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Immersed Boundary Method for Complex Flows

복잡한 형상 물체 주위에 형성되는 유체현상을 고정격자계를 사용하여 해석할 수 있는 가상경계기법 (Immersed Boundary Method)를 개발하였으며, 그 일례로 보행시 발생되는 난류현상을 예측하였다.

An immersed boundary method for time-dependent, three-dimensional, incompressible flows is presented in this paper. The incompressible Navier-Stokes equations are discretized using a low-diffusion flux splitting method for the inviscid fluxes and second-order central-differences for the viscous components. Higher-order accuracy achieved by using weighted essentially non-oscillatory (WENO) or total variation diminishing (TVD) schemes. An implicit method based on artificial compressibility and dual-time stepping is used for time advancement. The immersed boundary surfaces are defined as clouds of points, which may be structured or unstructured. Immersed-boundary objects are rendered as level sets in the computational domain, and concepts from computational geometry are used to classify points as being outside, near, or inside the immersed boundary. The velocity field near an immersed surface is determined from separate interpolations of the components tangent and normal to the surface. The tangential velocity near the surface is constructed as a power-law function of the local wall normal distance. Appropriate choices of the power law enable the method to approximate the energizing effects of a turbulent boundary layer for higher Reynolds number flows. Four different flow problems (flow past a circular cylinder, a NACA0012 airfoil, a sphere, and a stationary mannequin) are simulated using the present immersed boundary method, and the predictions show good agreement with previous computational and experimental results. Finally, the flow induced by realistic human walking motion is simulated as an example of a problem involving multiple moving immersed objects.

Choi et al. (2007) Journal of Computational Physics

Schematic illustrating classification of cell-centered points for a complex immersed body

Evolution of iso-surfaces of streamwise velocity and coherent vertical structures induced human walking motion at each time instant

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