Shock-shock Interaction Research Articles

Investigation of shock-shock interaction and Mach reflection in laterally colliding laser-blow-off plasmas

Interactions of two Li plasma plumes and shock waves are investigated at various pressures (∼10−5 to 3 mbar) in the argon gas ambient. Fast imaging and optical emission spectroscopy are used to study the plume dynamics and characteristic emission of plasmas. The plasma plumes are created in laser-blow-off geometry. The expansion of plasma plumes in the ambient gas leads to the formation of an interaction zone. The formation of interaction zone is dependent on the ambient pressure and below a certain pressure, no significant change is observed in the shape and size of the interaction plasma. In the higher pressure, formation of interaction zone and its shape are dependent on ambient pressure. Dynamics of seed plasmas and interaction zone are also affected by the shock-shock interactions. The shock-shock interaction depends on the angle of incidence (α) between two shock waves at the initial time of interaction but as the plumes expand, the shock-shock interaction does not follow α dependence.

Magnetohydrodynamic structure of a plasmoid in fast reconnection in low-beta plasmas: Shock-shock interactions

The shock structure of a plasmoid in magnetic reconnection in low-beta plasmas is investigated by two-dimensional magnetohydrodynamic simulations. Using a high-accuracy code with unprecedented resolution, shocks, discontinuities, and their intersections are resolved and clarified. Contact discontinuities emanate from triple-shock intersection points, separating fluids of different origins. Shock-diamonds inside the plasmoid appear to decelerate a supersonic flow. New shock-diamonds and a slow expansion fan are found inside the Petschek outflow. A sufficient condition for the new shock-diamonds and the relevance to astrophysical jets are discussed.

On the accuracy and robustness of a new flux splitting method

The high speed flow problems usually involve complex flow phenomena, such as strong shock waves, shock-shock interactions, and shear layers. Prediction of these problems requires robust, efficient and accurate numerical methods. A robust flux splitting method capable of capturing crisp shock profile and exact contact surface is presented. Here, the flux vector of the Euler equation is split into convective and pressure parts according to the Toro's formulation. The accuracy of the numerical method at the contact discontinuity is examined first. Sufficient conditions of shock stability for this new method are obtained through a linear perturbation analysis. Several carefully chosen test problems are numerically investigated, and the numerical results demonstrate the accuracy and robustness of the proposed scheme.

Luminescent measurement systems for the investigation of a scramjet inlet-isolator.

Scramjets have become a main focus of study for many researchers, due to their application as propulsive devices in hypersonic flight. This entails a detailed understanding of the fluid mechanics involved to be able to design and operate these engines with maximum efficiency even at their off-design conditions. It is the objective of the present cold-flow investigation to study and analyse experimentally the mechanics of the fluid structures encountered within a generic scramjet inlet at M = 5. Traditionally, researchers have to rely on stream-thrust analysis, which requires the complex setup of a mass flow meter, a force balance and a heat transducer in order to measure inlet-isolator performance. Alternatively, the pitot rake could be positioned at inlet-isolator exit plane, but this method is intrusive to the flow, and the number of pitot tubes is limited by the model size constraint. Thus, this urgent need for a better flow diagnostics method is addressed in this paper. Pressure-sensitive paint (PSP) has been applied to investigate the flow characteristics on the compression ramp, isolator surface and isolator sidewall. Numerous shock-shock interactions, corner and shoulder separation regions, as well as shock trains were captured by the luminescent system. The performance of the scramjet inlet-isolator has been shown to improve when operated in a modest angle of attack.

