THE EFFECT OF TEFLON ABLATION ON THE ELECTRON DENSITY IN VISCOUS SHOCK LAYER
泰氟龙烧蚀对黏性激波层电子密度的影响

In this paper, the viscous shock layer governing equations for non-equilibrium gas flows over sphere-cone with and without Teflon ablation are solved numerically to investigate the effect of Teflon ablation on electron density in the flow fields. The case considered here is a 10 deg half-angle sphere-cone with nose radius of 0.lm at altitude of 70km and Mach number of 20. The wall temperature is kept fixed at 800K. The chemical system used consists of 7 species (O2, N2, O, N, NO, NO~( ) and e? for clean-air and of 19 species (C2F4, F2CO, CF4, CF2, CO2, CO, F2, F, F? C, C2, C_(3) and the 7 clean-air species) for Teflon-air gas mixture. In order to investigate an effect of wall catalysis, the two extreme cases, namely the case of non-catalytic wall and the case of equilibrium-catalytic wall, are considered. The results of the solutions show that the Teflon ablation has the effect of reduction of electron density indeed. Furthermore, the intensity of this effect in the case of equilibrium catalytic wall is significantly greater than that in the case of non-catalytic wall, and the intensity of this effect in a far downstream section is significantly greater than that in the stagnation region. An analysis of the concerned results of the solutions shows that there are two main factors for reduction of electron density of the flow fields by Teflon ablation. The first is the reactions of attachment of electron to species F2 or F forming the negative ion F? the second is that in comparison with those in the case without ablation the flow parameters or their gradients which are concerned with the species conservation equation of species NO~( ) are changed numerically resulting in reduction of NO density, and consequently in reduction of electron density due to the electrical neutrality condition. Furthermore, only the second factor is important in the case of non-catalytic wall, whereas in the case of catalytic wall both the factors are significant.