Large-eddy simulation of spatial transition in plane channel flow

Spatial large-eddy simulations (LES) of forced transition in plane incompressible channel flow are presented and compared to temporal simulations. Using the fringe method, spectral Fourier discretization is employed also in the streamwise, spatially evolving flow direction. Various subgrid-scale (SGS) models are examined including the dynamic Smagorinsky model, high-pass filtered (HPF) eddy-viscosity models and the relaxation-term model (ADM-RT). The applicability of the fringe method in conjunction with SGS models is demonstrated. Good results are obtained even at rather low LES resolution at which a coarse-grid no-model calculation is inaccurate. The most accurate prediction of transitional flow structures is obtained using the ADM-RT model. For this model, a detailed comparison between spatial and temporal simulation results is given. A clear representation of the transitional flow structures by LES up to the multi-spike stage could be established. Our results also show that the SGS models behave similarly in temporal and spatial simulations, thus allowing us to perform SGS model testing with the more straightforward and inexpensive temporal approach. The same SGS models work well without any change also in the fully developed turbulent flow.

Acknowledgments

We would like to thank Neil Sandham for encouraging us to pursue the spatial/temporal comparisons presented in section 4.4. This work was supported by the Swiss National Science Foundation (SNF) and the Swiss National Supercomputing Centre (CSCS). Calculations have been performed at CSCS.