Numerical simulation of a precessing vortex breakdown

The objective of this work is to present the results of time-dependent numerical predictions of a turbulent symmetry breaking vortex breakdown in a realistic gas turbine combustor. The unsteady Reynolds-averaged Navier Stokes (URANS) equations are solved by using the k-is an element of two-equation model as well as by a full second-order closure using the Reynolds stress model of Speziale, Sarkar and Gatski (SSG). The results for a Reynolds number of 5.2 x 10(4), a swirl number of 0.52 and an expansion ratio of 5 show that the now is emerging from the swirler as a spiral gyrating around a zone of strong recirculation which is also asymmetric and precessing. These flow structures which are typical for the spiral type (S-type) vortex breakdown have been confirmed by PIV and local LDA measurements in a corresponding experimental setup. Provided that high resolution meshes are employed the calculations with both turbulence models are capable to reproduce the spatial and temporal dynamics of the flow. (c) 2005 Elsevier Inc. All rights reserved.