Quasi-Unsteady Transition Modelling of Periodic Wakes

Abstract

An approach is presented which models the unsteady effects of wakes in steady simulations. In particular, the laminar and transitional boundary layers of downstream blades are significantly altered by periodically impinging wakes, which are inherently present in turbomachinery flows. In the present approach, the source terms of a k-omega turbulence model are multiplied by a transition factor, which is a function of the wake Strouhal number. In this way the time-mean values of the boundary layer are reproduced in steady simulations. Besides an academic test case, which has been used for calibration of the model, the paper presents a turbine cascade and a 3-stage low pressure turbine. For these test cases the quasi-unsteady approach yields very good agreement with the measurements at significantly lower computational costs as compared to unsteady simulations. Hence, the method supports a fast and reliable industrial design of turbine airfoils.