Expansion Tunnel Research Articles

Magnetohydrodynamic drag force measurements in expansion tunnels using an accelerometer-based force balance

An accelerometer-based force balance has been used to measure the magnetohydrodynamic (MHD) drag force which arises when a magnetic field is present in a high-enthalpy ionised flow. This has been conducted using two expansion tunnels, with periods of steady test flow as low as 40μs . The use of this technique for MHD drag measurements is demonstrated and limitations are discussed. The results show that there is a measurable component of MHD drag in a flow-field where electrodynamic boundary conditions are matched to true flight. Furthermore, it is demonstrated that the measured forces can be attributed exclusively to the MHD effect, with good repeatability. The results indicated that at least 100μs of steady flow is required before the MHD force stabilises.

Development of a Fast-Response Diamond Calorimeter Heat Transfer Gauge

A robust fast-response calorimeter heat transfer gauge called the Diamond Heat Transfer Gauge has been developed for use in transient hypersonic ground test facilities. Gauges have been produced using discs of synthetic diamond thick as calorimeters with platinum thin-film resistance temperature detectors on the rear surface to measure temperature rise. Depending on calorimeter thickness and the grade of diamond used, the 99% rise time of the gauges is between 10.6 and . Test-time heat fluxes have been measured with the new gauges on a sharp wedge model and a blunt-nosed wedge model in flows with total enthalpies of over multiple shots in an expansion tunnel. Stagnation point measurements exceeded . Experimentally measured heat fluxes are shown to agree with surface-junction coaxial thermocouples and an empirical correlation on the stagnation point.

Influence and safety control of blasting vibration on existing lining for closely tunnel expansion

Based on the project of Erzhuangke expansion tunnel, this paper aims to investigate the influence of the blasting vibration caused by the expanded tunnel excavation on the adjacent existing lining, then a reasonable safety control criterion is proposed. The 3D finite element analysis, combined with field test, was employed to analyze peak particle velocity (PPV) and the maximum tensile stress of the existing lining under the closely tunnel blasting. The results demonstrate that the blasting vibration attenuation rate of existing lining is faster within the range of about 1.5B from the blasting source, then gradually tends to be flat, and the two sides are basically symmetrical distribution. However, the PPV and tensile stress of the side wall and arch waist of the existing lining nearest to the blasting source are significantly larger than those of other locations, so it is more likely to be damaged. The numerical simulation results are in good agreement with the field test, which also verifies the accuracy of the field test results and the rationality of the numerical simulation. Moreover, the safety control criterion based on the PPV and maximum tensile stress is established to ensure the operation safety of existing tunnels, and the PPV safety criterion of existing lining is 10.73 cm/s, so that the maximum allowable charge of a single section should be controlled within 41.05 kg.

Hypersonic Flow Simulation towards Space Propulsion Geometries

<div class="section abstract"><div class="htmlview paragraph">This work aims to expand the applicability of an open-source numerical tool to solve hypersonic gas dynamic flows for space propulsion geometries. This is done by validating the code using two well-known hypersonic test cases, the double cone and the hollow cylinder flare, used by the NATO Research and Technology Organization for the validation of hypersonic flight for laminar viscous-inviscid interactions (D. Knight, “RTO WG 10 - Test cases for CFD validation of hypersonic flight,” in 40th AIAA Aerospace Sciences Meeting & Exhibit, 2002). The Computational Fluid Dynamic (CFD) simulation is conducted using the two-temperature solver hy2Foam that is capable to study external aerodynamics in re-entry flows. In the present work the assessment of hy2Foam to solve hypersonic complex flow features with strong interactions including non-equilibrium effects was demonstrated. Freestream conditions with stagnation enthalpy of 5.44 MJ/kg and Mach number of 12.2, for the double cone case, and stagnation enthalpy of 5.07 MJ/kg and Mach number of 11.3 for the hollow cylinder case were considered. Comparison with newer existing numerical data and experimental data from LENS XX (Large Energy National Shock Expansion Tunnel Version 2) was also performed. Special attention was taken to the phenomenon of vibrational excitation of the molecules. Different vibrational non-equilibrium models were used and compared with the available data. Hy2Foam showed consistent results, with the vibrational non-equilibrium models reducing the discrepancies between numerical and experimental results.</div></div>

