Freestream Static Pressure Measurements in the T5 Reflected Shock Tunnel

Abstract

In hypervelocity reflected shock tunnels, accurate static pressure measurements are key to interpretation of spectroscopic measurements characterizing the freestream thermodynamic state, as well as in determining the arrival of driver gas in the test section. However, measurements are challenging due to the significant mechanical and aerodynamic loads that are present in such impulse facilities. A static pressure probe was built for use in the T5 Free Piston Shock Tunnel at the California Institute of Technology based on the design of Behrens. Test conditions covered stagnation enthalpy from 8 to 16MJ/kg and freestream pressure from 7 to 27 kPa. With proper protection using silicone gel and tubing, repeatable static pressure measurements with good signal quality and within 2.5% uncertainty were obtained. Nozzle startup processes and driver gas arrival are also evident in the pressure traces. A smaller version of the static pressure probe, more easily accommodated together with models for freestream measurements, was also tested to provide a measure of repeatability and shot-to-shot variation, together with a new companion pitot probe. Static pressure instrument responses are in good agreement with theoretical models and Navier-Stokes simulations.

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