Catching the radio flare in CTA 102

The temporal and spatial spectral evolution of the jets of AGN can be studied with multi-frequency, multi-epoch VLBI observations. The combination of both, morphological and spectral parameters can be used to derive source intrinsic physical properties such as the magnetic field and the non-thermal particle density. In the first two papers of this series, we analyzed the single-dish light curves and the VLBI kinematics of the blazar CTA 102 and suggested a shock-shock interaction between a traveling and a standing shock wave as a possible scenario to explain the observed evolution of the component associated to the 2006 flare. In this paper we investigate the core-shift and spectral evolution to test our hypothesis of a shock-shock interaction. We used 8 multi-frequency VLBA observations to analyze the temporal and spatial evolution of the spectral parameters during the flare. We observed CTA 102 between May 2005 and April 2007 using the VLBA at six different frequencies spanning from 2 - 86 GHz. After the calibrated VLBA images were corrected for opacity, we performed a detailed spectral analysis. From the derived values we estimated the magnetic field and the density of the relativistic particles. The detailed analysis of the opacity shift reveals that the position of the jet core is proportional to nu^-1 with some temporal variations. The value suggests possible equipartition between magnetic field energy and particle kinetic energy densities at the most compact regions. From the variation of the physical parameters we deduced that the 2006 flare in CTA 102 is connected to the ejection of a new traveling feature (t=2005.9) and the interaction between this shock wave and a stationary structure around 0.1 mas from the core. The source kinematics together with the spectral and structural variations can be described by helical motions in an over-pressured jet.

A hypersonic lift mechanism with decoupled lift and drag surfaces

In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The shock-shock interaction theory in conjunction with a three dimensional correction and checked with computational fluid dynamics (CFD) is used to analyze the lift and drag forces as function of the geometrical parameters and inflow Mach number. Through this study, though limited to only inviscid flow, we conclude that it is possible to obtain a high lift to drag ratio by suitably arranging the shock interaction generator.

Numerical Investigation of Hypersonic Double-Cone Flow

Hypersonic flow of Mach number 8 past a 25°-50° double cone geometry is numerically simulated at ReD=4.8E5. Complicated flow structures, including Type V shock-shock interaction, shock-boundary layer interaction, separation and reattachment at the corner are presented and discussed. The surface pressure and heat transfer rate distributions are also calculated and compared with the experimental data. Results show that both the 2nd order MUSCL and 5th order WENO could accurately reproduce the shock structures, while the higher order scheme could predict a more accurate size of separation zone. Generally, the size of the separation zone is underestimated with an overvalued pressure distribution after reattachment employing the full turbulent models. On the other hand, transition induced by the reattachment shock has been calculated using transition model and the results of pressure peak and the size of separation zone show good agreement with the experimental measurements.

Cylindrical blast wave propagation in an enclosure

A numerical study of propagation and interaction of cylindrical blast waves in an enclosure at different blast intensities is presented. The interest to study such flows stems from the need to bring in an updated description of the flow field and to predict the pressure loads on the structure. An implicit-unfactored high-resolution hybrid Riemann solver for the two-dimensional Euler equations is used. The char- acteristic values at the cell faces are evaluated by a modified MUSCL scheme. Numerical schlieren-type images are used for understanding the flows qualitatively. The investigation indicated that the resulting flow field is dominated by com- plex interacting shock systems due to the complex series of shock focusing events, shock-structure and shock-shock interactions. The pressure-load distribution and maximum overpressure are estimated.

PARTICLE ACCELERATION IN SHOCK–SHOCK INTERACTION: MODEL TO DATA COMPARISON

Shock-shock interaction is a well-established particle acceleration mechanism in astrophysical and space plasmas, but difficult to study observationally. Recently, the interplanetary shock collision with the bow shock of the Earth on 1998 August 10 was identified as one of the rare events where detailed in situ observations of the different acceleration phases can be made. Due to the advantageous spacecraft and magnetic field configurations, in 2011, Hietala et al. were able to distinguish the seed population and its reacceleration at the bow shock, as well as the Fermi acceleration of particles trapped between the shocks. They also interpreted their results as being the first in situ evidence of the release of particles from the trap as the two shocks collided. In the present study we use a global 2.5D test-particle simulation to further study particle acceleration in this event. We concentrate on the last phases of the shock-shock interaction, when the shocks approach and pass through each other. The simulation results verify that the main features of the measurements can be explained by shock-shock interaction in this magnetic geometry, and are in agreement with the previous interpretation of particle release. Shock-shock collisions of this type occur commonly in many astrophysical locations such as stellar coronae, planetary and cometary bow shocks, and the distant heliosphere.

