Detached Eddy Simulations: Analysis of a limit on the dissipation term for reducing spectral energy transfer at cut-off

Paper i proceeding, 2021

In Detached Eddy Simulations (DES[1] and IDDES [2]), part of the flow is URANS mode (where most of the turbulence is modeled by a RANS model)
and the other part is in LES mode (where most of the turbulence is resolved). Between these regions the partition of turbulent kinetic between URANS mode and LES mode changes seamlessly (as in IDDES) or somewhat more abruptly (as in DES). Looking at the energy spectrum this change of partition can be seen as a change of the cut-off wavenumber, κc. In this paper we formulate a limitation – based on perturbation analysis – on how to reduce the spatial change in partition.
This is achieved simply by setting a limit on the dissipation term in the k equation in the LES region. This slows down the spatial transition from RANS to LES at RANS-LES interfaces in boundary layers, embedded LES and – depending of boundary condition on k – at inlets. It is found to give at least as good results as the standard IDDES model. For the hump flow, the IDDES-PC model gives better results than the IDDES model.