The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic(MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet...The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic(MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented,taking into account thermal radiation and internal heat genberation/absorbtion.The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point.The Rosseland approximation is used to describe the radiative heat flux in the energy equation.The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung-Kutta method with the shooting technique.A comparison with previously published work has been carried out and the results are found to be in good agreement.The results are analyzed for the effect of different physical parameters,such as the variable viscosity and thermal conductivity,the ratio of free stream velocity to stretching velocity,the magnetic field,the porosity,the radiation and suction/injection on the flow,and the heat and mass transfer characteristics.The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ = 1.In addition,the imposition of fluid suction increases both the rate of heat and mass transfer,whereas fluid injection shows the opposite effect.展开更多
Design for structural integrity requires an appre-ciation of where stress singularities can occur in structuralconfigurations.While there is a rich literature devoted to theidentification of such singular behavior in ...Design for structural integrity requires an appre-ciation of where stress singularities can occur in structuralconfigurations.While there is a rich literature devoted to theidentification of such singular behavior in solid mechanics,to date there has been relatively little explicit identificationof stress singularities caused by fluid flows.In this study,stress and pressure singularities induced by steady flows ofviscous incompressible fluids are asymptotically identified.This is done by taking advantage of an earlier result thatthe Navier-Stokes equations are locally governed by Stokesflow in angular corners.Findings for power singularities areconfirmed by developing and using an analogy with solidmechanics.This analogy also facilitates the identification offlow-induced log singularities.Both types of singularity arefurther confirmed for two global configurations by applyingconvergence-divergence checks to numerical results.Eventhough these flow-induced stress singularities are analogousto singularities in solid mechanics,they nonetheless rendera number of structural configurations singular that were notpreviously appreciated as such from identifications withinsolid mechanics alone.展开更多
Based on the Navier-Stokes (N-S) equations of incompressible viscous fluids and the standard k-ε turbulence model with assumptions of steady state and two dimensional conditions, a simulation of the aerodynamic drag ...Based on the Navier-Stokes (N-S) equations of incompressible viscous fluids and the standard k-ε turbulence model with assumptions of steady state and two dimensional conditions, a simulation of the aerodynamic drag on a maglev train in an evacuated tube was made with ANSYS/FLOTRAN software under different vacuum pressures, blockage ratios, and shapes of train head and tail. The pressure flow fields of the evacuated tube maglev train under different vacuum pressures were analyzed, and then compared under the same blockage ratio condition. The results show that the environmental pressure of 1 000 Pa in the tube is the best to achieve the effect of aerodynamic drag reduction, and there are no obvious differences in the aerodynamic drag reduction among different streamline head shapes. Overall, the bluntshape tail and the blockage ratio of 0.25 are more efficient for drag reduction of the train at the tube pressure of 1 000 Pa.展开更多
Design for structural integrity requires an appreciation of where stress singularities can occur in structural configurations.While there is a rich literature devoted to the identification of such singular behavior in...Design for structural integrity requires an appreciation of where stress singularities can occur in structural configurations.While there is a rich literature devoted to the identification of such singular behavior in solid mechanics,only of late has there been much in the way of corresponding identifications of flow-induced stress singularities in fluid mechanics.These recent asymptotic identifications are for a single incompressible viscous fluid:Here the asymptotic approach is extended to apply to a configuration entailing two such fluids.For this configuration,various specifications leading to power or log singularities are determined.These results demonstrate that flow-induced stress singularities can occur in a structural container at a location where no singularities are identified within solid mechanics alone.展开更多
This paper is concerned with two-dimensional stagnation-point steady flow of an incompressible viscous fluid towards a stretching sheet whose velocity is proportional to the distance from the slit. The governing syste...This paper is concerned with two-dimensional stagnation-point steady flow of an incompressible viscous fluid towards a stretching sheet whose velocity is proportional to the distance from the slit. The governing system of partial differential equations is first transformed into a system of dimensionless ordinary differential equations. Analytical solutions of the velocity distribution and dimensionless temperature profiles are obtained for different ratios of free stream velocity and stretching velocity, Prandtl number, Eckert number and dimensionality index in series forms using homotopy analysis method(HAM). It is shown that a boundary layer is formed when the free stream velocity exceeds the stretching velocity, and an inverted boundary layer is formed when the free stream velocity is less than the stretching velocity. Graphs are presented to show the effects of different parameters.展开更多
