Numerical simulations of bubbly flows.

Dynamics of bubbly flows is studied by direct numerical simulations. The full Navier-Stokes equations are solved by a finite difference/front tracking technique that fully accounts for viscous, inertia, and surface tension effects, as well as deformability of the bubbles. Both two- and three-dimensional calculations are presented. Simulations of low Reynolds number, multi-bubble flows, in fully periodic domains show that the rise velocity of a freely evolving bubble cloud is higher than that of a regular array of bubbles with the same nondimensional numbers. Interactions of a few hundred two-dimensional bubbles at low Reynolds number suggests that the flow continuously evolves toward a state containing larger and larger scales. For moderate to high Reynolds numbers, simulations of up to 50 bubbles in two dimensions and 16 bubbles in three dimensions, in fully periodic domains, are presented. It is observed that, contrary to the low Reynolds number flows, the rise velocity of a freely evolving bubble cloud is smaller than that of the regular array counterpart. The variations of time-averaged statistics with the void fraction and the number of bubbles are investigated and it is shown that the rise velocity decreases with increase in void fraction. The dynamics of bubbly clouds in a shear flow is investigated and it is shown that the deformation of the bubbles has a major influence on the void distribution in the flow. While bubbles that do not deform migrate toward the downcoming flow, deformable bubbles migrate the other way. Preliminary investigations of polydispersed bubbly clouds in fully periodic domains show that while the transient evolution of flows with different initial conditions are not the same, the time-averaged statistics of the two flows are comparable. A brief account is given of the interactions of bubbles rising to an initially flat fluid surface, and the mechanism whereby the bubbles burst is explained.Ph.D.Mechanical Engineering and Scientific ComputingUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104455/1/9527618.pdfDescription of 9527618.pdf : Restricted to UM users only

Flow patterns and deformation modes of coaxial liquid columns in transverse electric fields

Steady-state flow patterns and deformation modes of coaxial liquid columns in transverse electric fields are studied analytically. The governing creeping flow equations are solved for Newtonian and (mutually) immiscible fluids in the framework of leaky dielectric theory. A detailed analysis of the electric and flow fields is presented and it is shown that there will be four possible flow patterns in and around the columns, in terms of the direction of the external flow (top-to-sides/bottom-to-sides vs. sides-to-top/sides-to-bottom) and the number of vortices (single vortex vs. double vortices) in the shell, and that the senses of the net electric shear stresses at the inner and the outer interfaces and their relative importance are the key parameters in setting these patterns. Equilibrium shapes of the interfaces are also found and it is shown that there are four distinct modes of deformation, depending on the governing nondimensional parameters of the problem. The instability of the jet is also examined qualitatively using the observations pertaining the instability of single-phase drops and jets and the scaling arguments based on the present solution

Numerical Modeling of Three-Dimensional Fluid Flow with Phase Change

We present a numerical method to compute phase change dynamics of three-dimensional deformable bubbles. The full Navier-Stokes and energy equations are solved for both phases by a front tracking/finite difference technique. The fluid boundary is explicitly tracked by discrete points that are connected by triangular elements to form a front that is used to keep the stratification of material properties sharp and to calculate the interfacial source terms. Two simulations are presented to show robustness of the method in handling complex phase boundaries. In the first case, growth of a vapor bubble in zero gravity is studied where large volume increase of the bubble is managed by adaptively increasing the front resolution. In the second case, growth of a bubble under high gravity is studied where indentation at the rear of the bubble results in a region of large curvature which challenges the front tracking in three dimensions

Compiling a template of teacher attributes and competencies based on upstream education documents

The purpose of this study was to develop a model of the characteristics and competencies of the teacher based on the upstream documents of education with a combination of quantitative and qualitative research method. The population of this study was all second-level teachers working in public high schools in Babol. The research instrument was a researcher-made questionnaire consisting of 53 questions in a 5-point Likert scale, which was adjusted using the Delphi method. Also, using the exploratory factor analysis and verifying the validity of the construct, the questionnaire was determined and 8 subscales were obtained which included Values, knowledge, motivations, health, abilities, hobbies, beliefs and moral qualities. The results of the composite reliability test for eight factors showed that this coefficient ranged from 0/70 to 0/94, indicating a favorable reliability for these factors. Also, the results of the internal consistency analysis of these 8 sub-scales showed that these coefficients ranged from 0/65 to 0/83 and the construct validity was 85/0. As the results of the model showed that all paths leading to the teacher's suitability pattern were positive and significant. The results also showed that among all eight factors of teacher's competency model, values, knowledge, motivations, health, abilities, pleasures, beliefs and moral qualities, respectively, had the highest factor load and factor weight on the factor The second rank showed the teacher's suitability pattern. Based on the results, teachers' beliefs and beliefs about teacher education, because they can be the driving force behind the rest of the factors, showed a higher factor load in the teacher's suitability model