• 한국전산유체공학회:학술대회논문집
• /
• 2006.10a
• /
• pp.7-8
• /
• 2006

The governing equations for high-speed lateral atomizing injector nozzle flow based on the LES-VOF model in conjunction with the CSF model are presented, and then an integrated parallel computation are performed to clarify the detailed atomization process of a high speed nozzle flow and to acquire data which is difficult to confirm by experiment such as atomization length, liquid core shapes, droplets size distributions, spray angle and droplets velocity profiles. According to the present analysis, it is found that the atomization rate and the droplets-gas two-phase flow characteristics are controlled by the turbulence perturbation upstream of the injector nozzle, hydrodynamic instabilities at the gas-liquid interface, shear stresses between liquid core and periphery of the jet. Furthermore, stable and a high-resolution computation can be attained in the high density ratio (pl/ pg = 554) conditions conditions by using our numerical method.

• Journal of ILASS-Korea
• /
• v.1 no.1
• /
• pp.63-75
• /
• 1996

The purpose of this study is to investigate the break-up characteristics by taking advantage of a two-phase coaxial nozzle. Air and water are utilized as working fluids and the mass ratio air/water has been controlled to characterize the atomization, diffusion and development of mixing process. By way of a photographic technique, conventional developing structures and diffusion angles have been analyzed systematically with variations of mass ratios. The turbulent flow components of the atomized particles were measured by a two channel LDV system and the data were treated by an on-lined measurement equipment. According to the photographic results the spreading angles decreased because the axial inertia moment was relatively higher than the lateral one with respect to the increase of mass ratio. It is found the jet flow diffuses linearly in a certain limit region while the atomizing characteristics, in terms of the distributions of particle diameters did not show particular differences. It may be expected that these fundamental results can be used as reference data in studying the atomization, breakup and diffusions.

• Journal of the Korean Solar Energy Society
• /
• v.30 no.6
• /
• pp.137-143
• /
• 2010

In this study, the ejector design was modeled using Fluent 6.3 of FVM(Finite Volume Method) CFD(Computational Fluid Dynamics) techniques to resolve the flow dynamics in the ejector. A vacuum system with the ejector has been widely used because of its simple construction and easy maintenance. Ejector is the main part of the desalination system, of which designs determine the efficiency of system. The effects of the ejector was investigated geometry and the operating conditions in the hydraulic characteristics. The ejector consists mainly of a nozzle, suction chamber, mixing tube(throat), diffuser and draft tube. Liquid is supplied to the ejector nozzle, the fast liquid jet produced by the nozzle entrains and the non condensable gas was sucked into the mixing tube. In the present study, the multiphase CFD modeling was carried out to determine the hydrodynamic characteristics of seawater-air ejector. Two-dimensional geometry was considered with the quadrilateral-mashing scheme. The gas suction rate increases with increasing Motive flow circulating rate.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.8 no.2
• /
• pp.39-45
• /
• 2004

Experiments were performed in a two-phase swirling spray facility that has been described elsewhere. Measurements of spray transport and drop size distribution are analyzed over wide ranges of air to liquid mass flow ratios, utilizing four different internal mixing pneumatic nozzles. The spatial distributions of mean velocities. fluctuating velocities, and velocity-diameter correlation were quantitatively analyzed. Also, the exponential correlation curves were obtained with ALR along the spray centerline, which indicated an approximately identical formulation regardless of ALR. It indicated that the atomization characteristics were remarkably superior in the case of 30o of swirl angle with higher ALR. Among other things. nozzle configuration is one of the significant parameters affecting spray phenomena from an internal mixing nozzle. Turbulence intensities are increasingly degenerated with an increase of nozzle configuration, allowing a rapid increment of drop size distribution.

