Доступ предоставлен для: Guest
TSFP DL Home Архив Исполнительный Комитет

DIRECT NUMERICAL SIMULATION FOR VERY LARGE-SCALE MOTIONS IN A TURBULENT BOUNDARY LAYER

Jae Hwa Lee
Dept. of Mechanical and Nuclear Engineering, UNIST, Ulsan 689-798, Korea; Sch. for Engr. of Matter, Transport & Energy Arizona State University Tempe, AZ 85287-6106, USA

Hyung Jin Sung
Department of Mechanical Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea

Аннотация

Direct numerical simulation (DNS) of a turbulent boundary layer (TBL) was performed to investigate the spatially coherent structures associated with very large-scale motions (VLSMs). The Reynolds number was varied in the range Retheta; = 570~2560. Inspection of the three-dimensional instantaneous fields showed that groups of hairpin vortices are coherently arranged in the streamwise direction and that these groups create significantly elongated low- and high-momentum regions with large amounts of Reynolds shear stress. Adjacent packet-type structures combine to form the VLSMs; this formation process is attributed to continuous stretching of the hairpins coupled with lifting-up and backward curling of the vortices. We employed the modified feature extraction algorithm developed by Ganapathisubramani et al. (2003) to identify the properties of the VLSMs of hairpin vortices. In the log layer, patches with the length greater than 3~4δ account for more than 40% of all the patches and these VLSMs contribute approximately 45% of the total Reynolds shear stress included in all the patches.