Supersonic wind tunnel

A supersonic wind tunnel is a wind tunnel that produces supersonic speeds (1.2<M<5) The Mach number and flow are determined by the nozzle geometry. The Reynolds number is varied by changing the density level (pressure in the settling chamber). Therefore, a high pressure ratio is required (for a supersonic regime at M=4, this ratio is of the order of 10). Apart from that, condensation of moisture or even gas liquefaction can occur if the static temperature becomes cold enough. This means that a supersonic wind tunnel usually needs a drying or a pre-heating facility. A supersonic wind tunnel has a large power demand, so that most are designed for intermittent instead of continuous operation.

Optimistic estimate: Pressure ratio ${\displaystyle \leq }$ the total pressure ratio over normal shock at M in test section:

${\displaystyle {\frac {P_{t}}{P_{amb}}}\leq \left({\frac {P_{t_{1}}}{P_{t_{2}}}}\right)_{M_{1}=M_{m}}}$

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