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Evanescent-Wave Visualizations of the Viscous Sublayer in Turbulent Channel Flow

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Technical Report,01 Sep 2014,31 May 2015

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Georgia Tech Research Corporation Georgia Tech Research Corporation United States

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The study of wall turbulence dates back more than a century. Recently, however, a number of studies suggest that the flow in the inner region i.e., the viscous sublayer and buffer layer is not universaland actually depends upon the specific type of wall turbulence. Many of these new insights on wall turbulence are recent because we have only recently developed the experimental techniques, such as volumetric particle-image velocimetry, to fully resolve wall turbulent flows. The objective of the study described here was to determine whether an even more recent technique, evanescent-wave particle tracking velocimetry PTV, could be used to visualize a plane with dimensions exceeding 100 wall units of the viscous sublayer parallel to the wall in fully-developed turbulent channel flow. Although the start of this study was delayed by visa issues, we have, after six months of work, demonstrated that the initial version of our evanescent wave illumination and imaging system can obtain high-quality images of the tracer particles with a temporal and spatial resolution suitable for wall turbulence that are suitable for PTV analysis, using only 30 of the available laser power.

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