Supersonic Shock Research Articles

Tailoring the dielectric properties of KDP crystals by shock waves for microelectronic and optoelectronic applications

In the present research article, authors report on tailoring the dielectric properties of potassium dihydrogen phosphate (KDP) crystals using supersonic shock waves that is proposed and demonstrated. The present experimentation involves an investigation of loading single pulse of shock waves with different Mach numbers such as 1.7, 1.9, 2.2, 2.4 and 2.5 on KDP crystals using shock tube. The crystalline nature and dielectric behavior of pre and post shock loaded KDP crystals are evaluated by PXRD and impedance analyzer techniques, respectively. Interestingly, shock wave loaded test materials show low dielectric constant compared to pre shock test crystal. Moreover, Mach 1.9 shock wave loaded test crystal shows the lowest dielectric constant compared to other Mach numbers and it is due to the reduction of lattice polarization and domain orientation changes. The experimental results clearly show that the test crystal can be a potential material for microelectronic and optoelectronic applications because it acquires low dielectric constant on shock exposure.

Control Oriented Model for Expander Cycle Scramjet

As a efficient and simple design, expander cycle is widely applied in LRE engineering, but it is seldomly used on scramjet research. In order to establish a complete mathematical model for expander cycle scramjet, a control-oriented model for expander cycle scramjet is proposed in this paper. This model consists of four major parts: combustor, cooling channel, turbo pump and nozzle and gives the result of pressure, temperature, mach number and velocity distribution of combustor and cooling channel and is capable of simulate both pure supersonic combustion mode and supersonic shock wave mode of the combustor. Each part is given by specific mathematical description, which contains the calculation of airflow, combustion, heat transfer and thermal cracking of kerosene. By putting all these parts together, a complete model is formed. This model is proposed to calculate the performance and condition of the engine precisely, comprehensively, swiftly and can be directly used in further study.

Impact of geometric, operational, and model uncertainties on the non-ideal flow through a supersonic ORC turbine cascade

Typical energy sources for Organic Rankine Cycle (ORC) power systems feature variable heat load and turbine inlet/outlet thermodynamic conditions. The use of organic compounds with heavy molecular weight introduces uncertainties in the fluid thermodynamic modeling. In addition, the peculiarities of organic fluids typically lead to supersonic turbine configurations featuring supersonic flows and shocks, which grow in relevance in the aforementioned off-design conditions; these features also depend strongly on the local blade shape, which can be influenced by the geometric tolerances of the blade manufacturing. This study presents an Uncertainty Quantification (UQ) analysis on a typical supersonic nozzle cascade for ORC applications, by considering a two-dimensional high-fidelity turbulent Computational Fluid Dynamic (CFD) model. Kriging-based techniques are used in order to take into account at a low computational cost, the combined effect of uncertainties associated to operating conditions, fluid parameters, and geometric tolerances. The geometric variability is described by a finite Karhunen-Loeve expansion representing a non-stationary Gaussian random field, entirely defined by a null mean and its autocorrelation function. Several results are illustrated about the ANOVA decomposition of several quantities of interest for different operating conditions, showing the importance of geometric uncertainties on the turbine performances.

