The supersonic wind tunnel facility SBR-50 at the University of Notre Dame was built in 2015 for experimental research related to shock wave (SW) interactions with obstacles and boundary layers (BL) as well as supersonic combustion and a plasma-based flow control. Currently, the facility provides the following range of flow parameters with a test section area at the nozzle exit of 76.2 × 76.2 mm: Mach number $M=2$ and 4, total pressure $p_0=$ 1–4 bar, stagnation temperature $T_0=$ 300–775 K, and typical duration of the steady-state flow $t=$ 0.5–2 s. One distinct feature of the facility is the Ohmic gas heater installed in a long plenum section. Objective of this study is to characterize flow in the SBR-50 facility, specifically the dynamics of the gas temperature. Two measuring methods were applied for collection of a detailed dataset: thermocouple measurements and schlieren-based thermal mark (laser spark) velocimetry. The experimental data are compared with 3D Navier–Stokes modelling of the gas parameters over the entire flowpath. Particularly, this study proves that the original facility schematics (the concept of a virtual piston in the plenum) allow for a longer operation with a constant stagnation temperature compared to a constant plenum volume with adiabatic cooling of the stored gas.

The problem considered in this work is shock wave (SW) positioning control in shock-dominated flows. Experiments are conducted to investigate the triggering effect of patterned near-surface electrical discharges on SW reflection from plane walls. In the wind tunnel, $M=4$, $P_0$ = 4 bar, a solid wedge SW generator is mounted on the upper wall. Q-DC filamentary electrical discharges were arranged on the opposite wall, so that the SW from the wedge impinged on the plasma filaments that are arranged flow-wise in either a row of three or a single central filament. Within the supersonic flow, narrow subsonic areas are actuated by electrical discharge thermal deposition, resulting in pressure redistribution, which, in turn, relocates the reflection of impinging SW to a predefined position. Mie scattering, schlieren imaging, and wall pressure measurements are used to explore the details of plasma-SW interaction. Using Mie scattering, the three-dimensional shape of the SW structure is mapped both before and after electrical discharge activation. Plasma-based triggering mechanisms are described in terms of the physical principles of flow control and a criterion for determining the effectiveness of the flowfield control.

A self-aligned focusing schlieren (SAFS) system combines the field of view of a conventional schlieren system with the defocus blur of a focusing schlieren system away from the object plane. It can be assembled in a compact form, measuring 1.2 m (4 ft) in length in the described case. The depth of field is sufficiently shallow to distinguish specific spanwise features in a supersonic flow field within a 76.2 mm (3 in) wide test section. As a result, the boundary-layer perturbations on windows and window-material defects and surface imperfections are blurred. Analytical forms are derived for depth of field and vignetting of the SAFS system. A laser spark velocity measurement in Mach 2 flow is performed by tracking the blast wave of a laser spark using 500 kHz SAFS imaging with a 200 ns optical pulse width. The flow Mach number and stagnation temperature are measured by comparing the blast-wave dynamics to an analytical solution. Additionally, schlieren image velocimetry is performed by analyzing natural flow perturbations in 500 kHz SAFS images using a self-correlation method. Comparing the spectra of gas density perturbations from the core flow and a near-wall region reveals a significant difference, with high-frequency prevalence at the boundary-layer location.

Several classical and non-classical reduced-order nucleation rate models are presented and compared to experimental values for the homogeneous nucleation rate of ${\mathrm{CO}}_2$ in supersonic nozzles. The most accurate models are identified and are used in simulations of a condensing supersonic expansion flow. Experimental results for the condensation onset point of ${\mathrm{CO}}_2$ in a variety of expansion facilities are presented and compared to simulations and to new data acquired at the SBR-50 facility at the University of Notre Dame.

This study focuses on the details of the geometry and dynamics of sidewall vortices observed in supersonic wind tunnels with a rectangular cross section of the nozzle and the test section. The formation of sidewall vortices limits the accuracy of the data measured during wind tunnels' testing due to a reduced area of uniform core flow results. Most of the test data presented in this work are generated using Mie scattering visualization for M = 4 flow, with CO2 seeded up to 7% mole fraction. The Mie scattering results are complemented by data from fast pressure sensor and schlieren visualization. It is shown that the formation of vortices is caused by a transverse pressure gradient realized in the supersonic nozzle due to the gas under-expansion. The vortex external mixing layer is strongly perturbed in time but remains globally geometrically similar with streamwise distance. The vortex-generated dominant flow disturbances are in the frequency range of f = 10–50 kHz, doubling the magnitude of baseline power spectral density. The authors' viewpoint is that sidewall vortex generation is a more generic phenomenon than was thought previously.