ANALYSIS OF VIBRO-ACOUSTIC PROPAGATION IN A MOBILE SCREW COMPRESSOR FOR THE DETERMINATION OF EMITTED ACOUSTIC POWER RADIATED OUTSIDE ITS HOUSING

Abstract eng:
The method for a numerical solution of the vibro-acoustic problem in a mobile screw compressor is proposed and in-house 3D finite element (FE) solver is developed. In order to reduce the complexity of the problem, attention is paid to the numerical solution of the acoustic pressure field in the compressor cavity interacting with the linear elastic compressor housing. Propagation of acoustic pressure in the cavity is mathematically described by the Helmholtz equation in the amplitude form and is induced by periodically varying surface velocity of the engine and compressor assembly. In accordance with prescribed boundary conditions, numerical solution of the Helmholtz equation for the distribution of acoustic pressure amplitudes within the cavity is performed using the finite element method on tetrahedral meshes. For the FE discretisation of the elastic compressor housing, a new 6-noded thin flat shell triangular finite element with 21 DOF based on the Kirchhoff plate theory was developed and implemented. The resulting strong coupled system of linear algebraic equations describing the vibro-acoustic problem, i.e., the problem of interaction between the air inside the cavity and the screw compressor housing, is solved numerically by well-known algorithms implemented in MATLAB. By considering two different benchmark test cases, the developed 3D FE solver is successfully verified against the numerical results provided by the professional computational FE system Radioss. Finally, the vibro-acoustic problem is solved in a simplified model of a real mobile screw compressor by prescribing experimentally measured acoustic velocity on the surface of the engine and compressor assembly. The numerical solution is carried out only with the professional computational FE system Radioss as our developed solver is still unable to process large-sized problems without encountering memory limits. Thus, for the assessment of results computed by Radioss, we use results acquired during experimental measurements on a real mobile screw compressor under operating conditions.

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