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Inflow Turbulence Effects on Large Eddy Simulations of the Flow around an Axisymmetric Hill



Rikhi Bose, Emil Simiu


Turbulent flow around an axisymmetric hill at Reynolds number Re H ∼ 1.3 × 10 5 with respect to the hill height is studied using resolved large-eddy simulations (LES). The purpose of the paper is to examine the effect of turbulence in the inflow boundary condition on the flow around the hill. To this end LES simulations were performed for the following inflow boundary conditions: (i) mean turbulent boundary-layer profile obtained experimentally, and (ii) unsteady turbulent velocity profiles from a precursor LES, with the mean profile of the precursor LES forced to agree with experimental results, all other flow parameters in the two simulations being identical. Comparisons with reliable experiments available in the literature showed that the flow, in particular the complex separation dynamics in the lee-side of the hill, is sensitive to the inflow boundary condition. It was found that the mean flow and turbulence statistics in the turbulent-inflow simulation are in good agreement with the experimental results both upstream and downstream of the hill. However, the steady-inlet simulation yields a thicker and longer separation region than was observed experimentally. Consequent recovery of the flow downstream is also delayed where an inner vortex rotating in the same direction accompanies an outer vortex in either side of the midspan plane; the inner vortex pair is not obtained in either the experiment or the turbulent-inflow simulation. Despite these significant discrepancies, the upstream-side flow and the separation location for both simulations are in reasonably good agreement with the experiment. This can be attributed to the fact that the pressure gradient set by the geometry dictates the separation initiation through the formation of an internal layer. Incoming turbulence in a simulation suppresses the separated shear layer by increasing the near-wall velocity gradient, thereby causing early reattachment as in the experiment.
Technical Note (NIST TN) - 2210
Report Number


Axisymmetric hill, Complex topography, large-eddy simulation (LES), Reynolds-Averaged Navier-Stokes Simulation (RANS), Turbulence.


Bose, R. and Simiu, E. (2022), Inflow Turbulence Effects on Large Eddy Simulations of the Flow around an Axisymmetric Hill, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed May 28, 2024)


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Created March 7, 2022, Updated November 29, 2022