Spectral measurements of hypervelocity flow in an expansion tunnel

Atmospheric reentry vehicles and planetary probes fly through the atmosphere at hypervelocity speed. At such speed, there is a significant proportion of heat load to the vehicle surface due to radiative heating. Accurate prediction needs a good knowledge of the radiation spectrum properties. In this paper, a high-speed camera and spectrograph coupled to an intensified charge-coupled device have been implemented to investigate the radiation flow over a semi-cylinder model. The experiments were carried out in the JF16 expansion tunnel with secondary shock velocity of 7.9 km·s−1. Results show that the emission spectrum comprises several atomic lines and molecular band systems. We give detailed data of the radiation spectrum, shock shape, shock detached distance and radiation intensity varying with space and wavelength. This valuable experimental dataset will be helpful to validate computational fluid dynamics codes and radiation models, which equates to increased prediction accuracy of radiation heating. Also, some suggestions for spectral measurement in hypervelocity flow field were list in the end.

Turbulent Aeroheating Measurements on a 7-Deg Cone in High-Enthalpy CO2 Flow

A database of heating and pressure measurements on a 7 deg half-angle cone in a high-enthalpy expansion tunnel in has been generated to support development and validation of computational models to be employed in the design of future Mars missions. Laminar, transitional, and turbulent simulations were performed at the test conditions for comparisons with the data. Close agreement was obtained for both fully laminar and fully turbulent conditions. For the remaining transitional/turbulent conditions, agreement to within, or slightly more than, the estimated experimental uncertainty was demonstrated. The influence of transition intermittency and transition length models on predicted heating levels was demonstrated, as were differences in turbulent heating predictions generated using various algebraic, one-equation, and two-equation turbulence models. These comparisons provide some measure of confidence in turbulent simulation capabilities; however, because the data were not obtained on a relevant entry vehicle geometry, it is not possible to fully quantify computational uncertainties for the definition of Mars mission aerothermodynamic environments at this time.

Assessment of CFD Capability for Hypersonic Shock Wave Laminar Boundary Layer Interactions

The goal of this study is to assess CFD capability for the prediction of shock wave laminar boundary layer interactions at hypersonic velocities. More specifically, the flow field over a double-cone configuration is simulated using both perfect gas and non-equilibrium Navier–Stokes models. Computations are compared with recent experimental data obtained from measurements conducted in the LENS XX (Large Energy National Shock Expansion Tunnel Version 2) at the Calspan University of Buffalo Research Center (CUBRC). Four separate cases of freestream conditions are simulated to examine the models for a range of stagnation enthalpies from 5.44 MJ/kg to 21.77 MJ/kg and Mach numbers from 10.9 to 12.82.

Blunt-Body Aerothermodynamic Database from High-Enthalpy Carbon-Dioxide Testing in an Expansion Tunnel

An extensive database of heating, pressure, and flowfield measurements on a 70 deg sphere-cone blunt-body geometry in high-enthalpy carbon-dioxide flow has been generated through testing in an expansion tunnel. This database is intended to support development and validation of computational tools and methods to be employed in the design of future Mars missions. The test was conducted in an expansion tunnel in order to avoid uncertainties in the definition of freestream conditions noted in previous studies performed in reflected shock tunnels. Data were obtained across a wide range of test velocity/density conditions that produced various physical phenomena of interest, including laminar and transitional/turbulent boundary layers, nonreacting to completely dissociated postshock gas composition and shock-layer radiation. Flowfield computations were performed at the test conditions, and comparisons were made with the experimental data. Based on these comparisons, it was recommended that computational uncertainties on surface heating and pressure for laminar reacting-gas environments could be reduced to and , respectively. However, for flows with turbulence and shock-layer radiation, sufficient validation-quality data were not obtained in this study to make any conclusions with respect to uncertainties for those phenomena, which highlighted the need for further research in these areas.

