Seven profiles of streamwise velocity and velocity fluctuations were measured in the incoming boundary layer and immediately upstream of a 24-degree compression corner in a M∞ = 2.8, ReΘ = 1750 shock-wave/turbulent boundary-layer interaction. The measurements were made with Krypton Tagging Velocimetry (KTV) in 99% N2/1% Kr flow. Globally seeding 1% Kr into the flow (premixed N2/Kr K-bottles from distributor) alters the major non-dimensional transport properties by 0.1-0.3%. The mean-velocity and velocityfluctuation profiles in the incoming supersonic turbulent boundary layer were found to agree with datasets in the literature, thus, the baseline flow was established. The meanvelocity profiles in the region immediately upstream of the 24-degree compression corner were found to agree with Direct Numerical Simulation (DNS) results available in the literature. In addition, the presence of a shear layer was detected, and its location and orientation are compared to that in the literature.

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In this work, we study the effect of the compression-corner angle on the streamwise turbulent kinetic energy (sTKE) and structure in Mach 2.8 flow. Krypton tagging velocimetry (KTV) is used to investigate the incoming turbulent boundary layer and flow over $8^{\circ }$, $16^{\circ }$, $24^{\circ }$ and $32^{\circ }$ compression corners. The experiments were performed in a 99 % $\text{N}_{2}$ and 1 % Kr gas mixture in the Arnold Engineering Development Complex (AEDC) Mach 3 Calibration Tunnel (M3CT) at $Re_{\unicode[STIX]{x1D6E9}}=1750$. A figure of merit is defined as the wall-normal integrated sTKE ($\overline{\text{sTKE}}$), which is designed to identify turbulence amplification by accounting for the root-mean-squared (r.m.s.) velocity fluctuations and shear-layer width for the different geometries. We observe that the $\overline{\text{sTKE}}$ increases as an exponential with the compression-corner angle near the root when normalized by the boundary-layer value. Additionally, snapshot proper orthogonal decomposition (POD) is applied to the KTV results to investigate the structure of the flow. From the POD results, we extract the dominant flow structures and compare each case by presenting mean-velocity maps that correspond to the largest positive and negative POD mode coefficients. Finally, the POD spectrum reveals an inertial range common to the boundary-layer and each compression-corner flow that is present after the first ${\approx}10$ dominant POD modes.

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In this paper, we investigate the boundary-layer profiles that form over a sharp, hollow cylinder in supersonic air and N 2 flows with a krypton tagging velocimetry (KTV) single-laser scheme. The supersonic flows are generated by the passage of the primary shock wave over the model in the Stevens shock tube. The experiments are performed in two gas mixtures doped with Kr: 99% N 2 /1% Kr, to model N 2 , and 75% N 2 /20% O 2 /5% Kr, to model air. The experimental setup allows us to vary the pressure and Reynolds number from 3-25 kPa and 1.5 × 10 5 to 1.5 × 10 6 m −1 , respectively, while the Mach number is kept fixed at 1.7. The static temperature and pressure (but not the velocity) are representative of typical large-scale high-enthalpy hypersonic impulse facilities. The KTV data points over the hollow cylinder are mapped to corresponding wall-normal locations above a flat plate, which enables comparison with the similarity solution for compressible boundary-layer flow. Agreement between the similarity solution and experimental results is excellent. Relative to previous two-laser KTV schemes, the single-laser approach used in this work has the advantage of being simpler and more cost effective, but it has a higher laserenergy requirement, 10 mJ/pulse in these experiments. Single-laser KTV is implemented by increasing the energy of the write-laser pulse to a sufficient level such that the Kr becomes partially ionized via a (2 + 1) resonance-enhanced, multiphoton ionization (REMPI) process with an excitation wavelength of 212.6 nm. The write step records the fluorescence that results primarily from the spontaneous emission from the two-photon excitation. After a prescribed delay, the read step records the fluorescence that results from the transitions that follow the recombination process. The signal-to-noise ratio (SNR) is sufficient to extract velocity profiles from single-shot, shock-tube experiments. Two-photon absorption cross-section calculations and emission spectra are presented to justify the chosen excitation wavelength and support our understanding of the Kr excitation and emission scheme.