Direct numerical simulation (DNS) of a turbulent flow over an axisymmetric hill has been carried out toudstudy the three-dimensional flow separation and reattachment that occur on the lee-side of theudgeometry. The flow Reynolds number is ReH = 6500, based on free-stream quantities and hill heightud(H). A synthetic inflow boundary condition, combined with a data feed-in method, has been used toudgenerate the turbulent boundary layer approaching to the hill. The simulation has been run using audtypical DNS resolution of Dxþ ¼ 12:5; Dzþ ¼ 6:5, and Dyþ1ud¼ 1:0 and about 10 points in the viscousudsublayer. It was found that a separation bubble exists at the foot of the wind-side of the hill and theudincoming turbulent boundary layer flow undergoes re-laminarization process around the crest of the hill.udThese lead to a significant flow separation at the lee-side of the hill, where a very large primary separationudbubble embedded with a smaller secondary separations have been captured. The present low-Reudsimulation reveals some flow features that are not observed by high-Re experiments, thus is useful forudfuture experimental studies.
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