A quasi-potential flow formulation for the prediction of the effect of the circulation on the acoustic shielding from a lifting body by means of a finite element method
University of Southampton - ISVR
Monday 1 june, 2015, 14:40 - 15:00
0.7 Lisbon (47)
This paper presents a new simplified approach for the prediction of the acoustic shielding from lifting bodies by means of a finite element method. It extends a method already validated for aerodynamic applications to Aeroacoustics on the basis of the small perturbation expansion. A numerical model to represent the effect of the circulation developed by a slender body on the noise radiation in an unbounded domain is provided. A quasi-potential flow formulation is adopted by introducing a simplified shear layer model: a frozen wake with finite thickness and extent. The effect of the sound diffraction in the wake region is accounted for by applying the continuity of pressure across the wake line in the aeroacoustic field. An incompressible steady mean flow is considered and the Kutta condition is applied to overcome the singularity at the trailing edge. The circulation in the mean flow is predicted by reducing the potential solution to a single-valued problem. The non- uniform base flow is superimposed on the wave propagation and the linear aeroacoustic problem is solved by means of the full acoustic potential equation. The finite element method is applied both to the solution of the base flow and to the acoustic radiation. The acoustic field scattered by a 2D airfoil from a line source in presence of a non-uniform base flow is predicted as a numerical example of the proposed model. The circulation modifies the extent of the acoustic shielding by altering the wave propagation around the slender body, the wave diffraction at the trailing edge and the refraction in the shear layer.
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