Proposta de um modelo de turbulência híbrido LES-URANS para escoamentos em ciclones

Abstract

Ciclones are separation devices used in several industries, such as grain, oil and minning. As they use the centrifugal acceleration to do the separation, the efficiency of the equipment is directly linked to the flow that occurs inside it. This flow is complex, three-dimensional, turbulent and multiphase, points that make its analysis difficult. With the computational advancement, it became possible to do this analysis using Computational Fluid Dynamics, which can correctly reproduce the flow and calculate some important variables if adequate turbulence models are used. The most used turbulence models in this type of analysis are the URANS with the RSM closure model and the LES model with the Smagorinsky subgrid model for closing the equations. The LES can provide more accurate results, but it needs a finer mesh and has a higher computational cost. To combine the advantages of these two models, the main objective of this work was to propose a hybrid LES-URANS model, using the Smagorinsky model and the RSM model to close the equations, applied to cyclones. To evaluate the new model, the numerical results were compared with results from the pure RSM model and with experimental data available in the literature. From the analysis of the mean and RMS results of the tangential and axial components of velocity, it was noticed that the hybrid model generated higher values for both the mean and the fluctuation. Higher average values increase the centrifugal force acting on the particles, improving efficiency, but also increase turbulence, which tends to disturb the separation. On the other hand, the fluctuations directly interfere in the particles movement, especially for the small ones. Furthermore, the analysis of the modeled and solved components of the turbulent kinetic energy showed that the hybrid model calculates more turbulent scales than the RSM. The combination of these behaviors made the hybrid model generate grade collection efficiency curves closer to the experimental one, even for the coarsest mesh.