Wave rotor to high pressure turbine transition duct flow analysis

Flow analysis performance predictions for three design configurations of the Allison/NASA Wave Rotor turbine transition duct are presented. Each of these ducts represent one of the three concepts that were chosen for assessment. The transition duct takes highly non-uniform flow from a 45 degree annular section at the wave rotor exit to a 180 degree half annulus just upstream of the first turbine rotor in a gas turbine engine. Two symmetric transition ducts were required to deliver the flow to the full turbine rotor blade row. The purpose of the numerical study was to determine which duct design provided the best performance. Criteria included aerodynamic efficiency and flow uniformity at the turbine rotor inlet. Two of the design concepts included vanes inside or at the end of the duct to turn the flow and guide it to the turbine rotor. The first design concept used the existing vane row from the baseline engine at the exit of the duct. The baseline engine was an Allison 250 turboshaft with 25 vanes in the first turbine nozzle row. The second design concept used fewer, but longer vanes embedded further upstream in the duct. The third design concept was a vaneless combined duct and volute. The flow calculations were 3-D, steady, fully viscous calculations which include predictions of loss in the duct and circumferential distortion of flow delivered to the turbine. Comparisons are made between the performance of the three design configurations using the best performing duct from each concept. These comparisons show that the first design concept produced the lowest loss, and delivered the most uniform flow to the turbine.