Acoustic measurements of a contra-rotating open rotor in an open jet wind-tunnel

Acoustic measurements of a scaled model of a contra-rotating open rotor engine were performed in an open wind tunnel facility. The motivation for the work presented here was to analyse the possibilities for quantitative acoustic measurements in an environment that was not designed for acoustic measurements and where reverberations, shear layer refraction and turbulence distort the sound field. Extensive acoustic measurements were performed using a linear microphone array with 104 microphones on the floor of the hall. Room acoustics effects were investigated with a reference sound source and the sound field of the rotors was measured for different configurations. The results show that reflections from the ceiling and side walls interfere with the direct sound field and influence the measured directivity due to strong local variations of the sound pressure level from one microphone position to the next. General trends and differences between the configurations can be shown from spatially averaged frequency spectra.