Agisilaos Kourmatzis

Characteristics of electrohydrodynamic roll structures in laminar planar Couette flow

The behaviour of an incompressible dielectric liquid subjected to a laminar planar Couette flow with unipolar charge injection is investigated numerically in two dimensions. The computations show new morphological characteristics of roll structures that arise in this forced electro-convection problem. The charge and velocity magnitude distributions between the two parallel electrodes are discussed as a function of the top wall velocity and the EHD Rayleigh number, T for the case of strong charge injection. A wide enough parametric space is investigated such that the observed EHD roll structures progress through three regimes. These regimes are defined by the presence of a single or double-roll free convective structure as observed elsewhere (Vazquez et al 2008 J. Phys. D 41 175303), a sheared or stretched roll structure, and finally by a regime where the perpendicular velocity gradient is sufficient to prevent the generation of a roll. These three regimes have been delineated as a function of the wall to ionic drift velocity Uw/kE, and the T number. In the stretched regime, an increase in Uw/kE can reduce charge and momentum fluctuations whilst in parallel de-stratify charge in the region between the two electrodes. The stretched roll regime is also characterised by a substantial influence of Uw/kE on the steady development time, however in the traditional non-stretched roll structure regime, no influence of Uw/kE on the development time is noted.

From Dilute to Dense Turbulent Sprays: Combustion, Auto-Ignition and Atomization

In line with the general theme of the International Workshop series on Turbulent Combustion of Sprays (TCS), this Chapter addresses relevant issues of turbulent flame structure, auto-ignition and atomization with reference to well-characterized burners that could be implemented by modelers with relative ease. The discussion of turbulent combustion is limited to dilute sprays stabilized on a simple piloted burner. Attention is shifted to the structure of the reaction zones and the challenges of computing chemical composition of flames of different fuels. Another section is dedicated to studying auto-ignition of turbulent dilute spray flames as observed in a hot vitiated co-flow. A common feature to all liquid fuels studied here is the presence of ignition kernels which grow (and sometimes extinguish) to induce flaming combustion further downstream. It is noted that this downstream region is responsible for the bulk of heat release and its local compositional structure depends on the parent fuel.

A Comparative Study of the Simulation of Turbulent Ethanol Spray Flames

Experimental data for a series of spray flames is utilized to perform analysis of validation studies conducted by multiple contributors. In this multiphase context, various choices for boundary conditions as well as modeling frameworks and formulations are evaluated. Both large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) approaches showed the ability to capture droplet evolution with regards to mean and fluctuating velocities. This accuracy is contingent on the proper specification of both droplet and gas phase velocities at the jet exit. The combined effect of combustion and evaporation model choices impacts the downstream volume flux of droplets and resulting gas phase temperature. Further investigation is required to isolate individual model effects for high-temperature spray-laden environments. Proposed solutions involve the simulation of a wider array of flow conditions or lowerlevel experiments to remove the effects of model coupling.

Airway geometry, airway flow, and particle measurement methods: implications on pulmonary drug delivery

ABSTRACT Introduction: The effectiveness of drug delivery to the lungs is inextricably linked to the fundamental interactions that occur between particles and flow in the extrathoracic airway. Research in this field requires time resolved in-vivo and in-vitro measurements of three separate, yet intricately linked parameters: i) airway flow, ii) airway geometry, and iii) drug particle characteristics. A number of recent significant developments have been made in the experimental diagnostic tools used to characterise these parameters. Areas covered: In this review paper, we summarize the key recent findings that have resulted from the implementation of laser and optical diagnostic tools towards characterization of airway flow, extrathoracic airway geometry and drug particle characteristics. These three areas are discussed together, enabling a critical review of the implications of recent experimental findings on likely future developments in drug delivery to the lungs. Expert opinion: Improvements in drug delivery systems will result through implementation of laser and optical based diagnostic methods that can spatially and temporally resolve particle and agglomerate shape, size and dynamic characteristics. Design of inhaler devices must be done in parallel to developing realistic in-vitro upper airway replicas that account for physiological differences between patient groups, as a function of respiratory disease severity.

Conditioned analysis of effervescent atomization

AbstractEffervescent atomizers have a number of significant advantages over conventional injectors. They can operate at much lower injection pressures, their atomization performance is largely inse...