Numerical study of transonic shock buffet instability mechanism

An investigation on transonic shock buffet instability mechanism by applying a combination of numerical simulations and dynamic mode decomposition (DMD) is presented. The unsteady flow simulations over OAT15A and NASA(SC)-0714 supercritical airfoil were performed by using unsteady Reynolds average Navier-Stokes equations with SA turbulent model, results are validated based on experimental data and analyzed by DMD. DMD was employed to extract the dynamic modes which describe the underlying global flow structure from flow field, the eigenvalues give frequency and growth rate corresponding to dynamic modes. The analysis results show that the buffet onset and buffet frequency analysed by dynamic mode decomposition agrees well with the available experimental data. The unsteadiness onset of flow is closely related to the instability of shear layers located between the separation and freestream, this unsteadiness drives the separation bubble broken and detach from airfoil periodically, which leads to the shock traveling along the upper surface.