One effective way of combining in a synergic way the properties of individual polymers is the manufacturing of multi-layered products, whose performance of is directly linked to the layers uniformity. Polymer multilayer co-extrusion is a manufacturing process wherein two or more polymers are fed to a common extrusion die to form a multi-layered product. The usual manufacturing approach starts by co-extruding two layers which are duplicated in one Interfacial Surface Generator Module (ISGM). The multiplication of the layers is achieved by dividing the flow of the two inlet layers in two individual streams, deforming and overlapping the two individual streams, which are subsequently joined to reach a four layer structure. This work comprises a computational based study aiming to improve the knowledge related to the design of ISGM, which was done with the support of the multiphase flow solvers from OpenFOAM computational library. Each ISGM comprises several geometric transformations, which can be made simultaneously or sequentially, producing effects on the velocity fields that impact the uniformity of the layers. The simultaneous combination of geometrical transformations, allows reducing both the device length and, in general, the total pressure drop. However, when specific effects are combined, the layers become unevenly distributed. To better understand the system behaviour, several configurations for the ISGM were studied, aiming to identify the geometry details that promote a non-uniform layer distribution. The results obtained showed the simultaneous combination of specific geometrical transformations that have a negative impact on the uniformity of the polymer layer thickness distribution, at the device outlet. Thus, configurations that promote this type of flow distribution should be avoided.

Suspensions consisting of solid particles dispersed in a liquid often exhibit complex flow properties that can not be adequately modeled with a simple Newtonian approach. The presently investigated suspension, which serves as a suspension or slurry electrode for zinc-air flow batteries, consists of a liquid electrolyte and microscopic zinc particles. To stabilize the suspension, i.e. prevent sedimentation of the metallic particles, the liquid electrolyte is gelled with a polymeric binder (polyacrylic acid, PAA). The binder induces significant shear-thinning properties of the liquid electrolyte phase accompanied by pronounced apparent slip at smooth walls. The addition of particles to the electrolyte further modifies the flow behavior and distinct thixotropic properties are observed.
Here we present a macroscopic, homogeneous approach to simulate the complex suspension flow based on the single-phase Navier-Stokes equations. The time-dependent rheological behavior of the bulk fluid is modeled with a structural kinetics approach, where the local history- and shear-dependent state of the material structure is described with a transported dimensionless parameter. The wall-fluid interaction, i.e. the wall slip, is modeled with a modified non-linear Navier slip law. Instead of trying to individually measure the isolated rheology and wall-slip parameters with a series of tailored experiments, measured velocity profiles were used as a reference to calibrate the models. Due to the opacity of the fluid, an ultrasound flow mapping technique (Ultrasound Imaging Velocimetry) was applied to measure two-dimensional flow fields in a reference experiment. The numerical model in combination with the obtained parameters reproduce the flow characteristics reasonably well for different flow conditions, especially the extended stagnation zones observed for the thixotropic suspension. The presented numerical models could consequently be used to investigate comparable fluid flows for relevant applications and identify critical flow situations. For example, in flow batteries with suspension electrodes stagnation zones must be avoided to prevent blockage of the flow channels due to build-up of solid residue from reaction products, e.g. ZnO in zinc-air flow batteries. Generally it is desirable to avoid such zero-flow zones in piping and fluidic equipment for complex (multiphase) fluids, which increase pressure drops and can possibly lead to sedimentation and ultimately blockages.

The cavitating flow through an axisymmetric nozzle was simulated using an Euler-Euler, an Euler-Lagrange, and a multi-scale Euler-Lagrange method. The Euler-Lagrange approach and the hybrid multi-scale Euler-Lagrange approach were implemented into OpenFOAM. In the Lagrangian methods, interactions between vapour bubbles and the liquid phase were considered in form of a two-way coupling. Main components of the Lagrangian approach - bubble dynamics and bubble motions - were verified and validated. The multi-scale Euler-Lagrange method captured large vapour volumes on an Eulerian frame, while small vapour volumes were treated as spherical Lagrangian bubbles. Procedures to transform vapour volumes between the Eulerian and the Lagrangian frame were verified. Numerical results of the flow through an axisymmetric nozzle were investigated in terms of spatial discretisation for the Euler-Euler approach and in terms of cavitation nuclei distribution for both Lagrangian based approaches. While the Euler-Euler method used information from the flow solution to assess cavitation-induced erosion, the multi-scale method predicted erosion based on collapse dynamics of Lagrangian bubbles. Numerical erosion predictions were compared to experimentally measured erosion patterns.

Cavitation in injection systems can lead to erosion and failure. However, cavitation is desired for an enhanced fuel jet breakup into small droplets leading to a more homogeneous combustion. We investigate both cavitation erosion and primary breakup in Diesel injectors with two different numerical methods. For both methods the needle movement corresponding to one injection cycle is prescribed as moving wall boundary condition.

The first method is tailored to the detection of erosion sensitive wall zones. It is a density-based, compressible flow solver with a non-viscous flux formulation for cavitating flow. Time integration is performed with a four stage low storage explicit Runge-Kutta scheme. This combination enables the simulation of wave dynamics and resolution of shock waves, which are crucial for erosion. Cavitation is modeled using a barotropic law. Since cavitation is inertia driven, no turbulence model is utilized. By applying erosion indicators at the walls of the injector we have been able to predict partially the experimentally found erosion prone regions for two different ship injector designs.

For the simulation of primary breakup the focus is on accurate calculation of turbulent structures with an LES, which is not possible with the upwind-based method for cavitating flow discussed above. Thus, we use a pressure-based, incompressible flow solver for this purpose. The three phases liquid and vaporous fuel as well as air are modeled with the Volume of Fluid (VOF) method. Phase change due to cavitation is taken into account by the mass transfer model of Sauer and Schnerr. Besides the in-nozzle flow the spray breakup is investigated up to 7 mm downstream of one nozzle hole. Primary breakup of the jet is assessed by detection of Euler ligaments and statistical evaluation of their properties. The LES is performed with the WALE model. The simulation method is validated by comparison with µLIF experimental results in the near nozzle region. A qualitative agreement is found regarding the structure and spray cone angle of the jet. At low lift cloud cavitation occurs, while at high lift string cavitation is observed. The cavitation types are in correspondence with distinct vortex structures and turbulence intensities.