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Title: Digital particle image velocimetry applied to a flow through a duct
Author: Entwistle, Jonathan David
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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Experiments have been performed on a fully-developed turbulent air flow in a square duct using the technique of Digital Particle Image Velocimetry (DPIV). Due to rapid refinement and development of this technique, a new system has been implemented and tested along with purpose-written software and a novel optical fibre delivery system. Fibre delivery is most desirable for PIV applications due to all-round flexibility, allowing measurements to be made in hazardous environments or where optical access is limited. Unfortunately, until now this was not possible with the Nd:YAG pulsed laser due to the ensuing high power densities produced causing irreversible damage at the input end of the fibre core. However, with the introduction of a Diffractive Optical Element to the launch conditions, it has been successfully shown it is possible to transmit laser light at power densities an order of magnitude higher than previously possible, thus providing sufficient illumination for the imaging of 1μm particles. Another advantage of fibre delivery is that it allows a volume to be traversed. Hence, 8 cross-sections of the flow were analysed using DPIV in order to demonstrate the behaviour of secondary motions which exist in the flow. These exist due to the non-circular geometry of the bounding conduit and the action of turbulence. This is not only a challenging application given the limited resolution of the recording media and the magnitude of such secondary circulations (which are approximately, 1-3% of the bulk velocity), but it is the first time that DPIV has been employed to investigate this complex flow regime which even to this day is not well understood. The statistics are most satisfactory and in good agreement with the measurements ascertained from numerical modelling and other experimental techniques. From a DPIV perspective, this demonstrates the ability of this technique with regards to resolving small-scale turbulent motions with an excellent degree of accuracy. Comparisons between the conventional methods of light generation and optical fibre delivery are also presented in terms of mean flow statistics. This provides a direct comparison to be made and therefore, allows future measurements to be carried out with confidence.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available