Influence of the stability of boundary vortex on drag reduction induced by transverse V-grooves Zhiping Li, Long He, Tianyu Pan, Yao Yin, Shaobin Li, Wei Yuan and Bo Meng Eur. Phys. J. E, 48 4-5 (2025) 24 Published online: 09 May 2025 DOI: 10.1140/epje/s10189-025-00490-7