The krypton tagging velocimetry (KTV) technique is applied to the turbulent boundary layer on the wall of the Mach 3 Calibration Tunnel at Arnold Engineering Development Complex (AEDC) White Oak. Profiles of velocity were measured with KTV and Pitot-pressure probes in the Mach 2.75 turbulent boundary layer comprised of 99% N_2/1% Kr at momentum-thickness Reynolds numbers of Ree = 800, 1400, and 2400. Agreement between the KTV- and Pitot-derived velocity profiles is excellent. The KTV and Pitot velocity data follow the law of the wall in the logarithmic region with application of the Van Driest I transformation. Also, the velocity data in the wake region are consistent with data from the literature for a turbulent boundary layer with a favorable pressure gradient history. A modification of the Mach 3 AEDC Calibration Tunnel is described which facilitates operation at several discrete unit Reynolds numbers consistent with AEDC Hypervelocity Tunnel 9 run conditions of interest. Moreover, to enable near-wall measurement with KTV, an 800 nm longpass filter was used to block the reflection and scatter from the 760.2 nm read-laser pulse. With the longpass filter, the 819.0 nm emission from the re-excited Kr can be imaged to track the displacement of the metastable tracer without imaging the reflection and scatter from the read laser off of solid surfaces.
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