Optical refraction from high mach number turbulent boundary layer structures

P. J. Erbland, M. R. Etz, W. R. Lempert, A. J. Smits, R. B. Miles

Research output: Contribution to conferencePaperpeer-review

2 Scopus citations

Abstract

An experimental and numerical study was conducted to investigate the grazing incidence refraction of optical rays due to interaction with the discrete structures present in a high Mach number turbulent boundary layer. This study was motivated by the development of the Radiatively Driven Hypersonic Wind Tunnel1 for which high energy laser light must be coupled into supersonic air with minimum wall heating. Data are presented to illustrate the instantaneous structure of the turbulent boundary layer over a flat plate in a Mach 8 flow, with and without normal sonic injection of helium through a transverse linear slot located just downstream of the boundary layer trip. The striking ability of helium injection to reduce the turbulent mixing is illustrated and discussed. A numerical model for propagating optical rays through an arbitrary density field was employed to examine the interaction of rays with the turbulent structures. Representative flow field images were analyzed using a bimodal density model with a density gradient at the turbulent structure interface in order to evaluate the first order sensitivity of the ray refraction to outer layer behavior. Ray tracing results are presented to illustrate these effects and implications regarding ray penetration to the wall and total reflection are discussed. Preliminary analyses revealed very weak refraction for densities corresponding to the experimental test conditions. However, strong refraction and scattering were observed for the high density conditions expected in a high pressure hypersonic wind tunnel. Helium injection, which smoothes the boundary layer interface, reduces the size of outer layer structures, and increases the density change from free stream to wall, may reduce ray penetration to the wall.

Original languageEnglish (US)
DOIs
StatePublished - 1998
Event36th AIAA Aerospace Sciences Meeting and Exhibit, 1998 - Reno, United States
Duration: Jan 12 1998Jan 15 1998

Other

Other36th AIAA Aerospace Sciences Meeting and Exhibit, 1998
CountryUnited States
CityReno
Period1/12/981/15/98

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Space and Planetary Science

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