Unsteady RANS modelling of wake-induced transition in linear LP-turbine cascades

Unsteady wake-blade interaction is an inevitable consequence of the relative motion between rotors and stators in turbomachines. The flow in a low-pressure stage has a relatively low Reynolds number, of order 10 5 , based on chord length, and a substantial proportion of the boundary layer on the blade surface is thus laminar or transitional. While the flow in a turbine accelerates, globally, the middle-to-rear portion of the suction side of a highly-loaded turbine blade is subjected to an adverse pressure gradient. This can easily lead, especially in laminar and transitional conditions, to separation and thus to a serious deterioration in performance. In this environment, the introduction of unsteady wakes reduces the trend towards boundary-layer separation, in a time-mean sense, resulting in a potentially important reduction in losses.