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Lin, E. P., Y. E. Kim i J. C. Hermanson. "Structure of Compression Waves on Supersonic Droplets". AIAA Journal 54, nr 2 (luty 2016): 777–81. http://dx.doi.org/10.2514/1.j054412.
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B Saheby, Eiman, Xing Shen i Anthony P. Hays. "Design and performance study of a parametric diverterless supersonic inlet". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, nr 2 (24.09.2019): 470–89. http://dx.doi.org/10.1177/0954410019875384.
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Diverterless supersonic inlet integration for a flight vehicle requires a three-dimensional compression surface (bump) design with an acceptable shock structure and boundary layer diversion; this results in a low drag induction system with acceptable propulsive efficiency. In this investigation, a computational fluid dynamics-based-generated bump is used to design an integrated diverterless supersonic inlet without any bleed mechanism on a forebody with a large wetted area. Numerical solution of the Navier–Stokes equations simulates the flow pattern of the configuration. The forebody design analysis includes simulating the effects of angle of attack and sideslip by dependent computational domains. Results demonstrate the ability of the bump surface to keep the shock structures in an operational mode even at high supersonic angles of attack. Analysis of shock structures and shock wave boundary layer interactions at supersonic maneuver conditions indicate that the aerodynamic efficiency of the diverterless supersonic inlet in conditions with a thick boundary layer and high angles of attack is sufficient to ensure operation throughout the supersonic flight envelope.
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Masud, J. "Flow field and performance analysis of an integrated diverterless supersonic inlet". Aeronautical Journal 115, nr 1170 (sierpień 2011): 471–80. http://dx.doi.org/10.1017/s0001924000006114.
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Abstract In this paper the computed flow and performance characteristics at low angle-of-attack (AOA) of an integrated diverterless supersonic inlet (DSI) are presented. The subsonic characteristics are evaluated at M∞ = 0·8 while the supersonic characteristics are evaluated at M∞= 1·7, which is near the design Mach number for the intake. In addition to the external flow features, the internal intake duct flow behaviour is also evaluated. The results of this study indicate effective boundary layer diversion due to the ‘bump’ compression surface in both subsonic and supersonic regimes. At M∞ = 1·7, the shockwave structure (oblique/normal shockwave) on the ‘bump’ compression surface and intake inlet is satisfactory at design (critical) mass flow rate. The intake duct flow behaviour at subsonic and supersonic conditions is generally consistent with ‘Y’ shaped intake duct of the present configuration. The secondary flow structure inside the duct has been effectively captured by present computations. The computed intake total pressure recovery at M∞ = 1·7 exhibits higher-than-conventional behaviour at low mass flow ratios, which is attributed to unique inlet design. Overall computed subsonic and supersonic total pressure recovery characteristics are satisfactory under the evaluated conditions and are also in agreement with wind tunnel test data.
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Knight, Doyle D., C. C. Horstman i Seymour Bogdonoff. "Structure of supersonic turbulent flow past a swept compression corner". AIAA Journal 30, nr 4 (kwiecień 1992): 890–96. http://dx.doi.org/10.2514/3.11006.
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Saheby, Eiman B., Xing Shen, Anthony P. Hays i Zhang Jun. "The inlet flow structure of a conceptual open-nose supersonic drone". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 235, nr 12 (25.02.2021): 1687–705. http://dx.doi.org/10.1177/0954410020983043.
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This study describes the aerodynamic efficiency of a forebody–inlet configuration and computational investigation of a drone system, capable of sustainable supersonic cruising at Mach 1.60. Because the whole drone configuration is formed around the induction system and the design is highly interrelated to the flow structure of forebody and inlet efficiency, analysis of this section and understanding its flow pattern is necessary before any progress in design phases. The compression surface is designed analytically using oblique shock patterns, which results in a low drag forebody. To study the concept, two inlet–forebody geometries are considered for Computational Fluid Dynamic simulation using ANSYS Fluent code. The supersonic and subsonic performance, effects of angle of attack, sideslip, and duct geometries on the propulsive efficiency of the concept are studied by solving the three-dimensional Navier–Stokes equations in structured cell domains. Comparing the results with the available data from other sources indicates that the aerodynamic efficiency of the concept is acceptable at supersonic and transonic regimes.
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GAO, B., i Z. N. WU. "A study of the flow structure for Mach reflection in steady supersonic flow". Journal of Fluid Mechanics 656 (21.05.2010): 29–50. http://dx.doi.org/10.1017/s0022112010001011.
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In this paper we study the waves generated over the slipline and their interactions with other waves for Mach reflection in steady two-dimensional supersonic flow. We find that a series of expansion and compression waves exist over the slip line, even in the region immediately behind the leading part of the reflected shock wave, previously regarded as a uniform flow. These waves make the leading part of the slipline, previously regarded as straight, deviate nonlinearly towards the reflecting surface. When the transmitted expansion waves from the upper corner first intersect the slipline, an inflexion point is produced. Downstream of this inflexion point, compression waves are produced over the slipline. By considering the interaction between the various expansion or compression waves, we obtain a Mach stem height, the shape and position of the slipline and reflected shock wave, compared well to computational fluid dynamics (CFD) results. We also briefly consider the case with a subsonic portion behind the reflected shock wave. The global flow pattern is obtained through CFD and the starting point of the sonic line is identified through a simple analysis. The sonic line appears to coincide with the first Mach wave from the upper corner expansion fan after transmitted from the reflected shock wave.
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Cassel, K. W., A. I. Ruban i J. D. A. Walker. "An instability in supersonic boundary-layer flow over a compression ramp". Journal of Fluid Mechanics 300 (10.10.1995): 265–85. http://dx.doi.org/10.1017/s0022112095003685.
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Separation of a supersonic boundary layer (or equivalently a hypersonic boundary layer in a region of weak global interaction) near a compression ramp is considered for moderate wall temperatures. For small ramp angles, the flow in the vicinity of the ramp is described by the classical supersonic triple-deck structure governing a local viscous-inviscid interaction. The boundary layer is known to exhibit recirculating flow near the corner once the ramp angle exceeds a certain critical value. Here it is shown that above a second and larger critical ramp angle, the boundary-layer flow develops an instability. The instability appears to be associated with the occurrence of inflection points in the streamwise velocity profiles within the recirculation region and develops as a wave packet which remains stationary near the corner and grows in amplitude with time.
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Liu, Yi, Zhi Guo Dou i Li Wei Duan. "Numerical Investigation of Cavity Flow Field Characteristics in Supersonic Flow". Applied Mechanics and Materials 789-790 (wrzesień 2015): 368–72. http://dx.doi.org/10.4028/www.scientific.net/amm.789-790.368.
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The cold flow field in a two dimensional cavity of supersonic combustor has been simulated numerically by using the compressible flow Navier-Stokes equation with theκ-ωSST turbulence model. The flow field structure of different cavity aft wall slope angle (16°,30° and 90°) , different fore aft wall height ratio (1 and 2) and different length depth ratio (3 and 5) are analyzed. The conclusions are as follows: As cavity aft wall slope angle decreases, the compression wave formed at cavity leading separation corner shifts into expansion wave, the shear layer moves into cavity gradually; As cavity fore aft wall height ratio increases from one to two, the expansion wave formed at cavity leading separation corner strengthens and there is no compression wave formed at;As cavity length depth ratio increases from three to five, the compression or expansion wave formed at cavity leading separation corner weakens, cavity bottom wall pressure tends to be constant and aft wall pressure rises.
