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Optical Methods for Data Processing in Heat and Fluid Flow by James Buick, John Cosgrove, Clive Greated

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23

Pulsed Laser Particle Image Velocimetry using a Fibre-optic Delivery System

S S Coltman and C A Greated

Abstract

The work outlined in this Chapter is concerned with the study of a particle laden turbulent airflow in a pipe of square cross-section. The velocity of the flow is obtained using a particle image velocimetry (PIV) setup where a novel fibre-optic delivery technique is employed (1, 2). Three sizes of glass beads were used as seeding particles in these experiments, with average diameters of 59 ±51, 173 ±53, and 471 ±120 mm, and all of density 2499 ±53 Kg m–3. These particles are referred to as small, medium, and large respectively throughout the rest of this Chapter. These experiments were repeated with a more conventional beam delivery system for comparison.

Measurements have shown that the velocity values obtained with the fibre setup are, in some cases, underestimated with respect to the direct beam results. This is because the fibre only illuminates the larger beads in the flow sufficiently for the camera to detect them. Both sets of results also show a skewness of the mean velocity profiles. This is possibly due to light being scattered by particles as it travels across the duct, again resulting in biased illumination of the particles.

23.1 Introduction

The work outlined here looks at the behavior of large particles in a fully developed turbulent airflow in a vertical square duct. The particle motion was measured with two different laser beam delivery systems, a ...

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