Expansion Tube Research Articles

Development of a Minipig Model of BINT From Blast Exposure Using a Repeatable Mobile Shock Expansion Tube.

The Office of Naval Research (ONR) sponsored the Blast Load Assessment Sense and Test (BLAST) program to provide an approach to operationally relevant monitoring and analysis of blast exposure for optimization of service member performance and health. Of critical importance in this effort was the development of a standardized methodology for preclinical large animal studies that can reliably produce outcome measures that cannot be measured in human studies to support science-based guidelines. The primary advantage of this approach is that, because animal studies report physiological measures that correlate with human neuropathology, these data can be used to evaluate potential risks to service members by accounting for the anatomical and physiological differences between humans and large animal models. This article describes the methodology used to generate a comprehensive outcome measure dataset correlated with controlled blast exposure. To quantify outcomes associated with a single exposure to blast, 23 age- and weight-matched Yucatan minipigs were exposed to a single blast event generated by a large-bore, compressed gas shock tube. The peak pressure ranged from 280 to 525kPa. After a post-exposure 72-hour observation period, the physiological response was quantified using a comprehensive set of neurological outcome measures that included neuroimaging, histology, and behavioral measures. Responses of the blast-exposed animals were compared to the sham-treated cohort to identify statistically significant and physiologically relevant differences between the two groups. Following a single exposure, the minipigs were assessed for structural, behavioral, and cellular changes for 3 days after exposure. The following neurological changes were observed: Structural-Using Diffusion Tensor Imaging, a statistically significant decrement (P < .001) in Fractional Anisotropy across the entire volume of the brain was observed when comparing the exposed group to the sham group. This finding indicates that alterations in brain tissue following exposure are not focused at a single location but instead a diffuse brain volume that can only be observed through a systematic examination of the neurological tissue. Cellular-The histopathology results from several large white matter tract locations showed varied cellular responses from six different stains. Using standard statistical methods, results from stains such as Fluoro-Jade C and cluster of differentiation 68 in the hippocampus showed significantly higher levels of neurodegeneration and increased microglia/macrophage activation in blast-exposed subjects. However, other stains also indicated increased response, demonstrating the need for multivariate analysis with a larger dataset. Behavioral-The behavior changes observed were typically transient; the animals' behavior returned to near baseline levels after a relatively short recovery period. Despite behavioral recovery, the presence of active neurodegenerative and inflammatory responses remained. The results of this study demonstrate that (1) a shock tube provides an effective tool for generating repeatable exposures in large animals and (2) exposure to blast overpressure can be correlated using a combination of imaging, behavioral, and histological analyses. This research demonstrates the importance of using multiple physiological indicators to track blast-induced changes in minipigs. The methodology and findings from this effort were central to developing machine-learning models to inform the development of blast exposure guidelines.

Development and commissioning of the T6 Stalker Tunnel

The T6 Stalker Tunnel is a multi-mode, high-enthalpy, transient ground test facility. It is the first of its type in the UK. The facility combines the original free-piston driver from the T3 Shock Tunnel with modified barrels from the Oxford Gun Tunnel. Depending on test requirements, it can operate as a shock tube, reflected shock tunnel or expansion tube. Commissioning tests of the free-piston driver are discussed, including the development of four baseline driver conditions using piston masses of either 36 kg or 89 kg. Experimental data are presented for each operating mode, with comparison made to numerical simulations. In general, high-quality test flows are observed. The calculated enthalpy range of the experimental conditions achieved varies from 2.7hbox { MJ kg}^{-1} to 115.0hbox { MJ kg}^{-1}.Graphical abstract

Magnetohydrodynamic Aerobraking Shock Stand-Off Measurements with Flight Representative Electrodynamic Boundary Conditions

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.

