Freestream Characterization and Condensation Detection in the AFOSR--Notre Dame Large Mach-6 Quiet Tunnel

A static pressure probe, pitot probes, and laser Rayleigh scattering have been deployed in the AFOSR--Notre Dame Large Mach-6 Quiet Tunnel to detect the onset of flow condensation. Thanks to upgrades to the fast-acting valve at its contraction exit, the facility is now operational. A pitot rake surveyed the nozzle exit plane. With the aluminum surrogate nozzle, this facility currently operates at a conventional noise level of 2.6%, freestream Mach number of 5.7, and Reynolds number up to 12.2 x 10^6 /m. Stagnation pressures and temperatures were varied to determine the conditions at which the supersaturated flow regime collapses. Deviation from the anticipated isentropic static pressure was used to assess condensation with the static probe. Laser Rayleigh scattering measured the freestream density, from which condensation was inferred. Those measurements were collected using a 10 Hz repetition rate, 335 nm wavelength laser, a 100 Hz, 266 nm wavelength laser, and a photodiode. Laser Rayleigh scattering detected condensation at higher temperatures than the static probe, probably due to its improved sensitivity to nucleation. These new findings are added to a compilation of non-equilibrium condensation results from a variety of hypersonic wind tunnels.