| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 105 === This paper performs a linear stability analysis to investigate the stability of plane Couette-Poiseuille flow in a two-layer system. There is fluid layer overlying a porous layer saturated with the same fluid. The effect of superimposed Couette flow on the associated Poiseuille flow in such a two-layer system is explored carefully. The result shows that the presence of Couette flow would destabilize the Poiseuille flow with a small value of depth ratio, which is defined by the ratio of the depth of fluid layer to the depth of porous layer, and induce a tri-modal neutral curves. At moderate value of depth ratio, the Couette component generally produces a stabilization effect on the flow. When the velocity of the upper moving wall is large enough, a bi-modal neutral curve appears and a shift of instability mode occurs from the long-wave fluid-layer mode to the porous-layer mode with higher wavenumber. These stability characteristics are remarkably different from those of the plane Couette-Poiseuille flow in a single fluid layer that the flow becomes absolutely stable when the wall velocity is over 70% of the maximum velocity of the Poiseuille component of flow. The stability of pure Couette flow in such a two-layer system is also studied. It is found that the flow is still absolutely stable with respect to infinitesimal disturbances, which is as same as the stability characteristic of single fluid layer plane Couette flow.
|
|---|
