离散边界层抽吸对转捩延迟的研究
Study of discrete boundary layer suction for transition delay
AI总结：
研究离散穿孔抽吸对布拉修斯边界层转捩的影响，通过热线风速仪获取数据评估最佳抽吸。发现抽吸体积流量是影响转捩延迟的更好指标，相同流量下不同排数穿孔抽吸效果相似，低雷诺数下抽吸转捩延迟大但归一化最佳流量略高。
AI中文摘要：
在本研究中，我们评估了通过离散穿孔进行抽吸对布拉修斯边界层转捩的影响。具体而言，利用热线风速仪获得的流向速度波动的间歇性和频谱来评估最佳抽吸，即能提供最大转捩延迟的抽吸。抽吸时的位移厚度雷诺数在1400至1600之间变化，孔排数为四排或十排。抽吸孔直径约为边界层位移厚度，从制造和维护角度看是实用尺寸。随着抽吸强度增加，转捩前沿向下游移动，在最佳抽吸时转捩延迟最大。当抽吸进一步增加时，转捩前沿又向上游移动。缩放分析支持的结果表明，抽吸体积流量比抽吸速度更能体现抽吸对转捩延迟的影响。特别是，只要抽吸体积流量相同，不同排数穿孔的抽吸对边界层转捩产生的影响大致相似。然而，排数较少的抽吸除了最佳抽吸体积流量略低外，还能提供略大的转捩延迟。结果还表明，在较低雷诺数下进行抽吸可提供显著更大的转捩延迟，但归一化最佳抽吸体积流量的值略高。
英文摘要：
In the present study we have assessed the effect of suction through discrete perforations on the transition of the Blasius boundary layer. In particular, the intermittency and the spectra of the streamwise velocity fluctuations, obtained using hot-wire anemometry, were used to evaluate the optimum suction, i.e., one that provides the greatest delay in transition. The displacement thickness Reynolds number at suction was varied between 1400 and 1600, while the number of rows of holes was either four or ten. The suction holes had diameter of the order of the displacement thickness of the boundary layer, a practical size from manufacturing and maintenance perspectives. As the suction strength was increased the transition front moved downstream, with the maximum delay in transition occurring at the optimum suction. When the suction was increased further, the transition front moved upstream again. The results, supported by a scaling analysis, showed that suction volume flow rate is a better indicator of the effects of suction on the transition delay than suction velocity. In particular, suction through different numbers of rows of perforations produces largely similar effects on the boundary layer transition, provided the suction volume flow rate remains the same. However, suction through fewer rows provided a slightly greater delay in transition in addition to a slightly lower optimum suction volume flow rate. The results also showed that suction applied at a lower Reynolds number provides a substantially greater transition delay but at slightly higher values of the normalized optimum suction volume flow rate.
