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TRANSITIONS AND INSTABILITIES OF FLOW IN A CHANNEL WITH A SUDDENLY EXPAN DED PART

具有突然扩展的 DED 部分的通道中流动的转变和不稳定性

基本信息

批准号：
09640494
负责人：
MIZUSHIMA Jiro
金额：
$ 2.05万
依托单位：
DOSHISHA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640494/
关键词：
CHANNEL FLOW SUDDEN EXPANSION STABILITY OF FLOW BIFURCATION TRANSITION TO TURBULENCE PITCHFORK BIFURCATION HOPF BIFURCATION 乱流遷移管路流れ流量分配

项目摘要

Transitions and instabilities of flow in a symmetric channel with a suddenly expanded and contracted part are investigated theoretically by three different methods, i.e. the time marching method for dynamical equations, the SOR iterative method and the finite element method for steady-state equations. Linear and weakly nonlinear stability theories are applied to the flow. The transitions are confirmed experimentally by flow visualizations and velocity measurements. It is found that the flow is steady and symmetric at low Reynolds numbers, becomes asymmetric at a critical Reynolds number, gets the symmetry back at another critical Reynolds number and becomes oscillatory at very large Reynolds numbers. Multiple stable steady-state solutions are found in some cases, which lead to a hysteresis. The critical conditions for the existence of the multiple stable steady-state solutions are determined numerically and compared with the results of the linear and weakly nonlinear stability analyses. An exchange of modes for oscillatory instabilities is found to occur in the flow as the aspect ratio, the ratio of the length of the expanded part to its width, is varied, and its relation with the impinging free shear layer instability (IFLSI) is discussed. Transitions of flow in a channel with an inlet and two outlets are also investigated and the pressure distribution in the flow fields is obtained numerically.

用三种不同的方法，即求解动力学方程的时间推进法、求解稳态方程的SOR迭代法和求解稳态方程的有限元方法，从理论上研究了具有突增和突缩部分的对称流道中流动的转变和不稳定性。将线性和弱非线性稳定性理论应用到流动中。流动显示和速度测量在实验上证实了这种转变。结果表明，流动在低雷诺数时是稳定的对称流动，在一个临界雷诺数时变得不对称，在另一个临界雷诺数时恢复对称，在很大雷诺数时变得振荡。在某些情况下，存在多个稳定的稳态解，这导致了迟滞现象。用数值方法确定了存在多个稳定定态解的临界条件，并与线性和弱非线性稳定性分析的结果进行了比较。结果表明，随着展弦比(扩展段长度与宽度之比)的变化，流动中发生了振荡不稳定性的模式转换，并讨论了它与撞击自由剪切层不稳定性(IFLSI)的关系。文中还研究了双进双出流道内的流动转变，得到了流场中的压力分布。