I completed this at UQ physics in 1999, here’s the abstract and the document itself. The device I constructed was originally intended for use with the scramjet project, although in my time was tested (successfully) on a small shock tunnel in the basement of Hawken. The shadowgraph images produced were spectacular although they seem to be MIA right now 🙂
Time resolved imaging in compressible flows using a Cranz-Schardin Camera
A Cranz-Schardin camera arrangement was devised and constructed to obtain time resolved shadowgraphs of the flow over a cylinder. Detached shock waves are clearly visible as well as some three dimensional effects. The camera system uses a high power AlInGaP light emitting diode (LED), the model HLMP-DG08 by Hewlett Packard. The diode has a narrow viewing angle (6o), high luminous intensity (6500mcd @ 20mA), with peak emission at 626nm and a FWHM1 of 17nm. Within the camera system, the LED is pulsed rapidly at high currents, serving as both shutter and light source. These pulses are separated temporally and spatially, back-lighting the object which is subsequently imaged onto the film plane. Generation of pulsed input to the sources is provided by CMOS2 circuitry coupled with an analogue driver stage for each channel, producing high current gain. The maximum output of the analogue driver stages was in the vicinity of 5 amps, producing sufficient light intensity in the LED’s to saturate a CCD3 camera. The light emitting diode is advantageous over lasers in this application for a number of reasons. Besides the obvious reduction in cost, LED’s are responsive (taures = 20ns) may be switched rapidly and have a fairly good signal to noise ratio for such a small, inexpensive device. The camera overall promises to be an invaluable diagnostic tool, at least in situations where competing luminosity can be reduced.
1. Full Width (at) Half Maximum (intensity).
2. Complementary Metal Oxide Semiconductor.
3. Charge Coupled Device.