Research Papers

Acousto-Elastic Interactions in High-Pressure CO2 Centrifugal Compressors

[+] Author and Article Information
Jithin Jith

Department of Applied Mechanics,
Indian Institute of Technology Madras,
Chennai 600 036, India

Sunetra Sarkar

Department of Aerospace Engineering,
Indian Institute of Technology Madras,
Chennai 600 036, India
e-mail: sunetra@iitm.ac.in

1Corresponding author.

Contributed by the Noise Control and Acoustics Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received March 15, 2017; final manuscript received May 17, 2017; published online August 2, 2017. Assoc. Editor: Ronald N. Miles.

J. Vib. Acoust 139(6), 061013 (Aug 02, 2017) (10 pages) Paper No: VIB-17-1105; doi: 10.1115/1.4036931 History: Received March 15, 2017; Revised May 17, 2017

Accurate determination of acousto-elastic natural frequencies in centrifugal compressors is important in order to avoid resonance events that may lead to machine failure. Compressors operating with CO2 at high pressures, especially near its transition to supercritical state, deal with a wide variation in density and speed of sound. Natural frequency behavior under these conditions is studied here. A finite element method (FEM) based coupled acousto-elastic solver has been developed to study the modal coupling and interactions between the impeller and the side-cavity modes for an idealized compressor geometry. Pressure in the side-cavities is increased up to a very high value of 20 MPa and existence of fluid- and structure-dominant acousto-elastic modes is observed. The variation of the natural frequencies of these modes with pressure exhibits contrasting trends as CO2 transitions from gaseous to supercritical state.

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Fig. 1

Variation of the density (left) and speed of sound (right) of CO2, predicted by various equations of state, as the pressure increases from 0.1 MPa to 20 MPa at a temperature of 55 °C

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Fig. 2

Sketch of the two-dimensional cross section (left) and top view (right) of the compressor geometry. Impeller is shown in gray.

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Fig. 3

Meshes used for solving the individual eigenproblems of (a) impeller disk and (b) side-cavities

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Fig. 4

Modeshapes of (a) z-displacement of the impeller disk and pressure of (b) out-of-phase and (c) in-phase side-cavity modes. Modes are numbered (0, 0), (1, 0), (2, 0), and (3, 0) clockwise from top left.

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Fig. 5

Coupling matrix entries for (a) the (2, 0) impeller mode (for each fluid mode number, black bars represent coupling with the out-of-phase mode and gray bars with the in-phase mode) and (b) the (2, 0) out-of-phase side-cavity mode

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Fig. 7

Variation of the ratio of acoustic energy (Ef) to structural energy (Es) of the coupled (a) structure-dominant modes and (b) fluid-dominant modes with pressure

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Fig. 8

Change in pressure modeshape of the (a) (2, 0) and (b) (3, 0) fluid-dominant out-of-phase mode as side-cavity pressure varies. The pressures are 1 MPa, 7 MPa, 14 MPa, and 20 MPa clockwise from top left.




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