An experimental and theoretical study of thermal blooming phenomena in a 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 0.5309 μM. The pipe wall roughness was varied by inserting an inner lining made of porous material. Two different inlet conditions to the pipe were considered in the experiments, namely, a straight inlet and a curved elbow. 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 OPDs were calculated directly from the temperature profiles, and comparison with the experimental values for the case with a straight inlet showed good agreement. The effects of a curved elbow inlet and pipe wall roughness on OPD were determined by comparison of the results with those for a straight inlet and smooth wall respectively.

Date Published: 15 September 1981
PDF: 12 pages
Proc. SPIE 0270, High Power Lasers and Applications, (15 September 1981); doi: 10.1117/12.931751

Published in SPIE Proceedings Vol. 0270:
High Power Lasers and Applications
Charles C. Tang, Editor(s)