Investigating the Relationship Between Aeroacoustics and Boundary Layer Behavior of Low Reynolds Number Propellers

Flow behavior and acoustic output of UAV-scale propellers are characterized through oil based surface flow visualization and far field microphone measurements. Three propeller sets are tested: one with increasing pitch at constant chord, one with varying chord at fixed twist, and one with matched pitch-to-diameter ratios operated at equal Reynolds numbers. Surface flow patterns point out regions of laminar and turbulent attachment and separation across blade span. Broadband acoustic spectra are measured in an anechoic environment and processed to isolate motor and ambient interference. Increased pitch and chord resulted in earlier transition and greater turbulent separation, corresponding to elevated broadband noise. Matched Reynolds configurations produced consistent flow and noise characteristics across diameters, confirming Reynolds number dominant over RPM or scale. Tonal and broadband components are separated to support accurate acoustic assessment.