Prediction of the Noise Radiation of Hermetic Compressors Utilizing the Compressor Simulation Program and FEMIBEM Analyses

The complexity arising from the interactions between the pulsating flow, gas cavity and shell structure has been the major obstacle in realizing the prediction of the radiated sound level of heiiDetic compressors by a numerical simulation. In this work, a numerical procedure combining a computer simulation program of the compressor process and the Finite Element Method (FEM)/Boundary Element Method (BEM) techniques is used to demonstrate the feasibility of such predictions. The simulation program is used to calculate the unsteady flow inputs to the inside shell cavity of the compressor. A FE.M/BEM approach is used to calculate the resulting shell motion and the radiated sound field. INTRODUCTION Shell cavity gas pulsation has been recognized as a major contributor to the total noise level of hermetic compressors [ 1]. Therefore, numerical prediction of the noise radiation from the hermetic compressor shell resulting from the gas pulsation inside its cavity has been desired for a long time. Numerous works based on analytic and numerical [2, 3] or experimental [ 1, 4] approaches can be found related to this task. However, no complete numerical simulation of the radiated noise of a hermetic compressor starting from its source mechanism has been reported. If the radiated noise induced by the pulsating flow in the shell cavity can be estimated with reasonable accuracy by a purely numerical method, it would be very useful for compressor designers. For example, it will allow a truly optimal suction muffler to be designed because it can be designed based on concrete data, not by a guesswork. Currently all necessary tools required for such a simulation are available. For example, four pole theories to be applied to three dimensional systems [2], FEM/BEM analysis software and compressor simulation programs are all available. Therefore, major obstacles related to this task are considered as the lack of a systematic procedure because of the complexity of the problem. It is the purpose of this paper to demonstrate that a numerical estimation of the shell noise radiation by fully considering all interaction aspects is feasible. In this work, a compressor simulation program is utilized to calculate the spectrum of the pulsating :tlow in the shell cavity at the suction muffler inlet of a low side reciprocating compressor. Then, the four pole method is applied to calculate the pulsating flow induced at the suction return pipe point according to the procedure developed in Reference [2]. Pressure response functions which are necessary to calculate the four poles are obtained by a BEM analysis. The natural modes of the shell are calculated by a FEM analysis and imported to the BEM model. Finally, the noise level radiated to the external free field is calculated by a BEM analysis. The geometry of the compressor used in this study was somewhat simplified, however, retaining most of its important characteristics. The results demonstrate that it is certainly possible to evaluate the sound radiation of hennetic compressors by a purely numerical simulation procedure.