High-Frequency Static Pressure Measurements in the T5 Reflected Shock Tunnel

Accurate time-resolved static pressure measurements are key to characterizing the freestream thermodynamic state in hypervelocity reflected shock tunnels. A series of three static pressure probes were built for use in the T5 Free-Piston Shock Tunnel at the California Institute of Technology based on the design of Behrens. Simultaneously, Tunable Diode Laser Absorption Spectroscopy (TDLAS) was used to infer static pressure from the pressure broadening of absorption features in nitric oxide rovibrational spectroscopic transitions from the mid-infrared fundamental band. Test conditions covered stagnation enthalpies from 8 to 16 MJ/kg and freestream pressures from 7 to 27 kPa. The pressure measurements from the first two static probe generations agreed in magnitude with the TDLAS pressure within error, but showed very different temporal responses due to the slower time responses of the two probes. Subsequently, a quicker time response static probe was designed and deployed in T5 in the 8 MJ/kg and 16 MJ/kg conditions. The pressure traces from the new probe agreed well in both magnitude and temporal response with the TDLAS-inferred pressure in both conditions. In addition, the new probe was able to resolve subtle temporal differences between differently tailored versions of the same condition. The updated static probe design allows for simultaneous high-frequency pressure measurement with test models and increases confidence in pressure broadening TDLAS measurements in high-enthalpy ground test facilities.