Simulation of vortex shedding behind a bluff body flame stabilizer using a hybrid U-RANS/PDF method

The present study aims at the investigation of the effects of turbulence-chemistry interaction on combustion instabilities using a probability density function (PDF) method. The instantaneous quantities in the flow field were decomposed into the Favre-averaged variables and the stochastic fluctuations, which were calculated by unsteady Reynolds averaged Navier-Stokes (U-RANS) equations and the PDF model, respectively. A joint fluctuating velocityfrequency-composition PDF was used. The governing equations are solved by a consistent hybrid finite volume/Monte-Carlo algorithm on triangular unstructured meshes. A nonreacting flow behind a triangular-shaped bluff body flame stabilizer in a rectilinear combustor was simulated by the present method. The results demonstrate the capability of the present method to capture the large-scale coherent structures. The triple decomposition was performed, by dividing the coherent Favre-averaged velocity into time-averaged value and periodical coherent part, to analyze the coherent and incoherent contributions to Reynolds stresses. A simple modification to the coefficients in the turbulent frequency model will help to improve the simulation results. Unsteady flow fields were depicted by streamlines and vorticity contours. Moreover, the association between turbulence production and vorticity saddle points is illustrated.