Experimental studies of fluid-borne noise generation in a marine pump.

184 Pages·2.5 MB·en_US

by  McGee, David Michael.

BOOS

EXPERIMENTAL STUDIES OF FLUID-BORNE
NOISE GENERATION IN A MARINE PUMP
by
David Michael McGee
B.S., United States Naval Academy (1986)
Submitted to the Department ofOcean Engineering and the Department ofMechanical
Engineering in Partial Fulfillment ofthe Requirements forthe Degrees of
NAVAL ENGINEER
and
MASTER OF SCIENCE IN MECHANICAL ENGINEERING
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
May, 1993
©
Massachusetts Institute ofTechnology, 1993. Allrights reserved.
t.i
EXPERIMENTAL STUDIES OF FLUID-BORNE
NOISE GENERATION IN A MARINE PUMP
by
David Michael McGee
Submitted to the Department ofOcean Engineering and
the Department ofMechanical Engineering in May 1993
in Partial Fulfillment ofthe Requirements for the Degrees of
Naval Engineer and Master ofScience in Mechanical Engineering
ABSTRACT
Experimental studies were carried out to determine the influence ofpump rotational
speed, flow rate, and the addition oflong-chain polymers on the broadband and tonal
noise generated from the fluid flow in a centrifugal waterpump.
A theoretical model is presented which relates the tonal noise generation to the static
pressure field at the impeller discharge. Using the pump in its original casmg,
measurements were made ofthe static pressure distribution at impeller exit under vanous
operating conditions. Attempts were made to correlate the static pressure field at
impeller exit with the observed acoustic spectra at pump inlet under these conditions.
The results showed fair agreement with the theory at shaft and blade passage frequencies
as well as some ofthe other harmonics. However, the unusually invariant flow
conditions at the impeller exit over awide range ofconditions limited the number of
conclusions which could be drawn from the experiments.
To further test the theory, an experimental diffuser was designed for the pump which
could be used to isolate the effects of interest. The diffuser was designed smuch that
pressure disturbances were far removed from the impeller, which resulted more
uniform conditions at the impeller exit. Results indicate that tonal noise levels at shaft
and blade passage frequencies are significantly reduced with the reduction ofstatic
pressure non-uniformities. Broadband noise levels did not differ appreciably between the
two geometries. A means was provided for imposing various pressure distributions on
the impeller exit but initial results were inconclusive.
Thesis Supervisor: Dr. Alan H. Epstein
Title: Professor of Aeronautics and Astronautics
Acknowledgments
This thesis could not have been completed without the support ofmany people. I
would like to offer sincere thanks to the following individuals who made this work
possible:
ProfessorAlan H. Epstein, forhis practical insight and guidance throughout the
project. His own enthusiasm andencouragement provided the motivation to accomplish
more in alimitedperiod oftime than I had imaginedpossible.
Professors K. Uno Ingard and Ian Waitz, fortheirpatience and continuing
support throughout the year. They aided immeasurably in the interpretation and
understanding ofthe results andplayed a large role in making the experience an
enjoyable one.
The Staffofthe M.I.T. Gas Turbine Laboratory. Inparticular, Bill Ames, Victor
Dubrowski, and Jimmy Letendre for all oftheir help in setting up the experimental
facility and in troubleshooting and correcting the numerous problems which arose. Also,
thanks to Holly Rathbun and Robin Courchesne for their assistance withpurchasing and
