10:30
Session 16: Propeller and rotorcraft noise modeling 1
Chair: Ulf Orrenius
10:30
20 mins
|
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.
|
10:50
20 mins
|
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.
|
11:10
20 mins
|
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.
|
|