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Niu, Keishiro. "Implosion motion and fuel compression in direct or indirect driven target". Laser and Particle Beams 7, nr 3 (sierpień 1989): 505–9. http://dx.doi.org/10.1017/s0263034600007473.
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When a one-shell three-layer cryogenic target is irradiated by a driver beam of total energy 10 MJ and pulse width 30 ns, the pusher pressure increases to 1013 Pa, accelerating fuel toward target center, and the fuel implosion velocity reaches 3 × 105 m/s. A spherical hollow target plays the role of a supersonic converging nozzle, and the fuel is compressed to 269 times the solid density in the supersonic region and to 3·51 × 104 times in subsonic region. Nonuniform beam-energy-deposition in pusher layer causes nonuniform pusher pressure and hence nonuniform implosion, which reduces fuel compression significantly. The smoothing of pusher pressure by radiative energy transfer, or gas-filled target instead of cryogenic hollow target can be used to reduce the defect of nonuniform implosion. At last, the structure of an indirect driven target is proposed to smooth out pusher pressure in spite of nonuniform beam irradiation.
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Watanabe, Yasumasa, Alec Houpt i Sergey Leonov. "Plasma-Assisted Control of Supersonic Flow over a Compression Ramp". Aerospace 6, nr 3 (12.03.2019): 35. http://dx.doi.org/10.3390/aerospace6030035.
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This study considers the effect of an electric discharge on the flow structure near a 19.4° compression ramp in Mach-2 supersonic flow. The experiments were conducted in the supersonic wind tunnel SBR-50 at the University of Notre Dame. The stagnation temperature and pressure were varied in a range of 294–600 K and 1–3 bar, respectively, to attain various Reynolds numbers ranging from 5.3 × 105 to 3.4 × 106 based on the distance between the exit of the Mach-2 nozzle and the leading edge of the ramp. Surface pressure measurements, schlieren visualization, discharge voltage and current measurements, and plasma imaging with a high-speed camera were used to evaluate the plasma control authority on the ramp pressure distribution. The plasma being generated in front of the compression ramp shifted the shock position from the ramp corner to the electrode location, forming a flow separation zone ahead of the ramp. It was found that the pressure on the compression surface reduced almost linearly with the plasma power. The ratio of pressure change to flow stagnation pressure was also an increasing function of the ratio of plasma power to enthalpy flux, indicating that the task-related plasma control effectiveness ranged from 17.5 to 25.
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ALHUSSAN, KHALED, i CHARLES GARRIS. "EFFECT OF CHANGING THROAT DIAMETER RATIO ON A STEAM SUPERSONIC PRESSURE EXCHANGE EJECTOR". Modern Physics Letters B 19, nr 28n29 (20.12.2005): 1715–18. http://dx.doi.org/10.1142/s0217984905010293.
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This paper will explain the structure of the flow induction in a non-steady supersonic fluid in which steam is the working fluid. The ratio of the throat diameter is varied and the analyses related to the induction processes are studied. This ejector is used for compression applications. The work to be presented herein is a Computational Fluid Dynamics investigation of the complex fluid mechanisms that occur inside a non-steady, three-dimensional, steam supersonic pressure exchange ejector, specifically with regard to the pressure exchange mechanisms and the induction processes between a primary fluid and a secondary fluid and how this is related to the shape of the aerodynamic shroud-diffuser surface. The results will show the correct throat diameter ratio that is capable of producing the desire affect of the flow induction in a three-dimensional supersonic, non-steady, viscous flow. The calculated throat diameter ration is about 2.90.
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Zhang, Hailong, Jiping Wu, Jian Chen i Weidong Liu. "Characteristics of Large-Scale Structures in Supersonic Planar Mixing Layer with Finite Thickness". Advances in Mechanical Engineering 6 (1.01.2014): 878679. http://dx.doi.org/10.1155/2014/878679.
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Nanoparticle-based planar laser scattering (NPLS) experiments and large eddy simulation (LES) were launched to get the fine structure of the supersonic planar mixing layer with finite thickness in the present study. Different from the turbulent development of supersonic planar mixing layer with thin thickness, the development of supersonic planar mixing layer with finite thickness is rapidly. The large-scale structures of mixing layer that possess the characters of quick movement and slow changes transmit to downriver at invariable speed. The transverse results show that the mixing layer is strip of right and dim and possess 3D characteristics. Meanwhile the vortices roll up from two sides to the center. Results indicate that the higher the pressure of the high speed side is, the thicker the mixing layer is. The development of mixing layer is restrained when the pressure of lower speed side is higher. The momentum thickness goes higher with the increase of the clapboard thickness. Through increasing the temperature to change the compression can affect the development of the vortices. The present study can make a contribution to the mixing enhancement and provide initial data for the later investigations.
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Yang, Tian-Peng, Jiang-Feng Wang, Fa-Ming Zhao, Xiao-Feng Fan i Yu-Han Wang. "Numerical analysis of exhaust jet secondary combustion in hypersonic flow field". Modern Physics Letters B 32, nr 12n13 (10.05.2018): 1840045. http://dx.doi.org/10.1142/s0217984918400456.
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The interaction effect between jet and control surface in supersonic and hypersonic flow is one of the key problems for advanced flight control system. The flow properties of exhaust jet secondary combustion in a hypersonic compression ramp flow field were studied numerically by solving the Navier–Stokes equations with multi-species and combustion reaction effects. The analysis was focused on the flow field structure and the force amplification factor under different jet conditions. Numerical results show that a series of different secondary combustion makes the flow field structure change regularly, and the temperature increases rapidly near the jet exit.
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McKENZIE, J. F., E. DUBININ i K. SAUER. "Nonlinear waves propagating transverse to the magnetic field". Journal of Plasma Physics 65, nr 3 (kwiecień 2001): 213–33. http://dx.doi.org/10.1017/s0022377801001076.
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We generalize the classical work of Adlam and Allen [Phil. Mag.3, 448 (1958)] on solitons in a cold plasma propagating perpendicular to the magnetic field to include the effects of plasma pressure. This is done by making extensive use of the properties of total momentum conservation (denoted by the term ‘momentum hodograph’, since it yields a locus in the plane of the electron and proton speeds in the direction of the wave) and the energy integral of the system as a whole. These relations elucidate the phase and integral curves of stationary flows, from which soliton solutions may be constructed. In general, only compressive solitons are permitted, and we have found an analytical expression for the critical fast Mach number as a function of the proton acoustic Mach number, which shows that it varies from its classical value of 2 (at large proton acoustic Mach numbers) to unity, where the incoming flow is proton-sonic. At the critical fast Mach number, two possible soliton-like solutions can be constructed. One is the classical compression, in which the magnetic field develops a cusp in the centre of the wave. The other is a compression in the magnetic field followed by a deep depression in the centre of the wave, which is completed by the mirror image of this signature of compression–rarefaction. This structure involves a smooth supersonic–subsonic transition in the proton flow. For Mach numbers in excess of the critical one, this kind of structure can also be constructed, but now the magnetic field is cusp-like at the points of maximum compression.
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Chen, Bing, Hongyang Chen, Tao Mo, Shenshen Liu i Hongyin Jia. "The analysis on the flow characteristics of supersonic inlet considering structural vibration". Journal of Physics: Conference Series 2441, nr 1 (1.03.2023): 012001. http://dx.doi.org/10.1088/1742-6596/2441/1/012001.
