An investigation into the failure of a non-linear eddy-viscosity model in capturing the laminarisation phenomenon

'Laminarisation' is an important phenomenon in various engineering and aerodynamic applications. In a recent work published by the lead author and his colleagues at the University of Manchester, a range of refined Reynolds-Averaged-Navier-Stokes (RANS) turbulence models were applied to an ascending pipe flow with mixed convection where significant flow relaminarisation was observed. It was shown that two of the most commonly used turbulence models namely k-ω-SST and non-linear k-ε turbulence models (both of which are based on the standard eddy-viscosity model) perform very poorly in capturing the flow relaminarisation. In the present work the reasons for the failure of the non-linear k-ε closure is investigated in depth with the aim of enhancing the performance of this model in various CFD applications.