Application of a k-ϵ turbulence model to the prediction of noise for simple and coaxial free jets

A numerical solution of a K-e turbulence model is used to provide local and statistical properties throughout simple and coaxial round jets. These are inserted into predictive formulas for jet noise based on Lighthill's theory: Ribner's formalism postulates locally isotropic turbulence superposed on mean flow; Goldstein and Rosenbaum's formalism generalizes this to accommodate the more realistic assumption of axisymmetry. Numerical jet noise predictions via the Ribner//k-ϵ model (designated Ra) and the Goldstein/K-ϵ model (designated Ga), and some variants, are compared with experiment. Only a single empirical factor is used. The Ga model, with its threefold longer axial scale, shows closer agreement with experiment than the Ra model. The predictive capacity of the Ga model is demonstrated by further calculations for coaxial jets. The results confirm the experimental observation of a minimum of acoustic radiation when the outer flow has 0.4 the velocity of the inner flow. An advantage of the K-ϵ method is that it yields information on the spatial and spectral distribution of the acoustic sources.