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Combined effects of Joule heating and nonuniform heat source/sink on unsteady MHD mixed convective flow over a vertical stretching surface embedded in a Darcy-Forchheimer porous medium

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Propulsion and Power Research 2022年第2期11卷 276-292页

作者： B.K.Sharma Rishu Gandhi Department of Mathematics Birla Institute of Technology and SciencePilani333031RajasthanIndia

This paper deals with an unsteady magnetohydrodynamics(MHD)heat and masstransfer for a viscous incompressible fluid through a vertical stretching surface embedded ina Darcy-Forchheimer porous medium in the presence of a non-uniform heat source/sink andfirst-order chemical reaction.The porous surface is subjected to a uniform transverse magneticfield.The influence of velocity,thermal,and concentration slip is also investigated.The governing equations are coupled non-linear partial differential equations,which have been converted via similarity transformation into a set of ordinary differential equations.The resultantsystem of non-linear ordinary differential equations has been solved numerically with the helpof the“MATLAB”BVP4C Solver.Results are presented graphically to analyze the effects ofvarious physical parameters discovered in the problem such as Hartmann number(M),Forchheimer number(Fr),Grashof number(Gr),solutal Grashof number(Gc),suction parameter(S),porosity parameter(el),dimensionless velocity slip(Sv),Prandtl number(Pr),dimensionless thermal slip(St),space-dependent heat source/sink parameter(eA1),temperature-dependent heat source/sink(eB)1),Eckert number(Ec),Schmidt number(Sc),chemical reaction parameter(g),unsteadiness parameter(A),and dimensionless concentration slip(Sc)on non-dimensionalvelocity ec0ðhÞ,temperature zðhÞ,and concentration efðhÞprofiles.The influence of these parameters on skin-friction coefficient(C)f),Nusselt number(Nu)x),and Sherwood number(Sh)x)areexpressed in tabular form.It is observed that an enhancement in Fr and el results in the declination of the velocity profile.There is an enhancement in temperature with an increment in theeA)1 and eB)1.The physical representation of flow characteristics that appeared in the problem ispresented using various graphs to depict real-world applications in industrial and engineeringoperations.The results were compared to previous studies,revealing that the two are in goodagreement.The novelty of the present investigation is:To interpre

关键词： Magnetohydrodynamics(MHD) unsteady Heat and mass transfer Non-Darcian porous medium Heat source Joule effect

A Study on the unsteady Flow Characteristics and Energy Conversion in the Volute of a Pump-as-Turbine Device

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Fluid Dynamics & Materials Processing 2021年第6期17卷 1021-1036页

作者： Senchun Miao Hongbiao Zhang Wanglong Tian Yinqiang Li School of Energy and Power Engineering Lanzhou University of TechnologyLanzhou730050China Jiangsu Shuangda Pump Valve Group Co. Ltd.Jingjiang214537China

To study the unsteady flow and related energy conversion process in the volute of a pump-as-turbine(PAT)device,six different working conditions have been considered.Through numerical calculation,the spatio-temporal variation of static pressure,dynamic pressure,total pressure and turbulent energy dissipation have been determined in each section of the volute.It is concluded that the reduction of the total power of two adjacent sections of the PAT volute is equal to the sum of the power lost by the fluid while moving from one section to the other and the power output from the two adjacent sections.For a fixed flow rate,the percentage of static pressure energy at the outlet of the PAT is roughly similar to that of the corresponding volute section,and both show a gradually increasing trend.The turbulent dissipation rate on each section of the PAT volute displays a similar a spatio-temporal behavior for different flow rates.

关键词： Pump as turbine volute energy conversion unsteady numerical simulation

unsteady Cavitating Flow around a Hydrofoil Simulated Using the Partially-Averaged Navier-Stokes Model

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Chinese Physics Letters 2012年第7期29卷 198-202页

作者：季斌罗先武吴玉林许洪元 State Key Laboratory of Hydroscience and Engineering Tsinghua UniversityBeijing 100084

