Laser diagnostics beyond two dimensions

Abstract

Laser-diagnostic imaging techniques have become a useful tool for measurement of quantities such as species concentration and temperature in reacting and nonreacting turbulent flows. These techniques are valuable for determining the spatial character of large-scale structures in these flows because of their capability for simultaneous measurement at a large number of points in a plane intersecting the flow. A basic characteristic of turbulence, however, is its 3-D nature and thus fully 3-D data would be desirable. A new experimental technique has been developed which can produce an instantaneous 3-D mapping of the gas concentration in an aerosol-seeded flow. Three-dimensional measurements are obtained by measuring the 2-D gas concentration distribution in many closely spaced parallel sheets. These measurements must all be completed in a short time to effectively freeze the flow. This is accomplished by sweeping a thin sheet of rapidly pulsed laser illumination (30-kHz pulses from a cavity-dumped argon-ion laser) through the flow and recording the scattered light intensity from different laser pulses on different regions of a computer-controlled detector. The resulting volume measurements can be visualized using computer graphics to display surfaces of constant material properties.