Closed-form analytical approach for calculating noise contours of directive aircraft noise sources

Abstract

This paper comes as an update to the simplified airport noise model RANE (Rapid Aviation Noise Evaluator) adding capability of including fully non-isotropic noise sources. RANE v2 is developed as a part of multidisciplinary acoustic assessment of novel aircraft, namely, for vehicles within the Urban Air Mobility sector, in order to produce ground contours around airports and helipads. The model uses three-dimensional noise exposure surfaces around a series of discretised segments that represent the aircraft flightpath. The main inputs are the Noise Radius a function of the sources’ Sound Power Level (PWL) which come in the form of Noise-Power-Distance curves, and the source three-dimensional directivity. The directivity function may take analytical or numerical form, allowing for experimental data inputs. This paper demonstrates the use of Spherical Harmonics as a form of directivity function with a closed-form analytical proof for calculating the noise exposure contours. Preliminary results and comparison against the FAA’s AEDT module for Helicopter Community Noise indicate that exposure contour coordinates may be estimated with little uncertainty. The incorporation of source directivity allows for the assessment of lateral attenuation, engine installation effects and transition operations (for vertical to horizontal flight and vice versa) via the assumption of individual source directivities and therefore complex noise surfaces. As a consequence of the analytical nature of the model, low computational requirements allows for fast exploration of the design space and parametric studies, with minimal input requirements. RANE v2 is currently being used to assess ground noise of two novel aircraft concepts; 1. a fixed wing fully electric General Aviation aircraft and 2. a Vertical Take-off and Landing (VTOL) enabled rotorcraft.