Showing papers on "Oblique shock published in 1979"

Thin sheets of energetic electrons upstream from the earth's bow shock

Abstract: ISEE spacecraft observations show that energetic (not less than 16 keV) electrons are injected into the region upstream from the earth's bow shock in a thin sheet which lies just behind the sheet of interplanetary magnetic field lines that are tangent to the shock surface. Lower energy electrons leave the shock over a much broader region. Although the energetic electron intensity varies, the sheet is nearly always present and may be a quasi-steady state feature of the bow shock. The electron velocity distribution in the thin sheet is strongly peaked and is responsible for excitation of electron plasma waves.

Domains and boundaries of non-stationary oblique shock-wave reflexions. 2. Monatomic gas

Abstract: Interferometric data were obtained in the 10 cm × 18 cm hypervelocity shock tube of oblique shock-wave reflexions in argon at initial temperatures and pressures of nearly 300 °K and 15 Torr. The shock Mach-number range covered was 2 [les ] Ms [les ] 8 over a series of wedge angles 2° [les ] θw [les ] 60°. Dual-wavelength laser interferograms were obtained by using a 23 cm diameter field of view Mach-Zehnder interferometer. In addition to our numerous results, the available data for argon and helium obtained over the last two decades were also utilized. It is shown analytically and experimentally that in non-stationary flows six domains exist in the (Ms, θw) plane where regular reflexion (RR), single-Mach reflexion (SMR), complex-Mach reflexion (CMR) and double-Mach reflexion (DMR) can occur. The transition boundaries between these regions were all established analytically. The experimental results from different sources substantiate the present analysis, and areas of disagreement which existed in the literature are now clarified and resolved. It is shown that real-gas effects have a significant influence on the size of the regions and their boundaries. In addition, isopycnics (constant density lines) are given for the four types of reflexion, as well as the density distribution along the wedge surface. This data should provide a solid base for computational fluid dynamicists in comparing numerical techniques with actual experimental results.

Comparison of Multiequation Turbulence Models for Several Shock Boundary-Layer Interaction Flows

Abstract: Several multiequation eddy viscosity models of turbulence are used with the Navier-Stokes equations to compute three classes of experimentally documented shock-separated turbulent boundary-layer flows. The types of flow studied are: (1) a normal shock at transonic speeds in both a circular duct and a two-dimensional channel; (2) an incident oblique shock at supersonic speeds on a flat surface; and (3) a two-dimensional compression corner at supersonic speeds. Established zero-equation (algebraic), one-equation (kinetic energy), and two-equation (kinetic energy plus length scale) turbulence models are each utilized to describe the Reynolds shear stress for the three classes of flows. These models are assessed by comparing the calculated values of skin friction, wall pressure distribution, velocity, Mach number, and turbulent kinetic energy profiles with experimental measurements. Of the models tested the two-equation model results gave the best overall agreement with the data.

Interaction of interplanetary shock waves with the bow shock-magnetopause system

Abstract: The collision of interplanetary shock waves with the bow-shock-wave-magnetopause system is considered both in the gas-dynamic and magnetohydrodynamic approximations. It is shown that the shock wave is reflected from the magnetopause as a rarefaction wave which, in turn, is reflected from the rearward side of the bow shock. This secondary rarefaction wave arrives at the magnetosphere after a time interval of 3--5 min after the interplanetary shock wave's arrival. The rarefaction wave decreases the flow pressure on the magnetosphere and causes the reverse (i.e., outward) motion of the magnetopause. With the help of an approximate solution of the differential equations the problem of rarefaction wave reflection from the magnetosphere is considered. The law of the subsolar point motion of the magnetosphere during the abrupt shock-like perturbation is obtained. The experimental data confirm the theoretical results.

Plasma wave turbulence associated with an interplanetary shock

Abstract: The present paper deals with interplanetary shocks, detected and analyzed to date, from the Helios 1 and 2 spacecraft in eccentric solar orbits. The plasma wave turbulence associated with the shock observed on March 30, 1976 is studied in detail. This event is of particular interest because it represents a clearly defined burst of turbulence against a quiet solar wind background both upstream and downstream of the shock. The shock itself is an oblique shock with upstream parameters characterized by a low Mach number, a low beta, and an abnormally large electron to ion temperature ratio. The types of plasma wave detected are discussed.

