Aerodynamic and Aeroacoustic Analysis of a Quadrotor Biplane Tailsitter

Unmanned aerial systems with vertical take-off and landing capability have seen rapid development with the advent of advanced air mobility. However, their high noise footprint remains a major obstacle to commercial deployment. This study investigates the aerodynamic mechanisms driving noise generation in such systems, focusing on a quadrotor biplane tailsitter analyzed in both hover and forward flight using a hybrid Reynolds-averaged Navier Stokes–large eddy simulation computational fluid dynamics (CFD) solver. Unsteady rotor–rotor and rotor–airframe interactions were characterized, and their acoustic impact quantified. Trimmed conditions were established via CFD and blade element momentum theory. The resulting surface pressure distribution was used to calculate the noise footprints of the aircraft, with tonal and interactional broadband noise estimated using the Ffowcs Williams–Hawkings acoustic analogy and rotor self-noise modeled using the Brooks, Pope, and Marcolini semiempirical model. To isolate the contributions of different interaction mechanisms, the rotor system was also analyzed in isolation. In hover, the presence of the airframe inhibits aerodynamic interactions between rotors, leading to a notable reduction in interactional broadband noise relative to the uninstalled rotor configuration. However, rotor–rotor interactions remain the dominant noise source, with the broadband component, after A-weighting, emerging as the most perceptible to human hearing. In forward flight, the freestream convects the wake downstream, weakening rotor–rotor interactional effects. Although rotor–wing interactions amplify airframe noise, rotor-generated noise remains the primary source in forward flight, with rotor self-noise becoming the most dominant component when A-weighting is applied.