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Aeroacoustic Characterization of Coa...

Jdiobe, Muwanika,

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Aeroacoustic Characterization of Coaxial Ducted Propellers/Rotors for Small UAVs /

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Aeroacoustic Characterization of Coaxial Ducted Propellers/Rotors for Small UAVs // Muwanika Jdiobe.
作者:	Jdiobe, Muwanika,
面頁冊數:	1 electronic resource (150 pages)
附註:	Source: Dissertations Abstracts International, Volume: 86-06, Section: B.
Contained By:	Dissertations Abstracts International86-06B.
標題:	Aerospace engineering. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31337043
ISBN:	9798346810025

Aeroacoustic Characterization of Coaxial Ducted Propellers/Rotors for Small UAVs /
Jdiobe, Muwanika,

Aeroacoustic Characterization of Coaxial Ducted Propellers/Rotors for Small UAVs /Muwanika Jdiobe. - 1 electronic resource (150 pages)

Source: Dissertations Abstracts International, Volume: 86-06, Section: B.

The growing interest in electric vertical takeoff and landing (eVTOL) aircraft has highlighted the need for a comprehensive understanding of the aerodynamic and acoustic characteristics of open versus ducted rotors. This numerical study investigates the aerodynamic performance and acoustic behavior of open and ducted coaxial counter-rotating propellers, with a focus on the effects of a duct and rotor axial spacing on the frequency spectrum and directivity of small UAV propeller noise. Using a high-fidelity numerical flow solver, charLES, which performs a compressible, wall-modeled Large Eddy Simulation (LES) capable of resolving turbulence and acoustics. A common UAV propeller with a diameter of 9.4-inches was modeled in the coaxial configuration, with variable spacing between the fore- and aft-rotor. A custom designed duct was created. Far-field noise propagation is computed using the permeable Ffowcs-Williams & Hawkings technique. The results demonstrate that the ducted configuration exhibits a 4% increase in total thrust compared to the open rotors, attributable to reduced tip leakages and improved inflow. Increasing axial rotor spacing between front and rear rotors leads to a slight increase in total predicted thrust due to reduced wake impingement on the rear rotor.Acoustically, the duct effectively shields only the blade passing frequency (BPF, 200 Hz) tone, despite duct mode analysis indicating that the BPF, 3BPF, and 5BPF tones all become cut-off. At frequencies above 1,500 Hz, the ducted configuration generates higher broadband noise levels due to the interaction between the duct boundary layer and the rotor tip vortices with higher turbulent intensity. The ducted configuration exhibits higher overall sound pressure levels (OASPL) and a distinct two-lobe directivity pattern, while the open configuration has a smeared directivity with lower OASPL in the fore arc due to BPF tone dominance. The fundamental tone at 200 Hz forms a directivity with the peak near 100◦ indicating a rotor-only tone, regardless of the rotor spacing; in contrast, the first harmonic tone at 400 Hz depicts a distinctive two-lobe pattern indicating an equally-split interaction tone between the front- and rear-rotor harmonics, except for the 1.5-inch spacing case. Both of the tone intensities decrease with the rotor spacing. The rotor spacing predominantly affects low-frequency tones (200 − 1500 Hz), which decrease their amplitude with increasing spacing, while high-frequency noise (2500 − 4000 Hz) dominated by broadband shows a little sensitivity to the rotor spacing. This suggests that the rotor spacing primarily impacts on large-scale structures in the wakes rather than small-scale features, such as turbulence and tip vortices in the wall boundary layer. This study contributes to the understanding of the aeroacoustic characteristics of ducted coaxial counter-rotating propellers and provides insights into the effects of duct integration and rotor spacing on UAV propeller noise. The findings can inform the design and optimization of quiet and efficient eVTOL propulsion systems.

English

ISBN: 9798346810025Subjects--Topical Terms:

1002622
Aerospace engineering.
Subjects--Index Terms:

Axial rotor spacing

Aeroacoustic Characterization of Coaxial Ducted Propellers/Rotors for Small UAVs /
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520 $a The growing interest in electric vertical takeoff and landing (eVTOL) aircraft has highlighted the need for a comprehensive understanding of the aerodynamic and acoustic characteristics of open versus ducted rotors. This numerical study investigates the aerodynamic performance and acoustic behavior of open and ducted coaxial counter-rotating propellers, with a focus on the effects of a duct and rotor axial spacing on the frequency spectrum and directivity of small UAV propeller noise. Using a high-fidelity numerical flow solver, charLES, which performs a compressible, wall-modeled Large Eddy Simulation (LES) capable of resolving turbulence and acoustics. A common UAV propeller with a diameter of 9.4-inches was modeled in the coaxial configuration, with variable spacing between the fore- and aft-rotor. A custom designed duct was created. Far-field noise propagation is computed using the permeable Ffowcs-Williams & Hawkings technique. The results demonstrate that the ducted configuration exhibits a 4% increase in total thrust compared to the open rotors, attributable to reduced tip leakages and improved inflow. Increasing axial rotor spacing between front and rear rotors leads to a slight increase in total predicted thrust due to reduced wake impingement on the rear rotor.Acoustically, the duct effectively shields only the blade passing frequency (BPF, 200 Hz) tone, despite duct mode analysis indicating that the BPF, 3BPF, and 5BPF tones all become cut-off. At frequencies above 1,500 Hz, the ducted configuration generates higher broadband noise levels due to the interaction between the duct boundary layer and the rotor tip vortices with higher turbulent intensity. The ducted configuration exhibits higher overall sound pressure levels (OASPL) and a distinct two-lobe directivity pattern, while the open configuration has a smeared directivity with lower OASPL in the fore arc due to BPF tone dominance. The fundamental tone at 200 Hz forms a directivity with the peak near 100◦ indicating a rotor-only tone, regardless of the rotor spacing; in contrast, the first harmonic tone at 400 Hz depicts a distinctive two-lobe pattern indicating an equally-split interaction tone between the front- and rear-rotor harmonics, except for the 1.5-inch spacing case. Both of the tone intensities decrease with the rotor spacing. The rotor spacing predominantly affects low-frequency tones (200 − 1500 Hz), which decrease their amplitude with increasing spacing, while high-frequency noise (2500 − 4000 Hz) dominated by broadband shows a little sensitivity to the rotor spacing. This suggests that the rotor spacing primarily impacts on large-scale structures in the wakes rather than small-scale features, such as turbulence and tip vortices in the wall boundary layer. This study contributes to the understanding of the aeroacoustic characteristics of ducted coaxial counter-rotating propellers and provides insights into the effects of duct integration and rotor spacing on UAV propeller noise. The findings can inform the design and optimization of quiet and efficient eVTOL propulsion systems.
546 $a English
590 $a School code: 0664
650 4 $a Aerospace engineering. $3 1002622
650 4 $a Acoustics. $3 879105
650 4 $a Engineering. $3 586835
650 4 $a Fluid mechanics. $3 528155
650 4 $a Mechanical engineering. $3 649730
653 $a Axial rotor spacing
653 $a Counter-rotating propeller noise
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653 $a UAV propeller noise
653 $a Large Eddy Simulation
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690 $a 0986
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720 1 $a Rouser, Kurt P. $e degree supervisor.
720 1 $a Paul, Ryan $e degree supervisor.
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791 $a Ph.D.
792 $a 2024
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