• 한국분무공학회지
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• 제9권4호
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• pp.1-8
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• 2004

Breakup characteristics of liquid sheets formed by the impingement of two water jets, such as a breakup length and a breakup wavelength of sheet, were investigated as increasing the injection velocity up to 30m/s and the ambient gas pressure up to 4.0MPa. While round edged orifices formed a laminar sheet which has no waves on the sheet when the injection velocity is low, sharp edged orifices formed a turbulent sheet which has impact waves irrespective of the injection velocity. Thus we compared the differences of breakup characteristics between them. The results showed that the aerodynamic force significantly affects the breakup of laminar sheet when the gas based Weber number is higher than unity, It was also found that the turbulent sheets have three breakup regimes, i.e. expansion regime, wave breakup regime and catastrophic breakup regime according to the gas based Weber number.

• 한국분무공학회지
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• 제7권4호
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• pp.32-41
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• 2002

The breakup characteristics of liquid sheets formed by like-doublet injector were investigated in the cold-flow and atmospheric ambient pressure condition. The sheet breakup wavelength, which induces the sheet to be broken into ligaments, as well as the sheet breakup length, which is important for the flame location, was measured using a stroboscopic light. The liquid ligaments are formed intermittently after the breakup of sheet, and the wavelength of ligaments has been believed to have a relation to the combustion instability of liquid rocket engine. Therefore, the wavelength of ligaments and the breakup length of ligaments into fine drops were also measured. Since these spray characteristics are affected by the flow characteristics of two liquid jets before they impinge on each other, we focused on the effects of orifice internal flow such as the cavitation phenomenon that occurs inside the sharp-edged orifice. From the experimental results, we found that the liquid jet turbulence delays the sheet breakup and makes shorter wavelengths for both sheets and ligaments. Since the turbulent strength of sharp-edged orifice is stronger than that of round-edged orifice, the shape of orifice entrance results in large differences in the spray characteristics. Using these results, we proposed empirical models on the spray characteristics of the like-doublet injector, and these models are believed to provide some useful and actual data for designing liquid rocket combustors.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.173-179
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• 2004

Breakup characteristics of liquid sheets formed by the impingement of two water jets, such as a breakup length and a breakup wavelength of sheet, were investigated as increasing the injection velocity up to 30m/s and the ambient gas pressure up to 4.0㎫. While round edged orifices formed a laminar sheet which has no waves on the sheet when the injection velocity is low, sharp edged orifices formed a turbulent sheet which has impact waves irrespective of the injection velocity. Thus we compared the differences of breakup characteristics between them. The results showed that the aerodynamic force significantly affects the breakup of laminar sheet when the gas based Weber number is higher than unity. It was also found that the turbulent sheets have three breakup regimes, i.e. expansion regime, wave breakup regime and catastrophic breakup regime according to the gas based Weber number.

• 한국분무공학회지
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• 제10권4호
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• pp.32-46
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• 2005

The breakup characteristics of liquid sheets formed by the impinging and swirl type injectors were studied as increasing the Weber number (or injection condition) and the ambient gas pressure to 4.0.MPa. In the case of impinging type injector. we compared the changes of breakup lengths between laminar and turbulent sheets. which are formed by the impingement of laminar and turbulent jets. respectively. The results showed that both sheets expand as increasing the injection velocity irrespective of the ambient gas density when the gas based Weber number is low. When the Weber number is high, however, the breakup of turbulent sheet depends on the hydraulic force of jets as well as the aerodynamic force of ambient gas which determines the breakup of laminar sheet. Using the experimental results. we could suggest empirical models on the breakup lengths of laminar and turbulent sheets. In the case of swirl type injector. as $We_l$, and ambient gas density increased, the disturbances on the annular liquid sheet surface were amplified by the increase of the aerodynamic forces. and thus the liquid sheet disintegrated near from the injector exit. Finally, the measured breakup length of swirl type injector according to the ambient gas density and $We_l$, was compared with the result by the linear instability theory. We found that the corrected breakup length relation derived from linear instability theory considering the attenuation of sheet thickness agrees well with our experimental results.

• International Journal of Automotive Technology
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• 제2권3호
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• pp.103-107
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• 2001

Many researches on pressure-swirl injectors due to the variety of application have been conducted on the effects of nozzle design, operating conditions, properties of liquid and ambient conditions on the flow and spray characteristics. The breakup length of conical emulsified fuel sheet resulting from pressure-swirl atomizer using in the oil burner was investigated with the digital image processing method with neat light oil and emulsion with water content of lotto% and the surfactant content of 1-3%. The injection pressure ranged from 0.1 to 1.2 MPa was selected. The various regimes for the stage of spray development within the experimental conditions selected in this study is newly suggested in terms of Ohnesorge number and injection pressure. The breakup length for both criteria show the same tendency even though the random nature of perforation and disintegration process of liquid sheet. The stage of spray development is widely different with the physical properties of liquid atomized, mainly viscosity of liquid. The breakup length decreases smoothly with increase in the injection pressure for the lower viscous liquid.

