Hybrid LES/RANS with wall treatment in tangential and impinging flow configurations

Scale-resolving simulation of high Reynolds number flows is a considerable numerical challenge. One approach to alleviate the matter is to relax near-wall resolution requirements of large eddy simulation (LES) with wall models or hybrid LES/Reynolds-averaged (RANS) methods. In-cylinder engine flows present a particular complexity as the process is inherently governed by wall tangential, wall normal and free shear flows with substantial temporal variation in Reynolds number and boundary layer gradients. In such conditions, robustness regarding wall-normal spacing would also be beneficial. Motivated by these factors, this study investigates the functionality of seamless and zonal hybrid LES/RANS methods in incompressible channel (Re_τ=590) and impinging jet (Re_D=23,000) flows using relatively coarse grids. Standard (Smagorinsky) and more recent (σ) subgrid-scale (SGS) models are utilized. As a novel contribution, we incorporate a recently developed RANS-based wall model in the zonal hybrid LES/RANS context with considerably coarser near-wall grids in the wall-normal direction. Results show (i) isotropy differences between the SGS models in both LES and hybrid LES/RANS cases and that (ii) the hybrid models mostly improve on corresponding LES results in terms of low-order statistics and wall friction. In addition, (iii) different hybrid implementations enhance different aspects of the solution, especially in the impinging jet flow. Results with the zonal method indicate only marginal interference with the core LES. Finally, (iv) combining zonal hybrid LES/RANS with the presented wall treatment provides favourable indications particularly in tangentially-dominated flow regions, while the complex jet stagnation region benefits from a moderately refined grid. This approach appears promising for decreased near-wall grid sensitivity in scale-resolving simulations.