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Abstract Inlet is the key part which can influence the performance of airframe-propulsion integration for the air-breathing vehicle. In supersonic or hypersonic condition, the local vibration of the structure will change the integrated performance greatly. The work is to study the influence of the structural vibration of the compression surface on the inlet’s performance, and the vibration factors such as amplitude, wavelength and frequency are evaluated. The influence of the vibration factors on the inlet’s performance is studied. The research shows that the structure of the flow field for the inlet is changed. The influence is more obvious when the vibration occurs to be more closed to the lip. Besides, the wavelength has more influence than the amplitude, and the influence of the frequency is smallest.
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He, Jia Wu, Xiao Ming Wang, Shi Ning Ma, Chang Qing Li i Chen Chen. "Characterization of Surface Strengthening Layer of 7A52 Aluminum Alloy by Supersonic Shot Peening and its Tribological Prop". Advanced Materials Research 148-149 (październik 2010): 1177–81. http://dx.doi.org/10.4028/www.scientific.net/amr.148-149.1177.
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To improve its surface global performance, 7A52 aluminum alloy was treated by means of supersonic shot peening, then the structure of surface strengthening layer was characterized and its tribological properties were investigated, too. It was found that after having been peened, surface hardness of 7A52 aluminum alloy increased by 80%, surface crystalline grains were refined, a surface compression stress layer with thickness of 320μm was fabricated, which reached maximum 210MPa at the distance of 80~100μm from the top treated surface; The alloy performs superb tribological properties under both unlubrication friction and lubrication friction.
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Zapryagaev, Valeriy, Ivan Kavun i Nikolay Kiselev. "Flow Feature in Supersonic Non-Isobaric Jet near the Nozzle Edge". Aerospace 9, nr 7 (13.07.2022): 379. http://dx.doi.org/10.3390/aerospace9070379.
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Using the example of studying the supersonic underexpanded jet initial section, the issue of interpreting the experimental visualization data and Pitot pressure measurement data using the results of numerical calculations (2d RANS k-ω SST) is discussed. It is shown that the gradient S-shaped feature of the gas-dynamic structure near the nozzle exit, observed in the form of a barrel shock, is a characteristic that separates the expansion and compression regions, and downstream is transformed into a barrel shock. It has been established that the reason for the observed S-shaped curvature of this feature is the axisymmetric nature of the jet flow.
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Wei, Pei, Zhengying Wei, Guangxi Zhao, Y. Bai i Chao Tan. "Optimal Design of Nozzle for Supersonic Atmosphere Plasma Spraying". High Temperature Materials and Processes 35, nr 7 (1.08.2016): 685–96. http://dx.doi.org/10.1515/htmp-2015-0036.
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AbstractThrough numerical simulation, key issues concerning the plasma jet features as well as the sizes of nozzle for supersonic atmosphere plasma spraying (SAPS) were analyzed in this paper. Numerical results were compared with the experimental measurements and a good agreement has been achieved. Due to the effect of mechanical compression, the increasing sizes of r1, r2, r3 and r4 (r1, r2, r3 and r4 are the sizes of nozzle) lead to a decrease in temperature and velocity of plasma jet. But large size of r5 can increase the external temperature and velocity of plasma jet, which benefit particles accelerating at the far downstream region. A new nozzle was designed based on the simulation results. Compared to the temperature and velocity of plasma jet in the original nozzle, the maximum temperature and velocity of plasma jet in new structure are increased by about 9.8% and 44.5%, which is a benefit to the particles to reach a higher speed and surface temperature.
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Sun, Mingbo, Neil D. Sandham i Zhiwei Hu. "Turbulence structures and statistics of a supersonic turbulent boundary layer subjected to concave surface curvature". Journal of Fluid Mechanics 865 (18.02.2019): 60–99. http://dx.doi.org/10.1017/jfm.2019.19.
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Supersonic turbulent flows at Mach 2.7 over concave surfaces for two different radii of curvature were investigated and compared with a flat plate turbulent boundary layer using direct numerical simulations. The streamwise velocity reduces in the outer part of the boundary layer due to compression, while it increases near the wall due to curvature, with a higher shape factor for the concave cases. The near-wall spanwise streak spacing reduces compared to the flat plate, with large-scale streaks and turbulence amplification also observed. Streamwise velocity iso-surfaces and streamlines show the generation of Görtler-like vortices, consistent with significant centrifugal effects. Abundant small vortices are shown to be associated with large baroclinic production of vorticity that is caused by the density and pressure gradients that are associated with concave compression. Profiles of turbulent kinetic energy and turbulent Mach number exhibit a characteristic two-layer structure in the concave boundary layer cases. In the outer layer, turbulence is greatly amplified, whereas a local balance exists in the inner layer. Turbulent energy budget analysis shows that both production and dissipation increase near the concave wall, whereas in the outer part of the boundary layer, the production is increased and ultimately balanced by convection and turbulent transport.
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Farahani, M., i A. Jaberi. "Study of buzz phenomenon using visualization of external shock structure". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, nr 7 (27.06.2018): 2690–98. http://dx.doi.org/10.1177/0954410018785261.
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An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and shock displacement were measured by inspection of visualization pictures in each test. The obtained data from shadowgraphs were compared with those obtained from pressure measurements, and good agreement was found between them. The results revealed that for a moderate value of mass flow rate, the frequency of shock oscillation decreases as Mach number increases. Further, by increasing angle of attack, the shock displacement of oscillation will increase. At non-zero angles of attack, the displacement and frequency of shock motion show different behaviors on the leeward and windward sides of the body.
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Pavalavanni, Pradeep Kumar, Min-Seon Jo, Jae-Eun Kim i Jeong-Yeol Choi. "Numerical Study of Unstable Shock-Induced Combustion with Different Chemical Kinetics and Investigation of the Instability Using Modal Decomposition Technique". Aerospace 10, nr 3 (15.03.2023): 292. http://dx.doi.org/10.3390/aerospace10030292.
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An unstable shock-induced combustion (SIC) case around a hemispherical projectile has been numerically studied which experimentally produced a regular oscillation. Comparison of detailed H2/O2 reaction mechanisms is made for the numerical simulation of SIC with higher-order numerical schemes intended for the use of the code for the hypersonic propulsion and supersonic combustion applications. The simulations show that specific reaction mechanisms are grid-sensitive and produce spurious reactions in the high-temperature region, which trigger artificial instability in the oscillating flow field. The simulations also show that specific reaction mechanisms develop such spurious oscillations only at very fine grid resolutions. The instability mechanism is investigated using the dynamic mode decomposition (DMD) technique and the spatial structure of the decomposed modes are further analyzed. It is found that the instability triggered by the high-temperature reactions strengthens the reflecting compression wave and pushes the shock wave further and disrupts the regularly oscillating mechanism. The spatial coherent structure from the DMD analysis shows the effect of this instability in different regions in the regularly oscillating flow field.
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McKENZIE, J. F. "The fluid-dynamic paradigm of the dust-acoustic soliton". Journal of Plasma Physics 67, nr 5 (czerwiec 2002): 353–62. http://dx.doi.org/10.1017/s0022377802001630.
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In most studies, the properties of dust-acoustic solitons are derived from the first integral of the Poisson equation, in which the shape of the pseudopotential determines both the conditions in which a soliton may exist and its amplitude. Here this first integral is interpreted as conservation of total momentum, which, along with the Bernoulli-like energy equations for each species, may be cast as the structure equation for the dust (or heavy-ion) speed in the wave. In this fluid-dynamic picture, the significance of the sonic points of each species becomes apparent. In the wave, the heavy-ion (or dust) flow speed is supersonic (relative to its sound speed), whereas the protons and electrons are subsonic (relative to their sound speeds), and the dust flow is driven towards its sonic point. It is this last feature that limits the strength (amplitude) of the wave, since the equilibrium point (the centre of the wave) must be reached before the dust speed becomes sonic. The wave is characterized by a compression in the heavies and a compression (rarefaction) in the electrons and a rarefaction (compression) in the protons if the heavies have positive (negative) charge, and the corresponding potential is a hump (dip). These features are elucidated by an exact analytical soliton, in a special case, which provides the fully nonlinear counterpoint to the weakly nonlinear sech2-type solitons associated with the Korteweg–de Vries equation, and indicates the parameter regimes in which solitons may exist.
