CALCULATION OF HIGH-LIFT CASCADES IN LOW PRESSURE TURBINE CONDITIONS USING A THREE-EQUATION MODEL

A three-equation model has been applied to the prediction of separation-induced transition in high-lift low-Reynolds-number cascade flows. Classical turbulence models fail to predict accurately laminar separation and turbulent reattachment, and usually over-predict the separation length, the main reason for this being the slow rise of the turbulent kinetic energy in the early stage of the separation process. The proposed approach is based on solving an additional transport equation for the so-called laminar kinetic energy, which allows the increase of the non-turbulent fluctuations in the pre-transitional and transitional region to be taken into account. The model is derived from that of Lardeau and Leschziner, which was originally formulated to predict bypass transition for attached flows, subject to a wide range of free-stream turbulence intensity. A new production term is proposed, based on the mean shear and a laminar eddy-viscosity concept. After a validation of the model for a flat-plate boundary layer, subjected to an adverse pressure gradient, the T106 and T2 cascades, recently tested at the von Karman Institute, are selected as test cases to assess the ability of the model to predict the flow around high-lift cascades in conditions representative of those in low-pressure turbines. Good agreement with experimental data, in terms of blade-load distributions, separation onset, reattachment locations and losses, is found over a wide range of Reynolds-number values.