On the accuracy of two-temperature models for hypersonic nonequilibrium flow

Due to the empirical assumptions, the widely-used two-temperature models for hypersonic nonequilibrium flow include considerable uncertainties. To overcome the limitations and shortcomings of two-temperature models, the modified Macheret-Fridman model is developed based on the correction method of the modified Marrone-Treanor model. Some typical test cases are employed to assess the accuracy of the modified and widely-used two-temperature models. Furthermore, the reason for improving the accuracy of modified two-temperature models is analyzed and discussed. This work indicates that the correction method based on the modified Marrone-Treanor model is easily applied and extended to the other widely-used two-temperature models, significantly improving their accuracy. In addition, modeling highly nonequilibrium dissociating flows requires considering three critical respects, i.e., the dissociation rates, the vibration-dissociation coupling effect, and the non-Boltzmann effect. The non-Boltzmann effect reduces the dissociation rates and vibrational energy per dissociation. Comparatively, the dissociation rates have more influence than changing the value of the non-Boltzmann factor for vibrational energy loss per dissociation. Future work can focus on enhancing the accuracy of the dissociation rates to improve the accuracy of widely-used two-temperature models.