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강신정(S.J. KNAG),타나하시 마모루(M. TANAHASHI),미야우치 토시오(T. MIYAUCHI),이영호(Y.H. LEE) 한국전산유체공학회 2001 한국전산유체공학회 학술대회논문집 Vol.2001 No.-
Secondary instability of flow past a circular cylinder is examined using direct numerical simulation at Reynolds number 220 and 250. The higher-order finite difference scheme is employed for the spatial distributions along with the second order Adams-Bashforth and the first order backward~Euler time integration. In x-y plane, the convection term is applied by the 5th order upwind scheme, and the pressure and viscosity terms are applied by the 4th order central difference. In spanwise, Navier-Stokes equation is distributed using Spectral Method. The critical Reynolds number for this instability is found to be about Re=190. The secondary instability leads to three-dimensionality with a spanwise wavelength about 4 cylinder diameters at onset (A-mode). Results of three-dimensional effect in wake of a circular cylinder are represented with spanwisc and streamwise vorticity contours as Reynolds numbers.
강신정(S. J. Kang),타나하시 마모루(M. Tanahashi),미야우치 토시오(T. Miyauchi),이영호(Y. H. Lee) 한국전산유체공학회 2001 한국전산유체공학회지 Vol.6 No.4
The flow past a circular cylinder forced to vibrate transversely is numerically simulated by solving the two-dimensional Navier-Stokes equations modified by the vibration velocity of a circular cylinder at a Heynolds number of 164. The higher-order finite difference scheme is employed for the spatial discretization along with the second order Adams-Bashforth and the first order backward-Euler time integration. The calculated cylinder vibration frequency is between 0.60 and 1.30 times of the natural vortex-shedding frequency. The calculated oscillation amplitude extends to 25% of the cylinder diameter and in the case of the lock-in region it is 60%. It is made clear that the cylinder oscillation has influence on the wake pattern, the time histories of the drag and lift forces, power spectral density and phase diagrams, etc. It is found that these results include both the periodic (lock-in) and the quasi-periodic (non-lock-in) state. The vortex shedding frequency equals the driving frequency in the lock-in region but is independent in the non-lock-in region. The mean drag and the maximum lift coefficient increase with the increase of the forcing amplitude in the lock~in state. The lock-in boundaries are also established from the present direct numerical simulation.