Structure and mixing of a meandering turbulent chemical plume: turbulent mixing and eddy diffusivity

• Turbulent mixing in a meandering non-buoyant chemical plume is far less understood than in a straight plume—partially due to difficulty separating the plume meander from the turbulent fluctuations. This study presents high-resolution measurements of the covariance of the turbulent fluctuations of velocity and concentration, i.e., the turbulent flux, in a phase-locked meandering plume, acquired by simultaneous particle tracking velocimetry and laser-induced fluorescence measurements. Analysis of the data reveals that the spatial distribution of the turbulent quantities is governed by the large-scale alternating-sign vortices that induce the plume meander. Further, the spatial variation of turbulent flux agrees well with the spatial variation of the phase-averaged concentration gradient. As a result, the eddy diffusivity framework effectively models the turbulent flux. As expected from turbulent mixing theory, the eddy diffusivity coefficient plateaus at a constant value once the plume width reaches the size of the largest eddies. However, when the plume width is less than the size of the largest eddies, the eddy diffusivity coefficient scales with the plume width to the n = 1 power. Analysis based on the measurements of the growth rate of the plume width yields a consistent prediction for the variation of the eddy diffusivity coefficient in the near field. Graphical abstract: [Figure not available: see fulltext.]

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NATURVETENSKAP  -- Annan naturvetenskap (hsv//swe)

NATURAL SCIENCES  -- Other Natural Sciences (hsv//eng)

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