Influence of Inlet Flow Profile, Fillet Radius and Trailing Edge Thickness on Secondary Flows in Turbine Vane Cascades

Abstract A detailed understanding of the flow structures is essential for designing turbine blades with high efficiency. Secondary flow losses, which are influenced by geometrical and aerodynamic parameters, represent a significant portion of the total loss in high pressure turbines, especially in modern low aspect ratio bladings. This study investigates the effects of inlet flow profiles, fillet radius and trailing edge thickness (TET) on secondary flow losses in cascades representative for second stage turbine vanes. The experimental investigation was conducted using a full annulus turbine cascade at TU Dresden, operating at engine-relevant Mach numbers and near-ambient temperatures. Two vane profiles with different blade loadings, referred to as front-loaded and aft-loaded, were designed and tested to evaluate the impact of the varying parameters on the secondary flow losses for each blade loading. Both designs were evaluated in their baseline geometry and with increased fillet radii and TET within an annular cascade divided into four sectors. The inlet flow profile was varied with exchangeable inlet grids. Five-hole probe measurements were conducted upstream and downstream of the vanes. Based on the experimental results, the effect of the geometric features and blade loading distribution on secondary flow losses will be discussed. The vane designs with increased TET and fillet radii generally experience higher losses, while the gradient and characteristic loss pattern differs for the two blade loading distributions. To complement these findings, computational fluid dynamics (CFD) simulations were performed, providing additional insights into the behavior of the secondary flow loss mechanisms. Based on the experimental and numerical results the differences due to the varying parameters will be discussed.