Turbulent separated inert and reactive flows over a triangular bluff body

Application Challenge AC2-12 © copyright ERCOFTAC 2019

CFD Simulations

Overview of CFD simulations

A series of numerical simulations was undertaken to study both inert and reactive flow over a the triangular bluff-body in order to replicate the experimental data and assess the different approaches and turbulence and combustion models [4,11]. The conventional Reynolds-averaged approach (RANS) with a family of the Launder-Sharma and realizable k-ε models has been used to calculate the non reactive flow. The details of the calculation approaches are described in [4,11]

A lean premixed propane/air bluff-body stabilized flame (Volvo test rig) was calculated using the Scale-Adaptive Simulation method (SAS) and Large-Eddy simulations (LES) as well as the conventional and unsteady Reynolds-averaged approach (RANS/URANS). RANS and SAS were closed by the standard k-ε and the k-ω Shear Stress Transport (SST) turbulence models, respectively. The conventional Smagorinsky and the k-equation sub-grid scale models were used for the LES closure. Effects of the sub-grid scalar flux modeling using the classical gradient hypothesis and Clark’s tensor diffusivity closures both for the inert and reactive LES flows are discussed. The Eddy Dissipation Concept (EDC) was used for the turbulence-chemistry interaction. Additionally, several RANS calculations were performed using the Turbulence Flame Speed Closure (TFC) model in Ansys Fluent to assess effects of the heat losses by modeling the conjugate heat transfer (hereafter CHT) between the bluff-body and the reactive flow. Also, the numerical results published by Ma et al. [12] and Jones et al. [13] are briefly discussed in the Best Practice Advise Section. Effects of the turbulent Schmidt number on the RAS results were discussed as well. Numerical results are compared with available experimental data. Reasonable consistency between experimental data and numerical results provided by RANS/URANS, SAS and LES was observed. In general, there is satisfactory agreement between present LES-EDC simulations, numerical results by other authors and measurements without requiring any major modification to the EDC closure constants, which gives a quite reasonable indication of the adequacy and accuracy of the method and its further application in turbulent premixed combustion simulations.

Effects of the turbulent Schmidt number on the RAS results were discussed as well. Numerical results are compared with available experimental data. Reasonable consistency between experimental data and numerical results provided by RANS/URANS, SAS and LES was observed. In general, there is satisfactory agreement between present LES-EDC simulations, numerical results by other authors and measurements without requiring any major modification to the EDC closure constants, which gives a quite reasonable indication of the adequacy and accuracy of the method and its further application in turbulent premixed combustion simulations.

Solution strategy

The calculations reported herein were performed using the finite-volume method implemented both in the commercial Ansys Fluent (AF hereafter) [15] and the open source OpenFOAM (OF hereafter) [16] (edcPisoFoam [12]) CFD codes. In the present study the RANS/URANS, SAS and LES approaches were used. It is worth noting that RANS results were obtained by AF, while URANS, SAS and LES results were obtained by OF.

Contributed by: D.A. Lysenko and M. Donskov — 3DMSimtek AS, Sandnes, Norway