EXPERIMENTAL INVESTIGATION OF THE TIME-AVERAGED FLOW IN AN INTERMEDIATE TURBINE DUCT

Intermediate turbine ducts are used in modern multi-spool jet engines to connect the high pressure turbine with the low-pressure turbine. The trend towards turbofan engines with larger by-pass ratios requires the radial off set between the high-pressure and low-pressure turbines to increase with a corresponding increase in radial off-set for the intermediate turbine ducts. Other improvements of the ducts is to make them shorter and more diffusing but this strive towards more aggressive design increases the risk for separation. This paper deals with an experimental investigation of the time-averaged mean flow field and turbulence development in an aggressive intermediate turbine duct (downstream a rotating turbine stage) using a 5-hole probe and 2-component hot-wire anemometry. In addition the duct endwall static pressure distribution is discussed. The investigation revealed the complex flow structure development within the duct, where co-rotating vortices emanating from the break-up of the tip gap shear-layer dominates the flow pattern.