Self-Consistent Computational Fluid Dynamics of Supersonic Drag Reduction via Upstream-Focused Laser-Energy Deposition

Abstract

We present applications of laser-energy deposition for drag reduction in supersonic flow. The system of chemically reactive Navier–Stokes equations describes the hydrodynamics where nonequilibrium effects are accounted for by means of a two-temperature model. The propagation and attenuation of the laser beam are modeled based on a kinetic approach for photons (radiative transfer equation). Multiphoton ionization, inverse bremsstrahlung (free-free radiation), cascade ionization, and shock hydrodynamics are coupled self-consistently without imposing an initial plasma seed to initiate the breakdown, as is often done in the literature. Simulations are conducted in supersonic airflow over a spherical blunt body to study the control of aerodynamic forces. Results confirm that the laser-induced thermal spot can be effectively used to control the shock structures with beneficial effects in terms of aerodynamic loads. As a matter of fact, the interaction of the downstream advected hot spot with the bow shock distorts the latter (the lensing effect) and leads to toroidal vortices due to baroclinic torque. Drag is momentarily decreased due to the formation of an expansion fan (related to the upstream movement of the bow shock) that generates a load reduction on the wall, as well as to the advection of the vortex region that remains attached to the wall. The results also demonstrate that the self-consistent computational framework is able to handle complex multiscale multiphysics flow control problems for predictive applications without the assistance of tuning parameters and/or simplifying assumptions inferred from the experiments.