Measurements of gas temperature and velocity in hypervelocity flows using diode-laser sensors

Abstract

Rapid measurements of temperature, velocity, and H2O partial pressures have been obtained in hypervelocity air flows generated in the Calspan 96-inch Hypersonic Shock Tunnel (Buffalo, New York) using diode-laser sensor systems developed at Stanford University. The measurements were determined from high-resolution water (H2O) and potassium (K) absorption lineshapes recorded every 100 (is by tuning the wavelengths of two DFB (InGaAsP) diode lasers and a Fabry-Perot (AlGaAs) diode laser independently at 10-kHz rates across H2O transitions (v,+v3 band) near 1392 nm and 1393 nm and potassium D, transitions (SI/2-»PI/2) near 770 nm. Two hardened probes incorporated the electro-optics required to pitch and detect the laser energy and were installed near the nozzle exit to minimize complications due to facility boundary layers. The probe targeting potassium, is a newly developed compact probe, measuring only 5 cm in overall width. Gas temperature was inferred from the Doppler width of H2O lineshapes. H2O partial pressure was determined from the measured absorbance of a single transition and the gas temperature. Gas velocities were determined from Doppler-shifted H2O and K absorption lineshapes. The measured gas temperatures and velocities were consistent with calculated steady-state values (500 K and 4.2 km/s, respectively) based on standard tunnel measurements. The results obtained demonstrate the applicability of diode-laser absorption diagnostics for direct multi-parameter measurements in the hypervelocity flowfields of high-enthalpy facilities.