Pressure measurements via water vapor absorption spectroscopy for application to post-detonation environments

This work presents laser absorption-based pressure measurements in a simulated post-detonation environment to experimentally study the dynamic range, accuracy, and sensitivity of optically measured gas pressures in dynamic flow fields. Experiments were conducted in Sandia National Laboratories' Multiphase and High-Temperature Shock Tubes using a micro-electromechanical system, tunable vertical cavity surface emitting laser (MEMS-VCSEL) scanning 7350-7900cm^-1 at 100 kHz to measure water vapor absorption spectra at pressures ranging from 0.25 to 67 atm and temperatures from 293 to 2300 K. Temperatures and pressures were inferred from the spectra in bath-gas mixtures of air, water vapor, and carbon dioxide to simulate broadening effects from the primary collision partners in post-detonation environments. In addition, partner-specific collisional broadening parameters from two different spectroscopic databases were evaluated under these conditions to understand the implications of data source selection on an engineering measurement. Across all conditions, laser absorption-based temperatures were on average within 2.6% of predicted values (RMSE of 71 K), and pressures were on average within 5.4% of sensor values (RMSE of 3.8 atm) for both databases. Numerical experiments based on synthetic spectra of simulated post-detonation gas mixtures suggest the pressure diagnostic to be accurate within 10% across a range of typical post-detonation conditions in cases when simplifying broadening assumptions regarding bath-gas collision partners are invoked.