Pulsed Laser Imaging of Flows, Flames and Plumes



For StarTrek fans we tested the USS Enterprise in our super-orbital expansion tube - X2. A scale model was placed in the test section and the facility used to generate a high speed gas flow of around 6.6 km/s. This was passed over the Enterprise for a duration of approximately 100 microseconds. We perform similar tests on other models investigating dissociation and ionisation processes which occur during atmospheric re-entry.

But the Enterprise isn't designed to enter an atmosphere??

Very true! However one could argue that this test was a simulation of the flight of the Enterprise where the Mach number of the flow is analogous to the Warp speed of the vehicle. The Mach number gives the speed of a vehicle relative to the speed of sound. The latter is determined by the atmosphere in which the vehicle is travelling (eg in air at room temperature, the speed of sound is about 300 m/s). The Warp speed is related to the speed of light (about 300,000,000 m/s in a vacuum). Hence the test simulates the effect of the motion of the vehicle on space-time (not on the atmosphere or space dust that it is travelling through)!

Our test had a Mach number of around 5, a bit below the full capabilities of the Enterprise. An image that we recorded at this speed can be seen adjacent (the green image). This was taken with a digital camera open to luminosity from the hot test gas present for the duration of the test. Note the highly intense regions in front of the blunt sections of the vehicle.

What did we learn?

A more quantitative study of the flow was done using holographic interferometry. An interferogram yields a picture with light and dark bands called fringes. Bends in the fringes indicate a change in the density of the gas. The image shows diagonal lines coming from the front of the Enterprise - these are the bow shock waves. Shocks are also seen emanating from other points on the vehicle. A crucial design point is the avoidance of "shock-shock" interactions where one shock wave hits another directly in front of the body. If this were to occur there would be catastrophic consequences for space-time in these regions. The image shows that the designers certainly knew their stuff - at this speed, the bow shocks pass comfortably outside the other sections of the vehicle. However at Warp 10, this may not be the case!

What else did we learn??

We found that, with shields down, the Enterprise is very susceptible to the ever increasing amount of space junk. The picture shows the Enterprise after our last test. A piece of "space junk" shown at the bottom right impacted the Enterprise at high speeds ripping it to pieces. It was fun while it lasted!

Read some feedback on this site at Slashdot.