Performance of Wall-Modeled LES with Boundary-Layer-Conforming Grids for External Aerodynamics

We investigate the error scaling and computational cost of wall-modeled large-eddy simulation (WMLES) for external aerodynamic applications. The NASA Juncture Flow is used as representative of an aircraft with trailing-edge smooth-body separation. Two gridding strategies are examined: 1) constant-size grid, in which the near-wall grid size has a constant value and 2) boundary-layer-conforming grid (BL-conforming grid), in which the grid size varies to accommodate the growth of the boundary-layer thickness. Our results are accompanied by a theoretical analysis of the cost and expected error scaling for the mean pressure coefficient Cp and mean velocity profiles. The prediction of Cp is within less than 5% error for all the grids studied, even when the boundary layers are marginally resolved. The high accuracy in the prediction of Cp is attributed to the outer-layer nature of the mean pressure in attached flows. The errors in the predicted mean velocity profiles exhibit a large variability depending on the location considered, namely, fuselage, wing-body juncture, or separated trailing edge. WMLES performs as expected in regions where the flow resembles a zero-pressure-gradient turbulent boundary layer such as the fuselage (< 5% error). However, there is a decline in accuracy of WMLES predictions of mean velocities in the vicinity of wing-body junctions and, more acutely, in separated zones. The impact of the propagation of errors from the underresolved wing leading edge is also investigated. It is shown that BL-conforming grids enable a higher accuracy in wing-body junctions and separated regions due to the more effective distribution of grid points, which in turn diminishes the streamwise propagation of errors.

Automated summary

The study reveals that the accuracy of wall-modeled large-eddy simulation in aircraft aerodynamics depends on grid strategies. Even when the boundary layers are marginally resolved, the prediction error of mean pressure coefficient remains small. However, the accuracy of WMLES predictions of mean velocity profiles decreases at wing-body junctions and separated regions.