Observations of Turbulence Structure in a Two Dimensional Channel Flow Reproduced by a Direct Numerical Simulation.

Recent computer development has enabled such a numerical simulation of turbulence as the direct numerical simulation (DNS). Direct numerical simulation provides valuable information of the flow field, such as the distributions of fluctuating velocity, pressure, and vorticity in the three dimensional space, which are difficult or often impossible to be obtained from experiments. In this study, the unsteady behavior of coherent structures in the two dimensional turbulent channel flow reproduced by a direct numerical simulation was visualized and animated with the aid of three dimensional computer graphics technique. The space-time relationship between vortical motions and streaks, ejections, sweeps was clearly observed from a moving frame at a speed of U+=14.0. In addition, it is found from the spectrum analysis that the coherent structures are constructed with relatively low wave number components of the fluctuating velocities and pressure.