The Optimization of Reynolds Stress Flow Control for the Backward-Facing Step with Synthetic Jet Based on Numerical Simulation and Test

Active flow control, which has great application prospects in aerodynamic design, can restrain flow separation and reduce drag. This paper provides a review on our works relating to the China–EU MARS research project. Backward-facing step (BFS) flow, with sudden expansion of cross-section and complex vortices between the free stream and the main vortex, is a typical kind of separated flow. Synthetic jet, which transports momentum with zero net mass flux and affects structure of the flow field with length scales higher than its characteristic length scales, is applied to control BFS flow field. The optimization processes for the backward-facing step flow control with synthetic jet based on both numerical simulation and experimental data are introduced. In the numerical simulation aspect, experimental and computational data are synthesized and a computational model is proposed based on physical characteristics of wind tunnel. An adaptive double stage surrogate model based optimization framework is constructed and applied to optimize parameters of the synthetic jet. Two optimal schemes with similar control effects are obtained through design optimization based on computational data, revealing two inherently different flow control mechanisms. Pressure coefficient, skin friction and Reynolds stress of the two schemes are compared and analyzed. The flow control scheme for one problem based on Reynolds stress may not be definite. In the experimental aspect, the synthetic jet device has non-linear oscillation of reciprocating piston actuator into a pipe and can eject/suck mass flux through a jet slot. An in-looped design optimization system based on experimental data adopting hybrid searching algorithm is constructed and applied to optimize parameters of the synthetic jet. Then, power consumed in driving reciprocator is considered to derive a multi-objective optimum scheme. Flow control mechanism of synthetic jet device is preliminarily revealed, with theoretical and experimental data analysis of velocity profiles and Reynolds stress distributions. The optimization process and the analysis of optimum state provide guidance to the design of active flow control devices.