THE VON KARMAN CONSTANT DETERMINED BY LARGE-EDDY SIMULATION

The present study explores the extent to which the logarithmic region of the adiabatic atmospheric boundary layer can be modeled using a thr ee-dimensional large eddy simulation. A value of the von Karman consta nt (kappa(LES)) is Obtained by determining the slope of a logarithmic portion of the velocity profile. Its numerical value is found to be de pendent on the value of the ''Smagorinsky-Model Reynolds number'', Re- SM: the value of kappa(LES) increases with Re-SM. Results indicate tha t kappa(LES) approaches a value of 0.35 as Re-SM reaches about 7.75 x 10(5) for the largest domain. The sensitivity of kappa(LES) to the pro file region over which it is evaluated has bean tested. Results show t hat kappa(LES) is not sensitive to the depth of this evaluation region when we employ five grids above the sub-grid buffer layer where sub-g rid-scale effects dominate. The maximum kappa(LES) is Obtained when th e lower boundary of the evaluation region is just above the top of the sub-grid-scale buffer layer. This result is consistent with modelled mean speed and resolved-scale shear stress profiles.