摘要 : Previous studies of shear dispersion in bounded velocity fields have assumed random velocities with zero Lagrangian time scale (i.e.? velocities are δ-function correlated in time). However, many turbulent (geophysical and engineer... 展开 Previous studies of shear dispersion in bounded velocity fields have assumed random velocities with zero Lagrangian time scale (i.e.? velocities are δ-function correlated in time). However, many turbulent (geophysical and engineering) flows with mean velocity shear exist where the Lagrangian time scale is non-zero. Here, the longitudinal (along-flow) shear-induced diffusivity in a two-dimensional bounded velocity field is derived for random velocities with non-zero Lagrangian time scale τ _L. A non-zero τ _L results in two-time transverse (across-flow) displacements that are correlated even for large (relative to the diffusive time scale τ _D) times. The longitudinal (along-flow) shear-induced diffusivity D _S is derived, accurate for all τ _L, using a Lagrangian method where the velocity field is periodically extended to infinity so that unbounded transverse particle spreading statistics can be used to determine D _S. The non-dimensionalized D _S depends on time and two parameters: the ratio of Lagrangian to diffusive time scales τ _L/τ _D and the release location. Using a parabolic velocity profile, these dependencies are explored numerically and through asymptotic analysis. The large-time D _S is enhanced relative to the classic Taylor diffusivity, and this enhancement increases with √τ _L. At moderate τ _L/τ _D = 0. 1 this enhancement is approximately a factor of 3. For classic shear dispersion with τ _L = 0, the diffusive time scale τ _D determines the time dependence and large-time limit of the shear-induced diffusivity. In contrast, for sufficiently large τ _L, a shear time scale τ _S = (τ _Lτ _D) ~(1/2), anticipated by a simple analysis of the particle's domain-crossing time, determines both the D _S time dependence and the large-time limit. In addition, the scalings for turbulent shear dispersion are recovered from the large-time D _S using properties of wall-bounded turbulence. 收起