In 2025, Metacomp contributed to the DPW-8 Buffet Working Group session at the AIAA Aviation Forum. The objective of this effort was to examine pre- and post-buffet flight regimes using unsteady CFD simulations of the ONERA OAT15A transonic airfoil. The flow was simulated at Mach 0.73 and a Reynolds number of 3×106, over a range of angles of attack from 1.36° to 3.90°.
RANS, URANS and hybrid RANS/LES (HRLES) simulations were conducted using the one-equation SA model[1] with rotational-curvature correction[2] and quadratic constitutive relations [3] as the baseline closure across RANS, URANS and HRLES. For HRLES, SARC(QCR)-based DDES[4] simulations also employed Deck and Renard’s enhanced-protection shielding functions[5].
Traditionally, scale-resolving methods such as HRLES require a convective CFL ≈ 1 in the LES regions. This becomes computationally expensive in situations where additional low-frequency motions are superimposed on the fine-scale turbulence (such as those from the buffet-induced shock motion). A large time-step[6] DDES method was explored in this work as a lower-cost approach to unsteady shock-wave boundary layer interaction (SWBLI) modeling.
For the ONERA OAT15A test case with a CFL-dependent filter-width adjustment, large time-step DDES can be performed on a much coarser grid at approximately 250x lower computational cost. These large time-step simulations limit the extent of the high-frequency broadband noise that can be captured, but show better agreement with mean pressure coefficient values compared with traditional HRLES, because the approach reduces modeled-stress depletion in the shock-wave/boundary-layer interaction region.
Fig. 2: Traditional HRLES – Cp and Pressure power spectral density at AoA 3.5 degrees
(57.3 M cell mesh).
Fig. 3: Large time-step HRLES – Cp & Pressure power spectral density at AoA 3.5 degrees
(2.2 M cell mesh).