An investigation has been made on an unsteady Couette flow of a viscous incompressible fluid through a porous me- dium in a rotating system. The solution of the governing equations has been obtained by the use of Lapl...An investigation has been made on an unsteady Couette flow of a viscous incompressible fluid through a porous me- dium in a rotating system. The solution of the governing equations has been obtained by the use of Laplace transform technique. It is found that the primary velocity decreases and the magnitude of the secondary velocity increases with an increase in rotation parameter. The fluid velocity components are decelerated by an increase of Reynolds number. An increase in porosity parameter leads to increase the primary velocity and the magnitude of the secondary velocity. It is also found that the solution for small time converges more rapidly than the general solution. The asymptotic behavior of the solution is analyzed for small as well as large values of rotation parameter and Reynolds number. It is observed that a thin boundary layer is formed near the moving plate of the channel and the thicknesses of the boundary layer increases with an increase in porosity parameter.展开更多
The combined influences of Hall currents and rotation on the MHD Couette flow of a viscous incompressible electrically conducting fluid between two infinite horizontal parallel porous plates channel in a rotating syst...The combined influences of Hall currents and rotation on the MHD Couette flow of a viscous incompressible electrically conducting fluid between two infinite horizontal parallel porous plates channel in a rotating system in the presence of a uniform transverse magnetic field have been carried out. The solutions for the velocity field as well as shear stresses have been obtained for small time as well as for large times by Laplace transform technique. It is found that for large times the Hall currents accelerates primary flow whereas it retards secondary flow while the rotation retards the primary flow whereas it accelerates the secondary flow. It is also found that the velocity components converge more rapidly for small time solution than the general solution. The asymptotic behavior of the solution is analyzed for small as well as large values of magnetic parameter M2, rotation parameter K2 and Reynolds number Re. It is observed that a thin boundary layer is formed near the moving plate of the channel and the thicknesses of the layer increases with increase in either Hall parameter m or Reynolds number Re while it decreases with increase in Hartmann number M. It is interesting to note that for large values of M2 , the boundary layer thickness is independent of the rotation parameter.展开更多
Unsteady hydromagnetic Couette flow of a viscous incompressible electrically conducting fluid in a rotating system is studied when the fluid flow within the channel is induced due to the impulsive movement of the one ...Unsteady hydromagnetic Couette flow of a viscous incompressible electrically conducting fluid in a rotating system is studied when the fluid flow within the channel is induced due to the impulsive movement of the one of the plates of the channel.The plates of the channel are considered porous and the magnetic field is fixed relative to the moving plate.Exact solution of the governing equations is obtained by Laplace transform technique.The expression for the shear stress at the moving plate is also obtained.Asymptotic behaviour of the solution is analyzed for small as well as large values of time t to highlight the transient approach to the final steady state flow and the effects of rotation,magnetic field and suction/injection.It is found that suction has retarding influence on the primary as well as secondary flow where as injection and time have accelerating influence on the primary and secondary flows.展开更多
This paper presents an experimental investigation of effects of a kind of streamwise-grooved blades on the flowfield in a compressor cascade.The flow field downstream the cascade and the boundary layer on the suctions...This paper presents an experimental investigation of effects of a kind of streamwise-grooved blades on the flowfield in a compressor cascade.The flow field downstream the cascade and the boundary layer on the suctionsurface were measured using a mini 5-hole pressure probe at different incidence angles.The flow field in thegroove cascade was compared with that in the smooth cascade.The measurement results indicate that:(1)thegroove surface can restrain the development of the boundary layer on the suction surface;(2)the grooves canrestrain the radial migration of the low-energy fluids in the boundary layer on the suction surface;(3)the grooveblades can reduce total pressure loss and flow blockage in the cascade at the incidence angles of 0°,5°and 8°;(4)the maximum benefit of 8.6% loss reduction was obtained at the incidence angle of 5° while negative benefit of-3.0% loss reduction occurred at the incidence angle of-5°.展开更多
This paper presents an experimental investigation of the turbulent boundary layers on both groove and smooth flat surfaces. The flow structures were shown in a water tunnel using the hydrogen-bubble flow visualization...This paper presents an experimental investigation of the turbulent boundary layers on both groove and smooth flat surfaces. The flow structures were shown in a water tunnel using the hydrogen-bubble flow visualization technique. The measurement results indicate that: (1) the grooves can effectively reduce accumulation of low-speed fluids, decrease the number of the low-speed streaks and depress oscillation of the streaks in the sublayer; (2) the grooves can restrain forming of the horseshoe vortices in the buffer region; (3) the grooves bate oscillation and kinking of the quasi-streamwise vortices and restrain production of the hairpin vortices and the ring vortices, reducing both frequency and intensity of the turbulence bursting; (4) the grooves directly affect the flow structures in the sublayer of the boundary layer and then modulate the flow field up to the buffer region and the logarithmic region by restraining development and interaction of the vortices.展开更多
文摘An investigation has been made on an unsteady Couette flow of a viscous incompressible fluid through a porous me- dium in a rotating system. The solution of the governing equations has been obtained by the use of Laplace transform technique. It is found that the primary velocity decreases and the magnitude of the secondary velocity increases with an increase in rotation parameter. The fluid velocity components are decelerated by an increase of Reynolds number. An increase in porosity parameter leads to increase the primary velocity and the magnitude of the secondary velocity. It is also found that the solution for small time converges more rapidly than the general solution. The asymptotic behavior of the solution is analyzed for small as well as large values of rotation parameter and Reynolds number. It is observed that a thin boundary layer is formed near the moving plate of the channel and the thicknesses of the boundary layer increases with an increase in porosity parameter.