Numerical simulations of unsteady cavitating flow around a NACA66-mod hydrofoil were performed using the partially-averaged Navier-Stokes method with different values of the resolution control parameters (f k =1.0-0.2,fε =1).With decreasing fk,the predicted cavitating flow becomes unsteady as the time-averaged turbulent viscosity at the rear part of the attached cavity is gradually reduced.For fk =0.9 and 0.8,the cavity becomes unstable and its length dramatically expands and shrinks,but the calculation fails to predict the vapor cloud shedding behavior observed experimentally.With smaller fk less than 0.7,the cloud shedding behavior is simulated numerically and the predicted cavity shedding frequency increases.With fk =0.2,the whole cavitating flow evolution can be reasonably reproduced including the cavity growth/destabilization observed previously.The reentrant flow along the suction surface of the hydrofoil is the main trigger to cause the vapor cloud shedding.The wall pressure along the hydrofoil surface oscillates greatly due to the dynamic cavity shedding.Comparing the simulations and experiments,it is confirmed that for the PANS method,resolution control parameters of fk =0.2and fε =1 are recommended for numerical simulations of unsteady cavitating flows.Thus,the present study shows that the PANS method is an effective approach for predicting unsteady cavitating flow over hydrofoils.

关键词： unsteady Navier averaged

Numerical Study of unsteady MHD Flow and Entropy Generation in a Rotating Permeable Channel with Slip and Hall Effects

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Communications in Theoretical Physics 2018年第11期69卷 641-650页

作者： Z.H.Khan O.D.Makinde R.Ahmad W.A.Khan State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resource & HydropowerSichuan University Key Laboratory of Advanced Reactor Engineering and Safety Ministry of Education Tsinghua University Faculty of Military Science Stellenbosch University School of Mathematics and Physics University of Queensland Faculty of Engineering Sciences GIK Institute of Engineering Sciences and Technology Department of Mechanical Engineering College of Engineering Prince Mohammad Bin Fahd University

This article investigates an unbiased analysis for the unsteady two-dimensional laminar flow of an incompressible, electrically and thermally conducting fluid across the space separated by two infinite rotating permeable walls.The influence of entropy generation, Hall and slip effects are considered within the flow analysis. The problem is modeled based on valid physical arguments and the unsteady system of dimensionless PDEs (partial differential equations) are solved with the help of Finite Difference Scheme. In the presence of pertinent parameters, the precise movement of the flow in terms of velocity, temperature, entropy generation rate, and Bejan numbers are presented graphically, which are parabolic in nature. Streamline profiles are also presented, which exemplify the accurate movement of the flow. The current study is one of the infrequent contributions to the existing literature as previous studies have not attempted to solve the system of high order non-linear PDEs for the unsteady flow with entropy generation and Hall effects in a permeable rotating channel. It is expected that the current analysis would provide a platform for solving the system of nonlinear PDEs of the other unexplored models that are associated to the two-dimensional unsteady flow in a rotating channel.

关键词： unsteady flow rotating permeable channel MHD slip hall effects entropy analysis finite difference method

unsteady Squeezing Flow of Jeffery Fluid between Two Parallel Disks

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Chinese Physics Letters 2012年第3期29卷 135-138页

作者： A.Qayyum M.Awais A.Alsaedi T.Hayat Department of Mathematics Quaid-I-Azam University 45320Islamabad 44000Pakistan Department of Mathematics Faculty of ScienceKing Abdulaziz UniversityP.O.Box 80257Jeddah 21589Saudi Arabia

We investigate an unsteady axisymmetric flow of a Jeffrey fluid between two parallel disks.The relevant partial differential equations are modeled and simplified by using appropriate transformations.The resulting ordinary differential system is solved and a series solution is obtained.Effects of various parameters of interest on the flow quantities are seen.It is found that the velocity profile increases when porosity and squeezing parameters are increased.

关键词： ordinary unsteady flow

Analytical Model of Temperature Field in unsteady Stage of Friction Plug Welding

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Transactions of Nanjing University of Aeronautics and Astronautics 2019年第5期36卷 789-797页

作者： YAN Chongjing ZHENG Yongle College of Mechanical and Electrical Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China Shanghai Aircraft Design and Research Institute Shanghai 201206P.R.China

The temperature field in unsteady phase greatly affects the quality of friction plug welding(FPW).An analytical model is put forward to correlate the process parameters and the temperature field in unsteady phase of FPW.Applying the von Mises criterion for plastic deformation and linearizing the heat flux,the model is achieved by Laplace transformation.The predicated peak temperature and peak time agree with the experiment data,with errors of about 4%and 8%,of AA7075-T6 FPW.

