Numerical Simulation of a Three-Dimensional Axisymmetric Hill: Performance Evaluation of Hybrid RANS–LES Models

Abstract

Computational fluid dynamics simulation of flow over a three-dimensional axisymmetric hill presents a unique set of challenges for turbulence modeling. The flow past the crest of the hill is characterized by boundary layer separation, complex vortical structures, and unsteady wake flow. As a result, traditional eddy-viscosity Reynolds-averaged Navier-Stokes (RANS) models have been found to perform poorly for this benchmark test case. Recent studies have focused on the use of large-eddy simulation (LES) and hybrid RANS-LES (HRL) methods to improve accuracy. In this study, several different HRL models are investigated and results from the different models are evaluated relative to each other, to an eddy-viscosity RANS model, and to previously documented high-fidelity large-eddy simulations and experimental data. Results obtained from the simulations in terms of mean flow statistics, surface pressure distribution, and turbulence characteristics are presented and discussed in detail. Results indicate that HRL models can significantly improve predictions over RANS models, but only when the development of turbulent velocity fluctuations in the separated shear layer and recirculation region are well resolved.

Inflow turbulence effects on large eddy simulations of the flow around an axisymmetric hill

“…Fig. 17 iii ______________________________________________________________________________________________________ Fig. 20 Contours of T KE in the cross-stream (y, z)-plane at x/H ≈ 3.63 from the experiment [38] and from current LES cases S and T .…”

“…This publication is available free of charge from: https://doi.org/10.6028/NIST.TN.2210 shed from the separation node, an extended red (blue) patch depicting the recirculating flow close to the wall as well as vortices ejected from the focal node farther away from the wall as in Fig. 18 (17), followed by an outer blue (extended red) patch showing the upstream realigned boundary-layer vorticity. The vorticity shown as the red (blue) patch for case T (S) between the two blue (red) patches is especially interesting.…”

“…Their zonal scheme yielded satisfactory mean flow statistics in the separation region and downstream wake structures with ≈ 3.5 million nodes, which was as effective as a conventional LES with 9.6 million nodes. In a more recent study in [17], the dynamic hybrid RANS-LES model developed in [20] provided reasonably accurate predictions, except for pressure distribution, the thickness of the recirculation layer, and turbulent stresses in a cross-stream plane downstream of the hill in the flow recovery region, which implied an erroneous wake structure.…”

“…Since the publication of the experimental results, several numerical efforts have been reported in, e.g., [8][9][10][11][12][13][14][15][16][17]. Reynolds-averaged Navier-Stokes (RANS) turbulence closure models have been used for the prediction of mean flows [8,10,11,18,19].…”

“…LES and hybrid LES-RANS simulations have performed better than the RANS models. Medium to high fidelity simulations have ranged from Detached-Eddy Simulations (DES) 1 ______________________________________________________________________________________________________ in [11], hybrid LES-RANS calculations [10,13,17], coarse LES reported in [9,11,12,15], and LES performed on comparatively fine meshes [14,16,19]. Researchers in [11] simulated this flow with RANS, DES and LES closures, with the same grid used for the DES and LES calculations.…”