Experimental determination of test gas caloric quantities in high-enthalpy ground testing is impeded by excessive pressure and temperature levels as well as minimum test timescales of short-duration facilities. Yet, accurate knowledge of test gas conditions and stagnation enthalpy prior to nozzle expansion is crucial for a valid comparison of experimental data with numerical results. To contribute to a more accurate quantification of nozzle inlet conditions, an experimental study on non-intrusive in situ measurements of the post-reflected shock wave stagnation temperature in a large-scale free-piston reflected shock tunnel is carried out. A series of 20 single-shot temperature measurements by resonant homodyne laser-induced grating spectroscopy (LIGS) is presented for three low-/medium-enthalpy conditions (1.2–2.1 MJ/kg) at stagnation temperatures 1100–1900 K behind the reflected shock wave. Prior limiting factors resulting from impulse facility recoil and restricted optical access to the high-pressure nozzle reservoir are solved, and advancement of the optical set-up is detailed. Measurements in air agree with theoretical calculations to within 1–15%, by trend reflecting greater temperatures than full thermo-chemical equilibrium and lesser temperatures than predicted by ideal gas shock jump relations. For stagnation pressures in the range 9–22 MPa, limited influence due to finite-rate vibrational excitation is conceivable. LIGS is demonstrated to facilitate in situ measurements of stagnation temperature within full-range ground test facilities by superior robustness under high-pressure conditions and to be a useful complement of established optical diagnostics for hypersonic flows.

过高的压力和温度水平以及短期设施的最小测试时间尺度阻碍了高焓地面测试中测试气体热量的实验确定。但是，准确了解测试气体条件和喷嘴膨胀之前的停滞焓对于有效比较实验数据和数值结果至关重要。为了有助于更准确地量化喷嘴入口条件，对大型自由活塞反射激波隧道中反射后激波停滞温度的非侵入式原位测量进行了实验研究。针对三种低/中焓条件（1.2–2），提出了通过共振零差激光诱导光栅光谱法（LIGS）进行的一系列20次单次温度测量。在反射冲击波后面的停滞温度1100–1900 K下为1 MJ / kg）。解决了由脉冲设备反冲和限制进入高压喷嘴容器的光学通道而导致的先前的限制因素，并详细介绍了光学装置的进展。空气中的测量值与理论计算值相吻合，在1％到15％的范围内，这是趋势反映出比完全热化学平衡更高的温度和比理想气体冲击跃变关系所预测的更低的温度。对于9-22 MPa范围内的停滞压力，由于有限速率的振动激励而产生的影响有限。