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서정천(J. C. Suh) 한국전산유체공학회 1998 한국전산유체공학회지 Vol.3 No.1
A vorticity-based method for the numerical solution of the two-dimensional incompressible Navier-Stokes equations is presented. The governing equations for vorticity, velocity and pressure variables are expressed in an integro-differential form. The global coupling between the vorticity and the pressure boundary conditions is fully considered in an iterative procedure when numerical schemes are employed. The finite volume method of the second order TVD scheme is implemented to integrate the vorticity transport equation with the dynamic vorticity boundary condition. The velocity field is obtained by using the Biot-Savarl integral. The 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 present formulation is validated by comparison with data from the literature for the two-dimensional cavity flow driven by shear in a square cavity. We take two types of the cavity flow: (i) driven by non-uniform shear on top lid and body forces for which the exact solution exists, and (ii) driven only by uniform shear (of the classical type).
서정천(J.-C. Suh) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
As an alternative for solving the incompressible Navier-Stokes equations) we present. a vorticity 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 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 method 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 arc 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 method is applied to deal with the early development of the flow around an impulsively started circular cylinder.
서정천(J. C. Suh) 한국전산유체공학회 1998 한국전산유체공학회지 Vol.3 No.1
A vorticity-based method for the numerical solution of the two-dimensional incompressible Navier-Stokes equations is presented. The governing equations for vorticity, velocity and pressure variables are expressed in an integro-differential form. The global coupling between the vorticity and the pressure boundary conditions is fully considered in an iterative procedure when numerical schemes are employed. The finite volume method of the second order TVD scheme is implemented to integrate the vorticity transport equation with the dynamic vorticity boundary condition. The velocity field is obtained by using the Biot-Savarl integral. The 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 present formulation is validated by comparison with data from the literature for the two-dimensional cavity flow driven by shear in a square cavity. We take two types of the cavity flow: (i) driven by non-uniform shear on top lid and body forces for which the exact solution exists, and (ii) driven only by uniform shear (of the classical type).
이준혁(J.H. Lee),김유철(Y.C. Kim),이경준(K.J. Lee),서정천(J.C. Suh) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
The Vortex-In-Cell(VIC) method combined with panel method is applied to the analysis of incompressible unsteady viscous flow. The dynamics of resulting flow is governed by the vorticity transport equation in Lagrangian form with vortex particle representation of the flow field. A regular grid which is independent to the shape of a body is used for numerical evaluation based on immersed boundary technique. With an introduction of this approach, the development and validation of the VIC method is presented with some computational results for incompressible viscous flow around two or three dimensional bodies such as wing section, sphere, finite wing and marine propeller.
보오텍스 방법에 의한 순간 출발하는 2차원 날개 주위의 점성유동 모사
이승재(S. J. Lee),김광수(K. S. Kim),서정천(J. C. Suh) 한국전산유체공학회 2004 한국전산유체공학회 학술대회논문집 Vol.2004 No.-
In the vortex particle method based on the vorticity-velocity formulation for solving the Navier-Stokes equations, the unsteady, incompressible, viscous laminar flow over a NACA 0012 foil is simulated. By applying an operator-splitting method, the "convection" and "diffusion" equations are solved sequentially at each time step. The convection equation is solved using the vortex particle method, and the diffusion equation using the particle strength exchange(PSE) scheme which is modified to avoid a spurious vorticity flux. The scheme is improved for variety body shape using one image layer scheme. For a validation of the present method, we illustrate the early development of the viscous flow about an impulsively started NACA 0012 foil for Reynolds number 550.
Penalized VIC 방법에서 장시간 유동 해석을 위한 원거리 와도 입자 처리
조은별(E.B. Jo),이승재(S.-J. Lee),서정천(J.-C. Suh) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.1
A penalized VIC method offers an efficient hybrid particle-mesh algorithm to simulate an incompressible viscous flow passing a solid body in an infinite domain. In this manner, the computational domain needs to be restricted to a relatively small region to reduce computational cost which would be very high in case of using a large domain. In this paper, we present how to dispose of far-field particles to avoid an unnecessarily large computational domain. The present approach constraints expansion of the domain and thus prevents the incremental computational cost. To validate the numerical approach, a flow around an impulsively started sphere was simulated for Reynolds numbers of 100 and 1000.
이광수(K.S. Kim),이승재(S.J. Lee),서정천(J.C. Suh) 한국전산유체공학회 2003 한국전산유체공학회 학술대회논문집 Vol.2003 No.-
A vorticity-velocity integra-differential formulation of incompressible Navier-Stokes equations is described, focusing on a scheme for calculating pressure fields in application of the Lagrangian vortex method in connection with panel methods. It deals with the dynamic coupling among velocity, vorticity and pressure, and the Helmholtz decomposition of the velocity field. through a comparative study with the Eulerian finite volume method, we provide an extensive understanding of the Lagrangian vortex methods for numerical simulations of viscous flows around arbitrary bodies.
김명수(M.S. Kim),김유철(Y.C. Kim),서정천(J.C. Suh) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
VIC (Vortex-In-Cell) method for viscous incompressible flow is presented to simulate the wake behind a modified NACA16 foil. With uniform rectangular grid, the velocity in field is calculated using streamfunction from vorticity field by solving the Poisson equation in which FFT(Fast Fourier Transform) is combined with 2nd order finite difference scheme. Here, LES(Large Eddy Simulation) with Smagorinsky model is applied for turbulence calculation. Effective viscosity is formulated using magnitude of strain tensor(or vorticity). Then the turbulent diffusion as well as viscous diffusion becomes particle strength exchange(PSE) with averaged eddy viscosity. The well-established panel method is combined to obtain the irrotational velocity and to apply the no-penetration boundary condition on the body panel. And wall diffusion is used for no-slip condition Numerical results of turbulent stresses are compared with experimental results (Bourgoyne, 2003). Before comparing process, LES(Large Eddy Simulation) SGS(Subgrid scale) stress is transformed Reynolds averaged stress (Winckelmans, 2001).