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Direct numerical simulation of turbulent boundary layer over an anisotropic compliant wall

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Acta Mechanica Sinica 2019年第2期35卷 384-400页

作者： Qian-Jin Xia Wei-Xi Huang Chun-Xiao Xu AML Department of Engineering MechanicsTsinghua University Beijing 100084 China

Direct numerical simulation of a spatially developing turbulent boundary layer over a compliant wall with anisotropic wall material properties is performed. The Reynolds number varies from 300 to approximately 860 along the streamwise direction, based on the external flow velocity and the momentum thickness. Eight typical cases are selected for numerical investigation under the guidance of the monoharmonic analysis. The instantaneous flow fields exhibit the traveling wavy motion of the compliant wall, and the frequency-wavenumber power spectrum of wall pressure fluctuation is computed to quantify the mutual influence of the wall compliance and the turbulent flow at different wave numbers. It is shown that the Reynolds shear stress and the pressure fluctuation are generally enhanced by the wall compliance with the parameters considered in the present study. A dynamical decomposition of the skin-friction coefficient is derived, and a new term (CW) appears due to the wall-induced Reynolds shear stress. The influence of the anisotropic compliant wall motion on the turbulent boundary layer through the wall-induced negative Reynolds shear stress is discussed. To elucidate the underlying mechanism, the budget analysis of the Reynolds stresses transportation is further carried out. The impact of the wall compliance on the turbulent flow is disclosed by examining the variations of the diffusion and velocity-pressure correlation terms. It is shown that increase of the Reynolds stresses inside the flow domain is caused by enhancement of the velocity-pressure correlation term, possibly through the long-range influence of the wall compliance on the pressure field, rather than diffusion of the wall-induced Reynolds shear stress into the fluid flow.

关键词： Turbulent boundary layer Anisotropic compliant wall Direct numerical simulation skin-friction coefficient Reynolds shear stress

A prediction of drag reduction by entrapped gases in hydrophobic transverse grooves

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Science China(Technological Sciences) 2013年第12期56卷 2973-2978页

作者： WANG Bao WANG JiaDao CHEN DaRong State Key Laboratory of Tribology Tsinghua University

The drag reduction effect of super-hydrophobic surface induced by the entrapped gas is unstable due to the gradual disappearance of the trapped *** this paper,a hydrophobic transverse grooved surface was designed to sustain gas in valleys.A detail numerical simulation was presented to investigate the flow field near the proposed *** water flowed over this surface,the entrapped gas was blocked by the ridges and the solid-liquid interface was replaced by the liquid-gas interface due to the entrapped gas,furthermore the micro-vortex formed in the *** there was an effective slippage between water and solid induced by the entrapped gas,the velocity gradient of boundary layer decreased,which contributed to a remarkable drag reduction ***,considering the extra undesired pressure drag reduction which negatively impacted the drag reduction effect of this method,the total drag coefficient including the viscous drag coefficient and the pressure coefficient was *** effective drag reduction rate of about 15%was achieved and the effect of this method was confirmed by experiments conducted in a high-speed water tunnel when grooves were optimized.

关键词： hydrophobic transverse groove gas skin-friction drag reduction computational fluid dynamics(CFD)

Numerical study of flow and heat transfer during oscillatory blood flow in diseased arteries in presence of magnetic fields

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Applied Mathematics and Mechanics(English Edition) 2012年第5期33卷 649-662页

作者： A.SINHA J.C.MISRA School of Medical Science and Technology Indian Institute of TechnologyKharagpur 721302India Department of Mathematics Institute of Technical Education and ResearchSiksha O Anusandhan UniversityBhubaneswar 751030India

A problem motivated by the investigation of the heat and mass transfer in the unsteady magnetohydrodynamic （MHD） flow of blood through a vessel is solved numerically when the lumen of the vessel has turned into the porous structure. The time-dependent permeability and the oscillatory suction velocity are considered. The computational results are presented graphically for the velocity, the temperature, and the concentration fields for various values of skin friction coefficients, Nusselt numbers, and Sherwood numbers. The study reveals that the flow is appreciably influenced by the presence of a magnetic field and also by the value of the Grashof number.

关键词： mass transfer radiation suction velocity skin-friction

General Solution for Unsteady Natural Convection Flow with Heat and Mass in the Presence of Wall Slip and Ramped Wall Temperature

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Communications in Theoretical Physics 2019年第6期71卷 647-657页

作者： Saeed Ullah Jan Sami Ul Haq Syed Inayat Ali Shah Ilyas Khan Muhammad Atif Khan Faculty of Mathematics and Statistics Ton Duc Thang UniversityHo Chi Minh CityVietnam Department of Mathematics Islamia College UniversityPeshawar25000Pakistan Department of Mathematics Kohat University of Science&TechnologyKohat26000Pakistan

This work is focused on the effect of heat and mass transfer with unsteady natural convection flow of viscous fluid along with ramped wall temperature under the assumption of the slip wall condition at the boundary. Analytical solutions are obtained by using Laplace transformation to the non-dimensional set of governing equations containing velocity, temperature and concentration. Moreover, the expression for skin-friction is derived by differentiating the analytical solutions of fluid velocity. Numerical tables for skin-friction, Sherwood number and Nusselt-number are examined. For the physical aspects of the flow, we use various values of involved physical parameters such as Prandtl number(Pr), slip parameter(η), Schmidt number(Sc), buoyancy ratio parameter(N), Sherwood number(Sh), and time(t). Additionally, the general solutions are plotted graphically and a comprehensive theoretical section of numerical discussions is included.