High-order fully implicit solver for all-speed fluid dynamics

We introduce a novel Newton–Krylov (NK)-based fully implicit algorithm for solving fluid flows in a wide range of flow conditions—from variable density nearly incompressible to supersonic shock dynamics. The key enabling feature of our all-speed solver is the ability to efficiently solve conservation laws by choosing a set of independent variables that produce a well-conditioned Jacobian matrix for the linear iterations of the global nonlinear iterative solver. In particular, instead of choosing to discretize the conservative variables (density, momentum, total energy), which is traditionally used in Eulerian high-speed compressible fluid dynamics, we demonstrate superior performance by discretizing the primitive variables—pressure–velocity–temperature in the very low-Mach flow limits or density–velocity–temperature/entropy in the shock dynamics range. Moreover, our method allows us to avoid direct inversion of the mass matrix in discrete time derivatives, which is usually an additional source for stiffness, especially pronounced when going to very high-order schemes with non-orthogonal basis functions. Here, we show robust solutions obtained for discontinuous finite element discretization up to seventh-order accuracy. Another important aspect of the solution algorithm is the Advection Upstream Splitting Method (AUSM), adopted to compute numerical fluxes within our reconstructed discontinuous Galerkin (rDG) spatial discretization scheme. The use of the low-Mach modification of the hyperbolic flux operator is found to be necessary for enabling robust simulations of very stiff liquids and metals for Mach numbers below $$M=10^{-5}$$ , which is well known to be very computationally challenging for compressible solvers. We demonstrate that our fully implicit rDG-NK solver with the $${\mathrm{AUSM}}^{+}$$ -up flux treatment produces efficient and high-resolution numerical solutions at all speeds, ranging from vanishing Mach numbers to transonic and supersonic, without substantial modifications of the solution procedures. (At high speed, we add limiting and use a simpler preconditioning of the Krylov solver.) Numerical examples include nearly incompressible constant-property flow past a backward-facing step with heat transfer, low-Mach variable-property channel flow of water at supercritical state, phase change and melt pool dynamics for laser spot welding and selective laser melting in additive manufacturing, and Mach 3 flow in a wind tunnel with a step.

Lost and found sunquake in the 6 September 2011 flare caused by beam electrons

The active region NOAA 11283 produced two X-class flares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class flare occurred on September 6, 2011 and was associated with the first of two homologous white light flares produced by this region, but no sunquake was found with it despite the one being detected in the second flare of 7 September 2011. In this paper we present the first observation of a sunquake for the 6 September 2011 flare detected via statistical significance analysis of egression power and verified via directional holography and time–distance diagram. The surface wavefront exhibits directional preference in the north-west direction We interpret this sunquake and the associated flare emission with a combination of a radiative hydrodynamic model of a flaring atmosphere heated by electron beam and a hydrodynamic model of acoustic wave generation in the solar interior generated by a supersonic shock. The hydrodynamic model of the flaring atmosphere produces a hydrodynamic shock travelling with supersonic velocities toward the photosphere and beneath. For the first time we derive velocities (up to 140 km s−1) and onset time (about 50 s after flare onset) of the shock deposition at given depths of the interior. The shock parameters are confirmed by the radiative signatures in hard X-rays and white light emission observed from this flare. The shock propagation in the interior beneath the flare is found to generate acoustic waves elongated in the direction of shock propagation, that results in an anisotropic wavefront seen on the solar surface. Matching the detected seismic signatures on the solar surface with the acoustic wave front model derived for the simulated shock velocities, we infer that the shock has to be deposited under an angle of about 30° to the local solar vertical. Hence, the improved seismic detection technique combined with the double hydrodynamic model reported in this study opens new perspectives for observation and interpretation of seismic signatures in solar flares.

Effect of shock waves on thermophysical properties of ADP and KDP crystals

Ammonium Dihydrogen Phosphate (ADP) and Potassium Dihydrogen Phosphate (KDP) crystals are grown by slow evaporation method at ambient temperature. The said crystals are utilized as a test specimen and subjected to one-dimensional ‘loading of shock waves’ generated by rupturing a paper diaphragm with Mach number of 1.9 using supersonic low energy table-top shock tube. Thermal diffusivity of crystal is measured using Photoacoustic spectrometer (PAS) for the normal and shock loaded crystals, thermal conductivity and thermal effusivity are computed for the given volumetric specific heat capacity of the crystals. XRD characterization studies reveals that KDP crystal has better immunity to shock wave than ADP crystal.

Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport

The impact of the -drift in the cross-field transport and its effect on the density and power scrape-off layer (SOL) width in the limit of low anomalous transport is studied with the fluid code SolEdge2D. In the first part of the work, the simulations are run with an isothermal reduced fluid model. It is found that a -drift dominated regime is reached in all geometries studied (JET-like, ASDEX-like and circular analytic geometries), and that the transition toward this regime comes along with the apparition of supersonic shocks, and a complex parallel equilibrium. The parametric dependencies of the SOL width in this regime are investigated, and the temperature and the poloidal magnetic field are found to be the principal parameters governing the evolution of the SOL width. In the second part of this paper, the impact of additional physics is studied (inclusion of the centrifugal drift, self-consistent variation of temperature and the treatment of the neutral species). The addition of centrifugal drift and neutral species are shown to play a role in the establishment of the parallel equilibrium, impacting the SOL’s width, although the role of the centrifugal drift is limited to a low diffusion level. Finally, the numerical results are compared with the estimate of the Goldston’s heuristic drift based model (HD-model), the starting point of our study, and which has shown good agreement with experimental scaling laws. We find that the particles SOL widths in the -drift dominated regime are at least two times smaller than the estimate of the HD-model. Moreover, in the parametric dependencies proposed by the HD-model, the dependency with is retrieved, but not the one on T.

Aerothermoelastic analysis of composite laminated trapezoidal panels in supersonic airflow

The aerothermoelastic properties of composite laminated trapezoidal panels considering the compressibility of supersonic airflow and shock wave are studied. Due to the irregular configuration of composite laminated trapezoidal panel and complex thermal fluid–structure interaction, it is impossible to solve this problem by analytical methods. An effective finite element method (FEM) is developed to establish temperature equation and aerothermoelastic equation of motion of the complex trapezoidal panel. The first order piston theory is employed to evaluate the aerodynamic pressure. Based on the developed FEM, the thermal diffusion equation and the Galerkin’s method are applied to establish the temperature equation of the panel, and the complex temperature distribution of the panel is obtained. Combining the thermal and aeroelastic models, the aerothermoelastic equation of motion of the composite trapezoidal panel is established using Hamilton’s principle. Through the numerical analyses, some useful and significant results are obtained, and the advantages and disadvantages of various parameters of the panels are summarized. Because of the aerodynamic heating under the supersonic airflow, the buckling of the panel caused by thermal effect and the flutter caused by supersonic airflow are discussed considering the influences of various parameters. The interaction of the thermal and aerodynamic forces is also analyzed.

Star formation induced by cloud–cloud collisions and galactic giant molecular cloud evolution

Abstract Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud–cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H i gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs $\gtrsim 10^{5.5}\,M_{\odot }$ (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

Real-Time Tomography of Gas-Jets with a Wollaston Interferometer

A tomographic gas-density diagnostic using a Single-Beam Wollaston Interferometer able to characterize non-symmetric density distributions in gas jets is presented. A real-time tomographic algorithm is able to reconstruct three-dimensional density distributions. A Maximum Likelihood-Expectation Maximization algorithm, an iterative method with good convergence properties compared to simple back projection, is used. With the use of graphical processing units, real-time computation and high resolution are achieved. Two different gas jets are characterized: a kHz, piezo-driven jet for lower densities and a solenoid valve-based jet producing higher densities. While the first jet is used for free electron laser photon beam characterization, the second jet is used in laser wake field acceleration experiments. In this latter application, well-tailored and non-symmetric density distributions produced by a supersonic shock front generated by a razor blade inserted laterally to the gas flow, which breaks cylindrical symmetry, need to be characterized.