Lagrangian-Eulerian formulations based on a generalized variational principle of fluid-solid coupling dynamics are established to describe flow-induced vibration of a structure under small deformation in an incompress...Lagrangian-Eulerian formulations based on a generalized variational principle of fluid-solid coupling dynamics are established to describe flow-induced vibration of a structure under small deformation in an incompressible viscous fluid flow. The spatial discretization of the formulations is based on the multi-linear interpolating functions by using the finite element method for both the fluid and solid structures. The generalized trapezoidal rule is used to obtain apparently non-symmetric linear equations in an incremental form for the variables of the flow and vibration. The nonlinear convective term and time factors are contained in the non-symmetric coefficient matrix of the equations. The generalized minimum residual(GMRES) method is used to solve the incremental equations. A new stable algorithm of GMRES-Hughes-Newmark is developed to deal with the flow-induced vibration with dynamical fluid-structure interaction in complex geometries. Good agreement between the simulations and laboratory measurements of the pressure and blade vibration accelerations in a hydro turbine passage was obtained,indicating that the GMRES-Hughes-Newmark algorithm presented in this paper is suitable for dealing with the flow-induced vibration of structures under small deformation.展开更多
In this paper, an analysis is made on the unsteady flow of an incompressible electrically conducting viscous fluid bounded by an infinite porous flat plate. The plate executes harmonic oscillations at a frequency n in...In this paper, an analysis is made on the unsteady flow of an incompressible electrically conducting viscous fluid bounded by an infinite porous flat plate. The plate executes harmonic oscillations at a frequency n in its own plane. A uniform magnetic field H0 is imposed perpendicular to the direction of the flow. It is found that the solution also exists for blowing at the plate. The temperature distribution is also obtained by taking viscous and Joule dissipation into account. The mean wall temperature θ0(0) decreases with the increase in the Hall parameter m. It is found that no temperature distribution exists for the blowing at the plate.展开更多
In this paper,the basic equations governing the flow and heat transfer of an incompressible viscous and electrically conducting fluid past a semi-infinite vertical permeable plate in the form of partial differential e...In this paper,the basic equations governing the flow and heat transfer of an incompressible viscous and electrically conducting fluid past a semi-infinite vertical permeable plate in the form of partial differential equations are reduced to a set of non-linear ordinary differential equations by applying a suitable similarity transformation.Approximate solutions of the transformed equations are obtained by employing the perturbation method for two cases,i.e.,small and large values of the suction parameter.From the numerical evaluations of the solution,it can be seen that the velocity field at any point decreases as the values of the magnetic and suction parameters increase.The effect of the magnetic parameter is to increase the thermal boundary layer.It is also found that the velocity and temperature fields decrease with the increase in the sink parameter.展开更多
The wellposedness problem for an anisotropic incompressible viscous fluid in R3, rotating around a vector B(t,x) := (b1(t,x),b2(t,x),b3(t,x)), is studied. The global wellposedness in the homogeneous case (B = e3) with...The wellposedness problem for an anisotropic incompressible viscous fluid in R3, rotating around a vector B(t,x) := (b1(t,x),b2(t,x),b3(t,x)), is studied. The global wellposedness in the homogeneous case (B = e3) with sufficiently fast rotation in the space B0,12 is proved. In the inhomogeneous case (B = B(t,xh)), the global existence and uniqueness of the solution in B0,21 are obtained, provided that the initial data are sufficient small compared to the horizontal viscosity. Furthermore, we obtain uniform local existence and uniqueness of the solution in the same function space. We also obtain propagation of the regularity in B2 21,1 under the additional assumption that B depends only on one horizontal space variable.展开更多
In this paper, an efficient multigrid fictitious boundary method (MFBM) coupled with the FEM solver package FEATFLOW was used for the detailed simulation of incompressible viscous flows around one or more moving NACA0...In this paper, an efficient multigrid fictitious boundary method (MFBM) coupled with the FEM solver package FEATFLOW was used for the detailed simulation of incompressible viscous flows around one or more moving NACA0012 airfoils. The calculations were carried on a fixed multigrid finite element mesh on which fluid equations were satisfied everywhere, and the airfoils were allowed to move freely through the mesh. The MFBM was employed to treat interactions between the fluid and the airfoils. The motion of the airfoils was modeled by Newton-Euler equations. Numerical results of experiments verify that this method provides an efficient way to simulate incompressible viscous flows around moving airfoils.展开更多
文摘The effect of variable viscosity and thermal conductivity on steady magnetohydrodynamic(MHD) heat and mass transfer flow of viscous and incompressible fluid near a stagnation point towards a permeable stretching sheet embedded in a porous medium are presented,taking into account thermal radiation and internal heat genberation/absorbtion.The stretching velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point.The Rosseland approximation is used to describe the radiative heat flux in the energy equation.The governing fundamental equations are first transformed into a system of ordinary differential equations using a scaling group of transformations and are solved numerically by using the fourth-order Rung-Kutta method with the shooting technique.A comparison with previously published work has been carried out and the results are found to be in good agreement.The results are analyzed for the effect of different physical parameters,such as the variable viscosity and thermal conductivity,the ratio of free stream velocity to stretching velocity,the magnetic field,the porosity,the radiation and suction/injection on the flow,and the heat and mass transfer characteristics.The results indicate that the inclusion of variable viscosity and thermal conductivity into the fluids of light and medium molecular weight is able to change the boundary-layer behavior for all values of the velocity ratio parameter λ except for λ = 1.In addition,the imposition of fluid suction increases both the rate of heat and mass transfer,whereas fluid injection shows the opposite effect.