Carbon Ablative Shock-Layer Radiation with High Surface Temperatures

Despite the prominence of carbon-based materials for use in thermal protection systems, much uncertainty remains in predicting thermochemical ablation rates at high surface temperatures. To address this issue, experiments using preheated graphite models with surface temperatures up to 3300 K were conducted in the X2 expansion tunnel at the University of Queensland. Calibrated shock-layer emission measurements in the wavelength region from 353 to 391 nm were taken to observe the effect of surface temperature on radiation from the CN violet and bands. Numerical simulations were conducted using US3D with modified Park as well as Zhluktov and Abe surface thermochemistry models. Lines of sight extracted from the flowfield data were simulated in NEQAIR to reproduce the experimental radiance profiles. It was found that the experimental CN radiance showed no significant dependence on surface temperature, whereas the numerical simulations predicted a monotonic increase with temperature for all surface models. Several potential mechanisms for these discrepancies have been identified and discussed.

Quantitative Emission Spectroscopy for Superorbital Reentry in Expansion Tube X2

A superorbital reentry flow was realized in the X2 expansion tunnel of the Centre for Hypersonics of the University of Queensland, resulting in measurements of electronic excitation temperature, electron density, and particle densities of neutral and ionized atomic nitrogen and oxygen. A rectangular cold wall model was exposed to a flow corresponding to a flight equivalent velocity. Vacuum ultraviolet optical emission spectroscopy in the wavelength range between 116 and 185 nm was conducted through a window at the stagnation point. Spatially resolved optical emission spectroscopy of the stagnation streamline in the near-infrared wavelength range from 695 to 880 nm was conducted, analyzing the flow from the side. Population densities of excited atomic states, electronic excitation temperatures, and electron and ion densities were determined by analyzing the radiative transport in the flowfield. Additionally, the flowfield was numerically simulated using the code URANUS. Agreement in electron density () and electron temperature () in the equilibrium region is observed between the numerical simulations and the measurement. Significant differences between measurement and simulation in the distribution of the electron temperature at the shock are attributed to the modeling of the URANUS electron temperature.

Expansion Tunnel Experiments of Earth Reentry Flow with Surface Ablation

The thermal protection system of a reentry vehicle must endure extreme heating loads, leading to high surface temperatures and associated phenomena such as thermochemical ablation. Accurate modeling and prediction of these processes are critical for determining heat-shield sizing requirements; however, large uncertainties still remain. Due to the high costs associated with flight tests, ground testing remains an economical option for addressing these uncertainties. In this study, experiments with electrically preheated graphite samples are conducted in the University of Queensland’s X-2 expansion tunnel. Calibrated spectral measurements of the shock-layer emissions are taken in the wavelength region of 353 to 391 nm, targeting the carbon–nitrogen violet band for surface temperatures from 1770 to 2410 K. It is observed that carbon–nitrogen concentrations clearly increased within the boundary layer at higher surface temperatures. Numerical simulations fail to reproduce this behavior and instead indicate that production should be relatively constant. Increased levels of carbon–nitrogen radiation with surface temperature are also found throughout the entire shock layer and even the freestream, another observation that is not predicted by the simulations. It is proposed that this effect is due to spallation; however, further experiments are required to verify this.

Numerical Modeling of Earth Reentry Flow with Surface Ablation

Vehicles entering planetary atmospheres at high speed require an ablative heat shield to withstand the high thermal energy flux to the body. The interaction between the ablative products and the flowfield is not well characterized. In this study, numerical simulations were conducted to investigate the influence of carbon ablation on shock-layer radiation. Data collected from experiments performed in the X-2 expansion tunnel at the University of Queensland were used to compare to the simulations. The model was a short half-cylinder made of isomolded graphite and was tested in Earth entry flow. The graphite model was heated within a temperature range of 1770–2410 K over the course of the experimental campaign. The radiation emitted from the CN violet bands was measured by ultraviolet spectrometry in a spectral range from 353 to 391 nm. The simulations used the Park as well as Zhluktov and Abe finite-rate surface kinetic models for determining the chemical state of the ablating boundary layer. The Park model consistently overpredicted the radiative heat fluxes, but better comparison was achieved when a modified nitridation rate was used. The Zhluktov and Abe predictions displayed good agreement with the measured radiative heat fluxes at 1770 K but remained well below the measured values at the higher wall temperatures. The lack of a nitridation mechanism in the Zhluktov and Abe model is suggested as the reason for these underpredictions.

