Quasiperpendicular high Mach number Shocks
Sulaiman, A H; Dougherty, M K; Burgess, D; Fujimoto, M; Hospodarsky, G B
2015-01-01
Shock waves exist throughout the universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasi-perpendicular shocks across two orders of magnitude in Alfven Mach number (MA) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted timescale of ~0.3 {\\tau}c, where {\\tau}c is the ion gyroperio...
Quasiperpendicular High Mach Number Shocks
Sulaiman, A. H.; Masters, A.; Dougherty, M. K.; Burgess, D.; Fujimoto, M.; Hospodarsky, G. B.
2015-09-01
Shock waves exist throughout the Universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this Letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasiperpendicular shocks across 2 orders of magnitude in Alfvén Mach number (MA ) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted time scale of ˜0.3 τc , where τc is the ion gyroperiod. In addition, we experimentally reveal the relationship between reformation and MA and focus on the magnetic structure of such shocks to further show that for the same MA , a reforming shock exhibits stronger magnetic field amplification than a shock that is not reforming.
Relativistic Electron Shock Drift Acceleration in Low Mach Number Galaxy Cluster Shocks
Matsukiyo, Shuichi; Yamazaki, Ryo; Umeda, Takayuki
2011-01-01
An extreme case of electron shock drift acceleration in low Mach number collisionless shocks is investigated as a plausible mechanism of initial acceleration of relativistic electrons in large-scale shocks in galaxy clusters where upstream plasma temperature is of the order of 10 keV and a degree of magnetization is not too small. One-dimensional electromagnetic full particle simulations reveal that, even though a shock is rather moderate, a part of thermal incoming electrons are accelerated and reflected through relativistic shock drift acceleration and form a local nonthermal population just upstream of the shock. The accelerated electrons can self-generate local coherent waves and further be back-scattered toward the shock by those waves. This may be a scenario for the first stage of the electron shock acceleration occurring at the large-scale shocks in galaxy clusters such as CIZA J2242.8+5301 which has well defined radio relics.
The influence of incident shock Mach number on radial incident shock wave focusing
Directory of Open Access Journals (Sweden)
Xin Chen
2016-04-01
Full Text Available Experiments and numerical simulations were carried out to investigate radial incident shock focusing on a test section where the planar incident shock wave was divided into two identical ones. A conventional shock tube was used to generate the planar shock. Incident shock Mach number of 1.51, 1.84 and 2.18 were tested. CCD camera was used to obtain the schlieren photos of the flow field. Third-order, three step strong-stability-preserving (SSP Runge-Kutta method, third-order weighed essential non-oscillation (WENO scheme and adaptive mesh refinement (AMR algorithm were adopted to simulate the complicated flow fields characterized by shock wave interaction. Good agreement between experimental and numerical results was observed. Complex shock wave configurations and interactions (such as shock reflection, shock-vortex interaction and shock focusing were observed in both the experiments and numerical results. Some new features were observed and discussed. The differences of structure of flow field and the variation trends of pressure were compared and analyzed under the condition of different Mach numbers while shock wave focusing.
Sundkvist, David; Krasnoselskikh, V; Bale, S D; Schwartz, S J; Soucek, J; Mozer, F
2012-01-13
Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.
Note: A high Mach number arc-driven shock tube for turbulence studies.
Titus, J B; Alexander, A B; Johnson, J A
2013-04-01
A high Mach arc-driven shock tube has been built at the Center for Plasma Science and Technology of Florida A&M University to study shock waves. A larger apparatus with higher voltage was built to study more stable shock waves and subsequent plasmas. Initial measurements of the apparatus conclude that the desired Mach numbers can be reached using only two-thirds the maximum possible energy that the circuit can provide.
Tanaka, Kento; Watanabe, Tomoaki; Nagata, Koji; Sasoh, Akihiro; Sakai, Yasuhiko; Hayase, Toshiyuki; Nagoya Univ Collaboration
2016-11-01
The interaction between homogeneous isotropic turbulence and normal shock wave is investigated by direct numerical simulations (DNSs). In the DNSs, a normal shock wave with a shock Mach number 1.1 passes through homogeneous isotropic turbulence with a low turbulent Mach number and a moderate turbulent Reynolds number. The statistics are calculated conditioned on the distance from the shock wave. The results showed that the shock wave makes length scales related to turbulence small. This effect is significant for the Taylor microscale defined with the velocity derivative orthogonal to the shock wave. The decrease in the Kolmogorov scale is also found. Statistics of velocity derivative are found to be changed by the shock wave propagation. The shock wave causes enstrophy amplification due to the dilatation/vorticity interaction. By this interaction, the vorticity components parallel to the shock wave is more amplified than the normal component. The strain rate is also amplified by the shock wave.
The Dynamics of Very High Alfvén Mach Number Shocks in Space Plasmas
Sundberg, Torbjörn; Burgess, David; Scholer, Manfred; Masters, Adam; Sulaiman, Ali H.
2017-02-01
Astrophysical shocks, such as planetary bow shocks or supernova remnant shocks, are often in the high or very-high Mach number regime, and the structure of such shocks is crucial for understanding particle acceleration and plasma heating, as well inherently interesting. Recent magnetic field observations at Saturn’s bow shock, for Alfvén Mach numbers greater than about 25, have provided evidence for periodic non-stationarity, although the details of the ion- and electron-scale processes remain unclear due to limited plasma data. High-resolution, multi-spacecraft data are available for the terrestrial bow shock, but here the very high Mach number regime is only attained on extremely rare occasions. Here we present magnetic field and particle data from three such quasi-perpendicular shock crossings observed by the four-spacecraft Cluster mission. Although both ion reflection and the shock profile are modulated at the upstream ion gyroperiod timescale, the dominant wave growth in the foot takes place at sub-proton length scales and is consistent with being driven by the ion Weibel instability. The observed large-scale behavior depends strongly on cross-scale coupling between ion and electron processes, with ion reflection never fully suppressed, and this suggests a model of the shock dynamics that is in conflict with previous models of non-stationarity. Thus, the observations offer insight into the conditions prevalent in many inaccessible astrophysical environments, and provide important constraints for acceleration processes at such shocks.
Particle-in-cell simulations of particle energization from low Mach number fast mode shocks
Park, Jaehong; Blackman, Eric G; Ren, Chuang; Siller, Robert
2012-01-01
Astrophysical shocks are often studied in the high Mach number limit but weakly compressive fast shocks can occur in magnetic reconnection outflows and are considered to be a site of particle energization in solar flares. Here we study the microphysics of such perpendicular, low Mach number collisionless shocks using two-dimensional particle-in-cell (PIC) simulations with a reduced ion/electron mass ratio and employ a moving wall boundary method for initial generation of the shock. This moving wall method allows for more control of the shock speed, smaller simulation box sizes, and longer simulation times than the commonly used fixed wall, reflection method of shock formation. Our results, which are independent of the shock formation method, reveal the prevalence shock drift acceleration (SDA) of both electron and ions in a purely perpendicular shock with Alfv\\'en Mach number $M_A=6.8$ and ratio of thermal to magnetic pressure $\\beta=8$. We determine the respective minimum energies required for electrons and ...
On the proper Mach number and ratio of specific heats for modeling the Venus bow shock
Tatrallyay, M.; Russell, C. T.; Luhmann, J. G.; Barnes, A.; Mihalov, J. D.
1984-01-01
Observational data from the Pioneer Venus Orbiter are used to investigate the physical characteristics of the Venus bow shock, and to explore some general issues in the numerical simulation of collisionless shocks. It is found that since equations from gas-dynamic (GD) models of the Venus shock cannot in general replace MHD equations, it is not immediately obvious what the optimum way is to describe the desired MHD situation with a GD code. Test case analysis shows that for quasi-perpendicular shocks it is safest to use the magnetospheric Mach number as an input to the GD code. It is also shown that when comparing GD predicted temperatures with MHD predicted temperatures total energy should be compared since the magnetic energy density provides a significant fraction of the internal energy of the MHD fluid for typical solar wind parameters. Some conclusions are also offered on the properties of the terrestrial shock.
Electron acceleration in a nonrelativistic shock with very high Alfv\\'en Mach number
Matsumoto, Y; Hoshino, M
2013-01-01
Electron acceleration associated with various plasma kinetic instabilities in a nonrelativistic, very-high-Alfv\\'en Mach-number ($M_A \\sim 45$) shock is revealed by means of a two-dimensional fully kinetic PIC simulation. Electromagnetic (ion Weibel) and electrostatic (ion-acoustic and Buneman) instabilities are strongly activated at the same time in different regions of the two-dimensional shock structure. Relativistic electrons are quickly produced predominantly by the shock surfing mechanism with the Buneman instability at the leading edge of the foot. The energy spectrum has a high-energy tail exceeding the upstream ion kinetic energy accompanying the main thermal population. This gives a favorable condition for the ion acoustic instability at the shock front, which in turn results in additional energization. The large-amplitude ion Weibel instability generates current sheets in the foot, implying another dissipation mechanism via magnetic reconnection in a three-dimensional shock structure in the very-hi...
Specularly reflected He sup 2+ at high Mach number quasi-parallel shocks
Energy Technology Data Exchange (ETDEWEB)
Fuselier, S.A.; Lennartsson, O.W. (Lockheed Palo Alto Research Lab., CA (United States)); Thomsen, M.F. (Los Alamos National Lab., NM (United States)); Russell, C.T. (Univ. of California, Los Angeles (United States))
1990-04-01
Upstream from the Earth's quasi-parallel bow shock, the Lockheed Plasma Composition Experiment on ISEE 1 often observes two types of suprathermal He{sup 2+} distributions. Always present to some degree is an energetic (several keV/eto 17.4 keV/e, the maximum energy of the detector) diffuse He{sup 2+} distribution. Sometimes, apparently when the Alfven Mach number, M{sub A}, is high enough and the spacecraft is near the shock (within a few minutes of a crossing), a second type of suprathermal He{sup 2+} distribution is also observed. This nongyrotropic, gyrating He{sup 2+} distribution has velocity components parallel and perpendicular to the magnetic field that are consistent with near-specular reflection of a portion of the incident solar wind He{sup 2+} distribution off the shock. Specularly reflected and diffuse proton distributions are associated with these gyrating He{sup 2+} distributions. The presence of these gyrating He{sup 2+} distributions suggests that specular reflection is controlled primarily by magnetic forces in high Mach number quasi-parallel shocks and that these distributions may be a seed population for more energetic diffuse He{sup 2+} distributions.
Schaeffer, D. B.; Fox, W.; Haberberger, D.; Fiksel, G.; Bhattacharjee, A.; Barnak, D. H.; Hu, S. X.; Germaschewski, K.
2017-07-01
We present the first laboratory generation of high-Mach-number magnetized collisionless shocks created through the interaction of an expanding laser-driven plasma with a magnetized ambient plasma. Time-resolved, two-dimensional imaging of plasma density and magnetic fields shows the formation and evolution of a supercritical shock propagating at magnetosonic Mach number Mms≈12 . Particle-in-cell simulations constrained by experimental data further detail the shock formation and separate dynamics of the multi-ion-species ambient plasma. The results show that the shocks form on time scales as fast as one gyroperiod, aided by the efficient coupling of energy, and the generation of a magnetic barrier between the piston and ambient ions. The development of this experimental platform complements present remote sensing and spacecraft observations, and opens the way for controlled laboratory investigations of high-Mach number collisionless shocks, including the mechanisms and efficiency of particle acceleration.
Anomalous flow deflection at planetary bow shocks in the low Alfven Mach number regime
Nishino, Masaki N.; Fujimoto, Masaki; Tai, Phan-Duc; Mukai, Toshifumi; Saito, Yoshifumi; Kuznetsova, Masha M.; Rastaetter, Lutz
A planetary magnetosphere is an obstacle to the super-sonic solar wind and the bow shock is formed in the front-side of it. In ordinary hydro-dynamics, the flow decelerated at the shock is diverted around the obstacle symmetrically about the planet-Sun line, which is indeed observed in the magnetosheath most of the time. Here we show a case under a very low density solar wind in which duskward flow was observed in the dawnside magnetosheath of the Earth's magnetosphere. A Rankine-Hugoniot test across the bow shock shows that the magnetic effect is crucial for this "wrong flow" to appear. A full three-dimensional Magneto- Hydro-Dynamics (MHD) simulation of the situation in this previously unexplored parameter regime is also performed. It is illustrated that in addition to the "wrong flow" feature, various peculiar characteristics appear in the global picture of the MHD flow interaction with the obstacle. The magnetic effect at the bow shock should become more conspicuously around the Mercury's magnetosphere, because stronger interplanetary magnetic field and slower solar wind around the Mercury let the Alfven Mach number low. Resultant strong deformation of the magnetosphere induced by the "wrong flow" will cause more complex interaction between the solar wind and the Mercury.
Schaeffer, Derek; Haberberger, Dan; Fiksel, Gennady; Bhattacharjee, Amitava; Barnak, Daniel; Hu, Suxing; Germaschewski, Kai
2016-01-01
Shocks act to convert incoming supersonic flows to heat, and in collisionless plasmas the shock layer forms on kinetic plasma scales through collective electromagnetic effects. These collisionless shocks have been observed in many space and astrophysical systems [Smith 1975, Smith 1980, Burlaga 2008, Sulaiman 2015], and are believed to accelerate particles, including cosmic rays, to extremely high energies [Kazanas 1986, Loeb 2000, Bamba 2003, Masters 2013, Ackermann 2013]. Of particular importance are the class of high-Mach number, supercritical shocks [Balogh 2013] ($M_A\\gtrsim4$), which must reflect significant numbers of particles back into the upstream to accommodate entropy production, and in doing so seed proposed particle acceleration mechanisms [Blandford 1978, McClements 2001, Caprioli 2014, Matsumoto 2015]. Here we present the first laboratory generation of high-Mach number magnetized collisionless shocks created through the interaction of an expanding laser-driven plasma with a magnetized ambient ...
Guo, Xinyi; Sironi, Lorenzo; Narayan, Ramesh
2014-10-01
Electron acceleration to non-thermal energies in low Mach number (Ms Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with Ms = 3 and a quasi-perpendicular pre-shock magnetic field. We find that about 15% of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p ~= 2.4. Initially, thermal electrons are energized at the shock front via shock drift acceleration (SDA). The accelerated electrons are then reflected back upstream where their interaction with the incoming flow generates magnetic waves. In turn, the waves scatter the electrons propagating upstream back toward the shock for further energization via SDA. In summary, the self-generated waves allow for repeated cycles of SDA, similarly to a sustained Fermi-like process. This mechanism offers a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.
Park, Jaehong; Workman, Jared C; Blackman, Eric G
2012-01-01
Low Mach number, high beta fast mode shocks can occur in the magnetic reconnection outflows of solar flares. These shocks, which occur above flare loop tops, may provide the electron energization responsible for some of the observed hard X-rays and contemporaneous radio emission. Here we present new 2D particle-in-cell simulations of low Mach number/high beta quasi-perpendicular shocks. The simulations show that electrons above a certain energy threshold experience shock-drift-acceleration. The transition energy between the thermal and non-thermal spectrum and the spectral index from the simulations are consistent with some of the X-ray spectra from RHESSI in the energy regime, $E\\lesssim 40\\sim 100$ keV. Plasma instabilities associated with the shock structure such as the modified-two-stream and the electron whistler/mirror instabilities are examined and compared with the numerical solutions of the kinetic dispersion relations.
Guo, Xinyi; Narayan, Ramesh
2014-01-01
Electron acceleration to non-thermal energies in low Mach number (M<5) shocks is revealed by radio and X-ray observations of galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Diffusive shock acceleration, also known as first-order Fermi acceleration, cannot be directly invoked to explain the acceleration of electrons. Rather, an additional mechanism is required to pre-accelerate the electrons from thermal to supra-thermal energies, so they can then participate in the Fermi process. In this work, we use two- and three-dimensional particle-in-cell plasma simulations to study electron acceleration in low Mach number shocks. We focus on the particle energy spectra and the acceleration mechanism in a reference run with M=3. We find that about 15 percent of the electrons can be efficiently accelerated, forming a non-thermal power-law tail in the energy spectrum with a slope of p~2.4. Initially, thermal electrons are energized at the shock front via shock drift a...
The influence of the Mach number of shock waves on turbulent mixing growth at an interface of gases
Nevmerzhitsky, N. V.; Sotskov, E. A.; Sen'kovsky, E. D.; Razin, A. N.; Ustinenko, V. A.; Krivonos, O. L.; Tochilina, L. V.
2010-12-01
The results of our experimental investigation of the turbulent mixing occurring at a Richtmayer-Meshkov instability driven by a shock wave (SW) in gases at different Mach numbers (M) ranging from ≈1.4 to ≈9 are presented in this paper. The experiments were performed by using an air shock tube with a channel section of 40×40 mm2. The SW passed from 'light' to 'heavy' gases. Air (helium) was used as a 'light' gas and Xe, CO2 and Ar were used as 'heavy' gases. The gases were initially separated by a thin (≈1 μm) polymer film, which was failed after the passing of the SW. A film of the flow was made using a high-speed camera by the Schlieren method.
Contribution from the Earth's Bow Shock to Region 1 Current under Low Alfvén Mach Numbers
Institute of Scientific and Technical Information of China (English)
PENG Zhong; HU You-Qiu
2009-01-01
@@ Using global MHD simulations of the solar wind-magnetosphere--ionosphere system, we investigate the depen-dence of the contribution from the Earth's bow shock (I1bs) to ionospheric region I field aligned current (FAC) (I1). It is found that I1bs increases with increasing southward interplanetary magnetic field (IMF) strength Bs, if the Alfven Mach number MA of the solar wind exceeds 2, a similar result as obtained by previous authors. However, if MA becomes close to or falls below 2, I1bs will decrease with B8 in both magnitude and percentage (i.e., I1bs/I1) because of the resultant reduction of the bow shock strength. Both the surface current density Jbs at the nose of the bow shock and the total bow shock current lb, share nearly the same relationship with MA, and vary non-monotonically with MA or Bs. The maximum point is found to be located at MA = 2.7. Three conclusions are then made as follows: (1) The surface current density at the nose, which is much easier to be evaluated, may be used to largely describe the behaviour of the bow shock instead of the total bow shock current. (2) The peak of the total bow shock current is reached at about MA = 2.7 when only Bs is adjusted. (3) The non-monotonic variation of the bow shock current with MA causes a similar variation of its contribution to region 1 FAC. The turning point for such contribution is found to be nearly MA= 2. The implication of these conclusions to the saturation of the ionospheric transpolar potential is briefly discussed.
Asymptotic Steady State Solution to a Bow Shock with an Infinite Mach Number
Yalinewich, Almog
2015-01-01
The problem of a cold gas flowing past a stationary object is considered. It is shown that at large distances from the obstacle the shock front forms a parabolic solid of revolution. The interior of the shock front is obtained by solution of the hydrodynamic equations in parabolic coordinates. The results are verified with a hydrodynamic simulation. The drag force and expected spectra are calculated for such shock, both in case of an optically thin and thick media. Finally, relations to astrophysical bow shocks and other analytic works on oblique shocks are discussed.
High Mach-number collisionless shock driven by a laser with an external magnetic field
Directory of Open Access Journals (Sweden)
Morita T.
2013-11-01
Full Text Available Collisionless shocks are produced in counter-streaming plasmas with an external magnetic field. The shocks are generated due to an electrostatic field generated in counter-streaming laser-irradiated plasmas, as reported previously in a series of experiments without an external magnetic field [T. Morita et al., Phys. Plasmas, 17, 122702 (2010, Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011] via laser-irradiation of a double-CH-foil target. A magnetic field is applied to the region between two foils by putting an electro-magnet (∼10 T perpendicular to the direction of plasma expansion. The generated shocks show different characteristics later in time (t > 20ns.
Chaotic behaviour of high Mach number flows
Varvoglis, H.; Ghosh, S.
1985-01-01
The stability of the super-Alfvenic flow of a two-fluid plasma model with respect to the Mach number and the angle between the flow direction and the magnetic field is investigated. It is found that, in general, a large scale chaotic region develops around the initial equilibrium of the laminar flow when the Mach number exceeds a certain threshold value. After reaching a maximum the size of this region begins shrinking and goes to zero as the Mach number tends to infinity. As a result high Mach number flows in time independent astrophysical plasmas may lead to the formation of 'quasi-shocks' in the presence of little or no dissipation.
de Gasperin, F; van Weeren, R J; Dawson, W A; Golovich, N; Wittman, D; Bonafede, A; Bruggen, M
2015-01-01
Diffuse radio emission in the form of radio halos and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z=0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope (GMRT) and the Westerbork Synthesis Radio Telescope (WSRT). We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index we obtained the Mach number of the shocks generating the two radio relics. For the southern shock we found M = 2.33^{+0.19}_{-0.26}, while the northern shock Mach number goes from M = 2.20^{+0.07}_{-0.14} in the north part down to M = 2.00^{+0.03}_{-0.08} in the southern reg...
Study on Mach stems induced by interaction of planar shock waves on two intersecting wedges
Institute of Scientific and Technical Information of China (English)
Gaoxiang Xiang; Chun Wang; Honghui Teng; Yang Yang; Zonglin Jiang
2016-01-01
The properties of Mach stems in hypersonic corner flow induced by Mach interaction over 3D inter-secting wedges were studied theoretically and numerically. A new method called “spatial dimension reduction” was used to analyze theoretically the location and Mach num-ber behind Mach stems. By using this approach, the problem of 3D steady shock/shock interaction over 3D intersecting wedges was transformed into a 2D moving one on cross sec-tions, which can be solved by shock-polar theory and shock dynamics theory. The properties of Mach interaction over 3D intersecting wedges can be analyzed with the new method, including pressure, temperature, density in the vicinity of triple points, location, and Mach number behind Mach stems. Theoretical results were compared with numerical results, and good agreement was obtained. Also, the influence of Mach number and wedge angle on the properties of a 3D Mach stem was studied.
Mach stem formation in reflection and focusing of weak shock acoustic pulses.
Karzova, Maria M; Khokhlova, Vera A; Salze, Edouard; Ollivier, Sébastien; Blanc-Benon, Philippe
2015-06-01
The aim of this study is to show the evidence of Mach stem formation for very weak shock waves with acoustic Mach numbers on the order of 10(-3) to 10(-2). Two representative cases are considered: reflection of shock pulses from a rigid surface and focusing of nonlinear acoustic beams. Reflection experiments are performed in air using spark-generated shock pulses. Shock fronts are visualized using a schlieren system. Both regular and irregular types of reflection are observed. Numerical simulations are performed to demonstrate the Mach stem formation in the focal region of periodic and pulsed nonlinear beams in water.
Hysteresis phenomenon of hypersonic inlet at high Mach number
Jiao, Xiaoliang; Chang, Juntao; Wang, Zhongqi; Yu, Daren
2016-11-01
When the hypersonic inlet works at a Mach number higher than the design value, the hypersonic inlet is started with a regular reflection of the external compression shock at the cowl, whereas a Mach reflection will result in the shock propagating forwards to cause a shock detachment at the cowl lip, which is called "local unstart of inlet". As there are two operation modes of hypersonic inlet at high Mach number, the mode transition may occur with the operation condition of hypersonic inlet changing. A cowl-angle-variation-induced hysteresis and a downstream-pressure-variation-induced hysteresis in the hypersonic inlet start↔local unstart transition are obtained by viscous numerical simulations in this paper. The interaction of the external compression shock and boundary layer on the cowl plays a key role in the hysteresis phenomenon. Affected by the transition of external compression shock reflection at the cowl and the transition between separated and attached flow on the cowl, a hysteresis exists in the hypersonic inlet start↔local unstart transition. The hysteresis makes the operation of a hypersonic inlet very difficult to control. In order to avoid hysteresis phenomenon and keep the hypersonic inlet operating in a started mode, the control route should never pass through the local unstarted boundary.
National transonic facility Mach number system
Kern, F. A.; Knight, C. W.; Zasimowich, R. F.
1985-01-01
The Mach number system for the Langley Research Center's National Transonic Facility was designed to measure pressures to determine Mach number to within + or - 0.002. Nine calibration laboratory type fused quartz gages, four different range gages for the total pressure measurement, and five different range gages for the static pressure measurement were used to satisfy the accuracy requirement over the 103,000-890,000 Pa total pressure range of the tunnel. The system which has been in operation for over 1 year is controlled by a programmable data process controller to select, through the operation of solenoid valves, the proper range fused quartz gage to maximize the measurement accuracy. The pressure gage's analog outputs are digitized by the process controller and transmitted to the main computer for Mach number computation. An automatic two-point on-line calibration of the nine quartz gages is provided using a high accuracy mercury manometer.
Numerical simulations of Mach stem formation via intersecting bow shocks
Hansen, E. C.; Frank, A.; Hartigan, P.; Yirak, K.
2015-12-01
Hubble Space Telescope observations show bright knots of Hα emission within outflowing young stellar jets. Velocity variations in the flow create secondary bow shocks that may intersect and lead to enhanced emission. When the bow shocks intersect at or above a certain critical angle, a planar shock called a Mach stem is formed. These shocks could produce brighter Hα emission since the incoming flow to the Mach stem is parallel to the shock normal. In this paper we report first results of a study using 2-D numerical simulations designed to explore Mach stem formation at the intersection of bow shocks formed by hypersonic "bullets" or "clumps". Our 2-D simulations show how the bow shock shapes and intersection angles change as the adiabatic index γ changes. We show that the formation or lack of a Mach stem in our simulations is consistent with the steady-state Mach stem formation theory. Our ultimate goal, which is part of an ongoing research effort, is to characterize the physical and observational consequences of bow shock intersections including the formation of Mach stems.
