The von Karman constant determined by large eddy simulation

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 (κ_LES) is obtained by determining the slope of a logarithmic portion of the velocity profile. Its numerical value is found the be dependent on the value of the Smagorinsky-Model Reynolds number, Re_SM: the value of κ_LES increases with Re_SM. Results indicate that κ_LES approaches a value of 0.35 as Re_SM reaches about 7.75×10⁵ for the largest domain. The sensitivity of κ_LES to the profile region over which it is evaluated has been tested. Results show that κ_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 κ_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 stress profiles.