Design and Testing of the Contra-rotating Turbine for the SCIMITAR Precooled Engine

Paper number

IAC-08.C4.5.3

Author

Mr. Richard Varvill, Reaction Engines Ltd., United Kingdom

Year

2008

Abstract

The SABRE hybrid engine for the SKYLON spaceplane contains a high pressure ratio air turbocompressor driven by a helium turbine. Due to the large disparity in speed of sound between the turbine and compressor the turbine has contra-rotating stages to improve efficiency and reduce the number of stages. The turbine has no stators in the conventional sense, the alternate rows of blades being in counter rotation and transmitting their power to two contra-rotating output shafts, one to each compressor spool. This maximises the whirl velocity change between the blade rows increasing the power/weight ratio and improving the turbine efficiency.
	
Recently the opportunity to design and test a contra-rotating turbine has arisen in the LAPCAT program. LAPCAT aims to develop propulsion technology for antipodal hypersonic flight at Mach 4 to 8. Reaction Engines have conceived the SCIMITAR precooled engine concept, which is derived from the SABRE launcher engine. The SCIMITAR engine also features an air turbocompressor (of reduced pressure ratio) driven by a contra-rotating helium turbine.

This paper describes the preliminary aerodynamic design and final optimisation of the turbine by genetic algorithm methods. To verify the turbine performance a model turbine was constructed and tested at REL’s B9 test site. This model turbine is full linear scale but uses argon as the working fluid rather than helium to reduce cost and power. This substitution is acceptable since both gases are monatomic and have the same ratio of specific heats giving matched pressure ratios and scaled velocity triangles throughout the turbine. To further reduce cost and power the turbine is operated in blowdown mode with reduced inlet temperature and pressure enabling cheap reinforced plastic blading. The final effect of these changes is to reduce the power to 0.5 percent of the full turbine whilst retaining the same Mach numbers and scalable Reynolds numbers.

The contra-rotating turbine technology is equally applicable to hypersonic cruise aircraft and SSTO air breathing launchers such as the SABRE/SKYLON combination.

Abstract document

IAC-08.C4.5.3.pdf

Manuscript document

IAC-08.C4.5.3.pdf (🔒 authorized access only).

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