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Experimental study of unsteady hydrodynamic force matrices on whirling centrifugal pump impellers

Jery, Belgacem (1987) Experimental study of unsteady hydrodynamic force matrices on whirling centrifugal pump impellers. California Institute of Technology , Pasadena, CA. (Unpublished)

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An experimental facility was constructed and instrumented. A study was conducted on a set of centrifugal flow pumps whose impellers were made to follow a controlled circular whirl motion. The aim was to characterize the steady and unsteady fluid forces measured on the impeller under various pump operating conditions. The postulation was that the unsteady lateral forces result from interactions between the impeller and the surrounding diffuser and or volute (via the working fluid), and that under certain flow regimes these forces can drive unstable lateral motions of the pump rotor. The lateral hydrodynamic forces were decomposed into their steady and unsteady parts, the latter being further expressed in terms of a generalized fluid stiffness matrix. A study of this matrix as a function of the whirl to pump speed ratio supported the following chief conclusions: i) the common assumption of matrix skew-symmetry is justified; ii) the magnitudes and signs of the matrix elements are such that rotor whirl can indeed be caused by the hydrodynamic forces, in pumps operated well above their first critical speed, iii) as expected, the matrix is very sensitive to the value of the flow coefficient, especially at flow rates below the design; iv) the commonly postulated quadratic variation of the matrix elements with the reduced whirl frequency, resulting in the so-called rotordynamic coefficients (stiffness, damping and inertia) is not justified for flow coefficients significantly below design; and v) surprisingly, it was discovered that the presence, number and orientation of diffuser guide vanes have little effect on the forces. Conclusions regarding the effect of impeller geometry could not be reached given the similarity of the tested designs. However, other results on phenomena such as skin friction and leakage flow are presented. Some of the findings are compared to experimental and theoretical data from other sources. Finally, the rotordynamic consequences of the results are discussed as the present data were applied by another author to the case of the Space Shuttle Main Engine's (SSME) High Pressure Oxidizer Turbopump (HPOTP).

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Additional Information:Report No. 200.22 on Contract NAS 8-33108. I would like to express my deepest thanks to my advisors, Professors Christopher Brennen, Allan Acosta and Thomas Caughey. Not only did they provide me with the best technical assistance but they also expressed friendship and genuine concern for my welfare during the years of my education. The help of several other people was instrumental in the success of various phases of this experimental work. I am particularly indebted to Dr. Haskell Shapiro from Shapiro Scientific Instruments, Corona Del Mar, California, for his assistance in the design of various electronic systems. Among the personnel of the Institute's Central Engineering Services my thanks go to N. Keidel, L. Johnson, G. Yamamota and M. Gerfen for their expert help with the design and construction of most of the mechanical components. Thanks also to G. Lundgren from the Aeronautics shop for directing the delicate task of machining the rotating dynamometer. Just as delicate was the task of instrumenting this dynamometer, which was successfully carried out by J. Hall from Microengineering II , Upland, CA. Thanks for many years of reliable operation. Thousands of hours were spent preparing the test rig and collecting data from the various experiments. Many of these hours were contributed by student colleagues and friends D. Adkins, R. Franz, N. Arndt, W. Goda, D. Brennen, S. Moriarty, M. Karyeaclis and P. Chen. I very much appreciated their efforts. The help of C. Lin with the graphics and S. Berkeley with the administrative tasks was also greatly appreciated. It takes substantial financial support to bring to term an experimental project of this magnitude. This support was generously provided by NASA's George C. Marshall Space Flight Center, Huntsville, Alabama. My advisors and I are very thankful for it. Rocketdyne Division of Rockwell International, Canoga Park, CA, provided a diffuser volute and half an SSME's HPOTP's double suction impeller for testing. Byron-Jackson Pumps Division of Borg-Warner Industrial Products Corp. Long Beach, CA, offered two test impellers. We are very grateful for these contributions. My personal financial needs were met through a grant from the Foundation ENSAM, a scholarship from the Scientific Mission of Tunisia, a Graduate Research Assistantship from the California Institute of Technology and a Research Fellowship from Byron-Jackson Pumps Division. I am forever indebted to all these sources. Some contributions are hard to describe with words, let alone quantify. These came from my family and close friends whose love, patience and encouragement meant so much to me. I say: thank you all for being there when I needed you most. This thesis is dedicated to my mother and father Fatma and Ammar, who never had a chance to learn how to read or write, but who taught me so much.
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NASA George C. Marshall Space Flight CenterNAS 8-33108
Scientific Mission of TunisiaUNSPECIFIED
Byron-Jackson Pumps DivisionUNSPECIFIED
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ID Code:45655
Deposited On:12 May 2014 17:54
Last Modified:03 Oct 2019 06:34

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