Laser-Strophometry High-Resolution Technique for Velocity Gradient M
This book describes techniques that allow the measurement of arbitrary velocity gradient components in fluids with high spatial and temporal resolution, e.g. turbulent fluids. The techniques are based on the properties of scattered laser light. The book g
- PDF / 3,395,122 Bytes
- 186 Pages / 430.8 x 666.2 pts Page_size
- 93 Downloads / 153 Views
This book is the result of two decades of research work which started with an accidental observation. One of my students, Dipl. phys. Volkmar Lenz, noticed that the speckle pattern of laser light scattered by a cuvette containing diluted milk performed a strange motion every time he came near the cuvette with his thumb. After thinking about this effect we came to the conclusion that this motion can only be caused by scattering particles with different velocities, as in the case of the diffraction pattern of an optical grating: A linear motion of the grating does not change the pattern whereas a rotation of the grating does. The observed speckle motion could then be explained qualitatively as produced by the inhomogeneous velocity of the convection within the cuvette which was produced by the heat of the thumb. The theoretical treatment of this effect revealed that the velocity gradient of the light scattering medium is responsible for the speckle motion. The idea to use this effect for developing measurement techniques for velocity gradients arose almost immediately. For that purpose we had to develop not only experimental set-ups to measure the pattern velocity but also the theory which describes the connection between this velocity and the velocity gradient. The result of this work together with the description of a method developed by another group forms the contents of this book. I am indebted to the students who worked in my laboratory and developed the measurement techniques. These were, in temporal order, Dr. Christoph Keveloh, Dr. Ulrich Schmidt, Dr. Holger Breyer, Dr. Hartmut Kriegs, and Dipl. phys. Rainer Schulz. They also read the manuscript and made lots of helpful comments which I gratefully accepted. I gratefully acknowledge the help of Dr. Matthias Renken in the production of many of the figures in the first part of the book. I furthermore thank Mr. Barry Rankin and my daughter Susanne Staude who helped substantially in the translation of the German manuscript. The final form of the manuscript was carefully read by Prof. Wilhelm Behrens whom I thank very much. Finally, I would like to see that this book raises interest in the field of velocity gradient measurements and causes researchers to apply and develop measurements methods along the lines described here and to obtain new and interesting results. Bremen, August 2001
Wilfried Staude
Symbols
x ˆ X ˆT X
x x+ ∇ bi cS dS dC ds e eP ei eo f fW gi i j, k, l, m, n nx k ki ko q r
vector tensor transpose of a tensor ensemble average time average dimensionless quantity ∂ ∂ ∂ nabla operator : ∇ = ( ∂x , ∂y , ∂z ) image width of lens i normalized correlation function of stochastic process S diameter of scattering area or scattering volume diameter of coherence area diameter of a volume specified by s unit-vector unit-vector in the direction in which the pattern velocity is measured unit-vector in the direction of the illuminating light wave unit-vector denoting the considered component of the scattered light wave focal length of a lens weight function object wid
Data Loading...