Curved duct separator for removing particulate matter from a carrier gas

Abstract: A separator for separating micron and submicron sized particles from a carrying gas, is disclosed. A carrier gas contains a component which is capable of condensation in the separator. The carrier gas is accelerated and flows at high velocity in a duct. The lower limit of the high velocity is approximately Mach 1.0. Due to the acceleration to the high velocity the static temperature of the carrying gas decreases. As a result, the condensable component condenses on micron and mainly on submicron sizes particles which act as nucleation sites. Liquid droplets formed during the condensation are in the micron size range. The paths of the high velocity flow of the carrier gas and of the solid and liquid particles carried therein is influenced by a combination of a centrifugal force and an oblique shock zone which is created within the high velocity flow. As a result, the particles travel a different path than the carrying gas and are effectively captured and disposed by an appropriately positioned receiving member.

Structure of flow in the separation region resulting from interaction of a normal shock wave with a boundary layer in a corner

Abstract: Oil—soot visualization, drainage tests, and a special schlieren method were used in an investigation into the corner interaction of a normal shock wave and a boundary layer. The combined use of these methods made it possible to obtain a number of new qualitative results on the flow structure in the perturbed region.

Supersonic inlet having variable area sideplate openings

Abstract: An inlet duct of generally rectangular configuration for supersonic aircraft in which a normal shock is produced in close proximity to the forward lip of the lower duct wall, and in which variable area sideplate openings are provided just upstream of the normal shock to achieve boundary layer control for the normal shock-boundary layer interaction during on-design operation and increasing flow area for spillage as the normal shock is moved forward during off-design operation.

Properties of two- and three-dimensional separation flows at supersonic velocities

Abstract: The results are given of experimental investigations into three-dimensional separation of a turbulent boundary layer in the neighborhood of oblique shock waves, wedge-shaped obstacles, and sweptback steps at Mach numbers M∞ = 2, 2.25, 2.5, 3, 4 and Reynolds numbers Re∞ = u∞/v = (30–36)· 106 m−1. The characteristic regimes of the separated flows are considered. There is a discussion of the results of comparison and generalization of the pressure distribution in the two- and three-dimensional separation regions, and empirical dependences are also given for determining some geometrical parameters of these regions. An analogy is found in the characteristic pressures, and pressure distribution for a number of two- and three-dimensional separation flows, which suggests that one could use some of the known methods of analysis of two-dimensional separation of a turbulent boundary layer to calculate estimates for the three-dimensional case. This is confirmed by a comparison of calculated and experimental data.

Unsteady Transonic Flows in a Two-Dimensional Diffuser.

Abstract: : Extensive measurements of shock position and pressure distributions (wall static, core flow static, and core flow total) were made, complemented by spark schlieren and high-speed schlieren photographic information. Measurements were made at shock Mach numbers up to 1.35, with and without excitation. The excitation amplitudes were low, with frequencies from 0 to 330 Hz. Unexcited flows displayed two dominant natural frequencies for attached flows (shock Mach numbers below 1.27) and one dominant peak for separated flows (shock Mach numbers above 1.28). The dominant frequencies depend strongly on shock strength. Diffuser response to excitation appears to follow patterns expected on the basis of low-amplitude (acoustic) wave propagation concepts, provided that the stream-wise variation of the flow speed is considered and realistic boundary conditions are applied at the ends of the channel. The study strongly suggests that the effective acoustic impedance associated with the shock/boundary-layer interaction zone is an important determinant of diffuser response to small-amplitude external perturbations.

Shockwave and Boundary Layer Interaction in the Presence of an Expansion Corner

Abstract: An investigation has been carried out to examine one aspect of supersonic jet-engine inlet flow, namely shock-wave and boundary-layer interaction in the presence of an expansion corner. The experiment was undertaken at Mach numbers of 1.8 and 2.5. The local Reynolds number per metre varied from 2.79 to 3.13 × 107 for M = 1.8 and from 4.20 to 6.4-8 × 107 for M = 2.5. Adiabatic turbulent boundary layers of about 6 mm thick on an expansion-corner plate were disturbed at different streamwise positions by oblique shocks with deflection angles of 4°, 6° and 8°. The pressure distributions, wave patterns and the extent of the separation regions were strongly influenced by the presence of the expansion corner, especially when the shock impingement positions were upstream of the corner. The pressure rise induced by the incident shock began to decrease in level when the shock impingement position was about 3-4 boundary-layer thicknesses upstream of the corner. As the incident shock moved towards the corner, the pressure rise and the extent of the separation region decreased. When the shock impingement position was at the corner, the reflected shock was effectively neutralised by the Prandtl-Meyer expansion; especially when the deflection angle of incident shock matched that of the expansion corner. The three dimensionality of the incident shock and separation region is due to the interactions between the glancing oblique incident shock and the tunnel’s sidewall boundary layers.

