Impacts of the source temperature and its distance on the statistical behavior of the convective air turbulence

Abstract

In this paper, anisotropy and inhomogeneity of an indoor convective air turbulence are studied using two-channel moire deflectometry by statistical analyzing of the angle of arrival (AA) fluctuations over about 1300 points on the wave front passing through the turbulent area. The beam of a laser source is expanded and collimated with a diameter of 18 cm by a telescopic system consisting of an aspheric lens and a telescope. This beam propagates horizontally through a turbulent area. A heater is used for generating a convection air turbulence. At the end of the turbulent medium, the distorted wave front enters the aperture of another telescope. By the aid of another telescopic system, the diameter of the beam is reduced to a value of 2 cm, and the beam enters to a two-channel moire deflectometer. This device is able to measure AA of the wave front being fluctuated due to the turbulence. By statistical analyzing of the AA fluctuations in two perpendicular directions on the transverse plane, the homogeneity and isotropy of the turbulent medium are investigated at different distances from the heater in the presence of different temperature gradients. Results show that the temperature gradient and the distance from the heat source have considerable impacts on the inhomogeneity and anisotropy of the convective air turbulence. With increasing the distance from the heat source and decreasing the temperature gradient, the homogeneity increases, while by increasing the temperature gradient and in high distances from the heater, it becomes more isotropic. Finally, we report a way for estimating the depth of boundary layer.