Multiphase flow and icing predictions with control-volume based finite-element method and PIV laser measurements.

摘要

A novel Eulerian dispersed-flow Two-Fluid model and an ice accretion model are developed. They are validated for applications involving droplet-air motion and ice interface tracking. Spatially averaged multiphase flow equations are developed and additionally modeled for interfacial form and shear drag forces. Scaling, order of magnitude and similarity methods are adopted for investigation of special near-wall dispersed-flow solutions. A novel multiphase flow exact closed form similarity solution is analytically derived for the droplet flow injected into an airstream at a flat plate. One- and two-phase closed form Lagrangian analytical solutions for dispersed phase/continuous phase (i.e. droplet/air) tracking are developed. Two numerical algorithms, a Control-Volume based Finite-Element dispersed-flow algorithm and an icing algorithm, are developed with a fixed grid approach, and incorporated into an existing PHASES numerical program. Grid and initial condition independence are obtained for several external flow situations, involving frontward steps with straight and curved surfaces. In icing applications at the ice and solid objects, the dispersed-droplet flow is modeled as a group of physical bodies impacting on a surface, while the air flow is modeled as a continuous flow. Drag/gravity is an important ratio when determining the degree of dispersed-flow inertial deflection from a continuous flow and near solid surfaces. An Eulerian, two-dimensional ice interface tracking algorithm is developed for ice shape evolution predictions. It is validated against analytically developed, closed form Lagrangian two-dimensional ice interface solutions. Furthermore, experimental studies are carried out for droplet and jet flows in the airstream and icing applications, involving water and spray-icing tunnels. Various indoor conditions are considered in the investigation of the droplet flow characteristics (i.e. droplet diameter and impact length geometries). A liquid spray nozzle systems (long and short distances) and liquid stream nozzle system are developed for velocity and trajectory flow measurements. In addition, a PIV laser based technique with low and high sense CCD chip cameras is used in the spray and stream flow experimental designs to predict the whole-field droplet velocities. Results with numerical, analytical and experimental validations involving droplet motion and ice shape evolution on various surfaces are presented.