Methods for Identifying Acoustic Emissions From the Front Face of a Small Piezoelectric Blower

143 Pages·2016·4.7 MB·English

Brigham Young University
BYU ScholarsArchive
All Theses and Dissertations
2012-12-12
Methods for Identifying Acoustic Emissions From
the Front Face of a Small Piezoelectric Blower
Brad K. Solomon
Brigham Young University - Provo
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Methods for Identifying Acoustic Emissions
from the Front Face of a Small
Piezoelectric Blower

Brad Solomon

A thesis submitted to the faculty of
Brigham Young University
in partial fulfillment of the requirements for the degree of

Master of Science

Jonathan D. Blotter, Chair
Scott D. Sommerfeldt
Kent L. Gee

Department of Mechanical Engineering

Brigham Young University

December 2012

Copyright © 2012 Brad Solomon

All Rights Reserved
ABSTRACT

Methods for Identifying Acoustic Emissions
from the Front Face of a Small
Piezoelectric Blower

Brad Solomon
Department of Mechanical Engineering, BYU
Master of Science

This thesis focuses on identifying acoustic noise generating components in piezoelectric
blowers through transverse velocity measurements and the development of a numerical fluid
model. Piezoelectric ceramics have proven useful for many industries and areas of research
involving: high precision actuators, noise control, ultrasonic devices, and many other areas. As
of late, a unique adaptation of piezoelectric ceramics is surfacing in the area of pumping and
cooling. Air pumps that use these ceramics replace the traditional electric motor, resulting in
lower power consumption, less moving parts, constant pressure gradients, lower overall weight,
and a low profile. The current drawback of this application is the acoustic radiation produced by
the blowers. Since these blowers are new to market, little research or development has been
done to characterize the noise emissions. This thesis studies the acoustic emissions from the front
face of a Murata piezoelectric blower.

Jet noise and structural vibrations are two acoustic sources of interest that are studied in
this research. A Direct Numerical Simulation (DNS) of the fluid flow through a Murata blower
is developed to better identify noise generating mechanisms. The model solutions predict trends
in sound pressure levels (SPL) of the jet noise and volumetric flow rates. Both the SPL and flow
rate are shown to be functions of critical geometrical dimensions within the flow path of a
Murata blower. Important dimensional components are identified as well as non-influential
ones. Design guidelines are given to reduce noise emission from the front side of a blower and
increase the volumetric flow rate. The results of this research have a direct impact on the
piezoelectric blower industry and future blower designs.

Keywords: piezoelectric blower, structural vibrations, jet noise, acoustic noise, plate radiation,
turbulence, DNS, CFD, transverse velocity, radiation resistance, sound power, sound pressure
level, volumetric flow rate, operational mode shape, anechoic, nozzle radius, nozzle length,
pumping chamber.
ACKNOWLEDGMENTS

I graduated from Southern Utah University in 2009 with a Bachelor’s degree in
Integrated Engineering. It was four years of electrical, mechanical, and civil engineering classes
and projects. None of which touched on acoustics or acoustical engineering. Knowing that I had
come from a different school and had a different background than most of his graduate students
Dr. Blotter invited me onto his acoustic research team. I am forever grateful for his invitation. I
came to Brigham Young University with virtually no knowledge or understanding of acoustics
and was exposed to new fields of study that I didn’t know existed. The excellent faculty and
environment at BYU has taught me two important life lessons: How to learn, and to love to learn.
Many doors have been opened because of these simple yet important lessons.
While earning my degree, I also had the opportunity to provide for my family. My wife
and I had two kids during this time. I want to thank Dr. Blotter not only for his advice and
direction turning this project but also for the financial support that he offered. His passion for
learning and engineering will affect me for life. I also want to thank Dr. Anderson, Dr.
Sommerfeldt, and Dr. Gee for their advice during this project. I would not have been able to
complete it without their input and direction. Many of my fellow engineering students helped
and guided me through classes and research. I want to personally thank Curtis Wiederhold for
his support in the acoustics research and David Jesse Daily for his support in the simulations.
Most importantly, I need to thank my wife Nicole and my two boys, Jett and Ryder.
They supported me with love, prayers, and understanding during numerous late nights of study.
I would not be who I am and could not of accomplished this research without their love. I love
my wife and I needed her support during this project. I know my mother also prayed for us. I
know the Lord blessed me because of my family’s prayers. I will forever be grateful for this
learning opportunity and the life skills I obtained from completing this project.
Lastly, I want to thank the NASA Grant Foundation and Murata Inc. for funding portions
of this research.
TABLE OF CONTENTS

