Damien Vadillo

Numerical studies of the influence of the dynamic contact angle on a droplet impacting on a dry surface

We numerically investigated liquid droplet impact behavior onto a dry and flat surface. The numerical method consists of a coupled level set and volume-of-fluid framework, volume/surface integrated average based multimoment method, and a continuum surface force model. The numerical simulation reproduces the experimentally observed droplet behavior quantitatively, in both the spreading and receding phases, only when we use a dynamic contact angle model based on experimental observations. If we use a sensible simplified dynamic contact angle model, the predicted time dependence of droplet behavior is poorly reproduced. The result shows that precise dynamic contact angle modeling plays an important role in the modeling of droplet impact behavior.

Evaluation of the inkjet fluid’s performance using the “Cambridge Trimaster” filament stretch and break-up device

This paper describes the design and initial results from the “Cambridge Trimaster,” a recently developed high speed filament stretch and break-up device that can be used for viscoelastic fluids with shear viscosities as low as 10 mPa s. Extensional viscosity and filament break-up behavior were studied optically using a high speed camera and extensional viscosity values determined for a series of mono-disperse polystyrene solutions up to a weight concentration of 5 wt % were measured as a function of the polymer loading. The transient stretching and break-up profiles recorded with the apparatus were observed and correlated with drop formation for drop-on-demand inkjet printing fluids. This allowed the filament break-up behavior to be ranked in terms of satellite drop and droplet filament behavior. Correlation with previous work on the jetting of similar low viscosity viscoelastic polymer solutions demonstrated the ability of this apparatus to characterize inkjet fluids.

The matching of polymer solution fast filament stretching, relaxation, and break up experimental results with 1D and 2D numerical viscoelastic simulation

This paper is concerned with the comparison of two numerical viscoelastic strategies for predicting the fast filament stretching, relaxation, and break up of low viscosity, weakly elastic polymeric fluids. Experimental data on stretch, relaxation, and breakup were obtained using a Cambridge Trimaster for a Newtonian solvent (diethyl phthalate) and three monodisperse polystyrene polymer solutions. Two numerical codes were tested to simulate the flow numerically. One code used a one-dimensional approximation coupled with the arbitrary Lagrangian–Eulerian approach and the other a two-dimensional axisymmetric approximation for the flow. In both cases, the same constitutive equations and mono and multimode parameter fitting were used, thereby enabling a direct comparison on both codes and their respective fit to the experimental data. Both simulations fitted the experimental data well and surprisingly the one-dimensional code closely matched that of the two-dimensional. In both cases, it was found necessary to...

A mathematical model of mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow

A microfluidic channel with a constriction produced poor mixing conditions under periodic electro-osmotic flow. However, the mixing performance may be enhanced significantly by altering other parameters. Numerical simulations are used to investigate the effect of the direct current electric field (EDC), phase difference (ϕ), and length of constriction (L). A mathematical model, based on the structural features of the Lagrange function rather than its application, is proposed to establish a relationship between the mixing performance and these three parameters. The feasibility analysis has been carried out, and the results are verified by the data from simulation and experiment.