摘要 :
An axisymmetric viscous shock tube simulation code is developed which keeps the shock and the contact discontinuity stationary in suitably constructed moving frames of reference. The flow field around the discontinuities is repres...
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An axisymmetric viscous shock tube simulation code is developed which keeps the shock and the contact discontinuity stationary in suitably constructed moving frames of reference. The flow field around the discontinuities is represented on fine grids which move with the frames attached to the waves. These moving grids are overset upon a coarse background grid of the entire facility, allowing efficient computation of the main discontinuities as they traverse the tube. Focus is placed upon accurate capture of the influence of wave speeds and viscous effects upon the shock and contact discontinuity as they traverse the tube. The code is extensively validated against experiments ranging from Mach 1.6-2.7 in a 26.8 mm diameter shock tube with Argon driver/driven gases and an initial pressure of 66.66 Pa. Agreement within 2％ is seen in velocity throughout the tube's length. Test times are predicted to within 6% across a broad range of test conditions. Unsteady diaphragm opening effects as well as turbulent transition are demonstrated to substantially influence experimental results of the well-known experiments of Duff (1959).
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摘要 :
An axisymmetric viscous shock tube simulation code is developed which keeps the shock and the contact discontinuity stationary in suitably constructed moving frames of reference. The flow field around the discontinuities is repres...
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An axisymmetric viscous shock tube simulation code is developed which keeps the shock and the contact discontinuity stationary in suitably constructed moving frames of reference. The flow field around the discontinuities is represented on fine grids which move with the frames attached to the waves. These moving grids are overset upon a coarse background grid of the entire facility, allowing efficient computation of the main discontinuities as they traverse the tube. Focus is placed upon accurate capture of the influence of wave speeds and viscous effects upon the shock and contact discontinuity as they traverse the tube. The code is extensively validated against experiments ranging from Mach 1.6-2.7 in a 26.8 mm diameter shock tube with Argon driver/driven gases and an initial pressure of 66.66 Pa. Agreement within 2％ is seen in velocity throughout the tube's length. Test times are predicted to within 6% across a broad range of test conditions. Unsteady diaphragm opening effects as well as turbulent transition are demonstrated to substantially influence experimental results of the well-known experiments of Duff (1959).
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Uranus and Neptune, known collectively as the Ice Giants, are the only two planets in the solar system that are yet to be explored with a dedicated mission. Planetary entry probe missions to the Ice Giants were proposed in 2010 by...
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Uranus and Neptune, known collectively as the Ice Giants, are the only two planets in the solar system that are yet to be explored with a dedicated mission. Planetary entry probe missions to the Ice Giants were proposed in 2010 by NASA and ESA which prompted a resurgence of interest in experimental simulation of the aeroheating environment that would be encountered by such a spacecraft. More recently, the 2023 - 2032 Decadal Survey recommended that NASA's highest priority new flagship mission should be a Uranus orbiter and probe with a launch date in the early 2030s. The Oxford T6 Stalker tunnel is the only facility in Europe capable of replicating the high speeds required for Ice Giant entry and is therefore a key stepping stone on the path to realising the goal of an Ice Giant mission. In the present work, a 1:10 scaled model of the Galileo probe has been tested at Ice Giant entry conditions. Conditions for nominal composition (85%H_2-15%He), Stalker substituted, and nominal composition with methane (0.5% and 5% CH_4) gas mixtures have been developed and validated for use with a new expansion nozzle via a Pitot rake survey. Test flows with flight equivalent velocities greater than 18 km/s have been produced with test times on the order of 30 μs. Heat flux into the model for the developed conditions has been inferred from temperature measurements with a series of coaxial thermocouples. High speed video, with and without schlieren, has been captured to aid in characterisation of the test conditions.
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The Ice Giants, Uranus and Neptune, represent a largely unexplored, interstitial class of planetary objects that fit between the Gas Giants and the smaller terrestrial worlds, such as Earth, in terms of their size and elemental co...
