Numerical simulation of a two-phase turbulent pipe-jet flow loaded with polydispersed solid admixture

• Published in: International journal of multiphase flow 1997, Vol.23 (4), p.765-796
• Main Authors: Frishman, F., Hussainov, M., Kartushinsky, A., Mulgi, A.
• Format: Article
• Language: English
• Subjects: Computer simulation; Dispersions; Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); inter-particle collisions; Jets; Mixtures; modelling; Multiphase and particle-laden flows; Nonhomogeneous flows; Particles (particulate matter); Physics; pinch-effect; Pipe flow; pipe-jet flow; pseudo-viscosity coefficients; Reynolds number; turbophoresis force; Turbulent flow; Viscosity
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/S0301-9322(97)00017-7

Results of the mathematical modelling of a two-phase turbulent pipe-jet flow carrying fine solid particles are presented. The numerical results are compared with experimental data obtained in our laboratory. The purpose of the joint study of these flows is connected with the efforts to explain the pinch-effect experimentally discovered by Laats and Frishman (1970) and Navoznov et al. (1979) (for the motion of fine solid particles in a jet). It is associated with the growth of particle mass concentration along the jet axis with its maximum at some distance from the outlet of the pipe. The effect of intensive scattering of large particles in the initial region of the two-phase turbulent jet was also discovered in those experimental investigations. The theoretical analysis made by Kartushinsky (1984) showed that these effects are linked not only with the properties of the motion of particles of different size in the turbulent jet, but also with the prehistory of the motion of such particles in a pipe. Our calculations of the pipe jet flow provide an opportunity to trace the development of the particle mass concentration and the velocity fields in the pipe and jet, excluding the necessity for artificially given initial boundary conditions in the jet for modelling the pinch-effect. The peculiarity of this simulation is in the closure of the equations of the motion of the dispersed phase. The inter-particle collisions in polydispersed flows are considered, since in real two-phase flows the dispersed admixture itself is a polydispersed medium and, thus, the inter-particle collisions play a significant role together with the turbulent diffusion of particles in modelling. The so-called pseudo-viscosity coefficients are introduced in the transport equations of mass, momentum and angular momentum of the dispersed phase for modelling the inter-particle collisions. The formulae for pseudo-viscosity coefficients take into account the properties of the particle motion (the linear and angular velocities and mass concentration of the dispersed phase), their relaxation features as well as collision parameters (the restitution and friction coefficients). The system of equations for the motion of each particle fraction is written and solved for a pipe jet flow. The exchange of the momentum in the fluctuating motion of the gaseous and dispersed phases is taken into account together with the inter-particle collisions. Such exchange of the momentum results to the additional forc