Flow Instability, Modelling and Control Workshop

The impact of roughness elements on flow separation

Flow Instability, Modelling and Control Workshop, UK Fluids Network, Southampton, March 2017

An aeroplane wing admires the mountains of Greenland

Previous experimental and numerical work suggests that dynamic roughness elements (small bumps that oscillate up and down) have the potential to suppress the separation of a laminar boundary layer or increase the critical angle of attack at which it takes place.  Our goal is to try to understand the physical mechanism behind this and attempt to determine the roughness parameters that are most beneficial.  In this talk, we’ll look at flow over a hump in a condensed boundary layer, as in the scenario of Smith & Daniels (1981).  The roughness elements will be placed in the region where the skin friction passes regularly through zero (the local separation point), which gives rise to an integro-differential equation for the boundary layer displacement function, corresponding to the leading order skin friction term.

The effect of static and dynamic roughness on both the local and global separation point will be presented, as well as the impact of roughness height, width, position and oscillation frequency.