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Experimental pitot pressure measurements in impulse facilities have typically had large-scale harmonic fluctuations associated with them. A combined experimental and numerical approach is used to investigate if a Helmholtz resonance is created from the shrouding that protects the pressure sensor from particle impact, rather than from disturbances being present in the freestream. To verify this experimentally, hydraulic oil was used to change the sound speed in the cavity. Numerical calculations of the pitot probe were used to show that both the steady and the expected transient inflow cause a Helmholtz resonance of similar period. However, a 5 % isothermal level of freestream noise was required to match the experimental fluctuation levels. Viscous effects were also shown to be significant during the initial transient response of the pressure measurement. A new pitot probe design was successfully tested and shown to be able to reduce the magnitude and period of the fluctuations. [ABSTRACT FROM AUTHOR]

This paper explores the operating envelope for the University of Queensland's free-piston driven X2 expansion tube to determine if flow conditions can be produced that generate a significant magnetohydrodynamic interaction. Numerical calculations are presented to demonstrate the existence of viable operating conditions to study magnetohydrodynamics. Argon is selected as the test gas due to its simple chemistry and low ionization enthalpy. A candidate flow condition is selected for detailed analysis and experimental validation. Finite-rate reacting argon numerical simulations indicate that relatively short shock-layer length scales for the models tested in X2 limit the degree of argon ionization that is generated. However, a strong interaction remains available, and use of a larger facility can fully mitigate this issue. It is shown that expansion tubes are capable of generating the required flowfield for these experiments, and important considerations for design of suitable test flows are identified. [ABSTRACT FROM AUTHOR]

Magnetohydrodynamic (MHD) aerobraking experiments were conducted in the large-scale X3 expansion tunnel at the University of Queensland. The test gas was argon flowing at approximately 5.7 km⋅s-1 for a quasi-steady period of 500 µs. A neodymium spherical permanent magnet, suspended by string and enclosed within a 65-mm-diameter spherical forebody, was used to generate the magnetic field. An accelerometer was attached to the rear of the magnet to measure streamwise motion, allowing the Lorentz force on the magnet to be deduced according to Newton's second law. The stagnation point magnetic flux density was varied by changing the internal streamwise location of the magnet within the forebody. Experimental results demonstrate a linear increase in MHD drag with magnetic field strength, which is in agreement with previous results from arcjet facilities. However, the MHD drag force was much lower in these experiments, even after accounting for shock density ratio and viscosity differences. This discrepancy could be due to the different freestream state generated by the two types of facilities. [ABSTRACT FROM AUTHOR]

Shape optimization of modern three-dimensional hypersonic inlets requires many geometric design parameters. Because the flow physics is complex, a Reynolds-averaged Navier-Stokes (RANS) analysis is also desirable when performing optimization. A computationally efficient means of handling many-parameter optimization with expensive cost functions is to use gradient-based searches informed by an adjoint flow solution. In this work, a discrete adjoint method for high-speed flows is documented. It is implemented in the open-source compressible-flow solver Eilmer. One difficulty with extending a hypersonic flow solver to include an adjoint solver is the differentiation of complex, nonlinear (and sometimes nondifferentiable) algorithms. Here, it is shown that difficulty can be overcome using flow Jacobians constructed with finite differences based on complex variables. The coupled flow and adjoint solvers are packaged together with a gradient-based optimizer. The flow and adjoint solvers are verified and validated for high-speed RANS analysis. The discrete adjoint method for optimization is demonstrated using the NASA P2 hypersonic inlet as a test case. The results show that the optimization method can remove an undesirable shock present in the original geometry, while achieving the desired compression ratio and improving overall performance metrics. [ABSTRACT FROM AUTHOR]

A set of experiments was conducted with the aim of evaluating total heat flux mitigation using magnetohydrodynamic flow control over ionized shock layers surrounding planetary entry vehicles. The University of Queensland's X2 expansion tube was used to generate a flow condition representative of a Mars return trajectory. Spherical permanent magnets were fitted into a scaled test model based on NASA's Stardust capsule. Thermocouples located at the stagnation point and shoulder of the test model, as well as thin-film heat transfer gauges located in the aft section, measured total heat flux for both magnetic and nonmagnetic experiments. High-speed imaging of the shock layer showed a significant increase in shock standoff when using the magnet, and polynomial fits were derived, describing standoff distance along the model's forebody. Despite significant noise affecting the heat flux gauges signals for the magnetic experiments, a simple methodology allowed to compare heat flux during the useful test time. It was found that the applied magnetic field significantly reduces total heat flux at the stagnation point and shoulder of the test model, although heat flux to the aft section was found to significantly increase. Reasonable agreement with the numerical predictions was found for the aft section of the test model, but discrepancies were observed at the other locations. [ABSTRACT FROM AUTHOR]

The expansion tube is the only type of ground test facility currently able to simulate high-Mach-number scramjet test flows. These access-to-space flow conditions are characterized by total pressures of the order of gigapascals. The University of Queensland's X2 expansion tube facility has recently been used to generate scramjet flow conditions between Mach 10 and 14, relevant to a 96 kPa dynamic pressure ascent trajectory, with total pressures up to 10 GPa. These experiments have matched flight enthalpy and Mach number while achieving test flow static pressures considerably higher than the true flight values. This demonstrates that Reynolds number can also be matched, even for subscale models, thereby addressing one of the major challenges for ground testing of high-Mach-number scramjet design concepts. The routine operation of expansion tubes at high flight enthalpies has already been established; but for operation at lower enthalpies (relevant to scramjet testing), the wave processes within these machines become more tightly coupled and difficult to tune. This paper details the combined analytical and numerical processes used to develop new flow conditions in the X2 facility. Experimental results are presented, and axisymmetric computational fluid dynamics analysis is used to fully characterize the test flow properties. [ABSTRACT FROM AUTHOR]

