On the initiation of surface waves by turbulent shear flow

• Type: Article in International Scientific Journal
• Date: 2006

Authors

Teixeira, MAC (Author) Other; Belcher, SE (Author) Other

Journal

The Journal is awaiting validation by the Administrative Services.

Title: DYNAMICS OF ATMOSPHERES AND OCEANS

Vol. 41

Pages: 1-27

ISSN: 0377-0265

Indexing

ISI Web of Knowledge - 22 Citations

Scopus - 27 Citations

Other information

Authenticus ID: P-004-NCM

DOI: 10.1016/j.dynatmoce.2005.10.001

Abstract (EN): An analytical model is developed for the initial stage of surface wave generation at an air-water interface by a turbulent shear flow in either the air or in the water. The model treats the problem of wave growth departing from a flat interface and is relevant for small waves whose forcing is dominated by turbulent pressure fluctuations. The wave growth is predicted using the linearised and inviscid equations of motion, essentially following Phillips [Phillips, O.M., 1957. On the generation of waves by turbulent wind. J. Fluid Mech. 2, 417-445], but the pressure fluctuations that generate the waves are treated as unsteady and related to the turbulent velocity field using the rapid-distortion treatment of Durbin [Durbin, P.A., 1978. Rapid distortion theory of turbulent flows. PhD thesis, University of Cambridge]. This model, which assumes a constant mean shear rate F, can be viewed as the simplest representation of an oceanic or atmospheric boundary layer. For turbulent flows in the air and in the water producing pressure fluctuations of similar magnitude, the waves generated by turbulence in the water are found to be considerably steeper than those generated by turbulence in the air. For resonant waves, this is shown to be due to the shorter decorrelation time of turbulent pressure in the air (estimated as proportional to 1/Gamma), because of the higher shear rate existing in the air flow, and due to the smaller length scale of the turbulence in the water. Non-resonant waves generated by turbulence in the water, although being somewhat gentler, are still steeper than resonant waves generated by turbulence in the air. Hence, it is suggested that turbulence in the water may have a more important role than previously thought in the initiation of the surface waves that are subsequently amplified by feedback instability mechanisms.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 27