• Title/Summary/Keyword: Large Body Force Flow

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On the Use of Momentum Interpolation Method for flows Involving A Large Body force (바디포오스가 큰 유동해석시 운동량보간법의 사용에 관한 연구)

  • Choi Seok-Ki;Kim Seong-O;Choi Hoon-Ki
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.553-556
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    • 2002
  • A numerical study on the use of the momentum interpolation mettled for flows with a large body force is presented. The inherent problems of the momentum interpolation method are discussed first. Numerical experiments are performed for a typical flow involving a large body force. The tact that the momentum interpolation method may result in physically unrealistic solutions is demonstrated. Numerical experiments changing the numerical grid have shown that a simple way of removing the physically unrealistic solution is a proper grid refinement where there is a large pressure gradient. An effective way of specifying the pressure and pressure correction at the boundary by a local mass conservation near the boundary is proposed, and it is shown that this method can effectively remove the inherent problem of the specification of pressure and pressure correction at the boundary when one uses the momentum interpolation method.

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A Study on the Use of Momentum Interpolation Method for Flows with a Large Body Force (바디포오스가 큰 유동에서 운동량보간법의 사용에 관한 연구)

  • Choi Seok-Ki;Kim Seong-O;Choi Hoon-Ki
    • Journal of computational fluids engineering
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    • v.7 no.2
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    • pp.8-16
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    • 2002
  • A numerical study on the use of the momentum interpolation method for flows with a large body force is presented. The inherent problems of the momentum interpolation method are discussed first. The origins of problems of the momentum interpolation methods are the validity of linear assumptions employed for the evaluation of the cell-face velocities, the enforcement of mass conservation for the cell-centered velocities and the specification of pressure and pressure correction at the boundary. Numerical experiments are performed for a typical flow involving a large body force. The numerical results are compared with those by the staggered grid method. The fact that the momentum interpolation method may result in physically unrealistic solutions is demonstrated. Numerical experiments changing the numerical grid have shown that a simple way of removing the physically unrealistic solution is a proper grid refinement where there is a large pressure gradient. An effective way of specifying the pressure and pressure correction at the boundary by a local mass conservation near the boundary is proposed, and it is shown that this method can effectively remove the inherent problem of the specification of pressure and pressure correction at the boundary when one uses the momentum interpolation method.

A Numerical Analysis of Supersonic Counter Jet Flow Effect on Performance of a Supersonic Blunt-Body (초음속 역분사 유동이 초음속 비행체 성능에 미치는 영향에 대한 수치해석적 연구)

  • Seo D. K.;Seo J. I.;Song D. J.
    • Journal of computational fluids engineering
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    • v.7 no.3
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    • pp.1-8
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    • 2002
  • The counter jet flow which is injected against the free stream at stagnation region of blunt body for improvement of aerodynamic performance has been studied by using upwind Navier-Stokes method. The variations of drag force and upwind forward penetration depth due to changes in the stagnation thermodynamic properties of counter jet flow such as total pressure, Mach number, and total temperature have been studied. The results show that the changes in the stagnation pressure and Mach number have large effects on the wall pressure and drag force, but the total temperature does not affect the wall pressure and drag force.

Cavitating-Flow Characteristics around a Horn-Type Rudder (혼 타 주위의 캐비테이팅 유동 특성에 대한 연구)

  • Choi, Jung-Eun;Chung, Seak-Ho;Kim, Jung-Hun
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.3 s.153
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    • pp.228-237
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    • 2007
  • The flow characteristics around a horn-type rudder behind an operating propeller of a high-speed large container carrier are studied through a numerical method in fully wetted and cavitating flow conditions. The computations are carried out in a small scale ratio of 10.00(gap space=5mm) to consider the gap effects. The Reynolds averaged Navier-Stokes equation for a mixed fluid and vapor transport equation applying cavitation model are solved. The axisymmetry body-force distribution technique is utilized to simulate the flow behind an operating propeller. The gap flow, the three-dimensional flow separation, and the cavitation are the flow characteristics of a horn-type rudder. The pattern of three-dimensional flow separation is analyzed utilizing a topological rule. The various cavity positions predicted by CFD were shown to be very similar to rudder erosion positions in real ship rudder. The effect of a preventing cavitation device, a horizontal guide plate, is also investigated.

A Numerical Study on the Flow Development around a Rotating Square-Sectioned U-Bend(II) - Turbulent Flow - (회전하는 정사각 단면 U자형 곡관 내부의 유동 발달에 관한 수치적 연구(II) -난류 유동-)

  • Lee, Gong-Hee;Baek, Je-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.6
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    • pp.850-858
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    • 2002
  • The present study investigates in detail the combined effects of the Coriolis force and centrifugal force on the development of turbulent flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a curved region of U-bend, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal force due to the curvature of U-bend. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct. On the other hand, under negative rotation, where these two forces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces. Under the condition that the value of Rossby number and curvature ratio is large, the flow field in a rotating U-bend can be represented by two dimensionless parameters : $K_{TC}$ =Re $\sfrac{1}{4}$√λand a body force ratio F=λ/Ro. Here, $K_{TC}$ has the same dynamical meaning as $K_{TC}$ =Re√λ for laminar flow.