Near-Surface Carbon-Dioxide Tunable Diode Laser Absorption Spectroscopy Concentration Measurements in Hypervelocity Flow

Measurements of carbon-dioxide concentration are made in the LENS-XX expansion tunnel at the Calspan—University at Buffalo Research Center to investigate the effects of surface catalysis in hypersonic flows. A tunable diode laser absorption spectroscopy setup probes the P36e absorption line of the combination band at . Numerical simulations are computed with data-parallel line relaxation using the specified reaction efficiency surface catalysis model. Absorption measurements adjacent to the surface of an aluminum cylinder correlate well with simulations indicating low catalytic efficiency at the surface. The velocity, density, freestream temperature, specific enthalpy, and stagnation point pitot pressure of the run are , , 1328.4 K, , and 31.6 kPa, respectively. Simulation of the absorption spectrum is performed using a nonhomogeneous line-by-line code using the high-resolution transmission molecular absorption database for spectroscopic parameters. Input data for the code are obtained from computational fluid dynamics simulations of the cylinder and facility. The specified reaction efficiency for the mechanism is determined inversely using detailed computational fluid dynamics and comparisons to experimental measurements. The best agreement was found for to 0.0005, indicating that the coupled line-by-line code and computational fluid dynamics approach is useful for assessing near-surface composition using tunable diode laser absorption measurements of hypersonic flows.

Microwave Shock-Speed Diagnostic Development and Analysis of Expansion Tunnel Viscous Effects

The development of a nonintrusive microwave shock-speed measurement for expansion tunnels is presented, based on microwave standing-wave reflection. Testing is performed in a large-scale expansion-tunnel facility, with the goal of characterizing viscous effects. Expansion tunnels generate high-enthalpy test conditions for short test times, and the test gas is never heated such that excessive freestream dissociation or ionization occurs. The microwave system measures primary and secondary shock speeds accurately and with high spatial resolution along the length of the facility, yielding more accurate freestream conditions. It is shown to be both practical and low cost. The high spatial resolution along the tunnel is used to assess shock-speed attenuation. Negligible shock attenuation is found over a wide range of test conditions and gases, attributed to the large diameter of the facility’s driven and expansion tubes. Shock-tube boundary-layer growth solutions based on Mirels’s theory (“Shock Tube Test Time Limitation Due to Turbulent-Wall Boundary Layer,” AIAA Journal, Vol. 2, No. 1, 1964, pp. 84–93) and a Pitot-probe survey confirm that, in the current facility, the test conditions should not be adversely affected by viscous effects. Mirels’s theory is also used to determine the displacement thicknesses for quasi-one-dimensional analyses, showing how viscous effects become significant in long, smaller-diameter facilities. The high spatial resolution allows for local shock-speed information to evaluate nonideal secondary-diaphragm ruptures. Additionally, when postshock electron-density levels are near the cutoff required for standing-wave reflection, test-gas velocities are measured rather than shock velocities.

Hypervelocity shock standoff on spheres in air

To provide data for the validation of computational fluid dynamics models, measurements of the shock standoff distance on spheres in hypervelocity flows have been made. Test flows of air at 8.7 and 9.7 km/s were generated in the X2 expansion tunnel fitted with a Mach 10 nozzle. High-speed video images were analysed with a least-squares shape-fitting algorithm. Assuming a spherical shock shape near the nose enabled increased resolution measurements beyond the native pixel size. Normalised shock standoff distances, \(\Delta \)/\(D\), in the range 0.03–0.04 were measured, with sphere diameters, \(D\), of 40, 60 and 80 mm.

Proposed Vertical Expansion Tunnel

It is proposed that the adverse effects from secondary diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. This proposed configuration is termed the vertical expansion tunnel. Two benefits are 1) the removal of the diaphragm particulates in the test gas after its rupture, and 2) the elimination of the wave system that is a result of a real secondary diaphragm having a finite mass and thickness. An inviscid perfect-gas analysis and quasi-one-dimensional Euler computations are performed to find the available effective reservoir conditions (pressure and mass specific enthalpy) and useful test time in a vertical expansion tunnel for comparison to a conventional expansion tunnel and a reflected-shock tunnel. The maximum effective reservoir conditions of the vertical expansion tunnel are higher than the reflected-shock tunnel but lower than the expansion tunnel. The useful test time in the vertical expansion tunnel is slightly longer than the expansion tunnel but shorter than the reflected-shock tunnel. If some sacrifice of the effective reservoir conditions can be made, the vertical expansion tunnel could be used in hypervelocity ground testing without the problems associated with secondary diaphragm rupture.