A small-scale dynamo in feedback-dominated galaxies – III. Cosmological simulations

Magnetic fields are widely observed in the Universe in virtually all astrophysical objects, from individual stars to entire galaxies, even in the intergalactic medium, but their specific generation has long been debated. Due to the development of more realistic models of galaxy formation, viable scenarios are emerging to explain cosmic magnetism, thanks to both deeper observations and more efficient and accurate computer simulations. We present here a new cosmological high-resolution zoom-in magnetohydrodynamic (MHD) simulation, using the adaptive mesh refinement (AMR) technique, of a dwarf galaxy with an initially weak and uniform magnetic seed field that is amplified by a small-scale dynamo driven by supernova-induced turbulence. As first structures form from the gravitational collapse of small density fluctuations, the frozen-in magnetic field separates from the cosmic expansion and grows through compression. In a second step, star formation sets in and establishes a strong galactic fountain, self-regulated by supernova explosions. Inside the galaxy, the interstellar medium becomes highly turbulent, dominated by strong supersonic shocks, as demonstrated by the spectral analysis of the gas kinetic energy. In this turbulent environment, the magnetic field is quickly amplified via a small-scale dynamo process and is finally carried out into the circumgalactic medium by a galactic wind. This realistic cosmological simulation explains how initially weak magnetic seed fields can be amplified quickly in early, feedback-dominated galaxies, and predicts, as a consequence of the small scale dynamo process, that high-redshift magnetic fields are likely to be dominated by their small scale components.

Generalised correlations of blow-off and flame quenching for sub-sonic and choked jet flames

Dimensionless groups suggested by the mathematical modelling of subsonic fuel jet flames, and extensive experimental data, have been reasonably successsful in correlating dimensionles flame heights and flame lift-off distances in terms of a dimensionless flow number. This approach is extended to the more exacting correlations that define regimes of flame quenching, blow-off, and lifted flames. Experimental data from these diverse sources are analysed, and the bounds of these regimes are expressed in terms of the critical minimum jet pipe diameter to avoid blow-off, normalised by the laminar flame thickness for the maximum burning velocity mixture, and the flow number. The regimes extend from low Reynolds number laminar flows in hypodermic tubes to high Reynolds number choked flows, with supersonic shocks.Data are well corrrelated in the subsonic regime for a range of hydrocarbon gases, in which critical pipe diameters for the avoidance of blow-off increase with flow number. Matters are more complex in the extended choked flow regime, in which there are less data. This regime of supersonic flow and shock waves is one of improved fuel/air mixing and enhanced reactivity, to such an extent that the critical pipe diameter, after reaching a maximum, decreases. Data are presented in this regime, and indeed over the full range of conditions, for methane, propane and hydrogen jet flames. Hydrogen exhibits more reactive characteristics than the hydrocarbons. In terms of the correlating parameters, whereas laminar flame thickness is related to that of the non-reacting preheat zone, such a zone is difficult to define with hydrogen, as a consequence of the upstream diffusion of H atoms, and this aspect is discusssed.

Local well-posedness of a multidimensional shock wave for the steady supersonic isothermal flow

In this paper, we prove the local existence, uniqueness and stability of a supersonic shock for the supersonic isothermal incoming flow past a curved cone. Major difficulties include constructing an appropriate solution and treating the Neumann boundary conditions and local stability condition.

Supersonic flow onto solid wedges, multidimensional shock waves and free boundary problems

When an upstream steady uniform supersonic flow impinges onto a symmetric straight-sided wedge, governed by the Euler equations, there are two possible steady oblique shock configurations if the wedge angle is less than the detachment angle—the steady weak shock with supersonic or subsonic downstream flow (determined by the wedge angle that is less than or greater than the sonic angle) and the steady strong shock with subsonic downstream flow, both of which satisfy the entropy condition. The fundamental issue—whether one or both of the steady weak and strong shocks are physically admissible solutions—has been vigorously debated over the past eight decades. In this paper, we survey some recent developments on the stability analysis of the steady shock solutions in both the steady and dynamic regimes. For the static stability, we first show how the stability problem can be formulated as an initial-boundary value type problem and then reformulate it into a free boundary problem when the perturbation of both the upstream steady supersonic flow and the wedge boundary are suitably regular and small, and we finally present some recent results on the static stability of the steady supersonic and transonic shocks. For the dynamic stability for potential flow, we first show how the stability problem can be formulated as an initial-boundary value problem and then use the self-similarity of the problem to reduce it into a boundary value problem and further reformulate it into a free boundary problem, and we finally survey some recent developments in solving this free boundary problem for the existence of the Prandtl-Meyer configurations that tend to the steady weak supersonic or transonic oblique shock solutions as time goes to infinity. Some further developments and mathematical challenges in this direction are also discussed.