关键词： friction plug welding(FPW) unsteady stage temperature field analytical model

Comparison of Aerodynamic Forces and Moments Calculated by Three-dimensional unsteady Blade Element Theory and Computational Fluid Dynamics

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Journal of Bionic Engineering 2017年第4期14卷 746-758页

作者： Loan Thi Kim Au Hoang Vu Phan Hoon Cheol Park Department of Advanced Technology Fusion and Artificial Muscle Research Center Konkuk University Seoul Korea

In previous work, we modified blade element theory by implementing three-dimensional wing kinematics and modeled the unsteady aerodynamic effects by adding the added mass and rotational forces. This method is referred to as unsteady Blade Element Theory （UBET）. A comparison between UBET and Computational Fluid Dynamics （CFD） for flapping wings with high flapping frequencies （〉30 Hz） could not be found in literature survey. In this paper, UBET that considers the movement of pressure center in pitching-moment estimation was validated using the CFD method. We investigated three three-dimensional （3D） wing kinematics that produce negative, zero, and positive aerodynamic pitching moments. For all cases, the instantaneous aerodynamic forces and pitching moments estimated via UBET and CFD showed similar trends. The differences in average vertical forces and pitching moments about the center of gravity were about 10% and 12%, respectively. Therefore, UBET is proven to reasonably estimate the aerodynamic forces and pitching moment for flight dynamic study of FW-MAV. However, the differences in average wing drags and pitching moments about the feather axis were more than 20%. Since study of aerodynamic power requires reasonable estimation of wing drag and pitching moment about the feather axis, UBET needs further im- provement for hilzher accuracy.

关键词： blade element theory unsteady computational fluid dynamics flapping wings biomimetic

Analysis of swirling flow effects on the characteristics of unsteady hot-streak migration

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Chinese Journal of Aeronautics 2016年第6期29卷 1469-1476页

作者： Wang Jingyu Ge Ning Sheng Chunhua Nanjing University of Aeronautics and Astronautics Nanjing 210016China Sun Yat-Sen University Guangzhou 510275China The University of Toledo OH 43606USA

The temperature of flow at the combustor exit is inherently non-uniform and the hot fluid is called hot-streak. An in-house CFD software, NUAA-Turbo, was used to carry out 3D unsteady simulations on the PW-E^3 single-stage high-pressure turbine. The hot-streak effect based on real stator and combustor counts was approximately evaluated by the contraction/dilatation method on the interface. The unsteady attenuation and migration process of hot-streaks in the turbine passage were well captured. The general performance parameters for different circumferential positions of hot-streaks were relatively consistent. Then, the influences of hot-streaks on blade surface temperature were investigated by comparing results under hot-streak and uniform inflow conditions. unsteady simulations with combined inlet hot-streak and swirling flow show that the core of a hot-streak migrates to the tip under the influence of a positive swirl, while the phenomenon is just opposite with a negative swirl. Therefore, the heat transfer environment of rotor blades shows great differences with different directions of inlet swirl.

关键词： High pressure turbine Hot-streak Interface contraction/dilatation Swirling flow unsteady flow

Numerical Analysis of unsteady Magneto-Biphase Williamson Fluid Flow with Time Dependent Magnetic Field

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Communications in Theoretical Physics 2019年第2期71卷 143-151页

作者： Madiha Bibi M.Y.Malik A.Zeeshan Department of Mathematics College of Sciences P.O.Box 9004 King Khalid University Department of Mathematics Quaid-I-Azam University Department of Mathematics and Statistics Faculty of Basic and Applied Sciences International Islamic University

Numerical investigation of the dusty Williamson fluid with the dependency of time has been done in current disquisition. The flow of multiphase liquid/particle suspension saturating the medium is caused by stretching of porous surface. The influence of magnetic field and heat generation/absorption is observed. It is assumed that particle has a spherical shape and distributed uniformly in fluid matrix. The unsteady two-dimensional problems are modeled for both fluid and particle phase using conservation of mass, momentum and heat transfer. The finalized model generates the non-dimensioned parameters, namely Weissenberg number, unsteadiness parameter, magnetic parameter,heat generation/absorption parameter, Prandtl number, fluid particle interaction parameter, and mass concentration parameters. The numerical solution is obtained. Locality of skin friction and Nusselt number is deliberately focused to help of tables and graphs. While inferencing the current article it is clearly observed that increment of Williamson parameter, unsteadiness parameter, magnetic parameter, volume fraction parameter, and mass concentration parameter reduces the velocity profile of fluid and solid particles as well. And increment of Prandtl number, unsteadiness parameter,volume fraction parameter, and mass concentration parameter reduces the temperature profile of fluid and solid particles as well.

关键词： unsteady flow multiphase Williamson fluid variable magnetic field permeable wall heat source/sink