IAHR Document Library

« Back to Library Homepage « Proceedings of the 2nd IAHR Europe Congress (Munich, 2012)

Development of Surface Velocity Divergence Model for Gas Transfer Phenomena in Open-Channel Flows

Author(s): Michio Sanjou; Iehisa Nezu

Linked Author(s): Michio Sanjou

Keywords: No Keywords

Abstract: It is very important to reveal gas transfer phenomena beneath air/water interface in ocean, lakes and rivers, when we consider global warming problems. Turbulence is generally produced by buoyancy convection, velocity shear near the air/water interface and bottom friction shear. The buoyancy convection is very significant for turbulence production in stratified lakes. In contrast, the winds over a free-surface promote the turbulence and related gas exchanges in ocean. A bed generated turbulence in streams such as openchannel flows plays significant roles on the gas transfer beneath the free-surface. Previous studies tried to connect the gas transfer velocity with a bulk-mean velocity, water depth, bed slope and friction velocity of the flume bed. A LIF technique allows us to measure local transfer velocity and thus effects of coherent turbulence structure on instantaneous gas transfer properties could be evaluated reasonably. Furthermore, many numerical researches are reported by using LES and DNS, and these turbulence simulations suggested that low speed streak and coherent vortex control the CO2 gas transfer from the interface to the bulk layer. However there still remains much uncertainty about contributions of turbulence to the gas transfer in rivers. In this study, we conducted the horizontal free-surface PIV in a laboratory flume together with DO measurements, and evaluated the gas transfer velocity and the surface velocity divergence in the open-channel flows. It was found that a standard surface divergence model (SD model) is insufficient for the open-channel conditions, and thus, a modified SD model could be developed herein.


Year: 2012

Copyright © 2024 International Association for Hydro-Environment Engineering and Research. All rights reserved. | Terms and Conditions