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The Ice Giants, Uranus and Neptune, represent a largely unexplored, interstitial class of planetary objects that fit between the Gas Giants and the smaller terrestrial worlds, such as Earth, in terms of their size and elemental composition and are therefore a missing link in our understanding of extrasolar planetary evolution. The scientific potential of a mission to the Ice Giants is well recognised and has been identified by NASA and ESA as a high priority on several occasions, most recently in the 2023 - 2032 Decadal Survey. The payload capacity of such a spacecraft is limited by the requirement for a bulky heat shield, made necessary by the paucity of ground test data for convective and radiative heat flux at proposed entry trajectories. This paper describes an experimental study of shock layer radiation via emission spectroscopy at Ice Giant entry conditions in the T6 free-piston driven wind tunnel. Significant engineering upgrades have been made to T6 that extend the performance envelope and allow operation with flammable test gases. Shock waves of up to 18.9 km/s were driven through H/He mixtures containing up to 5% CH_4 by mole. The magnitude of spectral radiance at the peak and in the immediate post-shock region appears to be strongly affected by the concentration of CH_4 in the test gas. Spectral fitting with the NEQAIR program shows that radiation in the 410 - 560 inn range is dominated by C2 and CH and has allowed the spatial evolution of mode temperatures and species concentrations to be extracted.
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Defunct satellites must be removed through uncontrolled re-entry into Earth's atmosphere. Ideally, satellite components 'burn up' due to the aerothermal heating loads in the upper atmosphere. This process is difficult to model due...
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Defunct satellites must be removed through uncontrolled re-entry into Earth's atmosphere. Ideally, satellite components 'burn up' due to the aerothermal heating loads in the upper atmosphere. This process is difficult to model due to a large portion of the heat load occurring at high altitudes under rarefied conditions and with non-equilibrium thermochemistry. Satellite demise models therefore require high quality validation data to ensure dangerous Earth impact events can be predicted and avoided. This study develops and demonstrates a test bed for obtaining spatially resolved heat flux measurements at high enthalpy, high altitude conditions. A new rarefied flow condition is commissioned in the free piston-driven T6 expansion tunnel. A total enthalpy of 20 MJ/kg is achieved, corresponding to a flight velocity of 6.3 km/s. The freestream Knudsen number is 0.01 and convective heat flux is matched to flight for vehicles 0.2 to 2 m in diameter at altitudes of 75-90 km. Flat-faced cylindrical models with a diameter of 10 mm, length of 20 mm and corner radii of 1 and 2 mm are used to represent satellite tanks. These are instrumented with platinum thin film heat transfer gauges which are coated in a thin silicon dioxide film to insulate them from free electrons in the mildly ionised flow.
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Shock tube experiments are used to investigate thermochemical properties of gases at high temperatures, such as those encountered during hypervelocity flight. However, considerable uncertainties surround the results obtained in sh...
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Shock tube experiments are used to investigate thermochemical properties of gases at high temperatures, such as those encountered during hypervelocity flight. However, considerable uncertainties surround the results obtained in shock tubes because of limitations in the ability to characterize the test gas properties which underlie experimental measurements. Poorly understood nonuniformities in what is often assumed to be a uniform post-shock flow are the source of these uncertainties. In this paper, a series of significant improvements to both understanding the nature of these nonuniformities, and analytically predicting them to accurately characterize shock tube experimental flows is summarized. These improvements include more efficient multidimensional simulations, identification of the variation of shock speed as the primary source of these nonuniformities, and production of an analytical methodology which is able to fully predict the nonuniformities. The methodology, entitled LASTA, is able to accurately reconstruct shock tube test gas properties to within 1 % of experimental measurements and multidimensional simulations. It also accounts for the shot-to-shot variations in measurements which are produced because of non-ideal facility effects. LASTA is used to show, when compared against experiments conducted in the Oxford T6 Stalker facility, that test gas thermochemical nonuniformities are highly dependent upon the variation of shock speed along the tube. It is also shown that these nonuniformities may be analytically predicted from experimental data with only the shock speed profile, fill conditions and tube geometry. Finally, high resolution experimental measurement of shock trajectory is shown to be crucial to accurate characterization of the test gas.
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