Abstract

Direct numerical simulation (DNS) of a turbulent flow over an axisymmetric hill has been carried out to
study the three-dimensional flow separation and reattachment that occur on the lee-side of the
geometry. The flow Reynolds number is ReH = 6500, based on free-stream quantities and hill height
(H). A synthetic inflow boundary condition, combined with a data feed-in method, has been used to
generate the turbulent boundary layer approaching to the hill. The simulation has been run using a
typical DNS resolution of Dxþ ¼ 12:5; Dzþ ¼ 6:5, and Dyþ1
¼ 1:0 and about 10 points in the viscous
sublayer. It was found that a separation bubble exists at the foot of the wind-side of the hill and the
incoming turbulent boundary layer flow undergoes re-laminarization process around the crest of the hill.
These lead to a significant flow separation at the lee-side of the hill, where a very large primary separation
bubble embedded with a smaller secondary separations have been captured. The present low-Re
simulation reveals some flow features that are not observed by high-Re experiments, thus is useful for
future experimental studies.