Test Time Increase by Delaying Driver Gas Contamination for Reflected Shock Tunnels

Sudani, Norikazu; Valiferdowsi, Bahram; Hornung, H. G.

doi:10.2514/2.1138

Cited by 21 publications

(12 citation statements)

References 7 publications

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“…-Driver-gas composition. Experiments performed using one of the driver-gas-contamination detectors mentioned above have shown that the onset of driver-gas contamination may be delayed by causing the condition to be slightly under-tailored [18]. This was achieved in our experiments by increasing the proportion of helium to argon in the compression tube to 80%/20%, while keeping the pressure of the mixture constant.…”

Section: Methodsmentioning

confidence: 89%

“…The arrival of driver gas is more difficult to determine because it is not usually accompanied by large changes in static pressure, pitot pressure or heat flux. Several techniques have been developed to determine the time of arrival of the driver gas, the most successful and commonly adopted of which use the change in shock angle on a wedge caused by the different ratio of specific heats for the diatomic test gas and the monatomic driver gas [18,14]. These techniques work well in large facilities, but are more difficult to implement and less precise in a small nozzle such as that of T2, shown in Fig.…”

Section: Flow Facility and Conditionsmentioning

confidence: 99%

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Investigation of hypersonic nozzle flow uniformity using NO fluorescence

2006

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Section: Methodsmentioning

confidence: 89%

Section: Flow Facility and Conditionsmentioning

confidence: 99%

Investigation of hypersonic nozzle flow uniformity using NO fluorescence

2006

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“…59 The degree of offtailoring has a large effect on the arrival time t dgc of driver gas at medium and high enthalpy ͑but not low enthalpy͒, with t dgc advanced by overtailoring and delayed by undertailoring. 60,61 Condition C4 was consistently overtailored and expected to suffer significant contamination by time t las . Condition C2, only marginally contaminated for a tailored interface, was consistently undertailored and thus expected to suffer contamination of no more than a few percent until several hundred microseconds after t las .…”

Section: Test Time Disturbances and Unsteadinessmentioning

confidence: 99%

Separation length in high-enthalpy shock/boundary-layer interaction

Davis

Sturtevant

2000

Physics of Fluids

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Experiments were performed in the T5 Hypervelocity Shock Tunnel to investigate nonequilibrium real-gas effects on separation length using a double-wedge geometry and nitrogen test gas. Local external flow conditions were estimated by computing the inviscid nonequilibrium flow field. A new scaling parameter was developed to approximately account for wall temperature effects on separation length for a laminar nonreacting boundary layer and arbitrary viscosity law. A classification was introduced to divide mechanisms for real-gas effects into those acting internal and external to viscous regions of the flow. Internal mechanisms were further subdivided into those arising upstream and downstream of separation. Analysis based on the ideal dissociating gas model and a scaling law for separation length of a nonreacting boundary layer showed that external mechanisms due to dissociation may decrease separation length at low incidence but depend on the free-stream dissociation at high incidence. A limited numerical study of reacting boundary layers showed that internal mechanisms due to recombination occurring in the boundary layer upstream of separation cause a slight decrease in separation length relative to a nonreacting boundary layer with the same external conditions. Correlations were obtained of experimentally measured separation length using local external flow parameters computed for reacting flow, which scales out external mechanisms but not internal mechanisms. These showed the importance of the new scaling parameter in high-enthalpy flows, a linear relationship between separation length and reattachment pressure ratio, and a Reynolds-number effect for transitional interactions. A significant increase in scaled separation length was observed in the experimental data at high enthalpy. The increase was attributed to an internal mechanism arising from recombination in the free-shear layer downstream of separation, perhaps altering its velocity profile. This real-gas effect depends on the combined presence of free-stream dissociation and a cold wall.

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“…Attempting to extend the duration of the test flow through the addition of an annular gas-bleed arrangement in the shock tube (as has been done previously, for example by Sudani et al (2000)) is unlikely to be successful at these conditions because the contaminating structures appear to be convected into the nozzle along the tube centreline. A particle trap arrangement on the shock tube centreline was investigated by Chue and Eitelberg (1998).…”

Section: Discussionmentioning

confidence: 99%

“…A vortex is seen to separate from the head of the driver gas structure near the shock tube centreline (frames 5600 and 5800 µs), and the contaminating driver gas accelerates along the centreline of the shock tube and into the nozzle throat (frames 6000 and 6200 µs). This mechanism causes the driver gas to arrive in the test flow prematurely here and is possibly the mechanism that causes driver gas to arrive prematurely in the test flow for over-tailored conditions in other facilities (Sudani et al, 2000).…”

Section: Over-tailored Mode Interactionmentioning

confidence: 99%

Simulation of a complete reflected shock tunnel showing a vortex mechanism for flow contamination

2006

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Abstract. Simulations of a complete reflected shock tunnel facility have been performed with the aim of providing a better understanding of the flow through these facilities. In particular, the analysis is focused on the premature contamination of the test flow with the driver gas. The axisymmetric simulations model the full geometry of the shock tunnel and incorporate an iris-based model of the primary diaphragm rupture mechanics, an ideal secondary diaphragm and account for turbulence in the shock tube boundary layer with the Baldwin-Lomax eddy viscosity model. Two operating conditions were examined: one resulting in an over-tailored mode of operation and the other resulting in approximately tailored operation. The accuracy of the simulations is assessed through comparison with experimental measurements of static pressure, pitot pressure and stagnation temperature. It is shown that the widely-accepted driver gas contamination mechanism in which driver gas 'jets' along the walls through action of the bifurcated foot of the reflected shock, does not directly transport the driver gas to the nozzle at these conditions. Instead, driver gas laden vortices are generated by the bifurcated reflected shock. These vortices prevent jetting of the driver gas along the walls and convect driver gas away from the shock tube wall and downstream into the nozzle. Additional vorticity generated by the interaction of the reflected shock and the contact surface enhances the process in the over-tailored case. However, the basic mechanism appears to operate in a similar way for both the over-tailored and the approximately tailored conditions. 2 R.

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Test Time Increase by Delaying Driver Gas Contamination for Reflected Shock Tunnels

Cited by 21 publications

References 7 publications

Investigation of hypersonic nozzle flow uniformity using NO fluorescence

Investigation of hypersonic nozzle flow uniformity using NO fluorescence

Separation length in high-enthalpy shock/boundary-layer interaction

Simulation of a complete reflected shock tunnel showing a vortex mechanism for flow contamination

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