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  • Cambridge University Press  (3)
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  • 1
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    Experiments on supersonic combustion ramjet propulsion in a shock tunnel (1995)
    Cambridge University Press
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    Publication Date: 1995-08-10
    Description: Measurements have been made of the propulsive effect of supersonic combustion ramjets incorporated into a simple axisymmetric model in a free piston shock tunnel. The nominal Mach number was 6, and the stagnation enthalpy varied from 2.8 to 8.5 MJ kg-1. A mixture of 13% silane and 87% hydrogen was used as fuel, and experiments were conducted at equivalence ratios up to approximately 0.8. The measurements involved the axial force on the model, and were made using a stress wave force balance, which is a recently developed technique for measuring forces in shock tunnels. A net thrust was experienced up to a stagnation enthalpy of 3.7 MJ kg-1, but as the stagnation enthalpy increased, an increasing net drag was recorded. Pitot and static pressure measurements showed that the combustion was supersonic. The results were found to compare satisfactorily with predictions based on established theoretical models, used with some simplifying approximations. The rapid reduction of net thrust with increasing stagnation enthalpy was seen to arise from increasing precombustion temperature, showing the need to control this variable if thrust performance was to be maintained over a range of stagnation enthalpies. Both the inviscid and viscous drag were seen to be relatively insensitive to stagnation enthalpy, with the combustion chambers making a particularly significant contribution to drag. The maximum fuel specific impulse achieved in the experiments was only 175 s, but the theory indicates that there is considerable scope for improvement on this through aerodynamic design. © 1995, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 2
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    Skin-friction measurements in high-enthalpy hypersonic boundary layers (2003)
    Cambridge University Press
    Details
    Publication Date: 2003-05-25
    Description: Skin-friction measurements are reported for high-enthalpy and high-Mach-number laminar, transitional and turbulent boundary layers. The measurements were performed in a free-piston shock tunnel with air-flow Mach number, stagnation enthalpy and Reynolds numbers in the ranges of 4.4-6.7, 3-13 MJ kg-1 and 0.16× 106-21 × 106, respectively. Wall temperatures were near 300 K and this resulted in ratios of wall enthalpy to flow-stagnation enthalpy in the range of 0.1-0.02. The experiments were performed using rectangular ducts. The measurements were accomplished using a new skin-friction gauge that was developed for impulse facility testing. The gauge was an acceleration compensated piezoelectric transducer and had a lowest natural frequency near 40 kHz. Turbulent skin-friction levels were measured to within a typical uncertainty of ±7%. The systematic uncertainty in measured skin-friction coefficient was high for the tested laminar conditions; however, to within experimental uncertainty, the skin-friction and heat-transfer measurements were in agreement with the laminar theory of van Driest (1952). For predicting turbulent skin-friction coefficient, it was established that, for the range of Mach numbers and Reynolds numbers of the experiments, with cold walls and boundary layers approaching the turbulent equilibrium state, the Spalding & Chi (1964) method was the most suitable of the theories tested. It was also established that if the heat transfer rate to the wall is to be predicted, then the Spalding & Chi (1964) method should be used in conjunction with a Reynolds analogy factor near unity. If more accurate results are required, then an experimentally observed relationship between the Reynolds analogy factor and the skin-friction coefficient may be applied.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 3
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    Test flow disturbances in an expansion tube (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-12-01
    Description: The operation of an expansion tube is investigated with particular attention given to the test flow disturbances which have limited their utility in the past. Theoretical bounds for the duration of uniform test flow are first explored using one-dimensional ideal-gas relations, together with shock-tube boundary-layer entrainment effects. It is seen that test flow duration is limited either by the arrival of the downstream edge of the test-gas unsteady expansion or by the arrival of the upstream edge of this expansion after it has been reflected from the driver-test gas interface. These bounds are seen to be in good agreement with measurements made with large driver-gas expansion ratios. For small expansion ratios additional disturbances are observed in the test gas. Similar disturbances are also observed in the driver gas. It is postulated that these disturbances first appear in the driver gas and are transmitted into the test gas before the test gas is expanded. These disturbances remain with the test gas as it is expanded and subsequently produce unsteady conditions at the test section. Theoretical calculations for the range of frequencies which occur in the test gas before the expansion are obtained by modelling the disturbances as acoustic waves. It is shown that only the high-frequency components of the disturbances in the driver gas can penetrate the driver-test gas interface and this provides a mechanism for suppressing disturbances in the test gas. Additional analytical calculations for the shift in frequency produced as an acoustic wave traverses an unsteady expansion are also presented and it is shown that all frequencies of a given acoustic wave mode converge to one frequency. This focusing of frequencies is seen to occur in three different facilities. © 1992, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
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