The instantaneous structure of turbulent boundary layers over surfaces with spanwise heterogeneity

Wangsawijaya, Dea Daniella, de Silva, Charitha, Baidya, Rio, Chung, Daniel, Marusic, Ivan and Hutchins, Nicholas (2019) The instantaneous structure of turbulent boundary layers over surfaces with spanwise heterogeneity. In The 11th International Symposium on Turbulence and Shear Flow Phenomena: TSFP11. 6 pp .

Abstract

Turbulent flows over surfaces with extensive roughness variation in the spanwise direction induce a secondary flow in the form of streamwise aligned counter-rotating vortices. In this study, we conduct cross-plane stereoscopic particle image velocimetry (SPIV) measurements over surfaces constructed from spanwise-alternating smooth and rough strips to emulate spanwise heterogeneity in a rough-walled surface. The half-spanwise-wavelength of the alternating rough and smooth strips S varies from S/δ = 0.32–3.63,relative to the spanwise-averaged boundary layer thickness,δ. Two limiting cases are observed when S/δ 1 and 1, where the size of secondary flow is limited by δ and S, respectively. Consequently, the regions away from the secondary flow scale according to their local shear stress when S/δ 1 and become spanwise homogeneous when S/δ 1. We observe that when S/δ ≈ 1, the secondary flow is particularly strong and appears to fill the entire wall normal extent of the boundary layer. In this condition, we observe that the spanwise location of the secondary flow is highly time-dependent.

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Contributors

Author: Dea Daniella Wangsawijaya

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