Laser Metrology in Fluid Mechanics E-Book

Alain Boutier

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 451

Veröffentlichungsjahr: 2013

Beschreibung

In fluid mechanics, non-intrusive measurements are fundamental in order to improve knowledge of the behavior and main physical phenomena of flows in order to further validate codes.
The principles and characteristics of the different techniques available in laser metrology are described in detail in this book.
Velocity, temperature and concentration measurements by spectroscopic techniques based on light scattered by molecules are achieved by different techniques: laser-induced fluorescence, coherent anti-Stokes Raman scattering using lasers and parametric sources, and absorption spectroscopy by tunable laser diodes, which are generally better suited for high velocity flows. The size determination of particles by optical means, a technique mainly applied in two-phase flows, is the subject of another chapter, along with a description of the principles of light scattering.
For each technique the basic principles are given, as well as optical devices and data processing. A final chapter reminds the reader of the main safety precautions to be taken when using powerful lasers.

Leseprobe

Contents

Preface

Introduction

Chapter 1: Basics on Light Scattering by Particles

1.1. Introduction

1.2. A brief synopsis of electromagnetic theory

1.3. Methods using Separation of variables

1.4. Rayleigh theory and the discrete dipole approximation

1.5. The T-matrix method

1.6. Physical (or wave) optics models

1.7. Geometrical optics

1.8. Multiple scattering and Monte Carlo models

1.9. Conclusion

1.10. Bibliography

Chapter 2: Optical Particle Characterization

2.1. Introduction

2.2. Particles in flows

2.3. An attempt to classify OPC techniques

2.4. Phase Doppler interferometry (or anemometry)

2.5. Ellipsometry

2.6. Forward (or “laser”) diffraction

2.7. Rainbow and near-critical-angle diffractometry techniques

2.8. Classical shadowgraph imaging

2.9. Out-of-focus interferometric imaging

2.10. Holography of particles

2.11. Light extinction spectrometry

2.12. Photon correlation spectroscopy

2.13. Laser-induced fluorescence and elastic-scattering imaging ratio

2.14. Laser-induced incandescence

2.15. General conclusions

2.16. Bibliography

Chapter 3: Laser-Induced Fluorescence

3.1. Recall on energy quantification of molecules

3.2. Laser-induced fluorescence principles

3.3. Applications of laser-induced fluorescence in gases

3.4. Laser-induced fluorescence in liquids

3.5. Bibliography

Chapter 4: Diode Laser Absorption Spectroscopy Techniques

4.1. High spectral resolution absorption spectroscopy in fluid mechanics

4.2. Recap on molecular absorption

4.3. Absorption spectroscopy bench

4.4. Applications in hypersonic

4.5. Other applications of diode laser absorption spectroscopy

4.6. Other devices for diode laser absorption spectroscopy

4.7. Perspectives and conclusion on diode laser absorption spectroscopy

4.8. Bibliography

Chapter 5: Nonlinear Optical Sources and Techniques

5.1. Introduction to nonlinear optics

5.2. Main processes in nonlinear optics

5.3. Nonlinear sources for optical metrology

5.4. Nonlinear techniques for optical diagnostic

5.5. Bibliography

Chapter 6: Laser Safety

6.1. Generalities on laser safety

6.2. Laser type and classification

6.3. Laser risks: nature and effects

6.4. Protections

6.5. Safety advice

6.6. Human behavior

Conclusion

Nomenclature

List of Authors

Index

First published 2013 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

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©ISTE Ltd 2013

The rights of Alain Boutier to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Control Number: 2012950203

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN: 978-1-84821-398-2

Preface

This book has been elaborated from lectures given in the framework of autumn schools organized since 1997 by AFVL – Association Francophone de Vélocimétrie Laser (French-speaking Association of Laser Velocimetry).

AFVL activities are especially dedicated to foster and facilitate transfer of knowledge in laser velocimetry and all techniques making use of lasers employed for metrology in fluid mechanics. Among the main objectives, a good use of laser techniques is looked at to fulfill requirements of potential applications in research and industry.

The authors of this book have thus shared their expertise within AFVL, which led them to write the various chapters within a teaching environment, which allows the reader to learn and perfect perspective both for his/her theoretical and practical knowledge.

Introduction

Introduction is written by Alain BOUTIER.

