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DIRECT NUMERICAL SIMULATION OF TURBULENT BOUNDARY LAYER OVER SPARSELY SPACED ROD ROUGHENED WALL

Muhammad Nadeem
Department of Mechanical Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea

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

Resumo

Direct Direct numerical simulations (DNSs) of spatially developing turbulent boundary layers (TBLs) over 2D rod-roughened walls were performed to investigate the structure of TBL over the sparsely distributed roughness element. 2D rod elements were employed periodically arranged in the streamwise direction with pitches of px/k = 8, 16, 32, 64 and 128, where px the streamwise spacing of the roughness and k is the roughness height. The frontal solidity (λf) of the present study ranges from 0.125 to 0.0078 that corresponds to the sparse distribution regime (λf < 0.15). The Reynolds number based on the momentum thickness was varied in the range Reθ = 300~1400 and the roughness height was k = 1.56θin, where θin is the momentum thickness at the inlet. The characteristics of the TBLs such as friction velocity, mean velocity and Reynolds stresses over the 2D rod-roughened walls were compared with the result from TBL over a smooth wall at the similar Reynolds number. The amplitude modulation analysis was performed to study the inner/outer layer interaction of TBL. It was shown that the interaction between the inner and outer layers is maximum for the case of px/k = 8, the rough wall flows support the Townsend's wall similarity hypothesis.