Numerical Simulations of Mach Stem Formation via Intersecting Bow Shocks
Hansen, Edward C; Hartigan, Patrick
2014-01-01
Hubble Space Telescope observations show bright knots of H$\\alpha$ emission within outflowing young stellar jets. Velocity variations in the flow create secondary bow shocks that may intersect and lead to enhanced emission. When the bow shocks intersect at or above a certain critical angle, a planar shock called a Mach stem is formed. These shocks could produce brighter H$\\alpha$ emission since the incoming flow to the Mach stem is parallel to the shock normal. In this paper we report first results of a study using 2-D numerical simulations designed to explore Mach stem formation at the intersection of bow shocks formed by hypersonic "bullets" or "clumps". Our 2-D simulations show how the bow shock shapes and intersection angles change as the adiabatic index $\\gamma$ changes. We show that the formation or lack of a Mach stem in our simulations is consistent with the steady-state Mach stem formation theory. Our ultimate goal, which is part of an ongoing research effort, is to characterize the physical and obse...
Low Mach Number Fluctuating Hydrodynamics for Electrolytes
Péraud, Jean-Philippe; Chaudhri, Anuj; Bell, John B; Donev, Aleksandar; Garcia, Alejandro L
2016-01-01
We formulate and study computationally the low Mach number fluctuating hydrodynamic equations for electrolyte solutions. We are interested in studying transport in mixtures of charged species at the mesoscale, down to scales below the Debye length, where thermal fluctuations have a significant impact on the dynamics. Continuing our previous work on fluctuating hydrodynamics of multicomponent mixtures of incompressible isothermal miscible liquids (A. Donev, et al., Physics of Fluids, 27, 3, 2015), we now include the effect of charged species using a quasielectrostatic approximation. Localized charges create an electric field, which in turn provides additional forcing in the mass and momentum equations. Our low Mach number formulation eliminates sound waves from the fully compressible formulation and leads to a more computationally efficient quasi-incompressible formulation. We demonstrate our ability to model saltwater (NaCl) solutions in both equilibrium and nonequilibrium settings. We show that our algorithm...
Effects of Fin Leading Edge Sweep on Shock-Shock Interaction at Mach 6
Berry, Scott A.; Nowak, Robert J.
1996-01-01
The effects of fin leading edge sweep on peak heating rates due to shock-shock interaction have been experimentally examined in the Langley 20-Inch Mach 6 Tunnel. The shock interaction was produced by the intersection of a planar incident shock (16.8 deg shock angle relative to the freestream, generated by a 9 deg wedge) with the bow shock formed around a O.5-inch diameter cylindrical leading edge fin. Heating distributions along the leading edge stagnation line have been obtained using densely spaced thin film resistive-type sensors. Schlieren images were obtained to illustrate the very complex shock-shock interactions. The fin leading edge sweep angle was varied from 15-degrees swept back to 45-degrees swept forward for a freestream unit Reynolds number of 2 x 10(exp 6)/ft. Two models were utilized during the study, one with 0.025-inch spacing between gage centers, and the other 0.015-inch spacing. Gage spatial resolution on the order of 0.015-in appeared to accurately capture the narrow spike in heating. Peak heating due to shock interaction was maximized when the fin was swept forward 15 deg and 25 deg, both promoting augmentations about 7 times the baseline value. The schlieren images for these cases revealed Type 4 and Type 3 interactions, respectively.
Low Mach number fluctuating hydrodynamics for electrolytes
Péraud, Jean-Philippe; Nonaka, Andy; Chaudhri, Anuj; Bell, John B.; Donev, Aleksandar; Garcia, Alejandro L.
2016-11-01
We formulate and study computationally the low Mach number fluctuating hydrodynamic equations for electrolyte solutions. We are interested in studying transport in mixtures of charged species at the mesoscale, down to scales below the Debye length, where thermal fluctuations have a significant impact on the dynamics. Continuing our previous work on fluctuating hydrodynamics of multicomponent mixtures of incompressible isothermal miscible liquids [A. Donev et al., Phys. Fluids 27, 037103 (2015), 10.1063/1.4913571], we now include the effect of charged species using a quasielectrostatic approximation. Localized charges create an electric field, which in turn provides additional forcing in the mass and momentum equations. Our low Mach number formulation eliminates sound waves from the fully compressible formulation and leads to a more computationally efficient quasi-incompressible formulation. We demonstrate our ability to model saltwater (NaCl) solutions in both equilibrium and nonequilibrium settings. We show that our algorithm is second order in the deterministic setting and for length scales much greater than the Debye length gives results consistent with an electroneutral approximation. In the stochastic setting, our model captures the predicted dynamics of equilibrium and nonequilibrium fluctuations. We also identify and model an instability that appears when diffusive mixing occurs in the presence of an applied electric field.
Design of a continuously variable Mach-number nozzle
Institute of Scientific and Technical Information of China (English)
郭善广; 王振国; 赵玉新
2015-01-01
A design method was developed to specify the profile of the continuously variable Mach-number nozzle for the supersonic wind tunnel. The controllable contour design technique was applied to obtaining the original nozzle profile, while other Mach- numbers were derived from the transformation of the original profile. A design scheme, covering a Mach-number range of 3.0
3D shock-bubble interactions at Mach 3
Hejazialhosseini, Babak; Koumoutsakos, Petros
2012-01-01
We present a simulation for the interactions of shockwaves with light spherical density inhomogeneities. Euler equations for two-phase compressible flows are solved in a 3D uniform resolution finite volume based solver using 5th order WENO reconstructions of the primitive quantities, HLL-type numerical fluxes and 3rd order TVD time stepping scheme. In this study, a normal Mach 3 shockwave in air is directed at a helium bubble with an interface Atwood number of -0.76. We employ 4 billion cells on a supercomputing cluster and demonstrate the development of this flow until relatively late times. Shock passage compresses the bubble and deposits baroclinic vorticity on the interface. Initial distribution of the vorticity and compressions lead to the formation of an air jet, interface roll-ups and the formation of a long lasting vortical core, the white core. Compressed upstream of the bubble turns into a mixing zone and as the vortex ring distances from this mixing zone, a plume-shaped region is formed and sustain...
A new numerical solver for flows at various Mach numbers
Miczek, F; Edelmann, P V F
2014-01-01
Many problems in stellar astrophysics feature low Mach number flows. However, conventional compressible hydrodynamics schemes frequently used in the field have been developed for the transonic regime and exhibit excessive numerical dissipation for these flows. While schemes were proposed that solve hydrodynamics strictly in the low Mach regime and thus restrict their applicability, we aim at developing a scheme that correctly operates in a wide range of Mach numbers. Based on an analysis of the asymptotic behavior of the Euler equations in the low Mach limit we propose a novel scheme that is able to maintain a low Mach number flow setup while retaining all effects of compressibility. This is achieved by a suitable modification of the well-known Roe solver. Numerical tests demonstrate the capability of this new scheme to reproduce slow flow structures even in moderate numerical resolution. Our scheme provides a promising approach to a consistent multidimensional hydrodynamical treatment of astrophysical low Ma...
Two-dimensional lattice Boltzmann model for compressible flows with high Mach number
Gan, Yanbiao; Xu, Aiguo; Zhang, Guangcai; Yu, Xijun; Li, Yingjun
2008-03-01
In this paper we present an improved lattice Boltzmann model for compressible Navier-Stokes system with high Mach number. The model is composed of three components: (i) the discrete-velocity-model by M. Watari and M. Tsutahara [Phys. Rev. E 67 (2003) 036306], (ii) a modified Lax-Wendroff finite difference scheme where reasonable dissipation and dispersion are naturally included, (iii) artificial viscosity. The improved model is convenient to compromise the high accuracy and stability. The included dispersion term can effectively reduce the numerical oscillation at discontinuity. The added artificial viscosity helps the scheme to satisfy the von Neumann stability condition. Shock tubes and shock reflections are used to validate the new scheme. In our numerical tests the Mach numbers are successfully increased up to 20 or higher. The flexibility of the new model makes it suitable for tracking shock waves with high accuracy and for investigating nonlinear nonequilibrium complex systems.
Effect of leading edge sweep on shock-shock interference at Mach 8
Glass, Christopher E.; Wieting, Allan R.; Holden, Michael S.
1989-01-01
These Mach 8 experimental results are applicable to the details of a shock-shock interference that may occur on an engine inlet of a hypersonic vehicle from a swept forebody shock interacting with a swept cowl leading edge bow shock or from a swept splitter plate shock interacting with a swept fuel injection strut bow shock. Peak surface pressure and heat transfer rate on the cylinder were about 10 and 30 times the undisturbed flow stagnation point value, respectively, for the 0 deg sweep test. A comparison of the 15 deg and 30 deg swept results with the 0 deg swept results shows that peak pressure was reduced about 13 percent and 44 percent, respectively, and peak heat transfer rate was reduced about 7 percent and 27 percent, respectively.
Unsteadiness of a shock train in Mach 2.0 flow
Hunt, Robin; Driscoll, James; Gamba, Mirko
2016-11-01
Experimental observations of the progression of flow unsteadiness within a shock train are presented. A downstream control valve is used to generate a shock train in the constant area test section of a wind tunnel with a freestream Mach number of 2.0. Even with nominally constant boundary conditions the shock train exhibits inherent unsteady motion about the time average position. At the conditions presented the shocks can be displaced by up to 0.35 duct heights. Better knowledge of the shock train's dynamics may allow us to introduce control algorithms to reduce the system's unsteadiness and thus minimize the associated mechanical and thermal loads. An edge detection algorithm is applied to the instantaneous frames of high speed Schlieren movies to track the location of morphological features within the shock system. Simultaneously, high speed pressure transducers record the pressure fluctuations along the bottom wall of the duct. The results indicate a complex frequency dependent dynamical system. A strong component of the dynamics involves a disturbance traveling upstream through the boundary layer. Once the disturbance reaches the leading shock foot the shocks respond in order with the most upstream shock moving first.
Effect of Mach number on the efficiency of microwave energy deposition in supersonic flow
Lashkov, V. A.; Karpenko, A. G.; Khoronzhuk, R. S.; Mashek, I. Ch.
2016-05-01
The article is devoted to experimental and numerical studies of the efficiency of microwave energy deposition into a supersonic flow around the blunt cylinder at different Mach numbers. Identical conditions for energy deposition have been kept in the experiments, thus allowing to evaluate the pure effect of varying Mach number on the pressure drop. Euler equations are solved numerically to model the corresponding unsteady flow compressed gas. The results of numerical simulations are compared to the data obtained from the physical experiments. It is shown that the momentum, which the body receives during interaction of the gas domain modified by microwave discharge with a shock layer before the body, increases almost linearly with rising of Mach number and the efficiency of energy deposition also rises.
Low Mach Number Fluctuating Hydrodynamics of Diffusively Mixing Fluids
Donev, A; Sun, Y; Fai, T; Garcia, A L; Bell, J B
2012-01-01
We formulate low Mach number fluctuating hydrodynamic equations appropriate for modeling diffusive mixing in isothermal mixtures of fluids with different density and transport coefficients. These equations eliminate the fast isentropic fluctuations in pressure associated with the propagation of sound waves by replacing the equation of state with a local thermodynamic constraint. We demonstrate that the low Mach number model preserves the spatio-temporal spectrum of the slower diffusive fluctuations. We develop a strictly conservative finite-volume spatial discretization of the low Mach number fluctuating equations in both two and three dimensions. We construct several explicit Runge-Kutta temporal integrators that strictly maintain the equation of state constraint. The resulting spatio-temporal discretization is second-order accurate deterministically and maintains fluctuation-dissipation balance in the linearized stochastic equations. We apply our algorithms to model the development of giant concentration fl...
Hryniewicki, M. K.; Gottlieb, J. J.; Groth, C. P. T.
2017-07-01
The transition boundary separating the region of regular reflection from the regions of single-, transitional-, and double-Mach reflections for a planar shock wave moving in air and interacting with an inclined wedge in a shock tube is studied by both analytical methods and computational-fluid-dynamic simulations. The analytical solution for regular reflection and the corresponding solutions from the extreme-angle (detachment), sonic, and mechanical-equilibrium transition criteria by von Neumann (Oblique reflection of shocks, Explosive Research Report No. 12, Navy Department, Bureau of Ordnance, U.S. Dept. Comm. Tech. Serv. No. PB37079 (1943). Also, John von Neumann, Collected Works, Pergamon Press 6, 238-299, 1963) are first revisited and revised. The boundary between regular and Mach reflection is then determined numerically using an advanced computational-fluid-dynamics algorithm to solve Euler's inviscid equations for unsteady motion in two spatial dimensions. This numerical transition boundary is determined by post-processing many closely stationed flow-field simulations, to determine the transition point when the Mach stem of the Mach-reflection pattern just disappears and this pattern then transcends into that of regular reflection. The new numerical transition boundary is shown to agree well with von Neumann's closely spaced sonic and extreme-angle boundaries for weak incident shock Mach numbers from 1.0 to 1.6, but this new boundary trends upward and above von Neumann's sonic and extreme-angle boundaries by a couple of degrees at larger shock Mach numbers from 1.6 to 4.0. Furthermore, the new numerically determined transition boundary is shown to agree well with very few available experimental data obtained from previous experiments designed to reflect two symmetrical moving oblique shock waves along a plane without a shear or boundary layer.
Hryniewicki, M. K.; Gottlieb, J. J.; Groth, C. P. T.
2016-12-01
The transition boundary separating the region of regular reflection from the regions of single-, transitional-, and double-Mach reflections for a planar shock wave moving in air and interacting with an inclined wedge in a shock tube is studied by both analytical methods and computational-fluid-dynamic simulations. The analytical solution for regular reflection and the corresponding solutions from the extreme-angle (detachment), sonic, and mechanical-equilibrium transition criteria by von Neumann (Oblique reflection of shocks, Explosive Research Report No. 12, Navy Department, Bureau of Ordnance, U.S. Dept. Comm. Tech. Serv. No. PB37079 (1943). Also, John von Neumann, Collected Works, Pergamon Press 6, 238-299, 1963) are first revisited and revised. The boundary between regular and Mach reflection is then determined numerically using an advanced computational-fluid-dynamics algorithm to solve Euler's inviscid equations for unsteady motion in two spatial dimensions. This numerical transition boundary is determined by post-processing many closely stationed flow-field simulations, to determine the transition point when the Mach stem of the Mach-reflection pattern just disappears and this pattern then transcends into that of regular reflection. The new numerical transition boundary is shown to agree well with von Neumann's closely spaced sonic and extreme-angle boundaries for weak incident shock Mach numbers from 1.0 to 1.6, but this new boundary trends upward and above von Neumann's sonic and extreme-angle boundaries by a couple of degrees at larger shock Mach numbers from 1.6 to 4.0. Furthermore, the new numerically determined transition boundary is shown to agree well with very few available experimental data obtained from previous experiments designed to reflect two symmetrical moving oblique shock waves along a plane without a shear or boundary layer.
Mathematical and numerical aspects of low mach number flows
Energy Technology Data Exchange (ETDEWEB)
Schochet, St.; Bresch, D.; Grenier, E.; Alazard, T.; Gordner, A.; Sankaran, V.; Massot, M.; Sery, R.; Pebay, P.; Lunch, O.; Mazhorova, O.; Turkel, O.E.; Faille, I.; Danchin, R.; Allain, O.; Birken, P.; Lafitte, O.; Kloczko, T.; Frick, W.; Bui, T.; Dellacherie, S.; Klein, R.; Roe, Ph.; Accary, G.; Braack, M.; Picano, F.; Cadiou, A.; Dinescu, C.; Lesage, A.C.; Wesseling, P.; Heuveline, V.; Jobelin, M.; Weisman, C.; Merkle, C.
2004-07-01
Low Mach number flows represent a significant part of the various flows encountered in geophysics, industry or every day life. Paradoxically, the mathematical analysis of the equations governing these flows is difficult and on the practical side, the research of numerical algorithms valid for all flow speeds is continuing to be a challenge. However, in the last decade, both from the theoretical and the numerical sides, significant progresses were made in the understanding and analysis of the equations governing these flows. This conference intends to provide an up-to-date inventory of recent mathematical and numerical results in the analysis of these flows by bringing together both mathematicians and numericists active in this area. In the framework of the conference, a numerical workshop is organized which proposes to compute several challenging low Mach number flows: liquid flow around non-cavitating and cavitating NACA0015 hydrofoil, natural convection with large temperature differences, free convection, free surface flow, vessel pressurization. This document brings together the descriptions of the test cases of the numerical workshop and the abstracts of the conference papers: A 3D high order finite volume method for the prediction of near-critical fluid flows (G. ACCARY, I. RASPO, P. BONTOUX, B. ZAPPOLI); low Mach number limit of the non-isentropic Navier-Stokes equations (T. ALAZARD); simulation of cavitation rolls past a forward step with a bubble model (O. ALLAIN, N. BLASKA, C. LECA); flux preconditioning methods and fire events (P. BIRKEN, A. MEISTER); an adaptive finite element solver for compressible flows: application to heat-driven cavity benchmarks in 2D and 3D (M. BRAACK); comparison of various implicit, explicit, centered and upwind schemes for the simulation of compressed flows on moving mesh (A. CADIOU, M. BUFFAT, L. Le PENVEN, C. Le RIBAULT); low Mach number limit for viscous compressible flows (R. DANCHIN); some Properties of the low Mach number
Mathematical and numerical aspects of low mach number flows
Energy Technology Data Exchange (ETDEWEB)
Schochet, St.; Bresch, D.; Grenier, E.; Alazard, T.; Gordner, A.; Sankaran, V.; Massot, M.; Sery, R.; Pebay, P.; Lunch, O.; Mazhorova, O.; Turkel, O.E.; Faille, I.; Danchin, R.; Allain, O.; Birken, P.; Lafitte, O.; Kloczko, T.; Frick, W.; Bui, T.; Dellacherie, S.; Klein, R.; Roe, Ph.; Accary, G.; Braack, M.; Picano, F.; Cadiou, A.; Dinescu, C.; Lesage, A.C.; Wesseling, P.; Heuveline, V.; Jobelin, M.; Weisman, C.; Merkle, C.
2004-07-01
Low Mach number flows represent a significant part of the various flows encountered in geophysics, industry or every day life. Paradoxically, the mathematical analysis of the equations governing these flows is difficult and on the practical side, the research of numerical algorithms valid for all flow speeds is continuing to be a challenge. However, in the last decade, both from the theoretical and the numerical sides, significant progresses were made in the understanding and analysis of the equations governing these flows. This conference intends to provide an up-to-date inventory of recent mathematical and numerical results in the analysis of these flows by bringing together both mathematicians and numericists active in this area. In the framework of the conference, a numerical workshop is organized which proposes to compute several challenging low Mach number flows: liquid flow around non-cavitating and cavitating NACA0015 hydrofoil, natural convection with large temperature differences, free convection, free surface flow, vessel pressurization. This document brings together the descriptions of the test cases of the numerical workshop and the abstracts of the conference papers: A 3D high order finite volume method for the prediction of near-critical fluid flows (G. ACCARY, I. RASPO, P. BONTOUX, B. ZAPPOLI); low Mach number limit of the non-isentropic Navier-Stokes equations (T. ALAZARD); simulation of cavitation rolls past a forward step with a bubble model (O. ALLAIN, N. BLASKA, C. LECA); flux preconditioning methods and fire events (P. BIRKEN, A. MEISTER); an adaptive finite element solver for compressible flows: application to heat-driven cavity benchmarks in 2D and 3D (M. BRAACK); comparison of various implicit, explicit, centered and upwind schemes for the simulation of compressed flows on moving mesh (A. CADIOU, M. BUFFAT, L. Le PENVEN, C. Le RIBAULT); low Mach number limit for viscous compressible flows (R. DANCHIN); some Properties of the low Mach number
The Density Variance--Mach Number Relation in Supersonic Turbulence: I. Isothermal, magnetised gas
Molina, F Z; Federrath, C; Klessen, R S
2012-01-01
It is widely accepted that supersonic, magnetised turbulence plays a fundamental role for star formation in molecular clouds. It produces the initial dense gas seeds out of which new stars can form. However, the exact relation between gas compression, turbulent Mach number, and magnetic field strength is still poorly understood. Here, we introduce and test an analytical prediction for the relation between the density variance and the root-mean-square Mach number in supersonic, isothermal, magnetised turbulent flows. We approximate the density and velocity structure of the interstellar medium as a superposition of shock waves. We obtain the density contrast considering the momentum continuity equation for a single magnetised shock and extrapolate this result to the entire cloud. Depending on the field geometry, we then make three different assumptions based on observational and theoretical constraints: B independent of density, B proportional to the root square of the density and B proportional to the density....
Increased Mach Number Capability for the NASA Glenn 10x10 Supersonic Wind Tunnel
Slater, J. W.; Saunders, J. D.
2015-01-01
Computational simulations and wind tunnel testing were conducted to explore the operation of the Abe Silverstein Supersonic Wind Tunnel at the NASA Glenn Research Center at test section Mach numbers above the current limit of Mach 3.5. An increased Mach number would enhance the capability for testing of supersonic and hypersonic propulsion systems. The focus of the explorations was on understanding the flow within the second throat of the tunnel, which is downstream of the test section and is where the supersonic flow decelerates to subsonic flow. Methods of computational fluid dynamics (CFD) were applied to provide details of the shock boundary layer structure and to estimate losses in total pressure. The CFD simulations indicated that the tunnel could be operated up to Mach 4.0 if the minimum width of the second throat was made smaller than that used for previous operation of the tunnel. Wind tunnel testing was able to confirm such operation of the tunnel at Mach 3.6 and 3.7 before a hydraulic failure caused a stop to the testing. CFD simulations performed after the wind tunnel testing showed good agreement with test data consisting of static pressures along the ceiling of the second throat. The CFD analyses showed increased shockwave boundary layer interactions, which was also observed as increased unsteadiness of dynamic pressures collected in the wind tunnel testing.
Low Mach Number Fluctuating Hydrodynamics of Multispecies Liquid Mixtures
Donev, A; Bhattacharjee, A K; Garcia, A L; Bell, J B
2014-01-01
We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure that generalizes our prior work on ideal mixtures of ideal gases and binary liquid mixtures. In this formulation we combine and extend a number of existing descriptions of multispecies transport available in the literature. The formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a 'solvent' species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the princi...
Statistical error in particle simulations of low mach number flows
Energy Technology Data Exchange (ETDEWEB)
Hadjiconstantinou, N G; Garcia, A L
2000-11-13
We present predictions for the statistical error due to finite sampling in the presence of thermal fluctuations in molecular simulation algorithms. The expressions are derived using equilibrium statistical mechanics. The results show that the number of samples needed to adequately resolve the flowfield scales as the inverse square of the Mach number. Agreement of the theory with direct Monte Carlo simulations shows that the use of equilibrium theory is justified.
Effects of nonuniform Mach-number entrance on scramjet nozzle flowfield and performance
Zhang, Pu; Xu, Jinglei; Quan, Zhibin; Mo, Jianwei
2016-12-01
Considering the non-uniformities of nozzle entrance influenced by the upstream, the effects of nonuniform Mach-number coupled with shock and expansion-wave on the flowfield and performances of single expansion ramp nozzle (SERN) are numerically studied using Reynolds-Averaged Navier-Stokes equations. The adopted Reynolds-averaged Navier-Stokes methodology is validated by comparing the numerical results with the cold experimental data, and the average method used in this paper is discussed. Uniform and nonuniform facility nozzles are designed to generate different Mach-number profile for the inlet of SERN, which is direct-connected with different facility nozzle, and the whole flowfield is simulated. Because of the coupling of shock and expansion-wave, flow direction of nonuniform SERN entrance is distorted. Compared with Mach contour of uniform case, the line is more curved for coupling shock-wave entrance (SWE) case, and flatter for the coupling expansion-wave entrance (EWE) case. Wall pressure distribution of SWE case appears rising region, whereas decreases like stairs of EWE case. The numerical results reveal that the coupled shock and expansion-wave play significant roles on nozzle performances. Compared with the SERN performances of uniform entrance case at the same work conditions, the thrust of nonuniform entrance cases reduces by 3-6%, pitch moment decreases by 2.5-7%. The negative lift presents an incremental trend with EWE while the situation is the opposite with SWE. These results confirm that considering the entrance flow parameter nonuniformities of a scramjet nozzle coupled with shock or expansion-wave from the upstream is necessary.
Low Mach Number Fluctuating Hydrodynamics of Binary Liquid Mixtures
Nonaka, A J; Bell, J B; Donev, A
2014-01-01
Continuing on our previous work [ArXiv:1212.2644], we develop semi-implicit numerical methods for solving low Mach number fluctuating hydrodynamic equations appropriate for modeling diffusive mixing in isothermal mixtures of fluids with different densities and transport coefficients. We treat viscous dissipation implicitly using a recently-developed variable-coefficient Stokes solver [ArXiv:1308.4605]. This allows us to increase the time step size significantly compared to the earlier explicit temporal integrator. For viscous-dominated flows, such as flows at small scales, we develop a scheme for integrating the overdamped limit of the low Mach equations, in which inertia vanishes and the fluid motion can be described by a steady Stokes equation. We also describe how to incorporate advanced higher-order Godunov advection schemes in the numerical method, allowing for the treatment of fluids with high Schmidt number including the vanishing mass diffusion coefficient limit. We incorporate thermal fluctuations in...
