• Title/Summary/Keyword: inviscid

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A Dynamic Characteristics of the Tube Flow with the Variations of the Axially-Positioned Super-Circled Orifice Shape (유동방향의 초원형 오리피스 형상 변화가 관유동에 미치는 동특성 연구)

  • Kim, Youn J.;Lee, Sang-Sub
    • Journal of Energy Engineering
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    • v.6 no.1
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    • pp.52-57
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    • 1997
  • Dynamic characteristics of compressible flow fields in super-circled constricted tube have been studied numerically. By applying MacCormack's explicit scheme, time marching method with predictor/corrector step, Euler equation is solved to find characteristics of fluid flow in a constricted tube where a two-dimensional inviscid compressible flow is assumed. The effects of tube diameter and aspect ratios on the pressure variations are discussed extensively. The results of the developed numerical schemes are compared with those of commercial FLUENT code, and show a good agreement.

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Vibration Analysis for Partially Immersed Shell Structure in Water with Gap from Bottom (부분적으로 물에 잠겨있는 Shell 구조물의 바닥면과 거리변화에 따른 진동해석 연구)

  • Koo, Jae-R.;Kwak, Moon-K.;Song, Oh-S.;Bae, Chun-H.
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.21 no.10
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    • pp.905-915
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    • 2011
  • The free flexural vibration of a hanged clamped-free cylindrical shell partially submerged in water with gap from bottom is investigated. The fluid is assumed to be inviscid and irrotational. The cylindrical shell is modeled by using the Rayleigh-Ritz method based on the Sanders shell theory. The kinetic energy of the fluid is derived by solving the boundary-value problem related to the fluid motion. The natural vibration characteristics of the partially submerged cylindrical shell are discussed with respect to the added virtual mass approach. In this study, experiments were carried out to confirm theoretical results. It was found that theoretical prediction is in good agreement with experimental results.

Geometry Realization of an Airplane and Numerical Flow Visualization (역설계에 의한 비행기의 형상 구현과 수치계산에 의한 유동 가시화)

  • Kim, Yang-Kyun;Kim, Sung-Cho;Kim, Jeong-Soo;Choi, Jong-Wook;Park, Jeong
    • Journal of the Korean Society of Visualization
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    • v.5 no.2
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    • pp.20-25
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    • 2007
  • The geometry of a commercial passenger airplane is realized based on a Boeing 747-400 model through the photographic scanning and reverse engineering. The each element consisting of the plane such as fuselage, wing, vertical fin, stabilizer and engines, is individually generated and then the whole body is assembled by the photomodeler. The maximum error in the realized airplane is about 1.4% comparing with the real one. The three-dimensional inviscid steady compressible governing equations are solved in the unstructured tetrahedron grid system, and in a finite volume method using STAR-CD when the airplane flies at the cruise condition. The pressure distribution on the surface and the wing-tip vortices are visualized, and in addition to the aerodynamics coefficients, lift and drag are estimated.

Numerical Simulation of Acoustic Field Interacting between a Vortex Ring and a Rigid Sphere (원형 고리와와 강체구의 상호작용에 의한 음향장 수치해석)

  • 유기완;이덕주
    • Journal of KSNVE
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    • v.7 no.2
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    • pp.215-222
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    • 1997
  • The flow and acoustic fields due to a vortex ring interaction with a rigid sphere are simulated numerically. The flow field is regarded as three-dimensional inviscid and incompressible. The vorticity is assumed to be concentrated inside the finite core of vortex filament. The vortex filament curve, described by parabolic blending curve function, is used to effectively solve the modified Biot-Savart equation. The interaction between a vortex ring and a rigid sphere using the parabolic blending curve is calculated. The trajectory of the vortex ring is obtained with several different initial positions between the ring and the sphere. The force variations acting on the sphere are calculated by using the boundary integral method. Finally, we can also obtain the acoustic signals at the far field observation positions from the force variations acting on the rigid surface. We can find that the dipole axis of the directivity patterns are rotated during the interacting phenomena.

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Natural Vibration Characteristics of Cantilever Plate Partially Submerged into Water (수중에 부분 몰수된 외팔보의 고유진동 특성)

  • Kwak, Moon K.;Yang, Dong-Ho;Lee, Jae-Ha
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2012.10a
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    • pp.229-230
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    • 2012
  • The free flexural vibration of a cantilever plate partially submerged in a fluid is investigated. The fluid is assumed to be inviscid and irrotational. The virtual mass matrix is derived by solving the boundary-value problem related to the fluid motion using elliptical coordinates. The introduction of the elliptical coordinates naturally leads to the use of the Mathieu function. Hence, the virtual mass matrix which reflects the effect of the fluid on the natural vibration characteristics is expressed in analytical form in terms of the Mathieu functions. The virtual mass matrix is then combined with the dynamic model of a thin rectangular plate obtained by using the Rayleigh-Ritz method. This combination is used to analyze the natural vibration characteristics of a partially submerged cantilever plate qualitatively. Also, the non-dimensionalized added virtual mass incremental factors for a partially submerged cantilever plate are presented to facilitate the easy estimation of natural frequencies of a partially submerged cantilever plate. The numerical results validate the proposed approach.

