Closed-loop Control Of A Turbulence Boundary Layer Based On Coherent Structures Recognition

Turbulence is involved in many industrial and engineering applications.Turbulent flow in vehicles and pipelines will generate significant shear stress on the surface of moving objects,which is one of the major sources of resistance.Therefore,it is of significance to reduce the shear stress generated by the turbulent boundary layer.Previous scholars did a lot of research on open-loop control of turbulent boundary layer and made a lot of achievements,but almost no one involved in closed-loop control.Based on the above,a closed-loop turbulent boundary layer control based on coherent structures recognition is proposed.In this paper,the closed-loop control method is explored experimentally.Experimental equipment is built in the wind tunnel.The actuator is two parallel spanwise-aligned PZT actuators,and the sensor is two wall hotwire,the control system is d SPACE controller,and the control algorithm are three kinds of PD control.The experimental scheme is that the voltage signal returned by the hot wire is firstly filtered by the CTA and then transmitted to the d SPACE controller.The signal is processed by the PD operation control and transfer function,the signal is output and amplified by a voltage amplifier,the actuators generates wall-to-wall vibration and thus reduces the wall shear stress.The purpose of the whole experiment is to optimize the control parameters to get the maximum drag reduction.The feed-forward PD control algorithm achieves a 33% drag reduction after the controller tuned.The feed-forward PD control and combined feed-forward PD and feed-back PD control does not achieve desired control performance,,it is due to the delay character of feed-back signal.At the same time,because feed-forward PD control algorithm generates vibration signal based on fluid information,it has the advantage of less energy input.The energy input is decreased by 25% and the control efficiency is improved by 46%.And it has better robustness than the open-loop control.The system can still have good control performance when the external conditions change.In addition,in order to investigate the mechanism behind the drag reduction better and confirm the reliability of drag reduction measurement,we also measure the controlled fluid disturbance range,compare the turbulent boundary layer velocity distribution,energy spectrum and the ave rage energy dissipation rate under controlled and uncontrolled condition respectively to verify the authenticity and accuracy of the results.