The demand for the development of urban air mobility (UAM) powered by electric systems has been steadily rising across private and public sectors. Most UAM flights incorporate a distributed electric propulsion system to enhance aircraft safety and reliability, which entails an increase in the number of rotors or propellers. Consequently, aerodynamics and aeroacoustics are significantly influenced by strong interactions between the rotor and the airframe. In this study, we conducted a computational investigation to examine the impact of rotor–airframe interaction on aerodynamic and aeroacoustic characteristics. This examination considered variations in airframe shape and the distance between the rotor and airframe. The aerodynamic analysis was executed using the lattice-Boltzmann method simulation, in which acoustic predictions were made using the Ffowcs Williams–Hawkings(FW–H) acoustic analogy with a permeable surface. The airframe consists of two geometries: a cylinder and a cone. Tip vortex breakdown and the transition into the turbulent wake state were captured in both airframes, and a fountain flow was affected by the downwash circulation generated under certain proximity of airframe cases. The acoustic prediction results showed that high-intensity noise radiated over the broad surface of the airframe in the conical airframe case. Significant thrust force fluctuations and an increase in noise level were observed at the smallest rotor tip clearance, S / R = 0.1, compared to the isolated rotor. Furthermore, the noise contribution of the rotor and airframe was compared, revealing that the airframe noise level was even higher than the rotor noise at S / R = 0.1.

1.
Urban Air Mobility,
eVTOL/Urban Air Mobility TAM Update: A Slow Take-off, But Sky's the Limit
(
Morgan Stanley
,
2021
).
2.
EASA,
Study on the Societal Acceptance of Urban Air Mobility in Europe
(
European Union Aviation Safety Agency
,
2021
).
3.
A. J.
Torija
,
Z.
Li
, and
R. H.
Self
, “
Effects of a hovering unmanned aerial vehicle on urban soundscapes perception
,”
Transp. Res., Part D
78
,
102195
(
2020
).
4.
D. S.
Little
,
J.
Majdalani
,
R. J.
Hartfield
, Jr.
, and
V.
Ahuja
, “
On the prediction of noise generated by urban air mobility (UAM) vehicles. I. Integration of fundamental acoustic metrics
,”
Phys. Fluids
34
(
11
),
116117
(
2022
).
5.
V.
Ahuja
,
D. S.
Little
,
J.
Majdalani
, and
R. J.
Hartfield
, Jr.
, “
On the prediction of noise generated by urban air mobility (UAM) vehicles. II. Implementation of the Farassat F1A formulation into a modern surface-vorticity panel solver
,”
Phys. Fluids
34
(
11
),
116118
(
2022
).
6.
H.
Lee
and
D. J.
Lee
, “
Rotor interactional effects on aerodynamic and noise characteristics of a small multirotor unmanned aerial vehicle
,”
Phys. Fluids
32
(
4
),
047107
(
2020
).
7.
W.
Zhou
,
Z.
Ning
,
H.
Li
, and
H.
Hu
, “
An experimental investigation on rotor-to-rotor interactions of small UAV propellers
,” AIAA Paper No. AIAA 2017-3744,
2017
.
8.
D.
Shukla
and
N.
Komerath
, “
Drone scale coaxial rotor aerodynamic interactions investigation
,”
J. Fluids Eng.
141
(
7
),
071106
(
2019
).
9.
N.
Intaratep
,
W. N.
Alexander
,
W. J.
Devenport
,
S. M.
Grace
, and
A.
Dropkin
, “
Experimental study of quadcopter acoustics and performance at static thrust conditions
,” in
Proceedings of 22nd AIAA/ CEAS Aeroacoustics Conferences
,
2016
.
10.
S. B.
Chae
,
S. C.
Lee
, and
J. H.
Kim
, “
Effects of rotor–rotor interaction on the wake characteristics of twin rotors in axial descent
,”
J. Fluid Mech.
952
,
A31
(
2022
).
11.
R.
Piccinini
,
M.
Tugnoli
, and
A.
Zanotti
, “
Numerical investigation of the rotor-rotor aerodynamic interaction for eVTOL aircraft configurations
,”
Energies
13
(
22
),
5995
(
2020
).
12.
Z.
Jia
and
S.
Lee
, “
High-fidelity computational analysis on the noise of a side-by-side hybrid VTOL aircraft
,”
J. Am. Helicopter Soc.
67
(
2
),
1
14
(
2022
).
13.
Z.
Jia
and
S.
