The relevance of droplet dynamics and related non-equilibrium phenomena in several industrial applications and manufacturing techniques calls for new advanced studies using the tools of thermodynamics and computational fluid dynamics.
With this Ph.D. project, we propose an investigation into the dynamics of droplets dispersed into a matrix of immiscible fluid in the presence of temperature and/or concentration gradients. These phenomena are common in several industrial applications and manufacturing techniques (e.g., thermal processing of metal alloys and organic emulsions or suspensions, techniques for material solidification or crystallization, etc.). The physical properties of many materials strongly depend on the multiphase morphology which is controlled to a great degree by particle motion and particle-particle interaction in the liquid phase during the related processing. The possibility that inclusions (drops or bubbles) change their position in space under the effect of various natural forces (e.g., buoyancy or thermal Marangoni effects) has to be regarded as a significant and relevant part of the required analysis or studies.
There are several sources of anisotropy or complexity in these problems, one being represented by surface-tension effects of thermal or solutal origin, the other being gravity itself. The former are responsible for the generation of a vector thrust directed as the imposed temperature gradient. The latter can cause a set of additional phenomena, which can roughly be classified as 1) droplet floatation or sedimentation according to its relative weight with respect to the matrix fluid and 2) convective buoyancy (due to the exchange of solute and/or heat between the droplet and the surrounding liquid). Convection, in turn, can result in the creation of unsteady jets at the droplet surface. These jets, in turn, can cause modulation effects in the otherwise regular motion of the droplet induced by thermal stresses, gravity or a combination of both.
Flows of thermogravitational and thermocapillary nature will be considered in various well-defined geometrical models, under various heating conditions, for a range of different fluids (including Newtonian and non-Newtonian fluids) and possible combinations of all these variants. Starting from relatively simple test cases (single droplet, two droplets in a tandem or side-by-side configuration), the student will progressively consider configurations and problems with an increasing degree of complexity, up to characterizing the dynamics in the presence of several droplets (regular or irregular “droplet arrays”).
Remarkably, these studies, will not be limited to the cases in which these types of convection (thermogravitational or thermocapillary) act separately. Significant effort will be also devoted to elucidate the possible “interplay” of several effects in situations where driving forces of different nature (gravity and surface tension) are simultaneously responsible for the generation of fluid motion. This subject (hybrid or mixed convection) is of a particular importance as the identification of the most dominant mechanism and/or the mutual interference of different mechanisms involved with a comparable intensity, may help the researchers in elaborating rational guidelines relating to physical factors that can increase the probability of success in the above-mentioned practical technological processes.
The research will involve the application of adequate numerical techniques. From a numerical-simulation standpoint, the project will benefit from a set of (already validated) numerical codes for the solution of the governing fluid-dynamics equations in their “complete”, non-linear, time-dependent and three-dimensional, formulation (with a variety of possible boundary conditions and involved physical forces).
The applicant will hold, or in the process of obtaining, an integrated Master’s degree or equivalent in Mechanical Engineering, Chemical Engineering, Materials Science, Materials Engineering, Metallurgy, Aeronautical or Aerospace Engineering, Physics, or another discipline related to the proposed research projects.
Experience with OpenFoam or Ansys Fluent will be appreciated (but it is not strictly required).
From a theoretical point of view, training will be provided to illustrate the 1) genesis of such flows, 2) governing parameters, 3) scaling properties, 4) typical flow structure and stability concepts. From a practical standpoint, the student will be trained to use available numerical tools. Accordingly, relevant information will also be provided on the underlying numerical techniques.
Proposed Start Date: October 2019
Please note the project is unfunded, therefore would be suitable to eligible applicants with self funding, or with the possibility of other sources of funding.
However, funding may be available for Home (UK) students who meet the requirements to be selected in the framework of the "Doctoral Training Partnership" of the University of Strathclyde with Engineering and Physical Sciences Research Council (EPSRC)
The opportunity is open to Home, EU and International applicants, who meet the required University of Strathclyde eligibility criteria. In particular the applicant must not have been awarded a previous Doctoral Degree.
 Lappa M., (2005) Assessment of VOF Strategies for the analysis of Marangoni Migration, Collisional Coagulation of Droplets and Thermal wake effects in Metal Alloys under Microgravity conditions, Computers, Materials & Continua, 2(1), 51-64.
 Lappa M., (2006), Oscillatory convective structures and solutal jets originated from discrete distributions of droplets in organic alloys with a miscibility gap, Phys. Fluids, 18 (4): 042105 (14 pages).
 Capobianchi P., Lappa M., Oliveira M., (2017), Walls and Domain shape effects on the thermal Marangoni Migration of Three-dimensional droplets, Physics of Fluids, 29(11), 112102 (17 pages).