Tonal acoustic predictions of a fixed pitch rotor in edgewise flight are developed based on rotor inflow measurements. The induced velocity of a fixed-pitch rotor in hover and edgewise flight was measured with stereoscopic particle image velocimetry (sPIV) in an anechoic wind tunnel. The edgewise flight measurements covered advance ratios ranging from 0.065 to 0.268. The ensemble averaged sPIV measurements showed that an increase in advance ratio led to a skewing of the maximum induced velocity towards the advancing side of the rotor and an increased area of upwash velocity at the front of the rotor disk. The measured mean velocity field was combined with blade element theory and Sears Unsteady Airfoil Theory to estimate the unsteady blade forces, which were used in analytical tonal noise predictions. The predictions were on average within 5 dB of measured sound pressure levels at the rotor blade passage frequency.
RizziSHuffDJrD, et al.Urban air mobility noise: current practice, gaps, and recommendations. NASA; TP - 20205007433, 2020.
2.
HuHYangYLiuY, et al.Effects of leading edge serrations on noise reduction and aerodynamic performance of multi-copter rotors during forward flight. AIAA Avaiation Forum, 2020.
3.
JamaluddinNSCelikABaskaranK, et al.Experimental analysis of rotor blade noise in edgewise turbulence. Aerospace2023; 10(6): 502.
4.
YangYLiuYLiY, et al.Aerodynamic and aeroacoustic performance of an isolated multicopter rotor during forward flight. AIAA J2020; 58(3): 1171–1181.
5.
PettingillNAZawodnyNSThurmanCS. Aeroacoustic testing of UAS-scale rotors for a quadcopter in hover and forward flight. 28th AIAA/CEAS Aeroacoustics Conference2022; 2022: 3110.
GoldschmidtJTingleHIfjuP, et al.“Acoustics and forces from a subscale electric vertical-takeoff-and-landing rotor in edgewise flight”. AIAA J2024; 62(8): 1–16.
8.
GoldschmidtJTingleHIfjuP, et al.Acoustics and forces from isolated and installed tandem eVTOL rotor configurations. AIAA 2023-0791. AIAA SCITECH 2023 Forum. 2023.
9.
Ffowcs WilliamsJEHawkingsDL. Sound generation by turbulence and surfaces in arbitrary motion. Proc Roy Soc Lond Math Phys Sci1969; 264: 321–342.
10.
JiaZLeeS. Acoustic analysis of a quadrotor evtol design via high-fidelity simulations. In: 25th AIAA/CEAS aeroacoustics conference, Delft, The Netherlands, 20 May 2019 – 23 May 2019.
11.
ZawodnyNSBoydDDBurleyCL. Acoustic characterization and prediction of representative, small-scale rotary-wing unmanned aircraft system components. In Proceedings of the 72nd American Helicopter Society (AHS) Annual Forum, West PalmBeach, FL, USA, 17–19 May 2016.
12.
FarassatF, “Theory of noise generation from moving bodies with an application to helicopter rotors”. NASA, 1975, TR R-451.
13.
GoldsteinME. Aeroacoustics. : McGraw-Hill, 1976, pp. 233–271.
14.
MarteJEKurtzDW. A review of aerodynamic noise from propellers, rotors, and lift fans. Tech. rep1970; 19(3): 227–249.
15.
GutinL. On the sound field of a rotating propeller. NACA, 1948, vol TM-1195.
16.
MorsePIngardKU. Theoretical acoustics: McGraw-Hill, 1968, pp. 739–747.
17.
LowsonMVOllerheadJB. A theoretical study of helicopter rotor noise. J Sound Vib1969; 9(2): 197–222.
18.
WrightSE. Sound radiation from a lifting rotor generated by asymmetric disk loading. J Sound Vib1969; 9(2): 223–240.
RogerMKucukcoskunK. Near-and-far field modeling of advanced tail-rotor noise using source-mode expansions. J Sound Vib2019; 453: 328–354.
21.
