• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.72-75
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• 2003

In this research, we focused on the effects of the orifice internal flow such as cavitation and hydraulic flip. The breakup characteristics such as the breakup length and trajectory were measured by changing the orifice diameter (d), the orifice length/orifice diameter (L/d), the injection pressure and the shapes (sharp and round) of orifice entrance to provide a lot of conditions of the orifice internal flow. It is found that cavitation bubbles that occur inside the sharp-edged orifice make the liquid jet ejecting from the orifice turbulent. In the orifices (L/d = 5), the hydraulic flip phenomenon is shown when the injection pressure is high. In case cavitation occurs it breaks up more earlier than that in case of non-cavitation. In case hydraulic flip occurs, since the area of the liquid jet becomes small, the breakup length is also small as that in case of cavitation. But the liquid column trajectories have a similar tendency irrespective of cavitation.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.2
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• pp.1-10
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• 2018

This study investigated the acoustic forcing effects on the liquid column breakup length and the trajectory of liquid jets in crossflows. Cold-flow tests with a single hole circular nozzle injector were carried out by changing the injection pressure and acoustic forcing amplitude. Additionally, spray images were obtained at 12 phase angles to investigate the influence of the phage angle. The results revealed that the liquid column breakup lengths generally decreased under the acoustic forcing conditions, in comparison to those under the non-acoustic forcing conditions. However, they were not affected by the variation in the phase angles. On the contrary, it was found that the acoustic forcing hardly influenced the liquid column trajectories.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.4
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• pp.216-230
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• 1999

A Galerkin finite element model for the analysis of harbor oscillation has been developed based on the extended mild-slope equation. Infinite elements are used to accomodate the radiation condition at infinity and joint elements to treat the matching conditions at the harbor entrance which include the energy loss due to flow separation. The numerical tests for rectangular harbors with fully or partially open entrances show that the energy loss at the harbor entrance considerably reduces the the amplification ratios at the innermost parts of the harbors and that the amplification ratios decrease considerably with increasing incident wave heights and jet lengths at the harbor entrance. Application of the model to the Gamcheon harbor show that when the incident wave amplitude is small the amplification ratios rather increase when the entrance energy loss is included than when ignored because of the shift of the resonance periods. Even though the entrance energy loss was insignificant for the measured long-period incident waves, it would be of great importance if the incident waves were large as in the attack of tsunamis. The resonance period of the Helmholtz mode at the Gamcheon Harbor was calculated to be 31 minutes, which agrees well with the measured one between 27 and 33.3 minutes. The measured resonance periods between 9.4 and 12.1 minutes and 5.2 and 6.2 minutes were also calculated by the numerical model as 10.4 minutes and 6.6 or 5.6 minutes, indicating good performance of the model. On the other hand, it was shown that a variety of oscillation modes exists in the Gamcheon Harbor and lateral resonances of considerable amplification ratios also exist at the periods of 3.6 and 1.6 minutes as in the Young-II Bay.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.2
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• pp.45-52
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• 2002

An experimental investigation on the structure and dynamic behavior of two dimensional over-expanded air jets exiting into water was carried out. The hish speed digital video imaging and static pressure distribution measurement were made to characterize the structure and time-dependant behavior of the jets. Mach number at the jet exit was 2.0 and was slightly less than the value predicted by the ideal nozzle calculation. Variance of jet spreading angle at different stagnation condition was measured as a function of mass flow rate. Periodic nature of the air jet distortion in water was observed and the frequency of the repetition was approximately 5-6 Hz for all cases tested. Three characteristic length scales were defined to characterize jet structure. $L_1$, maximum width of the plume when the periodic instability occurs, $L_2$, width of the jet where secondary reverse flow entrained jet flow and $L_3$, distance from the jet exit to the location where entrainment of the secondary reverse flow occurs. The ratio of $L_1$ and $L_2$ decreased with increasing stagnation pressure, i.e. mass flow rate. $L_3$ increased with increasing stagnation pressure. The temporal behavior of static pressure measurements also showed peak around frequency of 5, which corresponds the frequency obtained by visual measurements

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2000.09a
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• pp.126-132
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• 2000

하수처리장의 수중확산관에서 방류되는 부력제트는 초기혼합, 중력확장, 이송-확산 등의 과정이 시간적, 공간적으로 규모가 상이한 범위에서 일어나며, 하수방류 해역의 주변수 흐름은 지형특성과 조석의 영향을 받아 3차원적 비정상류 특성을 나타낸다. 이러한 부력제트의 거동을 모의하기 위해서는 일반적으로 근역과 원역을 분할하여 예측하는 방법을 사용하는데, 초기혼합 과정과 중력환장 과정을 예측하기 위해서는 정상상태는 가정한 특성길이 모형이나 제트적분 모형을 사용하고, 원역으로의 이송-확산 과정을 모의하기 위해서는 농도 모형이나 임자추적 모형등을 사용한다. (중략)

• Journal of the Korean Vacuum Society
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• v.22 no.3
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• pp.111-118
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• 2013

The influence of gas flow on the plasma generation in the atmospheric plasma jet is described with the theory of hydrodynamics. The plasma discharge is affected by the gas-flow streams with Reynolds number (Re) as well as the gas pressure with Bernoulli's theorem according to the gas flow rate inserted into the glass tube. The length of plasma column is varied with the flow types such as the laminar flow of Re<2,000 and the turbulent flow of Re>4,000 as it has been known in a general fluid experiments. In the laminar flow, the plasma column length is increased as the increase of flow rate. Since the pressure in the glass tube becomes low as the increase of flow velocity by the Bernoulli's theorem, the breakdown voltage of plasma discharge is reduced by the Paschen's law. Therefore, the plasma length is increased as the increasing flow rate with the fixed operation voltage. In the transition of laminar and turbulent flows, the plasma length is decreased. When the flow becomes turbulent as the flow rate is increasing, the plasma length becomes short and the discharge is shut down ultimately. In the discharge of laminar flow, the diameter of plasma beam exposed on the substrate surface is kept less than the glass diameter, since the gas flow is kept to the distinct distance from the nozzle of glass tube.

