On the effects of surface morphology on the structure of wall-turbulence

Abstract

Experiments were conducted in the fully-rough regime on surfaces with large relative roughness (h/δ ≈ 0.1) generated by regularly distributed LEGO™ bricks of uniform height, arranged in different configurations. Measurements were made with high resolution PIV on six different frontal solidities, λF, at fixed plan solidity, λP. Results indicate that the spatial underlying structure of the turbulence across the different surface morphologies is universal in both its shape and orientation in relation to the flow velocity. Harpin packets inclination with respect of the wall is also found to be consistent not only across the different wall surfaces but also when compared to previous studies on smooth walls. Slices of two-point correlations for both streamwise and wall-normal velocity fluctuations and Reynolds shear stresses present a good collapse across the entire y/δ range for all wall morphologies.