By Alexander Baklanov, Branko Grisogono, A. Baklanov, B. Grisogono
Most of practically-used turbulence closure types are in keeping with the idea that of downgra- ent delivery. for that reason the types convey turbulent uxes of momentum and scalars as items of the suggest gradient of the transported estate and the corresponding turbulent shipping coef cient (eddy viscosity, ok , warmth conductivity, okay , or diffusivity, okay ). Fol- M H D lowing Kolmogorov (1941), turbulent shipping coef cients are taken to be proportional to the turbulent pace scale, u , and size scale, l : T T ok ? ok ? okay ? u l . (1) M H D T T 2 frequently u is identi ed with the turbulent kinetic strength (TKE) consistent with unit mass, E ,and okay T is calculated from the TKE finances equation utilizing the Kolmogorov closure for the TKE dissipation price: ? ? E /t , (2) ok ok T the place t ? l /u is the turbulent dissipation time scale. This technique is justi ed whilst it T T T is utilized to impartial balance ows, the place l should be taken to be proportional to the gap T from the closest wall. despite the fact that, this system encounters dif culties in strati ed ows (both sturdy and uns- ble). The turbulent Prandtl quantity Pr = ok /K indicates crucial dependence at the T M H strati cation and can't be regarded as constant.
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Extra info for Atmospheric Boundary Layers: Nature, Theory and Applications to Environmental Modelling and Security
At first sight, these could be obtained numerically using an adequate turbulence-closure model. However, this way is too computationally expensive: the mean gradients close to the surface are very sharp, which requires very high resolution, not to mention that the adequate closure for strongly stable stratification can hardly be considered as a fully understood, easy problem. Hence the practically sound problem is to analytically express the surface fluxes τ∗ and F∗ through U1 = U |z=z 1 and 1 = |z=z 1 available in numerical models (and similarly for the fluxes of humidity and other scalars).
N. 51 (16) after Zilitinkevich et al. 5 4 Concluding remarks In this paper we employ a generalised similarity theory for the stably stratified sheared flows accounting for non-local features of the atmospheric stable ABL, follow modern views on the turbulent energy transformations rejecting the critical Richardson number concept, and use recent, high quality experimental and LES data to develop analytical formulations for the wind speed and potential temperature profiles across the entire ABL. Results from our analysis are validated using LES data from DATABASE64 covering the four types of ABL: truly neutral, conventionally neutral, nocturnal stable and long-lived stable.
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