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 three-dimensional large eddy simulation. A value of the von Karman constant (kappa(LES)) is Obtained by determining the slope of a logarithmic portion of the velocity profile. Its numerical value is found to be dependent on the value of the ''Smagorinsky-Model Reynolds number'', Re-SM: the value of kappa(LES) increases with Re-SM. Results indicate that 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 profile region over which it is evaluated has bean tested. Results show that 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-grid-scale effects dominate. The maximum kappa(LES) is Obtained when the 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.