Analytical investigation of propeller-wing interaction noise

This paper investigates the noise generated by propeller-wing configuration at take-off condition with the propeller mounted upstream. This study makes use of various axisymmetric noise models developed for contra-rotating propellers to estimate the noise generated by propeller-wing configuration and later integrate them to estimate total noise. First, using well-published theory, rotor-alone (loading, thickness, and self-noise) and interaction noise sources (viscous-wake, potential field, tip-vortex) including tonal and broadband components are estimated. Later, a systematic parametric study is carried out by changing the blade number and tip Mach, while maintaining the propeller thrust and blade solidity. The noise generated is represented by Overall Acoustic Sound Power Level (OSWLs), which is an integrated value over the emission angles and frequency range, in a matrix form for the range of blade number and tip Mach. This matrix shows the regions dominated by rotor-alone and interaction noise and found that the noise characteristics of a rotor in uninstalled conditions (rotor-alone) are significantly altered due to the presence of a wing (installed condition). Further, it is found that the balance between these regions shifts with the variation in separation distance between the propeller and the wing. These results are further discussed with the individual interaction noise source mechanism and their dominance at various blade numbers, tip Mach, and separation distances. In addition, the non-axisymmetric viscous-wake interaction noise is investigated for even and odd numbers of blades and found that viscous-wake interaction noise has considerable directivity in the azimuthal direction. The results presented in the study are preliminary findings of propeller-wing noise, however, it gives give a quantitative picture of the behaviour of various noise sources and their balance with respect to geometric and operating parameters. This study will help to understand the dominant noise sources involved in propeller-wing configuration and will provide a quick guide for designing a low-noise configuration.