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

Abstract

This is the published version of the paper.This version of the publication may differ from the final published version. Wind tunnel experiments were conducted in a low-turbulence environment (T u < 0.006%) on the stability of 3D boundary layers. The effect of two different distributions of discrete roughness elements (DREs) on crossflow vortices disturbances and their growth was evaluated. As previously reported, DREs are found to be an effective tool in modulating the behaviour of crossflow modes. However, the effect of 24µm DREs was found to be weaker than previously thought, possibly due to the low level of environmental disturbances herewith. 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, crossflow 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. Permanent repository link

Acoustic excitation of Tollmien–Schlichting waves due to localised surface roughness

“…of the conditioned signal in figure 3( a ) is plotted in figure 3( b ). Despite some electronic noise and mains hum (at ), model vibrations and sound (at as discussed in Placidi, van Bokhorst & Atkin (2017)), the spectrum shows a clear dominant peak at the forcing frequency.…”