Assessment of Turbulence Models for Predicting Coaxial Jets Relevant to Turbofan Engines

Authors: Mihaescu, M, Semlitsch, B., Fuchs, L.F., Gutmark, E.
Document Type: Article
Pubstate: Published
Journal: In the Proc. of The 15th International Conference on Fluid Flow Technologies (CMFF'12), J. Vad (Ed.)
Volume: 2   716-723
Year: 2012


A numerical study is carried out for analyzing the compressible, non-isothermal flow associated with a separate-flow exhaust nozzle system with conic plug. Within the steady-state Reynolds-averaged Navier-Stokes (RANS) framework three two-equation turbulence models are considered. These are the standard k-?, the standard k-?, and the Shear-Stress Transport (SST) k-? models. Additionally, the unsteady Large Eddy Simulation (LES) approach is employed. The results are compared with experimental Particle Imaging Velocimetry (PIV) flow data, in terms of time-averaged axial velocity and turbulence kinetic energy levels. The k-? turbulence model performed worst, overpredicting by large margins the length of the potential core region of the jet. The same model computed significantly lower turbulence kinetic energy levels, corresponding to a slower mixing rate, in the shear-layer between the secondary flow (i.e. the fan-stream) and the ambient air. A fair agreement was found between the PIV data and the predictions obtained with the LES approach, the standard k-?, and the SST k-? turbulence model, respectively. The largest differences were found at the location of eight equivalent diameters downstream distance from the tip of the center-body, probably due to a larger air entrainment in the experiment.