Lee
, “
Computational study on noise of urban air mobility quadrotor aircraft
,”
J. Am. Helicopter Soc.
67
(
1
),
1
15
(
2022
).
14.
S.
Li
and
S.
Lee
, “
Prediction of urban air mobility multi-rotor VTOL broadband noise using UCD-QuietFly
,”
J. Am. Helicopter Soc.
66
,
1
13
(
2021
).
15.
N. S.
Zawodny
and
D. D.
Boyd
, Jr.
, “
Investigation of rotor-airframe interaction noise associated with small-scale rotary-wing unmanned aircraft systems
,” in
American Helicopter Society 73rd Annual Forum
,
2017
.
16.
C. D.
Coffen
, “
Tilt rotor hover aeroacoustics
,”
NASA Contractor Report No. 177598
(
NASA
,
1992
).
17.
C. K.
Rutledge
,
C. D.
Coffen
, and
A. R.
George
, “
A comparative analysis of XV-15 tiltrotor hover test data and WOPWOP predictions incorporating the fountain effect
,”
NASA Contractor Report No. 189455
(
NASA
,
1991
).
18.
D. G.
Caprace
,
A.
Ning
,
P.
Chatelain
, and
G.
Winckelmans
, “
Effects of rotor-airframe interaction on the aeromechanics and wake of a quadcopter in forward flight
,”
Aerosp. Sci. Technol.
130
,
107899
(
2022
).
19.
D. A.
Wachspress
,
K. Y.
Michael
, and
K. S.
Brentner
, “
Rotor, airframe aeroacoustic prediction for EVTOL UAM aircraft
,” in
Vertical Flight Society's 75th Annual Forum and Technology Display
(
Penn State
,
2019
).
20.
Z.
Wang
,
Q.
Henricks
,
M.
Zhuang
,
A.
Pandey
,
M.
Sutkowy
,
B.
Harter
,
M.
McCrink
, and
J.
Gregory
, “
Impact of rotor-airframe orientation on the aerodynamic and aeroacoustic characteristics of small unmanned aerial systems
,”
Drones
3
(
3
),
56
73
(
2019
).
21.
L. A. J.
Zori
and
R. G.
Rajagopalan
, “
Navier–Stokes calculations of rotor-airframe interaction in forward flight
,”
J. Am. Helicopter Soc.
40
(
2
),
57
67
(
1995
).
22.
Y. M.
Park
and
S.
Jee
, “
Numerical study on interactional aerodynamics of a quadcopter in hover with overset mesh in OpenFOAM
,”
Phys. Fluids
35
(
8
),
085138
(
2023
).
23.
D.
Casalino
,
W. C. P.
Van der Velden
,
G.
Romani
, and
I.
Gonzalez-Martino
, “
Aeroacoustic analysis of urban air operations using the LB/VLES method
,” AIAA Paper No. AIAA 2019-2662,
2019
.
24.
I.
Gonzalez-Martino
,
G.
Romani
,
J.
Wang
, and
D.
Casalino
, “
Rotor noise generation in a turbulent wake using lattice-Boltzmann methods
,” AIAA Paper No. AIAA 2018-3447
2018
.
25.
C.
Thurman
,
J.
Baeder
,
N.
Zawodny
, and
J. D.
Baeder
, “
Computational prediction of broadband noise from a representative small unmanned aerial system rotor
,” in
76th Annual Forum & Technology Display
,
2020
.
26.
S.
Thibault
,
D.
Holman
,
S.
Garcia
, and
G.
Trapani
, “
CFD Simulation of a quad-rotor UAV with rotors in motion explicitly modeled using an LBM approach with adaptive refinement
,” AIAA Paper No. AIAA 2017-0583,
2017
.
27.
S.
Wen
,
J.
Han
,
Z.
Ning
,
Y.
Lan
,
X.
Yin
,
J.
Zhang
, and
Y.
Ge
, “
Numerical analysis and validation of spray distributions disturbed by quad-rotor drone wake at different flight speeds
,”
Comput. Electron. Agric.
166
,
105036
(
2019
).
28.
W. C. P.
Van der Velden
,
G.
Romani
, and
D.
Casalino
, “
Validation and insight of a full-scale S-76 helicopter rotor using the lattice-Boltzmann method
,”
Aerosp. Sci. Technol.
118
,
107007
(
2021
).
29.
S.
Chen
and
G. D.
Doolen
, “
Lattice Boltzmann method for fluid flows
,”
Annu. Rev. Fluid Mech.
30
(
1
),
329
364
(
1998
).
30.
