An Experimental Study on the Diffusion Characteristics of Turbulent Flow in a Low Speed Wind Tunnel

Abstract

This paper describes the results of a study on diffusion characteristics of turbulent flow in a wind tunnel, in which the turbulent flow was obtained by a grid. The lateral turbulent velocity deviation ranged from 1.01 to 1.14 times the longitudinal turbulent velocity deviation for mean wind velocities from 2 to 8 m/sec and mesh sizes of grid from 4.5 to 13.5 cm, and the isotropic condition was almost satisfied. The decay of turbulence was expressed with the equation /U＝m(x/M)⁻α, where : longitudinal turbulent velocity variance, U : mean wind velocity, x : distance from the grid, M : mesh size of the grid, and α, m are constants. From 11 tracer gas experiments, we obtained the Lagrangian correlation coefficient and found the Lagrangian and Eulerian correlation coefficients had similar shapes within the range of time-lag from 0 to 400 milliseconds. The ratios of the Lagrangian to Eulerian time scale, β, were between 4 and 11.