Lengthscales of motions that control air-water gas transfer in grid-stirred turbulence

H. Tsumori, Yuji Sugihara

    Research output: Contribution to journalArticle

    14 Citations (Scopus)

    Abstract

    The relationship between the gas transfer velocity and turbulent lengthscales is investigated experimentally in a grid-stirred turbulent flow. The horizontal velocity field at the water surface is measured using particle image velocimetry (PIV). The gas transfer velocity for oxygen is obtained through reaeration experiments. In addition, the gas transfer process by surface-renewal eddies is visualized using laser-induced fluorescence (LIF) technique, in which carbon dioxide is used as the tracer gas. The definition of the Taylor microscale holds that the root-mean-square (RMS) of the surface divergence is expressed by the square root of the turbulent kinetic energy divided by the Taylor microscale. Experimentally obtained data support this scaling. They show the gas transfer velocity to be proportional to the square root of the RMS of the surface divergence. These experimental results imply that the Taylor microscale is an important parameter for gas transfer velocity at the air-water interface. These relations indicate that a nondimensional gas transfer velocity is proportional to the - 1/4 power of a turbulent-macroscale Reynolds number, which is similar to a small-eddy model, assuming that turbulent eddies with the Kolmogorov scale control the gas transfer process. However, this Reynolds number dependence does not necessarily mean the superiority of turbulent eddies with the Kolmogorov scale in the gas transfer. The LIF visualizations in horizontal and vertical planes close to the air-water interface indicate that the horizontal CO2-concentration field has a fine spatial pattern, which resembles that of the surface divergence field, and that surface-renewal motions observed in the vertical plane have a larger lengthscale than the Kolmogorov scale. We infer from both PIV and LIF results that the Taylor microscale is an important lengthscale for air-water gas transfer.

    Original languageEnglish
    Pages (from-to)6-18
    Number of pages13
    JournalJournal of Marine Systems
    Volume66
    Issue number1-4
    DOIs
    Publication statusPublished - Jun 1 2007

    Fingerprint

    turbulence
    gases
    air
    gas
    water
    laser induced fluorescence
    eddy
    lasers
    divergence
    fluorescence
    Reynolds number
    carbon dioxide
    turbulent flow
    kinetic energy
    visualization
    tracer techniques
    tracer
    surface water
    oxygen
    kinetics

    All Science Journal Classification (ASJC) codes

    • Oceanography
    • Ecology, Evolution, Behavior and Systematics
    • Aquatic Science

    Cite this

    Lengthscales of motions that control air-water gas transfer in grid-stirred turbulence. / Tsumori, H.; Sugihara, Yuji.

    In: Journal of Marine Systems, Vol. 66, No. 1-4, 01.06.2007, p. 6-18.

    Research output: Contribution to journalArticle

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