Heat Transfer Measurements in an Expansion Tube Using Infrared Thermography

This paper presents two-dimensional heat transfer results for the first time in an expansion tube, using infrared thermography at a Mars entry condition. Experiments were performed in the X2 expansion tube at The University of Queensland in a Martian () test gas on a wedge model. Infrared filtering from 3.5 to was performed in data acquisition to remove significant radiation from the shock layer. Thermal images of a preheated surface from the infrared camera were used together with measurements from a fast response infrared sensor to obtain heat flux maps at a hypervelocity condition with flight duplicated enthalpy. Experimental heat flux results have an uncertainty of less than 10% and agreed with laminar convective theoretical correlations to within 16%, making thermography suitable for heat transfer measurements in expansion tubes. This technique has potential for future applications in studying wall/near-wall viscous phenomena dependent on surface temperatures in expansion tubes.

Hypervelocity Spherically-Blunted Cone Flows in Mars Entry Ground Testing

Bow-shock standoff distances over sphere and spherically-blunted cone geometries were examined through experiments in two facilities capable of high-stagnation enthalpy hypersonic flows simulating Mars planetary entry conditions. High-speed and high-resolution schlieren images were obtained in the California Institute of Technology T5 reflected shock tunnel and the Hypervelocity Expansion Tube to examine facility independence of the measurements. Accompanying reacting Navier–Stokes simulations were carried out. A recently developed unified model for sphere and sphere–cone behavior was first verified for high-stagnation enthalpy flows through simulations with thermal and chemical nonequilibrium. Shock standoff distance measurements in both facilities were found to be in good agreement with model predictions. The need to account for the divergence of the streamlines in conical nozzles was highlighted and an existing model extended to account for changes in shock curvature between parallel and conical flows. The contributions of vibrational and chemical nonequilibrium to the stagnation-line density profile were quantified using the simulation results comparing three chemical kinetic models.

Experimental and Computational Fluid Dynamics Study of Hayabusa Reentry Peak Heating

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%.

Expansion Tube Experiments of Magnetohydrodynamic Aerobraking for Superorbital Earth Reentry

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.

Detecting shock arrival in expansion tubes and shock tunnels using high-frequency photodiodes

Detecting shock arrival in expansion tubes and shock tunnels using high-frequency photodiodes

GPU and CPU Numerical Simulation of tTwo-Phase Mixtures with Phase Transition

The article presents the direct simulation results of two-phase mixtures with phase transition shock tube in dodecane, two-phase expansion tube in water and 2D heat and mass transfer in a vertical channel with sodium. For two versions of the code for CPU and GPU calculations possess efficient scaling in the wide range of grid sizes. Scaling for CPU version of the code is close to ideal and does not depend from the grid size and the number of nodes. Efficiency of scaling for GPU version of the code is limited by the size of calculation region per 1 node and could be varied for different models of processor. The value of scaling factor was demonstrated.

Technique Development for Investigating Axisymmetric Ablation Models in Hypersonic Impulse Facilities

Arcjet facilities have been used extensively for ablation and materials characterization but arcjets do not correctly simulate the hypervelocity flow during reentry. Impulse facilities can simulate aspects of hypervelocity reentry flows, but cannot duplicate the extended-duration thermal environments. To address such deficiencies in short-duration testing environments, a novel plasma technique for preheating axisymmetric samples of heat-shield materials has been developed. The heating technique has been demonstrated using a short-duration blow-down arrangement at the University of Southern Queensland. A 50-mm-diameter graphite disk sample with a uniform thickness of 2 mm was heated from the downstream side with plasma to approximately 2500 K, and then it was exposed to a cold Mach 4.5 flow. The disk was mounted on an experimental probe that was very similar to the European standard probe, normal to the flow. Future applications for the technique are expected to be found in expansion tube facilities that can simulate the true flow energy under reentry conditions.

