Design and Construction of a Two Shaft Test Turbine for Investigation of Mid Turbine Frame Flows

Abstract

In order to reduce the specific fuel consumption and consequently to minimise the CO2 emission of aircraft turbine engines, development and integration of a contra-rotating open rotor architecture and the geared turbofan concept are promising alternatives to the classical turbofan engines. The large dimensions of future contra-rotating fans lead to lower rotational speed and furthermore a bigger size of the powering low pressure stages. Therefore the flow leaving the high pressure turbine (HPT) has to be guided to the low pressure turbine (LPT) inlet at larger diameter, if possible without interference or separation. To minimise weight and costs of the aircraft engine the flow diverting mid turbine frame (MTF) has to be designed preferable short. Except for flow redirection this intermediate duct has to transfer the forces from the turbine bearings of both shafts to the turbine casing and further to the engine mount. Therefore the flow channel has to be equipped with thick rigid struts. These struts may also be used to accelerate the flow and take the function of the inlet vanes. In that case this so called integrated concept helps to reduce engine weight and length. One goal of the EU project DREAM is to analyse the flow through such a MTF with turning struts and a downstream arranged counter rotating LPT. The investigation of these complex interrelationships needs a test facility with engine representative conditions. To perform these investigations the continuously operating transonic test turbine facility (TTTF) at Graz University of Technology has been adapted. This test setup consists of a redesigned HPT, a new developed single-stage LPT and a turning mid turbine frame (TMTF). The aerodynamic design of the first setup was performed by MTU Aero Engines. The shafts of both turbines are mechanically independent, so the test rig allows a realistic two shaft turbine operation. To examine the highly 3-dimensional flow through the TMTF and the downstream LPT detailed measurements will be performed with conventional measurement techniques (temperature and pressure rakes, static pressure taps), oil flow visualisation as well as with 5-hole-probes for steady and fast response aerodynamic probe (FRAP) for unsteady measurements. Optical and acoustical measurements are planned to be used in following projects.