Supersonic thermal excitation-induced shock wave in black phosphorene

Thermal transport in low-dimensional materials possesses various novel features since anomalous energy carriers may heavily contribute. Black phosphorene exhibits excellent thermal properties and thus it attracts attention about the possible existence of anomalous energy carriers. In this paper, we find that shockwave appears as a dominant energy carrier in the zigzag direction of black phosphorene when a supersonic thermal excitation above a critical strength is exerted. Comparing with the diffusive thermal transport, shockwave carries a considerable amount of excitation energy and propagates faster than the local acoustic speed. It leads to a strong anisotropic enhancement in the transport speed of thermal energy in the zigzag direction, up to a factor of twofold compared with no shockwave. The linear increase of velocity with intensity and exponential decay of intensity with time of the shockwave are observed. Unlike solitary waves, the collision of shockwaves exhibits no phase shift in the spatial-temporal trajectory. Moreover, it shows that shockwave velocity decreases with tensile strain, which is favorable for modulation. Our results reveal a possible anomalous energy transport process and may help in designing black phosphorene-based thermal devices.

Phosphodiesterase-4 inhibition restored hippocampal long term potentiation after primary blast

Due to recent military conflicts and terrorist attacks, blast-induced traumatic brain injury (bTBI) presents a health concern for military and civilian personnel alike. Although secondary blast (penetrating injury) and tertiary blast (inertia-driven brain deformation) are known to be injurious, the effects of primary blast caused by the supersonic shock wave interacting with the skull and brain remain debated. Our group previously reported that in vitro primary blast exposure reduced long-term potentiation (LTP), the electrophysiological correlate of learning and memory, in rat organotypic hippocampal slice cultures (OHSCs) and that primary blast affects key proteins governing LTP. Recent studies have investigated phosphodiesterase-4 (PDE4) inhibition as a therapeutic strategy for reducing LTP deficits following inertia-driven TBI. We investigated the therapeutic potential of PDE4 inhibitors, specifically roflumilast, to ameliorate primary blast-induced deficits in LTP. We found that roflumilast at concentrations of 1nM or greater prevented deficits in neuronal plasticity measured 24h post-injury. We also observed a therapeutic window of at least 6h, but <23h. Additionally, we investigated molecular mechanisms that could elucidate this therapeutic effect. Roflumilast treatment (1nM delivered 6h post-injury) significantly increased total AMPA glutamate receptor 1 (GluR1) subunit expression, phosphorylation of the GluR1 subunit at the serine-831 site, and phosphorylation of stargazin at the serine-239/240 site upon LTP induction, measured 24h following injury. Roflumilast treatment significantly increased PSD-95 regardless of LTP induction. These findings indicate that further investigation into the translation of PDE4 inhibition as a therapy following bTBI is warranted.

Numerical modeling of a glow discharge through a supersonic bow shock in air

The interaction between a glow discharge and the bow shock of a Mach 3 air flow around a truncated conical model with a central spike is modeled, and comparison is made with prior experimental results. The KRONOS workflow for plasma modeling in flow fields, which has recently been developed at ONERA, was used for the modeling. Based on the quasi-neutral approximation, it couples hypersonic and reactive flow fields with electron chemistry, including the effect of non-Maxwellian electron energy distribution function. The model used for the discharge involves 12 species and 82 reactions, including ionization, electronic and vibrational excitation, and attachment. The simulations reproduce the main features of the discharge observed experimentally well, in particular, the very recognizable topology of the discharge. It was found from the simulations that behind the bow shock, in the afterglow, the negative ion flow ensures the electrical conduction and the establishment of the glow discharge. The influence of kinetic rates on the voltage-current characteristics is discussed.

