Prediction of Transonic Buffet by Delayed Detached-Eddy Simulation

A delayed detached-eddy simulation of the transonic buffet over a supercritical airfoil is performed. The turbulence modeling approach is based on a one-equation closure, and the results are compared to an unsteady Reynolds-averaged Navier-Stokes simulation using the same baseline model as well as experimental data. The delayed detached-eddy simulation successfully predicts the self-sustained unsteady shock-wave/boundary-layer interaction associated with buffet. When separation occurs, the flow exhibits alternate vortex shedding and a spanwise undulation. The method also captures secondary fluctuations in the boundary layer that are not predicted by unsteady Reynolds-averaged Navier-Stokes simulation. A map of flow separation emphasizes the differences between the delayed detached-eddy simulation and unsteady Reynolds-averaged Navier-Stokes flow topologies. Statistical pressure distributions and velocity profiles help assess the performance of each model. They indicate that the delayed detached-eddy simulation tends to overestimate the flow unsteadiness near the trailing edge. Instantaneous distributions of Reynolds-averaged Navier-Stokes and large-eddy simulation regions during buffet show that the delayed detached-eddy simulation enforces Reynolds-averaged Navier-Stokes mode near the airfoil even when the boundary layer gets very thick.