Weak Non-Parallel Effects on Chemically Reacting Hypersonic Boundary Layer Stability

Abstract

Advancing towards the correct modeling and subsequent understanding of laminar-toturbulent transition during atmospheric reentry is paramount for the future of aerospace technology. The coexistence of multiple physical phenomena and the grand amount of conditioning factors require the progressive extension of the applicability capabilities of the theoretical models. Past efforts have been mostly dedicated to investigate high-temperature and non-equilibrium effects using parallel stability theories. However, the implications of coupling these thermochemical phenomena with non-parallelism remains uncertain. Advanced state of the art thermodynamic and transport models are employed both in parallel and weakly non-parallel stability theories (LST and LPSE). A parametric study about the influence of nonlocal effects under different re-entry conditions and flow assumptions (i.e. CPG, TPG, CNE and LTE) showed that non-parallel effects stabilize/destabilize the boundary-layer, depending on the altitude and independently from the gas model employed. Particularly, they lead to a stronger destabilization of the 2nd Mackmode at the earliest points of the atmospheric re-entry flight envelope, reducing their effect until being weakly stabilizing at the lowest altitudes. Drastic N factor increments occurred assuming LTE, due to the presence of unstable supersonic modes, promoted by the boundary-layer cooling, caused by the intense chemical activity.