Modelling and Acoustic Optimization of an Intake System for an Internal Combustion Engine

259 Pages·2017·12.39 MB·English

UNIVERSITÀ DEGLI STUDI DI NAPOLI FEDERICO II
Scuola Politecnica e delle Scienze di Base

Corso di Dottorato in Ingegneria Industriale (XXIX Ciclo)
Dipartimento di Ingegneria Industriale

Tesi di Dottorato

Modelling and Acoustic Optimization of an Intake System for
an Internal Combustion Engine
Danilo D’Agostino

COORDINATORE
Ch.mo Prof. Ing. Michele Grassi

TUTORI
Ch.mo Prof. Ing. Fabio Bozza
Ing. Daniela Siano

Anno 2017

To my parents…

I
Acknowledgements

I am very grateful to my friends and colleagues Roberto Aiello and Maria Antonietta Panza for the
very interesting discussions on sociological and scientific topics and with whom I have shared three
incredible, unbelievable years. Their presence has been very important in this path of both personal
and professional growth.

My sincere thanks go to PhD Luigi Teodosio for his friendship and for the very valuable time we
spent together talking about various matters.

Thanks to my supervisors, Daniela Siano, who gave me the opportunity to start such journey in the
research environment, and prof. Fabio Bozza for his technical teachings and his support related to
the performed activities.

Thanks to all the people I have met during the PhD, for their support, encouragement and
suggestions.

Last but not the least, a special thank goes to my family and friends, for their unconditioned,
priceless love and presence.

Thanks to Claudia, for being as she is and for her support and understanding during all these
years.

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Abbreviations
CAE Computer Aided Design

1D One-Dimensional

3D Three-Dimensional

TL Transmission Loss

SI engine Spark Ignition engine

GA Genetic Algorithm

IPFM Interior Penalty Function Method

EPFM Exterior Penalty Function Method

FDM Feasible Direction Method

FE Finite Element

OSPL Overall Sound Pressure Level

IL Infinite Element

NR Noise Reduction

PDE Partial Differential Equation

CAD Computer Aided Design

IE Infinite Element

TM Transfer Matrix

FSI Fluid-Structure Interaction

CFD Computational Fluid Dynamic

IVO Inlet Valve Opening

VVA Variable Valve Actuator

WOT Wide Open Throttle

RANS Reynolds Average Navier-Stokes

OASPL Overall A-weighted Sound Pressure Level
III
SPL Sound Pressure Level

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Contents

Introduction………………………………………………………………………………………... 1
References……………………………………………………………………………..……….........8
Chapter 1: Basics of Fluid Flow…………………………………………………………………... 9
1.1 The divergence theorem……………………………………………………………………...9
1.2 Conservation equations…………………………………………………………………… 11
1.2.1 Reynolds Transport theorem…………………………………………………………17
1.2.2 Conservation of mass………………………………………………………………… 19
1.2.3 Conservation of momentum………………………………………………………….. 20
1.2.3.1 Stokes’ law….............................................................................................................23
References…………………………………………………………………………………….........26

Chapter 2: The Concept of Sound and its Propagation………………………………………... 27
2.2 The Sound……………………………………………………………………………………27
2.1.1 Frequency domain study of sound…………………………………………………….29
2.2 Sound propagation…………………………………………………………………………..33
2.2.1 1-D homogeneous classical wave equation……………………………………………34
2.2.1.1 Solution of the 1-D homogeneous classical wave equation……………………... 36
2.2.2 Homogeneous classical wave equation and solution……………………………….. 40
2.2.3 3-D propagation in tubes…………………………………………………………….. 43
2.3 Sound propagation in moving media……………………………………………………... 46
2.3.1 The convective wave equation and solution………………………………………….46
References…………………………………………………………………………………….........50

Chapter 3: Basics of Sound Propagation in Duct………………………………………………..51
3.1 Basic theory of acoustic filters……………………………………………………………...52
3.1.1 Specific acoustic impedance of an uniform tube…………………………………….53

3.1.2 Radiation impedance………………………………………………………………….55
3.1.3 A lumped inertance……………………………………………………………………60
3.1.4 End correction………………………………………………………………………... 61
3.1.5 A lumped compliance………………………………………………………………….62

3.1.6 Acoustic resonators…………………………………………………………………….63
3.1.6.1 Extended-tube (quarter-wave) resonator………………………………………...64
3.1.6.2 Helmholtz resonator……………………………………………………………….67
3.1.6.3 Concentric hole-cavity resonator…………………………………………………68
3.2 Acoustic filter performance parameters…………………………………………………...69
3.2.1 Insertion Loss………………………………………………………………………….70
3.2.2 Transmission Loss……………………………………………………………………. 72

3.2.3 Noise Reduction………………………………………………………………………..73

3.2.4 Simple area discontinuities…………………………………………………………... 76

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3.3 Introduction to the study of porous materials…………………………………………… 78
3.3.1 Equivalent fluid models……………………………………………………………….81
References…………………………………………………………………………………….........83

