Performance considerations for expansion tube operation with a shock-heated secondary driver

Gildfind, David; James, Christopher M.; Toniato, Pierpaolo; Morgan, Richard G.

doi:10.1017/jfm.2015.349

Cited by 33 publications

(47 citation statements)

References 22 publications

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“…The useful flow interval begins when the downstream edge of the expanded test gas reaches the test piece; and ends at the arrival of the downstream edge of the unsteady expansion. The current X3 configuration incorporates a secondary driver which consists of an additional volume of gas (helium) between the primary diaphragm and test gas, to improve performance [7], however is not discussed here. A schematic of X3's current configuration and the evolution of flow processes is shown in Fig.…”

Section: X3 Expansion Tubementioning

confidence: 99%

X3 expansion tube driver gas spectroscopy and temperature measurements

et al. 2017

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The University of Queensland's X3 facility is a large, free-piston driven expansion tube used for superorbital and high Mach number scramjet aerothermodynamic studies. X3's powerful test flow is initiated by firing its heavy piston into its driver gas -a mixture of argon and helium. Knowledge of the initial and transient temperature behavior of the driver gas is critical to correctly characterize the driver performance, losses and all subsequent expansion tube flow processes. However, the driver gas temperature is not currently measured during routine experimentation and there is limited evidence of its measurement in other international facilities. During recent scramjet flow development in X3, lower than expected experimentally measured shock speeds through helium indicated an effective driver temperature of approximately 2400 K, compared to a temperature of 3743 K at the time of diaphragm rupture for an ideal isentropic driver gas compression. These performance losses motivate this study, which examines initial and peak driver gas temperatures. The study shows that the initial steady-state driver gas temperature, once the filling process ceases, can be approximated by the external driver tube wall temperature. During filling, a net increase in driver gas temperature occurs due to compression heating, as well as, Joule-Thomson effect for helium. Optical emission spectroscopy was then used to resolve the peak driver gas temperature, during piston compression, for a Mach 10 scramjet operating condition. The driver gas emission spectrum exhibits a significant background radiation component, with prominent spectral lines attributed to contamination of the flow. A blackbody approximation of background radiation suggests a peak driver gas temperature of 3200±100 K. Application of the line-ratio method to two argon lines at 763.5 and 772.4 nm suggests a temperature of 3500±750 K. Comparison of these estimates to the ideal isentropic driver gas temperature at diaphragm rupture, 3743 K, suggests losses in the driver gas temperature during the compression process are not extensive for X3, and further that the lower than expected shock speeds are likely primarily due to pressure losses during driver gas expansion through the diaphragm and at the driver-to-driven tube area change. Nomenclature A = Einstein coefficient for spontaneous emission, s -1 a = sound speed, m/s c = speed of light = 3×10 8 m/s E = energy of the upper atomic state, eV g = statistical weight of upper atomic state h = Planck's constant = 4.136×10 -15 eV.s I = spectral intensity, counts K = Boltzmann's constant = 8.617×10 -5 eV/K L = spectral radiance, W/m 2 /sr/nm M = molecular weight, g/mol P i = driver gas initial pressure, Pa P p = driver gas pressure at rupture, Pa R = gas constant, J/mol/K T abs = absolute temperature, K T ex = excitation temperature, K T i = driver gas initial temperature, K T p = driver gas average peak temperature, K γ = ratio of specific heats λ = wavelength, m 1 Undergraduate, School of Mechanical and Mining Engineering, AIA...

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Section: X3 Expansion Tubementioning

confidence: 99%

X3 expansion tube driver gas spectroscopy and temperature measurements

et al. 2017

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“…The facilities of interest are the X2 and X3 at the University of Queensland. Full facility descriptions can be found in [2,3]. Timescales for expansion tube flows tend to scale with characteristic length.…”

Section: Fig 1 Expansion Tube Operation and Diaphragm Fragmentation mentioning

confidence: 99%

“…This paper analyses a representative low enthalpy, X2, scramjet condition in detail, Case 2f, as documented in [2] (see Figure 2 for fill conditions). Some data is presented for the high enthalpy Case 4e.…”

