Effect of artificial large-scale structures on bursting phenomenon in turbulent boundary layer

Abstract

In this study, the effect of artificial very-large-scale motions (AVLSMs) generated by a dielectric-barrier-discharge plasma actuator (DBD-PA) array on the bursting phenomenon in the near-wall region (y+≤40 in the present study) was experimentally investigated. The DBD-PA array was embedded in the wall where the turbulent boundary layer (TBL) was fully developed. A hot-wire rake consisting of nine I-type probes was used to measure the streamwise fluctuation velocity throughout the TBL at two positions downstream from the DBD-PA array. At both measurement positions in the streamwise direction, it was observed that the negative artificial very-large-scale motions (nAVLSM) flanked on two sides by positive motions (pAVLSM) could extend to above 0.3δ height from the wall. The bursting phenomenon was detected using the variable-interval time-averaging technique. It was observed that the bursting phenomenon in pAVLSM was suppressed, whereas it was enhanced in nAVLSM. Further investigation showed that the bursting frequency normalized by the inner variables in nAVLSMs is the same as that of pAVLSMs only at the secondary measurement position, which is far from the DBD-PA array. These results suggest that the quasi-steady quasi-homogeneous theory only holds when the TBL is sufficiently developed.