On Viscosity and Density Affecting Aeroelasticity of ONERA M6 Wing from Subsonic to Transonic Regimes

Preprint, 2023

The effects of fluid viscosity and density on the aeroelasticity of the ONERA M6 wing over a wide range of free-stream Mach numbers, spanning $0.6$--$1.1$, based on viscous and inviscid flow assumptions are studied. Both static and dynamic responses of the wing are examined. We employ a hybrid Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) method for the viscous flow, namely Delayed Detached-Eddy Simulation (DDES) with the Spalart-Allmaras (SA) turbulence model. The inviscid flow solver uses the Euler equations. A few selected cases are also analysed using Unsteady RANS (URANS). The flow solvers are strongly coupled to a structural analysis software, which uses a modal formulation. The structural responses are analysed using a constant free-stream density for all Mach numbers. In addition, higher densities are used for all Mach numbers in order to find the critical dynamic pressure where flutter is obtained. A substantial difference in the aeroelastic responses is found for Mach numbers ranging $0.875$--$0.95$, when comparing viscous and inviscid flow simulations. Furthermore, it is shown that viscosity is of minor importance at subsonic and supersonic speeds. At Mach number $0.8395$ it is shown that DDES provides close to identical structural responses as URANS. The largest difference of the predicted flutter boundaries is found in the transonic region. The flutter boundary for viscous flow stands out at Mach $0.925$ where it is $53 \%$ higher than the flutter boundary predicted by inviscid flow. Simulations with URANS showed that it would predict a lower flutter boundary at Mach $0.925$, compared to DDES.