This study, conducted at the University of Bristol’s aeroacoustic facility, explores the aeroacoustic characteristics of a 10-inch APC propeller in pusher configuration within ground effect conditions. Tested at a rotational speed of 7000 r/min, the propeller’s performance was evaluated at varying distances from the ground. Wall pressure fluctuations near the propeller were measured at eight radial points, complemented by far-field acoustic measurements. Consistent with previous research, distinctive thrust and torque behaviours were observed when operating both in and out of ground effect. Notably, a significant noise increase of approximately 5 dB was observed on the ground’s reflected side, while a reduction of about 14 dB was detected on the shielded side. Higher-order statistical analysis such as skewness and kurtosis revealed substantial effects of tip vortex impingement in ground effect conditions. This study applies two-point statistics and the Corcos model to analyze propeller-induced wall pressure fluctuations. The coherence function effectively captures the intricate dynamics of pressure variations across different spatial locations and frequencies. This approach offers novel insights into the behaviour of boundary layers and flow-induced pressures in the context of propellers operating in the ground effect. Wavelet decomposition was utilized to differentiate the influences of the boundary layer and the acoustic field. This comprehensive analysis highlights the intricate dynamics of propeller operation in ground effect, contributing valuable insights to the field of aeroacoustic research.
GoyalRCohenA. Advanced air mobility: opportunities and challenges deploying eVTOLs for air ambulance service. Appl Sci2022; 12(3): 1183.
2.
National Academies of Sciences, E. and Medicine. Advancing aerial mobility: a national blueprint. Washington, DC: The National Academies Press, 2020.
3.
HolmesBJOlcottPRSDMPGLMP. NASA strategic framework for on-demand air mobility. Technical Report. Washington, DC: NASA, 2017.
4.
RizziSAHuffDLDouglas BoydJ, et al.Urban air mobility noise: current practice, gaps, and recommendations. Technical Report. Washington, DC: NASA, 2020.
5.
JoYJardinTGojonR, et al.Prediction of noise from low Reynolds number rotors with different number of blades using a non-linear vortex lattice method. In: 25th AIAA/CEAS Aeroacoustics Conference,Delft, The Netherlands, 202615-23 May 2019, p.
6.
AntcliffKRMooreMDGoodrichKH. Silicon valley as an early adopter for on-demand civil VTOL operations. In: 16th AIAA Aviation Technology, Integration, and Operations Conference,Washington, D.C., 133466-17 June 2016, p.
7.
PattersonMDAntcliffKRKohlmanLW. A proposed approach to studying urban air mobility missions including an initial exploration of mission requirements. Technical Report. Washington, DC: NASA, 2018.
8.
LeeTELeishmanJGRamasamyM. Fluid dynamics of interacting blade tip vortices with a ground plane. J Am Helicopter Soc2010; 55(2): 22005–2200516.
9.
GaneshBKomerathN. Unsteady aerodynamics of rotorcraft in ground effect. In: 22nd AIAA Applied Aerodynamics Conference and Exhibit, Providence, Rhode Island, 16-19 August2004, p. 5287.
10.
KumarVMichaelN. Opportunities and challenges with autonomous micro aerial vehicles. Int J Robot Res2012; 31(11): 1279–1291.
11.
PowersCMellingerDKushleyevA, et al.Influence of aerodynamics and proximity effects. In: FlightQ (ed). Experimental robotics. Berlin: Springer International Publishing, 2013, pp. 289–302.
12.
GibertiniGGrassiDParoliniC, et al.Experimental investigation on the aerodynamic interaction between a helicopter and ground obstacles. Proc Inst Mech Eng G J Aerosp Eng2015; 229(8): 1395–1406.
13.
PapadopoulosCMitridisDYakinthosK. Conceptual design of a novel unmanned ground effect vehicle (UGEV) and flow control integration study. Drones2022; 6(1): 25.
14.
NirooeiM. Aerodynamic and static stability characteristics of airfoils in extreme ground effect. Proc Inst Mech Eng G J Aerosp Eng2018; 232(6): 1134–1148.
15.
HaoWTeoCKhooB, et al.Aerodynamic and stability characteristics of NACA4412 in ground effects. Int Jnl of Intel Unmanned Syst2013; 1(2): 145–153.
16.
Sanchez-CuevasPHerediaGOlleroA. Characterization of the aerodynamic ground effect and its influence in multirotor control. International Journal of Aerospace Engineering2017; 2017: 1–17.
17.
CheesemanIBennettW. The effect of the ground on a helicopter rotor in forward flight. Technical Report. Wharley End: Cranfield University, 1955.
18.
FradenburghEA. The helicopter and the ground effect machine. J Am Helicopter Soc1960; 5(4): 24–33.
19.
CurtissHCSunMPutmanWF, et al.Rotor aerodynamics in ground effect at low advance ratios. J Am Helicopter Soc1984; 29(1): 48–55.
20.
TannerPEOvermeyerADJenkinsLN, et al.Experimental Investigation of Rotorcraft Outwash in Ground Effect. Presented at the AHS 71st International Annual Forum,Virginia Beach, Virginia, May 5–7, 2015.
21.
EberhartGM. Modeling of ground effect benefits for multi-rotor small unmanned aerial systems at hover. Master’s Thesis. Athens, OH: Ohio University, 2017.
22.
KonuşMFSavaşÖ. Rotor vortex wake in close proximity of walls in hover. J Am Helicopter Soc2016; 61(4): 1–12.
