Aerodesign and validation of turning struts for an intermediate compressor duct

Compressor transition ducts, also referred to as S-shaped ducts, are used to connect the low- or intermediate-pressure compressor (LPC) with the high-pressure compressor (HPC) in 2- and 3-spool turbofan engine configurations respectively. This paper focuses on studies on a concept which aims to shorten the compressor module by introducing aerodynamically lifting/turning struts in the compressor transition duct. This concept is labeled fully turning, as the struts in the duct assume the complete aerodynamic function of the last row of stators of the LPC. Through CFD analysis and low-speed experimental evaluation, this concept is further developed with promising results. It is shown that there is potential to reduce the length of the compressor module by 25% of the duct length through elimination of the last stator row in the LPC, whilst providing comparable or improved aerodynamic performance compared to a conventional configuration. This paper presents a combined experimental and numerical study where a fully turning concept (without LPC OGV, having 45 deg turning in the duct) is compared back-to-back with a moderately turning concept (with an off-loaded LPC OGV and 20 deg turning in the duct). Numerical analysis of a conventional duct configuration (where the OGV remains, with symmetrical non-turning struts) is used as baseline.