Stagnation Temperature Measurements in a Shock-Tunnel Facility Using Laser-Induced Grating Spectroscopy

Abstract

Experimental determination of test gas temperature and enthalpy in ground testing is a challenging task, particularly regarding excessive pressure and temperature levels as well as minimum characteristic time scales available in transient facilities. Accurate knowledge of test gas conditions and stagnation enthalpy in reentry experiments is, however, crucial for a valid comparison with numerical results. Therefore, to contribute to a more accurate quantification of nozzle flow upstream boundary conditions, laser-induced grating spectroscopy is applied to the nozzle reservoir section of the piston-driven reflected shock tunnel High-Enthalpy Laboratory Munich for nonintrusive stagnation temperature measurement. Single-shot determination of post-shock wave gas temperature involves exact synchronization of the transient event in the test bench with the optical setup. Problems arising from impulse facility recoil are solved and discussed with respect to the laser light geometrical optical pathway. Employing minimum selective seeding by nitric oxide for improved signal intensity, gas temperatures of around 1100 K behind the reflected shock wave are measured by resonant laser-induced grating spectroscopy for a representative low-enthalpy operation condition in air, at pressure and enthalpy of 6 MPa and , respectively.