Shock Wave Boundary Research Articles

Generation of overpressure due to condensation in moist air jet

In the present study, a computational fluid dynamics method has been applied to investigate the effects of initial degree of supersaturation at reservoir condition on under-expanded sonic jet structures, such as Mach disk location and diameter, barrel shock wave and jet boundary. The axisymmetric nozzle geometry investigated was a converging nozzle with straight part. As a result, it was found that the overpressures due to condensation generate and the characteristics of flow with generation of overpressure due to condensation in the jet were different from those without condensation.

Numerical simulation of the interaction between reflected shock wave and near-wall boundary layer

The interaction of a shock wave, reflected from the flat end of a cylindrical shock tube, with a cocurrent gas flow at the side wall, is considered in the axisymmetric case. The Navier-Stokes system of equations has been numerically integrated in the thin layer approximation using a predictor-corrector scheme. The appearance of a recirculation gas flow structure behind the reflected shock front and the evolution of this structure in the reflected wave going away from the tube end are analyzed. The corresponding patterns of constant density lines and the velocity vector field are presented.

1609 正方形ダクト内における衝撃波と乱流境界層の干渉に関する実験的研究(S35-2 圧縮性流れの基礎と応用(2),S35 圧縮性流れの基礎と応用)

1609 正方形ダクト内における衝撃波と乱流境界層の干渉に関する実験的研究(S35-2 圧縮性流れの基礎と応用(2),S35 圧縮性流れの基礎と応用)

An adaptive sampling and windowing interrogation method in PIV

This study proposes a cross-correlation based PIV image interrogation algorithm that adapts the number of interrogation windows and their size to the image properties and to the flow conditions. The proposed methodology releases the constraint of uniform sampling rate (Cartesian mesh) and spatial resolution (uniform window size) commonly adopted in PIV interrogation. Especially in non-optimal experimental conditions where the flow seeding is inhomogeneous, this leads either to loss of robustness (too few particles per window) or measurement precision (too large or coarsely spaced interrogation windows). Two criteria are investigated, namely adaptation to the local signal content in the image and adaptation to local flow conditions. The implementation of the adaptive criteria within a recursive interrogation method is described. The location and size of the interrogation windows are locally adapted to the image signal (i.e., seeding density). Also the local window spacing (commonly set by the overlap factor) is put in relation with the spatial variation of the velocity field. The viability of the method is illustrated over two experimental cases where the limitation of a uniform interrogation approach appears clearly: a shock-wave–boundary layer interaction and an aircraft vortex wake. The examples show that the spatial sampling rate can be adapted to the actual flow features and that the interrogation window size can be arranged so as to follow the spatial distribution of seeding particle images and flow velocity fluctuations. In comparison with the uniform interrogation technique, the spatial resolution is locally enhanced while in poorly seeded regions the level of robustness of the analysis (signal-to-noise ratio) is kept almost constant.

Magnetohydrodynamic Energy-Bypass Procedure in a Three-Dimensional Scramjet

A generic configuration is employed to explore the kinematic and dynamic structure of the flowfield in a Mach 8 scramjet with and without magnetohydrodynamic (MHD-) bypass. Particular emphasis is placed on describing the three-dimensional interaction between the fluid and the electromagnetic field in a given plasma environment. Faraday-type operation is considered with coarsely segmented electrodes in a generator and accelerator respectively mounted on either side of a constant-area isolator/combustor element. The numerical procedure adopts a robust high-resolution technique to solve the governing equations, which include the full three-dimensional Navier-Stokes equations supplemented with electromagnetic source terms and a Poisson equation for consistency of the electric field with current continuity. Spatially variable combustion and plasma parameters are either specified or phenomenologically derived. Various three-dimensional features such as swept shock-wave boundary layer interactions have a profound impact on operation. Separated regions and vortical structures interface with the current, electric, and ponderomotive force fields to yield complex three-dimensional features that indicate that two-dimensional and inviscid analyses are inappropriate. The MHD generator shows the potential to efficiently slow down flow in the inlet, thus decreasing scramjet inlet length, and to reduce the total temperature of the flow. However, separation causes near-wall secondary eddy currents and local body force reversal, thus limiting the useful length of the generator. Accelerator operation is characterized by more prominent irreversibilities, especially near walls, where electric and body force field gradients are large. Trends in integrated pressure and viscous and magnetic force are summarized.

Study on shock wave and turbulent boundary layer interactions in a square duct at Mach 2 and 4

In this paper, the outline of the Mach 4 supersonic wind tunnel for the investigation of the supersonic internal flows in ducts was firstly described. Secondly, the location, structure and characteristics of the Mach 2 and Mach 4 pseudo-shock waves in a square duct were investigated by color schlieren photographs and duct wall pressure fluctuation measurements. Finally, the wall shear stress distributions on the side, top and bottom walls of the square duct with the Mach 4 pseudo-shock wave were investigated qualitatively by the shear stress-sensitive liquid crystal visualization method. The side wall boundary layer separation region under the first shock is narrow near the top wall, while the side wall boundary layer separation region under the first shock is very wide near the bottom wall.

