科研之友
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摘要
We apply turbulence analysis techniques to high-frequency (16 Hz), high-resolution (1.5 mm pixels) thermal infrared images to analyze spatial and temporal scales of mixing between discharging hot spring water (similar to 60 degrees C) and a stream (similar to 10 degrees C) at Breitenbush Hot Springs, Oregon. Optical flow velocimetry of the images provides insight to the transient two-dimensional flow fields of the plumes; correlation of these data sets through space and time indicates the timescales and length scales of turbulent structures within the mixing fluids. We positioned the 7.5 cm diameter discharge pipe so that hot spring water exited along either the surface or bottom of the 15 cm deep stream, conditions hereafter referred to as "shallow" or "deep." During shallow discharge, hot water exits as a jet with length scales of similar to 15 cm. During deep discharge, hot water reaches the surface as a region with similar to 15 cm length scale similar to 20 cm downstream of the inlet. The average temperatures and ratio of thermal variation to turbulent timescale provide a measure of mixing intensity and a means of comparing mixing rates throughout the region of interest. Lateral mixing at the surface dominates during shallow discharge, whereas the most efficient mixing during deep discharge occurs beneath the surface. The largest eddy diffusivities in both scenarios occur downstream of the jet and rising plume, suggesting that those structures must break apart for efficient mixing to occur. The coupled use of thermal imaging technology and optical velocimetry permits quantitative analysis of turbulent mixing in the field at a level of detail rarely achieved.
- 出版日期2011-7-28
