Decaimento da turbulência convectiva: uma estimativa do coeficiente de difusão turbulento na camada residual

Abstract

In this work is presented a model that describes the decay of the convective turbulent kinetic energy and that estimates the turbulent diffusion coefficient in the Residual Layer. The dynamic equation for energy spectrum function is obtained from Navier-Stokes equation. The terms that describe the inertial transfer of energy, the production or destruction of energy for thermal effect and the molecular dissipation are considered. The inertial transfer of energy is calculated from the Taylor’s statistical diffusion theory. The Heisenberg’s theory that is based on the concept of a kinematic turbulence viscosity to describe the inertial transfer of energy from the big to the small eddies is used. The term that describes the production or destruction of kinetic energy for thermal effect is obtained from the convective similarity theory considering the Pao’s hypothesis. This hypothesis supposes that energy is extracted of the medium flow in a continuous way, allowing do not explicit a scale of time characteristic. The dynamic equations that describe the turbulent flow are only valid in the three-dimensional space. For this reason it was obtained one spectrum 3-D for convective layer from a model proposed by Kristensen, and of a model for the one-dimensional spectra calculated by Degrazia. The turbulent diffusion coefficient is obtained from the Taylor’s statistical and the similarity convective theories. The results obtained in this work are compared with the LES model