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Banda-Barragán, W. E., M. Brüggen, C. Federrath, A. Y. Wagner, E. Scannapieco i J. Cottle. "Shock–multicloud interactions in galactic outflows – I. Cloud layers with lognormal density distributions". Monthly Notices of the Royal Astronomical Society 499, nr 2 (23.09.2020): 2173–95. http://dx.doi.org/10.1093/mnras/staa2904.
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ABSTRACT We report three-dimensional hydrodynamical simulations of shocks (${\cal M_{\rm shock}}\ge 4$) interacting with fractal multicloud layers. The evolution of shock–multicloud systems consists of four stages: a shock-splitting phase in which reflected and refracted shocks are generated, a compression phase in which the forward shock compresses cloud material, an expansion phase triggered by internal heating and shock re-acceleration, and a mixing phase in which shear instabilities generate turbulence. We compare multicloud layers with narrow ($\sigma _{\rho }=1.9\bar{\rho }$) and wide ($\sigma _{\rho }=5.9\bar{\rho }$) lognormal density distributions characteristic of Mach ≈ 5 supersonic turbulence driven by solenoidal and compressive modes. Our simulations show that outflowing cloud material contains imprints of the density structure of their native environments. The dynamics and disruption of multicloud systems depend on the porosity and the number of cloudlets in the layers. ‘Solenoidal’ layers mix less, generate less turbulence, accelerate faster, and form a more coherent mixed-gas shell than the more porous ‘compressive’ layers. Similarly, multicloud systems with more cloudlets quench mixing via a shielding effect and enhance momentum transfer. Mass loading of diffuse mixed gas is efficient in all models, but direct dense gas entrainment is highly inefficient. Dense gas only survives in compressive clouds, but has low speeds. If normalized with respect to the shock-passage time, the evolution shows invariance for shock Mach numbers ≥10 and different cloud-generating seeds, and slightly weaker scaling for lower Mach numbers and thinner cloud layers. Multicloud systems also have better convergence properties than single-cloud systems, with a resolution of eight cells per cloud radius being sufficient to capture their overall dynamics.
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Smith, M. D., P. W. J. L. Brand i A. Moorhouse. "Strong magnetic fields in bipolar outflows". Symposium - International Astronomical Union 147 (1991): 373–76. http://dx.doi.org/10.1017/s0074180900239703.
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A supersonic wind from a young star will produce regions of strong magnetic field in the stellar environment. The associated shocks compress the molecular gas, increasing the density n, pressure p, and field B. Crucially, the Alfvén speed, vA∝ B/n1/2, is also increased since the total shock compression is approximately of the form B ∝ n. But is there any evidence for such high vA- or ‘active cloud’ - regions within bipolar outflows? We indicate below one implication which has important observable consequences: fast shocks of low Alfvén number (v/vA) now arise. With a low ionization level, the C-shock structure is qualitatively different from the high Alfvén number flows which are common to ‘quiescent cloud’ conditions. The magnetic-field cushioning now allows molecular hydrogen to survive very fast shocks and broad H2 lines are feasible. We display results which show that the resolved broad lines and line ratio properties in the OMC-1 outflow can be explained with fast bow shocks moving through such active regions.
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Smith, M. D., P. W. J. L. Brand i A. Moorhouse. "Strong magnetic fields in bipolar outflows". Symposium - International Astronomical Union 147 (1991): 373–76. http://dx.doi.org/10.1017/s0074180900199085.
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A supersonic wind from a young star will produce regions of strong magnetic field in the stellar environment. The associated shocks compress the molecular gas, increasing the density n, pressure p, and field B. Crucially, the Alfvén speed, vA∝ B/n1/2, is also increased since the total shock compression is approximately of the form B ∝ n. But is there any evidence for such high vA- or ‘active cloud’ - regions within bipolar outflows? We indicate below one implication which has important observable consequences: fast shocks of low Alfvén number (v/vA) now arise. With a low ionization level, the C-shock structure is qualitatively different from the high Alfvén number flows which are common to ‘quiescent cloud’ conditions. The magnetic-field cushioning now allows molecular hydrogen to survive very fast shocks and broad H2 lines are feasible. We display results which show that the resolved broad lines and line ratio properties in the OMC-1 outflow can be explained with fast bow shocks moving through such active regions.
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Kiu, K. "Direct- and indirect-driven reactor targets". Laser and Particle Beams 11, nr 1 (marzec 1993): 97–107. http://dx.doi.org/10.1017/s0263034600006959.
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Theoretical and numerical analyses are given for direct- and indirect-driven reactor targets, from which 3-GJ fusion output energy is released. For a reactor target, which has a large radius and long implosion time, supersonic flow of imploding D–T fuel in the converging nozzle (in sphere) is important for adiabatic compression of fuel. For a direct-driven target, pellet gain depends much upon the region where the beam deposits its energy. Phase mixing is also important to increase the absorption rate of irradiating laser light. When a strong light with a phase is concentrated on a small region of target surface, collective electron motion on the target surface radiates electromagnetic waves, which reduce the electron motion. When beam irradiation on the target is not uniform, an indirect-driven target must be used because a direct-driven target is weak for nonuniform irradiation. For an indirect-driven reactor target, which requires a long implosion time, expansion of radiator and absorber layers causes the decrease in radiation temperature. There is the optimum target structure with respect to the aspect ratio (radiation gap distance).
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Zhang, Xin-Ming, Yan-Qing Wu i Feng-Lei Huang. "Multiscale Analysis of Particle Size-dependent Steady Compaction Waves in Granular Energetic Materials". International Journal of Nonlinear Sciences and Numerical Simulation 13, nr 2 (1.04.2012): 165–75. http://dx.doi.org/10.1515/ijnsns.2011.117.
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Abstract A multiscale model is used to analyze the compaction processes in granular HMX beds composed of different particle sizes (coarse particles, d=40 μm and microfine particles, d=4 μm). The localization strategy of Gonthier is extended to include changes in thermal energy induced by compression. The variation in yield strength caused by solid-liquid phase change is also considered. Analysis of the steady-state wave structure indicates that the compaction behavior of a porous material is dependent on particle size. For solid volume fraction φs < 0.88, the fine particle beds provide greater resistance to compaction than the coarse particle beds, and they propagate compaction waves that travel at faster speeds. When φs > 0.88, the physical state of the compacted bed has become very similar for the two materials. For subsonic compaction waves, the evolution of the grain temperature shows that large particles lead to large hot spots and high temperature and coarse particles are more shock sensitive at low shock pressures. For supersonic compaction waves, compression induced changes in thermal energy play an important role in localization strategy. It increases the localization sphere center radius. The dissipated energy is deposited over a larger localization volume so that the grain temperature near the intergranular contact surface is reduced significantly. The localization center radius further increases because of the decrease in the yield strength caused by solid–liquid phase change. Consequently, the peak grain temperature is reduced further.
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Strelnikov, G. O., N. S. Pryadko i K. V. Ternova. "Wave structure of the gas flow in a truncated nozzle with a long bell-shaped tip". Technical mechanics 2023, nr 1 (11.04.2023): 40–53. http://dx.doi.org/10.15407/itm2023.01.040.
