Active separation control: an overview of Reynolds and Mach numbers effects
Active separation control: an overview of Reynolds and Mach numbers effects
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主动分离控制：雷诺数和马赫数效应概述
DOI：
10.1016/j.ast.2004.06.007
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发表时间：
2004
影响因子：
5.6
通讯作者：
I. Wygnanski
中科院分区：
文献类型：
--
作者：
A. Seifert;D. Greenblatt;I. Wygnanski
本文作者及其合作者在雷诺数为3× 104 ×107的范围内，对二维周期性激励控制分离进行了实验研究。试验表明，在各种飞行条件下，采用振荡流激励的主动控制可以有效地延缓气流从气动表面分离，并使分离流重新附着到气动表面。在雷诺数低于105时，转捩不是自然发生的，也不能被动地强迫，主动分离控制可能是延迟分离和产生有用升力的唯一有效方法。主动分离控制的本质依赖于利用流动中固有的不稳定性，通常需要相对小幅度的激励。有效的激励频率在任何时候都在受控区域上产生一到四个涡流，而与雷诺数无关，并且扰动最好在容易分离的区域上被放大。周期性激励在性能效益方面大大上级稳定吹扫，并且消除了从控制观点来看不期望的突然流动响应。在没有激波的情况下，可压缩性的影响很弱，而伴随分离的不希望的影响，如涡脱落和抖振，可以大大减少或完全消除。只要在分离的上游引入激励，由激波/边界层相互作用引起的分离可以得到改善。
Separation control, by nominally two-dimensional periodic excitation, was studied experimentally by the authors and co-workers at Reynolds numbers ranging from 3×104to 4×107, including compressibility effects. The tests demonstrated that active control using oscillatory flow excitation can effectively delay flow separation from, and reattach separated flow to, aerodynamic surfaces at various flight conditions. At Reynolds number below 105, where transition does not occur naturally and cannot be passively forced, active separation control may be the only effective method for delaying separation and generating useful lift. The essence of active separation control relies on exploiting instabilities that are inherent in the flow, generally requiring relatively small amplitude excitation. Effective excitation frequencies generate one to four vortices over the controlled region at all times, irrespective of Reynolds number, and perturbations should preferably be amplified over the region that is susceptible to separation. Periodic excitation is vastly superior to steady blowing in terms of performance benefits and eliminates abrupt flow responses, which are undesirable from a control point of view. The effects of compressibility in the absence of shocks are weak and undesirable effects accompanying separation, such as vortex-shedding and buffet, can be significantly reduced or completely eliminated. Separation resulting from shock-wave/boundary-layer interaction can be ameliorated, providing that excitation is introduced upstream of separation.