Numerical Prediction of the Radiated Noise of Hermetic Compressors Under the Simultaneous Presence of Different Noise Sources

The prediction of the acoustic radiation of the compressor shell is resulting from a numerical vibro-acoustic model, involving the description of the compressor pump structure, compressor gas cavity and compressor shell structure, through the use of the FEM and BEM techniques. The presence of refrigerant and lubricating oil in the compressor cavity were taken into account, as well as the presence of external mounting grommets, as stiffness and damping, was considered. The model response was predicted under the simultaneous presence of different noise sources. Structural path: Unbalance forces and forces generated by compression cycle. Gas cavity path: Suction noise and cylinder head radiation. Noise sources were previously experimentally determined and then introduced in the model, so that phase relationships between different sources were taken into account in the prediction of the radiated noise. Due to the interaction between compressor body _,. cavity _,. shell structure, the model response was studied, considering a coupling between cavity and structure. Finally, the VIbration velocity field on the shell, was the boundary condition in a BEM model for the study of the external radiation. Pressure fields in free field condition, due to the simultaneous presence of the internal noise sources, as well as the contribution of each noise source, were the output of the model. Correlations of the model with measurements is quite good, especially for the frequency range controlled by structural noise sources. A model refinement was necessary, to take into account the structural damping physically present in the compressor. In this case, a modal damping factor was introduced based on experimental determination. Considering the frequency range of the radiated sound pressure, controlled by the gas cavity noise sources, the correlation with experimental measurements is not as good as expected. Generally, in this case, the prediction is higher than measurements, and was not feasible to find a model for the gas cavity damping factor as a function of frequency. Further investigations in this direction are still in course. The model was used for the prediction of the radiated noise of a new shell shape design, as well as of new compressor parts, having impact on the noise source modification. Correlation with the available data is shown in the paper.