A Closed-loop System For Aerodynamic Drag Reduction Of 25 Degree Ahmed Car Model

The active control of aerodynamic drag reduction for model car includes openloop control and closed-loop control.Closed-loop control is more convenient and flexible than open-loop control,and it has strong adaptability.The paper studied drag reduction of 25 degree Ahmed car model based on single steady blowing and two steady blowing by closed-loop control.The steady blowing actuators are distributed at different places of Ahmed car model rear window.In open-loop control experiment,pressure signals of 21 pressure holes on the surface of car model have been measured by pressure scanner at Re=1.34×105,1.67×105 and 2.0×105 respectively.Considering that it is hard to measure drag on a moving car,an appropriate pressure signal,whose location of the maximum is consistent with the location of maximum drag reduction rate,is used as feedback signal.Modified PID controller and extremum seeking with EKF which are used to adjust the flow automatically have been designed to closed-loop control for single steady blowing and double steady blowing respectively.A maximum drag reduction is searched under the combination of best paremeters.After choose an appropriate combination of paremeters,the system can achieve 12.2% of drag reduction within the convergence time 19 s under single steady blowing,and can reach 17.4% of drag reduction within the convergence time of 156 s under double steady blowing.In addition,the system has strong robustness to deal with largescale disturbances under single steady blowing.