Comparative Study of Heat Flux Instrumentation for Hypersonic Ground Test Facilities

Atmospheric reentry vehicles have wing-body configuration with blunt leading edges on wings and slender fuselage. These vehicles pass through several phases of flight during ascent / descent and therefore their aerodynamic performance parameters vary from rarefied flow conditions to hypersonic continuum flow to subsonic speeds before final full stop. Measurement of temperatures on hot spots in hypersonic flow remained a challenge for a mankind. Re-entry vehicle covers wide range of Mach, angles of attack, angles of side slip and control surface deflections during its complete mission profile. Still today, scientists are facing challenges in recording real time precise data from hypersonic ground test facilities. These facilities although provide insight to flow physics, surface temperature and location of hot spots, yet they cannot match enthalpy, noise, Reynolds number, binary scaling simulation parameter, non-equilibrium chemistry contribution to friction and catalytic heating during hypersonic flight. Thermal protection system encompasses boundary layer physics, gas to surface interaction, high temperature materials and internal thermal management. TPS materials will be evolved only after true measurement of temperature and heat transfer rate. This research includes study of intrusive, semi-intrusive and non-intrusive temperature measuring technologies. It is concluded that E-type coaxial surface junction thermocouples are best suited for high enthalpy flows because they are robust and can survive challenging hyper velocity environment. Thin film gauges having better signal levels and less noise with more consistent response time but are useful for low enthalpy flows only.