Scalar Measurements by Laser Induced Fluorescence

This study is concerned with the measurements of scalar variables in turbulent flows, by Laser Induced Fluorescence. We used solutions of water and rhodamine B, to study the properties of the fluorescent tracer and the characteristics of the fluorescence signal and its dependence on the instrumentation and other experimental conditions. It is shown that a linear relationship between light intensity and concentration is obtained, for laser power up to 600 mW and rhodamine B concentration up to 0.08 mg/l. We also demonstrated that the light absorption along the path was negligible for concentrations below 0.04 mg/l and defined the parameters for reliable measurements up to 2 mm away from the wall. The experimental uncertainty, determined in accordance with recent recommendations, was found to be between 5.5 and 15.6%. Based on the bootstrap technique, the confidence intervals downgraded as the order of the statistical moments increased. Flatness could be measured with a maximum uncertainty of about 25%. † Current address: Escola de Engenharia da Universidade do Minho, Campus de Azurém, 4800-058 Guimarães, Portugal ‡ Corresponding author.