Numerical Investigation of the Effects of ITD Length on Low Pressure Nozzle

The advantage of high efficiency, low SFC（Specific Fuel Consumption）, ultra-high bypass ratio turbofan engine attracts more and more attention in modern commercial engine. The intermediate turbine duct（ITD）, which connects high pressure turbine（HPT） with low pressure turbine（LPT）, has a critical impact on the overall performance of turbine by guiding flow coming from HPT to LPT without too much loss. Therefore, it becomes more and more urgent to master the technique of designing aggressive, even super-aggressive ITD. Much more concerns have been concentrated on the duct. However, in order to further improve turbine, LPT nozzle is arranged into ITD to shorten low pressure axle. With such design concept, it is obvious that LPT nozzle flow field is easily influenced by upstream duct structure, but receives much less interests on the contrary. In this paper, numerical method is used to investigate the effects of length of ITD with upstream swirl blades on LPT nozzle. Nine models with the same swirl and nozzle blades, while the length of ITD is the only parameter to be changed, will be discussed. Finally, several conclusions and advices for designers are summarized. After changing axial length of ducts, inlet and outlet flow field of nozzle differs, correspondingly. On the other hand, the shearing stress on nozzle blade（suction and pressure） surface presents individual feature under various inlet flow. In addition to that, ＂Clocking-like effect＂ is described in this paper, which will contribute much to the pressure loss and should be paid enough attention.