Universidad de Chile

Flow structure in the vicinity of air-water interfaces with surface shear stress and its relation with oxygen transfer

Principal investigator: Aldo Tamburrino

Project funded by the Chilean National Science and Technology Fund, FONDECYT (Project Nº 1020822)

Years: 2002-2004

This project corresponds to an experimental study about reaeration or oxygen transfer across an air-water interface, when a flow of air exists over the water surface. Two situations are considered, one corresponding to the case in which the liquid phase is driven solely by the air flow, and the other to the case in which, besides the effect of the air flow, the liquid phase exhibits a turbulent field of its own, induced by other forcing conditions. It is well known that the wind increases the oxygen transfer rate with respect to that under stagnant air conditions, however not enough is known regarding the mechanisms involved in this transfer process. In this project, a detailed experimental study of the flow structure of both gaseous and liquid phases is being carried out, to gain further knowledge about the effect of the wind-induced surface shear stress on the reaeration process. An experimental facility was built as part of the study, consisting of a wind tunnel coupled with a micro-jet agitated water tank. In the tank the water simply recirculates, thus increasing the residence time and helping to reduce the errors involved in measuring gas transfer. The turbulence level within the water tank is controlled by changing the velocity of the jets and the water depth. The turbulent structure of the air flow is measured with hot-film anemometry while the turbulent structure of the water flow is measured with the ADV technic. Flow visualization, PIV and PTV technics are also used to study the role of flow coherent structures on the transfer process. Gas transfer rates across the water surface are obtained from measurements of dissolved oxygen concentrations within the tank. The initial conditions of the experiments are obtained by depleting the oxygen dissolved in the water through chemical reactions. It is expected that this project will contribute to i) formulate phenomenological conceptual models to improve our present level of understanding and prediction capacity of the turbulent structure of water flows in the vicinity of the free surface under wind and turbulent forcing conditions, and ii) obtain relationships to quantify oxygen transfer rates in water bodies under the effect of wind.

Selected Publications:

Tamburrino, A. (2003). Scaling-Up of Gas Transfer Coefficient from Agitated Tank Measurements to Open Channel Flows, XXX IAHR Congress, Thessaloniki, Greece, Aug, 24,29.

Tamburrino, A. and Gulliver, J. (2002). Free-Surface Turbulence and Mass Transfer in a Channel Flow. AIChE Journal, Vol. 48, No. 12, pp.2732-2743.

Tamburrino, A. and Gulliver, J.S. (1999). Large flow structures in a turbulent open channel flow. Journal of Hydraulic Research, Vol. 37, No. 3, pp. 363-380.

Tamburrino, A. and Mourgues, A. (2002). Experimental study of the flow structure in the near free-surface region. Advances in Fluid Mechanics IV, Ghent, Belgium, May. 15-17, pp. 217-229.

Tamburrino, A. and Aravena, C. (2002). Reaeration Coefficient Determined from Agitated Water Tank Experiments. 5th Int.Conf. on Hydro-Science and Engineering, Warsaw, Poland, Sept. 18-21.

Tamburrino, A. y Aravena, C. (2002). Caracteristicas de la turbulencia en la superficie libre de un estanque agitado. XX Congreso Latinoamericano de Hidráulica, IAHR, La Habana, Cuba, Oct. 2-5.