variavel0=<b>Luben Cabezas-Gómez</b> - lubencg@sc.usp.br Núcleo de Engenharia Térmica e Fluidos, EESC-USP
<b>Luciano Vieira de Souza</b> - souzalv@sc.usp.br Núcleo de Engenharia Térmica e Fluidos, EESC-USP
<b>Fernando Eduardo Milioli</b> - milioli@sc.usp.br Núcleo de Engenharia Térmica e Fluidos, EESC-USP
<b>Abstract.</b> An evaluation is presented regarding the effect of different interface drag function correlations over the dynamics of formation,  dissipation  and breaking  of coherent  structures in  the  gas-solid flow  of  a circulating  fluidized  bed through numerical  simulation. The  numerical  simulation  is  performed  using  the  MICEFLOW  code,  which  includes  the  two-fluids  IIT`s  hydrodynamic  model  B.  The  methodology for cluster characterization that is used is based in the determination of four characteristics, related to average life time,  average  volumetric  fraction  of  solid,  existing  time  fraction  and  frequency  of  occurrence.  The  identification  of  clusters  is  performed  applying a criterion related to the time average value of the volumetric solid fraction. This methodology is applied to results of simulation  obtained  using  different  drag  function  correlations,  and  a  qualitative  analysis  is  performed  regarding  the  influence  of  this  important  parameter over the hydrodynamics of the flow including the evolution of coherent structures. The simulation predictions obtained using  the different drag function correlations are also compared to experiment, providing an additional analysis related to the behavior of gas  and solid axial velocity profiles and solid fraction. The analyses indicate that the choice of a correlation for the drag function should be  quite  judicious,  and  that  the  development  of  new  correlations  is  required  since  most  of  the  existing  correlations  were  developed for  homogeneous fluidization.
<b>Keywords.</b> coherent structures, drag function, numerical simulation, gas-solid flow, circulating fluidized bed.