Flow separation control of a sweeping jet actuator in a backward-facing ramp was studied using two-dimensional and stereoscopic particle-image velocimetry. The actuator was operated at a single supply rate pertaining to a jet velocity of 7.3 m/s and positioned at the streamwise location of 0.8 and 3.7 boundary layer thickness upstream of the separating edge. Three wind tunnel reference velocities corresponding to Reynolds numbers based on the boundary layer thickness of ${\mathrm{Re}}_{\delta }=2400$, 5200, and 9800 (jet-to-reference velocity ratios of 1, 0.5, and 0.3) were investigated, and the control effectiveness was assessed based on the size of the separation bubble. For all three Reynolds numbers, positioning the actuator nearer to the separating edge offered poorer flow separation control for measurement planes near the jet centerline. This was attributed to the upwash effect of the jet which directed high momentum fluid away from the wall leading to lower levels of entrainment, and the formation of a localized low-pressure region that coincided with the sharp change in ramp geometry leading to stronger adverse pressure gradients and lower streamwise velocities that were more likely to undergo flow reversal. At high jet-to-reference velocity ratios, the effect was accentuated, and a secondary separation bubble was observed. When the actuator was positioned further upstream, the primary streamwise vortices produced by the sweeping jet lifted away from the wall, and secondary flow structures induced near the wall contributed to higher levels of near-wall entrainment and improved flow control along the jet centerline. In contrast, for measurement planes far from the jet centerline, positioning the actuator nearer the separating edge was preferable. This was attributed to milder decay of the primary streamwise vortices, leading to stronger downwash effect and higher entrainment levels that were able to affect a wider spanwise area.

中文翻译：

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用于向后坡道的流量分离控制的清扫喷射执行器的观察结果

使用二维和立体粒子图像测速技术研究了后掠坡道中清扫喷头执行器的分流控制。致动器以对应于7.3 m / s的喷射速度的单一供应速率进行操作，并位于分离边缘上游0.8和3.7边界层厚度的沿流位置。基于雷诺数的边界层厚度，对应于雷诺数的三个风洞参考速度${\mathrm{关于}}_{\delta }=2400$，5200和9800（喷射速度与参考速度之比分别为1、0.5和0.3）进行了研究，并根据分离气泡的大小评估了控制效果。对于所有三个雷诺数，将执行器放置在靠近分离边缘的位置，对于靠近射流中心线的测量平面，流动分离控制会较差。这归因于射流的向上冲刷作用，该射流将高动量流体引向壁外，从而导致夹带水平降低，并且形成了局部低压区域，该区域与斜坡几何形状的急剧变化同时发生，从而导致了较强的逆向压力。梯度和较低的水流速度，它们更有可能发生逆流。在高喷射速度与参考速度的比率下，效果更加突出，并观察到二次分离气泡。当执行机构位于更上游时，由清扫喷头产生的初级涡流从壁上抬起，而在壁附近引起的次级流动结构则导致了更高水平的近壁夹带并改善了沿射流中心线的流量控制。相反，对于远离射流中心线的测量平面，将致动器定位在靠近分离边缘的位置是优选的。这归因于初级流向漩涡的温和衰减，从而导致更强的向下冲洗效果和更高的夹带水平，从而能够影响更宽的展向区域。壁附近引起的二次流动结构导致了更高水平的近壁夹带并改善了沿射流中心线的流动控制。相反，对于远离射流中心线的测量平面，将致动器定位在靠近分离边缘的位置是优选的。这归因于初级涡流的缓和衰减，从而导致更强的向下冲洗效果和更高的夹带水平，从而能够影响更宽的展向区域。壁附近引起的二次流动结构导致了更高水平的近壁夹带并改善了沿射流中心线的流动控制。相反，对于远离射流中心线的测量平面，将致动器定位在靠近分离边缘的位置是优选的。这归因于初级流向漩涡的温和衰减，从而导致更强的向下冲洗效果和更高的夹带水平，从而能够影响更宽的展向区域。