Progress in the use of non-linear two-equation models in the computation of convective heat-transfer in impinging and separated flows

The paper considers the application of the Craft et al. [6] non-linear eddy -viscosity model to separating and impinging flows. The original formulatio n was found to lead to numerical instabilities when applied to flow separat ing from a sharp corner. An alternative formulation for the variation of th e turbulent viscosity parameter c(mu) with strain rate is proposed which, t ogether with a proposed improvement in the implementation of the non-linear model, removes this weakness. It does, however, lead to worse predictions in an impinging jet, and a further modification in the expression for c(mu) is proposed, which both retains the stability enhancements and improves th e prediction of the stagnating flow. The Yap [24] algebraic length-scale co rrection term, included in the original model, is replaced with a different ial form, developed from that proposed by Iacovides and Raisee [10]. This r emoves the need to prescribe the wall-distance, and is shown to lead to sup erior heat-transfer predictions in both an abrupt pipe flow and the axisymm etric impinging jet. One predictive weakness still, however, remains. The p roposed model, in common with other near-wall models tested for the abrupt pipe expansion, returns a stronger dependence of Nusselt number on the Reyn olds number than that indicated by the experimental data.