Evaluation of Feedback Control System for Wall Turbulence with Micro Sensors and Actuators

Abstract

A prototype system for feedback control of wall turbulence is developed. and its performance is evaluated in a physical experiment. Arrayed micro hot film sensors with a spanwise spacing of 1 mm are employed for the measurement of the streamwise shear stress fluctuations, while arrayed magnetic actuators of 2.4 mm in spanwise width are used to introduce control input through wall deformation. A digital signal processor having a time delay of 0.1 ms is employed to drive output voltage for the actuators. Feedback control experiments are made in a turbulent air channel flow. A noise tolerant genetic algorithm is employed to optimize control parameters. It is found that the wall shear stress is decreased by about 6% experimentally for the first time. The Reynolds shear stress close to the wall is decreased by the present control. By using conditional average of a DNS database, it is demonstrated that wall induces wall normal velocity away from the wall, when high speed region is located above the actuator.