关键词： slip boundary condition heat and mass transfer skin-friction

On the mesh resolution of industrial LES based on the DNS of flow over the T106C turbine

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Advances in Aerodynamics 2019年第1期1卷 408-425页

作者： Mohammad Alhawwary Z.J.Wang Department of Aerospace Engineering University of KansasLawrenceKS66045US

A high-order Navier-Stokes solver based on the flux reconstruction(FR)or the correction procedure via reconstruction(CPR)formulation is employed to perform a direct numerical simulation(DNS)and large eddy simulations(LES)of a well-known benchmark problem–transitional flow over the low-pressure T106C turbine ***-refinement studies are carried out to assess the resolution requirement.A 4th order(p3)simulation on the fine mesh is performed with a DNS resolution to establish a"converged"solution,including the mean pressure and skin-friction distributions,and the power spectral density in the *** LES on the coarse and fine meshes with lower order schemes are conducted to assess the mesh and order dependence of the *** particular,we study the error in the transition location,the mean skin-friction distribution,and the mean lift and drag *** h-and p-refinement studies provide a much-needed guideline in h-and p-resolutions to achieve a certain level of accuracy for industrial LES applications.

关键词： Direct numerical simulations Large eddy simulations Transitional flows High-order FR/CPR T106C skin-friction

MHD Transient Flow with Hall Current Past an Accelerated Horizontal Porous Plate in a Rotating System

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Open Journal of Fluid Dynamics 2013年第4期3卷 278-285页

作者： Nazibuddin Ahmed Jiwan Krishna Goswami Dhruba Prasad Barua Department of Mathematics ADP College Nagaon India Department of Mathematics Gauhati University Guwahati India

An exact solution to the problem of an MHD transient flow with Hall current past a uniformly accelerated horizontal porous plate in a rotating system has been presented. The dimensionless governing equations of the flow problem are solved by Laplacetransform technique in closed form. A uniform magnetic field is assumed to be applied transversely to the direction of the flow. The expressions for velocity fields and skin-frictions are obtained in non-dimensional form. The primary and secondary velocity distributions and skin-frictions at the plate due to primary and secondary velocity field are demonstrated graphically and the effects of the different parameters namely, rotational parameter, Hartmann number, Hall parameter and acceleration parameter are discussed and the results are physically interpreted.

关键词： MHD Rotating System Transient Hall Current Mass Transfer skin-friction

Conjugate Effects of Heat and Mass Transfer on Natural Convection Flow along an Isothermal Sphere with Radiation Heat Loss

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Open Journal of Fluid Dynamics 2013年第2期3卷 86-94页

作者： Salina Aktar Mahmuda Binte Mostafa Ruma Md. Abdul Alim Department of Engineering & Technology Eastern University Dhaka Bangladesh Department of Mathematics Bangladesh University of Engineering and Technology Dhaka Bangladesh Department of Natural Science Stamford University Stamford Bangladesh

Conjugate effects heat and mass transfer on free convection flow across an isothermal sphere immersed in a viscous incompressible fluid in the presence of species concentration with radiation heat loss has been investigated in this paper. The governing boundary layer equations are first transformed into a non-dimensional form and the resulting nonlinear systems of partial differential equations are then solved numerically using Finite—difference method with Keller-box Scheme. We have focused our attention on the evaluation velocity profiles, temperature profiles and species concentration profiles of the fluid as well as the local skin friction coefficient, local heat transfer rate and local species concentration transfer rate for a wide range of radiation parameter Rd, Schmidt number Sc and Prandlt number Pr.

关键词： Natural Convection Radiation Heat Loss skin-friction Nusselt Number Schmidt Number Prandlt Number

Free Convection Flow between Vertical Plates Moving in Opposite Direction and Partially Filled with Porous Medium

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Applied Mathematics 2011年第8期2卷 935-941页

作者： Umesh Gupta Abhay Kumar Jha Rama Charan Chaudhary 不详

The laminar fully developed free-convection flow in a channel bounded by two vertical plates, partially filled with porous matrix and partially with a clear fluid, has been discussed when both the plates are moving in opposite direction. Two regions are coupled, by equating the velocity and shear stress at the interface. The momentum transfer in porous medium has been described by the Brinkman-extended Darcy model. The affect of Darcy number on flow velocity has been discussed in fluid region, interface region and porous medium with the help of graphs. Analytic method has been adopted to obtain the expressions of velocity and temperature. The skin-friction component has also been determined and presented with the help of tables.

关键词： Free Convection Porous Medium skin-friction