Simultaneous spatially resolved temperature, pressure, and velocity measurements in high-enthalpy gas environments using spectrally resolved laser-induced fluorescence of potassium vapor

Abstract

A novel, absorption lineshape-based, laser-induced fluorescence diagnostic has been developed for simultaneous, single-point measurements of temperature, pressure, and velocity in high-enthalpy flow environments. The technique uses wavelength-tuned, narrow-linewidth, continuous-wave lasers to excite atomic potassium vapor, which is used as a flow tracer. The laser pumps the potassium D2 electronic transition, near 766.7 nm, while fluorescence from both the D1 and D2 lines is monitored simultaneously. The technique uses spectral lineshape and line position for inferring flow field properties, eliminating the need for detailed, setup-dependent calibration factors for quantitative measurements. The technique was tested and validated in argon and nitrogen in a shock tube with temperatures, pressures, and velocities ranging from 1000-2600 K, 0.1\(-\)0.7 atm, and 650-1200 m/s. Measurement volumes and uncertainties were as low as 3.5 \(\hbox {mm}^3\) and 5%, respectively, and measurement rates were up to 100 kHz. Accurate understanding of temperature, pressure, and velocity enables a more complete characterization of a compressible flow system as other quantities, including mass flux, Mach number, thrust, and stagnation conditions, can be calculated.