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Research Papers: Multiphase Flows

A Review of the Dynamics of Cavitating Pumps

[+] Author and Article Information
Christopher Earls Brennen

Hayman Professor of Mechanical Engineering
Emeritus,
California Institute of Technology,
Pasadena, CA 91125

Manuscript received March 26, 2012; final manuscript received November 30, 2012; published online April 8, 2013. Assoc. Editor: Olivier Coutier-Delgosha.

J. Fluids Eng 135(6), 061301 (Apr 08, 2013) (11 pages) Paper No: FE-12-1153; doi: 10.1115/1.4023663 History: Received March 26, 2012; Revised November 30, 2012

This paper presents a review of some of the recent developments in our understanding of the dynamics and instabilities caused by cavitation in pumps. Focus is placed on presently available data for the transfer functions for cavitating pumps and inducers, particularly on the compliance and mass flow gain factor, which are so critical for pump and system stability. The resonant frequency for cavitating pumps is introduced and contexted. Finally, emphasis is placed on the paucity of our understanding of pump dynamics when the device or system is subjected to global oscillation.

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Figures

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Fig. 1

Scale model of the low pressure liquid oxygen pump impeller for the space shuttle main engine (SSME) in moderate cavitating conditions in water

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Fig. 2

Left: Typical transfer functions for a cavitating inducer obtained by Brennen et al. [2] for the 10.2-cm-diameter SSME inducer operating in water at 6000 rpm and a flow coefficient of φ1=0.07. Data is shown for four different cavitation numbers, σ= (A) 0.37, (C) 0.10, (D) 0.069, (G) 0.052, and (H) 0.044. Real and imaginary parts are denoted by the solid and dashed lines, respectively. The quasistatic pump resistance is indicated by the arrow. Right: Polynomial curves fitted to the data on the left. Adapted from Brennen et al. [2].

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Fig. 3

Dimensionless cavitation compliance (left) and mass flow gain factor (right) plotted against tip cavitation number for: (a) Brennen et al. [2] SSME 10.2-cm model inducer in water (solid squares); (b) Brennen et al. [2] SSME 7.6-cm model inducer in water (open squares); (c) Brennen and Acosta [11] J2-Oxidizer (circles) analysis; (d) Hori and Brennen [13] LE-7A LOX data (solid triangles); (e) Shimura [12] LE-7 LN2 data (open triangles)

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Fig. 4

Left: Nondimensional cavitation surge frequency as a function of cavitation number for the SSME model inducers at various speeds and flow coefficients, as shown. The theoretical prediction is the dashed line, (5σ)1/2 (adapted from [18]). Right: A dynamic model of the main flow and the parallel tip clearance backflow in a cavitating inducer.

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Fig. 5

Nondimensional time lags for the compliance, τC, and the mass flow gain factor, τM, as functions of the cavitation number for the SSME 10.2-cm model inducer in water. Taken from the data of Brennen et al. [2].

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Fig. 6

Real and imaginary parts of the dimensionless compliance (per bubble) of a stream of cavitating bubbles as functions of a reduced frequency based on the length of the cavitation zone, Ls, and its typical velocity, Us. Results shown for several cavitation numbers, σ, and bubble nuclei size, rN (from Ref. [23]).

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Fig. 7

Left: Schematic of the bubbly flow model for the dynamics of cavitating pumps. Right: Transfer functions for the SSME inducer at φ1=0.07 calculated from the bubbly flow model (adapted from Ref. [27]).

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Fig. 8

Dimensionless cavitation compliance (left) and mass flow gain factor (right) plotted against tip cavitation number for: (a) Brennen et al. [2] SSME 10.2-cm model inducer in water (solid squares); (b) Brennen et al. [2] SSME 7.6-cm model inducer in water (open squares); (c) Brennen [27] bubbly flow model results (short dash lines); (d) Brennen and Acosta [11] SSME low pressure oxidizer turbopump blade cavitation prediction (dot dash line); (e) Brennen and Acosta [11] J2-Oxidizer data (circles); (f) Brennen and Acosta [11] J2-Oxidizer blade cavitation prediction (long dash line); (g) Yonezawa et al. [28] quasistatic CFD cascade data (diamonds)

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Fig. 9

The four hydraulic system configurations whose dynamic responses are compared (reproduced from Ref. [13])

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Fig. 10

Model calculations (upper graphs) and test facility measurements (lower graphs) of the pump inlet pressure (left) and the inducer discharge pressure (right) from the cold test facility without an accumulator, the first configuration (reproduced from Ref. [13])

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Fig. 11

Model calculations (upper graphs) and test facility measurements (lower graphs) of the pump inlet pressure (left) and the inducer discharge pressure (right) from the cold test facility with an accumulator, the second configuration (reproduced from Ref. [13])

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Fig. 12

Model calculations (upper graphs) and test facility measurements (lower graphs) of the pump inlet pressure (left) and the inducer discharge pressure (right) from the hot-firing engine test, the third configuration (reproduced from Ref. [13])

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Fig. 13

Model calculations for the flight configuration subject to global acceleration. Upper graphs: in the absence of pump cavitation. Lower graphs: when the pump cavitation number is σ=0.02. Pressure amplitudes (left) and flow rate amplitudes (right) over a wide range of different oscillation frequencies and an oscillating acceleration magnitude of 0.1 m/s2. Solid, dashed, and dotted lines, respectively, present the pump discharge, inducer inlet, and tank outlet quantities (reproduced from Ref. [13]).

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