Performance of Hoods for Aircraft Exhaust-Gas Turbines

摘要

The performance of a turbosupercharger turbine was measured with three types of exhaust hood. The effectiveness of the turbine-hood combination was determined by measuring the turbine power and the thrust of the jet discharged from the hood at pressure ratios across the turbine and hood of 1.35, 1.7, and 2.0 for a range of blade-to-jet speed ratios from 0.1 to 0.9. Compressed air was used as the driving fluid. The results of these tests indicate that an exhaust hood should have an inlet area equal to the bucket-annulus area of the turbine and should be equipped with the straightening vanes. A system of vanes, the total chord of which was equal to the turbine pitch-line circumference, achieved complete straightening of the flow. Losses due to swirl were reduced, however, to about one-half their maximum by straightening vanes with a total chord 0.175 times the turbine pitch-line circumference. The flat-nozzle hood, which was designed to guide the gas from the round bucket-annulus section into a flat duct, imposed no greater losses than the best conical hood. The turning of high-velocity flow in a flat duct led to very large losses. A conventional short-turning-radius hood was found to give larger losses than the vaned-conical and flat-nozzle hoods.