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  • Title/Summary/Keyword: Incompressible fluids

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Turbulent Flow Analysis of a Circular Cylinder Using a Fractional Step Method (Fractional Step Method을 이용한 원형 실린더 주위의 난류 유동해석)

  • Park K. S.;Park W. G.
    • 한국전산유체공학회:학술대회논문집
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    • 2003.08a
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    • pp.152-157
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    • 2003
  • As computer capacity has been progressed continuously, the studies of the flow characteristics have been performing by the numerical methods actively. Recent numerical simulation has a tendency to require the higher-order accuracy in time, as well as in space. This tendency is more true in LES and acoustic noise simulation. In this study, 3-dimensional unsteady Incompressible Navier-Stokes equation was solved by numerical method using the fractional step method with the fourth order compact pade scheme to achieve high accuracy To validate the present code and algorithm, 3D flow-field around a cylinder was simulated. The drag coefficient and lift coefficient were computed and, then, compared with experiment. The present code will be tailored to LES simulation for more accurate turbulent flow analysis.

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Study on Improvement in Numerical Method for Two-phase Flows Including Surface Tension Effects (표면장력 효과를 고려한 이상유동 해석법 개선에 관한 연구)

  • Park, Il-Ryong
    • Journal of Ocean Engineering and Technology
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    • v.27 no.5
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    • pp.70-76
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    • 2013
  • The present paper proposes a coupled volume-of-fluid (VOF) and level-set (LS) method for simulating incompressible two-phase flows that include surface tension effects. The interface of two fluids and its motion are represented by a VOF method designed using high-resolution differencing schemes. This hybrid method couples the VOF method with an LS distancing algorithm in an explicit way to improve the calculation of the normal and curvature of the interface. It is developed based on a rather simple algorithm to be efficient for various practical applications. The accuracy and convergence properties of the method are verified in a simulation of a single gas bubble rising in a three-dimensional flow with a large density ratio.

ALGORITHMS TO APPLY FINITE ELEMENT DUAL SINGULAR FUNCTION METHOD FOR THE STOKES EQUATIONS INCLUDING CORNER SINGULARITIES

  • JANG, DEOK-KYU;PYO, JAE-HONG
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.23 no.2
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    • pp.115-138
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    • 2019
  • The dual singular function method [DSFM] is a solver for corner sigulaity problem. We already construct DSFM in previous reserch to solve the Stokes equations including one singulairity at each reentrant corner, but we find out a crucial incorrection in the proof of well-posedness and regularity of dual singular function. The goal of this paper is to prove accuracy and well-posdness of DSFM for Stokes equations including two singulairities at each corner. We also introduce new applicable algorithms to slove multi-singulrarity problems in a complicated domain.

Settlement of velocity dissemination with fluid parameters for the configuration of stretching cylinder

  • Jalil, Mudassar;Iqbal, Waheed;Hussain, Muzamal;Khadimallah, Mohamed A.;Alshoaibi, Adil;Baili, Jamel;Khedher, Khaled Mohamed;Ali, Elimam Abdallah;Tounsi, Abdelouahed
    • Steel and Composite Structures
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    • v.42 no.3
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    • pp.389-396
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    • 2022
  • This investigation in fluid mechanics surrounds around the variety of flow problems for different fluids along the stretching cylinder. Numerical procedure is carried out for the obtained resultant equations by Keller-Box technique. Numerical study of laminar, steady, viscous and incompressible two dimensional boundary layer flow of effects of suction and blowing on boundary layer slip flow of Casson fluid along permeable exponentially stretching cylinder has been carried out in the present draft. physical parameters i.e., Nusselt number and skin friction coefficient, suction parameter and the local Reynold number are investigated on velocity profile and elaborated through proper graphs and table.

