Turbulent Boundary Layer over various 2D Uniform Distributed Roughness Elements

Abstract

The effects of different geometries of 2D roughness elements on a zero pressure gradient (ZPG) turbulent boundary layer are investigated using single hot wire anemometry. The roughness consists of circular rods, prisms and sine-waves with two different heights, k = 1.6 and k = 2.4 mm, and two different streamwise spacing 8k and 16k (δ/k ranges from 27 to 40 where δ is the boundary layer thickness). The roughness causes a downward shift of the streamwise mean velocity profile known as the roughness function. The maximum shift is observed where the streamwise spacing = 8k. This work aims to characterise the roughness parameters and determine the dominant parameter affecting the turbulence statistics and drag coefficient. Outer layer similarity between smooth and rough wall data is observed when plotting the mean velocity profiles in the velocity defect form.