Sharif Digital Repository

Smoothed Particle Hydrodynamics (SPH) is a numerical Lagrangian meshless method which has numerous applications in astrophysics, hydrodynamics, free-surface flows, jets and sprays formation. Atomization of continuum liquid to fine droplets or in other words, liquid breakup processes are emerged in many engineering applications such as fuel sprays inside the combustion chamber of internal combustion engines that sizes of produced sprays significantly influence the engine’s efficiency. This research is accomplished to investigate the one-phase and two-phase flows of liquid jet breakup. For this aim, an open source code called SPHysics which solves the flow field by SPH method is utilized. This... 

In the present study, we are to investigate and calculate the drag coefficient in the secondary bag breakup regime in droplet experiment in which the liquid droplet falls into continuous air jet flow. A high speed camera is hired to record the pictures of this process. With the help of image processing techniques, parameters such as dimensionless diameter, growth of droplet, drag coefficient and etc. in secondary bag breakup regime are investigated. The liquid used in this experiments are water, gasoline and diesel fuel. Dimensionless number influencing the result of the experiment are weber and Ohnesorge numbers, with weber number ranging from 6.86 to 20.31 and Ohnesorge number ranging from... 

In this research, the numerical simulation of liquid jet ejecting for a series of elliptical orifices into gaseous phase with different aspect ratios, at Rayleigh flow regime and in a range of Weber numbers has been performed.
For simulations, the OpenFoam software was utilized, which its multiphase flow simulation solvers are based on volume of fluid (VOF) method. In order to achieve the most accurate results for axis-switching phenomenon and jet breakup length, the dynamic mesh refinement was used for all the examined cases. The results, which were validated with recent experimental and numerical works, indicate that jet breakup length raises by increasing Weber number from 20 to 300.... 

Drop deformation and breakup are of great importance in a wide variety of applications, from fuel combustion to agriculture, pharmaceutical processes, and coating. In this experimental study, droplet secondary bag breakup has been investigated. By conducting experiments on different fluids with a wide range of properties and in different conditions, the effects of different parameters on secondary bag breakup have been addressed. For this purpose, the breakup of these fluids, water, ethanol, glycerin, and SDS solution were scrutinized and by comparing their trajectory and morphological parameters, results are driven. Experimental conditions were such that the Weber number are from 11 to 17... 

Numerical simulation of flow fields inside and outside of a pressure-swirl injector is considered in the present study. Injector characteristics such as the injected liquid sheet thickness, liquid sheet breakup length, and spray angle can be accurately captured via numerical simulations and used for the design optimization of an injector. The flow fields inside of a pressure-swirl injector leading to the primary atomization process outside the injector have been simulated assuming laminar flow with periodic boundary conditions using a coupled volume of fluid (VOF) and a level set model for the two phase fluid. The ANSYS Fluent commercial program is used for simulations. The computational... 

The liquid breakup analysis and spray characteristics measurement of atomizer are very essential for the numerical modeling of the primary atomization in combustion chambers. The atomization process is irregular and random nature and is a chaotic phenomenon. This study was motivated by the lack of temporal analysis of the breakup process especially for the first and second wind-induced breakup regimes and the atomization regime. The aim of this study was to determine the location, velocity and structures of breakup liquid jet at different outlet pressures from 0.3 bar to 50 bar. The results indicate that the breakup length, ligament size, and the breakup time period are randomly varied in... 

Symmetric T junctions have been used widely in microfluidics to generate equal-sized microdroplets, which are applicable in drug delivery systems. A newly proposed method for generating unequal-size microdroplets at a T junction is investigated theoretically and experimentally. Asymmetric T junctions with branches of identical lengths and different cross-sections are utilized for this aim. A novel equation for the critical breakup of droplets at asymmetric T junctions and one for determining the breakup point of droplets are developed. A good agreement was observed between the theories (novel and previous) and the experiments  

Injecting liquid fuel into the cross flow of air provides high penetration of the liquid, rapid mixing with air, and increased efficiency. This method has widespread applications in the propulsion systems of gas turbines, scramjets, turbine blade cooling, and fuel injection for engine afterburners. One of the design strategies for future aircraft engines is to reduce pollutants using fuel spray into the cross flow instead of direct jet fuel injection and using renewable energy sources. The applications of cross flows include injecting fluid through rotating pressure injectors in exhaust flows, injecting fluid through pressure-rotating injectors in radial injectors, and using slinger...