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Analysis of Unsteady Confined Viscous Flows With Variable Inflow Velocity and Oscillating Walls

机译:可变流入速度和振荡壁的非定常约束粘性流分析

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The inflow velocities in various components of many engineering systems often display variations in time (fluctuations) during the operation cycle, which may substantially affect the flow-induced vibrations and instabilities of these systems. For this reason, the aeroelasticity study of these systems should include the effect of the inflow velocity variations, which until now has not been taken into account. This paper presents a fluid-dynamic analysis of the unsteady confined viscous flows generated by the variations in time of the inflow velocities and by oscillating walls, which is required for the study of flow-induced vibration and instability of various engineering systems. The time-accurate solutions of the Navier-Stokes equations for these unsteady flows are obtained with a finite-difference method using artificial compressibility on a stretched staggered grid, which is a second-order method in space and time. A special decoupling procedure, based on the utilization of the continuity equation, is used in conjunction with a factored alternate direction scheme to substantially enhance the computational efficiency of the method by reducing the problem to the solution of scalar tridiagonal systems of equations. This method is applied to obtain solutions for the benchmark unsteady confined flow past a downstream-facing step, generated by harmonic variations in time of the inflow velocity and by an oscillating wall, which display multiple flow separation regions on the upper and lower walls. The influence of the Reynolds number and of the oscillation frequency and the amplitudes of the inflow velocity and oscillating wall on the formation of the flow separation regions are thoroughly analyzed in this paper. It was found that for certain values of the Reynolds number and oscillation frequency and amplitudes, the flow separation at the upper wall is present only during a portion of the oscillatory cycle and disappears for the rest of the cycle, and that for other values of these parameters secondary flow separations may also be formed.
机译:许多工程系统的各个组件中的流入速度通常会在运行周期内显示时间变化(波动),这可能会严重影响这些系统的流动引起的振动和不稳定性。因此,这些系统的空气弹性研究应包括流入速度变化的影响,到目前为止尚未考虑到这一点。本文介绍了由流入速度随时间的变化和壁的振动而产生的非恒定约束流动的流体动力学分析,这对于研究各种工程系统的流致振动和不稳定性是必需的。 Navier-Stokes方程针对这些非恒定流的时间精确解是使用有限差分法在拉伸的交错网格上使用人工可压缩性获得的,该方法是时空的二阶方法。基于连续性方程的使用,一种特殊的解耦程序与因子交替方向方案结合使用,通过将问题简化为标量三对角方程组的解,从而显着提高了该方法的计算效率。此方法适用于获得通过下游面向步骤的基准非恒定约束流的解决方案,该解决方案是由流入速度随时间的谐波变化和振荡壁生成的,该振荡壁在上下壁上显示了多个分流区域。本文深入分析了雷诺数和振​​荡频率以及流入速度和振荡壁的振幅对分流区域形成的影响。已经发现,对于雷诺数和振​​荡频率以及振幅的某些值,仅在一部分振荡周期内才出现上壁的流动分离,而在其余的振荡周期内消失,而对于其他这些值则消失。还可形成二次流分离参数。

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