• 한국추진공학회지
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• 제19권3호
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• pp.89-95
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• 2015

7톤급 로켓엔진용 산화제펌프와 연료펌프에 대하여 물을 매질로 하는 성능시험을 수행하였다. 펌프는 전기모터로 구동되었고 설계 및 탈설계 유량비 조건에서 펌프의 수력성능과 흡입성능이 측정되었다. 양정-유량 곡선, 효율-유량 곡선, 양정-캐비테이션수 곡선을 얻었다. 개발된 펌프는 펌프 양정과 효율의 수력성능에 관한 설계요구조건을 만족시킬 수 있음을 확인하였다. 또한 흡입성능에 관한 설계요구조건을 만족시킨다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.495-509
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• 2019

The objective of this study is to analyze the compressibility effects of multiphase cavitating flow during the water-entry process. For this purpose, the water-entry of a projectile at transonic speed is investigated computationally. A temperature-adjusted Tait equation is used to describe the compressibility effects in water, and air and vapor are treated as ideal gases. First, the computational methodology is validated by comparing the simulation results with the experimental measurements of drag coefficient and the theoretical results of cavity shape. Second, based on the computational methodology, the hydrodynamic characteristics of flow are investigated. After analyzing the cavitating flow in compressible and incompressible fluids, the characteristics under compressible conditions are focused upon. The results show that the compressibility effects play a significant role in the development of cavitation and the pressure inside the cavity. More specifically, the drag coefficient and cavity size tend to be larger in the compressible case than those in the incompressible case. Furthermore, the influence of entry velocities on the hydrodynamic characteristics is investigated to provide an insight into the compressibility effects on cavitating flow. The results show that the drag coefficient and the impact pressure vary with the entry velocity, and the prediction formulas for drag coefficient and impact pressure are established respectively in the present study.

• 한국전산유체공학회지
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• 제19권2호
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• pp.17-23
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• 2014

Cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency in devices, such as propellers, pump impellers, nozzles, injectors, torpedoes, etc. Thus, the cavitating flow simulation is of practical importance for many engineering systems. In the present work, a two-phase flow solver based on the homogeneous mixture model has been developed. The solver employs an implicit preconditioning, dual time stepping algorithm in curvilinear coordinates. The flow characteristics around Clark-Y hydrofoil were calculated and then validated by comparing with the experimental data. The lift and drag coefficients with changes of angle of attack and cavitation number were obtained. The results show that cavity length and lift, drag coefficient increase with increasing angle of attack.

• Journal of Ship and Ocean Technology
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• 제8권1호
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• pp.31-41
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• 2004

A ducted marine propulsor has been widely used for the thruster of underwater vehicles for protecting collision damage, increasing propulsive efficiency, and reducing cavitation. Since a single-stage ducted propulsor contains a set of rotor and stator inside an annular duct, the numerical analysis becomes extremely complex and computationally expensive. However, the accurate prediction of viscous flow past a ducted marine propulsor is essential for determining hydrodynamic forces and the propulsive performances. To analyze a ducted propulsor having rotor-stator Interaction, the present work has solved 3D incompressible RANS equations on the sliding multiblocked grid. The flow of a single stage turbine flow was simulated for code validation and time averaged pressure coefficients were compared with experiments. Good agreement was obtained. The hydrodynamic performance coefficients were also computed.

• 대한조선학회논문집
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• 제58권4호
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• pp.214-224
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• 2021

Recently, as the technology of the supercavitating underwater vehicle is improved, the necessity of research for maneuvering characteristics of the supercavitating underwater vehicle has emerged. In this study, as a preliminary step to analyzing the maneuverability of a supercavitating underwater vehicle, the characteristics of cavity shapes and hydrodynamic forces generated in a supercavitating underwater vehicle with an angle of attack were evaluated numerically. First, the geometry was designed by modifying the shape of the existing supercavitating underwater vehicle. The continuity and the Navier-stokes equations are numerically solved, and turbulent eddy viscosity is solved by the k-ω SST model. The results present the characteristics of cavity shape and the hydrodynamic forces of the designed geometry with an angle of attack.