A review of upstream and bow shock energetic-particle measurements

Abstract: Measurements of energetic electrons and protons frequently observed in the interplanetary medium upstream from the bow shock are reviewed. Bursts of electrons with energy 0.5 to 100 keV and duration 1 to 100s (termed “spikes”) appear when the spacecraft is on a field line which is tangent to the bow shock surface. The electrons move upstream in a thin, curved sheet lying nearly along the interplanetary-magnetic-field direction. The thinness of the electron sheet shows that the electrons are accelerated only in a small region about the curve of tangency of the interplanetary magnetic field and the bow shock surface. The upstream ions, on the other hand, occupy a much larger spatial region. Some of the upstream ions, particularly those at the energies above 100 keV, may have magnetospheric origin. The mechanism of the ion acceleration is still not known nor is it ruled out that acceleration in the upstream region may take place. A variety of plasma waves is excited by the upstream particles.

Interaction of Weak Shock Waves with Screens and Honeycombs

Abstract: The interaction of weak shock waves with screens and honeycombs is examined to facilitate the design of a pulsed flowing gas laser system operating at a high repetition rate. Interactions with zero and finite base flow (M<0.3) are studied using a shock tube capable of generating weak shock waves. By reflecting the incident wave from the driven section end plate, interactions with and without base flow can be studied in a single experiment. A quasi-steady flow theory is developed to model shock interaction with screens, while a quasi-one-dimensional flow code is used for the interaction between shock waves and honeycombs. Comparisons between analytical and experimental results are made.

Propagation of magnetogasdynamic spherical shock waves in an exponential medium

Abstract: In this paper propagation of magnetogasdynamic spherical shock waves is considered in an exponentially increasing medium. The shock wave moves with variable velocity and the total energy of the wave is variable. It is shown that the magnetic field changes the flow velocity, density and pressure.

Collisionless shocks: simulation and laboratory experiments.

Abstract: In the laboratory the conditions can be created that are necessary for reproducing typical shock waves that have been observed in the interplanetary plasma. There is also the possibility of changing the experimental conditions over a wide range and thus of considering the effect of different mechanisms of energy dissipation. With small Mach numbers, the anomalous increase of resistance at the shock front prevents the shock front from steepening. At high Mach numbers, the anomalous resistivity cannot stop the steepening and the two-stream instability occurs.

Propagation of Plane Relativistic Shock Waves

Abstract: Similarity solutions for propagation of plane shock waves in a relativistic gas, where the nucleon number density varies linearly as distance from its edge at near vacuum is obtained. The shock front moves with constant speed and the solutions are applicable only to an isothermal medium or cold gas.

Shock profiles caused by different end conditions in one‐dimensional quiescent lattices

Abstract: Shock propagation in a one‐dimensional discrete lattice is generated by accelerating the end‐most particle from zero to its final velocity in a finite rise time after which the end particle is maintained at that velocity. The wave profiles for various rise times are compared to the zero‐time case in a quiescent lattice. For the anharmonic lattice the classical equations of motion of the atoms are solved numerically on the computer. A Morse‐type potential is assumed. For a finite rise time the amplitude of the wave passing through the surface atoms is diminished when compared with he zero‐time case. For the anharmonic lattice the head of the wave develops into a solitary wave train with an oscillatory tail, and for certain rise times and anharmonicity parameters an apparent envelope soliton forms behind the shock front. This envelope soliton travels much slower than the shock wave.

Fast-Acting Valves for Use in Shock Tubes : Part 2, Formation of shock waves

Abstract: In the previous paper, two kinds of fast-acting valves were developed to replace diaphragm-breaking as a means of generating shock waves in the conventional shock tubes. One of them, called a type-H valve is used in a shock tube in this paper, and the strength of shock wave generated by the valve and the correlation between the shock formation distance and the opening time of the valve are experimentally clarified. Furthermore, the experiments where a diaphragm is used are also performed, keeping all other operating conditions equal, and the results are compared with those by the valve. When the initial pressure ratio is comparatively small, valve produces as strong a plane shock wave as the conventional diaphragm shock tubes, although the shock Mach numbers are less than those produced by the breaking of diaphragm at a larger initial pressure ratio.

Dynamics of liquid films and thin jets

Abstract: The theory of liquid films and thin jets as one- and two-dimensional continuums is examined. The equations of motion have led to solutions for the characteristic speeds of wave propagation for the parameters characterizing the shape. The formal analogy with a compressible fluid indicates the possibility of shock wave generation in films and jets and the formal analogy to the theory of threads and membranes leads to the discovery of some new dynamic effects. The theory is illustrated by examples.