Courant Number and Mach Number Insensitive CE/SE Euler Solvers
Chang, Sin-Chung
2005-01-01
It has been known that the space-time CE/SE method can be used to obtain ID, 2D, and 3D steady and unsteady flow solutions with Mach numbers ranging from 0.0028 to 10. However, it is also known that a CE/SE solution may become overly dissipative when the Mach number is very small. As an initial attempt to remedy this weakness, new 1D Courant number and Mach number insensitive CE/SE Euler solvers are developed using several key concepts underlying the recent successful development of Courant number insensitive CE/SE schemes. Numerical results indicate that the new solvers are capable of resolving crisply a contact discontinuity embedded in a flow with the maximum Mach number = 0.01.
Extension of the pressure correction method to zero-Mach number compressible flows
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In the present paper,the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm.The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube prob-lems,and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10-5.The attenuation of sound waves in viscous medium was then simulated.The results agree well with the analytical solutions given by theoretical acoustics.This demonstrated that the present method could also be implemented in acoustics field simulation,which is crucial for thermoacoustic simulation.
Extension of the pressure correction method to zero-Mach number compressible flows
Institute of Scientific and Technical Information of China (English)
HE YaLing; HUANG Jing; TAO YuBing; TAO WenQuan
2009-01-01
In the present paper, the classical pressure correction method was extended into low Mach number compressible flow regime by integrating equation of state into SIMPLE algorithm. The self-developed code based on this algorithm was applied to predicting the lid-driven cavity flow and shock tube prob-lems, and the results showed good agreement with benchmark solutions and the Mach number can reach the magnitude of as low as 10-5. The attenuation of sound waves in viscous medium was then simulated. The results agree well with the analytical solutions given by theoretical acoustics. This demonstrated that the present method could also be implemented in acoustics field simulation, which is crucial for thermoacoustic simulation.
Low Mach number fluctuating hydrodynamics of multispecies liquid mixtures
Energy Technology Data Exchange (ETDEWEB)
Donev, Aleksandar, E-mail: donev@courant.nyu.edu; Bhattacharjee, Amit Kumar [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States); Nonaka, Andy; Bell, John B. [Center for Computational Science and Engineering, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Garcia, Alejandro L. [Department of Physics and Astronomy, San Jose State University, San Jose, California 95192 (United States)
2015-03-15
We develop a low Mach number formulation of the hydrodynamic equations describing transport of mass and momentum in a multispecies mixture of incompressible miscible liquids at specified temperature and pressure, which generalizes our prior work on ideal mixtures of ideal gases [Balakrishnan et al., “Fluctuating hydrodynamics of multispecies nonreactive mixtures,” Phys. Rev. E 89 013017 (2014)] and binary liquid mixtures [Donev et al., “Low mach number fluctuating hydrodynamics of diffusively mixing fluids,” Commun. Appl. Math. Comput. Sci. 9(1), 47-105 (2014)]. In this formulation, we combine and extend a number of existing descriptions of multispecies transport available in the literature. The formulation applies to non-ideal mixtures of arbitrary number of species, without the need to single out a “solvent” species, and includes contributions to the diffusive mass flux due to gradients of composition, temperature, and pressure. Momentum transport and advective mass transport are handled using a low Mach number approach that eliminates fast sound waves (pressure fluctuations) from the full compressible system of equations and leads to a quasi-incompressible formulation. Thermal fluctuations are included in our fluctuating hydrodynamics description following the principles of nonequilibrium thermodynamics. We extend the semi-implicit staggered-grid finite-volume numerical method developed in our prior work on binary liquid mixtures [Nonaka et al., “Low mach number fluctuating hydrodynamics of binary liquid mixtures,” http://arxiv.org/abs/1410.2300 (2015)] and use it to study the development of giant nonequilibrium concentration fluctuations in a ternary mixture subjected to a steady concentration gradient. We also numerically study the development of diffusion-driven gravitational instabilities in a ternary mixture and compare our numerical results to recent experimental measurements [Carballido-Landeira et al., “Mixed-mode instability of a
Hydrogen film cooling with incident and swept-shock interactions in a Mach 6.4 nitrogen free stream
Olsen, George C.; Nowak, Robert J.
1995-01-01
The effectiveness of slot film cooling of a flat plate in a Mach 6.4 flow with and without incident and swept oblique shock interactions was experimentally investigated. Hydrogen was the primary coolant gas, although some tests were conducted using helium as the coolant. Tests were conducted in the Calspan 48-Inch Shock Tunnel with a nitrogen flow field to preclude combustion of the hydrogen coolant gas. A two-dimensional highly instrumented model developed in a previous test series was used. Parameters investigated included coolant mass flow rate, coolant gas, local free-stream Reynolds number, incident oblique shock strength, and a swept oblique shock. Both gases were highly effective coolants in undisturbed flow; however, both incident and swept shocks degraded that effectiveness.
Federrath, Christoph; Schober, Jennifer; Banerjee, Robi; Klessen, Ralf S; Schleicher, Dominik R G; 10.1103/PhysRevLett.107.114504
2011-01-01
We study the growth rate and saturation level of the turbulent dynamo in magnetohydrodynamical simulations of turbulence, driven with solenoidal (divergence-free) or compressive (curl-free) forcing. For models with Mach numbers ranging from 0.02 to 20, we find significantly different magnetic field geometries, amplification rates, and saturation levels, decreasing strongly at the transition from subsonic to supersonic flows, due to the development of shocks. Both extreme types of turbulent forcing drive the dynamo, but solenoidal forcing is more efficient, because it produces more vorticity.
DSMC Simulation of High Mach Number Taylor-Couette Flow
Pradhan, Sahadev, , Dr.
2017-01-01
The main focus of this work is to characterise the Taylor-Couette flow of an ideal gas between two coaxial cylinders at Mach number Ma = (U_w /√{ kbT_w / m }) in the range 0.01 Boltzmann constant. The cylindrical surfaces are specified as being diffusely reflecting with the thermal accommodation coefficient equal to one. In the present analysis of high Mach number compressible Taylor-Couette flow using DSMC method, wall slip in the temperature and the velocities are found to be significant. Slip occurs because the temperature/velocity of the molecules incident on the wall could be very different from that of the wall, even though the temperature/velocity of the reflected molecules is equal to that of the wall. Due to the high surface speed of the inner cylinder, significant heating of the gas is taking place. The gas temperature increases until the heat transfer to the surface equals the work done in moving the surface. The highest temperature is obtained near the moving surface of the inner cylinder at a radius of about (1.26 r_1).
The Variation of Slat Noise with Mach and Reynolds Numbers
Lockhard, David P.; Choudhari, Meelan M.
2011-01-01
The slat noise from the 30P30N high-lift system has been computed using a computational fluid dynamics code in conjunction with a Ffowcs Williams-Hawkings solver. By varying the Mach number from 0.13 to 0.25, the noise was found to vary roughly with the 5th power of the speed. Slight changes in the behavior with directivity angle could easily account for the different speed dependencies reported in the literature. Varying the Reynolds number from 1.4 to 2.4 million resulted in almost no differences, and primarily served to demonstrate the repeatability of the results. However, changing the underlying hybrid Reynolds-averaged-Navier-Stokes/Large-Eddy-Simulation turbulence model significantly altered the mean flow because of changes in the flap separation. However, the general trends observed in both the acoustics and near-field fluctuations were similar for both models.
Hydrodynamic Flow and Jet Induced Mach Shocks at RHIC and LHC
Stöcker, H; Rau, P; Betz, Barbara; Rau, Philip; St\\"ocker, Horst
2007-01-01
We discuss the present collective flow signals for the phase transition to quark-gluon plasma (QGP) and the collective flow as a barometer for the equation of state (EoS). A study of Mach shocks induced by fast partonic jets propagating through the QGP is given. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. Results of a hydrodynamical study of jet energy loss are presented.
The density variance - Mach number relation in isothermal and non-isothermal adiabatic turbulence
Nolan, Chris A; Sutherland, Ralph S
2015-01-01
The density variance - Mach number relation of the turbulent interstellar medium is relevant for theoretical models of the star formation rate, efficiency, and the initial mass function of stars. Here we use high-resolution hydrodynamical simulations with grid resolutions of up to 1024^3 cells to model compressible turbulence in a regime similar to the observed interstellar medium. We use Fyris Alpha, a shock-capturing code employing a high-order Godunov scheme to track large density variations induced by shocks. We investigate the robustness of the standard relation between the logarithmic density variance (sigma_s^2) and the sonic Mach number (M) of isothermal interstellar turbulence, in the non-isothermal regime. Specifically, we test ideal gases with diatomic molecular (gamma = 7/5) and monatomic (gamma = 5/3) adiabatic indices. A periodic cube of gas is stirred with purely solenoidal forcing at low wavenumbers, leading to a fully-developed turbulent medium. We find that as the gas heats in adiabatic comp...
Low Mach number theory of freely cooling granular gases
Meerson, Baruch; Vilenkin, Arkady
2007-01-01
We use hydrodynamic equations to investigate the dynamics of a freely cooling dilute granular gas with nearly elastic particle collisions. We assume a narrow channel geometry and focus on the regime where the sound travel time through the system is much shorter than the typical cooling time of the gas. As a result, the pressure rapidly becomes almost homogeneous, while the Mach number is small. Eliminating the sound waves and employing Lagrangian coordinates, we reduce the full hydrodynamics to a single nonlinear/nonlocal equation of a reaction-diffusion type. This equation describes a broad class of flows and, in particular, can follow the development of strongly nonlinear states during clustering instability. Without heat diffusion, the reduced equation is exactly soluble and develops a finite-time density blowup with the same local features as those exhibited by the recently found family of exact solutions of the full set of ideal hydrodynamic equations (Fouxon et al. 2007). The heat diffusion, however, ar...
Turbomachinery for Low-to-High Mach Number Flight
Tan, Choon S.; Shah, Parthiv N.
2004-01-01
The thrust capability of turbojet cycles is reduced at high flight Mach number (3+) by the increase in inlet stagnation temperature. The 'hot section' temperature limit imposed by materials technology sets the maximum heat addition and, hence, sets the maximum flight Mach number of the operating envelope. Compressor pre-cooling, either via a heat exchanger or mass-injection, has been suggested as a means to reduce compressor inlet temperature and increase mass flow capability, thereby increasing thrust. To date, however, no research has looked at compressor cooling (i.e., using a compressor both to perform work on the gas path air and extract heat from it simultaneously). We wish to assess the feasibility of this novel concept for use in low-to-high Mach number flight. The results to-date show that an axial compressor with cooling: (1) relieves choking in rear stages (hence opening up operability), (2) yields higher-pressure ratio and (3) yields higher efficiency for a given corrected speed and mass flow. The performance benefit is driven: (i) at the blade passage level, by a decrease in the total pressure reduction coefficient and an increase in the flow turning; and (ii) by the reduction in temperature that results in less work required for a given pressure ratio. The latter is a thermodynamic effect. As an example, calculations were performed for an eight-stage compressor with an adiabatic design pressure ratio of 5. By defining non-dimensional cooling as the percentage of compressor inlet stagnation enthalpy removed by a heat sink, the model shows that a non-dimensional cooling of percent in each blade row of the first two stages can increase the compressor pressure ratio by as much as 10-20 percent. Maximum corrected mass flow at a given corrected speed may increase by as much as 5 percent. In addition, efficiency may increase by as much as 5 points. A framework for characterizing and generating the performance map for a cooled compressor has been developed
Parametric investigation of single-expansion-ramp nozzles at Mach numbers from 0.60 to 1.20
Capone, Francis J.; Re, Richard J.; Bare, E. Ann
1992-01-01
An investigation was conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of varying six nozzle geometric parameters on the internal and aeropropulsive performance characteristics of single-expansion-ramp nozzles. This investigation was conducted at Mach numbers from 0.60 to 1.20, nozzle pressure ratios from 1.5 to 12, and angles of attack of 0 deg +/- 6 deg. Maximum aeropropulsive performance at a particular Mach number was highly dependent on the operating nozzle pressure ratio. For example, as the nozzle upper ramp length or angle increased, some nozzles had higher performance at a Mach number of 0.90 because of the nozzle design pressure was the same as the operating pressure ratio. Thus, selection of the various nozzle geometric parameters should be based on the mission requirements of the aircraft. A combination of large upper ramp and large lower flap boattail angles produced greater nozzle drag coefficients at Mach number greater than 0.80, primarily from shock-induced separation on the lower flap of the nozzle. A static conditions, the convergent nozzle had high and nearly constant values of resultant thrust ratio over the entire range of nozzle pressure ratios tested. However, these nozzles had much lower aeropropulsive performance than the convergent-divergent nozzle at Mach number greater than 0.60.
Energy Technology Data Exchange (ETDEWEB)
Hull, Lawrence Mark [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Miller, Phillip Isaac [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Moro, Erik Allan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-11-28
In the instance of multiple fragment impact on cased explosive, isolated curved shocks are generated in the explosive. These curved shocks propagate and may interact and form irregular or Mach reflections along the interaction loci, thereby producing a single shock that may be sufficient to initiate PBX-9501. However, the incident shocks are divergent and their intensity generally decreases as they expand, and the regions behind the Mach stem interaction loci are generally unsupported and allow release waves to rapidly affect the flow. The effects of release waves and divergent shocks may be considered theoretically through a “Shock Change Equation”.
Edge, cavity and aperture tones at very low Mach numbers
Howe, M. S.
1997-01-01
This paper discusses self-sustaining oscillations of high-Reynolds-number shear layers and jets incident on edges and corners at infinitesimal Mach number. These oscillations are frequently sources of narrow-band sound, and are usually attributed to the formation of discrete vortices whose interactions with the edge or corner produce impulsive pressures that lead to the formation of new vorticity and complete a feedback cycle of operation. Linearized analyses of these interactions are presented in which free shear layers are modelled by vortex sheets. Detailed results are given for shear flows over rectangular wall apertures and shallow cavities, and for the classical jet edge interaction. The operating stages of self-sustained oscillations are identified with poles in the upper half of the complex frequency plane of a certain impulse response function. It is argued that the real parts of these poles determine the Strouhal numbers of the operating stages observed experimentally for the real, nonlinear system. The response function coincides with the Rayleigh conductivity of the ‘window’ spanned by the shear flow for wall apertures and jet edge interactions, and to a frequency dependent drag coefficient for shallow wall cavities. When the interaction occurs in the neighbourhood of an acoustic resonator, exemplified by the flue organ pipe, the poles are augmented by a sequence of poles whose real parts are close to the resonance frequencies of the resonator, and the resonator can ‘speak’ at one of these frequencies (by extracting energy from the mean flow) provided the corresponding pole has positive imaginary part.
DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number
Pradhan, Sahadev, , Dr.
2017-01-01
The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range Boltzmann constant. The variation of streamwise velocity, temperature, number-density, and mean free path along the wall normal direction away from the plate surface is studied. The qualitative nature of the streamwise velocity at high Mach number is similar to those in the incompressible limit (parabolic profile). However, there are important differences. The amplitudes of the streamwise velocity increase as the Mach number increases and turned into a more flatter profile near the wall. There is significant velocity and temperature slip at the surface of the plate, and the slip increases as the Mach number is increased. It is interesting to note that for the highest Mach numbers considered here, the streamwise velocity at the wall exceeds the sound speed, and the flow is supersonic throughout the flow domain.
Variation with Mach Number of Static and Total Pressures Through Various Screens
Adler, Alfred A
1946-01-01
Tests were conducted in the Langley 24-inch highspeed tunnel to ascertain the static-pressure and total-pressure losses through screens ranging in mesh from 3 to 12 wires per inch and in wire diameter from 0.023 to 0.041 inch. Data were obtained from a Mach number of approximately 0.20 up to the maximum (choking) Mach number obtainable for each screen. The results of this investigation indicate that the pressure losses increase with increasing Mach number until the choking Mach number, which can be computed, is reached. Since choking imposes a restriction on the mass rate of flow and maximum losses are incurred at this condition, great care must be taken in selecting the screen mesh and wire dimmeter for an installation so that the choking Mach number is
A Device for Measuring Sonic Velocity and Compressor Mach Number
1948-07-01
resonator (the only 4 NACA TN No. 1664 accurate measurement required) is measured, as shomn in figure 1, by means of a mercury manometer . The compressor Mach...tube vs not connected to the ccmpressor inlet until after calibration. The pressure in the device was measured by means of the mercury manometer . Fram
Study on Shock Wave and Turbulent Boundary Layer Interactions in a Square Duct at Mach 2 and 4
Institute of Scientific and Technical Information of China (English)
Hiromu SUGIYAMA; Ryojiro MINATO; Kazuhide MIZOBATA; Akira TOJO; Yohei MUTO
2006-01-01
In this paper, the outline of the Mach 4 supersonic wind runnel for the investigation of the supersonic internal flows in ducts was firstly described. Secondly, the location, structure and characteristics of the Mach 2 and Mach 4 pseudo-shock waves in a square duct were investigated by color schlieren photographs and duct wall pressure fluctuation measurements. Finally, the wall shear stress distributions on the side, top and bottom walls of the square duct with the Mach 4 pseudo-shock wave were investigated qualitatively by the shear stress-sensitive liquid crystal visualization method. The side wall boundary layer separation region under the first shock is narrow near the top wall, while the side wall boundary layer separation region under the first shock is very wide near the bottom wall.
Numerical Simulation of Low Mach Number Fluid - Phenomena.
Reitsma, Scott H.
A method for the numerical simulation of low Mach number (M) fluid-acoustic phenomena is developed. This computational fluid-acoustic (CFA) methodology is based upon a set of conservation equations, termed finite-compressible, derived from the unsteady Navier-Stokes equations. The finite-compressible and more familiar pseudo-compressible equations are compared. The impact of derivation assumptions are examined theoretically and through numerical experimentation. The error associated with these simplifications is shown to be of O(M) and proportional to the amplitude of unsteady phenomena. A computer code for the solution of the finite -compressible equations is developed from an existing pseudo -compressible code. Spatial and temporal discretization issues relevant in the context of near field fluid-acoustic simulations are discussed. The finite volume code employs a MUSCL based third order upwind biased flux difference splitting algorithm for the convective terms. An explicit, three stage, second order Runge-Kutta temporal integration is employed for time accurate simulations while an implicit, approximately factored time quadrature is available for steady state convergence acceleration. The CFA methodology is tested in a series of problems which examine the appropriateness of the governing equations, the exacerbation of spatial truncation errors and the degree of temporal accuracy. Characteristic based boundary conditions employing a spatial formulation are developed. An original non-reflective boundary condition based upon the generalization and extension of existing methods is derived and tested in a series of multi-dimensional problems including those involving viscous shear flows and propagating waves. The final numerical experiment is the simulation of boundary layer receptivity to acoustic disturbances. This represents the first simulation of receptivity at a surface inhomogeneity in which the acoustic phenomena is modeled using physically appropriate
Coumar, Sandra; Lago, Viviana
2017-06-01
This paper presents an experimental investigation, carried out at the Icare Laboratory by the FAST team, focusing on plasma flow control in supersonic and rarefied regime. The study analyzes how the Mach number as well as the ambient pressure modify the repercussions of the plasma actuator on the shock wave. It follows previous experiments performed in the MARHy (ex-SR3) wind tunnel with a Mach 2 flow interacting with a sharp flat plate, where modifications induced by a plasma actuator were observed. The flat plate was equipped with a plasma actuator composed of two aluminum electrodes. The upstream one was biased with a negative DC potential and thus, created a glow discharge type plasma. Experimental measurements showed that the boundary layer thickness and the shock wave angle increased when the discharge was ignited. The current work was performed with two nozzles generating Mach 4 flows but at two different static pressures: 8 and 71 Pa. These nozzles were chosen to study independently the impact of the Mach number and the impact of the pressure on the flow behavior. In the range of the discharge current considered in this experimental work, it was observed that the shock wave angle increased with the discharge current of +15% for the Mach 2 flow but the increase rate doubled to +28% for the Mach 4 flow at the same static pressure, showing that the discharge effect is even more significant when boosting the flow speed. When studying the effect of the discharge on the Mach 4 flow at higher static pressure, it was observed that the topology of the plasma changed drastically and the increase in the shock wave angle with the discharge current of +21 %.
Pedrosa, A. C. F.; Nagamatsu, H. T.; Hinckel, J. A.
1984-01-01
Heat transfer measurements were determined for a flat plate with and without pressure gradient for various free stream temperatures, wall temperature ratios, and Reynolds numbers for an inlet flow Mach number of 0.45, which is a representative inlet Mach number for gas turbine rotor blades. A shock tube generated the high temperature and pressure air flow, and a variable geometry test section was used to produce inlet flow Mach number of 0.45 and accelerate the flow over the plate to sonic velocity. Thin-film platinum heat gages recorded the local heat flux for laminar, transition, and turbulent boundary layers. The free stream temperatures varied from 611 R (339 K) to 3840 R (2133 K) for a T(w)/T(r,g) temperature ratio of 0.87 to 0.14. The Reynolds number over the heat gages varied from 3000 to 690,000. The experimental heat transfer data were correlated with laminar and turbulent boundary layer theories for the range of temperatures and Reynolds numbers and the transition phenomenon was examined.
Rikanati, A; Oron, D; Sadot, O; Shvarts, D
2003-02-01
Effects of high-Mach numbers and high initial amplitudes on the evolution of the single-mode Richtmyer-Meshkov shock-wave induced hydrodynamic instability are studied using theoretical models, experiments, and numerical simulations. Two regimes in which there is a significant deviation from the linear dependence of the initial velocity on the initial perturbation amplitude are defined and characterized. In one, the observed reduction of the initial velocity is primarily due to large initial amplitudes. This effect is accurately modeled by a vorticity deposition model, quantifying both the effect of the initial perturbation amplitude and the exact shape of the interface. In the other, the reduction is dominated by the proximity of the shock wave to the interface. This effect is modeled by a modified incompressible model where the shock wave is mimicked by a moving bounding wall. These results are supplemented with high initial amplitude Mach 1.2 shock-tube experiments, enabling separation of the two effects. It is shown that in most of the previous experiments, the observed reduction is predominantly due to the effect of high initial amplitudes.
Multiobjective Design Optimization of Supersonic Jet Engine in Different Cruise Mach Numbers
Ogawa, Masamichi; Sato, Tetsuya; Kobayashi, Hiroaki; Taguchi, Hideyuki
The aim of this paper is to apply a multi-objective optimization generic algorithm (MOGA) to the conceptual design of the hypersonic/supersonic vehicles with different cruise Mach number. The pre-cooled turbojet engine is employed as a propulsion system and some engine parameters such as the precooler size, compressor size, compression ratio and fuel type are varied in the analysis. The result shows that the optimum cruise Mach number is about 4 if hydrogen fuel is used. Methane fuel instead of hydrogen reduces the vehicle gross weight by 33% in case of the Mach 2 vehicle.
Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number
Battista, Francesco; Casciola, Carlo Massimo
2014-01-01
Supercritical fluids near the critical point are characterized by liquid-like densities and gas-like transport properties. These features are purposely exploited in different contexts ranging from natural products extraction/fractionation to aerospace propulsion. Large part of studies concerns this last context, focusing on the dynamics of supercritical fluids at high Mach number where compressibility and thermodynamics strictly interact. Despite the widespread use also at low Mach number, the turbulent mixing properties of slightly supercritical fluids have still not investigated in detail in this regime. This topic is addressed here by dealing with Direct Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number conditions found in many industrial applications, the numerical model is based on a suitable low-Mach number expansion of the governing equation. According to experimental observations, the weakly superc...
Le, G.; Russell, C. T.; Gosling, J. T.
1994-12-01
We use International Sun-Earth Explorer (ISEE) magnetic field and plasma data to examine dayside magnetopause crossing under conditions of low Mach number and strongly northward interplanetary magnetic field (IMF). When the solar wind Mach number is low, the IMF stregth and magnetoseath field stregth are large, and we expect the effects of magnetic reconection to be the strongest. When the IMF is strongly northward, we find that the location of the magnetopause boundary layer is very stationary in the space, and we observe many features that are common for both typical and low Mach numbers. However, under low Mach number conditions, we have observed some features that would be expected for cusp reconnection. The boundary layer near the subsolar region contains heated magnetosheath plasma with little hot magnetospheric component that has clearly entered the magnetosphere elsewhere. At least some of the structures present in the boundary layer are impulsive. Inside the boundary layer there is also clear evidence of acceleratedflow from the cusp region for strongly northward IMF at low Mach number. Reconnection beyond the cusp can explain the observed field, plasma, and flow signatures. Therefore at low Mach number, reconection is important in the formation of the boundary layer for northward IMF.
Dynamic transition from Mach to regular reflection of shock waves in a steady flow
CSIR Research Space (South Africa)
Naidoo, K
2014-07-01
Full Text Available decreased with increased rotation speed. The sensitivity of the transition angle to changing the rotation point from the trailing edge to the experimental model pivot point was investigated briefly at a free-stream Mach number of M=2.98 with M(subE)=-0...
Experimental Studies of Very-High Mach Number Hydrodynamics
1994-02-14
intensity of the from Rotman (1991. symbol R) shock amplification of the density fluctuations as a parameter, together with a turbulent kinetic energy...overlapsubgrid scale model while predicting an increase in the model where an algebraic identity provides a procedure for overall grid spectral energy... Rotman , and W. P. improvement in the dissipative near-wal region. Dannevik during the course of this work. Figure 8. indicates that for even steeper
Numerical Simulation of Shock Bubble Interaction with Different Mach Numbers
Yang, Jie; Wan, Zhen-Hua; Wang, Bo-Fu; Sun, De-Jun
2015-03-01
Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11232011 and 11402262, the 111 Project under Grant No B07033, and the China Postdoctoral Science Foundation Funded Project under Grant No 2014M561833.
