• Title/Summary/Keyword: 캐비테이션 형상

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Numerical analysis of liquid flow characteristics according to the design parameters of a bubble jet microactuator (마이크로 엑츄에이터의 설계변수에 따른 유동특성 해석)

  • Ko, Sang-Cheol
    • Journal of Advanced Marine Engineering and Technology
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    • v.40 no.7
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    • pp.605-612
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    • 2016
  • A numerical analysis was performed on the effect of the design parameters of a bubble jet type microactuator on its liquid flow characteristics. The numerical models included the ink flow from the reservoir, bubble formation and growth, ejection through the nozzle, and dynamics of the refilling process. Because the bubble behavior is a very important parameter for the overall actuator performance, the bubble growth and collapse phenomena in an open pool were simulated in the present study. The drop ejection and refill process were numerically predicted for various geometries of the nozzle, chamber, and restrictor of the bubble jet microactuator. The numerical results from varying the design parameters can help with predicting the performance and optimizing the design of a microactuator.

Generation of emulsions due to the impact of surfactant-laden droplet on a viscous oil layer on water (벤츄리 노즐 출구 형상과 작동 조건에 따른 캐비테이션 기포 발생 특성 연구)

  • Changhoon Oh;Joon Hyun Kim;Jaeyong Sung
    • Journal of the Korean Society of Visualization
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    • v.21 no.1
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    • pp.94-102
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    • 2023
  • Three design parameters were considered in this study: outlet nozzle angle (30°, 60°, 80°), neck length (1 mm, 3 mm), and flow rate (0.5, 0.6, 0.7, 0.8 lpm). A neck diameter of 0.5 mm induced cavitation flow at a venture nozzle. A secondary transparent chamber was connected after ejection to increase bubble duration and shape visibility. The bubble size was estimated using a Gaussian kernel function to identify bubbles in the acquired images. Data on bubble size were used to obtain Sauter's mean diameter and probability density function to obtain specific bubble state conditions. The degree of bubble generation according to the bubble size was compared for each design variable. The bubble diameter increased as the flow rate increased. The frequency of bubble generation was highest around 20 ㎛. With the same neck length, the smaller the CV number, the larger the average bubble diameter. It is possible to increase the generation frequency of smaller bubbles by the cavitation method by changing the magnification angle and length of the neck. However, if the flow rate is too large, the average bubble diameter tends to increase, so an appropriate flow rate should be selected.

Numerical Study on Hydraulic Fluid Flows Within Axial Piston Pumps (액셜 피스톤 펌프내 유압유 유동에 대한 수치해석적 연구)

  • Jeong, Jong-Hyun;Kim, Jong-Ki;Suh, Yong Kweon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.2
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    • pp.129-136
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    • 2010
  • Axial piston pumps have been widely used as power sources for hydraulic systems, but studies on the fluid flow within the pump have been usually performed using 1-D analysis because of the difficulties in considering the fluid compressibility, high-speed revolution, variation of the flow rate, and complicated geometry. The goal of this study was to understand the hydraulic fluid flow within axial piston pumps by using the 3-D numerical method and the process of generating discharge pressure ripples. To improve the convergence and robustness of the simulation model, a grid system was constructed with hexahedron-type grids around the valve plate. Furthermore, we employed an empirical formula to describe the relationship between the oil density and pressure. The CFD (computational fluid dynamics) results compared well with the experimental data.

A Potential-Based Panel Method for the Analysis of a 2-Dimensional Partially Cavitating Hydrofoil (양력판 이론에 의한 2차원 수중익의 부분 캐비티 문제 해석)

  • Chang-Sup,Lee
    • Bulletin of the Society of Naval Architects of Korea
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    • v.26 no.4
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    • pp.27-34
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    • 1989
  • A potential-based panel method is formulated for the analysis of a partially cavitating 2-dimensional hydrofoil. The method employs dipoles and sources distributed on the foil surface to represent the lifting and cavity problems, respectively. The kinematic boundry condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the inner flow region of the foil. The dynamic boundary condition on the cavity surface is satisfied by requiring that the potential vary linearly, i.e., the velocity be constant. Green's theorem then results in a potential-based boundary value problem rather than a usual velocity-based formulation. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with more improved accuracy than the zero-thickness hydrofoil theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. It was found that five iterations are necessary to obtain converged values, while only two iterations are sufficient for engineering purpose.

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On The Development of The Stern Form with Low Resistance and High Propulsive Efficiency for Full Ships (저저항(低抵抗) 고추진(高推進) 효율(效率)의 비대선(肥大船) 선미선형(船尾船型)의 개발(開發)에 관하여)

  • Ho-Chung,Kim;Chun-Ju,Lee;Young-Bok,Choi
    • Bulletin of the Society of Naval Architects of Korea
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    • v.27 no.3
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    • pp.89-99
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    • 1990
  • It is required to develop a hull form with low resistance and high propulsive efficiency for the improvement of the ship-board operational economy. Since the hull forms with low resistance frequently have lower propulsive efficiency and on the other hand the hull forms with higher propulsive efficiency don't show good resistance characteristics, it is always very difficult to obtain economical hull forms which require less propulsive power accordingly. Efforts have been made to pursue a stern form with excellent resistance and propulsion characteristics together by shaping the run of the so-called buttock-flow type stern, which is known to have good viscous resistance performance, like that of conventional aftbody(U-type or Hogner type) featured by high propulsive efficiency. First model tests confirmed that the above concept can be one of the alternative approaches to the design of the good stern form and by the continuing efforts thereafter for the refining of the concept, propelled by the first promising results, stern form of good resistance performance together with good propulsive efficiency has been realized to some extent. In addition, it is confirmed that the new new stern can have better cavitation and vibration characteristics due to uniform wake-fields and the compact engine room arrangement can be possible due to it's larger floor area in way of engine room double bottom as compared with usual barge stern.

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