamlines and isotherms contours as well as maximum temperature, Nusselt number and average Nusselt number along the heat source were considered. The present results are validated by favorable comparisons with previously published results. The results of the problem are presented in graphical and tabular forms and discussed. It is found that an increase in the Hartmann number results in a clear reduction in the rate of heat transfer; however, the increase in Rayleigh number enhances the nanofluid flow and heat transfer rate.

An approach for the optimization of laminar flow in diffusers is presented. The goal in our optimization process is to maximize diffuser performance and, in this way, pressure recovery by optimizing the geometry. Our methodology is the optimization through wall contouring of a given two-dimensional diffuser length ratio. The developed algorithm uses the CFD software: Fluent for the hydrodynamic analysis and employs surrogate modeling and an expected improvement approach to optimization. The non-uniform rational basic splines (NURBS) are used to represent the shape of diffuser wall with three to nine design variables, respectively. The framework is assisted by the construction of Kriging model, for the management of the problem. The CFD software and the Kriging model have been combined for a fully automated operation using some special control commands on the MATLAB platform. In order to seek a balance between local and global search, an adaptive sample criterion is employed. The optimal design exhibits a reasonable performance improvement compared with the reference design.

Research on vortex-induced vibrations (VIV) mainly involves experimental science but building laboratory setups to investigate the flow are expensive and time consuming. Computational fluid dynamics (CFD) methods may offer a faster and a cheaper way to understand this phenomenon depending on the solution approach to the problem. The context of this paper is to present the author’s computational approach to solve for vortex-induced vibrations which cover extensive explanations on the mathematical background, the grid structure and the turbulence models implemented. Current computational research on VIV for smooth cylinders is currently restricted to flows that have Reynolds numbers below 10,000. This paper describes the method to approach the problem with URANS and achieves to return satisfactory results for higher Reynolds numbers.The computational approach is first validated with a benchmark experimental study for rather low Reynolds number which falls into TrSL2 flow regime. Then, some numerical results up to =130,000, which falls into TrSL3 flow regime,are given at the end of the paper to reveal the validity of the approach for even higher Reynolds numbers.

Journal bearings are widely used in different machineries. Reynolds equation is the governing equation to predict pressure distribution and load bearing capacity in journal bearings. There are many analytical and numerical methods for solving this equation. The main disadvantage of these methods is their inability to analyze complex geometries. In this paper, a comprehensive method based on dynamic mesh method is developed to solve the conservation equations of mass, momentum and energy. This method has smaller error compared to other techniques. To verify the accuracy of this method, the bearings with different length to diameter ratios are analytically and numerically analyzed under different loads and compared with each other. In continue, the turbocharger’s bearing is numerically simulated and the effects of rotational speed change are studied. Finally, the turbocharger’s bearing with four axial grooves are simulated. The simulations results show that adding grooves to the turbocharger’s bearing causes the bearing eccentricity ratio and lubricant flow rate to increase and the attitude angle, rate of temperature rise and frictional torque to decrease.

The highest-level fluctuations in large pump-turbines are usually originated from rotor-stator interaction (RSI) in the vaneless region. Hence, the studies of RSI phenomenon and corresponding unsteady effects are significantly important to reduce the pressure fluctuations. In this paper, firstly, RSI in a pump-turbine, featuring 20 stay vanes, 20 guide vanes and 9 runner blades, is analyzed through diameter mode theory, which has been used widely. Then, 3-D unsteady numerical simulations are performed under six guide vane openings in turbine mode. The comparison including performance and pressure characteristics between numerical and experimental results shows a good agreement. Finally, best guide vane opening 21° is chosen to analyze the distribution of pressure fluctuations. The detailed investigation of numerical results shows that frequencies in the vaneless region at best guide vane opening are mainly blade passing frequency (BPF) and its harmonic frequencies caused from RSI. The variation of BPF and its harmonic frequencies is confirmed by diameter mode theory. For this type of the pump-turbine, the amplitude of 2BPF (18fn) shows the highest corresponding diameter mode k2=-2, which indicates two high pressure regions caused by the component of 18fn in the vaneless region. Furthermore, the two high-pressure regions rotate in the counterclockwise direction with rotational speed of the runner blades. This research could provide a basic understanding of RSI to have a further study for pressure fluctuations in pump-turbines.

