10:30
Propeller and rotorcraft noise modelling
10:30
20 mins
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On the modelling of a porous strut installed below a UAV propeller
Huachen Zhu, Michael Kingan, Xianghao Kong, Jiangying Liu
Abstract: In small unmanned aerial vehicle (UAV) systems, propellers operating in close proximity to a supporting strut often induce abrupt variations in aerodynamic loading, generating strong impulsive noise. Recent studies have shown that replacing a rigid strut with a porous one can effectively mitigate this interaction noise. This paper proposes a boundary element method (BEM) for predicting the unsteady pressure field around a porous strut located below a propeller. The proposed method models the acoustic propagation within the strut by modelling the porous medium as an equivalent fluid with properties determined using the Delany & Bazley model. This approach avoids the complexity of modelling this problem using a computational fluid dynamics/aeroacoustics (CFD/CAA) technique. The method involves solving two coupled Helmholtz integral equations: one describes the external field, and the other describes the field inside the porous medium. The proposed method was validated through equivalent finite element method (FEM) simulations, and the results show that the pressure fluctuations predicted by the BEM agree well with those obtained from the FEM simulations. This paper presents numerical examples of struts with varying flow resistivity to investigate the impact of flow resistivity on the propeller-strut interaction noise. The results show that the sound pressure level (SPL) around the strut is significantly affected by the flow resistivity of the porous material, and this effect is highly dependent on the frequency. A comparison of predictions made using the method with experimental measurement results is provided to further substantiate the accuracy and reliability of the proposed method.
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10:50
20 mins
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Streamlined numerical prediction of drone urban noise impact
Brendan H.P. Mullen, Pau Varela, Jorge García-Tíscar, Luis Miguel García-Cuevas
Abstract: The innovative aeromobility market is currently experiencing growth in civil and commercial applications. Increasingly, companies are proposing new missions of various sizes, whether manned or unmanned, based on VTOL (Vertical Take-Off and Landing) platforms. This growth has intensified the need for predictive models capable of estimating the acoustic impact on complete missions, as these increasingly take place in urban airspace, at least in some of their phases.
The modelling of aircraft performance and associated noise cannot be restricted solely to stationary or isolated conditions, where variations in speed, power, and configuration that significantly affect the sound signature are ignored. While the computational cost of calculating a complete mission is prohibitive, it is possible to capture the evolution of the acoustic field throughout the different operational phases of an aircraft. This work presents an aeroacoustic model for a complete mission, based on an EASA (European Aviation Safety Agency) Category C2 quadcopter, using trimmed, experimentally validated CFD (computational fluid dynamics) simulations.
URANS simulations are performed using Simcenter STAR-CCM+ calculation software, where the rotors are modelled using the Actuator Disc and Actuator Line Models, thereby reducing computational costs while maintaining fidelity for acoustic predictions. The simulations are coupled with a trimming algorithm based on P-I (Proportional-Integral) control, which determines the rotor attitude angles and angular rotation speeds to ensure that the force and moment equilibrium equations are satisfied, given the boundary conditions. The acoustic model is based on Hanson’s model for steady-state simulations and the Ffowcs Williams-Hawkings (FW-H) permeable formulation for transient cases, capturing the propagation of the noise to a set of receivers distributed on a sphere, as specified in ISO 3745. Then, this noise source is propagated to a 3D model of a selected urban environment through the CNOSSOS-EU methodology, as implemented in the NoiseModelling software package.
Individual simulations are validated through experimental tests in an anechoic chamber, where the isolated drone is placed, and windless propulsion system configurations are accurately reproduced. The comprehensive methodology enables the creation of mission-specific noise maps, which, in turn, facilitate design optimisation and the evaluation of compliance with potential regulatory limits on noise pollution.
Preliminary results demonstrate that integrating trimmed CFD simulations with medium-fidelity aeroacoustic models is a robust tool for predicting acoustic behaviour across a complete mission profile, enabling a balance between computational cost and physical representativeness.
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11:10
20 mins
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Propeller Noise Prediction in Oblique Inflow Conditions
Ole Bergmann
Abstract: The paper systematically reviews the considered inflow models and assesses their influence on thrust prediction and three-dimensional tonal noise radiation under inclined inflow conditions. The results demonstrate a pronounced sensitivity of tonal noise emissions and spatial radiation characteristics to the chosen inflow modelling approach, providing guidance for the selection of accurate yet computationally efficient models for preliminary drone noise prediction.
