A Combined Laser-Doppler Anemometer/Laser-Induced Fluorescence System for Turbulent Transport Measurements

Abstract

A combined laser-Dopplet anemometer (LDA) and laser-induced fluorescence (LIF) system is described which can provide nonintrusive simultaneous measurements of velocities and concentrations at a point in gases. This yields information needed to better understand turbulent transport of mass and heat-the latter by computation or analogy. The combined LDA/LIF system has potential for a variety of applications due to good spatial resolution and frequency response, acceptable performance at high turbulence intensities, capabilities for operation in dusty or particle-containing environments and near surfaces, and equipment costs that are not much greater than LDA itself. The present system is adapted for low-soeed flows near surfaces; using LDA for velocity measurements and resolving attendant problems of Mie scattering from LDA seeding particles and reflections from surfaces. The LDA/LIF system can be used to study turbulent mixing between two streams or turbulent transport from surfaces. The present system was developed for the former application; however, use of the technique to study transport from surfaces is discussed at the end of the paper.