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

Xiaonan Chen, Koji Iwano, Yasuhiko Sakai, Yasumasa Ito

This study investigated the effect of large-scale structures including large-scale motions (LSMs) and hairpin vortex in the log-region on the bursting phenomenon in the buffer layer using the simultaneous measurement of the streamwise velocity fluctuation in the log-region and buffer layer of the turbulent boundary layer (TBL) with a multi-channel hot-wire probe. The Reynolds number in the present study, calculated from the friction velocity uτ, was Reτ=δuτ/ν=1260, where δ is the boundary layer thickness and ν is the kinematic viscosity. The LSMs were classified as positive large-scale motions (pLSMs) and negative large-scale motions (nLSMs) based on their streamwise velocities. Their effect on the bursting that was detected by the Variable-Interval Time-Averaging (VITA) technique was visualized. As a result, it was evident that the bursting became active with the existence of the pLSMs, while it was suppressed with the nLSMs. In addition, hairpin vortex was observed by applying the VITA technique to the velocity fluctuation of the log-region. Further investigation revealed that the hairpin vortex can also be observed in the log-region with the condition that the bursting was detected in the buffer layer, suggesting that the existence of a hairpin vortex in the log-region slightly increased the bursting phenomenon near the wall.

International Journal of Heat and Fluid Flow

89

108811

108811