抄録
Thermal diffusion from a point source was experimentally investigated in uniform shear flows having velocity gradients of 2.6, 6.1 s^<-1> and in quasi-isotropic turbulence fields. Short-time dispersion accompanied by the plume's meandering motion was realized in the large-scale turbulence fields of R_λ=310, 410 and 490, with the spectra of temperature fluctuation had clear inertial ranges. For sheared small-scale turbulence of R_λ=50 and 100, the turbulent Prandtl number Pr_t, in almost unchanged in the streamwise direction. The Pr_t was larger than ordinary Pr_t≒1.0, and approached approximately Pr_t≒1.44〜1.88, in the region where the plume's active meandering motion was clearly observed in the sheared large-scale turbulence.