A Numerical Analysis of Counter Jet Flow Effect on the Blunt-Body Vehicle (역분사 유동이 초음속 비행체에 미치는 영향에 대한 수치해석적 연구)

  • Seo Duck Kyo;Seo Jeong Il;Song Dong Joo
    • 한국전산유체공학회:학술대회논문집
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    • 2002.05a
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    • pp.29-34
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    • 2002
  • TIn this study, the counter-jet flows which designed for improvement of aerodynamic performance of the blunt body vehicle have been analyzed. The variations of the drag force and jet penetration depth due to changes in the stagnation properties of counter jet new such as total pressure, mach number, and total temperature. The counter jet flow, which is injected toward incoming supersonic freestream at stagnation region of blunt cone-cylinder vehicle, have been studied by using upwind flux difference splitting navier-stokes method. The changes in the stagnation pressure and Mach number resulted in large effects on the wall pressure and drag force, on the other hand tile total temperature changes did not.

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Numerical Simulation of Flow Field Around a Rotating Flexible Foil Using the 3D HCIB Method (3차원 HCIB법을 이용한 회전하면서 변형하는 날개 주위 유동해석)

  • Shin, Sang-Mook;Nho, In-Sik
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.4
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    • pp.379-388
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    • 2008
  • A hybrid Cartesian/immersed boundary code is expanded to simulate flow field around a three-dimensional body which undergoes large dynamic deformation. Immersed boundary nodes are automatically distributed based on the edges crossing triangles on body boundary. Velocity vectors are reconstructed at those immersed boundary nodes along local normal lines to the boundary. The reconstruction of pressure is avoided using the hybrid staggered/non-staggered grid method. The developed code is validated through comparisons with other results on laminar flow over a sphere. The code is applied to simulate flow around a foil which is attached to a body of revolution and rotates under periodic deformation. The periodic variation of the tip vortex is observed and the effects of the deformation on hydrodynamic force acting on the body are investigated.

A Numerical Study on the Flow Development around a Rotating Square-Sectioned U-Bend (I) - Laminar Flow - (회전하는 정사각 단면 U자형 곡관 내부의 유동 발달에 관한 수치적 연구 (I) - 층류 유동)

  • Lee, Gong-Hui;Baek, Je-Hyeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.1
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    • pp.159-169
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    • 2002
  • The present study investigates in detail the combined effects of the Coriolis and centrifugal farce on the development of laminar flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a rotating curved region, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal farce due to the curvature of U-bend. When the values of Rossby number and curvature ratio are large, the flow field in a rotating U-bend can be represented by two dimensionless parameters ; the Dean number K$\_$LC/=Re/√λ and a body ratio F=λ/Po. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards, the directions of the two secondary flows are the same. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct with a larger f7c. On the other hand, in case of negative rotation, where two farces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces.

A Numerical Model of Large Scale Grid for Two-Dimensional Wake behind Bodies (저항물체 배후의 이차원 후류에 관한 대격자 수치모형)

  • 박일흠;이종섭;이문옥
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.10 no.2
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    • pp.83-92
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    • 1998
  • To evaluate the hydraulic resistance behind bodies in a large scale grid numerical model, a drag stress term which is formulated by the drag force is introduced in the depth-integrated Reynolds equations. And also, the applicability and problems of this model are discussed through various numerical experiments where the analytical solutions exist. In the case of a single body, the error range of velocity difference between analytical and numerical solutions is within $\pm$10% and the wake width behind the body shows a good agreement with the analytical solution. When the drag coefficient and the eddy viscosity are precisely decided, the numerical solutions behind a row of bodies will be efficiently used in real situations.

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Numerical Simulation of Flow around Variable Pitch Helically Elliptic Twisted Cylinder based on the Biomimetic Flow Control (생체모방 유동제어 기반 가변 피치 나선형 실린더 주위 유동 해석)

  • Moon, Jahoon;Yoon, Hyun Sik
    • Journal of the Society of Naval Architects of Korea
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    • v.57 no.2
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    • pp.96-103
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    • 2020
  • The new geometric disturbance is proposed to control the flow around the bluff body. The new geometry is characterized by the variable pitch which is applied on the Helically Elliptic Twisted (HET) cylinder. The performance of the HTE geometry as a biomimetic passive flow control was confirmed by Jung and Yoon (2014). The Large Eddy Simulation (LES) is used for the evaluation of the flow control performance of the Variable Pitch HTE (VPHTE) cylinder at Reynolds number (Re) of 3000 corresponding to the subcritical regime. The circular and HTE cylinders are also considered to compare the performance of the VPHTE cylinder at the same Re. The VPHTE cylinder gives the smallest values of the force coefficients than the circular and HTE cylinders. The drag and lift coefficients of the VPHTE cylinder are about 15.2% and 94.0% lower than those of the circular cylinder, respectively. Especially, the VPHTE cylinder achieves about 2.3% and 30.0% reduction of the drag coefficient and the root mean square of the lift coefficient than the HTE cylinder, respectively. Furthermore, The VPHTE cylinder forms more elongated and stabilized separated shear layer than the circular cylinder, which supports the reduction of the force coefficients.