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Research Papers: Flows in Complex Systems

A Dimensionless Scaling Parameter for Thermal Effects on Cavitation in Turbopump Inducers

[+] Author and Article Information
Daniel A. Ehrlich

The Aerospace Corporation,
Los Angeles, CA 90009-2957
e-mail: daniel.ehrlich@spacex.com

John W. Murdock

The Aerospace Corporation,
P.O. Box 92957—M4/967,
Los Angeles, CA 90009-2957
e-mail: john.w.murdock@aero.org

1Present address: Space Exploration Technologies, 1 Rocket Road, Hawthorne, CA 90250.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received December 6, 2013; final manuscript received November 23, 2014; published online January 13, 2015. Assoc. Editor: Satoshi Watanabe.

J. Fluids Eng 137(4), 041103 (Apr 01, 2015) (8 pages) Paper No: FE-13-1707; doi: 10.1115/1.4029260 History: Received December 06, 2013; Revised November 23, 2014; Online January 13, 2015

To characterize cryogenic pump performance, at least one parameter in addition to flow coefficient and cavitation number is required. This parameter arises because the heat of vaporization and other physical parameters change along the saturation line of liquids and results in a thermal effect on cavitation that has been observed and studied by previous researchers over a range of operating conditions and working fluids. These previous efforts have defined both dimensionless and dimensional parameters governing thermal effects in pumps. In the present work, a dimensionless parameter (DB) scaling thermal effects in a cavitating pump across different tip diameters, rotational speeds, and working fluids is derived using a model of bubble growth in a time-varying pressure field. Although the derivation is somewhat different than others have used, the result is similar and in some cases identical to that of others. Careful testing is carried out to experimentally validate this parameter with (deaerated) variable temperature water and with variable pump speed. The results show that within the accuracy of the data, the same head fall-off curve is obtained when either the water temperature or the pump speed is used to set the DBs. This suggests the proposed parameter can thermally scale cryogenic pumping conditions for suction performance when testing in hot water. Also examined is the effect of thermodynamics on inducer cavitation instabilities. The quasi-steady, dynamic environments at the pump inlet are compared in cold and superheated water. The cavitation instabilities of the test inducer are found to be dramatically changed by thermal effects. These findings emphasize the importance of considering both fluid mechanical and thermal scaling when designing a test program to evaluate the suction performance of a cryogenic pump.

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References

Figures

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Fig. 1

Variation of DB parameter for a 75 mm diameter inducer operating in water over a typical test facility operating range

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Fig. 2

Photo of The Aerospace Corporation's turbopump cavitation test facility

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Fig. 3

BNI test inducer installed in pump

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Fig. 4

Single phase pumping performance of the BNI inducer in cold water

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Fig. 5

Mean suction performance of the BNI inducer in cold water

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Fig. 6

Inducer flowfield images at ϕ = ϕdesign for a series of cavitation numbers (σ)

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Fig. 7

Thermal-effects test matrix (ϕ = ϕdesign, N = 4300 rpm)

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Fig. 8

Mean suction performance comparison for the thermal effects test matrix (ϕ = ϕdesign, N = 4300 rpm)

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Fig. 9

Dimensionless thermal effects scaling parameter validation test matrix

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Fig. 10

Mean suction performance comparison for DB validation test matrix

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Fig. 11

Dynamic pressure spectrogram from leading edge tip transducer (D plane) in cold water

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Fig. 12

Dynamic pressure power spectral density (PSD) from leading edge tip transducer (D plane) in cold water, t = 232 s, σ = 0.063

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Fig. 13

Dynamic pressure spectrogram from leading edge tip transducer (D plane) in hot water

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Fig. 14

Dynamic pressure PSD from leading edge tip transducer (D plane) in hot water, t = 274 s, σ = 0.063

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