The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number (Re) of 25,000, based on leading-edge diameter (D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.

使用电子扫描压力 (ESP) 和粒子图像测速 (PIV) 对雷诺数 ( Re ) 为 25,000进行实验研究，基于前缘，压力梯度对超过机翼模型前缘的分离边界层的影响直径 ( D )。对于β的三种情况（−30°，0°和+ 30°），检查了分离区域中边界层的特征及其经过重新连接位置后的发展。从压力和速度测量获得的平均数据中识别气泡参数，例如分离和过渡的开始以及重新附着的位置。从 ESP 获得的表面压力测量结果显示β 的壁静压力激增= -30°（襟翼向上偏转），而与基本情况相比，β = +30°（襟翼向下偏转）下降，β = 0°。粒子图像测速结果表明，与β = 0° 和 -30°相比，由于背景扰动的放大程度更高，因此在β = +30° 时，剪切层在分离开始后卷起较早。在过渡位置的下游，瞬时场测量显示β = +30° 的涡流被拉伸、迷失方向，并且有时更大的涡流，而对于β，观察到规则的、周期性脱落的涡流，保持其身份超过重新附着位置= 0° 和 -30°。最重要的是，这项研究对从模型下游端接收扰动的分离气泡的特征提出了新的见解，这些结果可以作为未来在类似环境下对翼型进行研究的基准。