1. Fig. 2 Sketch of a cross-section of the mean flowfield. Mean reattachment location marked as '. Adapted from Baca.24 where ri = UrefrP/&
2. The experimental configuration for the reattaching shear layer is illustrated in Figs. 1 and 2. The experimental model was originally designed by Baca.24 In this flow, a Mach 2.9 turbulent boundary layer forms on a flat plate and detaches at a backward-facing step. As a result, a free shear layer forms over a region of recirculating flow. The shear layer reattaches on a 20" ramp, passing through an oblique shock system, and a turbulent boundary layer develops on the ramp downstream. Surveys of the basic properties of the flowfield were performed in earlier experimental programs at the Princeton Mach 3 wind tunne120~24-27and similar configurations have been investigated in other facilities.28-30
3. Aseries of experiments was carried out in which the reattachment shock system was visualized using Rayleigh scattering from nanometer-scale contaminant particles in the flow. Illumination was provided by an wind tunnel. The experimental arrangement used optics with a UV-coating, and quartz windows provided optical access to the tunnel test section. Two lasers were used in the course of the experimental program: a Lambda-Physik argon fluoride laser with a wavelength of 193 nm and a frequency-quadrupled Continuum Nd:YAG laser with a wavelength of 266 nm. Both lasers provided a pulse on the order of several nanoseconds in duration at a repetition rate of 10 Hz, and delivered 20-50 mJ of energy per pulse. A doubleintensified ITT CID (Charge Integrated Device) camera recorded the light scattered from the laser sheet. The camera had a resolution of 388 by 244 pixels, and the light intensifier had a resolution of 180 lines. The video data were recorded on VHS video tape, and later digitized for analysis.