Experimental and Numerical Comparison of Two Turbine Vane Frame Designs

This paper presents an experimental study supported by numerical simulations of the performance of two turbine vane frames (TVFs) at various purge and TVF inlet swirl conditions representing both on- and off-design operation. The turbine vane frame (TVF) serves as a structural link connecting the last high-pressure turbine stage to the first low-pressure turbine stage, functioning as a vane row for the latter. The two configurations considered share a common fully purged high-pressure turbine stage, followed by distinct TVF and LPT rotor setups. Of the two TVFs considered, TVF1 features a single-splitter, while TVF2 incorporates a twin-splitter architecture. The experiments took place at Graz University of Technology's Transonic Test Turbine Facility (TTTF). The steady RANS simulations use 2D inlet boundary conditions derived from measurements and provide additional insights into critical flow phenomena. The dataset includes purge derivatives with three purge flow rates (PFR) of 0%, 50%, and 200%, the aero design point (ADP) with 100% PFR, and one swirl derivative with positive incidence for each case. Both configurations exhibit unique flow phenomena, leading to distinct ‘regions of sensitivity’ for each duct design. Due to the positive incidence and low aspect ratio strut design, TVF1 demonstrates a pronounced UPV that affects almost the entire span at the duct exit. Additionally, the UPV is found to be enhanced by the radial pressure gradient imposed by the duct’s second bend. In contrast, TVF2 experiences a region of low momentum flow at the hub, due to the combination of axial diffusion (as a result of area increase) and high flow turning. This low momentum flow region is manifested as a band of very low axial velocity, spread evenly around the circumference between the airfoil trailing edges and the LP-rotor. Purge variations exert differing impacts on the investigated geometries, with TVF2 showcasing greater robustness to purge derivatives.