In situ observations of particle acceleration in shock-shock interaction

[1] We use detailed multispacecraft observations to study the interaction of an interplanetary (IP) shock with the bow shock of the Earth on August 9–10, 1998. We can distinguish four different phases of particle acceleration in the shock-shock interaction: (1) formation of magnetic contact with IP shock and the seed population of energetic particles accelerated by it, (2) reacceleration of this population by the bow shock, (3) first order Fermi acceleration as the two shocks approach each other, and (4) particle acceleration and release as the shocks collide. Such a detailed analysis was made possible by the particularly advantageous quasi-radial interplanetary magnetic field configuration. To our knowledge this is the first time the last phase of acceleration at a shock-shock collision has been reported using in situ space plasma observations.

Catching the radio flare in CTA 102

Context: The blazar CTA 102 (z=1.037) underwent a historical radio outburst in April 2006. This event offered a unique chance to study the physical properties of the jet. Aims: We used multifrequency radio and mm observations to analyze the evolution of the spectral parameters during the flare as a test of the shock-in-jet model under these extreme conditions. Methods: For the analysis of the flare we took into account that the flaring spectrum is superimposed on a quiescent spectrum. We reconstructed the latter from archival data and fitted a synchrotron self-absorbed distribution of emission. The uncertainties of the derived spectral parameters were calculated using Monte Carlo simulations. The spectral evolution is modeled by the shock-in-jet model, and the derived results are discussed in the context of a geometrical model (varying viewing angle) and shock-shock interaction. Results: The evolution of the flare in the turnover frequency-turnover flux density plane shows a double peak structure. The nature of this evolution is dicussed in the frame of shock-in-jet models. We discard the generation of the double peak structure in the turnover frequency-turnover flux density plane purely based on geometrical changes (variation of the Doppler factor). The detailed modeling of the spectral evolution favors a shock-shock interaction as a possible physical mechanism behind the deviations from the standard shock-in-jet model.

Evidence for shock-shock interaction in the jet of CTA 102

AbstractWe have found evidence for interaction between a standing and a traveling shock in the jet of the blazar CTA 102. Our result is based in the study of the spectral evolution of the turnover frequency-turnover flux density (νm, Sm) plane. The radio/mm light curves were taken during a major radio outburst in April 2006.

Unsteady Aerodynamic Interaction between Two Bodies at Hypersonic Speed

This paper presents experimental results of unsteady aerodynamic interactions including Shock/Shock Interaction (SSI) and Shock/Boundary Layer Interaction (SBLI) between two bodies at hypersonic speed. These interactions can be seen in space vehicles consisting of multi-bodies, such as a TSTO, or at a scramjet engine inlet. The present study considers the effect of a flat plate below the SSI where a boundary-layer is developed on the plate surface. More specifically, the interacted flow for a combination of a flat plate (FP) and a hemi-circular cylinder (HCC) is examined at a hypersonic speed (M∞=8.1); the distributions of surface pressure and heat transfer rate are measured. To obtain various SSI patterns, the clearance between two bodies (FP and HCC) is changed. Results show that unsteadiness at the SSI point causes a feedback loop between the two bodies; a jet flow impinges on the FP, the effect of which propagates upstream where the jet impinges on the FP, and the aerodynamic and aerothermodynamic loads reach their maxima. Finally, we found that the feedback loop can be destroyed by installing a fence on the FP to reduce unsteadiness of flow field.

Three Successive and Interacting Shock Waves Generated by a Solar Flare

We discovered three successive Moreton waves generated by a single solar flare on 2005 August 3. Although this flare was not special in magnitude or configuration, Moreton waves (shock waves) successively occurred three times. Multiple shock waves generated during a single flare have not been reported before. Furthermore, the faster second-generated Moreton wave caught up and merged with the slower first-generated one. This is the first report of shock-shock interaction associated with a solar flare. The shock-plasma interaction was also detected. When the third-generated Moreton wave passed through an erupting filament, the filament was accelerated by the Moreton wave. In this event, filaments also erupted three times. On the basis of this observation, we consider that filament eruption is indispensable to the generation of Moreton waves.

