A new approach is proposed for the calculation of refraction vector as a gradient of the phase shift when testing
symmetrical flow with a parallel beam of light. It is assumed that the flow can be characterized by axial, conical or
central symmetry. This is observed, for example, at supersonic flows around bodies of revolution. The density field
between the bow shock wave and the body can be either calculated from the physics models or determined from the
optical testing. The refraction vector modeling is based on polynomial representation of the radial density distributions.
The confirmation of such representation is done by analysis of numerical data for various regimes of supersonic flows
around bodies of revolution (sharp-tipped and blunt cones, spheres, bodies with ogive nose). Analytical formulas were
obtained for refraction vector calculation in axial, conical and central symmetrical flows. For density field around a
sphere in a supersonic flow at Mach number M=4, which was calculated from a physics model, refraction vector
components were calculated for three different models. In the first model it is assumed that the phase change is taken
place only on the bow shock wave. The second model uses a linear polynomial representation of the radial distributions
based on density values calculated for the shock wave, symmetry axis and body surface. In the third model we used
interpolation of the density values calculated in discrete points and least square method for polynomial representation.
Results of the refraction vector calculations are illustrated by a set of graphics. The obtained formulas will be used
further for the flow study using computational flow schlieren imaging technology. A recommendation is given on
application of the formulas for this purpose.
Using our original method of interferometric data processing we have studied a radial density distribution in the flow separation range of a sphere flown in air at Mach number 2. This range contains a shock wave, a contact surface and a part of adjacent wake. The method is based on measurement of interferometric fringes and definition of light vector refraction component distributions normal to the symmetry axis. It is assumed that the interferometric picture has vertical fringes outside of the bow shock wave. The radial distributions are calculated according to the schlieren data processing. They were used for density field simulation and interferometric pictures visualization by the digital interferometry, some aspects of which were developed by authors early. The comparison of experimental interferometric pictures with the calculated pictures shows a possibility to use the considered method for study of the flow separation range. Results of the comparison are illustrated by examples of such interferometric pictures.
The method of interferometric picture simulation of axial symmetrical gas flows for any initial tuning of two-beam interferometer is developed for digital interferometry. The method is based on polynomial representation of the theoretical density fields. Computer - generated interferograms are calculated for powerful explosion with central symmetry and conical supersonic flow field around sharp-tip cone when density fields depend on one parameter only. Results can be used in analisys of interferometric picture in the real experimental conditions. In addition, the comparison of experimental with computer - generated pictures is used to affirm adequacy of the theoretical model for description of visualized phenomena.
We have obtained analytical formulas for the phase difference in case of two-beam interferometry of symmetrical flow with inner shocks. These formulas were analyzed for transparent media having axial, central and cylindrical symmetry. They were used to digitally synthesize the interferometric pictures in density distribution simulations.
It is of interest to study the interferometric fringes behavior in the areas near the inner shocks. It is proposed to use simple models for the density field simulation so results of the calculations can be compared with the experimental interferometric results. Using simulated density fields and digital interferometry, we have numerically created interferograms utilizing some of the continuous field techniques developed by authors early.
The comparison of the experimental interferometric pictures with the calculated pictures shows the possibility to use the developed technology to study flow fields with the inner shocks. The results of comparison are illustrated by examples of such interferometric pictures.
We have studied wave curl structures created behind the shock wave as it expands beyond the edge of the shock wave tube. A description of a large-scale shearing interferometer used for these studies is presented. A technique for quantitative automated analysis of the shearing interferograms is developed, which is well suited for registration of the interferograms using CCD sensors and data processing using PC. Physics of the gas-dynamics processes is analyzed. Main quantitative parameters of the gas are presented.
Laser holographic interferometer was used for visualization of axisymmetrical free flows at Mach number 6 in test section of the hypersonic wind tunnel. This interferometer was designed on a basis of Schlieren apparatus with restricted test beam diameter. So the visualization of all flow fields including its boundaries was impossible. Such visualization, however, is necessary for the calculation of radial density distributions from the interferometric data. It is of interest to study the density behavior near axis, where under theoretical prediction a local uniformity can exist. The interferometric measurements assure determination of flow core boundaries and ratios of nozzle exit pressure to the pressure in test section. It is proposed to do density fields simulation based on results of the theoretical calculation of jets at established pressure ratios. In addition, special simulation is used for description of the density uniformity near the axis. Using simulated density fields, theoretical interferograms were calculated using digital interferometry technique, which was developed by authors early. So it was defined the condition for revealing local perturbation of flow field near axis.
It is developed a new approach to the study interferometric pictures properties at flow visualization. Interferometric fringes are defined as family of solutions a differential equation, which establishes slope of the fringes as function of light refraction vector components and of initial tuning two beam interferometer parameters. The approach allows both to systematize knowledge about pictures and to make prediction they behavior depend on properties to be investigated density flow field and initial tuning parameters. On base the qualitative theory differential equation it is realized possibility to study symmetry, smoothness of fringe, singularity points of the pictures. Early some of the proposed ideas were used for statement models of 2D-density flow field under analysis experimental interferometric pictures to reduce duration of the data processing. It is assumed an application for the choice 3D density field models under the same analysis in complex flow to be investigated with aid of digital interferometry. Such flows take place at diffraction of shock waves. The singularities are illustrated by means of interferometric picture examples, which was visualized under experimental study 2D and 3D gas flows.
The color shadow method with video taping for the gasdynamic nonstationary process investigation of wind tunnel is described. Different schemes of this method realization using shadow devices IAB-451, IZK-462, IAB-459 and others are presented. Great potential of this method using the Central Research Institute of Machine Building wind tunnels is demonstrated on specific study of gas flow pattern and its uniformity intricate shape model gas stream flow around, interaction of jet streams and other are shown.
The automatic optical gas-and-dust analyzer for the determination of concentration of SO2, CO2, and other admixtures in the industrial exhaust has been presented. The efficiency of the device has been confirmed by the test in industrial conditions.
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