Yang Jun-cai

Simulation of Radiative Transfer in Nonequilibrium Plasmas Containing N and O Species Based on the Approximate Collision-Radiative Method

An approximate collision-radiative method is developed to calculate energy level populations of atoms and applied to simulate radiative transfer in a shock layer. Considering nonequilibrium plasmas with the electronic temperature below 20000 K, we introduce correction factors to the Saha—Boltzmann equation and simplify the master equation of the full collision-radiative model. Based on the method, the error of heat flux is smaller than 5% in a two-cell problem and smaller than 7% in the Stardust re-entry flow field compared with the correlated-k method. Furthermore, almost a factor of 2 is obtained in the improvement of computational efficiency compared with the nonequilibrium air radiation (NEQAIR) code. The results show that the present method is reliable and efficient.

Analysis of Atomic Electronic Excitation in Nonequilibrium Air Plasmas

Electronic excitation of atoms is studied in nonequilibrium air plasmas with the electronic temperature between 8000 K and 20000 K. By using the modified Saha—Boltzmann equation, our simplified method takes into account significant radiative processes and strong self-absorption of the vacuum ultraviolet lines. Calculations are carried out at three trajectory points of the Fire II flight experiment. Good agreement with the detailed collisional-radiative model is obtained, and the performance of this method in applications to highly nonequilibrium conditions is better than Parks quasi-steady-state model and Spradian-9.0. A short discussion on the influence of optical thickness of the vacuum ultraviolet radiation is also given. It costs about 2.9 ms on the average to solve one cell of the shock layer on a low cost computer, which shows that the present method is fast and efficient.

Optical Correlator for Star Identification and Tracking

Star tracker is one of the most important spacecraft attitude sensors which can achieve accuracies within several arc-seconds utilizing star identification and star tracking. The refresh rate and accuracy of star tracker are constrained as there are so many stars in the sky. A novel star identification and tracking method for star tracker using optical correlator is proposed to solve this problem of star map comparing and identification. The proposed optical correlator can optically execute the correlation operation between current star map and the standard star map constructed from the star catalog. The whole sky star identification can be completed within 100ms due to the inherent parallel computing ability of optical correlator. Star map motion can be tracking with an accuracy of up to 1/100 pixel. Computer simulations and experiments indicate that this method has great robustness to small signal-to-noise ratio, and improve the performance of star tracker remarkably.Star tracker is one of the most important spacecraft attitude sensors which can achieve accuracies within several arc-seconds utilizing star identification and star tracking. The refresh rate and accuracy of star tracker are constrained as there are so many stars in the sky. A novel star identification and tracking method for star tracker using optical correlator is proposed to solve this problem of star map comparing and identification. The proposed optical correlator can optically execute the correlation operation between current star map and the standard star map constructed from the star catalog. The whole sky star identification can be completed within 100ms due to the inherent parallel computing ability of optical correlator. Star map motion can be tracking with an accuracy of up to 1/100 pixel. Computer simulations and experiments indicate that this method has great robustness to small signal-to-noise ratio, and improve the performance of star tracker remarkably.