Experimental investigation of closed-loop active control to modulate coherent structures by mu-level method

Abstract

Abstract The experimental research on zero-net-mass-flux jet closed-loop active control was conducted in the wind tunnel. The mu-level method successfully detected burst events of the coherent structures. The streamwise velocity signals in the turbulent boundary layer were measured by HWA. The drag reduction rate of 16.7% is obtained comparable to that of the open-loop control and saves 75% of the input energy at the asynchronous 100 V/160 Hz control case, which reflects the advantages of the closed-loop control. The experimental findings indicate that the intensity increases in the near-wall region. The perturbation of the PZT vibrators on the skewness factor is concentrated in the region y + < 60. The generation of high-speed fluids is depressed and the downward effect of high-speed fluids weakens. The alteration of energy distribution and the discernible impact of modulation between structures of varying scales are observed. The correlation coefficient exhibits a strong positive correlation, which indicates that the large-scale structures produce modulation effect on small-scale ones. The occurrence of burst events is effectively suppressed. The disturbance has the characteristics of stable periodicity, positive and negative symmetry, low intermittency, and high pulsation strength. The conditional phase waveform shows that the fluctuation amplitude increases, indicating amplitude modulation effects on coherent structures.