Experiments on passive hypervelocity boundary layer control using a porous surface

Stabilization of Hypersonic Boundary Layers by Porous Coatings

“…We discuss results of calculations showing the second-mode stabilization on porous surfaces of various pore radii, spacing, and thickness. Then we brie y describe the experimental data of Rasheed et al 15 that con rm the theoretically based hypersonic boundary-layer stabilization by porous coatings given in this paper. These results were obtained in the T-5 Graduate Aeronautical Laboratories of the California Institute of Technology high-enthalpy wind tunnel on a sharp cone that they detail in Ref.…”

“…These results were obtained in the T-5 Graduate Aeronautical Laboratories of the California Institute of Technology high-enthalpy wind tunnel on a sharp cone that they detail in Ref. 15. Finally, we conclude the paper with a summary discussion and indicate possible future directions.…”

“…To evaluate the porous layer effect on the second-mode stability, we solve the eigenvalue problem (2-4) numerically using the admittance (14) or its limiting form (15) and the thermal admittance (19). We consider the boundary layer of a perfect gas with Prandtl number Pr D 0:71 and speci c heat ratio°D 1:4.…”

“…This trend is consistent with the admittance asymptotic behavior associated with Eqs. (10)(11)(12) and (15). For deep pores (3h À 1) of relatively small radius (jk v j ¿ 1), the admittance A is proportional to k v M p .T w / and decreases with the wall temperature as T ¡m =2 w .…”

Experiments on hypersonic boundary layer transition on blunt cones with acoustic-absorption coating

“…Analysis of stability [1,2] showed that the UAC is able to reduce essentially the degree of the 2nd-mode ampli¦cation and to increase in several times the laminar part length. This concept was experimentally checked in California Institute of Technology (Caltech) in the wind tunnel GALCIT T5 at Mach numbers í = 5 6 on a sharp cone [3]. The porous coating for absorbing the boundary layer disturbances presented a plate with equidistant cylindrical blind holes.…”