A Fully-implicit Velocity Pressure coupling Algorithm-IDEAL and Its Applications

  • SUN, Dong-Liang;QU, Zhi-Guo;He, Ya-Ling;Tao, Wen-Quan
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.1-13
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    • 2008
  • An efficient segregated algorithm for the coupling of velocity and pressure of incompressible fluid flow, called IDEAL Inner Doubly-Iterative Efficient Algorithm for Linked-Equations), has been proposed by the present authors. In the algorithm there exist double inner iterative processes for pressure equation at each iteration level, which almost completely overcome two approximations in SIMPLE algorithm. Thus the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate and stability of solution process. The performance of the IDEAL algorithm for three-dimensional incompressible fluid flow and heat transfer problems is analyzed and a systemic comparison is made between the algorithm and three other most widely-used algorithms (SIMPLER, SIMPLEC and PISO). It is found that the IDEAL algorithm is the most robust and the most efficient one among the four algorithms compared. This new algorithm is used for the velocity prediction of a new interface capturing method. VOSET, also proposed by the present author. It is found that the combination of VOSET and IDEAL can appreciably enhance both the interface capture accuracy and convergence rate of computations.

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A Fully-implicit Velocity Pressure coupling Algorithm-IDEAL and Its Applications

  • Sun, Dong-Liang;Qu, Zhi-Guo;He, Ya-Ling;Tao, Wen-Quan
    • 한국전산유체공학회:학술대회논문집
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    • 2008.10a
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    • pp.1-13
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    • 2008
  • An efficient segregated algorithm for the coupling of velocity and pressure of incompressible fluid flow, called IDEAL (Inner Doubly-Iterative Efficient Algorithm for Linked-Equations), has been proposed by the present authors. In the algorithm there exist double inner iterative processes for pressure equation at each iteration level, which almost completely overcome two approximations in SIMPLE algorithm. Thus the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate and stability of solution process. The performance of the IDEAL algorithm for three-dimensional incompressible fluid flow and heat transfer problems is analyzed and a systemic comparison is made between the algorithm and three other most widely-used algorithms (SIMPLER, SIMPLEC and PISO). It is found that the IDEAL algorithm is the most robust and the most efficient one among the four algorithms compared. This new algorithm is used for the velocity prediction of a new interface capturing method -VOSET, also proposed by the present author. It is found that the combination of VOSET and IDEAL can appreciably enhance both the interface capture accuracy and convergence rate of computations.

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Simulation of Pressure Oscillation in Water Caused by the Compressibility of Entrapped Air in Dam Break Flow (댐 붕괴 유동에서 갇힌 공기의 압축성에 의한 물의 압력 진동 모사)

  • Shin, Sangmook
    • Journal of the Society of Naval Architects of Korea
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    • v.55 no.1
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    • pp.56-65
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    • 2018
  • Pressure oscillation caused by the compressibility of entrapped air in dam break flow is analyzed using an open source code, which is a two-phase compressible code for non-isothermal immiscible fluids. Since compressible flows are computed based on a pressure-based method, the code can handle the equation of state of barotropic fluid, which is virtually incompressible. The computed time variation of pressure is compared with other experimental and computational results. The present result shows good agreements with other results until the air is entrapped. As the entrapped air bubbles pulsate, pressure oscillations are predicted and the pressure oscillations damp out quickly. Although the compressibility parameter of water has been varied for a wide range, it has no effects on the computed results, because the present equation of state for water is so close to that of incompressible fluid. Grid independency test for computed time variation of pressure shows that all results predict similar period of pressure oscillation and quick damping out of the oscillation, even though the amplitude of pressure oscillation is sensitive to the velocity field at the moment of the entrapping. It is observed that as pressure inside the entrapped air changes quickly, the pressure field in the neighboring water adjusts instantly, because the sound of speed is much higher in water. It is confirmed that the period of pressure oscillation is dominated by the added mass of neighboring water. It is found that the temperature oscillation of the entrapped air is critical to the quick damping out of the oscillations, due to the fact that the time averaged temperature inside the entrapped air is higher than that of surrounding water, which is almost constant.

