Design and Testing of the Contra-Rotating Turbine for the Scimitar Precooled Mach 5 Cruise Engine

R. Varvill; G. Paniagua; H. Kato; M. Thatcher (2009), JBIS, 62, 225-234

Refcode: 2009.62.225

Abstract:
Central to both engines is a turbo-compressor. With Scimitar in hypersonic flight the turbo-compressor takes in air via a precooler before compressing it for admission to the combustion chamber and subsequent expansion through the main nozzle to produce thrust. In subsonic flight it becomes the gas generator driving a high bypass ratio ducted fan through a hub turbine, the exhaust mixing with the duct flow and discharging through the bypass nozzle to produce thrust. In both modes the turbo-compressor is driven by a helium turbine which has contra rotating stages to improve its efficiency at low rotational speed and reduce the number of stages required. Due to the large speed of sound mismatch between the air compressor and the helium turbine it is possible to eliminate the turbine stators by contra rotating the spools. The compressor is divided into low pressure and high pressure spools although by normal gas turbine standards they are both low pressure ratio machines.