NO and OH Spectroscopic Vibrational Temperature Measurements in a Post-Shock Relaxation Region

Abstract

In this paper, spatial temperature profiles are examined in the nonequilibrium relaxation region behind a stationary shock wave in a hypervelocity air Mach 7.42 freestream. The normal shock wave is established through a Mach reflection from an opposing wedge arrangement in an expansion tube facility. Schlieren images confirm that the shock configuration is steady and the location is repeatable. Emission spectroscopy is used to identify dissociated species and to make vibrational temperature measurements using both the nitric oxide and the hydroxyl radical A-X band sequences. Temperature measurements are presented at selected locations behind the normal shock. LIFBASE is used as the simulation spectrum software for OH temperature-fitting; however, the need to access higher vibrational and rotational levels for NO leads to the use of an in-house developed algorithm. For NO, results demonstrate the contribution of higher vibrational and rotational levels to the spectra at the conditions of this study. Very good agreement is achieved between the experimentally measured NO vibrational temperatures and calculations performed using an existing state-resolved, three-dimensional forced-harmonic oscillator thermochemical model. The measured NO vibrational temperatures are significantly higher than the OH temperatures.

Expansion Tube Investigation of Shock Stand-Off Distances in High-Enthalpy CO2 Flow Over Blunt Bodies

“…26 For more information regarding the development, testing and performance verification of the thermocouples please see Flaherty and Austin. 27 The experimental set up for the spectroscopic experiments is described in more detail in Sharma et al 28 Briefly, spectra were collected using a SPEX 270M spectrometer and visualized with a Princeton Instruments PI-MAX MG:512SB intensified CCD camera system. Exposure was set to 100 μs.…”

“…Transmitted shock velocity is typically accurate to within ±43 m/s in this facility, and it is expected that similar error bars will exist for test gas velocity measurements. 28 theoretical test gas pitot pressure is determined from the Rayleigh pitot equation. Perfect gas calculations show the pitot pressure is most sensitive to the static pressure across the secondary contact surface (states 6 and 7).…”

“…28 Vibrational temperature measurements based on OH emission spectra were made in the relaxation region behind the normal shock created via a Mach reflection. 44 The experimental method was extended to obtain NO-based temperature measurements for the same flow field.…”

“…44 The experimental method was extended to obtain NO-based temperature measurements for the same flow field. 28 Emission spectroscopy using atomic, rather than molecular, species presents several advantages. The absence of rotational and vibrational internal energy modes significantly reduces the complexity of the spectral signature.…”

Evaluation of Hypervelocity Carbon Dioxide Blunt Body Experiments in an Expansion Tube Facility

“…Transmitted shock velocity, u t , is typically accurate to within ±43 m/s in the HET and it is expected that similar error bars will exist for test gas velocity measurements. 26 In the first column, the test conditions were generated by varying the acceleration section gas; here argon, helium, air and carbon dioxide are used. The test conditions are described in terms of the driven-accelerator gas combination.…”