Numerical study of separation bubbles with turbulent reattachment followed by a boundary layer relaxation

The flow characteristics of laminar separation bubbles in the vicinity of the turbulent reattachment and further downstream are highly complex. Useful contribution to knowledge in this area has in the past come from numerical and experimental work that has teen done on backward-facing steps. The general findings indicate that the recovery to an equilibrium boundary layer is extremely slow downstream of the turbulent reattachment. The objective of the present work is to get an insight into the flow characteristics of separation bubbles on smooth surfaces by obtaining sufficient data to be able to calculate balances of Reynolds stresses and turbulence kinetic energy along the entire length of the bubble, together with a significant portion of the relaxing boundary layer. A fully-resolved three-dimensional numerical simulation with the ability to accumulate the required statistical data has been made possible due to the large number of processing elements and the memory resources of the Gray T3D. Findings suggest that boundary layer relaxation is a significant part of a laminar separation bubble and should be included in model calculations.