Performance assessment on DES/DDES method for transient flow in a centrifugal turbomachine model subjects to rotor-stator interaction

We present an assessment of the performances of the detached eddy simulation (DES) and delayed detached eddy simulation (DDES) approaches in resolving the transient flow in a system of a centrifugal impeller and a vaned diffuser which is strongly destabilized by the rotor-stator interaction (RSI). The numerical results obtained by the DES and DDES approaches are compared against that from an independent large-eddy simulation (LES) investigation and that of a vaneless diffuser model. The time-averaged and fluctuating velocity, the nonlinear primary momentum transport term, and the two-point correlation of fluctuating pressure in the impeller, diffuser, and vaneless region are analyzed. The numerical results reveal that the diffuser vanes substantially perturb the flow inside the impeller, especially at the impeller outlet. The DDES approach cannot resolve the multi-scale flow structures in the vaneless region. The DES approach produces a time-averaged velocity field that is more consistent with the LES approach, and the DDES approach performs better for the reversed flow. For the transient behaviors, the DES approach is more sensitive to weak fluctuation, and for the pressure fluctuation in the impeller where the RSI significantly perturbs. The DDES approach gives a consistent two-point correlation of fluctuating pressure with the LES approach, while the DES approach could not give an accurate prediction.