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Titel Entrainment across density interfaces
VerfasserIn M. A. Sanchez, A. Carrillo, O. B. Mahjoub
Konferenz EGU General Assembly 2010
Medientyp Artikel
Sprache Englisch
Digitales Dokument PDF
Erschienen In: GRA - Volume 12 (2010)
Datensatznummer 250044895
 
Zusammenfassung
The structure of non-homogeneous turbulence affected by stratification and rotation is investigated both by means of laboratory and numerical experiments. The experiments investigate zero mean flow across a stably stratified density interface and are used to quantify the entrainment, the mixing efficiency and different types of dominant instability and the topological aspects of the turbulent cascades detected both horizontally and vertically [1,2]. Grid turbulence in a rotating stratified two layer system is measured with PIV as well as with sonic velocimetry. Observations of the horizontal and vertical velocity energy spectra as well as the structure functions are used to estimate local mixedness, entrainment and intermittency [3,4]. The method of estimation of the average eddy diffusivity from the time series images of a sharp density interface marked by fluoresceine also take anisotropy into account. but on the long run, horizontal ( and 2D type flow such as [5]) flow directions will average out so using a single integral length scale defined in Sanchez and Redondo(1998) varying in height will be enough together with the internal frequency. The method of calculating vertical fluxes in time allows to estimate different intermittency parameters as a function of local instability e.g. Kelvin/Helmholtz, Rayleigh-Taylor or Holbmoe[6-8]. Different concentration interfaces show different fractal dimensions, that are also a power function of the local Richardson number, this may be due to different levels of intermittency and thus different spectra, which are not necessarily inertial nor in equilibrium [8,9]. [1] Sanchez M.A. and Redondo J.M.Observations from Grid Stirred Turbulence. Applied Scientific Research 59, 191-204. 1998. [2] Redondo, J.M. and Cantalapiedra I.R. Mixing in Horizontally Heterogeneous Flows . Jour. Flow Turbulence and Combustion. 51, 217-222. 1993. [3] Castilla R, Redondo J.M., Gamez P.J., Babiano A. Coherent vortices and Lagrangian Dynamics in 2D Turbulence. Non-Linear Processes in Geophysics 14, 139-151. 2007. [4] Redondo J.M. Mixing efficiencies of different kinds of turbulent processes and instabilities, Applications to the environment in Turbulent mixing in geophysical flows. Eds. Linden P.F. and Redondo J.M. 131-157. 2002. [5] R. Kraichnan. Inertial ranges in two-dimensional turbulence. Phys. Fluids 10. 1967. [6] Linden P.F. and Redondo J.M. Molecular mixing in Rayleigh-Taylor instability. Phys. Fluids 3, 1269-1277. 1991. [7] Redondo J.M. and Garzon G. Multifractal structure and intermittency in Rayleigh-Taylor Driven Fronts. Ed. S. Dalziel www.damtp.cam.ac.uk/iwpctm9/proceedings/IWPCTM9/Papers/Programme.htm. 2004. [8] J.M. Redondo. Turbulent mixing in the Atmosphere and Ocean. Fluid Physics. 584-597. World Scientific. New York. 1994 [9]Mahjoub O.B. Redondo J.M. and Babiano A. 1997 Structure functions in complex flows, Journal of Flow Turbulence and Combustion 59, 299-313.