Effect of Non-equilibrium Condensation on Axisymmetric Under-expanded Jet

In the present study, a computational fluid dynamics work was performed to investigate the effects of initial degree of supersaturation at reservoir condition on under-expanded supersonic jet structures, such as Mach disk location and diameter, barrel shock wave and jet boundary locations. The axisymmetric nozzle geometry investigated was a contoured converging nozzle with long straight part. As a result, it was found that the characteristics of flow with occurrence of non-equilibrium condensation in the jet were different from those without condensation.

Discovery of explosion fragments outside the Vela supernova remnant shock-wave boundary

THE nearby (500 pc) Vela supernova remnant has presented several puzzles. Its true shape has been difficult to determine1, and as a result it has never been clear whether the pulsar seen in that part of the sky resulted from the same explosion that created the remnant 2. Here we present an X-ray image of the Vela supernova remnant which shows that the pulsar is close to the centre, and therefore most probably resulted from the same explosion. We see six extended X-ray features outside the blast-wave front, which apparently originated close to the pulsar. We propose that these features result from the passage through the surrounding medium of fragments formed by instabilities during the collapse and subsequent explosion of the progenitor star.

A radio-emitting X-ray "bullet" ejected by the Vela supernova

A massive star that explodes as a supernova produces an expanding remnant-a shell of gas-and leaves behind a neutron star. It has been suggested that instabilities during these explosions may create high-density clumps of ejecta 1,2 , but such fragments have never been found in a remnant containing a pulsar. Here we present X-ray and radio observations of a feature outside the shock-wave boundary of the Vela supernova remnant (associated with the pulsar PSR0833-45), which appears to be an ejected fragment, with a wake 3 . The feature, which has travelled nearly 50 pc from the site of PSR0833-45 but is only one parsec across, is a clear-cut case of a «bullet» of ejecta moving supersonically through the surrounding medium. The radio observations show non-thermal emission along the leading edge of the X-ray feature, indicating particle acceleration at the fragment's shock front

超音速流MHD発電機内の衝撃波-境界層相互作用

超音速流MHD発電機内の衝撃波-境界層相互作用

Heat transfer peculiarities in supersonic flows

A method of heat transfer and gas flow investigation based on the application of thermal sensitive coatings or thermocouple sensors and various visualization techniques is described. The thermal sensitive coatings and visualization reveal heat transfer peculiarities, and the complex nature of the method contributes to understanding the processes and generalization of quantitative results. Data concerning heat transfer on the leeward side of a blunt cone in the regions of the shock-wave boundary layer and bow wave interaction, in gaps and cavities of the orbiter's thermal insulation, and in the vicinity of them, are presented.

Over forty years of continuous research at UTIAS on nonstationary flows and shock waves

Analytical and experimental research on non-stationary shock waves, rarefaction waves and contact surfaces has been conducted continuously at UTIAS since its inception in 1948. Some unique facilities were used to study the properties of planar, cylindrical and spherical shock waves and their interactions. Investigations were also performed on shock-wave structure and boundary layers in ionizing argon, water-vapour condensation in rarefaction waves, magnetogasdynamic flows, and the regions of regular and various types of Mach reflections of oblique shock waves. Explosively-driven implosions have been employed as drivers for projectile launchers and shock tubes, and as a means of producing industrial-type diamonds from graphite, and fusion plasmas in deuterium. The effects of sonic-boom on humans, animals and structures have also formed an important part of the investigations. More recently, interest has focussed on shock waves in dusty gases, the viscous and vibrational structure of weak spherical blast waves in air, and oblique shock-wave reflections. In all of these studies instrumentation and computational methods have played a very important role. A brief survey of this work is given herein and in more detail in the relevant references.

Growth induced by multiple shock waves normally incident on plane gaseous interfaces

Experiments to measure the visual thickness of the mixing region produced by shock waves incident on continous and discontinous interfaces between gases of different densities have been carried out in a new vertical shock tube. The generation of vortical structures by shock-wave boundary layer interaction at the interface is observed and the need for experimental methods to distinguish the effects of resulting jets on the walls and windows of the shock tube is emphasized. Initially thick interfaces, smoothed by molecular diffusion, exhibit growth after being perturbed by acoustic noise induced during wave reverberation. Thin interfaces, whose perturbations are introduced by the rupture of the supporting plastic membrane, have a more rapid initial growth but the late time growth is comparable to that of the thicker interfaces. In both cases the rate of increase of the thickness of the interfaces is an order of magnitude less than reported by previous investigators.

