Wind Energy

50
Prediction of Wind Turbine Noise Generation
and Propagation based on an Acoustic Analogy
Drago¸s Moroianu and Laszlo Fuchs
The acoustical field behind a complete three dimensional wind turbine is considered
numerically. Noise generated by the spatial velocity variation, force
exerted by the blade on the fluid, and blade acceleration is taken into account.
The sources are extracted from a detailed, instantaneous flow field
which is computed using Large Eddy Simulations (LES). The propagation of
the sound is calculated involving an acoustic analogy developed by Ffowcs
Williams and Hawkings. It is found that the near field is dominated by the
blade passage frequency. The results, also include ground effects (sound wave
reflections) and the acoustical influence of a neighboring turbine.
50.1 Introduction
A very popular approach for aeroacoustic computations nowadays is a hybrid
method comprising two steps: a flow solution is providing the noise sources,
and then the acoustic waves generated by the noise sources are transported
through the whole computational domain [1]. In this paper, an LES solution
of an incompressible flow is used to extract the noise sources, and the
Ffowcs-Williams and Hawkings acoustic analogy is used to compute the noise
propagation.
50.2 Problem Definition
A three blade complete wind turbine, rotating with the angular speed of
60[rpm] in a wind of 10[m/s] is considered. The geometry is described in
Fig. 50.1.
The boundary conditions used for this geometry are the following: inflow
boundary condition on face abcd - normal velocity with a magnitude of
10 [m/s] and a turbulence intensity of I = 4% is imposed, outflow boundary