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11:30
20 mins
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Inverse Modeling of Aeroacoustic Phenomena of a Propellor
Isaac Bensignor, Camillo I. Andino Cappagli, Lourenco Lima Tercio Pereira, Roberto Merino-Martinez
Abstract: This work focuses on assessing the ability to infer relevant rotor performance characteristics from acoustic emissions. As the use of drones in urban and highly-populated environments grows, the identification of such vehicles becomes pertinent to regulators, government, and commercial operators. A suite of explicit statistical methods and machine learning approaches is developed to reconstruct rotor thrust and drag using only the pressure amplitudes of selected blade-passing-frequency (BPF) harmonics extracted from multi-microphone measurements. The approaches were applied to an experimental dataset from a variable-pitch, isolated rotor tested in the Anechoic Wind Tunnel at Delft University of Technology. Thrust and drag were measured with a load cell, and the radiated acoustic field was captured using a directivity microphone arc.
The accuracy and robustness of each method were studied through isolated propeller hover testing. Using the recorded data, the predicted qualities were determined on unseen data, and the variations upon increasing the number of microphones used for the different methods were studied. As different mathematical approaches were employed, the quality of the predictions and the necessary information for each method were quantified upon increasing the model’s complexity.
Overall, these approaches constitute new possible frameworks for determining blade loading characteristics in terms of received acoustic information. These methods would allow for the reconstruction and prediction of thrust and drag during more complex operational conditions from propeller experiments. Furthermore, thorough verification of the method could enable the prediction of loading information from whole flight vehicles, providing ground-based performance information during flight tests.
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11:50
20 mins
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What to expect from limited-fidelity drone simulations: a noise perspective
Federico N. Ramírez, Jorge García-Tíscar, Roberto Navarro, Luis Miguel García-Cuevas
Abstract: Acoustic annoyance is one of the main barriers that may hinder the growth of unmanned aerial vehicles usage in urban areas. Employing reliable noise prediction tools during the early stages of drone design would overcome this issue. However, acoustic simulations for multicopter configurations span a wide range of modeling fidelities, and their respective accuracy–cost trade-offs are still not clearly understood by the community. This work provides a noise-oriented assessment of widely-used simulation methods for multicopter drones, with a particular focus on their predictive capabilities and inherent limitations.
We compare popular aerodynamic models for multirotor simulations, including Blade Element Momentum Theory (BEMT); Vortex Particle Method (VPM); and Finite Volume Method (FVM) with different turbulence formulations. These aerodynamic solvers are coupled with established aeroacoustic analogies, notably the Hanson model for tonal noise prediction and the Ffowcs Williams–Hawkings (FW-H) formulation for calculating far-field noise spectra.
Numerical predictions are compared against experimental measurements obtained in an anechoic chamber and in a low-turbulence wind tunnel, covering several flight conditions. Metrics of comparison include aerodynamic forces, aircraft performance indicators, overall sound pressure levels, spectral content and directivity patterns. Based on these findings, practical guidelines are proposed to help designers and researchers select appropriate simulation tools depending on the design phase, available resources, and acoustic metrics of interest.
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12:10
20 mins
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Stator noise reduction technologies for quieter and more efficient drone propulsion
Matthew Mulcahy, Craig Gillespie, John Kennedy, Gareth Bennett
Abstract: While Advanced Air Mobility promises improved accessibility, transport efficiency and lower emissions, its societal acceptance is challenged by persistent concerns about noise pollution [1]. This research proposes the implementation of a stator in an Urban Air Mobility (UAM) vehicle to provide additional lift and minimise downwash swirl. For small drones, propellors are typically single stage and unducted, whereas the extra power available with larger vehicles such as VTOL “Air Taxis” for UAM, allows additional weight to be accommodated if justified. The current work investigates if recent research advances in open-rotor aircraft aeroengines might be translated to UAM Vehicles. While not eliminating downwash, the swirl reduction provided by the stator results in improved aerodynamic efficiency which may result in reduced fuel consumption.
Despite the benefits of stators, their adoption in open-rotor configurations has been limited by the annoying tonal noise generated through rotor-stator interaction [2, 3]. Although stators play a central role in producing interaction tones, noise‑reduction strategies for them remain underexplored. However, recent numerical and experimental studies have shown that leading-edge treatments can weaken unsteady loading and reduce interaction noise [4-7], yet their application to open-rotor and drone configurations has not been experimentally validated.
This work investigates advanced stator noise‑reduction concepts, including leading‑edge slits and serrations [7], lattice‑structured porous inserts, and multi‑chamber micro‑perforated panel absorbers inspired by the EU’s INVENTOR programme. A scaled rotor–stator assembly derived from NASA’s OR-ANCF geometry [8] has been manufactured using high‑resolution stereolithography to integrate sub‑millimetre lattice features.
Experiments conducted at Trinity College Dublin employ a four‑microphone far‑field array and dual thrust measurement; the modular stator architecture allows rapid interchangeability of treatments, enabling systematic assessment of the noise reductions and their associated aerodynamic penalties. The ongoing laboratory campaign will quantify the relative performance of each treatment type and identify the mechanisms by which leading‑edge and porous stator modifications weaken rotor‑wake impingement. These results will provide the first experimental evidence of their effectiveness in an open‑rotor context and form a foundation for future scaling in UAM vehicles and validation at higher TRL levels.
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