Fan Noise Prediction from Local Experimental Source Terms and Numerical Sound Propagation

G2 - Prediction of Axial Fan Noise by Hybrid Methods (ii)

Modeling and numerical approaches are favored ways to investigate the mechanisms of noise generation by fans. Several approaches are conceivable, from the simpler band-octave correlation to the costly and technically challenging aero acoustic computing.
In an industrial context, a mid-way approach, relying on experimental data to define the acoustic source term, and on well known computational method to propagate it, is still of interest.
The paper investigates a fan noise synthesis approach based on the following items:
- The noise source located on the fan blades is defined from experimental data obtained on wing profiles. This source is represented by a distribution of volumetric forces in a volume close to the blades, or by a surface source term.
- The noise is computed by propagating the source either by using analytical laws in an open space, or by using a finite element code to take into account the effects of the surroundings.
The test of the method has shown that the source term adjusted on the Brook-Pope-Marcolini trailing edge noise database was insufficient to represent the noise measured on a four-blades 800 mm fan. The pertinence of some auxiliary source terms liable to fill the gap between the model and the experimental results, as interaction between the tip blade and the volute, leading edge noise, blade-vortex interaction, is then evaluated.