The effect of neutral nonresonant collisions on the shape, shift, and intensity of atomic spectral-line profiles is reviewed. A general treatment for the study of an atomic spectral line is developed by establishing reasonable assumptions about the relevant collision processes and by finding an expression for the Fourier transform of the line profile. The authors look at parallel developments of other methods of calculation, consider special limits of practical interest, and illustrate numerical evaluations of complete line profiles. Interatomic potentials for use in line-profile calculations are described, and the problems imposed by nonadditivity and nonadiabaticity are also noted. The observation of line profiles by both conventional and tunable-laser techniques is surveyed. Representative experimental measurements of the widths and shifts of collision-broadened spectral line cores are tabulated, and the phenomena of satellites, oscillations, and power-law behavior of line wings are compared with theoretical expectations. The use of experimental results for the determination of excited atom-atom interactions, the prediction of collision broadening in stellar atmospheres, and the effect of foreign gases on laboratory standard wavelengths are also discussed.

The effect of neutral nonresonant collisions on atomic spectral lines

On the performance analysis of Savonius rotor with twisted blades

Collisional relaxation of atomic excited states, line broadening and interatomic interactions

Finite element analysis of fastening and joining: A bibliography (1990–2002)

The vortex ring generated subsequent to the diffraction of a shock wave from the open end of a shock tube is studied using particle image velocimetry. We examine the early evolution of the compressible vortex ring for three-exit shock Mach numbers, 1.1, 1.2, and 1.3. For the three cases studied, the ring formation is complete at about tUb/D=2, where t is time, Ub is fluid velocity behind shock as it exits the tube and D is tube diameter. Unlike in the case of piston generated incompressible vortex rings where the piston velocity variation with time is usually trapezoidal, in the shock-generated vortex ring case the exit fluid velocity doubles from its initial value Ub before it slowly decays to zero. At the end of the ring formation, its translation speed is observed to be about 0.7 Ub. During initial formation and propagation, a jet-like flow exists behind the vortex ring. The vortex ring detachment from the tailing jet, commonly referred to as pinch-off, is briefly discussed.

Vortex ring formation at the open end of a shock tube: A particle image velocimetry study

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.

Supersonic vortex rings

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. Nozzle flow conditions resulted in test section velocities up to 8·1 km 8 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.

Measurements of heat transfer to a flat plate in a dissociated high-enthalpy laminar air flow

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.

Fringe-orientation estimation by use of a Gaussian gradient filter and neighboring-direction averaging.

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.

Measurements of heat transfer in separated highenthalpy dissociated laminar hypersonic flow behind a step

Absorption linewidths of the Na D2 line in shock-tube-produced atmospheres are reported. Densities range from 3.6*1019 cm-3 to 1.2*1020 cm-3 with temperatures between 5000 and 10000K. Significant disagreement with previous work is found and discussed.

https://iopscience.iop.org/article/10.1088/0022-3700/12/3/012/pdf

J. P. Baird

Papers

Supersonic vortex rings

Measurements of heat transfer to a flat plate in a dissociated high-enthalpy laminar air flow

Fringe-orientation estimation by use of a Gaussian gradient filter and neighboring-direction averaging.

Measurements of heat transfer in separated highenthalpy dissociated laminar hypersonic flow behind a step

The width of the Na D2 resonance line ( lambda 5890) in atmospheres of helium and neon and atomic hydrogen