Application of a RG hybrid RANS/LES model to swirling confined turbulent jets

Abstract

A renormalization group (RG) based hybrid RANS/LES model is validated for turbulent swirling confined jets. The results are compared with the experimental data of Dellenback et al. (1988, Measurements in turbulent swirling flow through an abrupt axisymmetric expansion. AIAA Journal, 26(6), 669–681) and results for the same flows of an unsteady second-moment closure RANS simulation. A general quality/cost comparison is made between the hybrid RANS/LES and the second-moment closure simulations. In the final section, the hybrid RANS/LES result is further compared to a detached-eddy simulation, dynamic -equation LES and dynamic Smagorinsky LES for one of the flows, and the overall good quality of the RG hybrid RANS/LES model demonstrated.

keywords:

• Hybrid RANS/LES
• Turbulence modeling
• Second-moment closure

Notes

^†In contrast, in the hybrid RANS/LES model most of the total stress is carried by the resolved fluctuations, and an upwind scheme could significantly influence the results.

^‡A simple model that can take into account time filtering, is obtained by taking as filter width the maximum of Δ, and the length scale constructed from Δ t and , i.e. modify the filter width as η = max (Δ, ^1/2Δ t ^3/2).

^§Also, strong adjustment in the model constants (as can be done in DES) is not allowed in a − system, since empirical relations exist between the different constants (and so one can only adjust from one physical set to another physical set of constants).