Two-dimensional Navier--Stokes simulation of deformation and break up of liquid patches

The large deformations and break up of circular 2D liquid patches in a high Reynolds number (Re=1000) gas flow are investigated numerically. The 2D, plane flow Navier--Stokes equations are directly solved with explicit tracking of the interface between the two phases and a new algorithm for surface tension. The numerical method is able to pursue the simulation beyond the breaking or coalescence of droplets. The simulations are able to unveil the intriguing details of the non-linear interplay between the deforming droplets and the vortical structures in the droplet's wake.Comment: 13 pages including 4 postscript figures; Revised version as resubmitted to PRL. Title has change

Determination of the aerodynamic droplet breakup boundaries based on a total force approach

The determination of the critical Weg number separating the different breakup regimes has been extensively studied in several experimental and numerical works, while empirical and semi-analytical approaches have been proposed to relate the critical Weg number with the Ohl number. Nevertheless, under certain conditions, the Reg number and the density ratio ε may become important. The present work provides a simple but reliable enough methodology to determine the critical Weg number as a function of the aforementioned parameters in an effort to fill this gap in knowledge. It considers the main forces acting on the droplet (aerodynamic, surface tension and viscous) and provides a general criterion for breakup to occur but also for the transition among the different breakup regimes. In this light, the present work proposes the introduction of a new set of parameters named as Weg,eff and Cal monitored in a new breakup plane. This plane provides a direct relation between gas inertia and liquid viscosity forces, while the secondary effects of Reg number and density ratio have been embedded inside the effective Weg number (Weg,eff

Predicting droplet deformation and breakup for moderate Weber numbers

The present work examines numerically the deformation and breakup of free falling droplets subjected to a continuous cross flow. The model is based on the solution of the Navier–Stokes equations coupled with the Volume of Fluid (VOF) methodology utilized for tracking the droplet-air interface; an adaptive local grid refinement is implemented in order to decrease the required computational cost. Neglecting initially the effect of the vertical droplet motion, a 2D axisymmetric approximation is adopted to shed light on influential numerical parameters. Following that, 3D simulations are performed which include inertial, surface and gravitational forces. The model performance is assessed by comparing the results against published experimental data for the bag breakup and the sheet thinning breakup regimes. Furthermore, a parametric study reveals the model capabilities for a wider range of Weber numbers. It is proved that the model is capable of capturing qualitatively the breakup process, while the numerical parameters that best predict the experimental data are identified

Numerical investigation of aerodynamic droplet breakup in a high temperature gas environment

The Navier-Stokes equations, energy and vapor transport equations coupled with the VOF methodology and a vaporization rate model are numerically solved to predict aerodynamic droplet breakup in a high temperature gas environment. The numerical model accounts for variable properties and uses an adaptive local grid refinement technique on the gas-liquid interface to enhance the accuracy of the computations. The parameters examined include Weber (We) numbers in the range 15-90 and gas phase temperatures in the range 400-1000 K for a volatile n-heptane droplet. Initially isothermal flow conditions are examined in order to assess the effect of Weber (We) and Reynolds (Re) number. The latter was altered by varying the gas phase properties in the aforementioned temperature range. It is verified that the We number is the controlling parameter, while the Re number affects the droplet breakup at low We number conditions. The inclusion of droplet heating and evaporation mechanisms has revealed that heating effects have generally a small impact on the phenomenon due to its short duration except for low We number cases. Droplet deformation enhances heat transfer and droplet evaporation. An improved 0-D model is proposed, able to predict the droplet heating and vaporization of highly deformed droplets

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Rozwój ubezpieczeń publicznych w Polsce. T. 1 /

Dostępne również w formie elektronicznej

Theory and design of lumped linear three-terminal RC networks.

The theory of two-port three-terminal lumped linear RC networks has not yet been fully explored. In particular, there are no general 'necessary and sufficient' conditions for network synthesis, nor standard synthesis techniques for 'non-series-parallel' topologies. By using a digital computer and a technique of coefficient matching, allied with an optimisation routine, 'non-series-parallel' topologies can be synthesised as readily as 'series-parallel' topologies. Coefficient matching involves the construction of individual error functions, to measure the departure of the coefficients required from those currently achieved. The effect of modifying the method of function representation is investigated and it is demonstrated that for the best method the efficiency of the optimisation algorithm is greatly improved. The properties of closed form expressions for the normalising variable are examined. The network topology may require alteration as part of the design process. Criteria for the removal and addition of elements are discussed and their implementation in a computer program for network design without user interaction is described. The effectiveness of the approach is illustrated by the synthesis of a new 'non-series-parallel' network. Only one 'non-series-parallel' network with no 'series-parallel' equivalent has previously been published. It is demonstrated that there are many equivalent realizations with different topologies. The existence of 'non-series-parallel' networks, with no 'series- parallel' equivalents, containing as few as nine elements is verified. Analytical techniques for synthesising 'non-series-parallel.' networks must be developed before 'necessary and sufficient' conditions for all sets of admittance functions can be obtained. The properties of admittance functions with two finite poles are discussed. Several useful topological theorems are derived. Two simple 'non-series-parallel' networks are analysed, and their element values are obtained as expressions in terms of the residues at the poles of the required admittance functions. The existence of many other possible realizations is demonstrated by the use of equivalence transformations

Experimental investigation of liquid droplet break-up duration

http://deepblue.lib.umich.edu/bitstream/2027.42/6079/5/bac7504.0001.001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/6079/4/bac7504.0001.001.tx

Maternal pre-pregnancy body mass index and offspring temperament at 3 months: A brief report

Introduction: Pre-pregnancy obesity has been linked to emotional and behavioural problems in offspring, though it remains unclear when the presence of these difficulties first emerges. Method: We examined the association between maternal pre-pregnancy body mass index (BMI) and temperament at 3 months of age in the offspring of 16 women residing in Hamilton, Ontario. Infant temperament was measured using the Infant Behaviour Questionnaire Revised, which specifically examined surgency/extraversion, negative affectivity, and orienting/regulation. Results: A statistically significant association was observed between maternal BMI and infant negative affectivity (B=0.05, 95% CI=0.01-0.08), which remained significant after adjusting for confounding variables (B=0.04, 95% CI=0.01-0.08). Conclusion: The current study provides evidence that fetal exposure to high maternal BMI during pregnancy is associated with increased negative affectivity in infants at 3 months of age. The results suggest that the intrauterine environment associated with high maternal BMI may influence temperament at a very early stage in development