Particle acceleration by propagating interplanetary shocks

Abstract: The process of charged particle acceleration in interplanetary shocks has been simulated for typical parameters. Since space probe observations of charged particle fluxes are the principle means of inferring the action of an acceleration mechanism, the simulation was designed to follow particles backwards in time from a given observing point, usually 1 A.U. This allowed a full diagnosis of which observed particles had interacted with an oncoming shock, where the interacting occurred, and by how much the energy had been changed by the shock interaction. Simple assumptions about the pre‐shock energy spectrum allow the construction of a full temporal profile of the expected intensity, anisotropy, and energy spectrum. The simulations are apparently capable of reproducing the main features of the less than 10 MeV/nuc. ion flux enhancements observed at interplanetary shocks using only a laminar interplanetary magnetic field, Archimidean spiral, and a spherical oblique shock with typical speed, strength, and shock normal‐magnetic field angle.

Acoustic and Flow Characteristics of Cold High-speed Coaxial Jets

Abstract: Far-field noise of model coaxial supersonic cold jets exhausting from a coplanar convergent two-nozzle coaxial configuraton was investigated. The pressure ratio (velocity) of the outer annular jet was maintained higher than the inner round jet. For each outer-jet pressure ratio, the inner-jet operating pressure ratio for the "minimum" radiated noise was established. Experimental results on the noise reductions and the modifications of the shock structure and velocity distribution of coaxial jet flows at the "minimum" noise conditions are presented and are compared with those of a single convergent underexpanded round and annual jet at a wide range of operating pressure ratios.

Numerical solution of two-dimensional turbulent blunt body flows with an impinging shock

Abstract: AN implicit finite-difference method has been developed to compute two-dimensional, turbulent, blunt-body flows with an impinging shock wave. The complete timeaveraged Navier-Stokes equations are solved with algebraic eddy viscosity and turbulent Prandtl number models employed for shear stress and heat flux. The irregular-shaped bow shock is treated as a discontinuity across which the Rankine-Hugoniot equations are applied. A Type III turbulent shock interference flowfield has been computed and the numerical results compare favorably with existing experimental data. Contents The problem of shock interference heating arising from an extraneous shock wave impinging on a blunt body has been studied extensively during the past several years. In the Type III interference pattern, as described by Edney,l a shear layer originates at the intersection of the impinging shock and bow shock and interacts with the wall boundary layer. It has been shown1;2 that the heat transfer is strongly dependent on whether the shear layer is laminar, transitional, or turbulent. A method for computing laminar shock interference flowfields has been developed previously and applied to both two-dimensional3'4 and three-dimensional5 configurations. This method numerically computes the entire shock layer flowfield using the standard, unsplit, MacCormack finitedifference scheme6 to solve the complete set of compressible Navier-Stokes equations. In order to calculate turbulent shock interference flowfields, a turbulence model was added to the method. Unfortunately, this explicit method suffers from the fact that the allowable time step is proportional to the square of the grid spacing in viscous regions. In order to overcome this step size limitation, an implicit, noniterative, approximate-factorization, finite-difference scheme developed by Lindemuth and Killeen,7 McDonald and Briley,8 and Beam and Warming9 is used in the present study to solve the complete time-averaged Navier-Stokes equations. Although this scheme increases the computation time per step over that of the previous explicit scheme by a factor of 1.8 for turbulent calculations, it permits a time step that is many times greater than the explicit time step when fine meshes are

The three-dimensional shape of the bow shock.

Abstract: The radial distance to the bow shock obtained in earlier studies is first reviewed. Recently, HEOS 2 data have provided an extensive exploration of the bow shock location away from the ecliptic plane. These shock crossings have been used to find with a least-squares technique a conic surface that best describes the shock. The limitation of HEOS 2 observations is discussed in relation to both usual and unusual locations fo the bow shock. It seems clear from ≈2000 shock crossings which have been examined that, when the interplanetary magnetic field has a southward component, the shock is closer to the Earth, by 1R E, than when it has a northward component.

Shock waves in a transverse magnetic field

Abstract: Experimental and theoretical work on ionizing shock waves in a fully ionized plasma is reviewed for the case in which a magnetic field is imposed parallel to the plane of the shock front. The boundary conditions for ionizing shocks are discussed. It is shown that the additional boundary conditions required for ionizing shock waves follow from the ionizational stability of the gas ahead of the shock front. The front structure of ionizing shocks is analyzed qualitatively: some calculated results are also reported. Experimental results on magnetic structures are discussed. The physical mechanisms which shape the shock front in a plasma are examined. Some results calculated for the front structure in a plasma are reported.

The Transonic Integral Equation Method With Curved Shock Waves

Abstract: In the existing solutions of the extended integral equation method for transonic flows the shock wave has been assumed normal to the freestream. In this paper the effect of removing this assumption is investigated and flows with curved shock waves are examined.