Heat-transfer rates from a non-equilibrium hypersonic air flow to flat plates at zero and 12° incidence have been measured in a free piston shock tunnel at stagnation enthalpy levels up to 51 MJ kg−1. Nozzle flow conditions resulted in test section velocities up to 8·1 km 8−1 and in an experimental regime in which the free stream was chemically frozen and the flat-plate boundary layer was laminar. Estimates of the gas-phase and surface-reaction Damkohler numbers have been made and the heat-transfer results are discussed in this context. At the highest test-section densities non-equilibrium endothermic gas phase reactions involving oxygen atoms in the boundary layer are suggested as a possible mechanism for the observed low heattransfer rates.

We analyze the effect of image noise on the estimation of fringe orientation in principle and interpret the application of a texture-analysis technique to the problem of estimating fringe orientation in interferograms. The gradient of a Gaussian filter and neighboring-direction averaging are shown to meet the requirements of fringe-orientation estimation by reduction of the effects of low-frequency background and contrast variances as well as high-frequency random image noise. The technique also improves inaccurate orientation estimation at low-modulation points, such as fringe centers and broken fringes. Experiments demonstrate that the scales of the Gaussian gradient filter and the direction averaging should be chosen according to the fringe spacings of the interferograms.

Measurements of heat transfer in the separated region behind a rearward-facing step in a hypersonic high-enthalpy stream, are described. The range of enthalpies considered was much greater than those reported previously in the literature. High-response surface thermocouples were used to measure the heat-transfer rates. Flow visualization by way of interferograms, with a Mach-Zehnder interferometer, were obtained and improved visualization was further facilitated by digitizing the interferograms and using Fourier analysis to determine fringe positions. This then provided a phase map of the flow region in which the phase was colour coded to emphasize flow characteristics.

Experiments by Phan & Stollery (In Proc . 14 th International Symposium on Shock Tubes and Waves , pp. 519-526 (1983)) indicated the presence of a supersonic vortex ring with an embedded rearward-facing shock in the unsteady flow that follows the emergence of a normal shock from a circular tube. The vortex flow is supersonic in the sense that the on-axis flow is supersonic in the frame of reference of the vortex ring. In the present work this flow phenomenon is studied by using differential interferometry and a detailed description of the flow-starting process is given. A simplified quasi-steady calculation is performed and a comparison is made with previously measured pressures in the flow field. These results are in agreement with the physical description of the flow development.

We apply the representer method, a data assimilation algorithm, to single-phase Darcy flow in porous media. The measurement array that yields the assimilated data can be expressed as a vector of linear functionals of pressure. The a priori discretization errors in the representer method are analyzed in terms of the convergence properties of the underlying numerical schemes used in each part of the algorithm. We formulate some proof-of-concept numerical experiments that illustrate the error analysis.