Drift-based scrape-off particle width in X-point geometry

The Goldston heuristic estimate of the scrape-off layer width (Goldston 2012 Nucl. Fusion 52 013009) is reconsidered using a fluid description for the plasma dynamics. The basic ingredient is the inclusion of a compressible diamagnetic drift for the particle cross field transport. Instead of testing the heuristic model in a sophisticated numerical simulation including several physical mechanisms working together, the purpose of this work is to point out basic consequences for a drift-dominated cross field transport using a reduced fluid model. To evaluate the model equations and prepare them for subsequent numerical solution a specific analytical model for 2D magnetic field configurations with X-points is employed. In a first step parameter scans in high-resolution grids for isothermal plasmas are done to assess the basic formulas of the heuristic model with respect to the functional dependence of the scrape-off width on the poloidal magnetic field and plasma temperature. Particular features in the 2D-fluid calculations—especially the appearance of supersonic parallel flows and shock wave like bifurcational jumps—are discussed and can be understood partly in the framework of a reduced 1D model. The resulting semi-analytical findings might give hints for experimental proof and implementation in more elaborated fluid simulations.

An investigation on supersonic bevelled nozzle jets

This paper reports upon a numerical and experimental study on supersonic jets exhausting from bevelled nozzles with 30° and 60° exit inclination angles. To begin with, a simple but effective method to design a shock-free convergent–divergent circular jet nozzle to produce a well-conditioned supersonic Ma = 1.5 jet based on simple circular fillets is presented. Subsequently Reynolds-Averaged Navier–Stokes simulations of circular non-bevelled and bevelled nozzle jets were performed at over-expanded, perfectly expanded and under-expanded conditions. Lastly, these supersonic jets were visualized experimentally using a modified Z-type Schlieren system. Results show that the shock cell structure within the jet potential core changes from a diamond pattern to triangular and rectangular patterns as the nozzle pressure ratio and inclination angle are varied. Furthermore, jet plumes are deflected differently when the bevelled nozzles were operated at off-design conditions, with changes to the supersonic jet potential core length. Finally, quantitative analysis of the results reveals that bevelled nozzles are able to reduce the intensity of the supersonic jet shock cell structure considerably, which is potentially useful for broadband shock-associated noise mitigation purposes.

Embedded star clusters as sources of high-energy cosmic rays

Massive stars are mainly found in stellar associations. These massive star clusters occur in the heart of giant molecular clouds. The strong stellar wind activity in these objects generates large bubbles and induces collective effects that could accelerate particles up to high energy and produce gamma rays. The best way to input an acceleration origin to the stellar wind interaction in massive stellar cluster is to observe young massive star clusters in which no supernova explosion has occurred yet. This work aims to constrain the part of stellar wind mechanical energy that is converted into energetic particles using the sensitivity of the ongoing Fermi/LAT instrument. This work further provides detailed predictions of expected gamma-ray fluxes in the view of the on-set of the next generation of imaging atmospheric Cherenkov telescopes. A one-zone model where energetic particles are accelerated by repeated interactions with strong supersonic shocks occurring in massive star clusters was developed. The particle escape from the star cluster and subsequent interaction with the surrounding dense material and magnetic fields of the HII region was computed. We applied this model to a selection of eight embedded star clusters constricted by existing observations. We evaluated the gamma-ray signal from each object, combining both leptonic and hadronic contributions. We searched for these emissions in the Fermi/LAT observations in the energy range from 3 to 300 GeV and compared them to the sensitivity of the Cherenkov Telescope Array. No significant gamma-ray emission from these star clusters has been found. Less than 10% of stellar wind luminosities are supplied to the relativistic particles. Some clusters even show acceleration efficiency of less than 1%. The CTA would be able to detect gamma-ray emission from several clusters in the case of an acceleration efficiency of close to 1%.