The aerodynamic heating experienced by capsules entering into the atmospheres of Saturn, Uranus, and Neptune is greatly affected by chemically nonequilibrium processes occurring in the shock layers. There are several reaction schemes available in numerical predictions for hydrogen dissociation and ionization, and more experimental data would assist verifying these existing models. This paper reports the results of electron number density measurements conducted in the X2 expansion tube at the University of Queensland using a condition representative of a proposed Saturn entry, where significant nonequilibrium effects in the shock layer are expected. Electron number density along the stagnation streamline was obtained from Stark broadening. The data presented here provide independent measurements for evaluating the reaction schemes for the conditions created. It was found that the experimental data were qualitatively modeled by a contemporary kinetic model. Quantitative agreement between experimental and numerical data was found by adjusting the ionization rate coefficients from an existing reaction scheme by a factor of 25. This updated reaction rate set was also cross-validated with electron number density measurements in NASA's shock tube tests. The adjusted rates had better agreement than using the original rates, and quantitative agreement can be found in the high-density cases. [ABSTRACT FROM AUTHOR]

As scram jet engine development moves toward higher and higher speeds, it will be important to continue to ground test complete nose-to-tail configurations at true flight conditions. Above Mach 10, the freestream total pressure requirements can only be met by an expansion-tube facility. To establish the practicality of ground-testing complete scram jet configurations at high Mach numbers, an expansion-tunnel facility is used to test a generic two-dimensional scram jet at a Mach 10 replication condition. As the flow produced in an expansion-tube facility is transient in nature, a method for analyzing point measurements within the scram jet is developed. A transient numerical simulation of the engine configuration without fuel injection is used to verify the validity of the technique, as well as to provide a reference data set for comparison to experimental data. These experiments show that stable supersonic combustion is established during the test time. Using the developed transient analysis, accurate quasi-steady pressure data at true flight conditions can be inferred from scramjet test measurements in an expansion-tube facility. [ABSTRACT FROM AUTHOR]

This paper reports on an experimental study of magnetohydrodynamic aerobraking using an expansion tube facility, which can generate the correct electrodynamic boundary conditions for spacecraft atmospheric entry. Argon test gas was selected for its relatively simple chemistry, making it well suited to develop experimental test cases for numerical code development. Test models were constructed from either spherical neodymium permanent magnets or steel balls. Ceramic paint was used as an electrically insulating surface boundary condition for experiments where this was required. Finite-rate reacting computational fluid dynamics of the experimental configuration indicates that relatively long duration argon relaxation times lead to a highly nonequilibrium shock layer in which a significant Hall effect arises. This is important because it is expected that future flight vehicles using magnetohydrodynamic aerobraking technology will also be operated at flight conditions where Hall effect is strong. Shock stand-off was measured using high-speed luminosity imaging for various magnetic and nonmagnetic model configurations. Experimental results in this paper support previous numerical studies that found that only an electrically insulated model surface can generate a significant magnetohydrodynamic interaction when Hall effect is strong. [ABSTRACT FROM AUTHOR]

In this work, near-infrared and ultraviolet spectroscopic data collected during the Hayabusa spacecraft reentry is used as the basis for validating numerical and experimental studies using the compressible flow computational fluid dynamics code Eilmer3 and the University of Queensland's X2 expansion tube. Spectra generated numerically from simulations of the full-scale vehicle at the selected trajectory point at 1 s after peak total heating were compared with experimentally captured spectra over a binary-scaled and total-enthalpy-matched radiating shock layer around a 1/5-scale Hayabusa model, and both sets of data were compared with spectra obtained from flight. For the infrared results, experimental and simulated spectra, as well as simulated and flight spectra, compared well within an uncertainty margin of between 20 and 90% depending on the particular case being compared. Experimental and simulated ultraviolet results did not compare well; however, comparisons between simulated and flight ultraviolet spectra were more favorable, comparing well within an uncertainty of around 50%. [ABSTRACT FROM AUTHOR]

A set of magnetohydrodynamic (MHD) aerobraking experiments was conducted with the aim of simulating the Earth reentry environment for Mars return trajectories, and to study the effects of MHD flow control on the ionizing shock layer surrounding a planetary entry vehicle. The X2 expansion tube of the University of Queensland was used, which could provide realistic flowfield boundary conditions, where ionization is spontaneously generated within the shock layer as in true flight and the freestream is nonconducting. Suitable flow conditions providing strong MHD interaction at superorbital Earth reentry velocities were developed. Steel ball and neodymium permanent magnet models were tested, both uncoated and coated with electrically insulating high-temperature epoxy. Shock-layer high-speed imaging showed a significant increase in shock standoff distance for the magnetic models. The experimental shock standoff results generally agreed well with analytical and numerical shock standoff predictions. These experiments demonstrate that a strong MHD interaction can be generated for a Mars return trajectory with moderate magnetic field strengths. Furthermore, they provide a promising framework for future MHD aerobraking experiments to investigate MHD drag force and heat-flux mitigation. [ABSTRACT FROM AUTHOR]

The article presents a study which examines an ablating surface in expansion tunnel flow. Researchers conducted a one-dimensional semi-finite analysis in order to examine whether the surface temperature would be enough to produce vaporization of the insulation. They created an ablating shock layer with an epoxy coating on an axisymmetric model during steady test flow in a high-enthalpy superorbital expansion tunnel. Chemical reactions between the epoxy ablation gases and the air test gas produced high levels of cyanogen.