logistics.
Finally, this thesis is dedicated to my wife, Linda, whose unselfishness allowed
me topursue this endeavor and whose constant support kept me going through a difficult
three years. This work is truly the culmination ofajoint effort.
1
Table of Contents
List ofFigures 7
1. Introduction and Background 10
1.1. General Description ofPump Noise 1
1.2. Previous Work 12
1.3. Factors Affecting Fluid Noise 14
1.3.1. Fluid Flow in a Centrifugal Pump Volute 14
1.3.2. Pump Operating Point 16
1.4. Project Goals 17
1.5 Thesis Organization 17
2. Experimental Approach: The MIT Gas Turbine Laboratory
Pump Acoustics Facility 19
2.1. Description ofPump 19
2.1.1. Pump Impeller 20
2.1.2. Pump Casing 21
2.1.3. Pump Mount 22
2.2. The Acoustic Pump Loop 22
2.3. Acoustic Isolation 26
2.3.1. Acoustic Attenuation 26
2.3.2. Reflection and Standing Waves 27
2.3.3. Vibration 28
2.3.4. Elimination ofOther Acoustic Sources 28
2.3.5. Noise Propagation in Pipes 28
2.4. Instrumentation 29
2.4.1. Experimental Conditions Monitoring 29
2.4.2. Pump Impeller Exit Pressure 30
2.4.3. Acoustic Measurements 32
2.5. Data Acquisition and Processing 33
3. A Theoretical Model ofTonal Noise Generation in Centrifugal Pumps 37
3.1. The Whirling Pipe Model 37
3.2. The Area Function 39
3.3. The Unsteady Velocity Component 40
3.4. Pump Geometry Considerations 42
3.5. The Total Time Dependent Velocity and Sound Pressure 42
3.6. Acoustic Impedance at Pump Inlet and Outlet 44
3.7. An Example 45
.
4. Parametric Studies 48
4.1. General Discussion 48
4.1.1. Turbulence Noise 48
4.1.2. Reflection and Standing Waves 50
4.1.3. The Effects ofAir in the System 50
4.2. The Effect ofLong Chain Polymers 51
4.2.1. Experimental Procedure 51
4.2.2. Results 53
4.3. Broadband Noise Studies 56
4.3.1 The Effects ofPump Speed on Broadband Noise Generation 56
4.3.2. The Effects ofFlow Rate on Broadband Noise Generation 61
4.4. Harmonic Noise Studies 64
4.4.1. Impeller Discharge Pressure Profile 64
4.4.2. Fourier Decomposition ofStatic Pressure Measurements 67
4.4.3. The Effects ofPump Speed on Harmonic Noise Generation 69
4.4.4. The Effects ofFlow Rate on Harmonic Noise Generation 72
5. The Pump Acoustics Diffuser 75
5.1. Vaned Diffuser Design 75
5.2. Experimental Diffuser Design 77
5.2.1. The Acoustic Pump Diffuser 77
5.2.2. Perforated Basket Assembly 82
5.3. Pump Loop Modifications 83
5.4. Acoustic Considerations 85
5.4.1. Acoustic Attenuation 85
5.4.2. Reflection and Standing Waves 85
5.4.3. De-Aeration 85
6. Experimental Diffuser Studies 87
6.1. Acoustic Phenomena Associated with the Diffuser 87
6.1.1. Natural Modes ofthe Diffuser 87
6.1.2. The Diffuser as a Helmholtz Resonator 88
6.1.3. Sound/Flow Interaction 88
6.2. Experimental Conditions 90
6.2.1. Pump Loop Flow Resistance 90
6.2.2. Static Pressure Distribution 90
6.2.3. Loop Instability 91
6.3. Results 91
A
6.3.1. Typical Noise Spectrum 91
6.3.2. Comparison ofAcoustic Signatures ofthe Diffuser
and Original Volute 93
6.3.3. Effects ofSpeed and Flow Rate Variations 94
6.4. The Effects ofStatic Pressure Field Disturbances on Noise Generation 100
7. Conclusion 105
7.1 The Effect ofPolymers, Rotational Speed, and Flow Rate on Pump Noise 105
.
7.2. The Effect ofImpeller Exit Static Pressure Field 106
7.3. Recommendations for Future Work 106
8. References 108
Appendices
A. The Resonance Frequency ofan AirBubble inWater 112
B. PolymerTreatment Results 114
C. Speed/Flow Rate Effects on Broadband Noise 120
D. Speed/Flow Rate Effects on Tonal Noise 139
E. Acoustic Results with the Experimental Diffuser 162