Chemical Kinetics in Hypersonic Boundary Layers

In the inner part of the dissociated boundary layer around various bodies in hypersonic flow regime, a vibrational freezing zone has been observed. This freezing region takes place even if , in the outer part of the boundary layer, translation and vibration temperatures are in equilibrium and even if the wall may be considered as catalytic. This phenomenon can be attributed to the diffusion towards the wall of vibrationally excited molecules. The consequence of this behaviour is an increase of the dissociation rate constants in this region.. The present determination of such rate constants is carried out for two characteristic types of boundary layer, behind a reflected shock wave and close to a stagnation point, by using various physical models, such as state to state methods but also global models simpler to use. All methods can predict the general features of the freezing phenomenon and present a qualitative agreement, as far as similar assumptions are used.