合成射流微扰动对后台阶湍流分离流动控制的实验研究

Experiment research of active flow control of turbulent separated flow on backward-facing step using synthetic jet perturbation

后台阶流动是流体力学中一个经典的研究课题,代表着工程中一类横截面突扩的钝体绕流问题。后台阶流动分离会导致一些不利的影响,如高速旋涡的形成、流动损失、压力脉动以及气动噪声等。基于阵列式合成射流激励器对二维矩形后台阶湍流分离再附流动控制进行了研究,综合应用表面测压、七孔探针、粒子图像测速仪(PIV)和热线等多种实验手段,获取了后台阶的表面压力分布和非定常流场结构。结果表明:利用在台阶前缘形成的合成射流微扰动可使无量纲再附点长度降低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。热线结果表明,频率是后台阶分离流动控制的重要参数,当频率为260 Hz,扰动频率与剪切层涡脱落频率之比为1.32时,合成射流控制可使位于1/2倍频的剪切层能量增强,仅需消耗较小的能量即可实现流动控制的目的。

Backward-facing step flow is typical in the research of fluid mechanics and it mainly investigates the sudden ex- pansion of cross-sectional flow around a bluff body. Backward-facing step flow separation will lead to some adverse effects, such as high-speed vortex formation, flow losses, pressure pulsation and aerodynamic noise. Experimental investigation on separated reattachment flow control of two-dimensional backward-facing step turbulence with synthetic jet arrays is conduc- ted. The unsteady flow field structure of a backward-facing step and surface pressure distribution are measured with seven- hole probes particle image velocimetry （PIV）, hot wire anemometer, and pressure transducers as well. The results show that the perturbation of synthetic jet which is formed at the upper edge of the step can effectively decrease the non-dimen- sional length of reattachment flow by about 25 % at most, and synthetic jet control increases the turbulent kinetic energy and Reynolds stress along the downstream steps and enhances the mixing efficiency of the flow field. The hot wire results show that frequency is a key parameter of backward facing step flow separation control; when the disturbance frequency is 260 Hz, the ratio of disturbance frequency to shear layer vortex shedding frequency is 1.32,the synthetic jet control can be applied to enhancing the energy of separated shear layer at a half of disturbance frequency and the flow control can be achieved only with low consumption of energy.