The small-scale dynamo: Breaking universality at high Mach numbers
Schleicher, Dominik R G; Federrath, Christoph; Bovino, Stefano; Schmidt, Wolfram
2013-01-01
(Abridged) The small-scale dynamo may play a substantial role in magnetizing the Universe under a large range of conditions, including subsonic turbulence at low Mach numbers, highly supersonic turbulence at high Mach numbers and a large range of magnetic Prandtl numbers Pm, i.e. the ratio of kinetic viscosity to magnetic resistivity. Low Mach numbers may in particular lead to the well-known, incompressible Kolmogorov turbulence, while for high Mach numbers, we are in the highly compressible regime, thus close to Burgers turbulence. In this study, we explore whether in this large range of conditions, a universal behavior can be expected. Our starting point are previous investigations in the kinematic regime. Here, analytic studies based on the Kazantsev model have shown that the behavior of the dynamo depends significantly on Pm and the type of turbulence, and numerical simulations indicate a strong dependence of the growth rate on the Mach number of the flow. Once the magnetic field saturates on the current ...
Modeling plasma glow discharges in Air near a Mach 3 bow shock with KRONOS
Rassou, Sebastien; Labaune, Julien; Packan, Denis; Elias, Paul-Quentin
2016-09-01
In this work, plasma glow discharge in Air is modeled near a Mach 3 bow shock. Numerical simulations are performed using the coupling KRONOS which have been developed at ONERA. The flow field is modeled using the code CFD: CEDRE from ONERA and the electrical and plasma part by the EDF open-source code CODE_SATURNE. The plasma kinetic modeling consists on a two-term Boltzmann equation solver and a chemical reaction solver depending of the electric field. The coupling KRONOS is fully parallelized and run on ONERA supercomputers. The shock wave is formed by the propagation of a supersonic flow (M = 3) through a truncated conical model mounted with a central spike. Depending on the spike's voltage value, corona, glow or arc regime could be obtained in a steady flow. The parameters for the supersonic flow and the spike configurations are chosen to be in glow discharge regime and to reproduce the experimental setup. In our simulations, 12 species and 80 reactions (ionization, electronic or vibrational excitation, attachment etc ...) are considered to properly model the glow discharge and the afterglow. In a stationary flow, glow discharge is observed only at the upstream of the shock wave near the high voltage spike. Behind the bow shock, in the afterglow, negative ions are provided by electrons attachment with O2. The negative ions flow convection ensures the electrical conduction and the establishment of the glow discharge.
Energy Technology Data Exchange (ETDEWEB)
Dellacherie, St
2004-07-01
This work deals with the derivation of a diphasic low Mach number model obtained through a Mach number asymptotic expansion applied to the compressible diphasic Navier Stokes system, expansion which filters out the acoustic waves. This approach is inspired from the work of Andrew Majda giving the equations of low Mach number combustion for thin flame and for perfect gases. When the equations of state verify some thermodynamic hypothesis, we show that the low Mach number diphasic system predicts in a good way the dilatation or the compression of a bubble and has equilibrium convergence properties. Then, we propose an entropic and convergent Lagrangian scheme in mono-dimensional geometry when the fluids are perfect gases and we propose a first approach in Eulerian variables where the interface between the two fluids is captured with a level set technique. (author)
Transition in oblique shock/boundary layer interactions at Mach 5.92
Dwivedi, Anubhav; Shrestha, Prakash; Hildebrand, Nathaniel; Nichols, J. W.; Jovanovic, M. R.; Candler, G. V.
2016-11-01
We use the compressible flow solver US3D to perform DNS of an oblique shock wave interacting with a laminar boundary layer over an adiabatic flat plate at Mach 5 . 92 . Simulations are repeated with different spanwise extents. The adverse pressure gradient created by the shock causes the boundary layer to separate, leading to the formation of a recirculation bubble downstream. We consider interactions of various strengths by varying the shock angle. A sufficiently strong interaction causes the flow to become 3 - D , unsteady and eventually transition to turbulence. We observe long streamwise streaks downstream of the reattachment point which eventually break into turbulence. In the present work, we characterize the spatio-temporal dynamics of the unsteady separation bubble and these streaks using Fourier analysis and Sparsity Promoting Dynamic Mode Decomposition. To investigate the origin of these streaks we also analyze the role of linear Görtler instability resulting from the curvature of the streamlines induced by the separation bubble. Supported by ONR, Grant No. N00014-15-1-2522.
Mach number study of supersonic turbulence: The properties of the density field
Konstandin, Lukas; Girichidis, Philipp; Peters, Thomas; Shetty, Rahul; Klessen, Ralf S
2015-01-01
We model driven, compressible, isothermal, turbulence with Mach numbers ranging from the subsonic ($\\mathcal{M} \\approx 0.65$) to the highly supersonic regime ($\\mathcal{M}\\approx 16 $). The forcing scheme consists both solenoidal (transverse) and compressive (longitudinal) modes in equal parts. We find a relation $\\sigma_{s}^2 = \\mathrm{b}\\log{(1+\\mathrm{b}^2\\mathcal{M}^2)}$ between the Mach number and the standard deviation of the logarithmic density with $\\mathrm{b} = 0.457 \\pm 0.007$. The density spectra follow $\\mathcal{D}(k,\\,\\mathcal{M}) \\propto k^{\\zeta(\\mathcal{M})}$ with scaling exponents depending on the Mach number. We find $\\zeta(\\mathcal{M}) = \\alpha \\mathcal{M}^{\\beta}$ with a coefficient $\\alpha$ that varies slightly with resolution, whereas $\\beta$ changes systematically. We extrapolate to the limit of infinite resolution and find $\\alpha = -1.91 \\pm 0.01,\\, \\beta =-0.30\\pm 0.03$. The dependence of the scaling exponent on the Mach number implies a fractal dimension $D=2+0.96 \\mathcal{M}^{-0.3...
Winters, Andrew R.; Derigs, Dominik; Gassner, Gregor J.; Walch, Stefanie
2017-03-01
We describe a unique averaging procedure to design an entropy stable dissipation operator for the ideal magnetohydrodynamic (MHD) and compressible Euler equations. Often in the derivation of an entropy conservative numerical flux function much care is taken in the design and averaging of the entropy conservative numerical flux. We demonstrate in this work that if the discrete dissipation operator is not carefully chosen as well it can have deleterious effects on the numerical approximation. This is particularly true for very strong shocks or high Mach number flows present, for example, in astrophysical simulations. We present the underlying technique of how to construct a unique averaging technique for the discrete dissipation operator. We also demonstrate numerically the increased robustness of the approximation.
Rao, Pooja; She, Dan; Lim, Hyunkyung; Glimm, James
2015-11-01
The qualitative and quantitative effect of initial conditions (linear and non-linear) and high Mach number (1.3 and 1.45) is studied on the turbulent mixing induced by the Richtmyer-Meshkov instability in idealized ICF conditions. The Richtmyer-Meshkov instability seeds Rayleigh-taylor instabilities in ICF experiments and is one of the factors that contributes to reduced performance of ICF experiments. Its also found in collapsing cores of stars and supersonic combustion. We use the Stony Brook University code, FronTier, which is verified via a code comparison study against the AMR multiphysics code FLASH, and validated against vertical shock tube experiments done by the LANL Extreme Fluids Team. These simulations are designed as a step towards simulating more realistic ICF conditions and quantifying the detrimental effects of mixing on the yield.
Mahto, Navin Kumar; Choubey, Gautam; Suneetha, Lakka; Pandey, K. M.
2016-11-01
The two equation standard k-ɛ turbulence model and the two-dimensional compressible Reynolds-Averaged Navier-Stokes (RANS) equations have been used to computationally simulate the double cavity scramjet combustor. Here all the simulations are performed by using ANSYS 14-FLUENT code. At the same time, the validation of the present numerical simulation for double cavity has been performed by comparing its result with the available experimental data which is in accordance with the literature. The results are in good agreement with the schlieren image and the pressure distribution curve obtained experimentally. However, the pressure distribution curve obtained numerically is under-predicted in 5 locations by numerical calculation. Further, investigations on the variations of the effects of the length-to-depth ratio of cavity and Mach number on the combustion characteristics has been carried out. The present results show that there is an optimal length-to-depth ratio for the cavity for which the performance of combustor significantly improves and also efficient combustion takes place within the combustor region. Also, the shifting of the location of incident oblique shock took place in the downstream of the H2 inlet when the Mach number value increases. But after achieving a critical Mach number range of 2-2.5, the further increase in Mach number results in lower combustion efficiency which may deteriorate the performance of combustor.
Mach number scaling of helicopter rotor blade/vortex interaction noise
Leighton, Kenneth P.; Harris, Wesley L.
1985-01-01
A parametric study of model helicopter rotor blade slap due to blade vortex interaction (BVI) was conducted in a 5 by 7.5-foot anechoic wind tunnel using model helicopter rotors with two, three, and four blades. The results were compared with a previously developed Mach number scaling theory. Three- and four-bladed rotor configurations were found to show very good agreement with the Mach number to the sixth power law for all conditions tested. A reduction of conditions for which BVI blade slap is detected was observed for three-bladed rotors when compared to the two-bladed baseline. The advance ratio boundaries of the four-bladed rotor exhibited an angular dependence not present for the two-bladed configuration. The upper limits for the advance ratio boundaries of the four-bladed rotors increased with increasing rotational speed.
Flow-induced cylinder noise formulated as a diffraction problem for low Mach numbers
Gloerfelt, X.; Pérot, F.; Bailly, C.; Juvé, D.
2005-10-01
The role of surfaces in the mechanism of sound generation by low Mach number flows interacting with solid nonvibrating surfaces is well established by the classical aeroacoustic papers by Powell, Doak, Ffowcs Williams, Crighton, or Howe. It can be formulated as a problem of diffraction of the flow sources by the rigid body. The present study illustrates this statement in the case of flow-induced cylinder noise. Curle's formulation is analytically and numerically compared to a formulation based on an exact Green's function tailored to a cylindrical geometry. The surface integral of Curle's formulation represents exactly the diffraction effects by the rigid body. The direct and scattered parts of the sound field are studied. In this low Mach number configuration, the cylinder is compact, and the scattered (dipole) field dominates the direct (quadrupole) field. The classical properties of the scattering by a cylinder are retrieved by considering a point quadripole source near the cylinder surface.
Axisymmetric vortex method for low-Mach number, diffusion-controlled combustion
Lakkis, I
2003-01-01
A grid-free, Lagrangian method for the accurate simulation of low-Mach number, variable-density, diffusion-controlled reacting flow is presented. A fast-chemistry model in which the conversion rate of reactants to products is limited by the local mixing rate is assumed in order to reduce the combustion problem to the solution of a convection-diffusion-generation equation with volumetric expansion and vorticity generation at the reaction fronts. The solutions of the continuity and vorticity equations, and the equations governing the transport of species and energy, are obtained using a formulation in which particles transport conserved quantities by convection and diffusion. The dynamic impact of exothermic combustion is captured through accurate integration of source terms in the vorticity transport equations at the location of the particles, and the extra velocity field associated with volumetric expansion at low Mach number computed to enforced mass conservation. The formulation is obtained for an axisymmet...
Low Mach and Peclet number limit for a model of stellar tachocline and upper radiative zones
Directory of Open Access Journals (Sweden)
Donatella Donatelli
2016-09-01
Full Text Available We study a hydrodynamical model describing the motion of internal stellar layers based on compressible Navier-Stokes-Fourier-Poisson system. We suppose that the medium is electrically charged, we include energy exchanges through radiative transfer and we assume that the system is rotating. We analyze the singular limit of this system when the Mach number, the Alfven number, the Peclet number and the Froude number approache zero in a certain way and prove convergence to a 3D incompressible MHD system with a stationary linear transport equation for transport of radiation intensity. Finally, we show that the energy equation reduces to a steady equation for the temperature corrector.
Nearfield Unsteady Pressures at Cruise Mach Numbers for a Model Scale Counter-Rotation Open Rotor
Stephens, David B.
2012-01-01
An open rotor experiment was conducted at cruise Mach numbers and the unsteady pressure in the nearfield was measured. The system included extensive performance measurements, which can help provide insight into the noise generating mechanisms in the absence of flow measurements. A set of data acquired at a constant blade pitch angle but various rotor speeds was examined. The tone levels generated by the front and rear rotor were found to be nearly equal when the thrust was evenly balanced between rotors.
Bispen, Georgij; Lukáčová-Medvid'ová, Mária; Yelash, Leonid
2017-04-01
In this paper we will present and analyze a new class of the IMEX finite volume schemes for the Euler equations with a gravity source term. We will in particular concentrate on a singular limit of weakly compressible flows when the Mach number M ≪ 1. In order to efficiently resolve slow dynamics we split the whole nonlinear system in a stiff linear part governing the acoustic and gravity waves and a non-stiff nonlinear part that models nonlinear advection effects. For time discretization we use a special class of the so-called globally stiffly accurate IMEX schemes and approximate the stiff linear operator implicitly and the non-stiff nonlinear operator explicitly. For spatial discretization the finite volume approximation is used with the central and Rusanov/Lax-Friedrichs numerical fluxes for the linear and nonlinear subsystem, respectively. In the case of a constant background potential temperature we prove theoretically that the method is asymptotically consistent and asymptotically stable uniformly with respect to small Mach number. We also analyze experimentally convergence rates in the singular limit when the Mach number tends to zero.
A half-explicit, non-split projection method for low Mach number flows.
Energy Technology Data Exchange (ETDEWEB)
Pousin, Jerome G. (National Institute for Applied Sciences, France); Najm, Habib N.; Pebay, Philippe Pierre
2004-02-01
In the context of the direct numerical simulation of low MACH number reacting flows, the aim of this article is to propose a new approach based on the integration of the original differential algebraic (DAE) system of governing equations, without further differentiation. In order to do so, while preserving a possibility of easy parallelization, it is proposed to use a one-step index 2 DAE time-integrator, the Half Explicit Method (HEM). In this context, we recall why the low MACH number approximation belongs to the class of index 2 DAEs and discuss why the pressure can be associated with the constraint. We then focus on a fourth-order HEM scheme, and provide a formulation that makes its implementation more convenient. Practical details about the consistency of initial conditions are discussed, prior to focusing on the implicit solve involved in the method. The method is then evaluated using the Modified KAPS Problem, since it has some of the features of the low MACH number approximation. Numerical results are presented, confirming the above expectations. A brief summary of ongoing efforts is finally provided.
Agarwal, Shankar
2013-01-01
We calculate the cosmic Mach number M - the ratio of the bulk flow of the velocity field on scale R to the velocity dispersion within regions of scale R. M is effectively a measure of the ratio of large-scale to small-scale power and can be a useful tool to constrain the cosmological parameter space. Using a compilation of existing peculiar velocity surveys, we calculate M and compare it to that estimated from mock catalogues extracted from the LasDamas (a LCDM cosmology) numerical simulations. We find agreement with expectations for the LasDamas cosmology at ~ 1.5 sigma CL. We also show that our Mach estimates for the mocks are not biased by selection function effects. To achieve this, we extract dense and nearly-isotropic distributions using Gaussian selection functions with the same width as the characteristic depth of the real surveys, and show that the Mach numbers estimated from the mocks are very similar to the values based on Gaussian profiles of the corresponding widths. We discuss the importance of ...
Dixon, G. V.; Barringer, S. R.; Gray, C. E.; Leatherman, A. D.
1975-01-01
Computer programs and resulting tabulations are presented of pipeline length-to-diameter ratios as a function of Mach number and pressure ratios for compressible flow. The tabulations are applicable to air, nitrogen, oxygen, and hydrogen for compressible isothermal flow with friction and compressible adiabatic flow with friction. Also included are equations for the determination of weight flow. The tabulations presented cover a wider range of Mach numbers for choked, adiabatic flow than available from commonly used engineering literature. Additional information presented, but which is not available from this literature, is unchoked, adiabatic flow over a wide range of Mach numbers, and choked and unchoked, isothermal flow for a wide range of Mach numbers.
The Experimental Measurement of Aerodynamic Heating About Complex Shapes at Supersonic Mach Numbers
Neumann, Richard D.; Freeman, Delma C.
2011-01-01
In 2008 a wind tunnel test program was implemented to update the experimental data available for predicting protuberance heating at supersonic Mach numbers. For this test the Langley Unitary Wind Tunnel was also used. The significant differences for this current test were the advances in the state-of-the-art in model design, fabrication techniques, instrumentation and data acquisition capabilities. This current paper provides a focused discussion of the results of an in depth analysis of unique measurements of recovery temperature obtained during the test.
Convective heat transport in stratified atmospheres at low and high Mach number
Anders, Evan H
2016-01-01
Convection in astrophysical systems is stratified and often occurs at high Rayleigh number (Ra) and low Mach number (Ma). Here we study stratified convection in the context of plane-parallel, polytropically stratified atmospheres. We hold the density stratification ($n_{\\rho}$) and Prandtl number (Pr) constant while varying Ma and Ra to determine the behavior of the Nusselt number (Nu), which quantifies the efficiency of convective heat transport. As Ra increases and $\\text{Ma} \\rightarrow 1$, a scaling of Nu $\\propto$ Ra$^{0.45}$ is observed. As Ra increases to a regime where Ma $\\geq 1$, this scaling gives way to a weaker Nu $\\propto$ Ra$^{0.19}$. In the regime of Ma $\\ll 1$, a consistent Nu $\\propto$ Ra$^{0.31}$ is retrieved, reminiscent of the Nu $\\propto$ Ra$^{2/7}$ seen in Rayleigh-B\\'{e}nard convection.
A NOVEL SLIGHTLY COMPRESSIBLE MODEL FOR LOW MACH NUMBER PERFECT GAS FLOW CALCULATION
Institute of Scientific and Technical Information of China (English)
邓小刚; 庄逢甘
2002-01-01
By analyzing the characteristics of low Mach number perfect gas flows, a novel Slightly Compressible Model (SCM) for low Mach number perfect gas flows is derived. In view of numerical calculations, this model is proved very efficient,for it is kept within the p-v frame but does not have to satisfy the time consuming divergence-free condition in order to get the incompressible Navier-Stokes equation solutions. Writing the equations in the form of conservation laws, we have derived the characteristic systems which are necessary for numerical calculations. A cellcentered finite-volume method with flux difference upwind-biased schemes is used for the equation solutions and a new Exact Newton Relaxation (ENR) implicit method is developed. Various computed results are presented to validate the present model.Laminar flow solutions over a circular cylinder with wake developing and vortex shedding are presented. Results for inviscid flow over a sphere are compared in excellent agreement with the exact analytic incompressible solution. Three-dimensional viscous flow solutions over sphere and prolate spheroid are also calculated and compared well with experiments and other incompressible solutions. Finally, good convergent performaces are shown for sphere viscous flows.
Airfoil Aeroelastic Flutter Analysis Based on Modified Leishman-Beddoes Model at Low Mach Number
Institute of Scientific and Technical Information of China (English)
SHAO Song; ZHU Qinghua; ZHANG Chenglin; NI Xianping
2011-01-01
Based on modified Leishman-Beddoes(L-B)state space model at low Mach number(lower than 0.3),the airfoil aeroelastic system is presented in this paper.The main modifications for L-B model include a new dynamic stall criterion and revisions of normal force and pitching moment coefficient.The bifurcation diagrams,the limit cycle oscillation (LCO)phase plane plots and the time domain response figures are applied to investigating the stall flutter bifurcation behavior of airfoil aeroelastic systems with symmetry or asymmetry.It is shown that the symmetric periodical oscillation happens after subcritical bifurcation caused by dynamic stall,and the asymmetric periodical oscillation,which is caused by the interaction of dynamic stall and static divergence,only happens in the airfoil aeroelastic system with asymmetry.Validations of the modified L-B model and the airfoil aeroelastic system are presented with the experimental airload data of NACA0012 and OA207 and experimental stall flutter data of NACA0012 respectively.Results demonstrate that the airfoil aeroelastic system presented in this paper is effective and accurate,which can be applied to the investigation of airfoil stall flutter at low Mach number.
Opacity Broadening of $^{13}$CO Linewidths and its Effect on the Variance-Sonic Mach Number Relation
Correia, Caio; Lazarian, Alex; Ossenkopf, Volker; Stutzki, Jürgen; Kainulainen, Jouni; Kowal, Grzegorz; de Medeiros, José Renan
2014-01-01
We study how the estimation of the sonic Mach number ($M_s$) from $^{13}$CO linewidths relates to the actual 3D sonic Mach number. For this purpose we analyze MHD simulations which include post-processing to take radiative transfer effects into account. As expected, we find very good agreement between the linewidth estimated sonic Mach number and the actual sonic Mach number of the simulations for optically thin tracers. However, we find that opacity broadening causes $M_s$ to be overestimated by a factor of ~ 1.16 - 1.3 when calculated from optically thick $^{13}$CO lines. We also find that there is a dependency on the magnetic field: super-Alfv\\'enic turbulence shows increased line broadening as compared with sub-Alfv\\'enic turbulence for all values of optical depth for supersonic turbulence. Our results have implications for the observationally derived sonic Mach number--density standard deviation ($\\sigma_{\\rho/}$) relationship, $\\sigma^2_{\\rho/}=b^2M_s^2$, and the related column density standard deviatio...
Tests of Full-Scale Helicopter Rotors at High Advancing Tip Mach Numbers and Advance Ratios
Biggers, James C.; McCloud, John L., III; Stroub, Robert H.
2015-01-01
As a continuation of the studies of reference 1, three full-scale helicopter rotors have been tested in the Ames Research Center 40- by SO-foot wind tunnel. All three of them were two-bladed, teetering rotors. One of the rotors incorporated the NACA 0012 airfoil section over the entire length of the blade. This rotor was tested at advance ratios up to 1.05. Both of the other rotors were tapered in thickness and incorporated leading-edge camber over the outer 20 percent of the blade radius. The larger of these rotors was tested at advancing tip Mach numbers up to 1.02. Data were obtained for a wide range of lift and propulsive force, and are presented without discussion.
Low-Mach-number turbulence in interstellar gas revealed by radio polarization gradients
Gaensler, Bryan M; Burkhart, Blakesley; Newton-McGee, Katherine J; Ekers, Ronald D; Lazarian, Alex; McClure-Griffiths, Naomi M; Robishaw, Timothy; Dickey, John M; Green, Anne J; 10.1038/nature10446
2011-01-01
The interstellar medium of the Milky Way is multi-phase, magnetized and turbulent. Turbulence in the interstellar medium produces a global cascade of random gas motions, spanning scales ranging from 100 parsecs to 1000 kilometres. Fundamental parameters of interstellar turbulence such as the sonic Mach number (the speed of sound) have been difficult to determine because observations have lacked the sensitivity and resolution to directly image the small-scale structure associated with turbulent motion. Observations of linear polarization and Faraday rotation in radio emission from the Milky Way have identified unusual polarized structures that often have no counterparts in the total radiation intensity or at other wavelengths, and whose physical significance has been unclear. Here we report that the gradient of the Stokes vector (Q,U), where Q and U are parameters describing the polarization state of radiation, provides an image of magnetized turbulence in diffuse ionized gas, manifested as a complex filamenta...
Varsakelis, Christos; Papalexandris, Miltiadis V.
2017-01-01
A conundrum in non-equilibrium thermodynamics of heterogeneous mixtures with microstructure concerns the selection of thermodynamic currents and forces in the entropy production rate from the multitude of available options. The objective of this article is to demonstrate that the low-Mach-number approximation can narrow down this ambiguity. More specifically, by postulating that the post-constitutive equations are well behaved with respect to this perturbation analysis we assert that thermal non-equilibrium should be chosen as an independent force even if this requires the explicit manipulation of the entropy inequality. According to our analysis, alternative choices result in post-constitutive equations; the incompressible limit of which gives rise to questionable predictions.
Peng, Naifu; Yang, Yue
2016-11-01
We investigate the evolution of vortex-surface fields (VSFs) in viscous compressible Taylor-Green flows. The VSF is applied to the direct numerical simulation of the Taylor-Green flows at a range of Mach numbers from Ma = 0 . 6 to Ma = 2 . 2 for characterizing the Mach-number effects on evolving vortical structures. We find that the dilatation and baroclinic force strongly influence the geometry of vortex surfaces and the energy dissipation rate in the transitional stage. The vortex tubes in compressible flows are less curved than those in incompressible flows, and the maximum dissipation rate occurs earlier in high-Mach-number flows perhaps owing to the conversion of kinetic energy into heat. Moreover, the relations between the evolutionary geometry of vortical structures and flow statistics are discussed. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11522215 and 11521091), and the Thousand Young Talents Program of China.
Henneberry, Hugh M.; Snyder, Christopher A.
1993-01-01
An analysis of gas turbine engines using water and oxygen injection to enhance performance by increasing Mach number capability and by increasing thrust is described. The liquids are injected, either separately or together, into the subsonic diffuser ahead of the engine compressor. A turbojet engine and a mixed-flow turbofan engine (MFTF) are examined, and in pursuit of maximum thrust, both engines are fitted with afterburners. The results indicate that water injection alone can extend the performance envelope of both engine types by one and one-half Mach numbers at which point water-air ratios reach 17 or 18 percent and liquid specific impulse is reduced to some 390 to 470 seconds, a level about equal to the impulse of a high energy rocket engine. The envelope can be further extended, but only with increasing sacrifices in liquid specific impulse. Oxygen-airflow ratios as high as 15 percent were investigated for increasing thrust. Using 15 percent oxygen in combination with water injection at high supersonic Mach numbers resulted in thrust augmentation as high as 76 percent without any significant decrease in liquid specific impulse. The stoichiometric afterburner exit temperature increased with increasing oxygen flow, reaching 4822 deg R in the turbojet engine at a Mach number of 3.5. At the transonic Mach number of 0.95 where no water injection is needed, an oxygen-air ratio of 15 percent increased thrust by some 55 percent in both engines, along with a decrease in liquid specific impulse of 62 percent. Afterburner temperature was approximately 4700 deg R at this high thrust condition. Water and/or oxygen injection are simple and straightforward strategies to improve engine performance and they will add little to engine weight. However, if large Mach number and thrust increases are required, liquid flows become significant, so that operation at these conditions will necessarily be of short duration.
