Design, Performance Evaluation and Endwall Flow Structure Investigation of an S-Shaped Intermediate Turbine Duct

Annular S-shaped 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 engines with larger by-pass ratios requires the future intermediate turbine ducts to be shorter and have larger radial off-set. This paper deals with the design and performance evaluation of a state-of-the-art annular S-shaped intermediate turbine duct. The details of the design of the intermediate turbine duct are presented together with static pressure measurements and oil film flow visualization along the endwalls, and area traverses at the inlet and outlet planes using a 5-hole probe. The measurements were done for three operating points of the turbine. From the flow visualization no separation could be detected at design point conditions, but for off-design conditions regions of separation were detected on the guide vanes located within the inter-turbine duct. The pressure loss coefficient was shown to be comparable for the two cases with lowest swirl angle, but the design point showed a slightly lower pressure loss. For the case with the largest flow angle the pressure loss coefficient was clearly larger than for the other two cases, which can be associated with the separation found on the guide vanes.