15:30
Session 5: UAS/UAM noise modeling 2
Chair: Ingrid Legriffon
15:30
20 mins
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Noise mitigation using toroidal blade propeller in quadrotor UAV
Sai Kiran Reddy Adapa, Navrose Navrose
Abstract: This study aims to design two–loop toroidal propellers for noise reduction through parametric studies. First, aerodynamic calculations for toroidal as well as conventional propellers are carried out at high RPM in OpenFOAM by solving the Unsteady Reynolds Averaged Navier-Stokes (U-RANS) equations with k–ω SST turbulence model. The Ffowcs Williams Hawkings (FW-H) aeroacoustic analogy is then used to calculate the far-field noise spectrum. The analogy is implemented by coupling an open source library (Epikhin, Evdokimov, Kraposhin, Kalugin, & Strijhak, 2015) to flow solver. The validity of the coupled tool is verified for flow past a circular cylinder and conventional propeller (DJI Phantom 9450) in hover. The coupled tool is then used for Aeroacoustic study of conventional 2-blade, 4-blade and toroidal propellers in hover. For conventional propeller, with increase in number of blades, the thrust output and FOM increases. However, the far field noise characteristics is found out to be unaffected. Toroidal propellers with similar solidity as that of conventional four blade propeller yields increased thrust output when compared to conventional four blade propeller at increased tonal noise cost. In terms of OASPL, toroidal propellers showed increased noise characteristics in radial direction and decreased noise characteristics in axial direction. If toroidal propeller’s solidity is reduced to that of conventional two blade propeller, its FOM and noise characteristics improves, albeit with a penalty of thrust. The simulation framework is then extended to analyze propellers in a multi propeller configuration.
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15:50
20 mins
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Aerodynamic and Aeroacoustic Evaluation of Looped Propeller Blades with Biomimetic Modifications
Ewan Courts, Abdesselam Bouferrouk, Justin du Plessis
Abstract: This paper presents an aerodynamic and aeroacoustic assessment of looped propeller blades incorporating biomimetic leading-edge tubercles, trailing-edge serrations, hybrid configurations and a non-uniform whale flipper-inspired tubercle geometry, characterising the resulting performance trade-offs. Steady-state RANS was used to evaluate aerodynamic performance, while unsteady RANS (uRANS) with a sliding mesh provided transient flow data for the Ffowcs Williams–Hawkings (FW-H) acoustic analogy. The numerical framework was validated against experimental data. Results show that leading-edge tubercle geometries offer the best compromise within the tubercle family, achieving thrust within 3–5% of the baseline looped propeller. Trailing-edge serrations primarily influence power demand and efficiency, with selected configurations improving Figure of Merit by up to 5%. Hybrid tubercle–serration configurations provide partial improvements over serration-only designs but did not surpass the best tubercle configuration. No modified geometry consistently exceeded the baseline looped propeller in thrust, though several improved efficiency under specific operating conditions. Tonal noise was predicted with the FW-H analogy and broadband noise estimated using Fluent’s broadband noise model, with all aeroacoustic simulations performed at matched thrust for physically consistent comparison. Under matched-thrust conditions the biomimetic looped configurations exhibited tonal levels at the fundamental BPF comparable to the reference (1.4 dB spread; OASPL 48.9–51.1 dB), with dominant tonal energy shifting towards higher harmonics. Broadband acoustic power levels spanned 18.5 dB, from 44.8 dB for the reference to 63.3 dB for the hybrid, indicating strong sensitivity to blade design. The findings emphasise the importance of thrust-matched conditions for propeller noise assessment and inform the design of low-noise propulsion concepts.
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16:10
20 mins
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Numerical noise prediction of a tilting rotor in forward flight
Marco Picillo, Mattia Barbarino, Francesco Avallone
Abstract: In recent years, the noise generated by rotating blades has gained renewed importance due to the emergence and rapid growth of the Urban Air Mobility industry. Noise remains one of the most critical challenges to overcome, as it strongly affects public acceptance [1]. While noise generation mechanisms under steady operating conditions have been extensively investigated [2], noise prediction during transient maneuvers, representative of realistic Urban Air Mobility flight scenarios, remains insufficiently explored and highly challenging. During flight, drones and Vertical Take-Off and Landing vehicles experience complex inflow conditions resulting from non-uniform inflows and transitions between flight conditions. These effects significantly influence blade loading and, consequently, noise directivity [3]. One of the most common maneuvers in Urban Air Mobility operations is rotor tilting, which alters the angle between the rotor blades and the free-stream velocity, leading to a highly unsteady flow field. Noise generated by tilting rotors has been investigated experimentally [4] and numerically [3]; however, existing studies mainly address static tilting configurations, neglecting the time-dependent effects associated with dynamic maneuvers. In this work, the noise prediction of a tilting two-bladed drone propeller is investigated using a low-fidelity framework combining a Vortex Particle aerodynamic solver, FLOWUnsteady, with an acoustic solver based on Farassat’s formulation 1A for tonal noise prediction. The results highlight the differences between static and dynamic tilting maneuvers in terms of aerodynamic performance and noise characteristics.
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16:30
20 mins
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Design and Optimisation of a Low Noise Unmanned Aerial System Propeller
Nikki Brown, Dan Withey
Abstract: Unmanned Aerial Systems, commonly known as drones, have risen in popularity in recent years, with applications across industries including defence, healthcare, and recreational activities. One disadvantage of drone usage is the noise from the propellers. A high rate of rotation from the propeller is required to generate sufficient lift for the drone; however, the blade noise and the interaction between the blades and the turbulent flow they produce leads to loud, high frequency noise, causing annoyance and health concerns. Previous studies have explored novel blade shapes and features; however, these often come at a cost to the lift characteristics of the drone and are not widely accessible due to unique and complex designs. This report demonstrates the development of a novel propeller design to reduce noise, while also maintaining equivalent lift properties, through addition of a blade tip elbow. Employing computational methods through Computer Aided Design and Computational Fluid Dynamics, aerodynamic and acoustic properties of twenty-five propellers were analysed considering ranges of elbow length and an airflow-redirecting bend angle. Selected modifications were applied to an existing propeller design for simulation-based verification. Assessment was limited to a 75mm (3-inch) propeller diameter due to simulation software limitations. The modified propeller produced a reduction of up to 5.66dB, compared to the baseline model.
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