Diffusive radiation in Langmuir turbulence produced by jet shocks

Anisotropic distributions of charged particles including two-stream distributions give rise to generation of either stochastic electric fields (in the form of Langmuir waves, Buneman instability) or random quasi-static magnetic fields (Weibel and filamentation instabilities) or both. These two-stream instabilities are known to play a key role in collisionless shock formation, shock-shock interactions, and shock-induced electromagnetic emission. This paper applies the general non-perturbative stochastic theory of radiation to study electromagnetic emission produced by relativistic particles, which random walk in the stochastic electric fields of the Langmuir waves. This analysis takes into account the cumulative effect of uncorrelated Langmuir waves on the radiating particle trajectory giving rise to angular diffusion of the particle, which eventually modifies the corresponding radiation spectra. We demonstrate that the radiative process considered is probably relevant for emission produced in various kinds of astrophysical jets, in particular, prompt gamma-ray burst spectra, including X-ray excesses and prompt optical flashes.

Diffusive radiation in one-dimensional Langmuir turbulence

We calculate spectra of radiation produced by a relativistic particle in the presence of one-dimensional Langmuir turbulence which might be generated by a streaming instability in the plasma, in particular, in the shock front or at the shock-shock interactions. The shape of the radiation spectra is shown to depend sensitively on the angle between the particle velocity and electric field direction. The radiation spectrum in the case of exactly transverse particle motion is degenerate and similar to that of spatially uniform Langmuir oscillations. In the case of oblique propagation, the spectrum is more complex, it consists of a number of power-law regions and may contain a distinct high-frequency spectral peak. The emission process considered is relevant to various laboratory plasma settings and for astrophysical objects as gamma-ray bursts and collimated jets.

Re-initiation Processes of Detonation Wave Behind Slit-Plate (Influence of Slit-Plate Configuration)

Pressure and temperature behind a detonation wave are extremely high and have a potential to cause serious damages around it. Therefore, it is necessary from safety engineering point of view to decay the detonation wave with short distance from a generation of it. In this study, experiments are conducted in order to investigate behaviors of the detonation wave propagating into two pieces of slits, since the detonation wave might be quenched behind the slits by expansion waves generated at a corner of the slits and this behavior might be applicable to a technique of detonation-arrester. The detonation wave produced in a stoichiometric mixture of hydrogen and oxygen is propagated through the slits and behaviors of it are experimentally investigated by using a technique of pressure measurement, soot track record and high-speed schlieren photography. As a result, when the detonation wave propagated through the slits, a shock wave is decoupled with a reaction front. Two shock waves diffracted from the slits interact each other at center behind the slits, then this shock wave interaction induces a hot-spot enough to cause local explosion. Since, the shock wave is reflected from a tube-wall eventually, the detonation wave is re-initiated by mechanisms of shock-shock interaction or shock-wall interactions.

502 衝撃波干渉によるウェーブライダーの飛行制御について(流体工学III)

502 衝撃波干渉によるウェーブライダーの飛行制御について(流体工学III)

304 衝撃波干渉型ウェーブライダーの形状が流れ場に及ぼす影響の可視化解析(G.S.:流体工学I)

304 衝撃波干渉型ウェーブライダーの形状が流れ場に及ぼす影響の可視化解析(G.S.:流体工学I)

Numerical Studies of Laser-Induced Energy Deposition for Supersonic Flow Control

This work deals with the computational study of localized laser energy deposition in supersonic flows. A model for Nd:YAG laser energy deposition in air has been developed for this purpose. It is designed to predict the fluid dynamic effects of the energy deposition process in supersonic flows. The key physical processes are captured, including inverse bremsstrahlung absorption, evolution of the plasma shape and structure, air breakdown chemistry, and the subsequent fluid dynamics. The model is validated using measurements of experiments done in quiescent air. The effects of energy deposition in three-dimensional supersonic flow past sphere and a flow with Edney type IV shock-shock interaction were studied. The energy deposition was found to be effective in reducing the peak surface pressure, but not as effective in lowering the surface heat-transfer rate. In the case of flow with Edney type IV shock-shock interaction, a study was performed to find the optimal location for the energy deposition, for which there is maximum decrease in the surface pressure.