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In recent years, more and more attention has been paid to nozzles with an unconventional profile, which differs from that of the classical streamline-profiled Laval nozzle. In such nozzles, the flow fields typically include interacting supersonic and subsonic flows, often with recirculation regions and a complex wave structure of the flow. This work is concerned with a numerical study of the wave structure of the gas flow in a truncated supersonic nozzle with an elliptical bell-shaped tip whose length is long in comparison with the conical section upstream of the tip. The gas flow inside the nozzle and in the surrounding space was simulated using the ANSYS software package. The calculations were carried out in a non-stationary axisymmetric formulation based on the Reynolds-averaged Navier–Stokes equations closed with the use of the SST turbulence model with near-wall functions and a compressibility correction. In the calculations, the nozzle inlet pressure and the ambient pressure were varied. The correctness of the methodological approaches to the solution of the problem was confirmed in the authors’ previous works. The study showed the following. At low values of the nozzle inlet pressure (P0 < 50 bar) and an ambient pressure of 1 bar, the tip wall exhibits a developed separation zone with a large-scale vortex and a small-scale one (near the tip exit). The first "barrel" of the outflowing gas shows a "saddle" low-intensity compression wave structure. In the case of a separated flow, the tip wall pressure in the separation zone is about 15% less than the ambient pressure. At P0 > 100 bar, the tip wall pressure is nearly proportional to the nozzle inlet pressure. In the upper atmosphere, when going in a radial direction from the nozzle axis at the tip exit cross-section, the static pressure monotonically decreases, reaches a minimum, and then increases linearly to the its maximum value on the tip wall. In the case of a separated flow in the tip at a sea-level ambient pressure, the static pressure at the tip exit cross-section behaves in the same manner for inlet pressures P0 > 50 bar. At P0 = 50 bar, there exist two extrema: the pressure first deceases to its minimum value, then increases to its maximum value, and then decreases slightly to its value on the tip wall.
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Bracco, A., D. Bresnahan, P. Palmeirim, D. Arzoumanian, Ph André, D. Ward-Thompson i A. Marchal. "Compressed magnetized shells of atomic gas and the formation of the Corona Australis molecular cloud". Astronomy & Astrophysics 644 (24.11.2020): A5. http://dx.doi.org/10.1051/0004-6361/202039282.
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We present the identification of the previously unnoticed physical association between the Corona Australis molecular cloud (CrA), traced by interstellar dust emission, and two shell-like structures observed with line emission of atomic hydrogen (HI) at 21 cm. Although the existence of the two shells had already been reported in the literature, the physical link between the HI emission and CrA had never been highlighted until now. We used both Planck and Herschel data to trace dust emission and the Galactic All Sky HI Survey (GASS) to trace HI. The physical association between CrA and the shells is assessed based both on spectroscopic observations of molecular and atomic gas and on dust extinction data with Gaia. The shells are located at a distance between ~140 and ~190 pc, which is comparable to the distance of CrA, which we derived as (150.5 ± 6.3) pc. We also employed dust polarization observations from Planck to trace the magnetic-field structure of the shells. Both of them show patterns of magnetic-field lines following the edge of the shells consistently with the magnetic-field morphology of CrA. We estimated the magnetic-field strength at the intersection of the two shells via the Davis-Chandrasekhar-Fermi (DCF) method. Despite the many caveats that are behind the DCF method, we find a magnetic-field strength of (27 ± 8) μG, which is at least a factor of two larger than the magnetic-field strength computed off of the HI shells. This value is also significantly larger compared to the typical values of a few μG found in the diffuse HI gas from Zeeman splitting. We interpret this as the result of magnetic-field compression caused by the shell expansion. This study supports a scenario of molecular-cloud formation triggered by supersonic compression of cold magnetized HI gas from expanding interstellar bubbles.
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McKENZIE, J. F. "Electron acoustic–Langmuir solitons in a two-component electron plasma". Journal of Plasma Physics 69, nr 3 (kwiecień 2003): 199–210. http://dx.doi.org/10.1017/s002237780300206x.
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We investigate the conditions under which ‘high-frequency’ electron acoustic–Langmuir solitons can be constructed in a plasma consisting of protons and two electron populations: one ‘cold’ and the other ‘hot’. Conservation of total momentum can be cast as a structure equation either for the ‘cold’ or ‘hot’ electron flow speed in a stationary wave using the Bernoulli energy equations for each species. The linearized version of the governing equations gives the dispersion equation for the stationary waves of the system, from which follows the necessary – but not sufficient – conditions for the existence of soliton structures; namely that the wave speed must be less than the acoustic speed of the ‘hot’ electron component and greater than the low-frequency compound acoustic speed of the two electron populations. In this wave speed regime linear waves are ‘evanescent’, giving rise to the exponential growth or decay, which readily can give rise to non-linear effects that may balance dispersion and allow soliton formation. In general the ‘hot’ component must be more abundant than the ‘cold’ one and the wave is characterized by a compression of the ‘cold’ component and an expansion in the ‘hot’ component necessitating a potential dip. Both components are driven towards their sonic points; the ‘cold’ from above and the ‘hot’ from below. It is this transonic feature which limits the amplitude of the soliton. If the ‘hot’ component is not sufficiently abundant the window for soliton formation shrinks to a narrow speed regime which is quasi-transonic relative to the ‘hot’ electron acoustic speed, and it is shown that smooth solitons cannot be constructed. In the special case of a very cold electron population (i.e. ‘highly supersonic’) and the other population being very hot (i.e. ‘highly subsonic’) with adiabatic index 2, the structure equation simplifies and can be integrated in terms of elementary transcendental functions that provide the fully non-linear counterpart to the weakly non-linear sech$^{2}$-type solitons. In this case the limiting soliton is comprised of an infinite compression in the cold component, a weak rarefaction in the ‘hot’ electrons and a modest potential dip.
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Wang, Haojun. "Summary of Research Progress in Supersonic Compressor Cascade". Highlights in Science, Engineering and Technology 49 (21.05.2023): 362–67. http://dx.doi.org/10.54097/hset.v49i.8534.
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In compressors, supersonic/transonic flow is a hot topic in today's research. Its development directly affects the performance and function of compressors. The main purpose of supersonic cascade research is to increase its tip velocity, so as to improve its power capacity and boost ratio. In this paper, important research achievements since 2017 are summarized in the following aspects: the working principle of ultrasonic elements, unique intake Angle, shock wave structure and boundary layer interference. At the same time, the most widely used design blade shapes are introduced. Finally, the future development is prospected.
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Pineau, Pierre, i Christophe Bogey. "Steepened Mach waves near supersonic jets: study of azimuthal structure and generation process using conditional averages". Journal of Fluid Mechanics 880 (10.10.2019): 594–619. http://dx.doi.org/10.1017/jfm.2019.729.
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The azimuthal structure and the generation process of steepened acoustic waves are investigated in the near field of temporal round jets at Mach numbers of 2 and 3. Initially, the shear layers of the jets are in a laminar state and display instability waves whose main properties are close to those predicted from linear temporal analysis. Then, they transition to a turbulent state and generate high-intensity Mach waves displaying sharp compressions typical of those recorded for jets producing crackle noise. These waves are first shown to be poorly reproduced when only the axisymmetric mode is considered, but to be well captured with the first five azimuthal modes. Their generation process is investigated by performing conditional averages of the flow and acoustic fields triggered by the detection of intense positive pressure peak close to the jets. No steepened waves are visible in the conditionally averaged pressure profiles when the procedure involves only one azimuthal mode at a time. However, sharp compressions are obtained based on the first five modes taken together. In that case, the steep compressions are correlated over a limited portion of the jet circumference and are steeper as more azimuthal modes are considered. Moreover, a direct link is established between the steepened waves and the supersonic convection of large-scale coherent flow structures located in the supersonic core of the jets. This indicates that these waves constitute an extreme, nonlinear case of Mach wave radiation by these structures. In addition, the capacity of flow structures to generate sharp, steepened waves is related to their shapes. More particularly, flow structures with a large extent in the radial direction are shown to produce stronger and steeper Mach waves than those that are elongated in the flow direction.