Focused laser differential interferometer response to shock waves

The focused laser differential interferometer (FLDI) can be used to measure rapid density fluctuations non-intrusively in high-speed flow applications. Being a non-imaging shearing interferometer, FLDI response can be accurately modeled using a paraxial ray-tracing scheme. We present the details of a new numerical implementation of this scheme, capable of accepting flow-field input from analytical models, computational fluid dynamics (CFD) results, and experimental data. This implementation has previously been validated for static (laminar jet) and dynamic (ultrasound-generated) changes in index of refraction by Lawson et al. In this work, we examine the FLDI response to shock waves propagating at up to Mach 10, in Caltech’s hypervelocity expansion tube. While the timescale and approximate form of the signal can be recovered using a simple inviscid, planar shock model, it is found that the inclusion of viscous shock effects allows an accurate simulation of both the magnitude and detailed shape of the experimental response. This is a further analytical validation of the FLDI model that extends beyond the results of the existing dynamic validation case. The model implementation is then coupled to a CFD code, and predictions reproduce experimental FLDI response to a complex shock-dominated flow-field.

Emission Spectroscopy of Ionizing Superorbital Expanding Flow

This paper reports on the use of spectral techniques for measuring excitation levels of a radiating hypersonic flow undergoing a rapid expansion. The X2 expansion tube, located at The University of Queensland was used to generate a test case physically similar to superorbital flight conditions, where a argon test flow was first processed by an oblique shock and then by an expansion fan. Emission spectroscopy was conducted to determine the populations of electronic energy levels of the argon by measuring electromagnetic radiation intensity at visible and infrared wavelengths. Excitation temperatures were resolved along spatial lines above the model, from upstream of the shock to downstream of the expansion fan. These temperatures were found to increase from 9000 to 10,000 K between the shock and the expansion fan, with the temperature frozen in the expansion fan. Numerical simulations of the flow showed a similar trend, with the computed excitation temperature in the expansion fan also freezing. Shock precursor radiation was also detected, indicating that the excitation temperature upstream of the shock and through the expansion fan is likely to be influenced by radiation from the immediate postshock region.

Evolution of heat transfer at the stagnation point during the detached bow shock establishment

The diffraction of a shock wave over a stationary body is a problem of interest associated with the starting of shock tubes and expansion tubes which are well suited to studies of hypersonic flows. However, these facilities are characterized by very short test times. The transient parameters during the establishment of the detached bow shock in such impulsive facilities are important for both data processing and experimental design. In the present study, numerical simulations are conducted to investigate the diffraction of a normal shock wave over a sphere and the subsequent transient phenomena in a viscous perfect-gas flow field. The incident shock Mach number ranges from 3 to 5 with a specific heat ratio of 1.4. Based on the theoretical description of the reflected shock position during bow shock formation, approximate solutions for the time histories of the stagnation-point heat flux are also derived. The analytical and numerical results agree well. The results show that the stagnation-point pressure and heat flux approach their steady-state values much more rapidly than the shock detachment distance does.

A finite-element method for analysing solid expansion process and supervising material selection

Solid expansion technology is regarded as one of the revolutionary technologies that will change the future development of petroleum and gas industry. However, in the process of material selection of expandable tubular, there is always a contradiction between excessive expansion force and insufficient strength of expansion tube, which restricts the application and development of this technology to a great extent. In order to analyze the expansion performance of expansion tubes made of different materials, and the expansion conditions with different friction coefficients, different materials, different expansion cones and rates, finite element models were established by ABAQUS software in this paper to simulate the expansion tubes of several specifications. By comparing the experimental and simulation results, the reliability of the model analysis is demonstrated by the small error range. The influence of material mechanical properties, friction coefficient on expansive force after expansion were analyzed. Moreover, the material selection principle of expandable tubular is also discussed.

The Richtmyer–Meshkov instability of concave circular arc density interfaces in hydrodynamics and magnetohydrodynamics

