Experimental and Numerical Investigation of a Turbine Vane Frame with Splitters at Different Operating Points

One concept to improve the efficiency goals of aero-engines is a turbine vane frame (TVF). It is a transition duct in-between the high-pressure turbine (HPT) and the low-pressure turbine (LPT) and has three major purposes: guiding the flow to higher radii, incorporating the function of stator guide vanes of the first stage of the LPT, and passing structural components and oil pipes through the flow channel. The benefits of an aero-engine equipped with an aggressive TVF are the following; Due to the integration of the functionality of a stator vane row into the TVF not only the weight and the length of an aero-engine but also manufacturing costs can be reduced. A weight reduction leads directly to lower fuel consumption and therefore less CO2 emissions.From an aerodynamic point of view, a TVF is a complex component with multiple problematic areas where flow separations are possible to occur. The first problematic area is located at the shroud at the meridional bend of the TVF where the radius starts to increase. In this diffusing part of the TVF, the risk of separations increases further due to the deceleration of the flow. With the turning of the vanes and a decrease in static pressure at the vane’s suction sides another problematic area arises. However, because of the acceleration of the flow in the loaded part of the vanes, the TVF is less susceptible to flow separations in that section. The wide chord vanes necessary for the structural components and oil pipes, also provoke strong secondary flow structures. To reduce the negative effects of secondary flow the TVF investigated in the present paper features aft-loaded vanes and a pair of loaded splitter vanes between each of them.To experimentally investigate the aerodynamic performance of the mentioned component, the subsonic test turbine facility (STTF) at the Graz University of Technology was equipped with a TVF and downstream LPT-rotor. Aerodynamic measurements with five-hole-probes at five measurement planes and static pressure taps in the TVF were conducted for multiple operating points representing the start, cruise, and landing of an aircraft. In the present paper, the results of these measurements are discussed and compared to the results of numerical simulations. Finetuning of the simulations was performed to increase the accuracy of the numerical results and to achieve a better agreement with the measurements. The paper discusses the changed parameters in the numerical simulations and their effects on the flow field in the TVF