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Lynch and Brian Thurow
Department of Aerospace Engineering
The transition to turbulence in a jet is captured in three-dimensional detail using a recently developed high-speed 3-D flow visualization technique. In this image, the flow of a Reynolds number 9500 jet is seen to transition through various stages as it develops into a fully developed turbulent flow field. In the near-field of the jet, the flow is initially laminar and responds to the Kelvin-Helmholtz instability as it forms ring vortices. This is followed by the onset of azimuthal instabilities that take the form of long thin fingers of fluid periodically positioned around the periphery of the jet core. The interaction and growth of the azimuthal instabilities with the ring vortices leads to the complex and three-dimensional flow in the far field typically associated with turbulent flows.
The 3-D image presented here has a resolution of 312 x 260 x 100 pixels and was formed by imaging a high-repetition rate laser sheet that was scanned through the smoke seeded flow field using a galvanometric scanning mirror. High-speeds are made possible using a MHz rate pulse burst laser system that is able to produce a burst of 100 high energy, short duration pulses at 1,000,000 pulses per second. Images were captured using a 1,000,000 frames per second high-speed camera with a total exposure time of only 100 microseconds. The 3-D image was then reconstructed from the high-speed sequence of 100 images.
This work was sponsored by the Army Research Office under Grant No. W911NF-06-1-0400
Thurow, B., and Lynch, K., “Development of a
High-Speed Three Dimensional Flow Visualization Technique,” accepted
for publication in AIAA Journal, 2009.
Thurow, B., Satija, A. and Lynch, K., “3rd generation MHz rate pulse
burst laser system,” Applied Optics, Vol. 48, pp.2086-2093 2009.
Reporters can freely use this image. Credit: Brian Thurow, Auburn University.