Mechanical energy loss and design criteria of the intakes under wide design space considering vibrational non-equilibrium effect

The vibrational non-equilibrium effect caused by high-temperature often occurs in the flow of high Mach number air breathing aircraft. However, the evaluation methodology of mechanical energy loss and comprehensive understanding of the impacts of thermal non-equilibrium on intakes’ performance under wide design constraints remain underexplored. This work firstly introduces the effective total pressure recovery coefficient (σef) as a novel metric to precisely quantify mechanical energy dissipation in such non-equilibrium flows. Then, thermal non-equilibrium flow fields in two-dimensional, multi-stage planar compression intakes are simulated by employing a recently proposed method of non-equilibrium characteristics. Results show that the impacts of thermal non-equilibrium on the outlet Mach number and static temperature intensify with the increasing flight Mach number, compression level and capture height. Redistribution of internal energy modes leads to deviations exceeding 10 % in outlet Mach number and static temperature compared to predictions of calorically perfect gas (CPG) model. The competition between opposite variations of the vibrational entropy rise and the translational-rotational entropy rise, driven by the scale effects of the thermal non-equilibrium, leads to the non-monotonic variation of σef as capture height increases. Thermal non-equilibrium effects induce a maximum reduction in σef of 17.1 %. Leveraging symbolic regression, the first design feasible region map of CPG model is pioneered to rapidly delineate operability boundaries in practical application. The above insights suggest that special attention should be paid to scale effects and extra mechanical energy loss induced by the thermal non-equilibrium in the intake design.