Turbulent Wake Induced By a Steep Topography in Boundary-Layer Flows

Complex terrain, ranging from heterogeneous distribution of surface roughness and temperature to urban/suburban civil infrastructure, interacts with the turbulent boundary-layer flows and significantly affects the turbulent transport of momentum and scalars between the atmosphere and the land surface. Steep terrain often creates a complicated wake flow downstream, characterized by flow separation, reattachment, and development of a new boundary layer. The turbulent fluxes of momentum and scalars in the wake are challenging to predict even using the most advanced numerical models for land-atmospheric interaction. To address the effect of steep-slope topography on turbulent transport near the surface, a series of laboratory measurements of the wake flow and turbulent momentum fluxes were conducted using idealized steep topography models, e.g., 2D block and sinusoidal-shaped hills. We will present experimental results for the flow features and turbulent statistics in different regions of the wake, as well as the variation of surface momentum flux downwind of the topography models. The measurements are of great importance to inform parameterization of turbulence and surface fluxes in numerical models for flow over complex terrain.