Measurement of heat transfer in superorbital flows

Palmer, Robert A (2000). Measurement of heat transfer in superorbital flows PhD Thesis, School of Engineering, The University of Queensland.

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Author Palmer, Robert A
Thesis Title Measurement of heat transfer in superorbital flows
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2000
Thesis type PhD Thesis
Supervisor Richard Morgan
Total pages 174
Language eng
Subjects 09 Engineering
Formatted abstract
Experimental techniques were developed and applied to the problem o f quantifying heat transfer to blunt body models in superorbital expansion tube flows o f air. In particular, the influences of convective and radiant heat transfer were examined. Several expansion tube conditions were studied experimentally and analytically. The X I and X 2 expan­ sion tubes at the University of Queensland were used to produce these conditions. Total enthalpy levels of the flow conditions ranged from 26 to 105 M J/kg. Several o f these con­ ditions caused significant ionisation and complete dissociation of the model shock layer. Therefore, the experimental flow conditions  induced phenom ena which are important in superorbital reentry trajectories.

A thin-skin calorimeter heat-flux sensor was designed and developed. This sensor was suitable for  superorbital stagnation-point measurements because o f its durability, fast response (~ 3 /zs) and demonstrated ability to measure high heat flux levels (up to 530 M W /m2). Rigorous calibration and  analysis o f the sensor response indicated that the sensitivity o f the sensors could be modelled  by considering heat conduction in the copper calorimeter element and the attached constantan thermocouple wire. Expansion tube tests indicated that the calibrated sensor provided a precise,
repeatable measurement capability. An electronics system was developed for the heat flux sensor that minimised the electromagnetic interference induced by the expansion tube flow.

Verification o f the accuracy o f the heat flux sensor was achieved by comparison of measured results with CFD results and a commonly-used convective heat flux correla­ tion. The flow condition used for this verification was at relatively low enthalpy (26 M J/kg) and did not produce significant levels of radiant heating. The heat flux sensor was then applied to high enthalpy, radiating flow conditions characteristic of superorbital re-entry. The flowfield physics o f such flows is poorly understood and there is lim ited relevant experimental data. Measurements indicated that there were significant differences between the measured levels and predictions of commonly-used convective and radiative stagnation heating correlations.

The possibility of separating radiant and convective heat flux components using a reflective aluminium-coated sensor was investigated. It was found that this technique was not practically possible due to the vacuum ultraviolet wavelengths produced by superorbital flows. Therefore, measurements were restricted to total heat flux.

A strong indication of the role of radiant heating was given by the dependency of measured heat flux on small variations of the nominal flow conditions. An extremely strong dependence of measured heat flux on free stream velocity was detected at 13.7 km/s equivalent flight velocity. Sensitivity analysis of the flow processes in the expansion tube indicated that the strength of this dependence implied high levels of radiant flux in comparison with convective flux. A similar analysis of results at 11.1 km/s indicated that at that condition, radiant flux was probably a much lower proportion of total heat flux than at 13.7 km/s.

The measurements of this thesis indicate that for certain flow conditions, there is significant radiant transfer to the stagnation point of reentry models in superorbital expansion tube flows. The instrumentation and analysis techniques used are generally applicable to expansion tube flows and provide a strong foundation for future research.
Keyword Heat Transmission
Shock Tubes

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Mon, 04 Aug 2014, 16:32:11 EST by Asma Asrar Qureshi on behalf of Scholarly Communication and Digitisation Service