Large Eddy Simulations of a Transonic Airfoil Cascade

Abstract

Abstract The tip region of transonic blades in turbomachinery involves complex flow physics including shock wave/boundary layer interactions (SBLI). SBLI can lead to flow separation, transition from laminar to turbulent flow, and unsteadiness, which can affect the overall performance of the blade. In this paper, we present wall-resolved large eddy simulations (LES) of a transonic rotating cascade that is modeled after the tip region of a transonic diffusing blade. The calculations were performed using GENESIS, a high-order unstructured large eddy simulation solver. The convergence of the LES solution is assessed by varying the polynomial order of the solution from low to high order. LES simulations for a total of five operating conditions are presented, which cover the range of operation from unique incidence low operating line to stall and the associated shock wave/boundary layer interaction physics. The overall aerodynamics of the transonic passage airfoil are described based on the LES solutions as well as providing a detailed analysis of the boundary layer behavior. The changes in shock structure, boundary layer interaction physics, and associated losses with operating condition are highlighted. A low-frequency SBLI unsteadiness is observed in the cases where the boundary layer into the shock is laminar, and a scaling of the frequency is proposed. The scaling is based on the time scale of turbulent structures convecting from the shock to the trailing edge and acoustic disturbances then traveling back upstream.