Can a wind tunnel get up to scramjet speeds; ie. Mach 6-12?
There are some facilities which can simulate such speeds:
However, due to the speeds involved, the test runs are very short duration.
NASA Glenn Research Center has a hypersonic tunnel used for propulsion research that can reach Mach numbers between 5-7 and has about a 5 minute run time.
Many facilities that reach these speeds have very short run times because they are driven by releasing high pressure gas from an upstream reservoir. The tunnel can run until the reservoir is sufficiently used up.
Thank you. Do they test high velocity air-breathing engines like that, or using a more trial by fire method?
They definitely test these engines in wind tunnels. Ramjets and scramjets only work at high velocities and there is no way they would stick something untested on an aircraft and try to fly it.
There are numerous wind tunnels capable of that Mach number but that's not all you need to properly simulate the engine. You need something that can achieve the same Mach number, Reynolds number and stagnation enthalpy, and that is hard to come by. Most of the time you have to sacrifice one or more of those and limit the test to parameters not affected by the ones you had to let slide.
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