Aeroacoustic and Aerodynamic Importance of Unequal Rotor Rotation Speeds of a CROR

摘要

In this contribution, we answer the question of aeroacoustic and aerodynamic importance of the non-periodic nature of a Contra Rotating Open Rotor (CROR) for those specific cases in which the front and the aft rotor rotate with slightly different rotational speeds. A concept to handle the non-periodicity is concisely presented based on a simultaneous least-square minimalisation approach. The results show a minor influence of the non-periodicity on the aerodynamics of the CROR. As opposed to this, a significant influence is observed for the aeroacoustics. Based on an actual non-periodic CROR, differences between corrected and uncorrected signals exceeding 10dB in amplitude are observed in the propeller plane for frequencies below the 4th harmonic of the front rotor blade passing frequency (BPF). For upstream microphone positions, even the 1st rear BPF is highly affected by the correction procedure. Experimental validation confirms the non-periodic correction method which has been applied to the numerics. Furthermore, it reveals that ignoring the non-periodicity leads to a completely opposite conclusion regarding installation effects for the considered configurations.