RogerMMoreauS. Tonal-noise assessment of quadrotor-type UAV using source-mode expansions. Acoustics2020; 2(3): 674–690.
22.
BlakeWK. Mechanics of Flow-Induced Sound and Vibration: Complex Flow-Structure Interactions. Academic Press Inc.1986; 2: 843–890.
23.
HansonDBParzychDJ. Theory for noise of propellers in angular inflow with parametric studies and experimental verification. NASA-CR-4499, 1993.
24.
GillHLeeSRuhML, et al.Applicability of low-fidelity tonal and broadband noise models on small-scaled rotors. AIAA SCITECH 2023 Forum, 2023.
25.
ChenLBattyTGiacobelloM, et al.Prediction of small-scale rotor noise using a low-fidelity model-based framework. In: Acoustics 2019, sound decisions: moving forward with acoustics - proceedings of the annual conference of the Australian acoustical society. The University of Western, 2020.
26.
MisiorowskiMGandhiFOberaiAA, “Computational study on rotor interactional effects for a quadcopter in edgewise flight”. AIAA J2019; 57(12): 5309–5319.
27.
JohnsonW. Rotorcraft aeromechanics. Cambridge University Press, 2013.
28.
PetersDAHeCJ. Correlation of measured induced velocities with a finite-state wake model. J Am Helicopter Soc1991; 36(3): 59–70.
29.
HoadDR, “Rotor induced-inflow-ratio measurements and CAMRAD calculations”. NASA-TP-2946, 1990.
30.
ZhouWNingZLiH, et al., “An experimental investigation on rotor-to-rotor interactions of small UAV propellers”. In: 35th AIAA applied aerodynamics conference, Denver, Colorado, USA, 5-9 June 2017.
31.
de VriesRvan ArnhemNSinnigeT, et al.Aerodynamic interaction between propellers of a distributed-propulsion system in forward flight. Aero Sci Technol2021; 118: 107009.
32.
KrebsTBramesfeldGColeJ, “Transient thrust analysis of rigid rotors in forward flight”. Aerospace2022; 9(1): 28. https://www.mdpi.com/2226-4310/9/1/28
33.
SearsWR. Some aspects of non-stationary airfoil theory and its practical application. J Aeronaut Sci1941; 8(3): 104–108.
34.
MathewJBahrCCarrollB, et al.Design, fabrication, and characterization of an anechoic wind tunnel facility. In: 11th AIAA/CEAS aeroacoustics conference, Monterey, California, 23 May 2005 - 25 May 2005.
35.
AdatraoSSciacchitanoA. Elimination of unsteady background reflections in PIV images by anisotropic diffusion. Meas Sci Technol2019; 30(3): 035204.
36.
CunninghamR, C. The correction of current lifting rotor theory for the effects of the radial velocity component. Georgia Institute of Technology, 1962, vol 5.
37.
DrelaM. XFOIL: an analysis and design system for low reynolds number airfoils. Conference on low reynolds number aerodynamics. University Notre Dame, 1989.
38.
ViternaLAJanetzkeDC, “Theoretical and experimental power from large horizontal-axis wind turbines”. NASA-TM-82944, 1982.
39.
LengYYooHJardinT, et al.Aerodynamic modelling of propeller forces and moments at high angle of incidence. In: AIAA Scitech 2019 Forum, San Diego, California, 7-11 January 2019.
40.
AtassiHM. The sears problem for a lifting airfoil Revisited—New results. J Fluid Mech1984; 141: 109–122.
41.
TheodorsenT. General Theory of Aerodynamic Instability and the Mechanism of Flutter. NACA Report, 1935, vol 496.
GoldsteinM. Unified approach to aerodynamic sound generation in the presence of solid boundaries. J Acoust Soc Am1974; 56(2): 497–509.
47.
GoldschmidtJUkeileyL. Inflow and wake velocity measurements of a UAM rotor. 15th international symposium on particle image velocimetry, San Diego, California, USA, June 19-21, 2023.
