• Title/Summary/Keyword: Thrust coefficient

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Performance Improvement of Weis-Fogh Type Ship's Propulsion Mechanism Using Spring Type Elastic Wing

  • Ro, Ki-Deok;Cheon, Jung-Hui;Kim, Won-Cheol
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.1
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    • pp.52-61
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    • 2009
  • This experiment was conducted in attempt of improving hydrodynamic efficiency of the propulsion mechanism by installing a spring to the wing so that the opening angle of the wing in one stroke can be changed automatically, compared to the existing method of fixed maximum opening angle in Weis-Fogh type ship propulsion mechanism. Average thrust coefficient was almost fixed with all velocity ratio with the prototype, but with the spring type, thrust coefficient increased sharply as velocity ratio increased. Average propulsive efficiency was larger with bigger opening angle in the prototype, but in the spring type, the one with smaller spring coefficient had larger value. In the range over 1.0 in velocity ratio where big thrust can be generated, spring type had more than twice of propulsive efficiency increase compared to the prototype.

The Improvement of Aerodynamic Performance of Flapping-Airfoil Using Thickness Variation Airfoil (두께 변화가 있는 익형을 이용한 flapping-Airfoil의 공력성능 개선)

  • Lee Jung Sang;Kim Chongam;Rho Oh Hyun
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.787-790
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    • 2002
  • In this work, numerical experiments ave conducted to find out the optimal shape of flapping-airfoil using thickness variation airfoils. In the previous study of flapping-airfoil, we had found that the thrust efficiency of thicker airfoil is better than thinner one, but the latter has higher thrust coefficient. Therefore, we have combined thin(NACA0009) and thick(NACA0015)airfoil to overcome these demerits of each airfoil. Using this combined airfoil, we can achieve acceptable aerodynamic performances from thrust efficiency and coefficient points of view. In order to computational study, we have used parallel-implemented incompressible Wavier-Stokes solver. Computational results show how to design leading and trailing edge shapes.

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Numerical Investigation on Hydrodynamic Characteristics of a Centrifugal Pump with a Double Volute at Off-Design Conditions

  • Shim, Hyeon-Seok;Kim, Kwang-Yong
    • International Journal of Fluid Machinery and Systems
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    • v.10 no.3
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    • pp.218-226
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    • 2017
  • Severe radial thrust under off-design operating conditions can be a harmful factor for centrifugal pumps. In the present work, effects of geometry of a double volute casing on the hydrodynamic performance of a centrifugal pump have been investigated focusing on off-design conditions. Three-dimensional steady Reynolds-averaged Navier-Stokes analysis was carried out by using shear stress transport turbulence model. Numerical results for the hydrodynamic performance of the centrifugal pump were validated compared with experimental data. The hydraulic efficiency and radial thrust coefficient were used as performance parameters to evaluate the hydrodynamic characteristics of the centrifugal pump. The cross-sectional area ratio of the volute casing, the expansion coefficient of the rib structure, the distance between the rib starting point and volute entrance, and radius and width of the volute entrance, and length of the rib structure, were selected as geometric parameters. Results of the parametric study show that the performance parameters are significantly affected by the geometric variables and operating conditions. Optimal configurations of the double volute casing based on the design of experiments technique show outstanding performance in terms of the efficiency and radial thrust coefficient.

A Fundamental Study of Thrust-Vector Control Using a Dual Throat Nozzle (이중목 노즐을 이용한 추력벡터 제어에 관한 기초적 연구)

  • Shin, Choon-Sik;Kim, Heuy-Dong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.14 no.6
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    • pp.25-30
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    • 2010
  • Dual throat nozzle(DTN) is recently attracting much attention as a new concept of the thrust vectoring technique. This DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze the performance of a dual throat nozzle(DTN) at various mass flow rate of secondary flow and nozzle pressure ratios(NPR). Two-dimensional, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. The present computational results were validated with some experimental data available. Based upon the present results, The control effectiveness of thrust-vector is discussed in terms of the thrust coefficient and the discharge coefficient.

A Fundamental Study of Thrust-Vector Control Using a Dual Throat Nozzle (이중목 노즐을 이용한 추력벡터 제어에 관한 기초적 연구)

  • Shin, Choon-Sik;Kim, Heuy-Dong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.05a
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    • pp.339-342
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    • 2010
  • Dual throat nozzle(DTN) is recently attracting much attention as a new concept of the thrust vectoring technique of propulsion jet. This DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze the performance of a dual throat nozzle(DTN) at various mass flow rate of secondary flow. Two-dimensional, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. The present computational results were validated with some experimental data available. Based upon the present results, Thrust-vector control using a DTN is discussed in terms of the thrust coefficient and the coefficient of discharge.

