DNS and measurements of scalar transfer across an air-water interface during inception and growth of Langmuir circulation

7th International Symposium on Gas Transfer at Water Surfaces

Hafsi, A.^1 ; Ma, Y.^2 ; Buckley, M.^2 ; Tejada-Martinez, A.E.^1 ; Veron, F.^2

Civil and Environmental Engineering Department, University of South Florida, 4202 E. Fowler Avenue, Tampa

FL

33620-535, United States^1

School of Marine Science and Policy, College of Earth, Ocean and Environment, University of Delaware, Newark

DE

19716, United States^2

关键词: Air water interfaces;    Centimeter-scale;    Free-stream speed;    Gravity capillary waves;    Langmuir circulations;    Langmuir turbulence;    Scalar transfers;    Vertical transports;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/35/1/012006/pdf
DOI  :  10.1088/1755-1315/35/1/012006

来源: IOP

【 摘 要 】

Direct numerical simulations (DNS) of an initially quiescent coupled air-water interface driven by an air flow with free stream speed of 5 m/s have been conducted and scalar transfer from the air side to the water side and subsequent vertical transport in the water column have been analysed. Two simulations are compared: one with a freely deforming interface, giving rise to gravity-capillary waves and aqueous Langmuir turbulence (LT) characterized by small-scale (centimeter-scale) Langmuir cells (LC), and the other with the interface intentionally held flat, i.e., without LC. It is concluded that LT serves to enhance vertical transport of the scalar in the water side and in the process increases scalar transfer efficiency from the air side to the water side relative to the shear-dominated turbulence in the flat interface case. Furthermore, transition to LT was observed to be accompanied by a spike in scalar flux characterized by an order of magnitude increase. These episodic flux increases, if linked to gusts and overall unsteadiness in the wind field, are expected to be an important contributor in determining the long-term average of the air-sea gas fluxes.