Predicting the skin-friction drag when air or water passes over a rough surface is relatively trivial using empirical data like the Moody chart. However, this assumes the rough surface is everywhere uniform with no variations in the flow direction. In reality, however, surface roughness can abruptly change. Examples include a localised patches of rivets on an otherwise smooth aircraft fuselage, or a transition of wind passing over a grassy field to over a forest. Predicting the drag of these heterogeneous surfaces is much more challenging as we cannot rely on the Moody chart.
These abrupt surface changes result in complex internal boundary layers (IBLs) forming within the pre-existing boundary layer. The flow within the internal boundary layer has 'felt' the effect of the new surface, while that above still only feels the original upstream surface. The IBL grows upwards into the boundary layer until an equilibrium is reached with the new surface conditions, far downstream of the surface change. Understanding this growth rate is critical for aerodynamics, weather forecasting and vehicle design.
This project will use both CFD and wind-tunnel experiments to study internal boundary layers. CFD will be used to study how the boundary layer is affected by different surface roughness changes (e.g. smooth wall to a patch of rivets). These simulations will be validated using experiments conducted in the Newmarket Boundary Layer Wind Tunnel.
Undergraduate
Understanding the boundary layer dynamics of a step change in surface roughness, and the growth rate of the internal boundary layer.
Students should be enrolled in MECHENG 712 (Aerohydrodynamics) in semester 1 and, if possible, MECHENG 718 (Computational Fluid Dynamics) in semester 2. Students should have passed MECHENG 325.
Aerodynamics Lab (Newmarket 901 Lvl5, Lab)