文摘Design for structural integrity requires an appre-ciation of where stress singularities can occur in structuralconfigurations.While there is a rich literature devoted to theidentification of such singular behavior in solid mechanics,to date there has been relatively little explicit identificationof stress singularities caused by fluid flows.In this study,stress and pressure singularities induced by steady flows ofviscous incompressible fluids are asymptotically identified.This is done by taking advantage of an earlier result thatthe Navier-Stokes equations are locally governed by Stokesflow in angular corners.Findings for power singularities areconfirmed by developing and using an analogy with solidmechanics.This analogy also facilitates the identification offlow-induced log singularities.Both types of singularity arefurther confirmed for two global configurations by applyingconvergence-divergence checks to numerical results.Eventhough these flow-induced stress singularities are analogousto singularities in solid mechanics,they nonetheless rendera number of structural configurations singular that were notpreviously appreciated as such from identifications withinsolid mechanics alone.
基金supported by the Program for Changjiang Scholars and Innovative Research Team in University(PCSIRT) of the Ministry of Education of China(IRT0751)the National High Technology Research and Development Program of China (863 program: 2007-AA03Z203)+2 种基金the National Natural Science Foundation of China (Grant Nos. 50588201 and 50872116)the Research Fund for the Doctoral Program of Higher Education of China (SRFDP200806130023)the Fundamental Research Funds for the Central Universities (SWJTU09BR152, SWJTU09ZT24, and SWJTU11CX073)
文摘Based on the Navier-Stokes (N-S) equations of incompressible viscous fluids and the standard k-ε turbulence model with assumptions of steady state and two dimensional conditions, a simulation of the aerodynamic drag on a maglev train in an evacuated tube was made with ANSYS/FLOTRAN software under different vacuum pressures, blockage ratios, and shapes of train head and tail. The pressure flow fields of the evacuated tube maglev train under different vacuum pressures were analyzed, and then compared under the same blockage ratio condition. The results show that the environmental pressure of 1 000 Pa in the tube is the best to achieve the effect of aerodynamic drag reduction, and there are no obvious differences in the aerodynamic drag reduction among different streamline head shapes. Overall, the bluntshape tail and the blockage ratio of 0.25 are more efficient for drag reduction of the train at the tube pressure of 1 000 Pa.
文摘Design for structural integrity requires an appreciation of where stress singularities can occur in structural configurations.While there is a rich literature devoted to the identification of such singular behavior in solid mechanics,only of late has there been much in the way of corresponding identifications of flow-induced stress singularities in fluid mechanics.These recent asymptotic identifications are for a single incompressible viscous fluid:Here the asymptotic approach is extended to apply to a configuration entailing two such fluids.For this configuration,various specifications leading to power or log singularities are determined.These results demonstrate that flow-induced stress singularities can occur in a structural container at a location where no singularities are identified within solid mechanics alone.