Chapter 4: Finite Element Method in Acoustics…………………………………………………84
4.1 Problem statement…………………………………………………………………………..85

4.2 Galerkin procedure…………………………………………………………………………87
4.3 Convergence of the model…………………………………………………………………. 93

4.4 Modelling exterior acoustic problems…………………………………………………….96
References…………………………………………………………………………………….........99

Chapter 5: Acoustic Performance Analysis……………………………………………………..100
5.1 Transfer Matrix Method…………………………………………………………………. 101
5.1.1 Experimental evaluation of the TL: the impedance tube technology……………..105
5.1.1.1 Transfer Matrix formulation: the two-load method…………………………...107
5.2 Experimental procedure…………………………………………………………………. 108
5.3 Numerical procedure…………………………………………………………………….. 113
5.3.1 CAD preparation and FE models creation………………………………………... 113
5.3.1.1 Numeric purely acoustic models……………………………………………….. 116
5.3.1.2 Numeric structural-acoustic model……………………………………………..121
5.4 Experimental vs Numerical comparison: model validation…………………………… 126
References…………………………………………………………………………………….......132

Chapter 6: Gas-dynamic Noise Analysis………………………………………………………...133
6.1 Experimental analysis……………………………………………………………………. 135
6.2 Numerical analysis………………………………………………………………………...137
6.2.1 One-dimensional analysis…………………………………………………………....137
6.2.2 Three-dimensional acoustic analysis………………………………………………..144
References…………………………………………………………………………………….......154

Chapter 7: Aerodynamic Generation of Sound………………………………………………...155
7.1 The inhomogeneous wave equation and the Green’s function…………………………..157
7.2 Multipole expansion of sound fields……………………………………………………....161
7.2.1 Monopole source…………………………………………………………………….. 165
7.2.2 Dipole source………………………………………………………………………… 168
7.2.3 Quadrupole source………………………………………………………………….. 175
7.3 Lighthill’s Aeroacoustic Analogy………………………………………………………... 178
7.3.1 Modelling approach………………………………………………………………… 180
7.3.1.1 Monopole source term…………………………………………………………...183
7.3.1.2 Dipole source term……………………………………………………………….185
7.3.1.3 Quadrupole source term……………………………………………………….. 187
7.4 Introduction to turbulence modelling…………………………………………………….190
7.4.1 Reynolds Stress Equation…………………………………………………………….194
7.4.2 𝒌−𝜺 turbulence model……………………………………………………………...196
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References…………………………………………………………………………………….......200

Chapter 8: Geometric Optimization…………………………………………………………….201
8.1 Transmission Loss enhancement…………………………………………………………205
8.2 Gas-dynamic noise Analysis………………………………………………………………220
8.2.1 Problem statement…………………………………………………………………... 220
8.2.2 Analysis process……………………………………………………………………... 224
8.2.2.1 One-dimensional CFD analysis………………………………………………… 224
8.2.2.2 Three-dimensional CFD analysis………………………………………………..228
8.2.2.3 Three-dimensional acoustic analysis…………………………………………... 232
References…………………………………………………………………………………….......247

Chapter 9: Conclusions and Future Developments…………………………………………….248

VII
Introduction
Introduction
Noise is recognized as having a significantly adverse effects on our everyday lives, including
interference with communication, sleep disturbance, annoyance responses, performance effects as
well as health through psycho-physiological effects. As an everyday example, noise induced
annoyance is a very important problem occurring when people are constantly exposed to a noise
source, regardless of its intensity. Such evidence has been recognized by product designers
engineers within the world’s most innovative and successful companies, which try to incorporate
effective noise mitigation measures into their product design process. Such new project aspect has
become extremely important in the automotive industry too and it is possible to state that there is a
strong competition among automotive manufacturers to generally reduce the radiated noise levels.
In fact, nowadays, the concept of client perception quality of a vehicle, which represents the prior
target behind the production strategies of cars manufacturers, is quite changed with respect to a
dozen of years ago. In particular, among the factors identifying the quality of a vehicle, the concept
of delivered sound represents a critical aspect that manufacturers are focusing on, in order to be
more competitive on the global market. As matter of fact, poor sound quality can give the
impression of poor vehicle build quality or, for a customer point of view, can give the idea that
there is something wrong with the operations of the vehicle, as if something is not working properly
and is going to break. More precisely, the term sound quality refers to whether sounds are pleasant
or annoying. For example, if a properly tuned engine noise is something that may be appreciated by
customers, on the other hand it may strongly reduce the global comfort. Consequently, every
vehicle component is not only designed in order to ensure the achievements of its specific goal but
also considering the impact on the vehicle’s overall sound quality. Such a new design philosophy is
becoming more and more important as it is also testified by the increase in the noise emission
standards (e.g. Regulation (EU) N° 540/2014).
So, it may be stated that the acoustic project of a vehicle, considering all the components it is made
of, must satisfy a trade-off between acoustic comfort and perceived sound. However, as
schematically depicted in Figure 1, within a vehicle various noise sources are involved such as
powertrain noise, aerodynamic noise, rolling noise etc..
1