Background-oriented schlieren imaging of flow around a circular cylinder at low Mach numbers
Stadler, Hannes; Bauknecht, André; Siegrist, Silvan; Flesch, Robert; Wolf, C. Christian; van Hinsberg, Nils; Jacobs, Markus
2017-09-01
The background-oriented schlieren (BOS) imaging method has, for the first time, been applied in the investigation of the flow around a circular cylinder at low Mach numbers (Mnumbers of 0.1× 10^6 ≤ Re ≤ 6.0× 10^6. Even at ambient pressure and the lowest Reynolds number investigated, density gradients associated with the flow around the cylinder were recorded. The signal-to-noise ratio of the evaluated gradient field improved with increasing stagnation pressure. The separation point could easily be identified with this non-intrusive measurement technique and corresponds well to simultaneous surface pressure measurements. The resulting displacement field is in principle of qualitative nature as the observation angle was parallel to the cylinder axis only in a single point of the recorded images. However, it has been possible to integrate the density field along the surface of the cylinder by successive imaging at incremental angular positions around the cylinder. This density distribution has been found to agree well with the pressure measurements and with potential theory where appropriate.
Aerodynamic Characteristics of a Revised Target Drone Vehicle at Mach Numbers from 1.60 to 2.86
Blair, A. B., Jr.; Babb, C. Donald
1968-01-01
An investigation has been conducted in the Langley Unitary Plan wind tunnel to determine the aerodynamic characteristics of a revised target drone vehicle through a Mach number range from 1.60 to 2.86. The vehicle had canard surfaces and a swept clipped-delta wing with twin tip-mounted vertical tails.
Slot, H.J.; Moore, P.; Delfos, R.; Boersma, B.J.
2009-01-01
In this paper we present the experimental results of a detailed investigation of the flow and acoustic properties of a turbulent jet with Mach number 0·75 and Reynolds number 3·5 103. We describe the methods and experimental procedures followed during the measurements, and subsequently present the f
Rescaling of the Roe scheme in low Mach-number flow regions
Boniface, Jean-Christophe
2017-01-01
A rescaled matrix-valued dissipation is reformulated for the Roe scheme in low Mach-number flow regions from a well known family of local low-speed preconditioners popularized by Turkel. The rescaling is obtained explicitly by suppressing the pre-multiplication of the preconditioner with the time derivative and by deriving the full set of eigenspaces of the Roe-Turkel matrix dissipation. This formulation preserves the time consistency and does not require to reformulate the boundary conditions based on the characteristic theory. The dissipation matrix achieves by construction the proper scaling in low-speed flow regions and returns the original Roe scheme at the sonic line. We find that all eigenvalues are nonnegative in the subsonic regime. However, it becomes necessary to formulate a stringent stability condition to the explicit scheme in the low-speed flow regions based on the spectral radius of the rescaled matrix dissipation. With the large disparity of the eigenvalues in the dissipation matrix, this formulation raises a two-timescale problem for the acoustic waves, which is circumvented for a steady-state iterative procedure by the development of a robust implicit characteristic matrix time-stepping scheme. The behaviour of the modified eigenvalues in the incompressible limit and at the sonic line also suggests applying the entropy correction carefully, especially for complex non-linear flows.
Geometrical on-the-fly shock detection in SPH
Beck, Alexander M; Donnert, Julius M F
2015-01-01
We present an on-the-fly geometrical approach for shock detection and Mach number calculation in simulations employing smoothed particle hydrodynamics (SPH). We utilize pressure gradients to select shock candidates and define up- and downstream positions. We obtain hydrodynamical states in the up- and downstream regimes with a series of normal and inverted kernel weightings parallel and perpendicular to the shock normals. Our on-the-fly geometrical Mach detector incorporates well within the SPH formalism and has low computational cost. We implement our Mach detector into the simulation code GADGET and alongside many SPH improvements. We test our shock finder in a sequence of shock-tube tests with successively increasing Mach numbers exceeding by far the typical values inside galaxy clusters. For the all shocks, we resolve the shocks well and the correct Mach numbers are assigned. An application to a strong magnetized shock-tube gives stable results in full magnetohydrodynamic set-ups. We simulate a merger of ...
Seiff, Alvin; Wilkins, Max E.
1961-01-01
The aerodynamic characteristics of a hypersonic glider configuration, consisting of a slender ogive cylinder with three highly swept wings, spaced 120 apart, with the wing chord equal to the body length, were investigated experimentally at a Mach number of 6 and at Reynolds numbers from 6 to 16 million. The objectives were to evaluate the theoretical procedures which had been used to estimate the performance of the glider, and also to evaluate the characteristics of the glider itself. A principal question concerned the viscous drag at full-scale Reynolds number, there being a large difference between the total drags for laminar and turbulent boundary layers. It was found that the procedures which had been applied for estimating minimum drag, drag due to lift, lift curve slope, and center of pressure were generally accurate within 10 percent. An important exception was the non-linear contribution to the lift coefficient which had been represented by a Newtonian term. Experimentally, the lift curve was nearly linear within the angle-of-attack range up to 10 deg. This error affected the estimated lift-drag ratio. The minimum drag measurements indicated that substantial amounts of turbulent boundary layer were present on all models tested, over a range of surface roughness from 5 microinches maximum to 200 microinches maximum. In fact, the minimum drag coefficients were nearly independent of the surface smoothness and fell between the estimated values for turbulent and laminar boundary layers, but closer to the turbulent value. At the highest test Reynolds numbers and at large angles of attack, there was some indication that the skin friction of the rough models was being increased by the surface roughness. At full-scale Reynolds number, the maximum lift-drag ratio with a leading edge of practical diameter (from the standpoint of leading-edge heating) was 4.0. The configuration was statically and dynamically stable in pitch and yaw, and the center of pressure was less
A comparative study of scramjet injection strategies for high Mach numbers flows
Riggins, D. W.; Mcclinton, C. R.; Rogers, R. C.; Bittner, R. D.
1992-01-01
A simple method for predicting the axial distribution of supersonic combustor thrust potential is described. A complementary technique for illustrating the spatial evolution and distribution of thrust potential and loss mechanisms in reacting flows is developed. Wall jet cases and swept ramp injector cases for Mach 17 and Mach 13.5 flight enthalpy inflow conditions are numerically modeled and analyzed using these techniques. The visualization of thrust potential in the combustor for the various cases examined provides a unique tool for increasing understanding of supersonic combustor performance potential.
Variation of the ratio of specific heats across a detached bow shock
Chao, J. K.; Wiskerchen, M. J.
1974-01-01
Equations are derived which allow the ratio of specific heats behind the earth's bow shock to be evaluated if several pre-shock parameters (the specific-heat ratio, the Alfvenic Mach number, the sonic Mach number, and the angle between the shock normal at the stagnation point and the magnetic field) and the density jump across the shock are known. Numerical examples show that the dependence of the post-shock ratio on the pre-shock ratio is weak.
Meerson, Baruch; Fouxon, Itzhak; Vilenkin, Arkady
2008-02-01
We employ hydrodynamic equations to investigate nonstationary channel flows of freely cooling dilute gases of hard and smooth spheres with nearly elastic particle collisions. This work focuses on the regime where the sound travel time through the channel is much shorter than the characteristic cooling time of the gas. As a result, the gas pressure rapidly becomes almost homogeneous, while the typical Mach number of the flow drops well below unity. Eliminating the acoustic modes and employing Lagrangian coordinates, we reduce the hydrodynamic equations to a single nonlinear and nonlocal equation of a reaction-diffusion type. This equation describes a broad class of channel flows and, in particular, can follow the development of the clustering instability from a weakly perturbed homogeneous cooling state to strongly nonlinear states. If the heat diffusion is neglected, the reduced equation becomes exactly soluble, and the solution develops a finite-time density blowup. The blowup has the same local features at singularity as those exhibited by the recently found family of exact solutions of the full set of ideal hydrodynamic equations [I. Fouxon, Phys. Rev. E 75, 050301(R) (2007); I. Fouxon,Phys. Fluids 19, 093303 (2007)]. The heat diffusion, however, always becomes important near the attempted singularity. It arrests the density blowup and brings about previously unknown inhomogeneous cooling states (ICSs) of the gas, where the pressure continues to decay with time, while the density profile becomes time-independent. The ICSs represent exact solutions of the full set of granular hydrodynamic equations. Both the density profile of an ICS and the characteristic relaxation time toward it are determined by a single dimensionless parameter L that describes the relative role of the inelastic energy loss and heat diffusion. At L>1 the intermediate cooling dynamics proceeds as a competition between "holes": low-density regions of the gas. This competition resembles Ostwald
Measurement and Analysis of the Noise Radiated by Low Mach Number Centrifugal Blowers.
Yeager, David Marvin
An investigation was performed of the broad band, aerodynamically generated noise in low tip-speed Mach number, centrifugal air moving devices. An interdisciplinary experimental approach was taken which involved investigation of the aerodynamic and acoustic fields, and their mutual relationship. The noise generation process was studied using two experimental vehicles: (1) a scale model of a homologous family of centrifugal blowers typical of those used to cool computer and business equipment, and (2) a single blade from a centrifugal blower impeller placed in a known, controllable flow field. The radiation characteristics of the model blower were investigated by measuring the acoustic intensity distribution near the blower inlet and comparing it with the intensity near the inlet to an axial flow fan. Results showed that the centrifugal blower is a distributed, random noise source, unlike an axial fan which exhibited the effects of a coherent, interacting source distribution. Aerodynamic studies of the flow field in the inlet and at the discharge to the rotating impeller were used to assess the mean flow distribution through the impeller blade channels and to identify regions of excessive turbulence near the rotating blade row. Both circumferential and spanwise mean flow nonuniformities were identified along with a region of increased turbulence just downstream of the scroll cutoff. The fluid incidence angle, normally taken as an indicator of blower performance, was estimated from mean flow data as deviating considerably from an ideal impeller design. An investigation of the noise radiated from the single, isolated airfoil was performed using modern correlation and spectral analysis techniques. Radiation from the single blade in flow was characterized using newly developed expressions for the correlation area and the dipole source strength per unit area, and from the relationship between the blade surface pressure and the incident turbulent flow field. Results
Baumbick, R. J.
1974-01-01
Results of experimental tests conducted on a supersonic, mixed-compression, axisymmetric inlet are presented. The inlet is designed for operation at Mach 2.5 with a turbofan engine (TF-30). The inlet was coupled to either a choked orifice plate or a long duct which had a variable-area choked exit plug. Closed-loop frequency responses of selected diffuser static pressures used in the terminal-shock control system are presented. Results are shown for Mach 2.5 conditions with the inlet coupled to either the choked orifice plate or the long duct. Inlet unstart-restart traces are also presented. High-response inlet bypass doors were used to generate an internal disturbance and also to achieve terminal-shock control.
Calleja, John; Tamagno, Jose
1993-01-01
A series of air calibration tests were performed in GASL's HYPULSE facility in order to more accurately determine test section flow conditions for flows simulating total enthalpies in the Mach 13 to 17 range. Present calibration data supplements previous data and includes direct measurement of test section pitot and static pressure, acceleration tube wall pressure and heat transfer, and primary and secondary incident shock velocities. Useful test core diameters along with the corresponding free-stream conditions and usable testing times were determined. For the M13.5 condition, in-stream static pressure surveys showed the temporal and spacial uniformity of this quantity across the useful test core. In addition, finite fringe interferograms taken of the free-stream flow at the test section did not indicate the presence of any 'strong' wave system for any of the conditions investigated.
Drake, Hubert M; Mclaughlin, Milton D; Goodman, Harold R
1948-01-01
Results are presented of tests up to a Mach number of 0.92 at altitudes around 30,000 feet. The data obtained show that the airplane can be flown to this Mach number above 30,000 feet. Longitudinal trim changes have been experienced but the forces involved have been small. The elevator effectiveness decreased about one-half with increase of Mach number from 0.70 to 0.87. Buffeting has been experienced in level flight but it has been mild and the associated tail loads have been small. No aileron buzz or other flutter phenomena have been noted.
DIFFUSIVE SHOCK ACCELERATION AT COSMOLOGICAL SHOCK WAVES
Energy Technology Data Exchange (ETDEWEB)
Kang, Hyesung [Department of Earth Sciences, Pusan National University, Pusan 609-735 (Korea, Republic of); Ryu, Dongsu, E-mail: kang@uju.es.pusan.ac.kr, E-mail: ryu@canopus.cnu.ac.kr [Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764 (Korea, Republic of)
2013-02-10
We reexamine nonlinear diffusive shock acceleration (DSA) at cosmological shocks in the large-scale structure of the universe, incorporating wave-particle interactions that are expected to operate in collisionless shocks. Adopting simple phenomenological models for magnetic field amplification (MFA) by cosmic-ray (CR) streaming instabilities and Alfvenic drift, we perform kinetic DSA simulations for a wide range of sonic and Alfvenic Mach numbers and evaluate the CR injection fraction and acceleration efficiency. In our DSA model, the CR acceleration efficiency is determined mainly by the sonic Mach number M{sub s} , while the MFA factor depends on the Alfvenic Mach number and the degree of shock modification by CRs. We show that at strong CR modified shocks, if scattering centers drift with an effective Alfven speed in the amplified magnetic field, the CR energy spectrum is steepened and the acceleration efficiency is reduced significantly, compared to the cases without such effects. As a result, the postshock CR pressure saturates roughly at {approx}20% of the shock ram pressure for strong shocks with M{sub s} {approx}> 10. In the test-particle regime (M{sub s} {approx}< 3), it is expected that the magnetic field is not amplified and the Alfvenic drift effects are insignificant, although relevant plasma physical processes at low Mach number shocks remain largely uncertain.
Flow behind concave shock waves
Mölder, S.
2017-03-01
Curved shock theory is introduced and applied to calculate the flow behind concave shock waves. For sonic conditions, three characterizing types of flow are identified, based on the orientation of the sonic line, and it is shown that, depending on the ratio of shock curvatures, a continuously curving shock can exist with Type III flow, where the sonic line intercepts the reflected characteristics from the shock, thus preventing the formation of a reflected shock. The necessary shock curvature ratio for a Type III sonic point does not exist for a hyperbolic shock so that it will revert to Mach reflection for all Mach numbers. A demonstration is provided, by CFD calculations, at Mach 1.2 and 3.
Flow behind concave shock waves
Mölder, S.
2017-09-01
Curved shock theory is introduced and applied to calculate the flow behind concave shock waves. For sonic conditions, three characterizing types of flow are identified, based on the orientation of the sonic line, and it is shown that, depending on the ratio of shock curvatures, a continuously curving shock can exist with Type III flow, where the sonic line intercepts the reflected characteristics from the shock, thus preventing the formation of a reflected shock. The necessary shock curvature ratio for a Type III sonic point does not exist for a hyperbolic shock so that it will revert to Mach reflection for all Mach numbers. A demonstration is provided, by CFD calculations, at Mach 1.2 and 3.
Powers, Sheryll Goecke; Huffman, Jarrett K.; Fox, Charles H., Jr.
1986-01-01
The effectiveness of a trailing disk, or trapped vortex concept, in reducing the base drag of a large body of revolution was studied from measurements made both in flight and in a wind tunnel. Pressure data obtained for the flight experiment, and both pressure and force balance data were obtained for the wind tunnel experiment. The flight test also included data obtained from a hemispherical base. The experiment demonstrated the significant base drag reduction capability of the trailing disk to Mach 0.93 and to Reynolds numbers up to 80 times greater than for earlier studies. For the trailing disk data from the flight experiment, the maximum decrease in base drag ranged form 0.08 to 0.07 as Mach number increased from 0.70 to 0.93. Aircraft angles of attack ranged from 3.9 to 6.6 deg for the flight data. For the trailing disk data from the wind tunnel experiment, the maximum decrease in base and total drag ranged from 0.08 to 0.05 for the approximately 0 deg angle of attack data as Mach number increased from 0.30 to 0.82.
Miller, Rolf W.; Argrow, Brian M.; Center, Kenneth B.; Brauckmann, Gregory J.; Rhode, Matthew N.
1998-01-01
The NASA Langley Research Center Unitary Plan Wind Tunnel and the 20-Inch Mach 6 Tunnel were used to test two osculating cones waverider models. The Mach-4 and Mach-6 shapes were generated using the interactive design tool WIPAR. WIPAR performance predictions are compared to the experimental results. Vapor screen results for the Mach-4 model at the on- design Mach number provide visual verification that the shock is attached along the entire leading edge, within the limits of observation. WIPAR predictions of pressure distributions and aerodynamic coefficients show general agreement with the corresponding experimental values.
Lingren, Joe; Vanstone, Leon; Hashemi, Kelley; Gogineni, Sivaram; Donbar, Jeffrey; Akella, Maruthi; Clemens, Noel
2016-11-01
This study develops an analytical model for predicting the leading shock of a shock-train in the constant area isolator section in a Mach 2.2 direct-connect scramjet simulation tunnel. The effective geometry of the isolator is assumed to be a weakly converging duct owing to boundary-layer growth. For some given pressure rise across the isolator, quasi-1D equations relating to isentropic or normal shock flows can be used to predict the normal shock location in the isolator. The surface pressure distribution through the isolator was measured during experiments and both the actual and predicted locations can be calculated. Three methods of finding the shock-train location are examined, one based on the measured pressure rise, one using a non-physics-based control model, and one using the physics-based analytical model. It is shown that the analytical model performs better than the non-physics-based model in all cases. The analytic model is less accurate than the pressure threshold method but requires significantly less information to compute. In contrast to other methods for predicting shock-train location, this method is relatively accurate and requires as little as a single pressure measurement. This makes this method potentially useful for unstart control applications.
Spreading of Exhaust Jet from 16 Inch Ream Jet at Mach Number 2.0 / Fred Wilcox, Donald Pennington
Wilcox, Fred; Pennington, Donald
1952-01-01
An investigation of the jet-spreading characteristics of a 16 inch ram-jet engine was conducted in the 8 by 6 foot supersonic tunnel at a Mach number of 2.0; both a converging nozzle having a contraction ratio of 0.71 and a cylindrical extension to the combustion chamber were used. The jet boundaries determined by means of pitot pressure surveys were compared with boundaries calculated from one-dimensional continuity and momentum relations. For the cylindrical nozzle, the jet reaches its maximum diameter, 4 percent greater than calculated, about 0.6 nozzle-exit diameter downstream of the nozzle exit. The maximum diameter for the converging nozzle was 7 percent greater than calculated from one dimensional relations and occurred from 1 to 1.5 nozzle-exit diameters downstream of the exit. Non dimensional maximum jet diameters agreed closely with results of an investigation by Rousso and Baughman; these data were obtained with low-temperature jets exhausting into a stream at a Mach number of 1.91 from nozzles having exit diameters of 0.75 inch.
Performance characteristics of two multiaxis thrust-vectoring nozzles at Mach numbers up to 1.28
Wing, David J.; Capone, Francis J.
1993-01-01
The thrust-vectoring axisymmetric (VA) nozzle and a spherical convergent flap (SCF) thrust-vectoring nozzle were tested along with a baseline nonvectoring axisymmetric (NVA) nozzle in the Langley 16-Foot Transonic Tunnel at Mach numbers from 0 to 1.28 and nozzle pressure ratios from 1 to 8. Test parameters included geometric yaw vector angle and unvectored divergent flap length. No pitch vectoring was studied. Nozzle drag, thrust minus drag, yaw thrust vector angle, discharge coefficient, and static thrust performance were measured and analyzed, as well as external static pressure distributions. The NVA nozzle and the VA nozzle displayed higher static thrust performance than the SCF nozzle throughout the nozzle pressure ratio (NPR) range tested. The NVA nozzle had higher overall thrust minus drag than the other nozzles throughout the NPR and Mach number ranges tested. The SCF nozzle had the lowest jet-on nozzle drag of the three nozzles throughout the test conditions. The SCF nozzle provided yaw thrust angles that were equal to the geometric angle and constant with NPR. The VA nozzle achieved yaw thrust vector angles that were significantly higher than the geometric angle but not constant with NPR. Nozzle drag generally increased with increases in thrust vectoring for all the nozzles tested.
Syvertson, Clarence A; Gloria, Hermilo R; Sarabia, Michael F
1958-01-01
A study is made of aerodynamic performance and static stability and control at hypersonic speeds. In a first part of the study, the effect of interference lift is investigated by tests of asymmetric models having conical fuselages and arrow plan-form wings. The fuselage of the asymmetric model is located entirely beneath the wing and has a semicircular cross section. The fuselage of the symmetric model was centrally located and has a circular cross section. Results are obtained for Mach numbers from 3 to 12 in part by application of the hypersonic similarity rule. These results show a maximum effect of interference on lift-drag ratio occurring at Mach number of 5, the Mach number at which the asymmetric model was designed to exploit favorable lift interference. At this Mach number, the asymmetric model is indicated to have a lift-drag ratio 11 percent higher than the symmetric model and 15 percent higher than the asymmetric model when inverted. These differences decrease to a few percent at a Mach number of 12. In the course of this part of the study, the accuracy to the hypersonic similarity rule applied to wing-body combinations is demonstrated with experimental results. These results indicate that the rule may prove useful for determining the aerodynamic characteristics of slender configurations at Mach numbers higher than those for which test equipment is really available. In a second part of the study, the aerodynamic performance and static stability and control characteristics of a hypersonic glider are investigated in somewhat greater detail. Results for Mach numbers from 3 to 18 for performance and 0.6 to 12 for stability and control are obtained by standard text techniques, by application of the hypersonic stability rule, and/or by use of helium as a test medium. Lift-drag ratios of about 5 for Mach numbers up to 18 are shown to be obtainable. The glider studied is shown to have acceptable longitudinal and directional stability characteristics through the
A Study of the Complex Flow Features Behind a Diffracted Shock Wave on a Convex Curved Wall
adam muritala; skews beric; craig law
2015-01-01
The complex flow features behind a diffracted shock wave on a convex curved wall is investigated using large scale experimentation complemented by numerical computation. The study aimed at explaining the global flow behavior within the perturbed region behind the diffracted shock wave. Experiments were conducted in a purpose built shock tube that is capable of generating a range of incident shock Mach numbers Mn ≤ 1.6. Analysis of higher Mach number shocks on different wall geometries were ca...
A Reynolds Number Study of Wing Leading-Edge Effects on a Supersonic Transport Model at Mach 0.3
Williams, M. Susan; Owens, Lewis R., Jr.; Chu, Julio
1999-01-01
A representative supersonic transport design was tested in the National Transonic Facility (NTF) in its original configuration with small-radius leading-edge flaps and also with modified large-radius inboard leading-edge flaps. Aerodynamic data were obtained over a range of Reynolds numbers at a Mach number of 0.3 and angles of attack up to 16 deg. Increasing the radius of the inboard leading-edge flap delayed nose-up pitching moment to a higher lift coefficient. Deflecting the large-radius leading-edge flap produced an overall decrease in lift coefficient and delayed nose-up pitching moment to even higher angles of attack as compared with the undeflected large- radius leading-edge flap. At angles of attack corresponding to the maximum untrimmed lift-to-drag ratio, lift and drag coefficients decreased while lift-to-drag ratio increased with increasing Reynolds number. At an angle of attack of 13.5 deg., the pitching-moment coefficient was nearly constant with increasing Reynolds number for both the small-radius leading-edge flap and the deflected large-radius leading-edge flap. However, the pitching moment coefficient increased with increasing Reynolds number for the undeflected large-radius leading-edge flap above a chord Reynolds number of about 35 x 10 (exp 6).
Directory of Open Access Journals (Sweden)
Krishna Pandey
2016-01-01
Full Text Available A numerical analysis of the inlet-combustor interaction and flow structure through a scramjet engine at a flight Mach number M = 6 with parallel injection (Strut with circular inlet is presented in the present research article. Three different angles of attack (α=-4°, α=0°, α=4° have been studied for parallel injection. The scramjet configuration used here is a modified version of DLR scramjet model. Fuel is injected at supersonic speed (M=2 through a parallel strut injector. For parallel injection, the shape of the strut is chosen in a way to produce strong stream wise vorticity and thus to enhance the hydrogen/air mixing inside the combustor. These numerical simulations are aimed to study the flow structure, supersonic mixing, and combustion phenomena for the three different types of geometries along with circular shaped strut configuration.
Wolf, Stephen W. D.; Laub, James A.; King, Lyndell S.; Reda, Daniel C.
1992-01-01
A unique, low-disturbance supersonic wind tunnel is being developed at NASA-Ames to support supersonic laminar flow control research at cruise Mach numbers of the High Speed Civil Transport (HSCT). The distinctive design features of this new quiet tunnel are a low-disturbance settling chamber, laminar boundary layers along the nozzle/test section walls, and steady supersonic diffuser flow. This paper discusses these important aspects of our quiet tunnel design and the studies necessary to support this design. Experimental results from an 1/8th-scale pilot supersonic wind tunnel are presented and discussed in association with theoretical predictions. Natural laminar flow on the test section walls is demonstrated and both settling chamber and supersonic diffuser performance is examined. The full-scale wind tunnel should be commissioned by the end of 1993.