Boundary shock waves in a conducting gas

In this paper, we have postulated, in a conducting gas, the occurrence of a boundary shock wave, considered as a quick transition region in which the viscous effects are compressive and are confined to a thin layer adjacent to a surface. The analogues of the well known Rankine-Hugoniot jump relations, Prandtl relation, and other properties of a shock wave are derived and a discussion about the existence of a boundary shock wave is made.

Boundary shock waves

The possible occurrence of a viscous region near a surface from which there is rapid efflux of gas, accompanied by large heat transfer, is postulated and investigated theoretically. Such a viscous region, denoted as a boundary shock wave, may occur in the case of a large high-speed meteor entering the earth's atmosphere, when a very high rate of vaporization induces translational non-equilibrium. The conditions across a boundary shock wave and its structure are calculated from the appropriate macroscopic equations reduced to closed-form expressions under the restrictions of a perfect gas, flowing at constant total enthalpy.

Effect of Shock Boundary Layer Interaction on Aerofoil Pressure Distributions at Transonic Speeds

SummaryA method of improving pressure distributions predicted by inviscid theory over two-dimensional aerofoils at transonic speeds taking into account shock-wave turbulent boundary layer interaction as obtained in the case of the flat plate is described.The method was applied to a non-lifting circular arc aerofoil of eight per cent relative thickness. The shock wave location, pressure distribution and drag coefficient were calculated and compared with experimental and inviscid theoretical results.It has been found that the method gives results which are consistent with experimental results in various aspects.

Some Comments “On The Effect of Shock-Induced Turbulent Separation on the Shock-Wave Position in a Nozzle”

In Ref. 1, Professor D. W. Holder describes a very interesting experiment pertaining to shock wave position and boundary layer separation in supersonic nozzles at low Mach numbers (M ⩽ 1·4). A closer examination of this experiment indicates that the results may only be applicable in the Mach number range of M < 1·48, not in the range of M> 1·48.

Viscous Aerodynamic Characteristics in Hypersonic Rarefied Gas Flow

This paper considers the problem of calculating aerodynamic characteristics of blunt bodies at hypersonic speeds and at sufficiently high altitudes where the appropriate mean free path becomes too large for the use of familiar boundary-layer theory but not so large that free molecule concepts apply. Results of an order-of-magnitude analysis are presented to define the regimes of rarefied gas flow and the limits of continuum theory. Based on theoretical and experimental evidence, the complete Navier-Stokes equations are used as a model, except very close to the free molecule condition. This model may not necessarily give the shock wave structure in detail but satisfies overall conservation laws and should give a reasonably accurate picture of all mean aerodjmamic quantities. In this intermediate regime there are two fundamental classes of problems: a viscous class and a class, the latter corresponding to a larger degree of rarefaction. For the layer class there is a thin shock wave, but the shock layer region between the shock and the body is viscous, although the stresses and conductive heat transfer are small at the shock wave boundary. Here, the use of the Navier-Stokes equations with outer boundary conditions given by the Hugoniot relations is justified. For the layer class, the shock wave is no longer thin, and the Navier-Stokes equations can be used to give a solution which includes the shock structure and has free-stream conditions as outer boundary conditions. A simpler procedure is presented for incipient merged conditions where the shock may no longer be considered an infinitesimally thin discontinuity but where it has not thickened sufficiently to entail the fully analysis. In this case we approximate the shock by a discontinuity obeying conservation laws which include curvature effects, stresses, and heat conduction. For a sphere and cylinder it is shown that the Navier-Stokes equations can be reduced to ordinary differential equations for both the and layer class of problems. Solutions of these equations, when used in connection with hypersonic flow problems, are in general only valid in the stagnation region. To illustrate the layer solutions, numerical calculations have been performed for a sphere and cylinder with the assumption of constant density in the shock layer, which is a useful

Some Properties of the Compression Shock as in Turbine and Compressor Blade Passages

The generalized theory of the plane compression shock has been widely known for some forty years, but only recently has appreciable progress been made in its application to everyday engineering practice. In the fields of ballistics and aircraft engineering, the shock is still generally regarded as a most undesirable phenomenon to be avoided whenever possible. However, in the fluid dynamics of gas-turbine power plant a stage has now been reached at which the shock, far from being regarded as a nuisance, must be considered as a potential aerodynamic tool of considerable consequence. Starting with a brief mention of the isentropic expansion of a compressible fluid and the classical compression-shock theory, the paper introduces some practical definitions and conceptions concerning the description and classification of the various forms of the single shock. The phenomena associated with shock wave reflection and boundary layer interaction are then considered, and finally four examples are given of the occurrence of shocks in practice. Of these examples, two are from the aircraft and two from the gas-turbine field, and in all they demonstrate most of the phenomena considered.