Validation of time-domain single-passage methods for the unsteady simulation of a contra-rotating open rotor

Abstract

The growing pressure to reduce fuel consumption and cut emissions has triggered renewed interest in contra-rotating open rotor technologies. Open rotors achieve a significant reduction in fuel consumption by allowing large increases in bypass ratio without the weight and drag penalties which arise from simply scaling up a turbofan bypass duct. However, in addition to potential noise issues, open rotors are susceptible to self-exited or forced vibration because of their unducted, light-weight, highly swept blades. The prediction of aeroelastic instabilities requires numerical methods which can accurately model the unsteady environment. Compared to full circumference simulations, single-passage multi-row methods with phase-lagged boundary conditions can offer significant savings in computational time but need to be validated for contra-rotating open rotor geometries operating at angle of attack. This paper presents the application of a time-domain single-passage method with multi-frequency phase-lagged boundary conditions for the unsteady simulation of a contra-rotating open rotor rig at take-off operating conditions. The single-passage solution is compared to the reference full circumference solution as well as experimental measurements. It is demonstrated that the single-passage multi-row approach provides a good approximation for open rotors operating at angles of attack at significantly reduced computational cost.