A specialist meeting on Particle
Image Velocimetry and related optical methods, organised by UKALA, was hosted
by the Department of Mechanical Engineering at the University of Nottingham
on Wednesday the 22nd November. The venue for the meeting was the elegant
university Senate Chamber of the Trent Building. An exhibition of related
systems was held in the university Great Hall. Details of the speakers and
the meeting may be found overleaf.
Historical Preamble
The Great Hall at the University of Nottingham, the venue of the recent successful and well attended UKALA meeting, has the historical distinction of having been the venue of an address to students by Mahatma Ghandi in 1933. His advice to both UK and Indian students on that occasion was to value "character before career". This must give us pause for thought making us wonder how the advice was received on that occasion and how the changes in society since then have altered our perception of that ideal.
Opening Address.
Professor Brian Clayton, Dean of Engineering, Nottingham University.
The meeting opened with an address by Professor Brian Clayton in which an historical introduction to Nottingham University was given together with a summary of its very active interaction with industry. The industrial input to its research profile was highlighted and the importance placed on this interaction by the University described.
Introduction to UKALA
Dr John Turner, UKALA Chairman.
The opening address was followed by an introduction to UKALA, its aims
and purpose, by Dr John Turner, Department of Mechanical Engineering, University
of Manchester.
Dr Turner described the history of UKALA, its roots in laser Doppler anemometry
and its national importance in the context of fast developing technological
advances in Europe and United States in other styes of laser anemometry.
The need to include younger member in the organisation was highlighted with
preferential membership rates being offered to students.
Technical Presentations.
PIV: Introduction and current trends.
Professor Ian Grant, FLIC, Heriot-Watt University, Edinburgh.
The first technical presentation was given by Professor Ian Grant in which the evolution of PIV as a separate disciple was summarised. The distinctions between different formulations of the method and related processing methods were described. The relationship between seeding density and processing methods was discussed. Correlation, particle tracking, Fourier transformation methods and specialist hardware for analogue transformation analysis were described.
Professor Grant then presented some examples of the application of the
method in hostile engineering environments with emphasis on computer control
of experiments. The study of wind turbines both in laboratory and in field
conditions by his team using PIV was described. An aeronautical application,
pursued in collaboration with Glasgow University (Department of Aerospace
Engineering), was described where the interaction of helicopter rotor blades
with the wake of the upstream blade had been studied (blade-vortex-interaction).
The behaviour of ship wakes had also been studied using PIV.
In conclusion Professor Grant cited areas of current development in PIV
software and hardware in laboratories worldwide.
Resolution of directional
ambiguity using triple pulse, triple correlation PIV.
Prof D Greenhalgh, Cranfield University.
One common problem in PIV measurements is that a 180 degrees directional
ambiguity in the flow direction results if multiple particle images are
recorded without any means of image coding.
Professor Greenhalgh described a variation of the 'tagging' method where
a third, unequally spaced laser pulse is used to resolve the direction of
the flow. In order to process this type of image directly the Cranfield
group have developed a triple correlation method which utilises the extra
information in the three pulse images. The resulting triple-correlation
function has only one first order peak thus effectively eliminating the
ambiguity. Professor Greenhalgh described the implementation of his system
in a digital-PIV experiment where a counterflow burner consisting of two
opposing balanced air flows with a stagnation plane in the middle were investigated.
In his closing remarks Professor Greenhalgh highlighted the importance of
active particles, used in methods other than PIV, where the fluorescence
can be used to obtain particle trajectories in the flow.
Investigation of the deposition of particulate material upon ceramic filters.
Dr A Aroussi, University of Nottingham.
Dr Aroussi of the Department of Mechanical Engineering gave a presentation of his work on particle dynamics in the presence of filtering units. The project involves the use of computation fluid mechanics (CFD) to predict the trajectories and final deposition of particles as they pass in the bulk flow in the proximity of a filtering unit. The density, size and shape factor of the particles could all be included in the numerical simulation. The trajectories of the particles were predicted and their accumulation on the filter simulated. The PIV method is being used to obtain experimental verification of the predictions. The verification of the CFD code by the PIV studies is essential to the progress of this work to full scale simulation since verification by experiment will not be readily achievable at prototype scale.
Processing of PIV Images.
Mr A Hatem, University of Nottingham.
Mr A B Hatem, a PhD student from the Department of Mechanical Engineering, Nottingham University gave a talk on his doctoral studies in the area of PIV processing. His work is in the low seeding density domain so his work has primarily considered particle tracking methods. Working under the supervision of Dr Aroussi, Mr Hatem has considered the need to correlate with CFD predictions and to that end has been developing interpolation methods which allow a grid of body fitted co-ordinates to be generated using a progressive triangulation method. Mr Hatem has primarily been working in a low seeding density regime and has adopted some of the statistical methods commonly used to track individual particle trajectories.
Drop size and velocity measurement
in annular two phase flow.
Prof B Azzopardi, University of Nottingham.
Prof B J Azzopardi, from the Department Chemical Engineering, presented his work on the measurement of gas/liquid flow in pipes. This was motivated by the needs of the gas/oil production, the chemical and power industries. It focused on vertical upflow with the liquid flowing partially as drops and partially as a film on the pipe walls. Two techniques were employed. These were the laser diffraction method for drop size distribution determination and phase Doppler anemometry for size and velocity measurements. Laser anemometry was employed to obtain data on gas phase velocity and turbulence. The flow was seeded with 1 micron polystyrene particles. In all cases special test sections had been designed and used to eliminate the distortion of light by the curved wall of the pipe and the very wavy liquid film surface. The results obtained have provided useful insights into the physics involved and helped in the developments of-->mathematical models. The work is continuing to the next stage where the effect of inclination from the vertical is being examined.
Application of the swollen polymer technique in the measurement of heat transfer coefficients on film cooled surfaces.
Mr D Lampard, University of Nottingham.
Mr D Lampard, from the Department of Mechanical Engineering, gave a presentation of his work on interferometric methods of heat transfer measurement. The technique used an ingenious application of holographic interferometry to measure thermal processes on turbine blades. The blades were coated with polymer which was swollen with absorbed water. An initial holographic image was made of the blade surface coated with the polymer. The blade was then exposed to typical flow conditions for a period then returned to the holographic recording system where a six-point rigid mounting system ensured exact repositioning to within one-quarter of a wavelength of light. A second holographic exposure resulted in interference fringes. The fringes could be exactly related to the heat transfer processes which had taken place on the surface.
Exhibition and Laboratory
Visit.
Dr Aroussi arranged for demonstrations of commercial off-the-shelf PIV sytems in the Great Hall, each demonstrating different features, concurrently with the meeting. He also lead a tour of Engineering faculty laboratories where many of the studies in optical anemometry described during the conference were demonstrated.
An Invitation
from the Editor for your Work to be Featured in the Optical Diagnostics
in Engineering, 'ODE'.
We would like to invite you to have your work featured in ODE. Our aim
is to provide a regular means of reporting on activities in our field to
the laser user community world wide in a readable and informative style.
We would welcome articles, fims, animations and photographs describing your
work, laboratories and institutions and hope you will help to make this
venture successful and useful. The nature of the WWW ensures a cosmopoliton
and informed audience.and we are most anxious to draw in contributions from
similarly wide horizons.
March 1996.
Professor Ian Grant,
Editor, UKALA Newsletter,
Heriot-Watt University,
Edinburgh,
EH10 5PJ,
Scotland, UK.
tele: (44)-131-451-3156 ;
fax (44)-131-447-8660;
email; flic@igrant.demon.co.uk
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