Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources. gathenng and maintaining the data needed, and completing and reviewing this collection of information. AFRL-SR-AR-TR08-O109 SUPPLEMENTARY NOTES ABSTRACTTransitional shock wave / boundary layer interactions are studied with planar imaging techniques. The interaction is generated by a cylinder mounted on a flat plate in a Mach 5 flow. Planar laser scattering (PLS) and particle image velocimetry (PIV) are used to visualize the flow structure. Images are obtained in streamwise-spanwise planes (plan view). Earlier work focused on investigating similar interactions with tripped boundary layers, whereas the current work focuses on the case where transition occurs naturally.. One goal of this preliminary study was to see if repeatable interactions could be generated.. Imaging was conducted for three downstream locations of the cylinder. The PLS imaging revealed that the transitional interactions resulting from an untripped boundary layer are similar to those generated by tripping. In general it is observed that the separated flow region of transitional interactions exhibits larger variations in their scale and shape than fully turbulent interactions. When the cylinder is farthest upstream (5.3 diameters from leading edge) two types of separation shock are seen: an apparently laminar shock along the plate centerline and a turbulent one in the outboard region. As the cylinder is moved downstream (10.7 diameters), this dual structure is not as apparent, which is consistent with the upstream boundary layer becoming more turbulent. Finally, at 16 diameters downstream the interaction exhibits extreme variations in its shape, which we believe to be caused by sidewall interference. The PIV measurements largely confirm these qualitative observations. SUBJECT TERMS

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources. gathenng and maintaining the data needed, and completing and reviewing this collection of information. AFRL-SR-AR-TR08-O109 SUPPLEMENTARY NOTES ABSTRACTTransitional shock wave / boundary layer interactions are studied with planar imaging techniques. The interaction is generated by a cylinder mounted on a flat plate in a Mach 5 flow. Planar laser scattering (PLS) and particle image velocimetry (PIV) are used to visualize the flow structure. Images are obtained in streamwise-spanwise planes (plan view). Earlier work focused on investigating similar interactions with tripped boundary layers, whereas the current work focuses on the case where transition occurs naturally.. One goal of this preliminary study was to see if repeatable interactions could be generated.. Imaging was conducted for three downstream locations of the cylinder. The PLS imaging revealed that the transitional interactions resulting from an untripped boundary layer are similar to those generated by tripping. In general it is observed that the separated flow region of transitional interactions exhibits larger variations in their scale and shape than fully turbulent interactions. When the cylinder is farthest upstream (5.3 diameters from leading edge) two types of separation shock are seen: an apparently laminar shock along the plate centerline and a turbulent one in the outboard region. As the cylinder is moved downstream (10.7 diameters), this dual structure is not as apparent, which is consistent with the upstream boundary layer becoming more turbulent. Finally, at 16 diameters downstream the interaction exhibits extreme variations in its shape, which we believe to be caused by sidewall interference. The PIV measurements largely confirm these qualitative observations. SUBJECT TERMS

A new technique is currently under development that uses planar laser-induced fluorescence (PLIF) imaging of sublimated naphthalene to image the transport of ablation products in a hypersonic boundary layer. The primary motivation for this work is to understand scalar transport in hypersonic boundary layers and to develop a database for validation of computational models. The naphthalene is molded into a rectangular insert that is mounted flush with the floor of a Mach 5 wind tunnel. The distribution of naphthalene in the boundary layer is imaged by using PLIF, where the laser excitation is at 266 nm and the fluorescence is collected in the range of 320 to 380 nm. To investigate the use of naphthalene PLIF as a quantitative diagnostic technique, a series of experiments is conducted to determine the linearity of the fluorescence signal with laser fluence, as well as the temperature and pressure dependencies of the signal. The naphthalene fluorescence at 297 K is determined to be linear for laser fluence that is less than about 200 J/m 2. The temperature dependence of the naphthalene fluorescence signal is found at atmospheric pressure over the temperature range of 297K to 525K. A monotonic increase in the fluorescence is observed with increasing temperature. Naphthalene fluorescence lifetime measurements were also made in pure-air and nitrogen environments at 300 K over the range 3.3 kPa to 101.3 kPa. The results in air show the expected Stern-Volmer behavior with decreasing lifetimes at increasing pressure, whereas nitrogen exhibits the opposite trend. Preliminary PLIF images of the sublimated naphthalene are acquired in a Mach 5 turbulent boundary layer. Relatively low signal-to-noise-ratio images were obtained at a stagnation temperature of 345 K, but much higher quality images were obtained at a stagnation temperature of 375 K. Our results indicate that PLIF of sublimating naphthalene may be an effective tool for studying scalar transport in hypersonic flows.