• 한국항공우주학회지
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• 제34권7호
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• pp.97-104
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• 2006

분사조건과 주위기체 압력에 따라 스월 인젝터의 분무각과 분열길이를 측정함으로써, 스월 인젝터의 분무 및 분열특성에 대한 연구를 수행하였다. 분사조건으로 축방향 We 수(Wel)를 1554까지 주위기체 압력을 4.0MPa까지 증가시켰다. Wel과 주위기체 밀도(ρ)가 증가함에 따라 공기역학적 힘이 증가하여 원추형 액막 표면의 교란이 증가하게 되고, 따라서 분열이 빨리 일어난다. 결과에 따르면 주위기체 밀도에 따른 분무각의 변화가 분열이 일어나기 전과 후가 다르게 나타났다. 분열이전에는 분무각이 주위기체 밀도 변화에 관계없이 거의 일정하였으나, 분열이 일어나게 되면 분무각이 감소하게 된다. 또한 측정된 분열길이를 선형불안정이론과 비교해 보았는데, 액막두께의 감쇠를 고려한 수정된 이론이 측정결과와 상당히 유사한 결과를 얻을 수 있었다.

• Journal of Mechanical Science and Technology
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• 제17권5호
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• pp.726-739
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• 2003

A multi-dimensioanl model is being increasingly used to predict the thermo-flow field in the gas turbine combustor. This article addresses an integrated survey of modeling of the liquid spray formation and fuel distribution in gas turbine with high-shear nozzle/swirler assembly. The processes of concern include breakup of a liquid jet injected through a hole type orifice into air stream, spray-wall interaction and spray-film interaction, breakup of liquid sheet into ligaments and droplet,5, and secondary droplet breakup. Atomization of liquid through hole nozzle is described using a liquid blobs model and hybrid model of Kelvin-Helmholtz wave and Rayleigh-Taylor wave. The high-speed viscous liquid sheet atomization on the pre-filmer is modeled by a linear stability analysis. Spray-wall interaction model and liquid film model over the wall surface are also considered.

• 한국컴퓨터그래픽스학회논문지
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• 제25권1호
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• pp.13-22
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• 2019

본 논문에서는 입자 기반 유체 시뮬레이션에서 과하게 보존되는 액체 시트를 제거함으로써 유체 표면의 디테일을 개선시키는 새로운 방법을 제안한다. 지금까지 울퉁불퉁하고 구멍이 생기는 유체 표면의 고질적인 문제를 해결하기 위한 다양한 비등방성 접근법들은 제안되었지만, 액체 시트의 보존과 분해를 안정적으로 표현할 수 있는 방법은 제시되지 않았다. 본 연구에서는 비등방성 커널과 밀도를 기반으로 하여 물 입자를 동적으로 추가/삭제함으로 입자 기반 유체시뮬레이션에서 액체 시트의 보존과 분해라는 두 가지 특징을 동시에 표현할 수 있는 새로운 프레임워크를 제안한다. 이 방법은 입자 기반 유체 시뮬레이션 접근법에서 과하게 보존되는 액체 시트를 제거함으로써 분열되는 유체 시트의 특징을 잘 표현했으며, 결과적으로 노이즈를 없애 액체 시트의 품질을 개선시켰다.

• 한국분무공학회지
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• 제26권3호
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• pp.127-134
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• 2021

Fire sprinkler initial spray was analyzed by Large eddy simulation (LES) and Volume of Fluid (VoF) integrated method. The IsoAdvector geometric VoF was used to identify the liquid-gas interface clearly even with the large Courant-Friedrichs-Lewy number. To reduce the computational costs, sector meshes and Adaptive Mesh Refinement up to level 3 were used. Base mesh size was 1 mm, which is roughly equivalent to the initial sprinkler droplet. Top surface radius of boss and deflector size were modified to investigate the effects of sprinkler head design on primary breakup process. When top surface radius of boss was increased, vertical liquid sheet was formed. This phenomenon reduced the sheet breakup radius, sheet thickness and velocity. Due to reduced liquid sheet thickness, a large amount of ligaments was created from the liquid sheet. As a result, there was a dramatic decrease in volume per surface area, indicating an increase in breakup process. Spray pattern viewed in radial direction also changed when top surface radius of boss increased. When top surface radius of boss was increased, a T-shaped pattern was observed while a V-shaped pattern was observed in all other cases. When the deflector size increases, the spray pattern remains V-shaped, even if the top surface radius of boss increased. Further studies on promoting atomization of the water supplied to the lower part of the sprinkler head in the T-shape pattern should be conducted.

• 한국분무공학회지
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• 제12권3호
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• pp.138-145
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• 2007

In the present work, the breakup mechanism of highly viscous epoxy paints discharged from a fan spray nozzle was examined experimentally. The paints tested were non-Newtonian fluids, composed of epoxy resin, solid particles and other additives. The paint spray discharged from the nozzle was visualized and recorded using a digital camera with back illumination. Due to presence of the solid particles, perforation of liquid sheet was observed in most cases, even at low-Reynolds number conditions (Re < 15,000) where the aerodynamic-wave breakup mode is used to be dominant for pure liquids. However, with the increase of the particle concentration, the sheet became longer and the thickness at breakup became thinner to some extent. This is because, with higher concentration of solid particles, the stabilizing effect by the viscosity increase predominates over the destabilizing effect by perforation.