Since Leonardo’s pictorial conception of turbulence with helicity in c. 1517/18, turbulence has been of interest to scientists and engineers, including oceanographers. What is turbulence? The velocity (u) in a turbulent flow is a random function of position (x) and time (t). Alternatively, turbulence can be defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies dominate other forces that tend to damp them out. Turbulent energy can cascade from large to small eddy scales or from small to large. What is small-scale turbulence? The Fourier components for wave-numbers of magnitude ( , where is an integral length representing the size of the energy-containing eddies) can be designated as comprising the “small-scale” components of the turbulent motion. Within this range, the centre of turbulent dissipation is far from the center of energy, and the decay process involves transfer of turbulent energy, by inertial interaction, over a large range of wave-numbers. What is oceanic turbulence? Turbulent motions of different scales in the stably stratified ocean are significantly affected by the surface wind, the rotation, the buoyancy force, the density stratification and the bottom topography. This talk will present an overview of the major approaches/findings of small-scale turbulence which may be useful to oceanographers. The overall contents include: (i) the Kolmogorov-Obukhov scaling laws; (ii) the turbulent dissipation rate ( ); (iii) the Taylor’s turbulent diffusivity, the Richardson’s 4/3 law and turbulent dispersion; (iv) the wind wave turbulence; (v) the Kelvin-Helmholtz instability and internal wave turbulence; (vi) the Ozmidov length; (vii) the turbulent boundary layer and the von Kármán-Prandtl universal logarithmic law. Finally, some recent laboratory experimental results will be presented.
About the speaker:
Zhong Shi, Professor at School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University; Winners of The National Science Fund for Distinguished Young Scholars in 2002; Editorial Board of Springer/Environmental Fluid Mechanics; Visiting fellow and a life member at Wolfson College, University of Cambridge, U.K.