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Stably stratified air‐flow over a waved water surface. Part 2: Wave‐induced pre‐turbulent motions
Author(s) -
Druzhinin O. A.,
Troitskaya Y. I.,
Zilitinkevich S. S.
Publication year - 2015
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2678
Subject(s) - turbulence , reynolds number , laminar flow , mechanics , stratified flows , stratified flow , physics , instability , boundary layer , laminar sublayer , direct numerical simulation , flow (mathematics) , meteorology
Recent experimental and direct numerical simulation (DNS) studies have discovered that stably stratified boundary‐layer turbulence over a flat surface is characterized by the critical Reynolds number, Re L , based on the Obukhov turbulent length‐scale and the friction velocity, such that the transition from turbulent to laminar regime occurs at Re L ≈ 10 2 . We have performed DNS of stably stratified flows over both flat and waved surfaces for a wide range of bulk Reynolds numbers and Richardson numbers and revealed that the same threshold, Re L = 10 2 , holds true over waved surfaces. However, when the surface wave slope is sufficiently steep, the supercritically stratified flow involves wave‐induced, ‘pre‐turbulent’ flow patterns, most pronounced in the vicinity of the waved water surface. In the present article, we study basic properties of these motions through DNS and propose a theoretical model of their generation via secondary parametric resonance instability of two‐dimensional disturbances induced in the air‐flow by the surface waves.