On the effect of discrete roughness on crossflow instability in very low turbulence environment

Wind tunnel experiments were conducted in a low-turbulence environment (Tu < 0:006%) on the stability of 3D boundary layers. The effect of two different distributions of discrete roughness elements (DREs) on crossfl ow vortices disturbances and their growth was eval uated. As previously reported, DREs are found to be an effective tool in modulating the behaviour of crossfl ow modes. However, the effect of 24μm DREs was found to be weaker than previously thought, possibly due to the low level of environmental disturbances here with. Preliminary results suggest that together with the height of the DREs and their spanwise spacing, their physical distribution across the surface also intimately affects the stability of 3D boundary layers. Finally, crossfl ow vortices are tracked along the chord of the model and their merging is captured. This phenomena is accompanied by a change in the critical wavelength of the dominant mode