Hypersonic Laminar Flow Control Using a Porous Coating of Random Microstructure

Abstract

It is shown that a passive porous coating of random structure (felt metal) significantly delays transition on a sharp cone at zero angle of attack in the Mach=12 wind tunnel. A semi-empirical method is developed to predict acoustic properties of randomly structured coatings including effects of gas rarefaction. This method simplifies calculations of the boundary conditions on the porous coating and solving the boundary-layer stability problem. The transition onset points on coated and uncoated cone surfaces are calculated using the -method. With this approach theoretical predictions agree satisfactorily with the experimental data. For the first time it is demonstrated that porous coatings of random microstructure, which are synergistic with fiber-ceramic thermal protection systems (TPS), can be used for hypersonic laminar-flow control. This provides symbiotic reduction of aeroheating and reduced skin friction drag. It also leads to a new family of lightweight TPS. N e