Numerical Predictions of Propeller-Wing Interaction Induced Noise in Cruise and Off-Design Conditions

Abstract

Using numerical methods, the aeroacoustic field induced by the interaction of a 4-bladed NASA SR-2 propeller and its wake with a wing is investigated under cruise conditions (Mach 0.6). The SmartRotor code, a coupled vortex particle and panel method, which is integrated with an acoustic solver based on the Farassat 1A formulation of the Ffowcs-Williams Hawkings equation, was used. Three main areas were investigated: the effect of propeller tip geometry on the propeller's wake and blade tip vortex; the effect of integrating a wing in the tractor configuration, including the effect of its position, and wing local leading edge sweep; and the effect of operating the combined wing/propeller system in off-design conditions such as low forward speed or in non-axial inflow.It was discovered that tip sweep is effective at reducing propeller tip vortex strength with no adverse effect on noise. Modifying tip dihedral was found to always increase tip vortex strength. Integrating a wing in the wake of the propeller increased the broadband noise generated, but had little effect on harmonic noise. The downstream position of the wing was found to not affect noise while vertical offset from the propeller axis increased noise. The most important discovery was that applying local leading edge sweep to the wing in the region of the propeller's wake decreases noise proportionally to the change in the angle between the helical tip vortex and the wing's leading edge. These noise reductions were on the order of up to 1.3 dB for overall sound pressure level, and 7.5 dB at the blade passage frequency.iii Acknowledgements First on the list of many people to thank must be my supervisor, Professor Daniel Feszty. His constant enthusiasm and support of my work was invaluable whenever simulations weren't working or results seemed less than reasonable. At the same time, his way of providing guidance while allowing me to choose the direction of my research allowed me to follow up on interesting results and truly take ownership of this work. For this and so much more, thank you.

A Computational Study on the Aeroacoustics of a Multi-Rotor Unmanned Aerial System

“…Akkermans et al [32] investigated the effect of pitch angle on the noise generated by the propeller-wing system and have shown that this effect is negligible, although it should be noted that the tested range was limited to −5 • < θ < 10 • . A similar study was conducted by Boots [33] for three angles of attack, including θ = 0 • , 3 • , and 6 • , where results suggested that the noise level at the first BPF remains unchanged with increase in θ, while it increases at higher harmonics. This discrepancy between the results of the two studies may be due to having different configurations or using different coordinate systems.…”

Computational Aeroacoustic Prediction of Propeller Noise Using Grid-Based and Grid-Free CFD Methods

“…GENUVP was initially developed for the modeling of wind turbines, but was extended to simulate rotorcraft [113], [114], wind turbines [115], and propellers. The acoustic component of  In 2016, David Boots extended the code to parallel processing as well as validated it for certain propeller and wake cases [55], [58].…”

“…The specific geometrical input into the SmartRotor code is listed in Appendix A. Boots [55], [58] also performed this validation case in SmartRotor using the same simulation time step and the same number of chordwise and spanwise elements. However, as the geometrical description of the blade is not given, it is possible that there are slight differences in blade geometries.…”

“…A simulation was performed of this test case in order to obtain results at Transducer 7, which Boots did not simulate, for further comparison to STAR CCM+ data. Boots performed a verification of this validation study in [58] for spanwise elements, chordwise elements, timestep, and simulation length and their impact on OASPL, thrust, torque, and first harmonic. The final parameters chosen by Boots match the ones chosen in this chapter.…”

“…Planform view of 622 mm diameter SR-2 Propeller Blade[58], with dimensions in mm. Transducer locations relative to the propeller hub, with a description of the plan view (left) and the plane containing the propeller looking downstream (right)[12].…”