EVALUATIONG ANISOTROPY AND THERMODYNAMIC NON-EQUILIBRIUM IN HYPERSONIC TRANSITIONAL REGIME

The present paper is the logical continuation of a former paper by the present author where the limits, in terms of rarefaction, of the proper working of a Navier-Stokes (NS) and a Direct Simulation Monte Carlo (DSMC) code were fixed. That analysis relied on the comparison of the aerodynamic coefficients, from the two codes, of a typical capsule along a probable re-entry path to Earth from an interplanetary mission. As the basic principle of the DSMC method is valid at each rarefaction level, the limitation in using a DSMC code with decreasing rarefaction was verified to be due just to the computer capabilities. On the contrary with increasing rarefaction, the proper use of a NS code is affected by intrinsic limitations like: i) failure of the classical phenomenological equations, effects such as thermal and pressure diffusions, usually not included in the commercial NS solvers, ii) difference of the components of the translational temperature, of the pressure tensor and of the diffusion velocity of chemical species (anisotropy) and difference of the vibrational, rotational and traslational temperatures (thermodynamic non-equilibrium). In the present paper anisotropy and thermodynamic non-equilibrium are quantified and the relative importance evaluated. Both effects are correlated with the shock wave intensity and with the flow field rarefaction. It is verified that anisotropy and thermodynamic non-equilibrium increase with the shock wave intensity and with rarefaction and anisotropy is stronger than thermodynamic non-equilibrium. The re-entry to Earth of a capsule has been simulated by means of a DSMC code in the altitude interval 60-80 km, where the capsule experiences hypersonic, transitional regime