Acoustic Shielding and Scattering Effects of a Propeller Mounted Above a Flat Plate

Experiments were carried out within an aeroacoustic wind tunnel facility to investigate acoustic scattering and shielding effects of a propeller being placed above a semi-infinite flat plate. The position of the flat plate trailing edge was adjusted relative to the propeller which was tested in static conditions with a constant rotational rate of 5000 RPM. Far-field noise was collected by a pair of microphone arcs in the reflection and shadow zone regions respectively. Effects of installation on the overall sound pressure level and first blade passing frequency tone was studied. Moreover the magnitude-squared coherence and cross spectrum phase data between selected microphone pairs were analysed. Significant amplification and attenuation can be observed with changing relative locations due to complex acoustic interactions between the propeller and flat plate surface and trailing edge. There are locations with significant potential for noise attenuation and directivity manipulation in terms of tonal and broadband noise content of the propeller. Appreciable changes in the first blade passing frequency phase was seen when installed cases were compared to the baseline isolated propeller case. Reductions of up to 16.3 dB in the first blade passing frequency tone due to the presence of notable shielding were observed.