A NEW OPTICAL TECHNIQUE FOR PROBING CLEAR AIR TURBULENCE

Abstract

A new optical technique for probing the small scales turbulence has been developed. When light is transmitted through the atmosphere, it can scatter off vortex filaments in the air that are at different densities from the surrounding air, and hence, have different indices of refraction. These filaments, or eddies are distributed through a turbulent flow. Our experiment illuminated a turbulent flow with an expanded Gaussian laser beam. Two detectors, capable of translation perpendicular to the beam path, observed intensity fluctuations at different points. By analysis of two point spatial transmission correlation functions, the smallest length scales of clear air turbulence can be determined in real time without disturbing the flow. By changing the type of air flow, different length scales associated with different conditions have been measured optically. The measured scales agree with measurements done by hotwire techniques and correspond to the Kolmogorov microscale.