View Video Presentation: https://doi.org/10.2514/6.2022-2223.vid A static pressure probe has been employed in three hypersonic wind tunnels: the von Karman Institute (VKI) Longshot at a freestream Mach number of 14 and freestream unit Reynolds number of Re =1.5 – 3.5 ·106, the VKI H3 Mach-6 at M =6 and Re =3 ·107, and the Notre Dame arc-heated tunnel (ACT-1) at M =14 and Re =3 ·106 – 6 ·107. A computational analysis of the static pressure probe over the range of expected flow conditions was conducted using CFD++. Low freestream static temperatures ranging from 35–60 K were tested, with the expectation of encountering condensation, especially at the lower end of this range. To assess condensation, laser Rayleigh scattering measurements were collected using a 700 nm wavelength laser and photodiode. Freestream rebuilding methods using static pressure, Pitot pressure, and a heat flux probe indicate condensation during several low-temperature runs in Longshot. Measurements with the static probe in H3 were inconclusive due to damage to the Kulite at the time. Measurements in H3 with the laser and photodiode indicate either condensation or a high level of particulate in the flow. In ACT-1, the static and Pitot probes were insensitive to condensation during preliminary testing. Condensation may have been detected with laser Rayleigh scattering. Work is in progress to improve the instrumentation's accuracy and sensitivity.
Various methodologies used to derive free-stream conditions in hypersonic wind tunnels using different sets of experimental inputs are reviewed. The accuracy of a relevant but seldom used approach, involving free-stream static pressure measurements, is improved in the present work by solving numerically shock conservation equations and by accounting for the high-temperature effects typically expected in hypersonic flows (vibrational excitation, dissociation, and ionization). The numerical method implemented is also extended to handle free-stream thermal non-equilibrium provided that free-stream vibrational temperature measurements are available. The performances of the present approach are evaluated against conventional methods by determining free-stream flow properties in the von Karman Institute Longshot hypersonic wind tunnel. Uncertainties are quantified for each of the derived free-stream flow conditions. It is demonstrated that methodologies limited to Pitot pressure diagnostics in the test section fail to detect departures from ideal nozzle flow expansions, due to their inherent isentropic flow assumptions. Involving free-stream static pressure diagnostics does, however, improve the results, as validated by independent investigations. It is shown that the non-ideal nozzle flow expansion is not induced by free-stream thermal non-equilibrium since this phenomenon leads to opposite trends on free-stream flow properties with respect to those observed. Overall, free-stream static pressure probes represent a useful complement and their benefits for free-stream rebuilding methodologies are emphasized. The present free-stream rebuilding methodology is recommended to enhance the relevance of every hypersonic ground experiment.
This paper analyzes the nozzle start-up of the von Kármán Institute Longshot, an impulse hypersonic gun tunnel, using a combination of the Lagrangian L1D code (used to model the initial compression process of the test gas into a reservoir by an inertial piston) and unsteady Reynolds-averaged Navier–Stokes simulations to model the flow expansion through the appended nozzle. The influence of initial nozzle flow conditions on the duration of the start-up is investigated based on various simulated experiments, and it is verified that the shortest establishment time is obtained for the lowest initial pressure. The applicability of the numerical scheme is proved through a comparison of the inlet and outlet total and static conditions against experimental results at relevant conditions. Besides, the right running and left running shocks constituting the start-up shock system are tracked through the nozzle, and their propagation velocities are reported. Momentum and thermal boundary-layer establishment times are reported based on the temperature and velocity profiles predicted at the nozzle exit. Finally, the flow establishment time is compared against several criteria available in the literature. Additionally, new establishment and quasi-steady behavior criteria are presented, derived from the freestream static pressure and temperature evolution.
The operational map of the H3 Mach 6 blowdown wind tunnel, at the von Karman Institute for Fluid Dynamics (VKI), is extended towards lower Mach numbers with a new axisymmetric contoured nozzle to achieve Mach 5 testing conditions. Following the design, manufacturing, instrumentation and integration of the Mach 5 nozzle, an extensive commissioning campaign is initiated. The flow investigations rely on several intrusive and non-intrusive measurement techniques including free-stream static pressure measurements, a rake of pitot probes, total temperature probes and schlieren flow visualization. Results are compared with numerical predictions.
The objective of the present research is to develop an experimental setup in order to study the dynamic stability of slender bodies in the transonic regime. A semi-free oscillation approach is chosen to determine the aerodynamic damping coefficient. Based on the potentials of the installation environment (VKI S-1 Supersonic-Transonic wind tunnel) a wire suspension system is proposed. The nondimensionalized oscillation frequency is preserved between the flight vehicle and the wind tunnel model by a cable tensioning mechanism enabling the adjustment of the natural frequency. The oscillation of the test model is decomposed by a boundary identification technique applied to high-speed camera recordings. The analysis of the oscillation amplitudes yields the total damping. To separate the mechanical and the aerodynamic contributions tare measurements are performed without flow.
