Modelling three-dimensional jets in cross-flow with and without impingement using improved forms of second-moment closure

Abstract

A computational study is presented of two types of threedimensional jets, one being a twin-configuration involving a combination of impingement and weak cross-flow, and the other a free jet discharged into a strong normal stream. A primary objective of the study is to identify, in the context of a RANS modelling strategy, the predictive capabilities of second-moment closure relative to the eddy-viscosity approach. More specifically, two recent model forms are investigated and contrasted against the established and widely used closure of Gibson & ~ a u n d e r ~ ' ~ ] . One uses a different model for the influence of wall-induced pressure fluctuations on the turbulence-isotropisation process, which is expected to enhance the realism of modelling impingement-related features. The other is a more radical variant, containing a cubic isotropisation (pressure-strain) model which renders the closure realisable. The study provides evidence for the superiority of secondmoment closure in respect of several predicted flow characteristics. In particular, the new wall-reflection model is demonstrated to return a more realistic sensitivity of the stress field to impingement-induced normal strain, while the cubic model is shown to result in improvements to the representation of the wake region in the jet's leeward side following deflection by the strong cross-flow.