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Sciacovelli, L., P. Cinnella, C. Content i F. Grasso. "Dense gas effects in inviscid homogeneous isotropic turbulence". Journal of Fluid Mechanics 800 (30.06.2016): 140–79. http://dx.doi.org/10.1017/jfm.2016.393.
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A detailed numerical study of the influence of dense gas effects on the large-scale dynamics of decaying homogeneous isotropic turbulence is carried out by using the van der Waals gas model. More specifically, we focus on dense gases of the Bethe–Zel’dovich–Thompson type, which may exhibit non-classical nonlinearities in the transonic and supersonic flow regimes, under suitable thermodynamic conditions. The simulations are based on the inviscid conservation equations, solved by means of a ninth-order numerical scheme. The simulations rely on the numerical viscosity of the scheme to dissipate energy at the finest scales, while leaving the larger scales mostly unaffected. The results are systematically compared with those obtained for a perfect gas. Dense gas effects are found to have a significant influence on the time evolution of the average and root mean square (r.m.s.) of the thermodynamic properties for flows characterized by sufficiently high initial turbulent Mach numbers (above 0.5), whereas the influence on kinematic properties, such as the kinetic energy and the vorticity, are smaller. However, the flow dilatational behaviour is very different, due to the non-classical variation of the speed of sound in flow regions where the dense gas is characterized by a value of the fundamental derivative of the gas dynamics (a measure of the variation of the speed of sound in isentropic compressions) smaller than one or even negative. The most significant differences between the perfect and the dense gas case are found for the repartition of dilatation levels in the flow field. For the perfect gas, strong compressions occupy a much larger volume fraction than expansion regions, leading to probability distributions of the velocity divergence highly skewed toward negative values. For the dense gas, the volume fractions occupied by strong expansion and compression regions are much more balanced; moreover, strong expansion regions are characterized by sheet-like structures, unlike the perfect gas which exhibits tubular structures. In strong compression regions, where compression shocklets may occur, both the dense and the perfect gas exhibit sheet-like structures. This suggests the possibility that expansion eddy shocklets may appear in the dense gas. This hypothesis is also supported by the fact that, in dense gas, vorticity is created with equal probability in strong compression and expansion regions, whereas for a perfect gas, vorticity is more likely to be created in the strong compression ones.
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Konstandin, Lukas, Christoph Federrath, Ralf S. Klessen i Wolfram Schmidt. "Statistical properties of supersonic turbulence in the Lagrangian and Eulerian frameworks". Journal of Fluid Mechanics 692 (19.12.2011): 183–206. http://dx.doi.org/10.1017/jfm.2011.503.
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AbstractWe present a systematic study of the influence of different forcing types on the statistical properties of supersonic, isothermal turbulence in both the Lagrangian and Eulerian frameworks. We analyse a series of high-resolution, hydrodynamical grid simulations with Lagrangian tracer particles and examine the effects of solenoidal (divergence-free) and compressive (curl-free) forcing on structure functions, their scaling exponents, and the probability density functions of the gas density and velocity increments. Compressively driven simulations show significantly larger density contrast, more intermittent behaviour, and larger fractal dimension of the most dissipative structures at the same root mean square Mach number. We show that the absolute values of Lagrangian and Eulerian structure functions of all orders in the integral range are only a function of the root mean square Mach number, but independent of the forcing. With the assumption of a Gaussian distribution for the probability density function of the velocity increments for large scales, we derive a model that describes this behaviour.
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Liu, Jun, Jinsheng Cai, Dangguo Yang, Junqiang Wu i Xiansheng Wang. "Visualization and analysis of flow structures in an open cavity". Modern Physics Letters B 32, nr 12n13 (10.05.2018): 1840010. http://dx.doi.org/10.1142/s0217984918400109.
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A numerical study is performed on the supersonic flow over an open cavity at Mach number of 1.5. A newly developed visualization method is employed to visualize the complicated flow structures, which provide an insight into major flow physics. Four types of shock/compressive waves which existed in experimental schlieren are observed in numerical visualization results. Furthermore, other flow structures such as multi-scale vortices are also obtained in the numerical results. And a new type of shocklet which is beneath large vortices is found. The shocklet beneath the vortex originates from leading edge, then, is strengthened by successive interactions between feedback compressive waves and its attached vortex. Finally, it collides against the trailing surface and generates a large number of feedback compressive waves and intensive pressure fluctuations. It is suggested that the shocklets beneath vortex play an important role of cavity self-sustained oscillation.
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Wu Yu, Yi Shi-He, Chen Zhi, Zhang Qing-Hu i Gang Dun-Dian. "Experimental investigations on structures of supersonic laminar/turbulent flow over a compression ramp". Acta Physica Sinica 62, nr 18 (2013): 184702. http://dx.doi.org/10.7498/aps.62.184702.
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Tram, Le Ngoc, Lars Bonne, Yue Hu, Enrique Lopez-Rodriguez, Jordan A. Guerra, Pierre Lesaffre, Antoine Gusdorf i in. "SOFIA Observations of 30 Doradus. II. Magnetic Fields and Large-scale Gas Kinematics". Astrophysical Journal 946, nr 1 (1.03.2023): 8. http://dx.doi.org/10.3847/1538-4357/acaab0.
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Abstract The heart of the Large Magellanic Cloud, 30 Doradus, is a complex region with a clear core-halo structure. Feedback from the stellar cluster R136 has been shown to be the main source of energy creating multiple parsec-scale expanding-shells in the outer region, and carving a nebula core in the proximity of the ionization source. We present the morphology and strength of the magnetic fields (B-fields) of 30 Doradus inferred from the far-infrared polarimetric observations by SOFIA/HAWC+ at 89, 154, and 214 μm. The B-field morphology is complex, showing bending structures around R136. In addition, we use high spectral and angular resolution [C ii] observations from SOFIA/GREAT and CO(2-1) from APEX. The kinematic structure of the region correlates with the B-field morphology and shows evidence of multiple expanding-shells. Our B-field strength maps, estimated using the Davis–Chandrasekhar–Fermi method and structure-function, show variations across the cloud within a maximum of 600, 450, and 350 μG at 89, 154, and 214 μm, respectively. We estimated that the majority of the 30 Doradus clouds are subcritical and sub-Alfvénic. The probability distribution function of the gas density shows that the turbulence is mainly compressively driven, while the plasma beta parameter indicates supersonic turbulence. We show that the B-field is sufficient to hold the cloud structure integrity under feedback from R136. We suggest that supersonic compressive turbulence enables the local gravitational collapse and triggers a new generation of stars to form. The velocity gradient technique using [C ii] and CO(2-1) is likely to confirm these suggestions.
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Federrath, Christoph, Ralf S. Klessen i Wolfram Schmidt. "THE FRACTAL DENSITY STRUCTURE IN SUPERSONIC ISOTHERMAL TURBULENCE: SOLENOIDAL VERSUS COMPRESSIVE ENERGY INJECTION". Astrophysical Journal 692, nr 1 (10.02.2009): 364–74. http://dx.doi.org/10.1088/0004-637x/692/1/364.
