15:30
UAS/UAM noise modelling 2
15:30
20 mins
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Noise mitigation using toroidal blade propeller in quadrotor UAV
Sai Kiran Reddy Adapa, Navrose Navrose
Abstract: High level of noise from drones are a barrier to their increasing use in urban and militarily sensitive areas. Early experiments suggest that toroidal propeller can significantly reduce noise by decreasing blade tip vortices and the associated turbulence, while maintaining similar thrust performance [1]. The Helicopter Lab at IIT Kanpur has been designing quadrotor and rotary-wing unmanned vehicles for logistics and surveillance. Figure 1(b) shows such a quadrotor that suffers from excessive noise generation. This study aims to design an aerodynamically and acoustically efficient toroidal blade to be used in the quadrotor. Aerodynamic calculations for both toroidal and conventional propellers are carried out in OpenFOAM by solving the unsteady Reynolds average Navier-Stokes (U-RANS) equations, employing the k–ε turbulence model and dynamic mesh capabilities. The Ffowcs Williams Hawkings (FW-H) aeroacoustic analogy is used to calculate the far-field noise spectrum. The analogy is implemented by coupling open source libAcoustics libraries to flow solver. The validity of the coupled tool has been verified for flow past a circular cylinder. Using the coupled tool, we computed flow field and far field noise spectrum of a conventional propeller (DJI-9450) at 6000 rpm in hover. The calculations underpredicted the thrust which is attributed to inadequate mesh resolution near the blade. Presently we are recomputing using a finer mesh. We aim to use the coupled tool to further analyze toroidal propeller at similar angular velocity. The analysis will be extended to multi propeller configuration. Detailed results of our work will be presented at the conference.
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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: Looped propeller blades are a promising noise-mitigation concept for UAVs. However, such geometries are typically associated with reduced thrust and propulsive performance degradation compared with conventional designs. This paper presents aerodynamic and aeroacoustic assessment of looped propeller blades incorporating biomimetic leading-edge tubercles (bumps), trailing-edge serrations, hybrid configurations and whale flipper-inspired tubercles with the aim of characterising performance trade-offs. RANS and uRANS simulations were performed in ANSYS Fluent, using sliding mesh techniques and the k-ω SST turbulence model. The numerical framework was validated against experimental data, showing good correlation. The results show that while the baseline looped propeller exhibits a clear performance penalty relative to a conventional (non-looped) reference design, biomimetic modifications could offer somer performance benefits. In particular, leading-edge tubercle geometries were found to offer the best compromise within the tubercle family, achieving thrust levels within 3–5% higher than the baseline looped propeller. Trailing-edge serration designs primarily influence power demand and efficiency rather than thrust recovery, with selected configurations improving Figure of Merit (FoM) by up to 5%. Hybrid tubercle-serration configurations provide partial improvements relative to serration-only designs but did not offer additional gains over the best tubercle configuration. Overall, none of the modified geometries consistently surpassed the baseline looped propeller in thrust but several configurations demonstrated improved efficiency under specific operating conditions. Tonal noise was evaluated using the Ffowcs Williams-Hawkings (FW-H) acoustic analogy while broadband noise was estimated using Fluent’s broadband noise model. All aeroacoustic simulations were performed at matched thrust levels rather than matched rotational speeds, allowing physically consistent comparisons between tested geometries. Under such conditions, the biomimetic looped configurations exhibited tonal noise levels comparable to the conventional and baseline looped propellers, typically within 4%, with dominant tonal energy shifting towards higher harmonics. Broadband noise predictions showed notable variation between geometries indicating sensitivity to blade design. Overall, the results demonstrate that biomimetic modifications on looped propellers can reshape aerodynamic and aeroacoustic performance trends. The findings emphasise the importance of thrust-matched operating conditions for propeller noise assessment, and provide insight into how biomimetic modifications may influence aerodynamic and acoustic performance thereby informing the optimisation of low-noise UAV 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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