Large-eddy simulation of flow over a cylinder with from to : a skin-friction perspective

We present wall-resolved large-eddy simulations (LES) of flow over a smooth-wall circular cylinder up to ReD=8.5× 10⁵ , where ReD is Reynolds number based on the cylinder diameter D and the free-stream speed U∞ . The stretched-vortex subgrid-scale (SGS) model is used in the entire simulation domain. For the sub-critical regime, six cases are implemented with 3.9× 10³ ReD 10⁵ . Results are compared with experimental data for both the wall-pressure-coefficient distribution on the cylinder surface, which dominates the drag coefficient, and the skin-friction coefficient, which clearly correlates with the separation behaviour. In the super-critical regime, LES for three values of ReD are carried out at different resolutions. The drag-crisis phenomenon is well captured. For lower resolution, numerical discretization fluctuations are sufficient to stimulate transition, while for higher resolution, an applied boundary-layer perturbation is found to be necessary to stimulate transition. Large-eddy simulation results at ReD=8.5× 10⁵ , with a mesh of 8192× 1024× 256 , agree well with the classic experimental measurements of Achenbach ( J. Fluid Mech. , vol. 34, 1968, pp. 625–639) especially for the skin-friction coefficient, where a spike is produced by the laminar–turbulent transition on the top of a prior separation bubble. We document the properties of the attached-flow boundary layer on the cylinder surface as these vary with ReD . Within the separated portion of the flow, mean-flow separation–reattachment bubbles are observed at some values of ReD , with separation characteristics that are consistent with experimental observations. Time sequences of instantaneous surface portraits of vector skin-friction trajectory fields indicate that the unsteady counterpart of a mean-flow separation–reattachment bubble corresponds to the formation of local flow-reattachment cells, visible as coherent bundles of diverging surface streamlines.