Interactions Between Propagating Wakes and Flow Instabilities in the Presence of a Laminar Separation Bubble
Interactions Between Propagating Wakes and Flow Instabilities in the Presence of a Laminar Separation Bubble
复制标题
存在层流分离气泡时传播尾流与流动不稳定性之间的相互作用
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
R. Thomas
中科院分区：
文献类型：
--
作者：
J. Gostelow;R. Thomas
在强扩散自相似压力分布下，对平板上的层流分离进行了实验研究。这就形成了细长的层状分离气泡。边界层速度导线是在许多纵向站点上进行的。使用单一的热线，结合使用单独的轨迹、相位平均和时间平均。为了补充这一点，安装了麦克风阵列，以给出压力扰动的瞬时等高线，并研究随时间变化的流动特性。传声器数据与在逆压梯度下，在分离点上游预测的不稳定性的强烈放大是一致的。在Tollmien-Schlichting(T-S)频率的驱动下，这些不稳定性发展成为在分离气泡剪切层中发展的湍流斑点。气泡的再附着是由分离剪切层的转变引起的。在过渡的后期，海浪最强。一旦失去了相干性，在湍流层中，振幅就会减弱。尾迹扰动被注入到流动中，并在整个流场中被跟踪。尾迹相互作用导致湍流斑块穿透壁面。斑块之后是平静的区域，在每个湍流条带之后的过渡区中，可以检测到波活动减少的区域。在平静区域末端的一小段时间内，粘性不稳定波继续向下游传播一段相当长的距离，与平静区域一致，在另外一个湍流区域。版权所有©2006，ASME
Laminar separation was investigated experimentally on a flat plate under a strongly diffusing self-similar pressure distribution. This gave a long and thin laminar separation bubble. Boundary layer velocity traverses were performed at numerous longitudinal stations. Using a single hot wire a combination of individual traces, phase averaging and time averaging was used. To supplement this, an array of microphones was installed to give instantaneous contours of pressure perturbation and to investigate the time dependent flow features. Microphone data were consistent with the strong amplification, under the adverse pressure gradient, of instabilities predicted far upstream of the separation point. Driven at the Tollmien-Schlichting (T-S) frequency, these instabilities grew into turbulent spots developing in the shear layer of the separation bubble. Reattachment of the bubble was caused by transition of the separated shear layer. The waves were strongest in the later stages of transition. Once the coherence was lost, in a turbulent layer, the amplitude became diminished. Wake disturbances were injected into the flow and traced through the flow field. The wake interaction resulted in turbulent patches which penetrated to the wall. Following the patches was the calmed region, detectable as a region of reduced wave activity in the transition region following each turbulent strip. For a short time at the end of the calmed region the viscous instability waves continued to propagate for a considerable distance downstream, in concert with the calmed region, in an otherwise turbulent zone.Copyright © 2006 by ASME