Description
Project relates to the study of turbulent gas flows loaded by solid particles. Such flows are widespread in nature and engineering. They are complex and influenced by various physical phenomena. Reveal of crucial factors and apply of knowledge to design of manufacturing processes and devices are the key targets of the project. Project aims at a better theoretical understanding of physical processes accompanying channel particulate flows, and it intends to elaborate adequate methods for optimal design of technical devices. Main attention is paid to rigorous mathematical models to describe complicated phenomena for engineering applications. Donor partner focuses attention on effect of interparticle collisions and cohesive mechanisms on forming of particles clusters. Partnership will allow to find joined solution for hydrodynamic and interparticle collisions effects and contribute to the further development both of theory of particulate flows and designing of specific technical devices.
Summary of project results
The project had two key objectives. Firstly, this was the elaboration and implementation of the closure of the averaged momentum equations of the disperse phase by introducing set of the Reynolds stress equations obtained within PDF formalization. Secondly, the given closure has been applied for numerical modelling of the inter-particle collisions in the turbulent particulate channel flows. The project was aimed at a better theoretical understanding of physical processes accompanying channel particulate flows, and it intended to elaborate adequate methods for optimal design of technical devices. A main attention was paid to rigorous mathematical models to describe complex phenomena for engineering applications with considering of the adhesion processes, which lead to agglomeration or uneven behaviour of the particulate matter. The project focused on the theoretical study and the numerical simulation of the inter-particle collisions in the turbulent particulate channel flows. During the project realization, the Estonian team developed 3D numerical model for combined equations for the dispersed phase in turbulent flows. The model was based on 3D Reynolds Stress Turbulence Model (RSTM) for simulation of the carrier gas phase and Probability Dense Function (PDF) formalism for the dispersed phase. The model was validated by application for 3D RANS numerical simulation of various turbulent channel particulate flows. A distinctive feature of the elaborated model is the possibility of solving the transport equations for each component of the Reynolds stresses of the dispersed phase. The model has several important advantages over the Lagrangian approach for the simulation of turbulent particulate flows: 1) direct simulation of the particles’ concentration 2) direct simulation of the particles’ influence on a carrier flow 3) absence of basic limits for the parameters of a particulate flow, namely, the flow Reynolds number and value of the particles’ concentration. The turbulent dispersion of solid particles has been calculated for each flow type by means of the elaborated 3D model. In case of uniform shear horizontal channel flow the effect of the orientation of the velocity shear appears through the decrease of the particles’ dispersion in case of directional coincidence between shear and gravity as compared with case II of their mutual perpendicularity.
Summary of bilateral results
The main task of the Norwegian partner was modeling of inter-particle collisions in multiphase flows with emphasis on cohesive interactions. This was applied to the hard-sphere collision model, and the effect of cohesive mechanisms on forming of particle clusters. The focus was on so-called Lagrangian approach, which tracks individual particles. The initial plan sent in the project proposal in 2013 was: (i) development of the model solely for dry particles and finally (ii) apply the model to flows with a large number of particles. In the course of the project, this objective was accomplished and later extended to wet particles, that is, the final outcome of the project was even larger than planned. The final model was published as journal papers and conference presentations. Next, the Norwegian partner worked on Population Balance Modeling with the focus on particle-particle interactions. This technique is embedded in the Eulerian approach, which was also the main tool of research of the Estonian partner. Finally, it was decided to extend the project to experimental research where the main focus was on rapid particulate flows (dust dispersion prior to explosions). Neither PBM nor the experimental research was planned in the initial project proposal and therefore accomplishing of these additional tasks was very positive for the project outcome. The results of the collaboration of the Estonian and Norwegian teams were presented during the 9th International Conference on Multiphase Flow (May 22-27, 2016, Firenze) and further discussed during the visit of the Estonian scientists to University of Bergen (August 14-19, 2016).