Measurement of transient gas temperature distributions by Abel inversion and computer tomography.

The modified reversal method, numerical Abel inversion, and optical computer tomography techniques have been developed and used to measure absorption coefficient and temperature distributions in the quasi-steady flame of a Hefner candle and within the tube flow of a single-stage gas gun. The well-defined flame of the Hefner candle was used to compare the three methods. The reversal method, as expected, gave results averaged over the flame width. Both the Abel inversion and tomography produced similar radial temperature profiles but tomography proved to be less sensitive to experimental errors. The gaseous propellant mixtures Osub2/Hsub2/He and Osub2/Hsub2/He/CO have been used to drive the gas gun. Tomography, for the first time, has yielded the radial temperature and absorption coefficient profiles of a gun tube flow. The absorption coefficient distributions indicate axial and radial segregation of lighter and heavier gas components in the tube flow. The temperature profiles demonstrat e a discrepancy with the velocity profiles, i.e., the thermal boundary layer is much thinner than the velocity boundary layer. This does not comply with current interior ballistic modelling which often relies on Reynolds' analogy to compute thermal boundary layers. However, Reynolds' analogy is strictly applicable only to steady state problems but not to transient phenomena.