Title page for ETD etd-05092009-040709
|Type of Document
||An investigation of velocity bias with a three-component LDA in open channel flow
||Master of Science
|Dancey, Clinton L.
|Brown, Eugene F.
|Roe, Larry A.
- Laser Doppler velocimeter
|Date of Defense
Data collected with a three-component laser Doppler anemometer system is used
to investigate velocity bias. The data is collected in the viscous layer of a fully developed
turbulent open water flow at a Reynolds number of 14,766 based on the flow depth. The
data collected at a relatively low data rate is analyzed using different correction methods
including: straight forward arithmetical averaging, inverse velocity and transit time
weighting. The streamwise mean velocity components, the RMS values and the kinematic
Reynolds stress are computed using the various weighting methods and are conlpared to a
three-component inverse velocity bias correction model which is taken to represent the
"true" values. The three-component inverse velocity bias correction results are in general
accordance with the expected behavior in open channel flow and are comparable to the
results reported by other researchers employing different experimental techniques. The
results of this study show that the bias is sensitive to the correction method used and the
theory that the mean streamwise velocity error (without correction) is proportional to the
square of the turbulence intensity is confirmed experimentally. Averaging the data without
correcting it produced the largest bias while the results from the different inverse velocity
techniques were approximately the same although the level of the bias varied with the
turbulence variable that was analyzed. As reported in the literature, the transit time
weighting method requires accurate determination of the residence time. The relatively
poor performance of the transit time method in the present comparison is attributed to the
poor accuracy in the measurement of the residence time.
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