• Journal of Energy Engineering
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• v.8 no.2
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• pp.298-308
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• 1999

Experimental study on characteristics of direct contact condensation of steam discharged into a sub-cooled water pool has been performed using five different sizes of horizontal nozzle over a wide range of steam mass fluxes and pool temperatures. Steam condensation phenomena have been observed visually and by taking pictures of steam jets using a high speed video camera. Two different steam jet shapes such as ellipsoidal shape and conical shape were typically observed for a stable steam jet, depending on the steam mass flux and pool temperature. The steam jet expansion ratio and the steam jet length as well as the condensation heat transfer coefficients were determined. The effect of steam mass flux, pool temperature, and nozzle diameter on these parameters were also discussed. Empirical correlations for the steam jet lengths and the condensation heat transfer coefficients as a function of steam mass flux and condensation driving potential were established. The axial and radial temperature distributions in steam jet and in surrounding water were measured. The effect of steam mass flux, pool temperature, and nozzle diameter were also discussed. The condensation regime map, which consists of six regimes such as chugging, transient chugging, condensation oscillation, stable condensation, bubble condensation oscillation, and intermittent oscillation condensation, were established. In addition, the dynamic pressures at the pool wall were measured. The close relation of dynamic pressure and steam condensation mode, which is also dependent on steam mass flux and pool temperature, was found.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.65-76
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• 1996

A screw propeller is usually accepted as a propulsor of many kinds of ships. However, for high speed vessels, screw propeller has large cavitation area on the blades so propeller efficiency is decreased and erosion can be happened. To avoid this problem, supercavitating propeller and waterjet are generally used for high speed vessels. In this paper, we introduced the self-propulsion test procedure which has been developed for high speed vessels in Hyundai Maritime Research Institute. The model ship used in experiment represents catamaran about 5.3 m in length. To minimize the experimental errors, two impellers were driven by a single motor. Thrust was calculated by converting the measured pressure to flow rates at the nozzle exit. The test procedure is composed of resistance test, self propulsion test and analysis. In order to measure the pressure, pressure tabs were installed around the nozzle exit and connected to the pressure sensor by vinyl tube.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.65-65
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• 2021

보를 월류하는 흐름에 대하여 하류 수심이 보의 높이보다 낮고, 보 월류 후 수심의 공액수심보다 작거나 크고 같은 경우를 각각 자유도수와 수중도수라고 한다. 수중도수가 발생하는 경우 하류 수심이 보의 경사면을 따라 흐르는 하강류를 덮게 되며 유속을 감쇄시키기 때문에 최대 유속은 자유도수에 비해 매우 작게 발생한다. 그러나 수중도수는 자유도수에 비해 에너지 감쇄 효율이 낮기 때문에 도수구간의 거리가 증가하게 된다. 따라서 인명피해를 발생시키는 도수구간 재순환영역의 길이를 검토하는 것이나 보 하류 바닥보호공 길이 설계를 위해 수중도수에서의 흐름에 대하여 검토하는 것은 중요하다. 본 연구에서는 k-ω SST 난류모형을 이용하여 보 월류 후 발생하는 수중도수를 수치모의하고 평균흐름과 난류량의 종방향 변화에 대하여 검토하였다. 기존 실험수로에 k-ω SST 난류모형을 사용하여 모형의 적용성을 검토하였다. 다양한 하류 수심을 설정하여 평균흐름과 난류량에 대한 침수도의 영향 및 자유도수 계산결과와 벽면 제트 결과를 함께 비교하였다. 검토 결과 수중도수는 평균흐름과 난류량의 변화율이 자유도수보다 작고 벽면 제트보다는 큰 것을 확인하였다. 또한 침수도가 증가되면서 평균흐름과 난류량의 변화율이 작아지는 것을 확인하였다. 이것은 침수도의 변화에 따른 역압력경사의 차이에 의한 것으로 판단된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.41-52
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• 2016

When the queue length of congestion vehicles in tunnel fire is extended beyond tunnel length, the capacity of smoke control system needs to be increased in line with ventilation resistance. However, the vehicle queue length is not defined, so a rational equation is necessary in current fire prevention guideline. This study is intended to propose an equation to calculate the queue length considering the number of vehicles in queue in tunnel fire and evaluate the applicability by tunnel length as well. When it comes to normal tunnel, it is necessary to compare the vehicle queue length with tunnel length up to the length of 1,200 m in a bid to avoid applying the vehicle queue length excessively in case of fire. As a result of evaluation of applicability to model a tunnel, saving the number of jet fan for smoke control appeared to be effective. Besides, quantitative approach to explain the vehicle queue length through the relationship between the percentage of large vehicles and tunnel length was presented. Consequently, when the queue length of the congestion vehicles exceeds the tunnel length in determining the capacity of smoke control system in case of fire, the number of vehicles beyond the tunnel length needs to be excluded from estimating the ventilation resistance by vehicles.