LIST OF TABLES ....................................................................................................................... ix
LIST OF FIGURES ..................................................................................................................... xi
1 INTRODUCTION ................................................................................................................. 1
1.1 The Problem and Motivation .......................................................................................... 1
1.2 Objective and Goals ........................................................................................................ 4
1.3 Hypothesis ...................................................................................................................... 5
1.4 Work Scope and Thesis Outline ..................................................................................... 7
1.5 Background ..................................................................................................................... 8
2 ACOUSTICAL NOISE CHARACTERISTICS OF A BLOWER ................................. 11
2.1 Noise Induced from Structural Vibrations .................................................................... 11
2.1.1 Plate Radiation Theory ............................................................................................. 12
2.1.2 Experimental Setup and Results ............................................................................... 14
2.2 Characteristics of Jet Noise ........................................................................................... 21
2.2.1 Directionality of Jet Noise and Comparison to Blower Measurements .................... 22
2.2.2 Spectral Characteristics of Jet Noise and Comparison to Blower Measurements .... 26
2.3 Testing Conclusions ...................................................................................................... 30
3 DNS FLOW MODELING .................................................................................................. 31
3.1 Turbulence Theory and DNS Modeling ....................................................................... 32
3.2 Model Build Procedure (ADINA) ................................................................................ 36
3.2.1 Constructing Geometry (ADINA) ............................................................................ 37
3.2.2 Boundary Conditions and Loading ........................................................................... 43
3.2.3 Parameter Inputs and Solving Process ...................................................................... 48
3.2.4 Post Processing Results (Ensight) ............................................................................. 51
v
3.3 Model Verification ........................................................................................................ 52
3.3.1 Jet Formation ............................................................................................................ 53
3.3.2 Model Convergence .................................................................................................. 54
3.3.3 Velocity Profile Reference ........................................................................................ 57
3.3.4 Frequency Spectrum Reference ................................................................................ 62
3.4 Model Benefits and Limitations ................................................................................... 67
4 RESULTS ............................................................................................................................ 71
4.1 Nozzle Radius ............................................................................................................... 74
4.2 Nozzle Height ............................................................................................................... 77
4.3 Inlet Radius ................................................................................................................... 79
4.4 Inlet Gap Distance ........................................................................................................ 80
4.5 Pump-Chamber Nozzle Radius ..................................................................................... 81
4.6 Chamfer Dimension ...................................................................................................... 83
4.7 Pump-Chamber Volume ............................................................................................... 84
4.8 Results Summary .......................................................................................................... 86
5 CONCLUSIONS ................................................................................................................. 89
5.1 Summary ....................................................................................................................... 89
5.1.1 Acoustic Noise Characterization ............................................................................... 89
5.1.2 DNS Blower Model .................................................................................................. 89
5.1.3 Results ....................................................................................................................... 90
5.2 Recommendations ......................................................................................................... 90
REFERENCES ............................................................................................................................ 93
Appendix A. Test Procedures and settings ............................................................................... 97
A.1 SLDV Transverse Velocity Measurement Settings .......................................................... 97
A.2 Sound Power Calculation Code (MatLab) ........................................................................ 99
vi
A.3 Structural Mode Sound Power Calculation Code (MatLab) ........................................... 104
A.4 Directivity Plotting and Power Spectral Density Code (Matlab) .................................... 106
A.5 Frequency Spectrum Code (MatLab) .............................................................................. 109
A.6 Results from Blower Load Measurement and Approximation ....................................... 112
A.7 ADINA Model Build File ............................................................................................... 114
A.8 ADINA Time Function ................................................................................................... 119
A.9 ADINA Parameters List .................................................................................................. 120
A.10 FSL Script Files ............................................................................................................ 121
A.11 Ensight Batch Script Tools ........................................................................................... 122
A.12 Velocity Profile of Model Code (MatLab) ................................................................... 126
A.13 Overall Sound Pressure Level of Model Code (MatLab) ............................................. 128
A.13 PIV Measurement Setup and Results ............................................................................ 129
A.14 Directivity Testing with Mufflers ................................................................................. 133

vii
LIST OF TABLES

Table 1-1: Research objective and steps ..............................................................................5
Table 2-1: Structural vibration contribution to radiated sound power. ..............................20
Table 3-1: Grid independence validation chart. .................................................................57
Table 3-2: Theoretical equations for jet velocity profiles ..................................................59
Table 4-1: Summary of model data and rank of influence. ..............................................87
Table 7-1: Summary of muffler results. ...........................................................................135

ix
LIST OF FIGURES

Figure 1-1: A size comparison of a Murata piezoelectric blower. .......................................1
Figure 1-2: A cross sectional view of the blower with blue arrows showing path of air. ...2
Figure 1-3: A cross sectional view of a blower demonstrating the operating principle. .....3
Figure 2-1: Subdivision of a panel into elemental radiators. .............................................13
Figure 2-2: SLDV measurement test setup (LEFT), Microphone placement (RIGHT). ...15
Figure 2-3: Transverse velocity spectrum of the front blower face. ..................................15
Figure 2-4: Audible transverse velocity spectrum of the front blower face. .....................16
Figure 2-5: Operational mode shape of blower face at 14.36 kHz. ...................................17
Figure 2-6: Operational mode shape of blower face at 6.75 kHz ......................................17
Figure 2-7: Operational mode shape of blower face at 2.93 kHz ......................................18
Figure 2-8: Sound power measurement setup for front face of blower. ............................19
Figure 2-9: Sound power spectrum measured from the front face of a blower. ................20
Figure 2-10: Directivity plot for a low-velocity jet. ..........................................................23
Figure 2-11: Directivity plots of a piezoelectric blower. ...................................................24
Figure 2-12: Power spectrum density plot for frequencies above the driving frequency. .25
Figure 2-13: Components and velocity profile of a subsonic jet at a nozzle exit. .............26
Figure 2-14: Baffle and microphone setup for near field spectral testing. ........................28
Figure 2-15: Positions of microphone relative to nozzle for spectral testing. ...................28
Figure 2-16: Frequency spectra of a blower’s air stream. .................................................29
Figure 3-1: Cross sectional plane passing through the nozzle axis. ..................................37
Figure 3-2: Normal view of cross section, basis of model geometry. ...............................38
Figure 3-3: Course mesh of the air flow path. ...................................................................39
Figure 3-4: Labeled ADINA AUI Icon bar and drop-down lists. ......................................40
xi