23.
HanHXiangCXuB, et al.Aerodynamic performance and analysis of a hovering micro-scale shrouded rotor in confined environment. Adv Mech Eng2019; 11(4): 168781401882332.
24.
JardinTProthinSMagañaCG. Aerodynamic performance of a hovering microrotor in confined environment. J Am Helicopter Soc2017; 62(2): 1–7.
25.
KnightMHegnerRA. Analysis of ground effect on the lifting airscrew. Technical Report. Washington, DC: National Advisory Committee for Aeronautics, 1941.
26.
HaydenJS. The effect of the ground on helicopter hovering power required. In: Proceedings AHS 32nd Annual Forum, Washington, D.C., 10–12 May 1976, p. 1976-0001.
27.
JohnsonBLeishmanJGSydneyA. Investigation of sediment entrainment using dual-phase, high-speed particle image velocimetry. J Am Helicopter Soc2010; 55(4): 042003.
28.
SyalMLeishmanJG. Predictions of brownout dust clouds compared to photogrammetry measurements. J Am Helicopter Soc2013; 58(2): 1–18.
29.
SydneyALeishmanJG. Time-resolved measurements of rotor-induced particle flows produced by a hovering rotor. J Am Helicopter Soc2014; 59(2): 1–16.
30.
MylaporeARSchmitzFH. An experimental investigation of ground effect on a quad tilt rotor in hover. J Am Helicopter Soc2015; 60(1): 1–14.
31.
SmithBHealyRGandhiF, et al.eVTOL rotor noise in ground effect. In: Vertical Flight Society's 77th Annual Forum & Technology Display, Virtual Event,10-14 May 2021, Vol 1.
32.
HansonLJawaharHKVemuriSS, et al.Experimental investigation of propeller noise in ground effect. J Sound Vib2023; 559: 117751.
33.
CorcosGM. The structure of the turbulent pressure field in boundary-layer flows. J Fluid Mech1964; 18(3): 353–378.
34.
MayerYDJawaharHKSzőkeM, et al.Design and performance of an aeroacoustic wind tunnel facility at the University of Bristol. Appl Acoust2019; 155: 358–370.
35.
KimK-SLeeC-MHwangG-Y, et al.Effect of the number of poles on the acoustic noise from BLDC motors. J Mech Sci Technol2011; 25(2): 273–277.
36.
HansonLPBaskaranKPullinSF, et al.Aeroacoustic and aerodynamic characteristics of propeller tip geometries. In: 28th AIAA/CEAS Aeroacoustics Conference,Southampton, UK, 133075-17 June 2022.
37.
HansonLPBaskaranKZangB, et al.Aeroacoustic interactions of a trailing edge mounted propeller and flat plate. In: 28th AIAA/CEAS Aeroacoustics Conference,Southampton, UK, 132937-17 June 2022.
38.
HansonLBaskaranKZangB, et al.Acoustic shielding and scattering effects of a propeller mounted above a flat plate. Inter Noise2023; 265(2): 5013–5024.
39.
StephensonJHWeitsmanDZawodnyNS. Effects of flow recirculation on unmanned aircraft system (UAS) acoustic measurements in closed anechoic chambers. J Acoust Soc Am2019; 145(3): 1153–1155.
40.
HeXLeangKK. Quasi-steady in-ground-effect model for single and multirotor aerial vehicles. AIAA J2020; 58(12): 5318–5331.
41.
GleggSDevenportW. Aeroacoustics of low Mach number flows: fundamentals, analysis, and measurement. London: Academic Press, 2017.
42.
MeijeringASchroederW. Experimental analysis of separated transitional transonic airfoil flow. In: 15th AIAA computational fluid dynamics conference, 2001, p. 2987.
43.
ChabertTDandoisJGarnierE, et al.Experimental detection of a periodically forced turbulent boundary layer separation. Exp Fluid2013; 54(2): 1–14.
44.
Kamliya JawaharHAlihan Showkat AliSAzarpeyvandM. Aeroacoustic analysis of slat tones. In: INTER-NOISE and NOISE-CON Congress and Conference Proceedings, Washington, D.C., 1-5 August 2021, Vol263, pp. 5650–5663.
45.
Kamliya JawaharHMeloniSCamussiR, et al.Intermittent and stochastic characteristics of slat tones. Phys Fluids2021; 33(2): 025120.
46.
AddisonPS. The illustrated wavelet transform handbook: introductory theory and applications in science, engineering, medicine and finance. Boca Raton, FL: CRC Press, 2017.
47.
CamussiRMeloniS. On the application of wavelet transform in jet aeroacoustics. Fluids2021; 6(8): 299.
48.
MeloniSJawaharHK. A wavelet-based time-frequency analysis on the supersonic jet noise features with chevrons. Fluids2022; 7(3): 108.
49.
MeloniSDi MarcoAMancinelliM, et al.Wall-pressure fluctuations induced by a compressible jet flow over a flat plate at different Mach numbers. Exp Fluid2019; 60(3): 48.
50.
MeloniSMancinelliMCamussiR, et al.Wall-pressure fluctuations induced by a compressible jet in installed configuration. AIAA J2020; 58(7): 2991–3000.
51.
MeloniSDi MarcoAMancinelliM, et al.Experimental investigation of jet-induced wall pressure fluctuations over a tangential flat plate at two Reynolds numbers. Sci Rep2020; 10(1): 1–11.