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Fernando, Emerick M., i Alexander J. Smits. "A supersonic turbulent boundary layer in an adverse pressure gradient". Journal of Fluid Mechanics 211 (luty 1990): 285–307. http://dx.doi.org/10.1017/s0022112090001574.
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This investigation describes the effects of an adverse pressure gradient on a flat plate supersonic turbulent boundary layer (Mf ≈ 2.9, βx ≈ 5.8, Reθ, ref ≈ 75600). Single normal hot wires and crossed wires were used to study the Reynolds stress behaviour, and the features of the large-scale structures in the boundary layer were investigated by measuring space–time correlations in the normal and spanwise directions. Both the mean flow and the turbulence were strongly affected by the pressure gradient. However, the turbulent stress ratios showed much less variation than the stresses, and the essential nature of the large-scale structures was unaffected by the pressure gradient. The wall pressure distribution in the current experiment was designed to match the pressure distribution on a previously studied curved-wall model where streamline curvature acted in combination with bulk compression. The addition of streamline curvature affects the turbulence strongly, although its influence on the mean velocity field is less pronounced and the modifications to the skin-friction distribution seem to follow the empirical correlations developed by Bradshaw (1974) reasonably well.
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Sepahi-Younsi, Javad, i Behzad Forouzi Feshalami. "Performance Evaluation of External and Mixed Compression Supersonic Air Intakes: Parametric Study". Journal of Aerospace Engineering 32, nr 5 (wrzesień 2019): 04019066. http://dx.doi.org/10.1061/(asce)as.1943-5525.0001048.
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Kobayashi, Masato I. N., Tsuyoshi Inoue, Kengo Tomida, Kazunari Iwasaki i Hiroki Nakatsugawa. "Nature of Supersonic Turbulence and Density Distribution Function in the Multiphase Interstellar Medium". Astrophysical Journal 930, nr 1 (1.05.2022): 76. http://dx.doi.org/10.3847/1538-4357/ac5a54.
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Abstract Supersonic flows in the interstellar medium (ISM) are believed to be a key driver of the molecular cloud formation and evolution. Among molecular clouds’ properties, the ratio between the solenoidal and compressive modes of turbulence plays important roles in determining the star formation efficiency. We use numerical simulations of supersonic converging flows of the warm neutral medium (WNM) resolving the thermal instability to calculate the early phase of molecular cloud formation, and we investigate the turbulence structure and the density probability distribution function (density PDF) of the multiphase ISM. We find that both the solenoidal and compressive modes have their power spectrum similar to the Kolmogorov spectrum. The solenoidal (compressive) modes account for ≳80% (≲20%) of the total turbulence power. When we consider both the cold neutral medium (CNM) and the thermally unstable neutral medium (UNM) up to T ≲ 400 K, the density PDF follows the lognormal distribution, whose width σ s is well explained by the known relation from the isothermal turbulence as σ s = ln ( 1 + b 2 2 ) (where b is the parameter representing the turbulence mode ratio and is the turbulent Mach number). The density PDF of the CNM component alone (T ≤ 50 K), however, exhibits a narrower σ s by a factor of ∼2. These results suggest that observational estimations of b based on the CNM density PDF requires the internal turbulence within each CNM clump but not the interclump relative velocity, the latter of which is instead powered by the WNM/UNM turbulence.
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Ren, Zhaoxin, Bing Wang i Fan Zhang. "Effects of Flow Compressibility on Two-Phase Mixing in Supersonic Droplet-Laden Flows". International Journal of Aerospace Engineering 2020 (7.12.2020): 1–13. http://dx.doi.org/10.1155/2020/8815205.
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This research addresses a numerical analysis on the effects of flow compressibility on the characteristics of droplet dispersion, evaporation, and mixing of fuel and air according to the simulation of the spatially developing supersonic shear flows laden with evaporating n-decane droplets. A sixth-order hybrid WENO numerical scheme is employed for capturing the unsteady wave structures. The influence of inflow convective Mach number ( M c ), representing the high-speed flow compressibility, on the two-phase mixing is analyzed, in which M c is specified from 0.4 to 1.0. It is found that the shearing vortex is compressed spatially as M c increases, associated with the alternate distributions of compression and expansion regimes in the flow field. The flow compressibility changes not only the vortex structures but also the aerothermal parameters of the shear flows, and further influences the dispersion and evaporation of droplets. The two-phase mixing efficiency is observed to decrease as M c increases.
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Filippi, Alessandro A., i Beric W. Skews. "Supersonic flow fields resulting from axisymmetric internal surface curvature". Journal of Fluid Mechanics 831 (13.10.2017): 271–88. http://dx.doi.org/10.1017/jfm.2017.643.
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An experimental and numerical study was conducted to examine the effects of internal surface curvature and leading-edge angle on the shock waves and steady flow fields produced by axisymmetric ring wedges. Test models with leading-edge-radius-normalised internal radii of curvature of $R_{c}=\{1,1.5,2\}$ and leading-edge angles of $\unicode[STIX]{x1D6FC}=\{0^{\circ },4^{\circ },8^{\circ }\}$ were manufactured and tested. Experimental shadowgraph and schlieren results were obtained for Mach numbers ranging from 2.8 to 3.6 using a blowdown supersonic wind tunnel with accompanying numerical results for additional insight. The higher the internal surface curvature and leading-edge angle, the greater the flow fields were impacted. As a result, steeper compression waves were formed, thus curving the shock wave more noticeably. The internal surface curvature and leading-edge angle were both found to have an effect on the trailing-edge expansion fans. This altered the shape of downstream shock wave structures. The highest curvature models produced steady double reflection patterns due to the imposed internal surface curvature. The effects of conical and curved internal surfaces were explored for the presence of flow-normal curvature and the curving of the attached shock waves.
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Volov, Vyacheslav, Nikolay Elisov i Anton Lyaskin. "Numerical Investigation of the Secondary Swirling in Supersonic Flows of Various Nature Gases". Energies 14, nr 23 (3.12.2021): 8122. http://dx.doi.org/10.3390/en14238122.
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Despite the application of vortex tubes for cooling, separating gas mixtures, vacuuming, etc., the mechanism of energy separation in vortex tubes remains an object of discussion. This paper studies the effect of secondary swirling in supersonic flows on the energy separation of monatomic and diatomic gases. The approach used is a numerical solution of the Reynolds-averaged Navier-Stokes equations, closed by the Reynolds Stress Model turbulence model. The modelling provided is for a self-vacuuming vortex tube with air, helium, argon, and carbon dioxide. According to the results of the calculations, the effect of secondary swirling is inherent only in viscous gases. A comparison was made between obtained total temperature difference, the level of secondary swirling and power losses on expansion from the nozzle, compression shocks, friction, turbulence, and energy costs to develop cascaded swirl structures. Our results indicate that helium and argon have the highest swirling degree and, consequently, the highest energy separation. Moreover, it can be concluded that the power costs on the development of cascaded vortex structures have a significant role in the efficiency of energy separation.
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Liu, Yanming, Hong Zhang i Pingchao Liu. "Flow control in supersonic flow field based on micro jets". Advances in Mechanical Engineering 11, nr 1 (styczeń 2019): 168781401882152. http://dx.doi.org/10.1177/1687814018821526.