• Corrosion Science and Technology
• /
• v.12 no.2
• /
• pp.85-92
• /
• 2013

This work is concerned with an evaluation of dynamic boric acid corrosion (BAC) of low alloy steel for reactor pressure vessel of a pressurized water reactor (PWR). Mockup test method was newly established to investigate dynamic BAC of the low alloy steel under various conditions simulating a primary water leakage incident. The average corrosion rate was measured from the weight loss of the low alloy steel specimen, and the maximum corrosion rate was obtained by the surface profilometry after the mockup test. The corrosion rates increased with the rise of the leakage rate of the primary water containing boric acid, and the presence of oxygen dissolved in the primary water also accelerated the corrosion. From the specimen surface analysis, it was found that typical flow-accelerated corrosion and jet-impingement occurred under two-phase fluid of water droplet and steam environment. The maximum corrosion rate was determined as 5.97 mm/year at the leakage rate of 20 cc/min of the primary water with a saturated content of oxygen within the range of experimental condition of this work.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.7
• /
• pp.841-848
• /
• 1997

Combustion of gaseous fuel combustor in a high temperature vitiated air stream was studied with computer simulation. It is for application to afterburner of gas turbine engine which the exact mechanism is not yet clarified. As the jet velocity from fuel nozzle is very high and the geometry of combustor is three dimensional complex structure, many time and money are required to have good results. To consider this demerit, it is simplified to 2-dimensional and modified with the nozzle hole area to same area of annual status. As the thickness of annual is too thin, it is to divide with the many grids for reasonable results. Accordingly, new method which injected fuel mass, momentum and energy are added to source terms of each governing conservation equation as a source terms is introduced like as two phase analysis. Reaction rate is determined by taking into account the Arrhenius reaction based on a single step reaction mechanism. It is focused to temperature and product concentration distribution at each equivalence ratio of inlet hot product.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.6
• /
• pp.2073-2082
• /
• 1991

The vaporization and combustion of liquid spray in a cylindrical shape combustor was studied numerically. Mixture of liquid drops and air was assumed to be ejected from the center-hole and assisting air from the concentric annulus with swirling. Eulerian-Lagrangian scheme was adopted for the two phase calculation, and the interactions between the phases were considered with the PSIC model. Also adopted were the infinite conductivity model for drop vaporization, the equation of Arrhenius and the eddy break-up model for reaction rate, and the k-epsilon model for turbulence calculations. Gas flow patterns, drop trajectories and contours of temperature and mass fractions of the gas species were predicted with swirl number, drop diameter, and equivalence ratio taken as parameters. Calculations show that the vaporization and the consequent combustion efficiency enhance with the increase of the swirl number and/or with the decrease of drop size, and the higher maximum temperature is attained with the higher equivalence ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.57-60
• /
• 2006

The instability analysis of submerged gas flow into liquid is studied, which assumes gas and liquid as viscous and irrotational. At low mass flow rate of gas, injected gas plume is collection of bubbles, and increase of gas flow rate makes plume as a jet. It is well known that the transition from bubbling to jetting occurs in the transonic region. But previous works neglect viscous effect of gas flow into liquid. This paper concerns about an application of viscous potential flow theory in cylindrical gas flow into liquid. The growth rate versus wave number and mach number is compared with various condition including inviscid and viscous flow.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.252-255
• /
• 2008

In this study, the characteristics of crossing a river of Ground Armored Vehicle (GAV) were evaluated by numerical method and real size tests. 3-D hybrid mesh systems were constructed by 3-D models of the GAV, and a commercial software, FLUENT, was used in numerical analysis. In order to deal with multi-phase problem (air and water), Volume Of Fluid (VOF) method was used, and Moving and Deforming Mesh (MDM) was adapted for unsteady motion of GAV. There were two steps in this research. Firstly, stability of the GAV which cruised a river was evaluated by changing several shapes of water-proof-front-wing of the GAV in steady state, and compared results (free surface shape and drag value in 10km/h) with those of real size tests. Secondly, results of unsteady analysis considering weight and moment of inertia of the GAV were presented. There were showed a maximum velocity with a designed water jet and dynamic stability including pitch, roll, and yaw moment. Based on these results, the optimal shape of water-proof-front-wing of the GAV was determined for a proto-type of the GAV.

• Journal of computational fluids engineering
• /
• v.18 no.4
• /
• pp.9-16
• /
• 2013

Cavitation on an axi-symmetric hemispherical head-form body was studied using an Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To consider compressibility effects on the vapor phase and cavity interface, a pressure-based compressible flow CFD code was developed. To validate the developed CFD code, cavitating flow around the hemispherical head-form body was simulated using pressure-based incompressible and compressible CFD codes and validated against existing experimental data in the three-way comparison. The cavity shedding behavior, length of re-entrant jet, drag history, and Strouhal number of the hemispherical head-form body were compared between two CFD codes. The results, in this paper, suggested that the computations of cavitating flow with compressibility effects improve the description of cavity dynamics.