Monitoring of the Unsteady Water Vapor Condensation in a High Speed Flow Using Tunable Diode Laser Absorption Spectroscopy

Tunable diode laser absorption spectroscopy (TDLAS) and light sheet technique were introduced to monitor the unsteady water vapor condensation in a high speed flow generated by an expansion system. The expansion system with an adjustable expansion outlet was designed to mimic the expansion process of the supersonic nozzle with different expansion time scales. Two near infrared water vapor absorption transitions (7168.44nm&7095.87nm) and one methane absorption transition (6047.05nm) were applied in the TDLAS measurement to infer the gas information during the condensation process. In specific, the time dependent condensation processes were monitored with different water vapor concentration and different expansion time scales. The light sheet results visually revealed the condensation phenomena during the expansion process, while TDLAS results quantitively followed the condensation process. As a result, different onset condensation temperatures were observed with different water vapor concentration.