论文标题

基于Lagrange乘数的最佳控制技术,用于高速边界层的条纹衰减

A Lagrange multiplier-based optimal control technique for streak attenuation in high-speed boundary layers

论文作者

Es-Sahli, Omar, Sescu, Adrian, Koshuriyan, M. Z. A., Hattori, Yuji, Hirota, Makoto

论文摘要

高振幅的无流湍流和表面粗糙度元件可以激发层流边界层的流动充足以引起流向方向的涡流。这些涡流类似于伸长条纹,具有替代水平速度的跨度变化。下游,通过无粘性的二级不稳定性机制,最终向湍流过渡,涡流“摆动”。我们制定了一种最佳控制算法,以抑制流向涡流系统的生长速率。考虑到较高的雷诺数渐近框架,我们将完整的可压缩Navier-Stokes方程减少到非线性压缩边界区域方程(NCBRE)。然后,我们通过将原始约束优化问题适当转换为不受约束的形式的适当转换来实现Lagrange乘数的方法,以以伴随的可压缩边界区域方程(ACBRE)和相应的最佳条件的形式获得干扰方程。用于高苏打和高超音速流的ACBRE方法的数值溶液揭示了所有考虑的构型的动能和壁剪应力的显着降低。我们提出了轮廓图,以证明控制迭代率增加的定性效果。我们的结果表明,由于ACBRE算法,主要的涡流不稳定性逐渐沿跨方向变平。

High-amplitude free stream turbulence and surface roughness elements can excite a laminar boundary layer flow sufficiently to cause streamwise oriented vortices to develop. These vortices resemble elongated streaks having alternate spanwise variations of the streamwise velocity. Downstream, the vortices `wobble' through an inviscid secondary instability mechanism and, ultimately, transition to turbulence. We formulate an optimal control algorithm to suppress the growth rate of the streamwise vortex system. Considering a high Reynolds number asymptotic framework, we reduce the full compressible Navier-Stokes equations to the nonlinear compressible boundary region equations (NCBRE). We then implement the method of Lagrange multipliers via an appropriate transformation of the original constrained optimization problem into an unconstrained form to obtain the disturbance equations in the form of the adjoint compressible boundary region equations (ACBRE) and corresponding optimality conditions. Numerical solutions of the ACBRE approach for high-supersonic and hypersonic flows reveal a significant reduction in the kinetic energy and wall shear stress for all considered configurations. We present contour plots to demonstrate the qualitative effect of increased control iterations. Our results indicate that the primary vortex instabilities gradually flatten in the spanwise direction thanks to the ACBRE algorithm.

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