Schneider, T.; Botta, N.; Geratz, K. J.; Klein, R.
1999-11-01
When attempting to compute unsteady, variable density flows at very small or zero Mach number using a standard finite volume compressible flow solver one faces at least the following difficulties: (i) Spatial pressure variations vanish as the Mach number M→0, but they do affect the velocity field at leading order; (ii) the resulting spatial homogeneity of the leading order pressure implies an elliptic divergence constraint for the energy flux; (iii) violations of this constraint crucially affect the transport of mass, preventing a code to properly advect even a constant density distribution. We overcome these difficulties through a new algorithm for constructing numerical fluxes in the context of multi-dimensional finite volume methods in conservation form. The construction of numerical fluxes involves: (1) An explicit upwind step yielding predictions for the nonlinear convective flux components. (2) A first correction step that introduces pressure gradients which guarantee compliance of the convective fluxes with a divergence constraint. This step requires the solution of a first Poisson-type equation. (3) A second projection step which provides the yet unknown (non-convective) pressure contribution to the total flux of momentum. This second projection requires the solution of another Poisson-type equation and yields the cell centered velocity field at the new time. This velocity field exactly satisfies a divergence constraint consistent with the asymptotic limit. Step (1) can be done by any standard finite volume compressible flow solver. The input to steps (2) and (3) involves solely the fluxes from step (1) and is independent of how these were obtained. Thus, our approach allows any such solver to be extended to compute variable density incompressible flows.
Marchionna, N. R.; Diehl, L. A.; Trout, A. M.
1973-01-01
Tests were conducted to determine the effect of inlet air humidity on the formation of oxides of nitrogen (NOx) from a gas turbine combustor. Combustor inlet air temperature ranged from 506 K (450 F) to 838 K (1050 F). The tests were primarily run at a constant pressure of 6 atmospheres and reference Mach number of 0.065. The NOx emission index was found to decrease with increasing inlet air humidity at a constant exponential rate: NOx = NOx0e-19H (where H is the humidity and the subscript 0 denotes the value at zero humidity). the emission index increased exponentially with increasing normalized inlet air temperature to the 1.14 power. Additional tests made to determine the effect of pressure and reference Mach number on NOx showed that the NOx emission index varies directly with pressure to the 0.5 power and inversely with reference Mach number.
Pendergraft, Odis C., Jr.; Burley, James R., II; Bare, E. Ann
1986-01-01
An investigation has been conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of upper and lower external nozzle flap geometry on the external afterbody/nozzle drag of nonaxisymmetric two-dimensional convergent-divergent exhaust nozzles having parallel external sidewalls installed on a generic twin-engine, fighter-aircraft model. Tests were conducted over a Mach number range from 0.60 to 1.20 and over an angle-of-attack range from -5 to 9 deg. Nozzle pressure ratio was varied from jet off (1.0) to approximately 10.0, depending on Mach number.
Shock wave of vapor-liquid two-phase flow
Institute of Scientific and Technical Information of China (English)
Liangju ZHAO; Fei WANG; Hong GAO; Jingwen TANG; Yuexiang YUAN
2008-01-01
The shock wave of vapor-liquid two-phase flow in a pressure-gain steam injector is studied by build-ing a mathematic model and making calculations. The results show that after the shock, the vapor is nearly com-pletely condensed. The upstream Mach number and the volume ratio of vapor have a great effect on the shock. The pressure and Mach number of two-phase shock con-form to the shock of ideal gas. The analysis of available energy shows that the shock is an irreversible process with entropy increase.
Practical computational aeroacoustics for compact surfaces in low mach number flows
DEFF Research Database (Denmark)
Pradera-Mallabiabarrena, Ainara; Keith, Graeme; Jacobsen, Finn
2011-01-01
compared to the wavelength of interest. This makes it possible to focus on the surface source term of the Ffowcs Williams-Hawkings equation. In this paper, in order to illustrate the basic method for storing and utilizing data from the CFD analysis, the flow past a circular cylinder at a Reynolds number...
The Shock and Vibration Digest. Volume 15, Number 5
1983-05-01
propagation theory it is shown that the M.A. Serna, R. Aviles, and J.G. de Jalon source term may produce attenuation effects against the Catedra de Mecanica ...Escuela Superior de Ingenieros typical nonlinear steepening of the waves. Industriales di Bilbao, Spain, Mech. Mach. Theory, 17_ (6), pp 397-403 (1982
Mack, R. J.
1974-01-01
Wing models were tested in the high-speed section of the Langley Unitary Plan wind tunnel to study the effects of the leading-edge sweep angle and the design lift coefficient on aerodynamic performance and efficiency. The models had leading-edge sweep angles of 69.44 deg, 72.65 deg, and 75.96 deg which correspond to values of the design Mach-number-sweep-angle parameter (beta cotangent A) sub DES of 0.6, 0.75, and 0.9, respectively. For each sweep angle, camber surfaces having design lift coefficients of 0,0.08, and 0.12 at a design Mach number of 2.6 were generated. The wind-tunnel tests were conducted at Mach numbers of 2.3, 2.6, and 2.96 with a stagnation temperature of 338.7 K (150 F) and a Reynolds number per meter of 9.843 times 10 to the 6th power. The results of the tests showed that only a moderate sweeping of the wing leading edge aft of the Mach line along with a small-to-moderate amount of camber and twist was needed to significantly improve the zero-lift (flat camber surface) wing performance and efficiency.
MacArt, Jonathan F.; Mueller, Michael E.
2016-12-01
Two formally second-order accurate, semi-implicit, iterative methods for the solution of scalar transport-reaction equations are developed for Direct Numerical Simulation (DNS) of low Mach number turbulent reacting flows. The first is a monolithic scheme based on a linearly implicit midpoint method utilizing an approximately factorized exact Jacobian of the transport and reaction operators. The second is an operator splitting scheme based on the Strang splitting approach. The accuracy properties of these schemes, as well as their stability, cost, and the effect of chemical mechanism size on relative performance, are assessed in two one-dimensional test configurations comprising an unsteady premixed flame and an unsteady nonpremixed ignition, which have substantially different Damköhler numbers and relative stiffness of transport to chemistry. All schemes demonstrate their formal order of accuracy in the fully-coupled convergence tests. Compared to a (non-)factorized scheme with a diagonal approximation to the chemical Jacobian, the monolithic, factorized scheme using the exact chemical Jacobian is shown to be both more stable and more economical. This is due to an improved convergence rate of the iterative procedure, and the difference between the two schemes in convergence rate grows as the time step increases. The stability properties of the Strang splitting scheme are demonstrated to outpace those of Lie splitting and monolithic schemes in simulations at high Damköhler number; however, in this regime, the monolithic scheme using the approximately factorized exact Jacobian is found to be the most economical at practical CFL numbers. The performance of the schemes is further evaluated in a simulation of a three-dimensional, spatially evolving, turbulent nonpremixed planar jet flame.
Plasma ion stratification by weak planar shocks
Simakov, Andrei N.; Keenan, Brett D.; Taitano, William T.; Chacón, Luis
2017-09-01
We derive fluid equations for describing steady-state planar shocks of a moderate strength ( 0 shock Mach number) propagating through an unmagnetized quasineutral collisional plasma comprising two separate ion species. In addition to the standard fluid shock quantities, such as the total mass density, mass-flow velocity, and electron and average ion temperatures, the equations describe shock stratification in terms of variations in the relative concentrations and temperatures of the two ion species along the shock propagation direction. We have solved these equations analytically for weak shocks ( 0 shocks, and they have been used to verify kinetic simulations of shocks in multi-ion plasmas.
Kubiak, M A; Bzowski, M; Sokol, J M; Fuselier, S A; Galli, A; Heirtzler, D; Kucharek, H; Leonard, T W; Moebius, D J McComas E; Park, J; Schwadron, N A; Wurz, P
2016-01-01
With the velocity vector and temperature of the pristine interstellar neutral (ISN) He recently obtained with high precision from a coordinated analysis summarized by McComas et al.2015b, we analyzed the IBEX observations of neutral He left out from this analysis. These observations were collected during the ISN observation seasons 2010---2014 and cover the region in the Earth's orbit where the Warm Breeze persists. We used the same simulation model and a very similar parameter fitting method to that used for the analysis of ISN He. We approximated the parent population of the Warm Breeze in front of the heliosphere with a homogeneous Maxwell-Boltzmann distribution function and found a temperature of $\\sim 9\\,500$ K, an inflow speed of 11.3 km s$^{-1}$, and an inflow longitude and latitude in the J2000 ecliptic coordinates $251.6^\\circ$, $12.0^\\circ$. The abundance of the Warm Breeze relative to the interstellar neutral He is 5.7\\% and the Mach number is 1.97. The newly found inflow direction of the Warm Bree...
Myllys, M. E.; Kilpua, E.; Lavraud, B.
2015-12-01
We have investigated the effect of key solar wind driving parameters on the solar wind-magnetosphere coupling efficiency and saturation of the cross polar cap potential (CPCP) during sheath and magnetic cloud driven storms. The particular focus of the study was on the coupling efficiency dependence with Alfven Mach number (MA).Since we are studying the instantaneous coupling efficiency instead of the average efficiency over the whole solar wind structure, we needed to take into account the communication time between the solar wind and the magnetosphere. We present the results of the time delay analysis between geomagnetic indices (PCN, AE and SYM-H) and the interplanetary electric field y-component (EY, GSM coordinate system) and Newell and Borovsky functions. The study shows that the MA has a clear effect to the saturation of the PCN index, which can be used as a proxy of the polar cap potential. The higher the MA the higher the limit EY value after which the saturation starts to occur. Thus, the coupling efficiency increases as a function of MA. Also, the AE index saturates during high solar wind driving but the saturation is not MA depended. However, the results also suggest that the MA it is not the primary cause for the PCN saturation.
Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang
2016-09-01
A numerical method to concurrently characterize both aeroacoustic scattering and noise sources at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband acoustic excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both acoustic propagation and noise generation. The present work studies the aero-acoustic characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for acoustic scattering matrices and power spectral densities of broad-band noise are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.
The Shock and Vibration Digest. Volume 13. Number 7
1981-07-01
predicted from first principles [70]. Grabec and Leskovar [71] showed that it is not practically feasible to use acoustic emission analysis to evaluate...145-150 (1976). 14. Peters , J. and Mergeay, M., "Dynamic Analysis of Machine Tool Using Complex Modal Method," Ann. CIRP, 25(1), pp 257-261 (1976...namics and Process Parameters," Intl. J. Mach. Tool. Des. Res., 16 (4), pp 301-318 (1976). 71. Grabec, I. and Leskovar ." Acoustic Emission of a
Eaves, R. H.; Buchanan, T. D.; Warmbrod, J. D.; Johnson, C. B.
1972-01-01
Heat transfer tests for two delta wing configurations were conducted in the hypervelocity wind tunnel. The 24-inch long models were tested at a Mach number of approximately 10.5 and at angles of attack of 20, 40, and 60 degrees over a length Reynolds number range from 5 million to 23 million on 4 May to 4 June 1971. Heat transfer results were obtained from model surface heat gage measurements and thermographic phosphor paint.
Neiner, G. H.; Cole, G. L.; Arpasi, D. J.
1972-01-01
Digital computer control of a mixed-compression inlet is discussed. The inlet was terminated with a choked orifice at the compressor face station to dynamically simulate a turbojet engine. Inlet diffuser exit airflow disturbances were used. A digital version of a previously tested analog control system was used for both normal shock and restart control. Digital computer algorithms were derived using z-transform and finite difference methods. Using a sample rate of 1000 samples per second, the digital normal shock and restart controls essentially duplicated the inlet analog computer control results. At a sample rate of 100 samples per second, the control system performed adequately but was less stable.
Geometrical shock dynamics for magnetohydrodynamic fast shocks
Mostert, W.
2016-12-12
We describe a formulation of two-dimensional geometrical shock dynamics (GSD) suitable for ideal magnetohydrodynamic (MHD) fast shocks under magnetic fields of general strength and orientation. The resulting area–Mach-number–shock-angle relation is then incorporated into a numerical method using pseudospectral differentiation. The MHD-GSD model is verified by comparison with results from nonlinear finite-volume solution of the complete ideal MHD equations applied to a shock implosion flow in the presence of an oblique and spatially varying magnetic field ahead of the shock. Results from application of the MHD-GSD equations to the stability of fast MHD shocks in two dimensions are presented. It is shown that the time to formation of triple points for both perturbed MHD and gas-dynamic shocks increases as (Formula presented.), where (Formula presented.) is a measure of the initial Mach-number perturbation. Symmetry breaking in the MHD case is demonstrated. In cylindrical converging geometry, in the presence of an azimuthal field produced by a line current, the MHD shock behaves in the mean as in Pullin et al. (Phys. Fluids, vol. 26, 2014, 097103), but suffers a greater relative pressure fluctuation along the shock than the gas-dynamic shock. © 2016 Cambridge University Press
Yu, Rixin; Yu, Jiangfei; Bai, Xue-Song
2012-06-01
We present an improved numerical scheme for numerical simulations of low Mach number turbulent reacting flows with detailed chemistry and transport. The method is based on a semi-implicit operator-splitting scheme with a stiff solver for integration of the chemical kinetic rates, developed by Knio et al. [O.M. Knio, H.N. Najm, P.S. Wyckoff, A semi-implicit numerical scheme for reacting flow II. Stiff, operator-split formulation, Journal of Computational Physics 154 (2) (1999) 428-467]. Using the material derivative form of continuity equation, we enhance the scheme to allow for large density ratio in the flow field. The scheme is developed for direct numerical simulation of turbulent reacting flow by employing high-order discretization for the spatial terms. The accuracy of the scheme in space and time is verified by examining the grid/time-step dependency on one-dimensional benchmark cases: a freely propagating premixed flame in an open environment and in an enclosure related to spark-ignition engines. The scheme is then examined in simulations of a two-dimensional laminar flame/vortex-pair interaction. Furthermore, we apply the scheme to direct numerical simulation of a homogeneous charge compression ignition (HCCI) process in an enclosure studied previously in the literature. Satisfactory agreement is found in terms of the overall ignition behavior, local reaction zone structures and statistical quantities. Finally, the scheme is used to study the development of intrinsic flame instabilities in a lean H2/air premixed flame, where it is shown that the spatial and temporary accuracies of numerical schemes can have great impact on the prediction of the sensitive nonlinear evolution process of flame instability.
Geometrical on-the-fly shock detection in smoothed particle hydrodynamics
Beck, A. M.; Dolag, K.; Donnert, J. M. F.
2016-05-01
We present an on-the-fly geometrical approach for shock detection and Mach number calculation in simulations employing smoothed particle hydrodynamics (SPH). We utilize pressure gradients to select shock candidates and define up- and downstream positions. We obtain hydrodynamical states in the up- and downstream regimes with a series of normal and inverted kernel weightings parallel and perpendicular to the shock normals. Our on-the-fly geometrical Mach detector incorporates well within the SPH formalism and has low computational cost. We implement our Mach detector into the simulation code GADGET and alongside many SPH improvements. We test our shock finder in a sequence of shock tube tests with successively increasing Mach numbers exceeding by far the typical values inside galaxy clusters. For all shocks, we resolve the shocks well and the correct Mach numbers are assigned. An application to a strong magnetized shock tube gives stable results in full magnetohydrodynamic setups. We simulate a merger of two idealized galaxy clusters and study the shock front. Shock structures within the merging clusters as well as the cluster shock are well captured by our algorithm and assigned correct Mach numbers.
The Shock and Vibration Digest. Volume 18, Number 11
1986-11-01
CA, Feb 3-6, 1986, Vol. 1, pp 736-742, 4 figs, 1 table, 4 tefs KEY WORDS: Modal analysis. Spectrum analysis, Duffing oscillators The second...suggested (but not confirmed) that there might be a greater ten- dency for the system to vibrate in the subcon- ductor oscillation range of...Cascades, Shock exc tation structure. At low reduced frequencies, the shock-induced loads can destabilize bending oscillations sufficiently to
The Shock and Vibration Digest. Volume 17, Number 2
1985-02-01
Seismicity, Groundwater rium Emanations from Rock Specimens Chemistry , and Groundwater Radon in under Pressure," Acta Seismol. Sin., 2, (2), Southern...The keynote address was given by Colonel The 55th Shock and Vibration Symposium, Craig 0. Schaum , Deputy for Engineering sponsored by the Shock and...It was hosted by the Aeronau- cussed developments at ASD. Colonel tical Systems Division of Wright-Patterson Schaum traced the early developments in
The Shock and Vibration Digest. Volume 13, Number 5
1981-05-01
Gierice E.E.Ungar The Shock and Vibration Digett I* a monthly publication of the Shock and Vibratlo,, Information Center. The goal of the Digett ...of Multi- 99. Spanos, P-T.D., "Numerical Simulations of a Story Buildings Subjected to Ground Motion," Van der Pol Oscillator," Computing Math. Bull...analysis. The (called the 0-Modl) for displacement-time analysis of technique is illustrated by its application to a small hori- multi- story reinforced
Allan Brian G.; Owens, Lewis, R.
2006-01-01
This paper will investigate the validation of a NASA developed, Reynolds-averaged Navier-Stokes (RANS) flow solver, OVERFLOW, for a boundary-layer-ingesting (BLI) offset (S-shaped) inlet in transonic flow with passive and active flow control devices as well as the baseline case. Numerical simulations are compared to wind tunnel results of a BLI inlet conducted at the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. Comparisons of inlet flow distortion, pressure recovery, and inlet wall pressures are performed. The numerical simulations are compared to the BLI inlet data at a freestream Mach number of 0.85 and a Reynolds number of approximately 2 million based on the length of the fan-face diameter. The numerical simulations with and without wind tunnel walls are performed, quantifying effects of the tunnel walls on the BLI inlet flow measurements. The wind tunnel test evaluated several different combinations of jet locations and mass flow rates as well as a vortex generator (VG) vane case. The numerical simulations will be performed on a single jet configuration for varying actuator mass flow rates at a fix inlet mass flow condition. Validation of the numerical simulations for the VG vane case will also be performed for varying inlet mass flow rates. Overall, the numerical simulations were able to predict the baseline circumferential flow distortion, DPCPavg, very well for comparisons made within the designed operating range of the BLI inlet. However the CFD simulations did predict a total pressure recovery that was 0.01 lower than the experiment. Numerical simulations of the baseline inlet flow also showed good agreement with the experimental inlet centerline surface pressures. The vane case showed that the CFD predicted the correct trends in the circumferential distortion for varying inlet mass flow but had a distortion level that was nearly twice as large as the experiment. Comparison to circumferential distortion measurements for a 15 deg clocked 40 probe
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
On super-sonic or trans-sonic planar cascade wind tunnel of free jet intermittent type, wind blowing experiments were performed on the typical sections of stator and rotor blades in the last stage of ultra-ultra-critical steam turbine with extra-long blade of 1200mm. The influences of attack angle and Mach number on the aerodynamic performances of these sections of the blade profiles were verified, and their operating ranges were also specified.
Keenan, James A.; Kuhlman, John M.
1991-01-01
A computational study was conducted on two wings, of aspect ratios 1.244 and 1.865, each having 65 degree leading edge sweep angles, to determine the effects of nonplanar winglets at supersonic Mach numbers. A Mach number of 1.62 was selected as the design value. The winglets studied were parametrically varied in alignment, length, sweep, camber, thickness, and dihedral angle to determine which geometry had the best predicted performance. For the computational analysis, an available Euler marching technique was used. The results indicated that the possibility existed for wing-winglet geometries to equal the performance of wing-alone bodies in supersonic flows with both bodies having the same semispan. The first wing with winglet used NACA 1402 airfoils for the base wing and was shown to have lift-to-pressure drag ratios within 0.136 percent to 0.360 percent of the NACA 1402 wing-alone. The other base wing was a natural flow wing which was previously designed specifically for a Mach number of 1.62. The results obtained showed that the natural wing-alone had a slightly higher lift-to-pressure drag than the natural wing with winglets.
Energy Technology Data Exchange (ETDEWEB)
Li, Pak Shing; Klein, Richard I. [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Martin, Daniel F. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); McKee, Christopher F., E-mail: psli@astron.berkeley.edu, E-mail: klein@astron.berkeley.edu, E-mail: DFMartin@lbl.gov, E-mail: cmckee@astro.berkeley.edu [Physics Department and Astronomy Department, University of California, Berkeley, CA 94720 (United States)
2012-02-01
Performing a stable, long-duration simulation of driven MHD turbulence with a high thermal Mach number and a strong initial magnetic field is a challenge to high-order Godunov ideal MHD schemes because of the difficulty in guaranteeing positivity of the density and pressure. We have implemented a robust combination of reconstruction schemes, Riemann solvers, limiters, and constrained transport electromotive force averaging schemes that can meet this challenge, and using this strategy, we have developed a new adaptive mesh refinement (AMR) MHD module of the ORION2 code. We investigate the effects of AMR on several statistical properties of a turbulent ideal MHD system with a thermal Mach number of 10 and a plasma {beta}{sub 0} of 0.1 as initial conditions; our code is shown to be stable for simulations with higher Mach numbers (M{sub rms}= 17.3) and smaller plasma beta ({beta}{sub 0} = 0.0067) as well. Our results show that the quality of the turbulence simulation is generally related to the volume-averaged refinement. Our AMR simulations show that the turbulent dissipation coefficient for supersonic MHD turbulence is about 0.5, in agreement with unigrid simulations.
Li, Pak Shing; Klein, Richard I; McKee, Christopher F
2011-01-01
Performing a stable, long duration simulation of driven MHD turbulence with a high thermal Mach number and a strong initial magnetic field is a challenge to high-order Godunov ideal MHD schemes because of the difficulty in guaranteeing positivity of the density and pressure. We have implemented a robust combination of reconstruction schemes, Riemann solvers, limiters, and Constrained Transport EMF averaging schemes that can meet this challenge, and using this strategy, we have developed a new Adaptive Mesh Refinement (AMR) MHD module of the ORION2 code. We investigate the effects of AMR on several statistical properties of a turbulent ideal MHD system with a thermal Mach number of 10 and a plasma $\\beta_0$ of 0.1 as initial conditions; our code is shown to be stable for simulations with higher Mach numbers ($M_rms = 17.3$) and smaller plasma beta ($\\beta_0 = 0.0067$) as well. Our results show that the quality of the turbulence simulation is generally related to the volume-averaged refinement. Our AMR simulati...
Molecular dynamics simulations of microscopic structure of ultra strong shock waves in dense helium
Liu, Hao; Kang, Wei; Zhang, Qi; Zhang, Yin; Duan, Huilin; He, X. T.
2016-12-01
Hydrodynamic properties and structure of strong shock waves in classical dense helium are simulated using non-equilibrium molecular dynamics methods. The shock speed in the simulation reaches 100 km/s and the Mach number is over 250, which are close to the parameters of shock waves in the implosion process of inertial confinement fusion. The simulations show that the high-Mach-number shock waves in dense media have notable differences from weak shock waves or those in dilute gases. These results will provide useful information on the implosion process, especially the structure of strong shock wave front, which remains an open question in hydrodynamic simulations.
Energy Technology Data Exchange (ETDEWEB)
Kubiak, Marzena A.; Swaczyna, P.; Bzowski, M.; Sokół, J. M. [Space Research Centre of the Polish Academy of Sciences (CBK PAN), 00-716 Warsaw (Poland); Fuselier, S. A.; McComas, D. J. [Southwest Research Institute, San Antonio, TX (United States); Galli, A.; Wurz, P. [Physikalisches Institut, Universität Bern, Bern (Switzerland); Heirtzler, D.; Kucharek, H.; Leonard, T. W.; Möbius, E.; Park, J.; Schwadron, N. A., E-mail: mkubiak@cbk.waw.pl [Space Science Center and Department of Physics, University of New Hampshire, Durham, NH (United States)
2016-04-15
Following the high-precision determination of the velocity vector and temperature of the pristine interstellar neutral (ISN) He via a coordinated analysis summarized by McComas et al., we analyzed the Interstellar Boundary Explorer (IBEX) observations of neutral He left out from this analysis. These observations were collected during the ISN observation seasons 2010–2014 and cover the region in the Earth's orbit where the Warm Breeze (WB) persists. We used the same simulation model and a parameter fitting method very similar to that used for the analysis of ISN He. We approximated the parent population of the WB in front of the heliosphere with a homogeneous Maxwell–Boltzmann distribution function and found a temperature of ∼9500 K, an inflow speed of 11.3 km s{sup −1}, and an inflow longitude and latitude in the J2000 ecliptic coordinates 251.°6, 12.°0. The abundance of the WB relative to ISN He is 5.7% and the Mach number is 1.97. The newly determined inflow direction of the WB, the inflow directions of ISN H and ISN He, and the direction to the center of the IBEX Ribbon are almost perfectly co-planar, and this plane coincides within relatively narrow statistical uncertainties with the plane fitted only to the inflow directions of ISN He, ISN H, and the WB. This co-planarity lends support to the hypothesis that the WB is the secondary population of ISN He and that the center of the Ribbon coincides with the direction of the local interstellar magnetic field (ISMF). The common plane for the direction of the inflow of ISN gas, ISN H, the WB, and the local ISMF is given by the normal direction: ecliptic longitude 349.°7 ± 0.°6 and latitude 35.°7 ± 0.6 in the J2000 coordinates, with a correlation coefficient of 0.85.
