A coupling of computational methods for CROR installation effects

This paper deals with the computation of CROR installation effects in terms of tone noise within three separated steps. The first step aims at computing the aeroacoustic sources of a CROR by a CFD approach, namely a URANS method applied to counter-rotative propellers. The second step computes the acoustic field radiated by the isolated CROR. It is based on the Ffowcs-Williams and Hawkings (FW-H) surface integral method and uses the blade pressure fluctuations computed by CFD as input data. The last step computes the acoustic field scattered by the aircraft geometry within the Boundary Element Method using the incident acoustic field previously computed. This approach in three steps is applied on a 1/7 scale model of a regional aircraft design equipped with two CRORs and tested in windtunnel. The paper first focuses on the aeroacoustic study of the CROR including the effects of pylon and incidence. The numerical prediction of the CROR noise in take-off conditions is then compared to the experimental measurements of the isolated engine. The isolated CROR noise computation is globally underestimated compared to the measurements because it doesn’t take into account the acoustic reflections occuring in the windtunnel but a qualitative agreement is found between the computation and the measurements. Finally, the computation of CROR installation effects is presented in one of the aircraft configuration tested in windtunnel, showing a global increase of the tones when the CROR is installed in comparison with the isolated configuration.