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An Analysis of Dynamic Characteristics of Tilling Pad Thrust Bearings (틸팅 패드 추력베어링의 동특성 해석)

  • 김종수
    • Tribology and Lubricants
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    • v.13 no.3
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    • pp.33-41
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    • 1997
  • In this paper the linearized stiffness and damping coefficients of tilting pad thrust bearing are calculated by the perturbation method. The coefficients are obtained for a wide range of pivot positions. The effects of exciting frequency and pad mass on stiffness and damping coefficients are investigated. Critical frequencies due to the tilting motions of the pad are presented and are shown to be strongly influenced by the pivot position and the pad mass.

Thrust Characteristics of Through-type Pintle Nozzle at Operating Altitudes Conditions (작동 고도에 따른 관통형 핀틀 노즐의 추력 특성 연구)

  • Jeong, Kiyeon;Hong, Ji-Seok;Heo, Junyoung;Sung, Hong-Gye;Yang, Juneseo;Ha, Dongsung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.20 no.4
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    • pp.59-67
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    • 2016
  • Numerical simulations have been performed to investigate thrust characteristics of a through-type pintle nozzle with or without flow separation at various operating altitudes. The low Reynolds number $k-{\varepsilon}$ with compressibility correction proposed by Sarkar are applied. The detail flow structures are observed and static pressures along nozzle wall are compared with experimental results. The flow separation in the pintle nozzle disappears and jet plume strongly expands as its operating altitude increases. To evaluate the thrust characteristics, the momentum term and pressure term of thrust are analyzed. Thrust and thrust coefficient at altitude 20 km are about 10% more than them at the ground 0km.

Measurement of Cavitation-Induced Pressure Fluctuation in a Large Cavitation Tunnel (대형 공동 수조에서의 변동 압력 계측)

  • Na, Yun-Cheol;Kang, Kwan-Hyoung;Kim, Young-Gi;Lee, Mu-Yeol
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.791-796
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    • 2000
  • The cavitation-induced fluctuating pressure of the container ship named "Sydney Express" is measured in Samsung Large Cavitation Tunnel(SCAT). In the measurements, a complete ship model is employed. The effects of thrust coefficient and cavitation number on cavity pattern and cavitation-induced fluctuating pressure were investigated experimentally. It is demonstrated that the fluctuating pressure coefficient is very sensitive to the cavitation number. The results of cavitation and pressure fluctuations are compared with those of ITTC and HSVA, which shows fairly good agreement. It is exhibited that the removal of rudder can significantly change the loading condition of a propeller, and can reduce the fluctuating pressure coefficient almost by half.

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A Evaluation Method of Operational Performance for Air-operated Gate Valve (공기구동 게이트밸브의 운전 성능평가 방법에 관한 연구)

  • Kim, Dae-Woong;Park, Sung-Keun;Kang, Shin-Cheul;Kim, Yang-Suk
    • The KSFM Journal of Fluid Machinery
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    • v.12 no.2
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    • pp.31-38
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    • 2009
  • The valve performance has been evaluated from the theoretical equation based on design information such as packing thrust, spring preload and friction coefficient(${\mu}$). The accuracy of those data can be lower than that of vendor's initial design data. Especially, the friction coefficient can be degraded with time than the original condition and the valve performance calculated using the previous friction coefficient can not be available. Accordingly, this paper is describing a new performance evaluation method of valve based on diagnostic test data which are acquired from a site valve tested in static and dynamic conditions. Especially, this paper provides a new method using friction coefficient(${\mu}$) which is derived from the diagnostic test data acquired in the valve's design basis condition.

Numerical Study of a Flapping Flat Plate for Thrust Generation (플랩핑 평판의 추력발생에 대한 수치적 연구)

  • An, Sang-Joon;Kim, Yong-Dae;Maeng, Joo-Sung;Han, Chul-Heui
    • 유체기계공업학회:학술대회논문집
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    • 2006.08a
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    • pp.209-212
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    • 2006
  • Insect and birds in nature flap their wings to generate fluid dynamic forces that are required for the locomotion. Most of the previous published papers discussed mainly on the effect of flapping parameters such as flapping frequency and amplitude on the thrust at a fixed Reynolds number. However, it is not much known on the values of the flapping parameters that the flapping wing requires to generate the thrust at the low Reynolds number flow. In this paper, the onset of the thrust generation is investigated using the lattice Boltzmann method. The wake patterns and velocity profiles behind a flat plate in heaving oscillation are investigated for the heaving amplitude of 0.5C. The time-averaged thrust coefficient value is investigated by changing the reduced frequency from 0.125 to 3.0 for three values of heaving amplitude (h/C=0.25, 0.325, 0.50). It is also found that the critical Strouhal number over which the flat plate starts to produce the thrust is around 0.1 and the thrust is an exponential function of the Strouhal number.

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