Diffusive Shock Acceleration at Cosmological Shock Waves
Kang, Hyesung
2012-01-01
We reexamine nonlinear diffusive shock acceleration (DSA) at cosmological shocks in the large scale structure of the Universe, incorporating wave-particle interactions that are expected to operate in collisionless shocks. Adopting simple phenomenological models for magnetic field amplification (MFA) by cosmic-ray (CR) streaming instabilities and Alfv'enic drift, we perform kinetic DSA simulations for a wide range of sonic and Alfv'enic Mach numbers and evaluate the CR injection fraction and acceleration efficiency. In our DSA model the CR acceleration efficiency is determined mainly by the sonic Mach number Ms, while the MFA factor depends on the Alfv'enic Mach number and the degree of shock modification by CRs. We show that at strong CR modified shocks, if scattering centers drift with an effective Alfv'en speed in the amplified magnetic field, the CR energy spectrum is steepened and the acceleration efficiency is reduced significantly, compared to the cases without such effects. As a result, the postshock C...
The Shock and Vibration Digest. Volume 13. Number 8
1981-08-01
Failure of a Ball Bearing Steel and Its Relation to the Inclina- tion of the Principal Residual Stress K. Maeda, N. Tsushima, and H. Muro NTN...impulsiv« sounds are discussed. 81-1733 Shock Test Pulse Display and Analyas G.R. Henderson GHI Systems, Inc., Ranchos Palos Verdes , CA, Test, 43
The Shock and Vibration Digest. Volume 16, Number 11
1984-11-01
in smooth end Structures Volume 1. Speid Topics in Eartquake .. turbulent single-vibration testing of reactor components Ground Motioe including... Mexico , Albuquerque, NM 87131, seatingoperationsduringInstallation. Shock Vib. Bull., No. 54, Pt. 2, pp 143-153 (June 1984) 4 figs, 11 refs (Proc
50 kHz PIV of a Swept-Ramp Shock-Wave Boundary-Layer Interaction at Mach 2
Vanstone, Leon; Musta, Mustafa Nail; Seckin, Serdar; Saleem, Mohammad; Clemens, Noel
2016-11-01
The interaction from a 30° sweep, 22.5° compression ramp in a Mach 2 flow is examined using wide-field 5Hz and 50 kHz PIV. The high-speed PIV is fast enough to resolve the large-scale unsteady motions of the SWBLI and can be band-pass filtered to investigate the driving mechanisms of unsteadiness and the widefield PIV allows comparisons with mean flow-fields. Preliminary investigation looked at three distinct frequency bands: 10-50 kHz (0.025-0.25 U∞ /δ99), 1-10 kHz (0.025-0.25 U∞ /δ99), and 0-1 kHz (0-0.025 U∞ /δ99). The unsteadiness associated with 10-50 kHz shows no correlation with the upstream boundary layer and accounts for 40% of the amplitude. The unsteadiness associated with 1-10 kHz is correlated with the upstream boundary-layer and also accounts for 40% of unsteadiness. This frequency is similar to those of boundary-layer superstructures. The unsteadiness associated with 0-1 kHz shows the strongest correlation with the upstream boundary-layer but accounts for only 20% of the amplitude. Clearly a range of unsteadiness mechanisms are present, with significant amplitude associated with higher frequencies. Future work will focus on expanding these findings with surface pressure and additional PIV. This work is sponsored by the AFOSR under Grant FA9550-14-1-0167 with Ivett Leyva as the program manager. This source of support is gratefully acknowledged. Further, Mustafa Musta thanks the Scientific and Technological research Council of Turkey.
Shock detachment from curved wedges
Mölder, S.
2017-03-01
Curved shock theory is used to show that the flow behind attached shocks on doubly curved wedges can have either positive or negative post-shock pressure gradients depending on the freestream Mach number, the wedge angle and the two wedge curvatures. Given enough wedge length, the flow near the leading edge can choke to force the shock to detach from the wedge. This local choking can preempt both the maximum deflection and the sonic criteria for shock detachment. Analytical predictions for detachment by local choking are supported by CFD results.
Shock detachment from curved wedges
Mölder, S.
2017-09-01
Curved shock theory is used to show that the flow behind attached shocks on doubly curved wedges can have either positive or negative post-shock pressure gradients depending on the freestream Mach number, the wedge angle and the two wedge curvatures. Given enough wedge length, the flow near the leading edge can choke to force the shock to detach from the wedge. This local choking can preempt both the maximum deflection and the sonic criteria for shock detachment. Analytical predictions for detachment by local choking are supported by CFD results.
Institute of Scientific and Technical Information of China (English)
翟永玺; 张堃元; 王磊; 李永洲; 张林
2014-01-01
A parametric research on the curved compression surface with controllable Mach number distri-bution was commenced to find the effect regularity of design parameters on the performance parameters of curved compression surface. On this basis,a polynomial response surface proxy model was built to make a multi-objec-tive optimization,and a hypersonic curved shock two-dimensional inlet was designed based on the optimization result, the performance was compared with the three-ramp compression inlet which was designed under the same constraints. Results indicate among the design parameters, the initial compress angle θ and the factor C and factor md1 affect most. The flow coefficient of the innovative inlet is up to 0.769 at Mach 4,when Mach num-ber ranges from 4 to 7,the two inlets have equally the same mass capture ratio,while the innovative inlet has high total pressure recovery of throat and outlet section. Compared with the relative three-ramp inlet , the total pressure recovery of throat section of the innovative inlet increased by 6.5%at Mach 4, 8.4%at Mach 6, and 10.7%at Mach 7.%针对一种马赫数分布可控的二元高超弯曲压缩面进行参数化研究，获得其设计参数对压缩面性能的影响规律，在此基础上建立多项式响应面代理模型并进行多目标优化，基于优化结果设计了二元弯曲激波进气道，并与同等约束条件下的三楔进气道进行比较。结果表明：压缩面初始压缩角θ与马赫数梯度函数中的设计参数md1，C对压缩面性能影响最为显著；Ma∞=4.0时弯曲激波进气道流量系数达0.769，与三楔进气道相比，在Ma∞=4～7工作范围内的流量捕获能力相当，但其喉道、出口截面的总压恢复系数均高于三楔进气道，在Ma∞=4，6，7工况下，喉道截面总压恢复分别有6.5%，8.4%和10.7%的提高。
Existence Regions of Shock Wave Triple Configurations
Bulat, Pavel V.; Chernyshev, Mikhail V.
2016-01-01
The aim of the research is to create the classification for shock wave triple configurations and their existence regions of various types: type 1, type 2, type 3. Analytical solutions for limit Mach numbers and passing shock intensity that define existence region of every type of triple configuration have been acquired. The ratios that conjugate…
The Shock and Vibration Digest. Volume 15, Number 11
1983-11-01
Korn, and M.P. Rossow many crashworthy features, including a high energy landing gear, crushable fuselage structure, stroking crew seats, high Dept...characteristics in a front fork and a rear shock absorber was independently developed for both com- pression and extension strokes . The model includes...8217 • u I4- technique of ferromagnetic resonance ( FMR ). The method 83-2325 developed must be suited to inspect test objects where Balancing of Linkages
The Shock and Vibration Digest. Volume 14, Number 9
1982-09-01
Division of General Dynamics, San Diego, CA 3. Pershing li Pyrotechnic Shock Test and Test Simulation - M.E, HUGHES, Martin Marietta Corporation, Or...Degree of Freedom Systems - D.I.G. JONES, Air Force Wright Aeronauti- cal Laboratories, Wright Patterson AFB, OH and A. MUSZYNSKA, Bentiy Nevada ...Response of the Imperial County Services Building during the 1979 Imperial Valley Earthquake J.M. Pauschke Ph.D. Thesis, Stanford Univ., 222 pp (1982
The Shock and Vibration Digest. Volume 15, Number 4
1983-04-01
Klein Memorial lecture, became reality at the 50th Shock and Vibration Symposium in 1979. These sessions have continued to provide new and interesting...Meher-Homji, C 834 Mehl, J.B 822 Meier, G.E.A 779 Meneses , H.P 781 Meyer, R.C 709 Michaelsen, J.F 828 Miklowitz,J 838,839 Miles, J.H 774 Miller
The Shock and Vibration Digest. Volume 15, Number 12
1983-12-01
Allen Curtis from Hughes Alraf Company discussd the Impact of MILSTD10D on laboratory shock and vibration test procedures. Jack Robinson from the Army...157 Kanada, S............... 473 Jack ins, P.D ............. 1871 Johnson, D.H ............. 175 Kanao, M ............... 312 Jackson, C...Vibratin [Earthquake Engineering Research Institute] San Institute, 101 W 55th St., Suite 206, Clarendon Francisco. CA (EEP1-WEE, 2620 Telegraph Nills , IL
Shrout, B. L.; Corlett, W. A.; Collins, I. K.
1979-01-01
The tabulated results of surface pressure tests conducted on the wing and fuselage of an airplane model in the Langley Unitary Plan wind tunnel are presented without analysis. The model tested was that of a supersonic-cruise airplane with a highly swept arrow-wing planform, two engine nacelles mounted beneath the wing, and outboard vertical tails. Data were obtained at Mach numbers of 2.30, 2.96, and 3.30 for angles of attack from -4 deg to 12 deg. The Reynolds number for these tests was 6,560,000 per meter.
Holland, Scott D.; Murphy, Kelly J.
1993-01-01
Since mission profiles for airbreathing hypersonic vehicles such as the National Aero-Space Plane include single-stage-to-orbit requirements, real gas effects may become important with respect to engine performance. The effects of the decrease in the ratio of specific heats have been investigated in generic three-dimensional sidewall compression scramjet inlets with leading-edge sweep angles of 30 and 70 degrees. The effects of a decrease in ratio of specific heats were seen by comparing data from two facilities in two test gases: in the Langley Mach 6 CF4 Tunnel in tetrafluoromethane (where gamma=1.22) and in the Langley 15-Inch Mach 6 Air Tunnel in perfect gas air (where gamma=1.4). In addition to the simulated real gas effects, the parametric effects of cowl position, contraction ratio, leading-edge sweep, and Reynolds number were investigated in the 15-Inch Mach 6 Air Tunnel. The models were instrumented with a total of 45 static pressure orifices distributed on the sidewalls and baseplate. Surface streamline patterns were examined via oil flow, and schlieren videos were made of the external flow field. The results of these tests have significant implications to ground based testing of inlets in facilities which do not operate at flight enthalpies.
The shock tube as a device for testing transonic airfoils at high Reynolds numbers
Cook, W. J.; Presley, L. L.; Chapman, G. T.
1978-01-01
A performance analysis of gas-driven shock tubes shows that transonic airfoil flows with chord Reynolds numbers in the range of 100 million can be generated behind the primary shock in a large shock tube. A study of flow over simple airfoils has been carried out at low and intermediate Reynolds numbers to assess the testing technique. Results obtained from schlieren photos and airfoil pressure measurements show that steady transonic flows similar to those observed for the airfoils in wind tunnels can be generated within the available testing time in a shock tube with either properly-contoured test section walls or a properly-designed slotted-wall test section. The study indicates that the shock tube is a useful facility for studying two-dimensional high Reynolds number transonic airfoil flows.
The Shock and Vibration Digest, Volume 14, Number 4
1982-04-01
Voorhees, C, MeUger, W.W., and Wilding , R., "Spacecraft Modal Testing Using Systematic Multi-Shakers Sine-Dwell Testing Techniques," Shock Vib. Bull...Center University of Wisconsin 610 Walnut St. Madison, Wl 53706 44 ^-v,*«,jj;.,a_w v;,r .., :f&L-x,^:-a.>ji2 SHORT COURSES MAY ADVANCED...Kanpur, India , J. Mech. Engrg. Sei., 23 (1),pp 37-44 (Feb 1981) Key Words: Bearings, Journal bearings. Squeeze film bearings Dynamically loaded
A Study of the Complex Flow Features Behind a Diffracted Shock Wave on a Convex Curved Wall
Directory of Open Access Journals (Sweden)
adam muritala
2015-01-01
Full Text Available The complex flow features behind a diffracted shock wave on a convex curved wall is investigated using large scale experimentation complemented by numerical computation. The study aimed at explaining the global flow behavior within the perturbed region behind the diffracted shock wave. Experiments were conducted in a purpose built shock tube that is capable of generating a range of incident shock Mach numbers Mn ≤ 1.6. Analysis of higher Mach number shocks on different wall geometries were carried out using numerical code that has been validated by earlier authors. Many flow features that were only distinct at high Mach numbers are clearly identified at low Mach numbers in the present investigation. The separation point moves upstream at incident shock Mach number Mn = 1.5 but moves downstream at higher Mach numbers and is nearly stationary at Mn = 1.6. At incident shock Mach number 3.0 the movement of the separation point tends to be independent of the wall curvature as the wall radius approaches infinity. The present investigatio is important in the design of high speed flow devices and in the estimation of flow resistance on supersonic devices and space vehicles.
Capone, F. J.
1982-01-01
An investigation to determine the aeropropulsive characteristics of nonaxisymmetric nozzles on an F-18 jet effects model was conducted in the Langley 16-foot transonic tunnel and the AEDC 16-foot supersonic wind tunnel. The performance of a two dimensional convergent-divergent nozzle, a single expansion ramp nozzle, and a wedge nozzle was compared with that of the baseline axisymmetric nozzle. Test data were obtained at static conditions and at Mach numbers from 0.60 to 2.20 at an angle of attack of 0 deg. Nozzle pressure ratio was varied from jet-off to about 20.
Suprathermal electrons at Saturn's bow shock
Masters, A; Sergis, N; Stawarz, L; Fujimoto, M; Coates, A J; Dougherty, M K
2016-01-01
The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically onl...
Hartigan, P; Frank, A; Hansen, E; Yirak, K; Liao, A S; Graham, P; Wilde, B; Blue, B; Martinez, D; Rosen, P; Farley, D; Paguio, R
2016-01-01
Supersonic outflows from objects as varied as stellar jets, massive stars and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures and therefore a higher-excitation spectrum than an oblique one does. In this paper we summarize the results of a series of numerical simulations and laboratory experiments designed to quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and ...
Converging cylindrical shocks in ideal magnetohydrodynamics
Pullin, D. I.
2014-09-01
We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also of a parameter measuring the local strength of the magnetic field. For the line current case, two approaches are explored and the results compared in detail. The first is geometrical shock-dynamics where the restricted shock-jump conditions are applied directly to the equation on the characteristic entering the shock from behind. This gives an ordinary-differential equation for the shock Mach number as a function of radius which is integrated numerically to provide profiles of the shock implosion. Also, analytic, asymptotic results are obtained for the shock trajectory at small radius. The second approach is direct numerical solution of the radially symmetric MHD equations using a shock-capturing method. For the axial magnetic field case the shock implosion is of the Guderley power-law type with exponent that is not affected by the presence of a finite magnetic field. For the axial current case, however, the presence of a tangential magnetic field ahead of the shock with strength inversely proportional to radius introduces a length scale R = √μ0/p0 I/(2π) where I is the current, μ0 is the permeability, and p0 is the pressure ahead of the shock. For shocks initiated at r ≫ R, shock convergence is first accompanied by shock strengthening as for the strictly gas-dynamic implosion. The diverging magnetic field then
Converging cylindrical shocks in ideal magnetohydrodynamics
Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.
2014-09-01
We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also of a parameter measuring the local strength of the magnetic field. For the line current case, two approaches are explored and the results compared in detail. The first is geometrical shock-dynamics where the restricted shock-jump conditions are applied directly to the equation on the characteristic entering the shock from behind. This gives an ordinary-differential equation for the shock Mach number as a function of radius which is integrated numerically to provide profiles of the shock implosion. Also, analytic, asymptotic results are obtained for the shock trajectory at small radius. The second approach is direct numerical solution of the radially symmetric MHD equations using a shock-capturing method. For the axial magnetic field case the shock implosion is of the Guderley power-law type with exponent that is not affected by the presence of a finite magnetic field. For the axial current case, however, the presence of a tangential magnetic field ahead of the shock with strength inversely proportional to radius introduces a length scale R=sqrt{μ _0/p_0} I/(2 π ) where I is the current, μ0 is the permeability, and p0 is the pressure ahead of the shock. For shocks initiated at r ≫ R, shock convergence is first accompanied by shock strengthening as for the strictly gas-dynamic implosion. The diverging magnetic field
Directory of Open Access Journals (Sweden)
Moritz Schulze
2016-10-01
Full Text Available The interaction of a plane acoustic wave and a sheared flow is numerically investigated for simple orifice and perforated plate configurations in an isolated, non-resonant environment for Mach numbers up to choked conditions in the holes. Analytical derivations found in the literature are not valid in this regime due to restrictions to low Mach numbers and incompressible conditions. To allow for a systematic and detailed parameter study, a low-cost hybrid Computational Fluid Dynamic/Computational Aeroacoustic (CFD/CAA methodology is used. For the CFD simulations, a standard k–ϵ Reynolds-Averaged Navier–Stokes (RANS model is employed, while the CAA simulations are based on frequency space transformed linearized Euler equations (LEE, which are discretized in a stabilized Finite Element method. Simulation times in the order of seconds per frequency allow for a detailed parameter study. From the application of the Multi Microphone Method together with the two-source location procedure, acoustic scattering matrices are calculated and compared to experimental findings showing very good agreement. The scattering properties are presented in the form of scattering matrices for a frequency range of 500–1500 Hz.
Kainulainen, Jouni
2012-01-01
Measuring the mass distribution of infrared dark clouds (IRDCs) over the wide dynamic range of their column densities is a fundamental obstacle in determining the initial conditions of high-mass star formation and star cluster formation. We present a new technique to derive high-dynamic-range, arcsecond-scale resolution column density data for IRDCs and demonstrate the potential of such data in measuring the density variance - sonic Mach number relation in molecular clouds. We combine near-infrared data from the UKIDSS/Galactic Plane Survey with mid-infrared data from the Spitzer/GLIMPSE survey to derive dust extinction maps for a sample of ten IRDCs. We then examine the linewidths of the IRDCs using 13CO line emission data from the FCRAO/Galactic Ring Survey and derive a column density - sonic Mach number relation for them. For comparison, we also examine the relation in a sample of nearby molecular clouds. The presented column density mapping technique provides a very capable, temperature independent tool f...
Investigation of shock focusing in a cavity with incident shock diffracted by an obstacle
Zhang, Q.; Chen, X.; He, L.-M.; Rong, K.; Deiterding, R.
2017-03-01
Experiments and numerical simulations were carried out in order to investigate the focusing of a shock wave in a test section after the incident shock has been diffracted by an obstacle. A conventional shock tube was used to generate the planar shock. Incident shock Mach numbers of 1.4 and 2.1 were tested. A high-speed camera was employed to obtain schlieren photos of the flow field in the experiments. In the numerical simulations, a weighted essentially non-oscillatory (WENO) scheme of third-order accuracy supplemented with structured dynamic mesh adaptation was adopted to simulate the shock wave interaction. Good agreement between experiments and numerical results is observed. The configurations exhibit shock reflection phenomena, shock-vortex interaction and—in particular—shock focusing. The pressure history in the cavity apex was recorded and compared with the numerical results. A quantitative analysis of the numerically observed shock reflection configurations is also performed by employing a pseudo-steady shock transition boundary calculation technique. Regular reflection, single Mach reflection and transitional Mach reflection phenomena are observed and are found to correlate well with analytic predictions from shock reflection theory.
Tavelli, Maurizio; Dumbser, Michael
2017-07-01
addition, all the volume and surface integrals needed by the scheme depend only on the geometry and the polynomial degree of the basis and test functions and can therefore be precomputed and stored in a preprocessing stage. This leads to significant savings in terms of computational effort for the time evolution part. In this way also the extension to a fully curved isoparametric approach becomes natural and affects only the preprocessing step. The viscous terms and the heat flux are also discretized making use of the staggered grid by defining the viscous stress tensor and the heat flux vector on the dual grid, which corresponds to the use of a lifting operator, but on the dual grid. The time step of our new numerical method is limited by a CFL condition based only on the fluid velocity and not on the sound speed. This makes the method particularly interesting for low Mach number flows. Finally, a very simple combination of artificial viscosity and the a posteriori MOOD technique allows to deal with shock waves and thus permits also to simulate high Mach number flows. We show computational results for a large set of two and three-dimensional benchmark problems, including both low and high Mach number flows and using polynomial approximation degrees up to p = 4.
Energy Technology Data Exchange (ETDEWEB)
Core, X.
2002-02-01
The isobar approximation for the system of the balance equations of mass, momentum, energy and chemical species is a suitable approximation to represent low Mach number reactive flows. In this approximation, which neglects acoustics phenomena, the mixture is hydrodynamically incompressible and the thermodynamic effects lead to an uniform compression of the system. We present a novel numerical scheme for this approximation. An incremental projection method, which uses the original form of mass balance equation, discretizes in time the Navier-Stokes equations. Spatial discretization is achieved through a finite volume approach on MAC-type staggered mesh. A higher order de-centered scheme is used to compute the convective fluxes. We associate to this discretization a local mesh refinement method, based on Flux Interface Correction technique. A first application concerns a forced flow with variable density which mimics a combustion problem. The second application is natural convection with first small temperature variations and then beyond the limit of validity of the Boussinesq approximation. Finally, we treat a third application which is a laminar diffusion flame. For each of these test problems, we demonstrate the robustness of the proposed numerical scheme, notably for the density spatial variations. We analyze the gain in accuracy obtained with the local mesh refinement method. (author)
Institute of Scientific and Technical Information of China (English)
Tsukasa Irie; Tsuyoshi Yasunobu; Hideo Kashimura; Toshiaki Setoguchi; Kazuyasu Matsuo
2003-01-01
When the shock wave propagating in the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end, and unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. The pulse jet transits to spherical shock wave with the increase in the strength of shock wave. The strength is dependent on the Mach number of shock wave, which attenuates by propagation distance from the open end. In this study, the mechanism of generating the unsteady pulse jet, the characteristics of the pressure distribution in the flow field and the emission of shock wave from straight circular tube which has the infinite flange at open end are analyzed numerically by the TVD method. Strength of spherical shock wave, relation of shock wave Mach number, distance decay of spherical shock wave and directional characteristics are clarified.
Mizukaki, Toshiharu; Borg, Stephen E.; Danehy, Paul M.; Murman, Scott M.
2014-01-01
This paper presents the results of visualization of separated flow around a generic entry capsule that resembles the Apollo Command Module (CM) and the Orion Multi-Purpose Crew Vehicle (MPCV). The model was tested at flow speeds up to Mach 0.4 at a single angle of attack of 28 degrees. For manned spacecraft using capsule-shaped vehicles, certain flight operations such as emergency abort maneuvers soon after launch and flight just prior to parachute deployment during the final stages of entry, the command module may fly at low Mach number. Under these flow conditions, the separated flow generated from the heat-shield surface on both windward and leeward sides of the capsule dominates the wake flow downstream of the capsule. In this paper, flow visualization of the separated flow was conducted using the background-oriented schlieren (BOS) method, which has the capability of visualizing significantly separated wake flows without the particle seeding required by other techniques. Experimental results herein show that BOS has detection capability of density changes on the order of 10(sup-5).
Devade, Kiran D.; Pise, Ashok T.
2017-01-01
Ranque Hilsch vortex tube is a device that can produce cold and hot air streams simultaneously from pressurized air. Performance of vortex tube is influenced by a number of geometrical and operational parameters. In this study parametric analysis of vortex tube is carried out. Air is used as the working fluid and geometrical parameters like length to diameter ratio (15, 16, 17, 18), exit valve angles (30°-90°), orifice diameters (5, 6 and 7 mm), 2 entry nozzles and tube divergence angle 4° is used for experimentation. Operational parameters like pressure (200-600 kPa), cold mass fraction (0-1) is varied and effect of Mach number at the inlet of the tube is investigated. The vortex tube is tested at sub sonic (0 tube is observed for CMF up to 0.5. Experimental correlations are proposed for optimum COP. Parametric correlation is developed for geometrical and operational parameters.
The Shock and Vibration Digest. Volume 16, Number 8
1984-08-01
have been examined [57]. the problem of shallow shells by using the Ritz method with algebraic polynomial trial functions Nonlinear analysi. A number...investigate the motion. Nonlinear differential equations have been vibrational behavior of turbine blades [42]. Experi- converted into nonlinear algebraic ...22 (4), Mech., Trans. ASME, 48 (3), pp 559-562 pp 247-264 (1980). (1981). 120. Tadws, R.N. and Rotman , M., "Dynamic Re- 130. Genta, G., Gola, M., et
Numerical simulation of transient inviscid gas flows in a shock tube
Yang, J. Y.; Lombard, C. K.; Nagaraj, N.; Bershader, D.
1985-01-01
Time-dependent upwind high resolution schemes for solving the Euler equations were developed and applied to simulate 1-D and 2-D transient inviscid gas flows in a shock tube. Using obstacles of different geometries, a series of calculations were carried out to investigate the transient complex shock-wave diffraction phenomena. Shock-wave and objects interactions with shock Mach-number Ms ranging from 2 to 20 were considered. Comparison with analytical and available experimental results indicate good agreement. Display of detailed flow structures including multiple Mach shocks, slip surfaces, and vortex are also given.
The Shock and Vibration Digest. Volume 14, Number 7
1982-07-01
Houbolt and Eichenbaum [103-105] have dealt with GLA in three-dimensional gusts. But a number of ’^’estigations have been carried out with respect to...of an Active Control System for Helicopter Vibration Reduction and Gust Response Alleviation," NASA CR-152377 (1980). 103. Eichenbaum , F.D...Thesis, Polytechnic Inst. of New York (1978). 5. Martin , C.R., "A Modal Control Approach for Active Control of Multi-Story Structures," Ph.D. Thesis
Hybrid Simulations of Particle Acceleration at Shocks
Caprioli, Damiano
2014-01-01
We present the results of large hybrid (kinetic ions - fluid electrons) simulations of particle acceleration at non-relativistic collisionless shocks. Ion acceleration efficiency and magnetic field amplification are investigated in detail as a function of shock inclination and strength, and compared with predictions of diffusive shock acceleration theory, for shocks with Mach number up to 100. Moreover, we discuss the relative importance of resonant and Bell's instability in the shock precursor, and show that diffusion in the self-generated turbulence can be effectively parametrized as Bohm diffusion in the amplified magnetic field.
