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|Title:||Photon correlation velocimetry for the fluid flow through turbomachinery.|
|Authors:||Ross, Michael McLean.|
|Presented at:||University of Leicester|
|Abstract:||This thesis is concerned with the application of photon correlation velocimetry to the design of products which employ rotating components in fluids. Two examples are considered, viz. The development of turbines and compressors for power generation. The development of propulsor design for use on underwater powered vehicles. The former required the measurement of high speed gas flows (up to Mach 1.8) both within cascades and in a model turbine. The latter entailed tests on models in both a water tunnel and a wind tunnel with flow velocities of up to 15 meters per second and 50 meters per second respectively. In each case a 50 nanosecond digital correlator was used and the optical systems were designed to operate within constraints set by this, the nature of the expected flows, the optical access available and the information sought. In all three applications, a backscatter geometry had to be used. Laser Doppler velocimetry was employed in the propulsor design. However, since the upper Doppler frequency limit of the correlator was 10 Mz., the high speeds encountered in the turbine and compressor models necessitated the use of laser transit velocimetry. Details of the systems design, the optics and data reduction software are given. Some experimental results of measurements made within cascades and rotating components are presented and their significance concerning the velocimeters used are discussed. The chief conclusions which are drawn from the work are: In many flow configurations of practical interest in gas and steam turbines, transit velocimetry with photon correlation can be used to measure mean velocity to within 1% and turbulence intensity to within 1%. However, in some regions, particularly where the turbulence intensity exceeds approximately 15%, the results are not easy to interpret. Despite the low upper limit to Doppler frequency that can be managed by the 50 nanosecond correlator, its power in processing low-light-level and noisy signals enabled it to be used effectively with a Doppler velocimeter for the measurement of flows within propulsor blading both in a water tunnel and in a wind tunnel. When used with Doppler velocimetry, the inherent averaging mode of operation of the correlator permitted the measurement of mean velocity to within 1%. It also provided a measure of turbulence intensity, which was self consistent to within 2%, although the relationship between this and the standard deviation of velocity was ambiguous. Analysis of the properties of photon correlation in laser velocimetry indicated scope for future work in two directions. Firstly, photon correlation responds to uncertainties arising from particle and velocity biasing in a different way from other signal processors such as burst counters. By carrying out measurements using both types of processor it may be possible to reduce these uncertainties. Secondly, the power of photon correlation in processing low-light-level signals should permit the use of a convenient backscatter arrangement of a reference beam laser Doppler velocimeter to measure the line-of-sight velocity component.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Engineering|
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