Concave circular arc density interfaces (CDIs) are relevant to a deformed diaphragm separating different pressure gases in a shock tunnel or an expansion tube, where it is known that the Richtmyer–Meshkov instability (RMI) limits facility performance. Considering CDIs characterized by different curvatures (κ), numerical investigations of the RMI in both hydrodynamics (hydro) and magnetohydrodynamics (MHD) are performed. In the hydro cases, the largest curvature case appears to be the most unstable one, with the largest amounts of vorticities deposited on the CDIs. In the MHD cases, the interplay between the RMI and the magnetic field is investigated. On the one hand, the RMI can be compressed by magnetic fields. The stronger the magnetic field is, the smoother the density interface will be. The magnetic pressure alleviates pressure deviations along two sides of the CDIs, reducing baroclinic effects. Meanwhile, the magnetic tension force induces Alfvén waves, which transport vorticities away from density interfaces. On the other hand, magnetic fields can be amplified by the RMI, indicating that more amplification occurs when the initial magnetic field is weak, and magnetic lines are severely distorted in such cases. Besides, the evolutions of the kinetic energy and the magnetic energy are discussed. The results indicate that there is no energy transfer between them, and the magnetic energy mainly concentrates on the MHD wave fronts. The change of the enstrophy against time demonstrates that the vorticity energy decreases when the strength of initial magnetic fields increases.

Thermo-mechanical coupling analysis of expansion tubes: Theoretical prediction and experimental investigation

Thick-walled expansion tubes have been widely used in high-speed trains as passive energy-absorbing devices. Previous studies mainly focused on thin-walled expansion tubes with thickness less than 5 mm, and the theoretical model is in good agreement with experiments. However, a deviation of about 4.3% for the thick-walled tubes with a thickness of 15 mm is found between the predictive reaction force and experimental results. In this study, the thermal effect was investigated for the deviation. Firstly, a modified theoretical model was proposed by a plastic hinge moving method. Secondly, the temperature distribution was calculated, and a new reaction force was obtained by the temperature-dependent material properties. A thermal reduction coefficient was used to represent the ratio of the reaction force considering the temperature effect or not. Finite element simulations and experimental measurements were performed to verify the current model. The results show that the thermal reduction coefficient is mainly affected by the geometrical structure, material properties, and ambient temperature. The deformation modes of expansion tubes can be divided into point contact mode and surface contact mode, as the increase of the expansion angle. The deformation of the point contact mode is similar, so is the reaction force and the thermal reduction coefficient. The thermal reduction coefficient can vary from 0.98 to 0.97 for the thickness of 7–33 mm. This study provides a better understanding of the temperature effect on expansion tubes and an evaluation method with higher accuracy for the design.

Survey of CO2 Radiation Experimental Data in Relation with Planetary Entry

This paper focuses on a survey of experimental data related to radiation into CO2 plasma flows, which are encountered during Mars and Venus entries. The review emphasizes on VUV and IR radiation, since recent experimental efforts has been devoted to these wavelength ranges since they contribute mostly to CO2 plasma radiation. The main objective of the study is to identify the most attractive datasets for future crosscheck comparisons with the results obtained during future test campaigns with ESTHER shock-tube. The survey accounts for the results obtained in shock-tubes, expansion tube and plasma arc-jets for Mars and Venus test campaigns. The experimental results obtained for propulsion related studies have also been considered.

Expansion Tube Test Flow Design for Magnetohydrodynamic Aerobraking

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.

Temperature Measurement of HEK-X Expansion Tube Flow by Laser Absorption Spectroscopy

Temperature Measurement of HEK-X Expansion Tube Flow by Laser Absorption Spectroscopy

Expansion based composite tubes as energy absorbers for improved specific energy absorption: FEA based study

Thin tubes made of metals or composites are normally used as energy absorbers in the automobiles in a sacrificial manner. To lessen the operational cost the vehicles are to be made of lightweight materials like aluminum and composites. The tubes made of composite exhibit better specific energy absorption characteristics during an impact compared to their metallic counterparts. In most of the design implementations with either metals or composites, the energy absorption happens in the form of tubular compression. But the design of such absorbers should be tweaked to obtain controlled force–displacement patterns, under multiple dynamic conditions (Speeds of impact). Studies have revealed energy absorbers in the form of expansion metallic tubes can exhibit smooth force–displacement characteristics that are independent of impact velocities. The present study explores the use of tubes made of composite materials as expansion tubes to further improve specific energy absorption capacity.