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

Regular paper

University of Southampton - ISVR

Monday 1 june, 2015, 14:40 - 15:00

0.7 Lisbon (47)

Abstract:

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.