The meandering bend features of large-scale structures and the related coherent structures

Abstract

The present study aimed to investigate the meandering bend features of large-scale structures, including large-scale motions (LSMs) and very-large-scale motions (VLSMs) and the relationship between these meandering features and small-scale hairpin vortex structures in a turbulent boundary layer (TBL). A multichannel hot-wire probe was used to measure the streamwise fluctuation velocity in the log-region. The LSMs and VLSMs were extracted based on their streamwise length, and the position of the hairpin vortex was determined using the Variable-Interval Time-Averaging (VITA) technique. The meandering bend features of LSMs and VLSMs were calculated from each extracted meandering segment of the structure. In addition, the meandering of the LSMs and VLSMs was highly related to the distribution of the VITA events, indicating that the LSMs and VLSMs were formed from the hairpin vortex packets. Further investigation revealed that the meandering bend direction of LSMs/VLSMs was independent of the asymmetry of the VITA events, suggesting that the asymmetry of the detected small-scale hairpin vortex has nearly no effect on the meandering bend of the LSMs/VLSMs.