Kalamaras, George (1984) Investigation of the capability of a photon-correlator LDA system for the measurement of mean velocity and turbulence intensity in constrained gas-air mixtures. (MPhil thesis), Kingston Polytechnic, .

Abstract

A study of the capability of the Photon-Correlation technique for the measurement of mean and fluctuating (turbulent) velocity distribution in constrained gas-air mixtures, with particular application to single and co-flowing streams of air containing argon was performed. A critical evaluation of the "gradient transport hypothesis" and the associated phenomenological derivations has been made. A thorough introduction into the Laser Doppler Anemometer parameters and limitations has been also given. . As a check on the accuracy and reliability of the LDA method, LDA measurements were compared with hot wire measurements in a free jet under the same flow conditions. Then the LDA was adapted for use in measuring velocities at any axial, radial or azimuthal position in a pipe, thanks to a purpose designed and built traversing mechanism. Measurements have been taken using the Dual Beam (fringe) configuration in forward-scatter mode (although both forward-and back-scattering have been tested), and using only those light scattering particles occuring naturally in air. Results include mean velocity profiles, turbulence intensities and Reynolds stress diStribution. It has been found that the injector created a wake, which produced a steep depression in the centre-line mean velocity and increased the turbulence intensity level. When injection was taken place, the injector walls were creating a wake. Injected excess velocity was higher than the coflowing air velocity for-more than 180 injector diameters downstream for turbulent flow, 180 diameters for transitionally turbulent" flow, and 90 diameters downstream for the laminar flow. During injection, the centre-line mean velocity reached its maximum value 27 injector diameters downstream for turbulent flow, 18 diameters downstream for "transitionally turbulent" flow and at the injector's exit for laminar flow. An explanation of this finding has been given. It was also found that the "eddy diffussivity" model was not adequate for this mixing flow. The results demonstrated the usefulness of the Photon-Cor¬relation technique in both laminar and turbulent flows, and showed that it could be very effective in air-gas mixtures for detailed and accurate investigations.

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