The effect of sweep on performance of open rotor under different advance ratio

Abstract

Contra rotating open rotor (CROR) is expected to be next generation propulsion engine due to its excellent fuel economy. Its lower fuel consumption comes from higher propulsion efficiency compared to conventional turbofan engines. It is expected to replace the high-speed subsonic military turbofan engine and has a great potential for commercial applications. Because of the high flight Mach number, the aerodynamic performance of CROR, especially the propulsion efficiency, at different work points was influenced by the stacking line. In this paper, the effect of sweep on aerodynamic performance of CROR was investigated. The aerodynamic performance is computed by Reynolds averaged Navier Stokes. The Numerical simulation method is validated by NASA's historical baseline F7A7 open rotor. The design point's aerodynamic performance of CRORs with different swept type were compared. Furthermore, the CRORs with different swept type were compared under different advance ratios. Through the above way, the mechanism and phenomenon that explain the reason for the influence of sweep line was obtained. To obtain the influence of aft sweep lines on the aerodynamic performance in a certain design space. The aft sweep lines were built by CST line. A sweep line was parameterized by six parameters. Sampling is done by design of experiment using the Latin hypercube sampling. 20 sample points were finally obtained. The result shows that the swept type greatly influence the performance of CROR under both design point and off-design point. At the design point, the propulsion efficiency of aft sweep is improved by 5.05% compared with the baseline, and the propulsion efficiency of forward sweep is improved by 1.28% compared with the baseline. The thrust of aft sweep is 13.1% higher than that of baseline, and the thrust of forward sweep is 7.51% lower than that of baseline. The performance of rear rotor is sharply under the influence of front rotor. Front rotor's performance has different tendency of change with different sweep lines under different advance ratios compared to rear rotor's. Swept type influence the tendency of changes in segments' thrust under different advance ratio. When advance increases, forward swept blade shows better thrust holding capacity. The swept type significantly changed the shock wave distribution in the channel and structure of tip vortex. The change of tip vortex causes the change of inlet flow angle. For aft swept CRORs, the CROR with larger axial relative distance usually have a higher propulsion efficiency. Meanwhile, the CROR with higher thrust coefficient obtains higher propulsion efficiency, which means that a good aft sweep line design can improve both thrust coefficient and propulsion efficiency.