Extended Abstract (216K)6A.3
Stably stratified boundary layer simulations with a non-local closure model
N. M. Colonna, Università del Piemonte Orientale, Alessandria, Italy; and E. Ferrero and U. Rizza
Simulations of stable boundary layer are nowadays essential in describing many geophysical flows both in the atmosphere and the ocean.
Reynolds Averaged Navier-Stokes (RANS) models have been largely developed in the last years for shear driven and buoyancy
driven buondary layer, while in the SBL RANS models performances are not yet completely assessed. In the present work a third-order
turbulence model is used to study the stable boundary layer (SBL).
The simulated case reproduces a flow over a flat surface in horizontally homogeneous
conditions. The simulation is carried out cooling from below the boundary layer at a constant and uniform rate
switched on at the initial time. The newness consists in the fact that turbulence in SBL is generally
considered local (at least as first approximation) while our model, resolving the third order moments (TOMs) dynamical equations, accounts
for the non-local transport which, as assessed in several previous works, is generally essential in describing the turbulence flows.
The model employed for the simulation has been tested and validate for shear driven and buoyancy driven boundary layers. The model solves dynamical equations for all
the moments up to the TOMs (following Canuto 1992 [1]) and the Quasi-Normal approximation, with a proper correction (proposed by us in a previous work [2]) to correctly damp
the TOMs, is adopted to close the fourth order moments (FOMs).
Here we present the comparison between our TOM model results and LES in the SBL. Furthermore the TOM model results are compared with the results of a SOM
model in order to verify the effective improvement apported by including the TOMs in the model. The general agreement is satisfactory.
[1] V.M. Canuto, "Turbulent convection with overshooting: Reynolds stress approach", Astroph. J. vol. 392, pp 218-232, 1992.\\
[2] E.Ferrero and N.M. Colonna, "Non local treatment of the buoyancy- shear-driven boundary layer", J. Atmos. Sci. vol. 63, pp 2653-2662, 2006.
Session 6A, BOUNDARY LAYER PROCESSES IN GLOBAL AND REGIONAL CLIMATE OR WEATHER PREDICTION MODELS—IV
Tuesday, 10 June 2008, 10:30 AM-12:15 PM, Aula Magna Vänster
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