Z. L.
Yang
,
T. N.
Dinh
,
R. R.
Nourgaliev
, and
B. R.
Sehgal
, “
Evaluation of the Darcy's law performance for two-fluid flow hydrodynamics in a particle debris bed using a lattice-Boltzmann model
,”
Heat Mass Transfer
36
(
4
),
295
304
(
2000
).
31.
M. E.
Kutay
,
A. H.
Aydilek
, and
E.
Masad
, “
Laboratory validation of lattice Boltzmann method for modeling pore-scale flow in granular materials
,”
Comput. Geotech.
33
(
8
),
381
395
(
2006
).
32.
A.
Zarri
,
E.
Dell'Erba
,
W.
Munters
, and
C.
Schram
, “
Aeroacoustic installation effects in multi-rotorcraft: Numerical investigations of a small-size drone model
,”
Aerosp. Sci. Technol.
128
,
107762
(
2022
).
33.
G.
Romani
and
D.
Casalino
, “
Rotorcraft blade-vortex interaction noise prediction using the lattice-Boltzmann method
,”
Aerosp. Sci. Technol.
88
,
147
157
(
2019
).
34.
S.
Shubham
, “
Computational aeroacoustic investigation of co-rotating rotors for urban air mobility
,” M.S. thesis (
Delft University of Technology
,
2020
).
35.
N.
Gourdain
,
R.
Serré
,
T.
Jardin
,
G.
Delattre
, and
J. M.
Moschetta
, “
Analysis of the flow produced by a low-Reynolds rotor optimized for low noise applications—Part 1: Aerodynamics,
” in 43rd European Rotorcraft Forum (
2017
).
36.
R. B.
Kotapati
,
R.
Shock
, and
H.
Chen
, “
Lattice-Boltzmann simulations of flows over backward-facing inclined steps
,”
Int. J. Mod. Phys. C
25
(
1
),
1340021
(
2014
).
37.
H.
Chen
,
S.
Chen
, and
W. H.
Matthaeus
, “
Recovery of the Navier-Stokes equations using a lattice-gas Boltzmann method
,”
Phys. Rev. A
45
(
8
),
R5339
R5342
(
1992
).
38.
F.
Avallone
,
W. C. P.
Van Der Velden
,
D.
Ragni
, and
D.
Casalino
, “
Noise reduction mechanisms of sawtooth and combed-sawtooth trailing-edge serrations
,”
J. Fluid Mech.
848
,
560
591
(
2018
).
39.
N. S.
Liu
and
T. H.
Shih
, “
Turbulence modeling for very large-eddy simulation
,”
AIAA J.
44
(
4
),
687
697
(
2006
).
40.
C.
Teruna
,
L.
Rego
,
D.
Casalino
,
D.
Ragni
, and
F.
Avallone
, “
A numerical study on aircraft noise mitigation using porous stator concepts
,”
Aerospace
9
(
2
),
70
(
2022
).
41.
Y.
Li
,
Z.
Ma
,
P.
Zhou
,
S.
Zhong
, and
X.
Zhang
, “
A numerical investigation of the aerodynamic and aeroacoustic interactions between components of a multi-rotor vehicle for urban air mobility
,”
J. Sound Vib.
571
,
118002
(
2024
).
42.
P. V.
Diaz
and
S.
Yoon
, “
High-fidelity computational aerodynamics of multi-rotor unmanned aerial vehicles
,” AIAA Paper No. AIAA 2018-1266,
2018
.
43.
N. S.
Zawodny
,
D. D.
Boyd
, Jr.
, and
C. L.
Burley
, “
Acoustic characterization and prediction of representative, small-scale rotary-wing unmanned aircraft system components
,” in
American Helicopter Society 72nd Annual Forum
(
2016
).
44.
C.
Nardari
,
D.
Casalino
,
F.
Polidoro
,
V.
Coralic
,
P. T.
Lew
, and
J.
Brodie
, “
Numerical and experimental investigation of flow confinement effects on UAV rotor noise
,” AIAA Paper No. AIAA 2019-2497,
2019
.
45.
W. S.
Choi
,
Y. S.
Choi
,
S. Y.
Hong
,
J. H.
Song
,
H. W.
Kwon
, and
C. M.
Jung
, “
Turbulence-induced noise of a submerged cylinder using a permeable FW-H method
,”
Int. J. Nav. Archit. Ocean Eng.
8
(
3
),
235
242
(
2016
).
46.
Y. H.
Yu
, “
Rotor blade–vortex interaction noise
,”
Prog. Aerosp. Sci.
36
(
2
),
97
115
(
2000
).
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