基于合成射流的二维后台阶分离流主动控制

Active control of 2D backward facing step separated flow based on synthetic jet

作为一种新的流动控制激励器,合成射流技术在流动分离控制、降低压力脉动和抑制噪声等方面具有广阔的应用前景。实验利用合成射流主动控制技术对二维后台阶湍流分离再附流动控制进行了研究,应用表面测压、粒子图像测速(PIV)和热线等多种实验测试技术对后台阶表面压力分布、流场结构以及剪切层特性进行了测试。结果表明,在台阶前缘施加合成射流可有效减小回流区范围和降低再附长度,当合成射流的动量系数为0.301×10-3时,可使再附点长度减小25%。合成射流控制使得沿台阶下游的湍动能和雷诺应力增强,提高了台阶下游流场的混合效率。热线动态结果表明频率是后台阶分离流动控制的关键参数,当频率为260Hz、激励频率与剪切层涡脱落频率之比为1.32、激励频率等同于旋涡脱落频率时,合成射流控制效果最好,仅需消耗较小的能量即可实现流动控制的目的。

As a new type of flow control actuator,synthetic jet has a potentially broad application in the fields of flow separation control,pressure pulsation reduction and noise suppression.Experimental investigation on 2Dbackward facing step turbulent separated and reattachment flow control with synthetic jet arrays is conducted,in which the surface pressure distribution of backward facing step,the field structure and the prominent features of shear layer are tested with many experimental devices such as pressure transducers,particle image velocimetry（PIV）and hot wire anemometer.The results show that the perturbation of synthetic jet which is formed at the upper edge of the step can effectively reduce the recirculation zone and reattachment length;when the synthetic jet momentum coefficient is 0.301×10-3,the non-dimensional length of reattachment decreases by 25% at most.Synthetic jet control increases the turbulent kinetic energy and Reynolds stress along the downstream steps and enhances the mixing efficiency of the flow field along the downstream steps.The hot wire test results show that frequency is the key parameter of backward facing step flow separation control;when the disturbance frequency is260 Hz,the ratio of disturbance frequency to shear layer vortex shedding frequency is 1.32 and the forcing frequency is equivalent to the vortex shedding frequency,the effect of synthetic jet control is the best and the flow control can be achieved only with low consumption of energy.