• 상하수도학회지
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• 제28권1호
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• pp.25-32
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• 2014

In order to investigate the effective pretreatment methods in WAS(=waste activated sludge) solubilization, the values of SCOD yield per unit SS (SCOD/gSS.hr) were compared. After the hydrodynamic cavitation with pH of 12.5, SCOD increased to 7800 mg/L, SS decreased to 45 % and the solubilization rate was 29 %. Combination of alkality (pH 12.5) and the cavitation seems to be the optimal condition for sludge solubilization. After the cavitational pretreatment, efficiencies of anaerobic digestion of the unfiltered sludge(the control), raw sludge and pretreated sludge were evaluated with BMP(=biochemical methane potential) tests. For evaluation of the biodegradability characteristics of pretreated sewage sludge, the methane production has been measured for 6 months. The methane production of pretreated sludge increased 1.4 times than that of untreated sludge. The result indicates that the cavitationally pretreated sludge was a better biodegradability substrate in anaerobic condition compared to raw sludge. It is obvious that cavitational pretreatment could enhance not only solubilization but also biodegradability of WAS. In conclusion, cavitational pretreatment of WAS to convert the particulate into soluble portion was shown to be effective in enhancing the digestibility of the WAS.

• 대한조선학회논문집
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• 제57권1호
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• pp.35-44
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• 2020

Propeller cavitation extent, pressure fluctuation induced by cavitation, pressure distribution on propeller blade, total velocity distribution and nominal wake distribution for a MR Taker were computed in both conditions of model test and sea trial using a code STAR-CCM⁺. Then some of the results were compared with model test data at LCT and full-scale measurement (Ahn et al (2014); Kim et al (2014)] in order to confirm the availability of a numerical prediction method and to get the physical insight of local flow around a ship and propeller. The nominal wake distributions computed and measured by LDV velocimeter on the variation of on-coming velocity show the wake contraction characteristics proposed by Hoekstra (1974). The numerical prediction of propeller cavitation extent on a blade angular position and pressure fluctuation level on each location of pressure sensors are very similar with the experimental results.

• 대한조선학회논문집
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• 제53권6호
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• pp.494-502
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• 2016

The accurate assessment of hull-appendage interaction in the early design stage is important to control the inflow to the propeller plane, which can cause undesirable hydrodynamic effects in terms of cavitation phenomenon. This paper describes a numerical analysis for the flow around a fully appended surface ship model for which KRISO has carried out a model test in the Large Cavitation Tunnel(LCT). This numerical study was performed with the LCT model test in a complementary manner for a good reproduction of the wake distribution of surface ships. A second order accurate finite volume method provided by a commercial computational fluid dynamics(CFD) program was used to solve the governing Reynolds Averaged Navier-Stokes(RANS) equations, where the SST $k-{\omega}$ model was used for turbulence closure. The numerical results were compared to available LCT experimental data for validation. The calculations gave good predictions for the boundary layer profiles on the walls of the empty cavitation tunnel and the wake at the propeller plane of the fully appended hull model in the LCT.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제27회 춘계학술대회
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• pp.167-172
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• 1998

An algorithm of Thermal-elastohydrodynamic lubrication analysis for the piston ring is developed. This algorithm contains cavitation boundary condition so it automatically satisfies conservation of mass. 1-D Reynolds equation and 2-D energy equation are solved simultaneously by using Gauss-Jordan method and Newton-Raphson method. Minimum film thickness and friction force are calculated for 1 cycle. There is little difference between the results caculated by isothermal rigid and EHL analysis in entire cycle. In the results of THL, shear heating effect and temperature boundary condition affect the minimum film thickness and friction force prediction. The minimum film thickness and the friction force calculated by THL are lower than those caculated using isothermal assumption.

• KSTLE International Journal
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• 제2권2호
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• pp.146-149
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• 2001

Recently, laser printers have been developed to have high-speed laser scanner with hydrodynamic bearings. Among the bearings, herringbone grooved bearing (HGB) produces hydrodynamic pressure by high-speed rotating and so make the surfaces between the shaft and sleeve separated. Accordingly, the bearings with non-contact rotation are suitable to high-speed rotating and have long bearing life and reliability. HGB is a kind of journal bearing and uses oil for a lubricant. HGB has excellent stiffness and load carrying capacity. Also, HGB is leakage-free due to groove pumping action. Consequently, HGB is valuable to be applied to high-performance devices such as hard disk drive, copier, and so on.