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A NUMERICAL AND EXPERIMENTAL STUDY OF TURBULENT BOUNDARY LAYER WITH ROD-ROUGHENED WALL

Seung-Hyun Lee
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yusong-gu, Daejeon, 305-701; Korea Institute of Machinery & Materials 104 Sinseongno, Yuseong-gu, Daejeon 305-701, Korea

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

Abstract

The effects of surface roughness on a turbulent boundary layer (TBL) were investigated using direct numerical simulations (DNS) and particle image velocimetry (PIV). The roughness elements used were periodically arranged two-dimensional spanwise rods, and the roughness height was k/δ=0.05 for DNS and k/δ=0.0165, 0.032 for PIV. In PIV measurements, the friction velocity uτ for smooth and rough walls was estimated by fitting of mean velocity profile. Introduction of the roughness elements increased the wake strength and the turbulent stress not only in the roughness sublayer but also in the outer layer. This indicates the existence of interaction between inner and outer layers. Iso-contours of mean velocities and Reynolds stresses in the roughness sublayer obtained by PIV measurements show a good agreement with DNS results.