Prediction of generator set noise in the far field using panel contribution analysis and scale modeling

Noise standards often call for the measurement of sound pressure level several meters away from a source. Measurements are typically performed in a large anechoic chamber or on a test pad weather permitting. This paper suggests an approach that can be used to predict the sound pressure level without the need for a large anechoic environment. Panel contribution analysis is used with a scale model employed when determining transfer functions. The machinery surface is first divided into patches. Transfer functions between the volume velocity of each patch and the sound pressure at a receiver are measured reciprocally using a scale model. The volume velocity of each patch is measured using a P-U probe. The contribution from a single patch can be determined by multiplying the patch volume velocity with its respective transfer function. The sound pressure level at the receiver point is then found by summing up all the contributions. Contributions can be summed taking into account the phasing between sources or neglecting it. The method was applied to a generator set and the sound pressure level was predicted at a point 4.9 m away. Predicted results compare reasonably well with direct measurement.