• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.1
• /
• pp.23-30
• /
• 2004

In the Lagrangian vortex particle method based on the vorticity-velocity formulation for solving the incompressible Navier-Stokes equations, a numerical scheme for calculating pressure fields is presented. Implementation of the numerical method is directly connected with the well-established surface panel methods, just by dealing with the dynamic coupling among vorticity field. Assuming the vorticity and the velocity fields are to be calculated in time domain analysis, the pressure calculation for a complete set of solution at present time step is performed in a similar way to the one used in the Eulerian description. For a validation of the present method, we illustrate the early development of the viscous flow about an impulsive started circular cylinder for Reynolds number 550. The comparative study with the Eulerian finite Volume method provides an extensive understanding and application of the mesh-free Lagrangian vortex methods for numerical simulation of viscous flows around arbitrary bodies of general shape.

• Journal of the Society of Naval Architects of Korea
• /
• v.51 no.4
• /
• pp.328-333
• /
• 2014

A hybrid particle-mesh method based on the vorticity-velocity formulation for solving the incompressible Navier-Stokes equations is a combination of the Vortex-In-Cell(VIC) method for convection and the penalization method for diffusion. The key feature of the numerical methods is to determine velocity and vorticity fields around a solid body on a temporary grid, and then the time evolution of the flow is computed by tracing the convection of each vortex element using the Lagrangian approach. Assuming that the vorticity and velocity fields are to be computed in time domain analysis, pressure fields are estimated through a complete set of solutions at present time step. It is possible to obtain vorticity and velocity fields prior to any pressure calculation since the pressure term is eliminated in the vorticity-velocity formulation. Therefore, pressure field is explicitly treated by solving a suitable Poisson equation. In this paper, we propose a simple way to numerically implement the vorticity-velocity-pressure formulation including a penalty term. For validation of the proposed numerical scheme, we illustrate the early development of viscous flows around an impulsive started circular cylinder for Reynolds number of 9500.

• 한국전산유체공학회:학술대회논문집
• /
• 2002.10a
• /
• pp.47-52
• /
• 2002

We present an improved Lagrangian vortex method in 2-D incompressible unsteady viscous flows, which is based on a mesh-free integral approach of the velocity-vorticity formulation. Vorticity fields are represented by discrete vortex blobs that are updated by the Lagrangian vorticity transport with the particle strength exchange scheme. Velocity fields are expressed in a form of the Helmholtz decomposition, which are calculated by a fast algorithm of the Biot-Savart integration with a smoothed kernel and by a well-established panel method. No-slip condition is enforced through viscous diffusion of vorticity from a solid body into field. The vorticity flux is determined in such a way that spurious slip velocity vanishes. Through the comparison with the existing finite volume scheme for the transient vortical flows around an impulsively started cylinder at Reynolds number Re=550, we would obtain a more accurate scheme for vortex methods in complicated flows.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.610-615
• /
• 2003

This experiment has been carried out to find the structure of turbulent boundary layer with instantaneous velocity fields obtained in stream-wall-normal planes using a stereo-PIV (Particle Image Velocimetry) method. And it has been measured perpendicular plane and horizontal plane with hairpin vortex structure by Reynolds number change and made third dimension shape for section of horizontal plane through stereo-PIV. In the outer layer hairpin vortices occur in streamwise-aligned packets that propagate with small velocity dispersion. A streaky structure is composed of counter-rotating vortex. According as y+ increases, streaky structure's interval space decrease, and it shows that hairpin shape of prior research is vertified. The objective of the present research is to gain a better understanding of coherent structures in the outer of wall turbulence by experimentally examining coherent structures.

• Journal of the Society of Naval Architects of Korea
• /
• v.49 no.1
• /
• pp.26-32
• /
• 2012

The 3-D unsteady viscous flow around an impulsively started rotating marine propeller is simulated using VIC(Vortex-In-Cell) method which is adequate to analyze the strong vortical flow around complicatedly-shaped body. The computational procedure is governed by the vorticity transport equation in Lagrangian form. In order to solve the equation, a regular grid which is independent to the shape of a body is introduced and each term of the equation is evaluated numerically on the grid by applying immersed boundary concept. In this paper, the overall algorithm including the formulation of governing equations and boundary conditions is described and some computational results are presented with discussing their physical validity.

• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.78-85
• /
• 2011

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.

• Journal of the Korea Computer Graphics Society
• /
• v.23 no.1
• /
• pp.17-24
• /
• 2017

We propose an efficient method to express water spray effects by adaptively modeling air particles in particle-based water simulation. In real world, water and air continuously interacts with each other around free surfaces and this phenomenon is commonly observed in waterfall or sea with rough waves. Due to thin spray water, the interfaces between water and air become vague and the interactions between them lead to heavy vortex phenomenon. To express this phenomenon, we propose methods of 1) generating adaptive air cell in particle-based water simulation, 2) expressing water spray effects by creating and evolving air particles in the adaptive air cells, and 3) guaranteeing robustness of simulation by solving drifting problem occurred when adjacent air particles are insufficient. Experiments convincingly demonstrate that the proposed approach is efficient and easy to use while delivering high-quality results.

• Journal of computational fluids engineering
• /
• v.22 no.1
• /
• pp.51-58
• /
• 2017

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.

• Journal of computational fluids engineering
• /
• v.19 no.2
• /
• pp.72-78
• /
• 2014

A hybrid particle-mesh method as the combination between the Vortex-In-Cell (VIC) method and penalization method has been achieved in recent years. The VIC method, which is based on the vorticity-velocity formulation, offers particle-mesh algorithms to numerically simulate flows past a solid body. The penalization method is used to enforce boundary conditions at a body surface with a decoupling between body boundaries and computational grids. The main advantage of the hybrid particle-mesh method is an efficient implementation for solid boundaries of arbitrary complexity on Cartesian grids. However, a numerical simulation of flows in large domains is still not too easy. In this study, a multi-domain approach is thus proposed to further reduce computation cost and easily implement it. We validate the implementation by numerical simulations of an incompressible viscous flow around an impulsively started circular cylinder.

• 한국가시화정보학회:학술대회논문집
• /
• 2003.11a
• /
• pp.31-34
• /
• 2003

The near wake behind a sinusoidal cylinder has been investigated quantitatively using hot-wire anemometer and qualitative. The mean velocity and turbulence intensity were measured in streamwise and spanwise direction. The results show that the wake in the saddle plane has a longer vortex formation region and rapid reversed flow than that in nodal plane. The elongated vortex formation region of sinusoidal cylinder is related with drag reduction. In addition, the flow visualized with particle tracing method support the flow characteristics of sinusoidal cylinder measured by hot-wire.