The Components of the System enable diverse types of imaging, acquisition of image data, and processing of the data to extract information on multiple aspects of high-speed combustion flows.
Asystem of scientific instrumentation and data-processing equipment has been assembled for research and education in turbulence, mixing, and chemical reactions (especially combustion) in high-speed laminar and turbulent flows. The system is designed to enable study of temporally varying, three- dimensional structures in flow regimes that have been inaccessible to prior instrumentation systems, with emphasis on flow regimes relevant to the operation of ramjet and scramjet engines.

The system (see figure) includes components for planar laser-induced fluorescence (PLIF); flame-speed, ignition, and extinction measurements of laminar flames at variable pressure; tracking flow structures in a high-speed mixing layer using highspeed color schlieren imaging; laserbeam manipulation and volume scanning for three-dimensional turbulence measurements; and an expanded computational infrastructure for processing experimental and numerical- simulation data.

  • The PLIF instrumentation is augmented with an intensified charge-coupled- device image detector and associated data-acquisition components.
  • Flame measurements are made by means of particle-streak velocimetry, using a continuous-wave laser beam modulated with a Pockels cell. The measurements enable the study of details of profiles of such relatively high-speed flames as those encountered in the combustion of ethylene and other rapidly burning fuels, thereby contributing to understanding of flame structures and enabling extensive testing of chemical-kinetic models.
  • The color schlieren imaging is performed by means of a high-speed color camera containing a complementary metal oxide/semiconductor image detector, an associated flashlamp, and other support components. The measurement data extracted from the color schlieren images are providing details of turbulent mixing in important flow geometries for both subsonic internal flows (as in diffusers) and supersonic internal flows (as in scramjet engines).
  • The subsystem for laser-beam manipulation and volume scanning includes mirrors, servoactuators, motion controllers, and an optical scanner. This subsystem enables three-dimensionally spatially resolved measurements of fully developed turbulence as a function of time.
  • The processing and visualization of the data acquired by this system are enhanced through upgrades of the memory circuits, central processing units, and tape backup units of previously available data-acquisition and visualization computers.

This work was done by Paul E. Dimotakis of California Institute of Technology for the Air Force Research Laboratory.

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System for Imaging Turbulent Combustion Flows

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This article first appeared in the October, 2007 issue of Defense Tech Briefs Magazine.

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