The passive control of flow-separation at averaged Reynolds Number (Re=3.42×105) using self-adapting flexible-flaps in the upper side of the wing, is presented. The two-way Fluid-Structure Interaction (FSI) in an elastic-layer up on the airfoil (NACA 0012) is investigated numerically by Coupling between the Transient Structural and Fluid Flow (Fluent) in ANSYS-Workbench14.0. During the fluid-structure interaction, the transient deformation of the elastic-layer provokes the modification of the flow topology at large-scale. There are reductions of the size and intensity of the vortex-shedding and an increase in the Strouhal number. This explains the increase of the lift-to-drag ratio. The study of the flap flexibility shows that the deformation of the elastic-layer and the variation of aeronautical efforts are inversely proportional to the Young Modulus.

In the present study, Lattice Boltzmann method is employed to investigate a two dimensional mixed convection heat transfer of Al2O3-water nanofluid in a horizontal annulus between a cold outer cylinder and the hot, rotating inner cylinder. To do so, the double lattice Boltzmann equation is utilized for the base fluid and the nanoparticles to describe the dynamic as well as the thermal behavior of nanofluid. Moreover, different forces such as Brownian, drag and gravity acting on the nanoparticles are taken into consideration. Calculations have been performed for Rayleigh number ranging from 103 to 2×104, Reynolds number from 5 to 120, vertical and horizontal eccentricity from -0.75 to 0.75 with volume fraction of nanoparticles from 0 to 0.1. The current computational results reveal that by adding nanoparticles, the mean Nusselt number for Ra 104, it decreases. Also, with Re>80, the mean Nusselt number increases with increasing Reynolds number; although for low Reynolds number this rising trend is not observed. Besides, when the inner cylinder moves vertically upward from the center, the addition of nanoparticles increases Nusselt number relative to the base fluid.

This paper presents a direct second-order finite-difference solution of the two-point boundary value problem derived from the classical third-order Blasius problem using the Crocco-Wang transformation. Noting the end-point singularity introduced by the Crocco-Wang transformation due to a zero boundary condition, the method provides special handling of this singularity to ensure second-order accuracy. Additionally, the method uses an extrapolation procedure to obtain results of increased accuracy. We compare our computed solution with an approximate analytical solution and numerical solutions previously reported and find that our results are in excellent agreement.

In this article, unsteady boundary layer flow formed over a vertical surface due to impulsive motion and buoyancy is investigated. The mathematical model which properly accounts for space and temperature-dependent internal heat source in a flowing fluid is incorporated into the energy equation. This model is presented in this study as a term which accounts for two different forms of internal heat generation during the short time period and long time period. Due to the fluid flow under consideration, the influence of thermal-diffusion and diffusion-thermo are incorporated into the governing equation since it may not be realistic to assume that both effects are of smaller order of magnitude than the effects described by Fourier’s or Fick’s law. The corresponding effect of internal heat source on viscosity is considered; the viscosity is assumed to vary as a linear function of temperature. The flow model is described in terms of a highly coupled and nonlinear system of partial differential equations. The governing equations are non-dimensionalized by using suitable similarity transformation which unraveled the behavior of the fluid flow at short time and long time periods. The dimensionless system of non-linear coupled partial differential equations (PDEs) is solved using Bivariate Spectral Relaxation Method (BSRM). A parametric study of selected parameters is conducted and results of the surface shear stress, heat transfer and mass transfer at the wall are illustrated graphically and physical aspects of the problem are discussed.

The effect of variable gravity on the free convection in a horizontal porous layer with viscous dissipation is investigated. The bottom boundary is taken as adiabatic and there is a non-uniform temperature distribution along the upper boundary. The effect of viscous dissipation is significant and the top boundary temperature distribution is assumed to have a constant gradient. The gravity varieslinearlywiththeheight. Alinearstabilityanalysisofthebasicflowiscarriedout. Thecritical horizontal Rayleigh number is calculated for oblique roll disturbances. The longitudinal rolls are found to be the most unstable ones. The viscous dissipation has a destabilizing effect. There is a drastic decrease in the value of critical horizontal Rayleigh number when modified variable gravity parameter changes from−1 to 1.

In this paper, the evolution of an acceleration wave for the system of partial differential equations describing one dimensional, unsteady, axisymmetric motion of transient pinched plasma has been considered. The amplitude of the acceleration wave propagating along the characteristic associated with the largest eigenvalue has been evaluated. The interaction of the strong shock with the acceleration wave has been investigated. Effects of ambient density exponent and magnetic induction has been investigated.