ランダムフーリエモードとランダムフライトの複合モデルによる流体粒子の拡散に関する研究

抄録

To investigate the motion of fluid particles round a cylinder in turbulent flows, we have developed a new model simulating the trajectory of particles: the combined model of Kinematic Simulation (KS) and Random Flight (RF). The large-scale turbulence is simulated by a sum of random Fourier modes varying in space and time, and the small-scale turbulent fluctuation is simply modelled by ITO type of stochastic differential equation with a memory time comparable to a Lagrangian integral time scale T^L_S of small-scale motion. The Lagrangian properties of fluid particles in homogeneous isotropic turbulence with uniform mean flow has been examined. Some new results have been obtained using this new model: (a) the cross-correlation of the displacements by the large and small scale motions is negligibly small; (b) the random small-scale motion causes the decorrelation of the large-scale velocity; (c) the value of T^L_S used in RF is estimated from pure KS.