On the Vorticity and Pressure Boundary Conditions for Viscous Incompressible Flows (비압축성 점성유동의 와도와 압력 경계조건)

  • Suh J.-C.
    • 한국전산유체공학회:학술대회논문집
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    • 1998.05a
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    • pp.15-28
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    • 1998
  • As an alternative for solving the incompressible Navier-Stokes equations, we present a vorticity-based integro-differential formulation for vorticity, velocity and pressure variables. One of the most difficult problems encountered in the vorticity-based methods is the introduction of the proper value-value of vorticity or vorticity flux at the solid surface. A practical computational technique toward solving this problem is presented in connection with the coupling between the vorticity and the pressure boundary conditions. Numerical schemes based on an iterative procedure are employed to solve the governing equations with the boundary conditions for the three variables. A finite volume method is implemented to integrate the vorticity transport equation with the dynamic vorticity boundary condition . The velocity field is obtained by using the Biot-Savart integral derived from the mathematical vector identity. Green's scalar identity is used to solve the total pressure in an integral approach similar to the surface panel methods which have been well-established for potential flow analysis. The calculated results with the present mettled for two test problems are compared with data from the literature in order for its validation. The first test problem is one for the two-dimensional square cavity flow driven by shear on the top lid. Two cases are considered here: (i) one driven both by the specified non-uniform shear on the top lid and by the specified body forces acting through the cavity region, for which we find the exact solution, and (ii) one of the classical type (i.e., driven only by uniform shear). Secondly, the present mettled is applied to deal with the early development of the flow around an impulsively started circular cylinder.

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Stable Anisotropic Freezing Modeling Technique Using the Interaction between IISPH Fluids and Ice Particles (안정적이고 이방성한 빙결 모델링을 위한 암시적 비압축성 유체와 얼음 입자간의 상호작용 기법)

  • Kim, Jong-Hyun
    • Journal of the Korea Computer Graphics Society
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    • v.26 no.5
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    • pp.1-13
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    • 2020
  • In this paper, we propose a new method to stable simulation the directional ice shape by coupling of freezing solver and viscous water flow. The proposed ice modeling framework considers viscous fluid flow in the direction of ice growth, which is important in freezing simulation. The water simulation solution uses the method of applying a new viscous technique to the IISPH(Implicit incompressible SPH) simulation, and the ice direction and the glaze effect use the proposed anisotropic freezing solution. The condition in which water particles change state to ice particles is calculated as a function of humidity and new energy with water flow. Humidity approximates a virtual water film on the surface of the object, and fluid flow is incorporated into our anisotropic freezing solution to guide the growth direction of ice. As a result, the results of the glaze and directional freezing simulations are shown stably according to the flow direction of viscous water.

COMPARISON OF COMMERCIAL AND OPEN SOURCE CFD CODES FOR AERODYNAMIC ANALYSIS OF FLIGHT VEHICLES AT LOW SPEEDS (저속 비행체 공력해석을 위한 상용 및 오픈 소스 CFD 코드 비교)

  • Park, D.H.;Kim, C.W.;Lee, Y.G.
    • Journal of computational fluids engineering
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    • v.21 no.2
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    • pp.70-80
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    • 2016
  • The comparison of two commercial codes(FLUENT and STAR-CCM+) and an open-source code(OpenFOAM) are carried out for the aerodynamic analysis of flight vehicles at low speeds. Tailless blended-wing-body UCAV, main wing and propeller of HALE UAV(EAV-3) are chosen as geometries for the investigation. Using the same mesh, incompressible flow simulations are carried out and the results from three different codes are compared. In the linear region, the maximum difference of lift and drag coefficients of UCAV are found to be less than 2% and 5 counts, respectively and shows good agreement with wind tunnel test data. In a stall region, however, the reliability of RANS simulation is found to become poor and the uncertainty according to code also increases. The effect of turbulence models and meshes generated from different tools are also examined. The transition model yields better results in terms of drag which are much closer to the test data. The pitching moment is confirmed to be sensitive to the existence and the location of transition. For the case of EAV-3 wing, the difference of results with κω SST model is increased when Reynolds number becomes low. The results for the propeller show good agreement within 1% difference of thrust. The reliability and uncertainty of three codes is found to be reasonable for the purpose of engineering use. However, the physical validity and reliability of results seem to be carefully examined when κω SST model is used for aerodynamic simulation at low speeds or low Reynolds number conditions.