基金supported by the National Natural Science Foundation of China (No. 50476083)
文摘This paper is concerned with two-dimensional stagnation-point steady flow of an incompressible viscous fluid towards a stretching sheet whose velocity is proportional to the distance from the slit. The governing system of partial differential equations is first transformed into a system of dimensionless ordinary differential equations. Analytical solutions of the velocity distribution and dimensionless temperature profiles are obtained for different ratios of free stream velocity and stretching velocity, Prandtl number, Eckert number and dimensionality index in series forms using homotopy analysis method(HAM). It is shown that a boundary layer is formed when the free stream velocity exceeds the stretching velocity, and an inverted boundary layer is formed when the free stream velocity is less than the stretching velocity. Graphs are presented to show the effects of different parameters.
基金supported by the National Natural Science Foundation of China (No. 50839003)the Natural Science Foundation of Yunnan Province (No. 2008GA027)
文摘Lagrangian-Eulerian formulations based on a generalized variational principle of fluid-solid coupling dynamics are established to describe flow-induced vibration of a structure under small deformation in an incompressible viscous fluid flow. The spatial discretization of the formulations is based on the multi-linear interpolating functions by using the finite element method for both the fluid and solid structures. The generalized trapezoidal rule is used to obtain apparently non-symmetric linear equations in an incremental form for the variables of the flow and vibration. The nonlinear convective term and time factors are contained in the non-symmetric coefficient matrix of the equations. The generalized minimum residual(GMRES) method is used to solve the incremental equations. A new stable algorithm of GMRES-Hughes-Newmark is developed to deal with the flow-induced vibration with dynamical fluid-structure interaction in complex geometries. Good agreement between the simulations and laboratory measurements of the pressure and blade vibration accelerations in a hydro turbine passage was obtained,indicating that the GMRES-Hughes-Newmark algorithm presented in this paper is suitable for dealing with the flow-induced vibration of structures under small deformation.
基金supported by the National Research Foundation of South Africa Thuthuka Programme
文摘In this paper, an analysis is made on the unsteady flow of an incompressible electrically conducting viscous fluid bounded by an infinite porous flat plate. The plate executes harmonic oscillations at a frequency n in its own plane. A uniform magnetic field H0 is imposed perpendicular to the direction of the flow. It is found that the solution also exists for blowing at the plate. The temperature distribution is also obtained by taking viscous and Joule dissipation into account. The mean wall temperature θ0(0) decreases with the increase in the Hall parameter m. It is found that no temperature distribution exists for the blowing at the plate.
文摘In this paper,the basic equations governing the flow and heat transfer of an incompressible viscous and electrically conducting fluid past a semi-infinite vertical permeable plate in the form of partial differential equations are reduced to a set of non-linear ordinary differential equations by applying a suitable similarity transformation.Approximate solutions of the transformed equations are obtained by employing the perturbation method for two cases,i.e.,small and large values of the suction parameter.From the numerical evaluations of the solution,it can be seen that the velocity field at any point decreases as the values of the magnetic and suction parameters increase.The effect of the magnetic parameter is to increase the thermal boundary layer.It is also found that the velocity and temperature fields decrease with the increase in the sink parameter.
基金Supported by NSFC(10871175,10931007,10901137)Zhejiang Provincial Natural Science Foundation of China(Z6100217)Program for New Century Excellent Talents in University
文摘The wellposedness problem for an anisotropic incompressible viscous fluid in R3, rotating around a vector B(t,x) := (b1(t,x),b2(t,x),b3(t,x)), is studied. The global wellposedness in the homogeneous case (B = e3) with sufficiently fast rotation in the space B0,12 is proved. In the inhomogeneous case (B = B(t,xh)), the global existence and uniqueness of the solution in B0,21 are obtained, provided that the initial data are sufficient small compared to the horizontal viscosity. Furthermore, we obtain uniform local existence and uniqueness of the solution in the same function space. We also obtain propagation of the regularity in B2 21,1 under the additional assumption that B depends only on one horizontal space variable.
基金Supported by National 863 Plan Project of Ministry of Science and Technology of China under Grant No. 2006AA09Z354National Natural Science Foundation of China under Grant No. 10672101.
文摘In this paper, an efficient multigrid fictitious boundary method (MFBM) coupled with the FEM solver package FEATFLOW was used for the detailed simulation of incompressible viscous flows around one or more moving NACA0012 airfoils. The calculations were carried on a fixed multigrid finite element mesh on which fluid equations were satisfied everywhere, and the airfoils were allowed to move freely through the mesh. The MFBM was employed to treat interactions between the fluid and the airfoils. The motion of the airfoils was modeled by Newton-Euler equations. Numerical results of experiments verify that this method provides an efficient way to simulate incompressible viscous flows around moving airfoils.
