Supersonic Combustion Tunnel

The supersonic combustion facility at Stanford is a large-scale two-stream wind tunnel capable of generating both reacting and nonreacting mixing layers. The two main flows in this blowdown facility are supplied from high-pressure tanks and regulated via closed-loop PID control. A compressor may be used to charge the tanks with cleaned and dried atmospheric air or nitrogen from a cryogenic source; other gases may be supplied from high-pressure cylinders.

A hydrogen-fueled vitiation heater allows the high-speed stream to be heated to temperatures between 550 and 1900 K. Make-up oxygen may be supplied in order that the stream discharged from the burner be restored to atmospheric oxygen concentration. The high-speed stream is accelerated into the test section through a converging-diverging nozzle; replacement nozzle centerbodies allow the test-section Mach number to vary up to 2.5. For reacting experiments, hydrogen fuel is metered into an inert (nitrogen, helium, or argon) low-speed stream, resulting in combustion in the mixing layer formed in the test section between the ambient-temperature, fuel-bearing low-speed stream and the high-temperature, oxidizing high-speed stream.

[RIG]

In the photograph above, the facility control panel appears at the far left. The piping carrying the two streams may be seen entering the red framework at the far left. The vitiation heater appears in the upper (high-speed) stream between the first two columns of the framework. To the right of the second column lie the conjoined high- and low-speed plenums (silver); continuing to the right, the test section windows (here copper, usually quartz), are held within black frames. Proceeding out of the picture to the right is the diffuser, through which the flows recover the required pressure to be exhausted from the building. The exhaust duct (not shown) contains nitrogen and atomized-water dilution ports in order to passivate the unburned hydrogen in the exhaust stream of reacting experiments.

In order to resist the high heat-transfer rates of the reacting experiments, the facility is constructed largely of cooled copper members. The vitiation heater is cooled by a separate system, and the wind tunnel walls are preheated before each experiment in order to minimize condensation. The experiment sequence is entirely computer-controlled, and typically lasts thirty seconds. Interlocks to hydrogen detectors, water flow meters, thermocouples and an ultraviolet sensor on the burner monitor the facility and shut it down in the event of an anomaly.

For nonreacting experiments, the vitiation heater may still be used in order to elevate the convective Mach number. The experimental procedure is substantially similar to that for the reacting experiments, although somewhat simpler.

[TEST SECTION]

The photograph above shows the wind tunnel with one sidewall removed, revealing the high- and low-speed plenums on the left, separated by the splitter plate. The supersonic nozzle on the high-speed (upper) stream is formed by the upper contraction and the splitter tip, with which the splitter plate terminates and the test section begins. The test section window opening is visible in the far wall. The upper and lower walls of the wind tunnel consist of outer structural walls and inner, adjustable guide walls. This design enables the pressure gradient in the test section to be adjusted to suit different cases. The black tubing running to the components in the photograph carries cooling water.

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