文摘The combined influences of Hall currents and rotation on the MHD Couette flow of a viscous incompressible electrically conducting fluid between two infinite horizontal parallel porous plates channel in a rotating system in the presence of a uniform transverse magnetic field have been carried out. The solutions for the velocity field as well as shear stresses have been obtained for small time as well as for large times by Laplace transform technique. It is found that for large times the Hall currents accelerates primary flow whereas it retards secondary flow while the rotation retards the primary flow whereas it accelerates the secondary flow. It is also found that the velocity components converge more rapidly for small time solution than the general solution. The asymptotic behavior of the solution is analyzed for small as well as large values of magnetic parameter M2, rotation parameter K2 and Reynolds number Re. It is observed that a thin boundary layer is formed near the moving plate of the channel and the thicknesses of the layer increases with increase in either Hall parameter m or Reynolds number Re while it decreases with increase in Hartmann number M. It is interesting to note that for large values of M2 , the boundary layer thickness is independent of the rotation parameter.
文摘Unsteady hydromagnetic Couette flow of a viscous incompressible electrically conducting fluid in a rotating system is studied when the fluid flow within the channel is induced due to the impulsive movement of the one of the plates of the channel.The plates of the channel are considered porous and the magnetic field is fixed relative to the moving plate.Exact solution of the governing equations is obtained by Laplace transform technique.The expression for the shear stress at the moving plate is also obtained.Asymptotic behaviour of the solution is analyzed for small as well as large values of time t to highlight the transient approach to the final steady state flow and the effects of rotation,magnetic field and suction/injection.It is found that suction has retarding influence on the primary as well as secondary flow where as injection and time have accelerating influence on the primary and secondary flows.
基金The authors would like to acknowledge National Natural Science Foundation of China for the support projects Grant No.50376002.
文摘This paper presents an experimental investigation of effects of a kind of streamwise-grooved blades on the flowfield in a compressor cascade.The flow field downstream the cascade and the boundary layer on the suctionsurface were measured using a mini 5-hole pressure probe at different incidence angles.The flow field in thegroove cascade was compared with that in the smooth cascade.The measurement results indicate that:(1)thegroove surface can restrain the development of the boundary layer on the suction surface;(2)the grooves canrestrain the radial migration of the low-energy fluids in the boundary layer on the suction surface;(3)the grooveblades can reduce total pressure loss and flow blockage in the cascade at the incidence angles of 0°,5°and 8°;(4)the maximum benefit of 8.6% loss reduction was obtained at the incidence angle of 5° while negative benefit of-3.0% loss reduction occurred at the incidence angle of-5°.
基金Project funded by National Natural Science Foundation of China, Grant No.50376002.
文摘This paper presents an experimental investigation of the turbulent boundary layers on both groove and smooth flat surfaces. The flow structures were shown in a water tunnel using the hydrogen-bubble flow visualization technique. The measurement results indicate that: (1) the grooves can effectively reduce accumulation of low-speed fluids, decrease the number of the low-speed streaks and depress oscillation of the streaks in the sublayer; (2) the grooves can restrain forming of the horseshoe vortices in the buffer region; (3) the grooves bate oscillation and kinking of the quasi-streamwise vortices and restrain production of the hairpin vortices and the ring vortices, reducing both frequency and intensity of the turbulence bursting; (4) the grooves directly affect the flow structures in the sublayer of the boundary layer and then modulate the flow field up to the buffer region and the logarithmic region by restraining development and interaction of the vortices.