In fluid mechanics, non-intrusive measurements are fundamental to improve knowledge about flow behavior. Flow maps of velocity, temperature and concentration, as well as particle granulometry in two-phase flows, uniquely help in understanding the physical phenomena inside flows, which in turn enables code validation.

Different techniques are required for velocity measurements using spectroscopic principles, based on light scattering by molecules: laser-induced fluorescence, coherent anti-Stokes Raman scattering and tuneable laser diode. They are generally better suited for characterization of high-velocity flows. These devices also very often allow access to temperatures and concentrations of species present in reactive flows. Chapter 2 is especially dedicated to the determination of particle granulometry by optical means, measurement techniques being more adapted to two-phase flows studies; whereas Chapter 1 describes light scattering principles. For each technique, basic principles are described, as well as optical setups and signal processors.

The last chapter (Chapter 6) is dedicated to laser safety; it sums up the main precautions that must be taken for any device using an intense laser source.

Another book by the same authors, titled “Laser Velocimetry in Fluid Mechanics”, describes the various techniques of velocity measurement based on particle scattering. These velocity measurement techniques give access to the mean velocity field, as well as to detailed turbulence knowledge.

Chapter 1

Basics on Light Scattering by Particles

Chapter written by Fabrice ONOFRI and Séverine BARBOSA.

1.1. Introduction

This chapter introduces the basic concepts of the properties of electromagnetic waves, and the models and theories that describe the light scattering properties of small particles (droplets, bubbles, nanoaggregates, etc.) that are encountered in fluid mechanics and mechanical engineering problems. Light scattering models are fundamental to understanding the principles of optical particle characterization (OPC) techniques (see Chapter 2) and, to a lesser extent, laser velocimetry techniques1. Recognizing the need for an abbreviated format, this chapter covers the following topics:

– the basic properties of electromagnetic waves interacting with linear materials (propagation, polarization, absorption, phase shift, etc.);

– quantities and concepts commonly used to describe the elastic interaction of electromagnetic waves with particles (scattering matrix, cross-sections, scattering diagrams, radiation pressure, photon mean free path, etc.);

– rigorous theories describing the absorption and scattering properties of highly symmetric particles (Lorenz–Mie theory (LMT) and Debye theory);

– asymptotic models that are computationally efficient but only valid for particles that are small or large with respect to the wavelength, or for particular refraction index ranges: Rayleigh (electrostatic dipoles), Fraunhofer (edge) diffraction, Airy (rainbow phenomena) and geometrical optics approximations;

– semi-analytical and numerical methods allowing us to model the optical properties of complex-shaped nanoparticles or nanoparticulate systems (the T-matrix method, the discrete dipole approximation and the Monte Carlo method).

Chapters 3 and 5 complement the present chapter by addressing molecular diagnostics based on inelastic and nonlinear scattering.

1.2. A brief synopsis of electromagnetic theory

1.2.1. Maxwell’s equations

The general form of Maxwell’s equations for an isotropic and linear medium may be written as follows:

[1.1]

where represents the electric displacement (i.e. a vector), is the electric field, is the magnetic induction, is the magnetic field, ρF is the electric charge density and is the electric current density [BOR 02]. Electromagnetic fields are related to excitations by the following expressions:

[1.2]

where ε0 and μ0 denote the permittivity and magnetic permeability of free space, respectively, and and denote the polarization and magnetization in a volume of the medium, respectively. Simple constitutive laws relate the electrical and magnetic properties of a linear medium:

[1.3]

where σ, μ and χ denote its electrical conductivity, magnetic permeability and electrical susceptibility, respectively.

[1.4]

When a material is illuminated by a very intense beam of light (to get us thinking, let us say when |E| > 100 kV/m), the amplitude of the electrical field induced within the material is no longer proportional to the amplitude of the incident field. In this case, the material polarizability is composed of a set of contributions corresponding to increasingly nonlinear responses of the material (e.g. [BOR 02] and [BAS 95a]):

[1.5]

where the superscript (n) indicates the number of photons involved in the induced response and:

– χ(1) is responsible for the usual observed mechanisms: Rayleigh, Mie and spontaneous Raman scattering; spontaneous absorption and fluorescence (see Chapter 3).

– χ(2) (zero for gases) induces frequency doubling phenomena (e.g. frequency doubling crystals used by most particle image velocimetry systems (PIV, i.e. Nd-YAG lasers) and stimulated Raman scattering.