Wind tunnel modeling of hourly observed atmospheric diffusion by oscillating blade cascade

Horizontal plume spread increases greatly with averaging time. For hourly averaging, plume spreads are much greater in the horizontal direction than in the vertical. The ratio of horizontal to vertical spread was found to be as large as 6. Conventional method cannot reproduce such anisotropic diffusion characteristic in wind tunnel experiments. The author has developed an oscillating blade cascade as a solution to the problem. Since the blade cascade generates strong secondary flow in the test section, a horizontal wind fluctuation of more than 11° has been achieved, which is similar to the standard deviation of wind direction averaged over 1 h under neutral condition. butions of mean wind velocity, turbulence intensity, and spectral structures were also similar to those observed in the atmospheric boundary layer. -averaged plume spread in horizontal and vertical directions could be simulated in the wind tunnel on 1:5000 scale, with appropriate selection of random motion amplitude of the blade cascade and ground roughness arrangement. Thus, the oscillating blade cascade method is useful to model large-scale plume diffusion from a continuous source such as thermal power plant stacks.