3.3. Measurement of Density by Analysis of Electron Beam Excited Radiation
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Cited by 6 publications
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An experimental study of density fluctuations in the hypersonic boundary layer on a flat plate
The stability of hypersonic flows is a very important problem in designing heat-protection systems for recoverable spacecraft and hypersonic aircraft. A great number of theoretical and experimental investigations of the stability of sub-and supersonic flows have been carried out. However, the results of these studies cannot be completely applied for high hypersonic Mach numbers because of the qualitative features of flow and the development of disturbances under these conditions [1]. On the other hand, the experimental studies of disturbance characteristics for free-stream Math numbers are few in number. In these studies, only some disturbance characteristics have been obtained, and they are hardly comparable because of the considerable differences in conditions of measurements. This is due to the difficulty of constructing special hypersonic facilities and with the problems of using traditional aerodynamic methods of disturbance measurements in low-density flows with a high stagnation temperature, which are typical of hypersonic wind tunnels.The electron-beam technique [8, 9] has obvious advantages under these conditions. It allows the density to be measured in rarefied flows. Fluctuations in the boundary layer on the walls of the working section of a wind tunnel [2, 3] and in the shear layer in the Eiffel chamber of a hypersonic wind tunnel [4] have been studied using this method.In most continuous-hypersonic wind tunnels, it is not possible to ensure the high Reynolds numbers necessary for transition studies. Nevertheless, it is important to study the characteristics of initial disturbances near the leading edge of a body at which a laminar flow occurs. These disturbances affect substantially the development and spectrum of disturbances preceding the laminar-turbulent transition. For low unit Reynolds numbers, a detailed spatial study of the characteristics of these initial disturbances is possible in a comparatively thick hypersonic boundary layer.A method of density and density-fluctuation measurements in hypersonic flows using electron-beam fluorescence of nitrogen is described in the present paper. The method allows one to obtain spectra, phase velocities, spatial correlations, wave-propagation angles, and growth rates of natural disturbances. The characteristics of density fluctuations in a hypersonic boundary layer on a flat plate with a sharp leading edge at zero angle of attack were studied for Moo = 21 and Tw/To = 0.26-0.29 (Tw is the model surface temperature and To is the stagnation temperature) for Reynolds numbers Rez = 2.6. 104-1.7 9 105 calculated from the longitudinal x coordinate and free-stream parameters.1. Experimental Equipment. The measurements were performed in a T-327 hypersonic nitrogen wind tunnel at the Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences [10]. The tunnel includes a graphite gas heater in the nozzle plenum chamber, a device for shock starting, and a system of gas exhaust into a vacuum chamber. The running time is 30 sac. ...
An experimental study of density fluctuations in the hypersonic boundary layer on a flat plate
The stability of hypersonic flows is a very important problem in designing heat-protection systems for recoverable spacecraft and hypersonic aircraft. A great number of theoretical and experimental investigations of the stability of sub-and supersonic flows have been carried out. However, the results of these studies cannot be completely applied for high hypersonic Mach numbers because of the qualitative features of flow and the development of disturbances under these conditions [1]. On the other hand, the experimental studies of disturbance characteristics for free-stream Math numbers are few in number. In these studies, only some disturbance characteristics have been obtained, and they are hardly comparable because of the considerable differences in conditions of measurements. This is due to the difficulty of constructing special hypersonic facilities and with the problems of using traditional aerodynamic methods of disturbance measurements in low-density flows with a high stagnation temperature, which are typical of hypersonic wind tunnels.The electron-beam technique [8, 9] has obvious advantages under these conditions. It allows the density to be measured in rarefied flows. Fluctuations in the boundary layer on the walls of the working section of a wind tunnel [2, 3] and in the shear layer in the Eiffel chamber of a hypersonic wind tunnel [4] have been studied using this method.In most continuous-hypersonic wind tunnels, it is not possible to ensure the high Reynolds numbers necessary for transition studies. Nevertheless, it is important to study the characteristics of initial disturbances near the leading edge of a body at which a laminar flow occurs. These disturbances affect substantially the development and spectrum of disturbances preceding the laminar-turbulent transition. For low unit Reynolds numbers, a detailed spatial study of the characteristics of these initial disturbances is possible in a comparatively thick hypersonic boundary layer.A method of density and density-fluctuation measurements in hypersonic flows using electron-beam fluorescence of nitrogen is described in the present paper. The method allows one to obtain spectra, phase velocities, spatial correlations, wave-propagation angles, and growth rates of natural disturbances. The characteristics of density fluctuations in a hypersonic boundary layer on a flat plate with a sharp leading edge at zero angle of attack were studied for Moo = 21 and Tw/To = 0.26-0.29 (Tw is the model surface temperature and To is the stagnation temperature) for Reynolds numbers Rez = 2.6. 104-1.7 9 105 calculated from the longitudinal x coordinate and free-stream parameters.1. Experimental Equipment. The measurements were performed in a T-327 hypersonic nitrogen wind tunnel at the Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences [10]. The tunnel includes a graphite gas heater in the nozzle plenum chamber, a device for shock starting, and a system of gas exhaust into a vacuum chamber. The running time is 30 sac. ...
The study of hypersonic flow about different types of bodies has assumed increasing importance with the progress that has been made in the design of spacecraft. Existing hypersonic wind runnels do not permit complete modeling of flight conditions at high Math numbers (M~, > 20). In addition, only certain gasdynamic parameters can be measured in experiments. This has enhanced the importance of methods for numerically modeling hypersonic flows. Such modeling makes it possible to simultaneously determine all of the parameters of a flow within the framework of the chosen model throughout the investigated region. However, no modeling is absolute, and the results must be substantiated by comparison with experimental data. On the other hand, combining these two approaches also gives the researcher greater confidence that the experimental methodology is correct.A common object of investigation is the flow on a plate with a sharp edge at a zero angle of attack. The electron-beam [1-4] and electron-probe [5] methods were used earlier to measure the distribution of mean density near the sharp edge of a plate for low Reynolds numbers (Re x < 3-104). There is no measurement data for higher Reynolds numbers. Results of a numerical study of hypersonic flow past a plate in a locally self-similar approximation were presented in [6]. This problem was solved more accurately in [7], where allowance was made for the structure of the shock wave (SW). The region of applicability of the Rankine-Hugoniot conditions on the wave were determined. Both investigations studied the region near the leading edge of the plate, where the local Reynolds numbers were on the order of 104 .In this study, we describe the experiment and present results of use of the method of electron-beam fluorescence to measure profiles of density in the flow of nitrogen about a plate at a zero angle of attack. The experiments were conducted with a Mach number for the incoming flow M~, = 21 and a unit Reynolds number per meter Re 1 = 6-105. The model of a viscous shock layer was used to develop an algorithm to calculate hypersonic flow about the plate. We present calculated prof'fles of velocity, temperature, and density. The latter are compared with the experiment in a number of the sections.1. Experimental Method. The measurements were made in hypersonic nitrogen wind tunnel T-327 at the ITPM (Institute of Theoretical and Applied Mechanics of the Siberian branch of the Russian Academy of Sciences) [8] with stagnation parameters Po = 8 MPa, T O = 1100 K. The radius of the uniform core of the flow was 5-10 -2 m, while the density of the particles in the flow was 7.1021 m -3. The density of the flow decreased rapidly outside the core, reaching = 6.1020 m -3 at a distance of 0.1 m from the axis.The plate model was in the form of a trapezoid. The widths of the leading and trailing edges were 8-10 -2 and 6-10 -2 m and the length of the plate L = 3.6.10 -1 m. The leading edge of the plate had the form of a wedge with an angle of 7 ~ The radius of curvature of "the leading e...
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