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Parallel 3-D Aerodynamic Shape Optimization on Unstructured Meshes

  • Lee, Sang-Wook;Kwon, Oh-Joon
    • International Journal of Aeronautical and Space Sciences
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    • v.4 no.1
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    • pp.45-52
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    • 2003
  • A three-dimensional aerodynamic shape optimization technique in inviscid compressible flows is developed by using a parallel continuous adjoint formulation on unstructured meshes. A new surface mesh modification method is proposed to overcome difficulties related to patch-level remeshing for unstructured meshes, and the effect of design sections on aerodynamic shape optimization is examined. Applications are made to three-dimensional wave drag minimization problems including an ONERA M6 wing and the EGLIN wing-pylon-store configuration. The results show that the present method is robust and highly efficient for the shape optimization of aerodynamic configurations, independent of the number of design variables used.

Flow Field Analysis of a Centrifugal Fan (원심형 홴의 유동해석에 관한 연구)

  • Shin, Dong-Shin;Im, Jong-Soo;Kim, Chang-Seong;Rho, O-Hyun;Lee, Soo-Gab
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.1 s.2
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    • pp.43-49
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    • 1999
  • Flow field and near-field noise of a centrifugal fan has been studied with an efficient compressible method and STAR-CD. The flow field of the centrifugal fan is assumed to be two-dimensional. Most of the compressible studies have been done by inviscid solver because viscous simulation shows little difference. The near field noise is estimated in terms of sound pressure level in frequency domain transformed from the computed pressure fluctuations using FFT. The simulation has been done on various design elements such as impeller blade shapes, the number of blades and cut-off clearance. The comparison shows that the number of blades has a significant effect on near-field noise without losing aerodynamic performance.

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Aerodynamic Design of the Axial Fan (축류 송풍기의 공력학적 설계)

  • Sohn, Sang-Bum;Joo, Won-Gu;Cho, Kang-Rae;Nam, Hyung-Baik;Yoon, In-Kyu;Nam, Leem-Woo
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.1 s.2
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    • pp.22-28
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    • 1999
  • In this study, a preliminary design method of the axial fan was systematically established based on the two-dimensional cascade theory. Flow deviation, lift coefficient, distribution of velocity and pressure coefficient on blade surfaces were predicted by an inviscid flow theory of Martensen method, which was also applied to select an airfoil for required performance in the present design process. The aerodynamic performance of designed blades can be predicted quickly and reasonably by using the through-flow calculation method in the preliminary design process. It would be recommendable to adopt three-dimensional viscous flow calculation at the final design refinement stage.

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Numerical Simulation of Projectiles in Detonable Gases

  • Moon, Su-Yeon;Lee, Chooung-Won;Sohn, Chang-Hyun
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2001.11a
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    • pp.43-47
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    • 2001
  • A numerical parametric study is conducted to simulate shock-induced combustion with a variation in freestream conditions. The analysis is limited to inviscid flow and includes chmical nonequilibrium. A steady combustion front is established if the freestream Mach number is above the Chapman-Jouguet speed of the mixture. On the other, an unsteady reaction fi:ont is established if the freestream Mach number is below or at the Chapman-Jouguet speed of the mixture. The three cases have been simulated for Machs 4.18, 5.11, and 6.46 with a projectile diameter of 15 mm. Machs 4.18 and 5.11 shows an unsteady reaction front, whereas Mach 6.46 represents a steady reaction front. Thus Chapman-Jouguet speed is one of deciding factor for the instabilities to trigger. The instabilities of the chemical front with a variation of projectiles diameters will be investigated.

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Heat and Mass Transfer Enhancement of a pendant droplet on heated horizontal surface by acoustic resonance (가열된 평판위에 매달려 있는 액적의 음향공진에 의한 열 및 물질 전달 촉진에 관한 연구)

  • Moon, Jong-Hoon
    • Proceedings of the SAREK Conference
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    • 2005.11a
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    • pp.335-340
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    • 2005
  • Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. The evaporation was observed at atmosphere pressure. The droplet was recorded throughout the entire evaporation process and transient variations of the volume was measured. The evaporation process of oscillating droplet with thermofoil has been also observed to investigate analyzing the resonance effect on the thermal characteristics of droplet. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. During imposing the acoustic wave, the pendant droplet makes a rotating motion in its longitudinal axis which is a new shape oscillation mode. The evaporation rate of a pendant droplet at resonant frequency is significantly enhanced.

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