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Published on: March 5, 2014
Ultrafast time-gated ballistic-photon imaging and shadowgraphy in optically dense rocket sprays
Jacob B Schmidt1, Zane D Schaefer, Terrence R Meyer
1Department of Mechanical Engineering, Iowa State University, Ames, Iowa 50011, USA.
Applied Optics
|February 3, 2009
Summary
Time-gated ballistic-photon imaging enhances rocket spray analysis by improving contrast and visualizing liquid breakup. This technique offers time-resolved imaging in dense sprays, revealing details missed by conventional methods.
Area of Science:
- Fluid Dynamics and Imaging
- Optical Physics
Background:
- Conventional shadowgraphy struggles with image contrast in dense spray environments.
- Time-gated ballistic-photon imaging uses ultrashort optical gates to differentiate ballistic from scattered photons.
Purpose of the Study:
- To adapt time-gated ballistic-photon imaging for analyzing high-speed rocket sprays.
- To improve image contrast and observe liquid-breakup phenomena in moderately dense sprays.
Main Methods:
- Application of an optical-Kerr-effect time gate (approx. 2 ps) to ballistic-photon imaging.
- Imaging of rocket sprays with optical densities between 1.5 and 2.
- Direct comparison with non-time-gated shadowgraphy.
Main Results:
- Achieved significant image contrast enhancement (approx. 6.6:1) for liquid-core structures.
- Demonstrated transparency of dense droplet fields to ballistic photons, unlike conventional shadowgrams.
- Enabled time-resolved, single-shot imaging with sufficient signal levels.
Conclusions:
- Time-gated ballistic-photon imaging effectively visualizes liquid-breakup processes in dense rocket sprays.
- The technique provides complementary information to conventional shadowgraphy, revealing hidden flowfield features.
- Facilitates a deeper understanding of primary and secondary atomization in sprays.