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The flow field around supersonic aircraft is usually accompanied by complex flow phenomena, such as shock wave and shock wave/boundary layer interaction, which cause some adverse effects on aircraft performance. Seeking effective flow control methods has been a hot topic for many researchers. As an important method to improve the flow characteristics in supersonic flows, micro jet technology and its control mechanism have been paid much attention. In this article, we used compression corner calculation model and conducted detailed numerical investigations in the supersonic flow field with different injection pressure ratios, various actuation positions, and different nozzle types. The interaction between the micro jets and supersonic upstream flows generates complex flow structures, which contain bow shocks, barrel shocks, Mach disk, counter-rotating vortex pairs, and so on. The flow characteristics with micro jet schemes are superior to those in the no-control case. The controlling performance of micro jet is mainly determined by the following aspects. First, the downwash effect of counter-rotating vortex pairs can bring high-energy fluid into the bottom of the boundary layer to activate low-energy fluid and then strengthen the ability of resisting the flow separations. Second, the bow shock, which is generated upstream of the micro jet, significantly decelerates the downstream flows. Thus, the shock intensity at the corner is weakened and the characteristic of shock wave/boundary layer interaction is improved. In addition, the effective function range of MJ, that is, the distance between the counter-rotating vortex pair and the wall surface, is also an important factor. When both the counter-rotating vortex pairs and the bow shock are further from the wall, the flow characteristics around the corner in a larger area can be improved. Research shows that the micro jet scheme with Laval nozzle gives better controlling effect on shock wave/boundary layer interaction when the injection pressure radio is set to be 0.6, with the actuation location being 20 times the jet outlet diameter upstream of the corner.
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Hah, C., i A. J. Wennerstrom. "Three-Dimensional Flowfields Inside a Transonic Compressor With Swept Blades". Journal of Turbomachinery 113, nr 2 (1.04.1991): 241–50. http://dx.doi.org/10.1115/1.2929092.
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The concept of swept blades for a transonic or supersonic compressor was reconsidered by Wennerstrom in the early 1980s. Several transonic rotors designed with swept blades have shown very good aerodynamic efficiency. The improved performance of the rotor is believed to be due to reduced shock strength near the shroud and better distribution of secondary flows. A three-dimensional flowfield inside a transonic rotor with swept blades is analyzed in detail experimentally and numerically. A Reynolds-averaged Navier–Stokes equation is solved for the flow inside the rotor. The numerical solution is based on a high-order upwinding relaxation scheme, and a two-equation turbulence model with a low Reynolds number modification is used for the turbulence modeling. To predict flows near the shroud properly, the tip-clearance flow also must be properly calculated. The numerical results at three different operating conditions agree well with the available experimental data and reveal various interesting aspects of shock structure inside the rotor.
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Prestipino, Santi, Alessandro Sergi, Ezio Bruno i Paolo V. Giaquinta. "A variational mean-field study of clusterization in a zero-temperature system of soft-core bosons". EPJ Web of Conferences 230 (2020): 00008. http://dx.doi.org/10.1051/epjconf/202023000008.
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We work out the ground-state diagram of weakly-repulsive penetrable bosons, using mean-field theory with a Gaussian ansatz on the single-particle wave function. Upon compression, the fluid transforms into a cluster supersolid, whose structure is characterized for various choices of the embedding space. In Euclidean space, the stable crystals are those with the most compact structure, i.e., triangular and fcc in two and three dimensions, respectively. For particles confined in a spherical surface, as the sphere radius increases we observe a sequence of transitions between different cluster phases, all having a regular or semiregular polyhedron as supporting frame for the clusters. The present results are relevant for the behavior of ultracold bosons weakly coupled to a Rydberg state.
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Gulizia, Stefan, A. Trentin, S. Vezzù, Silvano Rech, Peter King, Mahnaz Z. Jahedi i Mario Guagliano. "Characterisation of Cold Spray Titanium Coatings". Materials Science Forum 654-656 (czerwiec 2010): 898–901. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.898.
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Cold spray is a solid state spray deposition process utilizing a supersonic De Laval nozzle to accelerate fine particles to high velocities. Particles plastically deform on impact to the substrate and to each other to create dense well adhered structures. In this study, the microstructure and mechanical properties of cold spray Titanium coatings deposited using nitrogen gas at different gas temperature and pressure were examined. In general, it was found that gas-atomised CP-titanium powder is capable of producing dense coating structures on aluminium alloy (Al6061) substrates. The micro-hardness, oxygen and nitrogen content of the coatings were found to be slightly higher than powder in the as-received condition. It was also found the coating residual stress was purely compressive when cold spray is conducted at high gas pressure and temperature.
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Burne, Sofía, César Bertucci, Nick Sergis, Laura F. Morales, Nicholas Achilleos, Beatriz Sánchez-Cano, Yaireska Collado-Vega, Sergio Dasso, Niklas J. T. Edberg i Bill S. Kurth. "Space Weather in the Saturn–Titan System". Astrophysical Journal 948, nr 1 (1.05.2023): 37. http://dx.doi.org/10.3847/1538-4357/acc738.
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Abstract New evidence based on Cassini magnetic field and plasma data has revealed that the discovery of Titan outside Saturn’s magnetosphere during the T96 flyby on 2013 December 1 was the result of the impact of two consecutive interplanetary coronal mass ejections (ICMEs) that left the Sun in 2013 early November and interacted with the moon and the planet. We study the dynamic evolution of Saturn's magnetopause and bow shock, which evidences a magnetospheric compression from late November 28 to December 4 (at least), under prevailing solar wind dynamic pressures of 0.16–0.3 nPa. During this interval, transient disturbances associated with the two ICMEs are observed, allowing for the identification of their magnetic structures. By analyzing the magnetic field direction, and the pressure balance in Titan’s induced magnetosphere, we show that Cassini finds Saturn’s moon embedded in the second ICME after being swept by its interplanetary shock and amid a shower of solar energetic particles that may have caused dramatic changes in the moon’s lower ionosphere. Analyzing a list of Saturn's bow shock crossings during 2004–2016, we find that the magnetospheric compression needed for Titan to be in the supersonic solar wind can be generally associated with the presence of an ICME or a corotating interaction region. This leads to the conclusion that Titan would rarely face the pristine solar wind, but would rather interact with transient solar structures under extreme space weather conditions.
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RASHEED, A., N. L. TSINTSADZE, G. MURTAZA i R. CHAUDHARY. "Nonlinear structure of ion-acoustic solitary waves in a relativistic degenerate electron–positron–ion plasma". Journal of Plasma Physics 78, nr 2 (24.11.2011): 133–41. http://dx.doi.org/10.1017/s0022377811000481.
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AbstractArbitrary amplitude and small amplitude ion-acoustic solitary waves (IASWs) have been investigated in a relativistic, collisionless, unmagnetized, and degenerate dense electron–positron–ion plasma. The arbitrary amplitude IASWs have been studied by using the Sagdeev-type pseudo-potential approach. Along with approximate solution, the exact amplitude solitary structure has also been studied numerically. The electrons and positrons are assumed to follow the corresponding Fermi distribution function and the ions are described by the hydrodynamic equations. A new dispersion relation for the ion-acoustic wave has been derived for the relativistic Thomas–Fermi plasma. An energy balance-like equation involving the Sagdeev-type pseudo-potential has been investigated and it has been shown that the concentration of plasma particles has significant effect on the permitted Mach number range of IASWs. Also, it has been pointed out that the only compressional supersonic IASWs can propagate in the relativistic Thomas–Fermi plasma. The present work would be helpful to understand the excitation of the nonlinear ion-acoustic waves in a degenerate plasma, such as in superdense white dwarfs and in the cores of massive planets.