Experimental and Numerical Investigation ofHypervelocity Carbon Dioxide Flow over Blunt Bodies

This paper represents ongoing efforts to study high-enthalpy carbon dioxide flows in anticipation of the upcoming Mars Science Laboratory and future missions. The work is motivated by observed anomalies between experimental and numerical studies in hypervelocity impulse facilities. In this study, experiments are conducted in the hypervelocity expansion tube that, by virtue of its flow acceleration process, exhibits minimal freestream dissociation in comparison with reflected shock tunnels, simplifying comparison with simulations. Shock shapes of the laboratory aeroshell at angles of attack of 0, 11, and 16 deg and spherical geometries are in very good agreement with simulations incorporating detailed thermochemical modeling. Laboratory shock shapes at a 0 deg of attack are also in good agreement with data from the LENS X expansion tunnel facility, confirming results are facility-independent for the same type of flow acceleration. The shock standoff distance is sensitive to the thermochemical state and is used as an experimental measurable for comparison with simulations and two different theoretical models. For low-density small-scale experiments, it is seen that models based upon assumptions of large binary scaling values do not match the experimental and numerical results. In an effort to address surface chemistry issues arising in high-enthalpy groundtest experiments, spherical stagnation point and aeroshell heat transfer distributions are also compared with the simulation. Heat transfer distributions over the aeroshell at the three angles of attack are in reasonable agreement with simulations, and the data fall within the noncatalytic and supercatalytic solutions.

Scramjet Experiments in an Expansion Tunnel: Evaluated Using a Quasi-Steady Analysis Technique

As scramjet 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 scramjet configurations at high Mach numbers, an expansion-tunnel facility is used to test a generic two-dimensional scramjet 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 scramjet 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.

Comparison of Mach 10 Scramjet Measurements from Different Impulse Facilities

A comparison is made between scramjet pressure data taken in two different impulse facilities, a reflected shock tunnel and an expansion tunnel, to provide verification of flow similarity. A two-dimensional hydrogen-fueled scramjet was tested in both facilities at a Mach 10, 66 kPa dynamic pressure, flight-replication condition. The entire flowfield was reproduced, including the inlet, combustor, and thrust nozzle. The expansion-tunnel model was a 40%-scaled model of that investigated in the shock tunnel, as the generated core flow was smaller. Applying density-length scaling, the density of the freestream was increased by a factor of 2.5 in the expansion tube to maintain similarity between the experimental setups. Results show agreement within the experimental uncertainty between the two data sets at similar fuel equivalence ratios, indicating the repeatability of scramjet pressure measurements, independent of the experimental facility used. It is further demonstrated that density-length scaling is appropriate for the flows generated in the investigated scramjet engines. Verification is also provided of the analysis technique used to process experimental scramjet data sets that involve transient inflow conditions. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Observation of an Ablating Surface in Expansion Tunnel Flow

The observation of an ablating surface in expansion tunnel flow was reported. A one-dimensional (1-D) semi-infinite analysis was performed using an empirical estimation of the stagnation-point heat flux. A surface temperature change for epoxy of 178 K in 50 μs was calculated, which is sufficient for the epoxy coating to commence ablation during the steady test period. The 10% temperature penetration depth is 6 μm in 50 μs. The luminosity from substantial portions of the model and shock-layer flow was visualized using a Shimadzu HPV1 high-speed charge-coupled device (CCD) video camera recording at 500 kfps with a 1 μs exposure time. The uniform image response over the axisymmetric model implies the shock-layer gas irradiance is high immediately behind the shock and decreases rapidly as the model surface is approached. The measurements showed that use of an epoxy coating results in greatly increased CN and C2 radiation, much greater than when no coating is employed.