Direct numerical simulation of a turbulent flow over an axisymmetric hill

• We have further developed a fully 3-D high-order DNS code for a low-Re turbulent flow simulation.
• We have advanced a previous LES study of same flow problem, but applying DNS approach.
• We have carried out detailed study of 3d separated turbulent flow over an axisymmetric hill.
• Obtained DNS (statistics) database would be useful for turbulence model development and future low-Re experiment.

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 ReHReH = 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 Δx+=12.5,Δz+=6.5, and Δy1+=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.