11:10
Noise propagation and low-noise route planning
11:10
20 mins
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Incorporation of Ambient Sound Levels into UAS Flight Path Optimisation
Nathan Green, Carlos Ramos-Romero, Antonio T Martinez
Abstract: Research on the environmental noise impacts of unmanned aircraft systems (UAS) remains limited, and their effects within cities and urban areas are not yet fully understood. This study investigates how existing ambient sound levels can be incorporated into the calculation of UAS flight paths with the specific objective of reducing observable sound exposure at street level. Three approaches to flight-path optimisation are compared. The first approach incentivises routing over areas predicted to have relatively high broadband ambient noise levels, derived from Strategic Noise Mapping. The second compares the broadband ambient sound levels with the predicted broadband sound level of a UAS in flight. The third incorporates both ambient and predicted UAS sound levels but additionally examines their spectral content to calculate a detectability likelihood factor (d’).
All methods were implemented in Geospatial Information Systems (GIS) software to generate friction layers for least-cost path analysis, enabling the identification of “optimum” routes. Although this research does not propose a single preferred methodology, it highlights key differences among the resulting flight paths, explains where and why deviations occur, and illustrates how these outcomes depend on the initial input parameters. The findings also raise important questions regarding future methodologies for assessing the environmental noise impacts of UAS operations and decision making for route optimisation.
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11:30
20 mins
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From aeromechanics to auralization – a comprehensive analysis model of a novel eVTOL concept
Daniel Eble, Daniel Redmann, Michael W. Bauer, Julia V. Lippold, Susanne Bartels
Abstract: A comprehensive aeroacoustics model was implemented to predict and auralize propeller noise of a novel generic tilt-rotor concept design. The eVTOL has six rotors, two of which are tilted forward in airplane mode, with additional lift generated by a wing-canard configuration.
The aeroacoustics toolchain was developed in-house and has been demonstrated to provide reliable predictions in both near- and far-field conditions. Validation was performed against wind-tunnel measurements, including the HART-II database, as well as partly self-conducted full-scale flight tests and noise certification data from a wide range of Leonardo helicopters, encompassing conventional configurations as well as the AW609 tiltrotor. Across these validation cases, simulations showed good agreement with measured noise. The modular in-house software covers multiple fidelity levels, including six-degree-of-freedom free-flight trim, a state-of-the-art vortex particle wake method for aerodynamics, and the Farassat 1A formulation of the FW-H equations for tonal noise prediction. Broadband noise is mostly estimated using semi-empirical models based on the aerodynamic simulation outputs.
Within the publicly funded research project PAULA, the focus of this work was the generation of audio files for the tilt-rotor concept during two transient flight maneuvers – take-off and approach – evaluated at multiple ground-based microphone locations in an extended vertiport environment. These data were used by the project partner DLR to assess the potential impact of air-taxi noise in laboratory listening tests. As a first step, a feasible trim and control strategy was developed, enabling take-off in helicopter mode with all six rotors providing lift, followed by a gradual transition to airplane mode with only the two center rotors spinning and delivering forward thrust. Using the take-off trajectory made available by the associated partner Lilium the aeromechanical simulations supplied all inputs required for the MUAA semi-empirical noise prediction tool that was used within PAULA to create the sound files. These results included tilt angle of the center rotors as well as rpm, power required, thrust and mean lift coefficient for all six rotors.
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11:50
20 mins
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Combined drone and road-traffic noise modelling for dynamic exposure assessment in cities
Sacha Baclet, Ulf Tengzelius, Ulf Orrenius, Romain Rumpler
Abstract: Urban noise exposure assessment is generally performed with static sources and long-term average indicators such as Lden or LAeq. This approach is poorly suited to both emerging urban air mobility and road traffic. Indeed, drone operations are intermittent, highly route-dependent, and temporally concentrated, while road traffic noise varies strongly on short time scales, due to the dynamics of individual vehicles. This contribution introduces a methodology to model dynamic population noise exposure in urban environments which merges drone noise and road traffic noise in a unified simulation framework.
In this novel methodology, road traffic is modelled using a microscopic traffic simulation, producing vehicle trajectories, speeds, and accelerations at fine temporal resolution (1 second). Using the CNOSSOS-EU noise emission and propagation models, the resulting noise levels are simulated dynamically at receiver locations. Drone operations are modelled as moving aerial sources with specified flight trajectories and characteristics (altitude, speed, operational phases), generating time-varying sound levels which are also propagated to ground receivers. The two contributions are energetically summed to produce exposure time series and derived indicators (e.g., short-term LAeq, noise events, exceedance), enabling comparisons between scenarios that include or exclude drones.
The methodology is then applied to a Swedish test case, in the city of Stockholm, showing its feasibility, and revealing early results on the interactions between drone overflights and traffic noise, depending on the time of day.
By enabling scenario testing, the proposed methodology will enable the optimisation of drone route and scheduling, linking drone operation to population exposure while including the contribution of road traffic. More elaborate scenarios will be studied in the future.
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12:10
20 mins
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Flight Test Characterization of Multirotor Aircraft Noise Variability
Joel Sundar Rachaprolu, Eric Greenwood
Abstract: This paper presents an analysis characterizing the measured directivity and variability of noise radiated by a multirotor Uncrewed Aerial System (UAS). A flight test campaign was conducted using a hexacopter at Midstate Regional Airport near Penn State University. The ground-based microphone array layout consisted of 17 inverted ground-plane microphones and 3 elevated microphones. The hexacopter was instrumented with encoded motors to measure rotor phase and angular speed, and with real-time kinematic GPS to measure position and attitude.
The analysis is conducted for several steady-state and transient flight conditions, including hover, forward flight, ascent, descent, and approach and turn maneuvers. For the steady-state conditions, the directivity of the radiated noise is characterized for the overall aircraft as well as for individual rotor tonal and broadband components. A Vold-Kalman based source separation approach is implemented to separate and characterize tonal noise sources on a rotor-to-rotor basis. The time- and frequency- domain features along with the spatial variations of the radiated noise for all these noise sources are characterized. The acoustic analysis is done in conjunction with the time-synchronized aircraft states such as flight path and orientation. This is to examine the aircraft noise characteristics with the variations in the aircraft states, and the results shows that the directivity of radiated noise in forward flight is dominated by the tonal component.
The inherent variability of UAS noise due to the variable-RPM flight control strategies is also investigated. The flight test campaign consists of repeated measurements for various operating conditions, measured on the same test days with similar weather conditions and within hours of each other. The results show that the noise variability is strongly influenced by the variations in aircraft orientation and rotor states. The analysis shows that the variability in the tonal components is dependent on the rotor speeds, but broadband noise exhibits less dependence on rotor speed and more sensitivity to ambient wind conditions. These results provide new insight into the directivity and variability of multirotor UAS noise sources.
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