EXPERIMENTAL AND ANALYTICAL INVESTIGATIONS OF THERMAL BLOOMING IN AXIAL PIPE FLOW

Abstract
An experimental and theoretical study of thermal blooming phenomena in a high energy laser beam propagating in an axial turbulent pipe flow is presented. The experiments were conducted by using a 250 watt CW CO₂ laser as the heat source and a mixture of CO₂ and N₂ as the absorbing medium. The optical path difference (OPD) caused by the heating of the gas by the beam were measured by holographic interferometry, using a krypton laser at 0.5208 µm. The theory was developed by modifying an existing numerical code in order to include the volumetric heating due to absorption of the laser radiation by the flowing gas. The theoretical OPD's were calculated directly from the temperature profiles, and comparison with the experimental values showed good agreement.