Section: Fig 1 Expansion Tube Operation and Diaphragm Fragmentation mentioning

confidence: 99%

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CFD Analysis of Early Diaphragm Removal in Expansion Tubes

Burgess

Gildfind

2016

AMM

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Abstract. Impulse facilities generate transient high-velocity gas flows for ground testing in aerodynamics. The expansion tube is the facility type with the highest performance capability in terms of total flow enthalpy and total pressure, and is particularly useful for studies of atmospheric re-entry, chemical kinetics, scramjet flight and supersonic combustion. In operation, a thin film diaphragm that initially partitions two tube sections is required to rupture under the force of a shock-wave. Fragmented pieces are accelerated with the flow and can damage test models and instrumentation, and the rupture process itself affects flow properties. It has been proposed to replace the diaphragm with a fast open valve that clears the tube prior to shock arrival. This paper investigates the effect of early valve opening on the test flow.An inviscid, axisymmetric model was created using Eilmer3, a compressible CFD solver developed at the University of Queensland. Early valve opening was simulated at varying times for instantaneous diaphragm removal. The result was the formation of a secondary shock and expansion wave. The primary shockwave reaches the test section at a higher velocity due to passing through the expansion wave, creating a faster, higher-pressure test flow, but also higher temperature, leading to substantially reduced Mach number. The interactions with the secondary waves were found to cause unsteadiness in test flow properties.

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“…UQ's program aimed to establish why test flows were often noisy and unsteady, and how this [4].) 6 problem could be eliminated. They found that the key to preventing these disturbances was conducting tests in what is known as an over-tailored configuration.…”

Section: Shock Expansion Tunnelsmentioning

confidence: 99%

A new method of measuring shock expansion tube test flow velocities

Crombie¹

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[Email address] ii AcknowledgementsThere are several individuals without whom the completion of this body of work would not have been possible. These people should not go without acknowledgement.Firstly, thanks must go to Tim Cullen for being one the people who conducted testing in the University of Queensland's X2 shock Expansion Tube facility on my behalf.Secondly Christopher James, who also conducted experiments and was very generous with his time in helping me to understand the results.Thirdly, The University of Queensland and the department of hypersonics who made their facilities available for experimentation along with a significant manufacturing budget to produce all the required instruments. AbstractShock expansion tubes are an important tool in the field of hypersonic research. However, these facilities possess a major weakness in the fact there is a great deal of uncertainty associated with the properties of the test flows that they produce.In an attempt to better characterise these properties, an instrument which was capable of measuring the velocity of the test flows produced by shock expansion tubes was to be designed and tested. This instrument would consist of two pitot probes which would be mounted in a shock tube at different locations to detect the arrival of the test gas. Based on the time difference between the arrival of this gas at each probe, its velocity could be calculated.Two probes were designed and manufactured for the testing of this concept in the University of Queensland's X2 shock expansion tube. The design, shown in the image to the right, was created with consideration given to the facts that the probe had to; be structurally capable of withstanding the hypersonic flow environment, protect the pressure transducer from this harsh environment, respond rapidly to changes in pitot pressure, be able to take measurements through the thickest boundary layers, create the smallest disturbance to the test flow possible, and record data which was not adversely affected by noise.This design was tested in the X2, which was configured to produce two high enthalpy test flows with velocities of 9468.1m/s and 9656.5m/s.Over the two experiments, the probes measured the velocity of the two test flows to within 3% of the current best estimates, although determining the arrival time of the test gas at each probe was difficult and there was large potential for error. The data recorded by the two probes was also sufficiently noise free and the instruments responded rapidly to any changes in pitot pressure.There was also no evidence that the probes were significantly disrupting the test flow, however further testing was required to confirm this. In summary, the design was a success and further testing was warranted to confirm these results and develop the concept further.iv

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Performance considerations for expansion tube operation with a shock-heated secondary driver

Cited by 33 publications

References 22 publications

X3 expansion tube driver gas spectroscopy and temperature measurements

X3 expansion tube driver gas spectroscopy and temperature measurements

CFD Analysis of Early Diaphragm Removal in Expansion Tubes

A new method of measuring shock expansion tube test flow velocities

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