Finite Element Analysis for Acoustic Behavior of a Refrigeration Compressor

When structures in contact with a fluid vibrate there will be an interaction between the two systems. Geometry and motion of structure induce fluid dynamic forces, which in turn alter the structural behavior. A variety of such problems occurs in several engineering applications and is collectively called as Fluid- Structure-Interaction (FSI) problems. Analysis of fluid-structure-interaction problem, assuming fluid to be compressible, is highly useful in the study of acoustic behavior of such structures. Refrigeration compressor is a perfect example of such structure. In refrigeration compressor due to reciprocating motion of piston cylinder mechanism, pressure pulsations occur in acoustic cavity present between the shell and the rigid block which houses the motor and piston-cylinder mechanism. Due to high density associated with the fluids in the cavity, fluid loading on the structure is likely to occur; this will in turn influence the dynamic behavior of the shell. This present work deals with shell-cavity systems of a compressor, comprising fluids like lubricating oil, refrigerant and bubble in between oil and refrigerant. The objective of the present work is to analyze the acoustic behavior of such FSI problems. First, eigenvalue analysis is performed on the structure and fluid separately. Subsequently FSI is defined and eigenvalue problem is solved for the coupled system. Harmonic response analyses have been performed imposing disturbances on the rigid block at different interfaces with oil and refrigerant. Far field acoustic analysis of the compressor is performed and results are analyzed. Validation of this result is done using Boundary Element (BE) Method based software, SYSNOISE. Influence of location of disturbance on sound pressure level (dB) is studied and discussed.

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