Structure of flow separation and reattachment behind an axisymmetric hill

Abstract

Large-eddy simulation of a high Reynolds number, turbulent flow over an axisymmetric hill of height H = 2δ, where δ is the incoming turbulent boundary layer thickness, is simulated and compared with the experimental data [1]. The flow is highly three dimensional and is characterized by unsteady separations and re-attachments on the lee-side of the hill. Comparisons with measurements indicate reasonable agreement for the mean surface pressure distribution, the mean streamwise and spanwise flow profiles, and the velocity fluctuation profiles. The boundary layer separates on the lee-side of the hill and the separated shear flow is observed to merge and form a counter-rotating vortex pair (CRVP) downstream. Flow pattern over the hill surface is observed to have the same sense of rotation as the respective vortex in CRVP on either side. The separation and re-attachment process is shown to be strongly controlled by the three-dimensional pressure gradient caused by body shape and size.

Keywords:

• LES
• Separation
• Reattachment
• Vorticity
• CRVP

Acknowledgements

This work is supported by the Office of Naval Research (ONR). High performance computing (HPC) resources are provided by the Department of Defense (DOD) Major Shared Resources Centers (MSRC) at Naval Oceanographic Office (NAVOCEANO), Maui High Performance Computing Center (MHPCC), and U.S. Army Engineer Research and Development Center (ERDC).