Numerical Characterisation of the Aeroacoustic Signature of Propeller Arrays for Distributed Electric Propulsion

Abstract

This paper presents an investigation of the aerodynamic and aeroacoustic interaction of propellers for distributed electric propulsion applications. The rationale underlying the research is related to the key role that aeroacoustics plays in the establishment of the future commercial aviation scenario. The sustainable development of airborne transportation system is currently constrained by community noise, which limits the operations of existing airports and prevents the building of new ones. In addition, the substantial saturation of the existing noise abatement technologies inhibits the further development of the existing fleet, and imposes the adoption of disruptive configurations in terms of airframe layout and propulsion technology. Simulation-based data may help in clarifying many aspects related to the acoustic impact of such innovative concepts. Blended-wing-body equipped with distributed electric propulsion is one of the most promising, due to the beneficial effect of the substantial shielding induced by its geometry. Nevertheless, the novelty of the layout requires a thorough investigation of specific aspect for which no previous experience is available. Herein, the interaction between propellers is analysed for a fixed propeller geometry, as a function of their mutual distance and compared to the acoustic pattern of the isolated one. The aerodynamic results have been obtained using a boundary integral formulation for unsteady, incompressible, potential flows which accounts for the interaction between free wakes and propellers. For the aeroacoustic analyses, the Farassat 1A boundary integral formulation for the solution of the Ffowcs Williams and Hawkings equation has been used. These results provide an insight into the minimum distance between propellers to avoid aerodynamic/aeroacoustic interaction effects, which is an important starting point for the development of distributed propulsion systems.

A Computational Study on the Aeroacoustics of a Multi-Rotor Unmanned Aerial System

“…In addition, a new peak at BPF/2 appears. The appearance of this peak agrees with the findings Bernardnini [36] reported to the literature. The case with four-propellers also experiences 4-5 dB noise increase at BPF and a smaller level of increase in other tonal harmonics, except BPF/2, in which a 6-7 dB growth may be observed.…”

“…Additionally, tilting the propellers shifts the location of maximum SPL downstream. Increasing the number of propellers to four, leads to a significant growth in noises at high-frequency or broadband noise [22], in addition to manifestation of a low-frequency disturbance, which is not present in the isolated propeller noise spectra [36]. When the spacing between the tip of the adjacent propellers in a quadrotor is small, the level of fluctuations they impose on each other's loads becomes significant [35].…”

Noise of Future Aircraft Propulsion: Sources and Design Considerations

“…However, results are questionable since the work focused more on aerodynamics for takeoff distance reduction and only a low fidelity semiempirical model was used for noise assessment. Bernardini et al (2020) have studied the effect of interaction between rotors of a distributed propulsion array. Par ticularly, the distance between consecutive rotors, with specific geometry and a radius of 1.48 meters, was considered.…”

“…However, the positioning of the propellers must be carefully designed. A tiptotip distance, L, smaller than the quarter of the propeller diameter, (0.25D), may produces more aerodynamic interactions and thus noise (Bernardini et al, 2020). The directivity of noise will also be affected, emitting stronger towards the front direction.…”

Sound-Quality-Based Decision Making in Multiobjective Optimisation of Operations for Sustainable Airport Scenarios

“…Since the Multi Objective Optimisation (MOP) solution is composed of a set of non-dominated points, the sound quality assessment is applied to select the optimal trajectories. The aircraft operations have been optimised within the in-house Multidisciplinary Conceptual Robust Design Optimisation (MCRDO) framework FRIDA (Framework for Innovative Design in Aeronautics [12,15,16,18,[20][21][22]). The two objectives to be minimised are the Sound Exposure Level (SEL) 60 dBA contour area and the amount of fuel burnt during the entire airport operation.…”