Non-equilibrium structure of triple points using the 10-moment model

We address the non-equilibrium structure of triple points, the region of confluence of three shocks and a shear layer arising in gas dynamics. The structure of triple points and their reflections in diatomic gases was computed in two dimensions using a diatomic extension of the 10-moment model. This approximate Boltzmann model allows for the accurate modelling of the relaxation process of translational and rotational temperatures within the shock structure and shear layers. The initial flow field was prescribed based on idealised three-shock theory, and the interaction between the triple-point and a plane of symmetry was studied. While the large-scale dynamics of triple-shock reflections was found to be in excellent agreement with the Euler model, the non-equilibrium calculation permitted us to establish the unique structure of the triple-point region. We discovered the presence of an internal shock inside the triple point, oriented normal to the flow. Its internal interaction with the Mach shock is responsible for the presence of an internal hot spot, generating temperatures significantly exceeding those expected from the treatment of each shock as discontinuities. We also provide a detailed appraisal of principal translational temperatures associated with these internal hot spots. The important role of this temperature anisotropy inside triple points on cellular detonations is briefly discussed.