Ventilation 2012 Page 1 / 6 3D UNSTATIONARY SIMULATIONS OF A FREE-FALLING PARTICLE JET USING A GRANULAR-KINETIC HYBRID MODEL Z. Zeren 1,3 , H. Neau 1,3 , R. Ansart 2,3 , O. Simonin 1,3 and E. Belut 4 1 Université de Toulouse ; INPT, UPS ; IMFT 2 Allée du Professeur Camille Soula, F-31400 Toulouse, France 2 Université de Toulouse ; INPT, UPS ; LGC ; 4 Allée Émile Monso BP 84234 31432 Toulouse Cedex 4, France 3 CNRS ; Fédération de recherche FERMaT ; F-31400 Toulouse, France 4 Département IP INRS – Centre de Lorraine Rue du Morvan CS 60027 54419 Vandoeuvre cedex - France Abstract Dust generation during the handling of bulk materials in free falls or at the impact on a stockpile can be a serious source of danger for the operator health. Proper design of control systems of fugitive dust requires the knowledge of the behavior of the free falling powder. 3D simulations of granular flow of fine particles falling from a silo under the effect of gravity are implemented to study the influences of different parameters such as the particle-particle frictional viscosity model, the mesh and the turbulence model on the particle phase behavior after the exit of the silo. The results are compared with the experimental ones. Our simulations show that the granular flow behavior inside the silo is correctly captured in mean, this is to say that the simulations generate the solid mass flux at the outlet of the silo that agrees well with the experimental measurement. However, the mean vertical particle velocity in the dispersion chamber is largely overestimated and it is practically not affected by the modifications of the parameters mentioned. Particles fall vertically at the center of the domain in collective motion without much interaction with the surrounding fluid field, which do not allow us to obtain the radial dispersion of the fines. Some future prospects to the problem are discussed. Keywords: Frictional viscosity model, two fluid models, silo configuration, particle free fall 1 Introduction Granular flows are at the heart of many industrial devices and naturally occurring processes. So far, researchers have shown that the fine particles (small in diameter) pouring from a silo configuration have large tendency to be rejected from the main vertical core flow, in radial direction, causing airborne dust (Ansart, 2009). Belt and Simonin (2009) simulated this kind of granular flow without the silo, by imposing the solid mass flux at the silo outlet using an Euler-Euler type code. Their attempt was not successful in generating the instabilities leading to the radial dispersion of fines. Current state of knowledge on the granular flows does not allow explaining the mechanism of this dispersion, which can result in the fine particle deposition on the surfaces, product lost, health problems for the staff working in dusty environments and even fires and explosions. In this work, we extend the study of Belt and Simonin (2009) to the inclusion of a silo to couple the free flow of particles to the granular flow inside the silo. This brings the difficulties of solving a granular flow in quasi-static regime; however, the instabilities generated in such a high volume fraction flows could be the possible cause of the radial dispersion of fines in the dispersion chamber.