An inversion temperature method based on the relative radiance of the OH spectrum in the ultraviolet band

Abstract

In non-steady and high-speed flowing high-temperature environments, local thermal non-equilibrium phenomena are widely present. Therefore, if the Boltzmann distribution, which uses a single temperature to describe the energy level distribution of molecules, is adopted, a large error may exist. To solve this problem, a two-temperature / three-temperature model is often used to calculate the spectral radiation characteristics of OH in local thermodynamic non-equilibrium states. In this paper, taking the BSUV-2 aircraft at a flight altitude of 100 km as an example, The OH radiation characteristics in shock waves with a wavelength range of 305nm-315nm were calculated using the two-temperature model. By comparing the relative spectral radiance of experimental spectra and calculated spectra of OH, the optimal calculation range of vibrational temperature was determined to be 2000K-4000K. This method of measuring rotational temperature has significant advantages in low-resolution situations. After determining the rotational temperature, by simulating and calculating the normalized OH spectral radiance corresponding to different vibrational temperatures in the wavelength range of 270nm-340nm, it was found that the maximum intensity peak G1 is not affected by temperature, while the second largest intensity peak G2 has a linear relationship with temperature. Therefore, we can use the ratio of G1 to G2 to invert the range of rotational temperature. This study shows that using a two-temperature thermodynamic non-equilibrium model in local thermodynamic non-equilibrium states can achieve temperature inversion and accurately describe the spectral radiation characteristics of OH molecules, providing an important reference for related research fields.