Aerodynamic pre-design and performance evaluation of counter rotating hybridised compressor concepts: modelling approach

Abstract Prior research on regional turboprop aircraft found significant reduction of $$CO_2e$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>C</mml:mi> <mml:msub> <mml:mi>O</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi>e</mml:mi> </mml:mrow> </mml:math> block emissions through hybridisation by supplying part of the power for propulsion through electric drives. This paper explores integrating hybridisation concepts directly into the compressor and propulsion system. This is commonly known as a Cycle-Integrated Parallel Hybrid and is intended to improve operability of the compressor and the engine. This is achieved by driving certain compressor rotors electrically. Possible concepts are counter rotating rotors which are individually driven by electric motors. To evaluate this, a tailored design toolchain is implemented, featuring mean line analysis models used for aerodynamic compressor pre-design, off-design analysis, and an optimisation approach. Apart from an adapted compressor geometry, the presented methodology can be applied to derive control laws for compressor operation. Furthermore, the compressor map is extended. This is a consequence of the new design parameter, the speed ratio, having a direct impact on operating behaviour. This allows the investigation of implications arising from adjusting this value in operation. The introduction of electric machinery driving the counter rotating rotor poses additional constraints for compressor aerodynamic design by limiting circumferential speeds.