Measurements of colliding shock wave and supersonic gas flow (original) (raw)
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Journal of Fluid Mechanics, 2004
A comprehensive numerical and experimental study of normal shock waves in hypersonic axisymmetric jets of N 2 is presented. The numerical interpretation is based on the quasi-gasdynamic (QGD) approach, and its generalization (QGDR) for the breakdown of rotational-translational equilibrium. The experimental part, based on diagnostics by high-sensitivity Raman spectroscopy, provides absolute density and rotational temperatures along the expansion axis, including the wake beyond the shock. These quantities are used as a reference for the numerical work. The limits of applicability of the QGD approach in terms of the local Knudsen number, the influence of the computational grid on the numerical solution, the breakdown of rotation-translation equilibrium, and the possible formation of a recirculation vortex immediately downstream from the normal shock wave are the main topics considered.
Radiative characterization of supersonic jets and shocks in a laser-plasma experiment
Plasma Physics and Controlled Fusion, 2021
The interaction of supersonic laser-generated plasma jets with a secondary gas target was studied experimentally. The plasma parameters of the jet, and the resulting shock, were characterized using a combination of multi-frame interferometry/shadowgraphy, and x-ray diagnostics, allowing for a detailed study of their structure and evolution. The velocity was obtained with an x-ray streak camera, and filtered x-ray pinhole imaging was used to infer the electron temperature of the jet and shock. The topology of the ambient plasma density was found to have a significant effect on the jet and shock formation, as well as on their radiation characteristics. The experimental results were compared with radiation hydrodynamic simulations, thereby providing further insights into the underlying physical processes of the jet and shock formation and evolution.
Optical probing of laser-induced shock waves in air
Applied Physics B-lasers and Optics, 1996
Shock Waves (SW) were produced in air by focusing the (0.25 J, 6 ns) second-harmonic (2 = 532 nm) Nd : YAG laser light into a stainless-steel cylindrical cell at a pressure from 200 to 760 Torr. The laser fluence at the focal point is > 5 GW/cm 2. The spatial variation and consequently the time evolution of the radial propagation velocity U of the generated shock waves were measured via a simple optical system utilizing a HeNe laser beam triply intersecting the propagating shock wave at three successive positions. Using a reflector, we were able to probe the traveling SW in six consecutive positions during its round trip. Good agreement was obtained between the experimental results and the predictions of the point strong explosion theory. It is shown that this method is simple with a fairly good precision. It therefore appears to be useful for the determination of the SW dynamic parameters, namely its Mach number, the pressure at the SW front, the thickness of the compressed air layer and the energy consumed in producing this layer.
Measured characteristics of flow and combustion in supersonic flame/shock wave interaction
37th Joint Propulsion Conference and Exhibit, 2001
Characteristics of flow and combustion in a supersonic combustor were investigated experimentally to understand the effect of shock waves on the supersonic jet flame of the simple geometry. A hydrogen jet flame was stabilized on the axis of a Mach 2.5 supersonic wind tunnel, and to explain why some flames were greatly stabilized, schlieren images, wall static pressures, and pitot pressures were measured. The purpose of this study was to provide database of wall static pressures, pitot pressures and schlieren images for numerical analyst to assess chemistry models of numerical simulations on supersonic flame/shock wave interaction. Also, in order to explain enhancing mechanism of flame stability when shock waves were present, characteristics of supersonic flow in a supersonic flame/shock wave interaction were discussed. Wedge induced shock wave at the fuel nozzle edge and the resulting impinging shock waves on the hot recirculation zone were believed to enhance supersonic flame stabilization.
Bow Shock Wave Mitigation by Laser-Plasma Energy Addition in Hypersonic Flow
Journal of Spacecraft and Rockets, 2008
Experimental results of bow shock wave mitigation by laser-plasma energy addition in a low-density Mach 7 hypersonic flow conducted in a shock tunnel are presented. A high-power pulsed CO 2 laser operating with 7 J of energy and 30 MW of peak power was used to generate the plasma ahead of a hemispherical model installed in the tunnel test section. The schlieren technique was used to visualize the time evolution of energy addition to the flow by laser-induced plasma and the interaction between this disturbed region and the inherent bow shock formed on the model by hypersonic flow. A complete mitigation of the bow shock profile under action of the energy addition was observed. The impact pressure on the hemispherical model measured at the stagnation point reveals the correlation between the schlieren images and the pressure reduction.
Symmetric and asymmetric shocked gas jets for laser-plasma experiments
The Review of scientific instruments, 2021
Shocks in supersonic flows offer both high density and sharp density gradients that are used, for instance, for gradient injection in laser-plasma accelerators. We report on a parametric study of oblique shocks created by inserting a straight axisymmetric section at the end of a supersonic "de Laval" nozzle. The effect of different parameters, such as the throat diameter and straight section length on the shock position and density, is studied through computational fluid dynamics (CFD) simulations. Experimental characterizations of a shocked nozzle are compared to CFD simulations and found to be in good agreement. We then introduce a newly designed asymmetric shocked gas jet, where the straight section is only present on one lateral side of the nozzle, thus providing a gas profile well adapted for density transition injection. In this case, full-3D fluid simulations and experimental measurements are compared and show excellent agreement.
Supersonic liquid jets: Their generation and shock wave characteristics
Shock Waves, 2002
The generation of high-speed liquid (water and diesel fuel) jets in the supersonic range using a vertical single-stage powder gun is described. The effect of projectile velocity and mass on the jet velocity is investigated experimentally. Jet exit velocities for a set of nozzle inner profiles (e.g. straight cone with different cone angles, exponential, hyperbolic etc.) are compared. The optimum condition to achieve the maximum jet velocity and hence better atomization and mixing is then determined. The visual images of supersonic diesel fuel jets (velocity about 2000 m/s) were obtained by the shadowgraph method. This provides better understanding of each stage of the generation of the jets and makes the study of their characteristics and the potential for auto-ignition possible. In the experiments, a pressure relief section has been used to minimize the compressed air wave ahead of the projectile. To clarify the processes inside the section, additional experiments have been performed with the use of the shadowgraph method, showing the projectile travelling inside and leaving the pressure relief section at a velocity of about 1100 m/s.
Imaging of a transverse, sonic jet in supersonic flow
27th Joint Propulsion Conference, 1991
The structure of a non-reacting transverse sonic jet in a supersonic flow is visualized by three different experimental techniques: single-shot planar Rayleigh/Mie scattering and laser-induced fluorescence, and conventional spark schlieren photography. R a y l e i g w e scattering sites are provided by the condendon of ethanol vapor; biacetyl is used as a seed for laser-induced fluorescence. The planar laser techniques reveal largescale turbulent structure in the pansverse jet that cannot be m l v e d using the schlieren method. Regions of unmixed gas are seen to penetrate well awass the centerline of the jet The large-scale smcplre persists far downstream (at least 25 orifice diameters) of the jet injection site. .