Treanor, C. E.; Hall, J. G.
1982-10-01
The present conference on shock tubes and waves considers shock tube drivers, luminous shock tubes, shock tube temperature and pressure measurement, shock front distortion in real gases, nonlinear standing waves, transonic flow shock wave turbulent boundary interactions, wall roughness effects on reflected shock bifurcation, argon thermal conductivity, pattern generation in gaseous detonations, cylindrical resonators, shock tunnel-produced high gain lasers, fluid dynamic aspects of laser-metal interaction, and the ionization of argon gas behind reflected shock waves. Also discussed are the ionization relaxation of shock-heated plasmas and gases, discharge flow/shock tube studies of singlet oxygen, rotational and vibrational relaxation, chemiluminescence thermal and shock wave decomposition of hydrogen cyanide and hydrogen azide, shock wave structure in gas-particle mixtures at low Mach numbers, binary nucleation in a Ludwieg tube, shock liquefaction experiments, pipeline explosions, the shock wave ignition of pulverized coal, and shock-initiated methane combustion.
Lanfranco, M. J.; Sparks, V. W.; Kavanaugh, A. T.
1973-01-01
An experimental investigation was conducted in a 9- by 7-foot supersonic wind tunnel to determine the effect of plume-induced flow separation and aspiration effects due to operation of both the orbiter and the solid rocket motors on a 0.019-scale model of the launch configuration of the space shuttle vehicle. Longitudinal and lateral-directional stability data were obtained at Mach numbers of 1.6, 2.0, and 2.2 with and without the engines operating. The plumes exiting from the engines were simulated by a cold gas jet supplied by an auxiliary 200 atmosphere air supply system, and by solid body plume simulators. Comparisons of the aerodynamic effects produced by these two simulation procedures are presented. The data indicate that the parameters most significantly affected by the jet plumes are the pitching moment, the elevon control effectiveness, the axial force, and the orbiter wing loads.
Miser, James W; Stewart, Warner L
1957-01-01
A blade design study is presented for a two-stage air-cooled turbine suitable for flight at a Mach number of 2.5 for which velocity diagrams have been previously obtained. The detailed procedure used in the design of the blades is given. In addition, the design blade shapes, surface velocity distributions, inner and outer wall contours, and other design data are presented. Of all the blade rows, the first-stage rotor has the highest solidity, with a value of 2.289 at the mean section. The second-stage stator also had a high mean-section solidity of 1.927, mainly because of its high inlet whirl. The second-stage rotor has the highest value of the suction-surface diffusion parameter, with a value of 0.151. All other blade rows have values for this parameter under 0.100.
Voit, Charles H; Guentert, Donald C; Dugan, James F
1950-01-01
A complete stage of an axial-flow compressor was designed and built to investigate the possibility of obtaining a high pressure ratio with an acceptable efficiency through the use of the optimum combination of high blade loading and high relative inlet Mach number. Over-all stage performance was investigated over a range of flows at equivalent tip speeds of 418 to 836 feet per second. At design speed (836 ft/sec), a peak total-pressure ration of 1.445 was obtained with an adiabatic efficiency of 0.89. For design angle of attack at the mean radius, a total-pressure ratio of 1.392 was obtained.
Suprathermal Electrons at Saturn's Bow Shock
Masters, A.; Sulaiman, A. H.; Sergis, N.; Stawarz, L.; Fujimoto, M.; Coates, A. J.; Dougherty, M. K.
2016-07-01
The leading explanation for the origin of galactic cosmic rays is particle acceleration at the shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR shocks. However, the Cassini spacecraft has shown that the shock standing in the solar wind sunward of Saturn (Saturn's bow shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's bow shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (process involves interaction with whistler waves at the shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong shocks around young SNRs. A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ˜1 MeV).
基于预处理HLLEW格式的全速域数值算法%Preconditioning HLLEW Scheme for Flows at All Mach Numbers
Institute of Scientific and Technical Information of China (English)
刘中玉; 张明锋; 郑冠男; 杨国伟
2016-01-01
Based on HLLEW ( Harten⁃Lax⁃Van Leer⁃Einfeldt⁃Wada) scheme, low speed preconditioning technology is introduced to develop a three⁃dimensional Navier⁃Stokes solver for flows at all Mach numbers. Low speed preconditioning techniques is introduced to reconstruct dissipative term in HLLEW scheme and preconditioning HLLEW scheme is proposed. Implicit time⁃marching method is constructed based on preconditioning Jacobian Matrix. Results of NACA 4412 incompressible flow and RAE 2822 transonic flow with preconditioning HLLEW scheme are compared with results by original method and experimental data. It shows that preconditioning HLLEW method improves accuracy and convergence rate for low speed flow. It can be applied for flows at all Mach numbers.%基于HLLEW（ Harten⁃Lax⁃Van Leer⁃Einfeldt⁃Wada）格式引入预处理技术发展适合求解全速域流场的三维Navier⁃Stokes求解器。引入低速预处理技术，重新构造HLLEW格式的耗散项，给出预处理后的HLLEW格式，并根据预处理后的雅克比矩阵构造相应的隐式时间推进方程。利用预处理方法求解 NACA 4412低速不可压流动与RAE 2822跨声速可压缩流动，并与实验结果及原有方法的计算结果对比。结果表明：预处理HLLEW格式不仅提高低速不可压缩流动的计算效率和精度，也保持了对可压缩流动的处理能力，是一种适用于全速域流场数值模拟的有效方法。
Heavy gas relaxation in a light gas shock wave at small Prandtl number
Fernandez-Feria, R.
2016-09-01
The shock wave structure of a binary mixture with very different molecular weights is analyzed using a two-fluid theory in the limit of small Prandtl (Pr) number of the light gas. In particular, the case in which both the density ratio and Λ =Pr/δ Sc are order unity or below is considered, where δ ≪1 is the molecular mass ratio and Sc is the Schmidt number. Approximate analytical solutions are given for weak, and for moderately strong, shock waves. In the former case the solution is continuous, while in the latter case the light gas shock exhibits a discontinuity and the heavy gas relaxes towards the final equilibrium state.
Application of shock tubes to transonic airfoil testing at high Reynolds numbers
Cook, W. J.; Chaney, M. J.; Presley, L. L.; Chapman, G. T.
1978-01-01
Performance analysis of a gas-driven shock tube shows that transonic airfoil flows with chord Reynolds numbers of the order of 100 million can be produced, with limitations being imposed by the structural integrity of the facility or the model. A study of flow development over a simple circular arc airfoil at zero angle of attack was carried out in a shock tube at low and intermediate Reynolds numbers to assess the testing technique. Results obtained from schlieren photography and airfoil pressure measurements show that steady transonic flows similar to those produced for the same airfoil in a wind tunnel can be generated within the available testing time in a shock tube with properly contoured test section walls.
THE INTERACTION BETWEEN SHOCK WAVES AND SOLID SPHERES ARRAYS IN A SHOCK TUBE
Institute of Scientific and Technical Information of China (English)
SHI Honghui; Kazuki YAMAMURA
2004-01-01
When a shock wave interacts with a group of solid spheres, non-linear aerodynamic behaviors come into effect. The complicated wave reflections such as the Mach reflection occur in the wave propagation process. The wave interactions with vortices behind each sphere's wake cause fluctuation in the pressure profiles of shock waves. This paper reports an experimental study for the aerodynamic processes involved in the interaction between shock waves and solid spheres. A schlieren photography was applied to visualize the various shock waves passing through solid spheres. Pressure measurements were performed along different downstream positions. The experiments were conducted in both rectangular and circular shock tubes. The data with respect to the effect of the sphere array,size, interval distance, incident Mach number, etc., on the shock wave attenuation were obtained.
Inlet boundary conditions for shock wave propagation problems in air ducts
Fashbaugh, R. H.
1992-03-01
Shock waves propagating into air ducting systems are numerically studied using data from Kriebel (1972). Small-scale junctions mounted in shock tubes with an incident shock wave are considered. The stagnation pressure ratio through a duct inlet is evaluated for various junction types. The logarithm of this ratio varies linearly with the Mach number of the flow behind the incident shock wave. The static pressure inside the inlet is established using experimental data with given Mach numbers of the incident and inlet flows. A constant stagnation enthalpy through the inlet junction is assumed to establish inflow to the duct.
On the Effects of Viscosity on the Shock Waves for a Hydrodynamical Case—Part I: Basic Mechanism
Directory of Open Access Journals (Sweden)
Huseyin Cavus
2013-01-01
Full Text Available The interaction of shock waves with viscosity is one of the central problems in the supersonic regime of compressible fluid flow. In this work, numerical solutions of unmagnetised fluid equations, with the viscous stress tensor, are investigated for a one-dimensional shock wave. In the algorithm developed the viscous stress terms are expressed in terms of the relevant Reynolds number. The algorithm concentrated on the compression rate, the entropy change, pressures, and Mach number ratios across the shock wave. The behaviour of solutions is obtained for the Reynolds and Mach numbers defining the medium and shock wave in the supersonic limits.
Regularized Moment Equations and Shock Waves for Rarefied Granular Gas
Reddy, Lakshminarayana; Alam, Meheboob
2016-11-01
It is well-known that the shock structures predicted by extended hydrodynamic models are more accurate than the standard Navier-Stokes model in the rarefied regime, but they fail to predict continuous shock structures when the Mach number exceeds a critical value. Regularization or parabolization is one method to obtain smooth shock profiles at all Mach numbers. Following a Chapman-Enskog-like method, we have derived the "regularized" version 10-moment equations ("R10" moment equations) for inelastic hard-spheres. In order to show the advantage of R10 moment equations over standard 10-moment equations, the R10 moment equations have been employed to solve the Riemann problem of plane shock waves for both molecular and granular gases. The numerical results are compared between the 10-moment and R10-moment models and it is found that the 10-moment model fails to produce continuous shock structures beyond an upstream Mach number of 1 . 34 , while the R10-moment model predicts smooth shock profiles beyond the upstream Mach number of 1 . 34 . The density and granular temperature profiles are found to be asymmetric, with their maxima occurring within the shock-layer.
On the electron-ion temperature ratio established by collisionless shocks
Vink, Jacco; Bykov, Andrei; Gabici, Stefano
2014-01-01
Astrophysical shocks are often collisionless shocks, in which the changes in plasma flow and temper- atures across the shock are established not through Coulomb interactions, but through electric and mag- netic fields. An open question about collisionless shocks is whether electrons and ions each establish their own post-shock temperature (non-equilibration of temperatures), or whether they quickly equilibrate in the shock region. Here we provide a simple relation for the minimal amount of equilibration to expect. The basic assumption is that the enthalpy-flux of the electrons is conserved separately, but that all parti- cle species should undergo the same density jump across the the shock, in order for the plasma to remain charge neutral. This assumption results in an analytic treatment of electron-ion equilibration that agrees with observations of collisionless shocks: at low Mach numbers < 2 the electrons and ions are close to equilibration, whereas for Mach numbers above M ~ 60 the electron-ion tempera...
A specially curved wedge for eliminating wedge angle effect in unsteady shock reflection
Wang, He; Zhai, Zhigang; Luo, Xisheng; Yang, Jiming; Lu, Xiyun
2017-08-01
A curved wedge with a specific shape is designed and manufactured to guarantee the wedge angle unvaried during the cylindrically converging shock moving along the wedge. Thus the variation of the wedge angle caused by the wedge will be eliminated in unsteady shock reflection. Different initial wedge angles are considered to observe regular reflection and Mach reflection. When Mach reflection occurs, it is found that direct Mach reflection is persisted over the wedge without wave pattern transitions, which differs from our previous work with varied wedge angles [Zhang et al. "Reflection of cylindrical converging shock wave over a plane wedge," Phys. Fluids 28, 086101 (2016)]. Moreover, the Mach stem is nearly straight when the wedge angle is relatively large, and the trajectory of triple point can be well predicted by three-shock theory. It is believed that the straight Mach stem results from the coupling effect of the converging shock and the convexly curved wedge, which exert opposite effects on the Mach stem curvature. As the wedge angle reduces, the three-shock theory prediction deviates from the present results owing to the curved Mach stem. Stronger vortices are produced near the wall, which are caused by the interaction of two shear layers, and whether the stronger vortices will be generated near the wall depends on the reflection number of the shock wave over the tube wall and wedge. The length of disturbed shock front in the Mach reflection is found to increase nonlinearly due to the unsteady feature of the flow. The growth rate of length reduces as the shock converges because of the geometrical contraction effect. Further the lengths of the Mach stem and the disturbed shock front are compared, and the results show that although the difference exists between them, both of them show a similar variation tendency. Compared with our previous work with varied wedge angles, the variation of the wedge angle has great effects on the Mach stem length and wave
CSIR Research Space (South Africa)
Naidoo, K
2011-06-01
Full Text Available et al. (1999) investigated the effect of continuous rapid wedge rotation on the point of transition with Euler CFD on moving meshes. In contrast to the work by Markelov et al. (1999), Khotyanovsky et al. (1999) considered larger move- ments... between the three-dimensional Euler CFD predictions of Ivanov et al. (2001) and their measurements from experiments with the finite aspect ratio wedge. This agreement established confidence in their two-dimensional Mach stem predictions with Euler CFD...
Study of the shock structure of supersonic, dual, coaxial, jets
Energy Technology Data Exchange (ETDEWEB)
Lee, K. H.; Lee, J. H.; Kim, H. D. [Andong National Univ., Andong (Korea, Republic of)
2001-07-01
The shock structure of supersonic, dual, coaxial jet is experimentally investigated. Eight different kinds of coaxial, dual nozzles are employed to observe the major features of the near field shock structure of the supersonic, coaxial, dual jets. Four convergent-divergent supersonic nozzles having the Mach number of 2.0 and 3.0, and are used to compare the coaxial jet flows discharging from two sonic nozzles. The primary pressure ratio is changed in the range between 4.0 and 10.0 and the assistant jet pressure ratio from 1.0 to 4.0. The results obtained show that the impinging angle, nozzle geometry and pressure ratio significantly affect the near field shock structure, Mach disk location and Mach disk diameter. The annular shock system is found depending the assistant and primary jet pressure ratios.
Nonthermal radiation from relativistic electrons accelerated at spherically expanding shocks
Kang, Hyesung
2014-01-01
We study the evolution of the energy spectrum of cosmic-ray electrons accelerated at spherically expanding shocks with low Mach numbers and the ensuing spectral signatures imprinted in radio synchrotron emission. Time-dependent simulations of diffusive shock acceleration (DSA) of electrons in the test-particle limit have been performed for spherical shocks with the parameters relevant for typical shocks in the intracluster medium. The electron and radiation spectra at the shock location can be described properly by the test-particle DSA predictions with the instantaneous shock parameters. However, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws, because the shock compression ratio and the flux of injected electrons at the shock gradually decrease as the shock slows down in time. So one needs to be cautious about interpreting observed radio spectra of evolving shocks by simple DSA models in the test-particle regime.
STEREO interplanetary shocks and foreshocks
Energy Technology Data Exchange (ETDEWEB)
Blanco-Cano, X. [Instituto de Geofisica, UNAM, CU, Coyoacan 04510 DF (Mexico); Kajdic, P. [IRAP-University of Toulouse, CNRS, Toulouse (France); Aguilar-Rodriguez, E. [Instituto de Geofisica, UNAM, Morelia (Mexico); Russell, C. T. [ESS and IGPP, University of California, Los Angeles, 603 Charles Young Drive, Los Angeles, CA 90095 (United States); Jian, L. K. [NASA Goddard Space Flight Center, Greenbelt, MD and University of Maryland, College Park, MD (United States); Luhmann, J. G. [SSL, University of California Berkeley (United States)
2013-06-13
We use STEREO data to study shocks driven by stream interactions and the waves associated with them. During the years of the extended solar minimum 2007-2010, stream interaction shocks have Mach numbers between 1.1-3.8 and {theta}{sub Bn}{approx}20-86 Degree-Sign . We find a variety of waves, including whistlers and low frequency fluctuations. Upstream whistler waves may be generated at the shock and upstream ultra low frequency (ULF) waves can be driven locally by ion instabilities. The downstream wave spectra can be formed by both, locally generated perturbations, and shock transmitted waves. We find that many quasiperpendicular shocks can be accompanied by ULF wave and ion foreshocks, which is in contrast to Earth's bow shock. Fluctuations downstream of quasi-parallel shocks tend to have larger amplitudes than waves downstream of quasi-perpendicular shocks. Proton foreshocks of shocks driven by stream interactions have extensions dr {<=}0.05 AU. This is smaller than foreshock extensions for ICME driven shocks. The difference in foreshock extensions is related to the fact that ICME driven shocks are formed closer to the Sun and therefore begin to accelerate particles very early in their existence, while stream interaction shocks form at {approx}1 AU and have been producing suprathermal particles for a shorter time.
Generation and evolution of interplanetary slow shocks
Directory of Open Access Journals (Sweden)
C.-C. Wu
Full Text Available It is well known that most MHD shocks observed within 1 AU are MHD fast shocks. Only a very limited number of MHD slow shocks are observed within 1 AU. In order to understand why there are only a few MHD slow shocks observed within 1 AU, we use a one-dimensional, time-dependent MHD code with an adaptive grid to study the generation and evolution of interplanetary slow shocks (ISS in the solar wind. Results show that a negative, nearly square-wave perturbation will generate a pair of slow shocks (a forward and a reverse slow shock. In addition, the forward and the reverse slow shocks can pass through each other without destroying their characteristics, but the propagating speeds for both shocks are decreased. A positive, square-wave perturbation will generate both slow and fast shocks. When a forward slow shock (FSS propagates behind a forward fast shock (FFS, the former experiences a decreasing Mach number. In addition, the FSS always disappears within a distance of 150R_{⊙} (where R_{⊙} is one solar radius from the Sun when there is a forward fast shock (with Mach number ≥1.7 propagating in front of the FSS. In all tests that we have performed, we have not discovered that the FSS (or reverse slow shock evolves into a FFS (or reverse fast shock. Thus, we do not confirm the FSS-FFS evolution as suggested by Whang (1987.
Jackson, Charles M., Jr.; Harris, Roy V., Jr.
1960-01-01
An investigation has been made in the Langley 4- by 4-foot supersonic pressure tunnel at a Mach number of 1.99 to determine the longitudinal stability and control characteristics of a reentry model consisting of a lenticular-shaped body with two fin configurations (horizontal fins with end plates). Effects of deflecting the larger size fins as pitch-control surfaces were also investigated. The results indicate that the body alone was unstable from an angle of attack of 0 deg to about 55 deg where it became stable and remained so to 90 deg. The addition of fins provided positive longitudinal stability throughout the angle-of-attack range and increased the lift-drag ratio of the configuration. Reducing the horizontal-fin area at the inboard trailing edge of the fin had only a small effect on the aerodynamic characteristics of the vehicle for the condition of no fin deflection. Deflecting the fins, appeared to be an effective means of pitch control and had only a small effect on lift-drag ratio.
Sayadi, Taraneh; Hamman, Curtis; Moin, Parviz
2011-11-01
Transition to turbulence via spatially evolving secondary instabilities in compressible, zero-pressure-gradient flat plate boundary layers is numerically simulated for both the Klebanoff K-type and Herbert H-type disturbances. The objective of this work is to evaluate the universality of the breakdown process between different routes through transition in wall-bounded shear flows. Each localized linear disturbance is amplified through weak non-linear instability that grows into lambda-vortices and then hairpin-shaped eddies with harmonic wavelength, which become less organized in the late-transitional regime once a fully populated spanwise turbulent energy spectrum is established. For the H-type transition, the computational domain extends from Rex =105 , where laminar blowing and suction excites the most unstable fundamental and a pair of oblique waves, to fully turbulent stage at Rex = 10 . 6 ×105 . The computational domain for the K-type transition extends to Rex = 9 . 6 ×105 . The computational algorithm employs fourth-order central differences with non-reflective numerical sponges along the external boundaries. For each case, the Mach number is 0.2. Supported by the PSAAP program of DoE, ANL and LLNL.
Directory of Open Access Journals (Sweden)
Matthias Bauer
2016-10-01
Full Text Available This paper discusses wind tunnel test results aimed at advancing active flow control technology to increase the aerodynamic efficiency of an aircraft during take-off. A model of the outer section of a representative civil airliner wing was equipped with two-stage fluidic actuators between the slat edge and wing tip, where mechanical high-lift devices fail to integrate. The experiments were conducted at a nominal take-off Mach number of M = 0.2. At this incidence velocity, separation on the wing section, accompanied by increased drag, is triggered by the strong slat edge vortex at high angles of attack. On the basis of global force measurements and local static pressure data, the effect of pulsed blowing on the complex flow is evaluated, considering various momentum coefficients and spanwise distributions of the actuation effort. It is shown that through local intensification of forcing, a momentum coefficient of less than c μ = 0.6 % suffices to offset the stall by 2.4°, increase the maximum lift by more than 10% and reduce the drag by 37% compared to the uncontrolled flow.
Seo, Jung Hee; Mittal, Rajat
2011-02-20
A new sharp-interface immersed boundary method based approach for the computation of low-Mach number flow-induced sound around complex geometries is described. The underlying approach is based on a hydrodynamic/acoustic splitting technique where the incompressible flow is first computed using a second-order accurate immersed boundary solver. This is followed by the computation of sound using the linearized perturbed compressible equations (LPCE). The primary contribution of the current work is the development of a versatile, high-order accurate immersed boundary method for solving the LPCE in complex domains. This new method applies the boundary condition on the immersed boundary to a high-order by combining the ghost-cell approach with a weighted least-squares error method based on a high-order approximating polynomial. The method is validated for canonical acoustic wave scattering and flow-induced noise problems. Applications of this technique to relatively complex cases of practical interest are also presented.
Bzowski, M; Kubiak, M A; Sokol, J M; Fuselier, S A; Galli, A; Heirtzler, D; Kucharek, H; Leonard, T W; McComas, D J; Moebius, E; Schwadron, N A; Wurz, P
2015-01-01
We analyzed observations of interstellar neutral helium (ISN~He) obtained from the Interstellar Boundary Explorer (IBEX) satellite during its first six years of operation. We used a refined version of the ISN~He simulation model, presented in the companion paper by Sokol_et al. 2015, and a sophisticated data correlation and uncertainty system and parameter fitting method, described in the companion paper by Swaczyna et al 2015. We analyzed the entire data set together and the yearly subsets, and found the temperature and velocity vector of ISN~He in front of the heliosphere. As seen in the previous studies, the allowable parameters are highly correlated and form a four-dimensional tube in the parameter space. The inflow longitudes obtained from the yearly data subsets show a spread of ~6 degree, with the other parameters varying accordingly along the parameter tube, and the minimum chi-square value is larger than expected. We found, however, that the Mach number of the ISN~He flow shows very little scatter an...
Lewis, B. W.
1961-01-01
A limited investigation of the deterioration characteristics of 22 refractory materials was conducted by exposing them to a stagnation temperature of 3,800 F in a Mach number 2 ceramic-heated jet at the Langley Research Center. The materials tested were six materials whose major constituent was silicon carbide, five cermets whose major constituent was titanium carbide, six materials whose major constituents were metal borides, four cermets containing alumina, and one silicon nitride model. Tests consisted of obtaining weight change and appearance changes for 1/2-inch-diameter hemispherical-nose cylindrical models exposed to the air jet for 30 seconds at a time for a total of four runs or 2 minutes exposure. Curves of weight changes plotted against the number of 30-second tests in the jet were obtained. Estimates of average surface temperature near the stagnation point of the model were obtained by use of a special temperature-measuring camera. The models were examined before and after the completion of the tests for possible changes in microstructure; no significant changes were found. The data obtained were analyzed with the view that the oxidation characteristics of the materials were the main factor in deterioration of the materials under the conditions of the tests. It was concluded that only those materials which changed in weight the least could be recommended for further extensive application-oriented evaluations. The following materials fell in this category: silicon carbide - silicon, chromium - 28-percent alumina cermet, titanium boride - 5-percent boron carbide. The remainder of the materials tested had oxidation characteristics which appeared to be too severely limiting of their general applications to flight vehicles.
Hartigan, P.; Foster, J.; Frank, A.; Hansen, E.; Yirak, K.; Liao, A. S.; Graham, P.; Wilde, B.; Blue, B.; Martinez, D.; Rosen, P.; Farley, D.; Paguio, R.
2016-06-01
Supersonic outflows from objects as varied as stellar jets, massive stars, and novae often exhibit multiple shock waves that overlap one another. When the intersection angle between two shock waves exceeds a critical value, the system reconfigures its geometry to create a normal shock known as a Mach stem where the shocks meet. Mach stems are important for interpreting emission-line images of shocked gas because a normal shock produces higher postshock temperatures, and therefore a higher-excitation spectrum than does an oblique shock. In this paper, we summarize the results of a series of numerical simulations and laboratory experiments designed to quantify how Mach stems behave in supersonic plasmas that are the norm in astrophysical flows. The experiments test analytical predictions for critical angles where Mach stems should form, and quantify how Mach stems grow and decay as intersection angles between the incident shock and a surface change. While small Mach stems are destroyed by surface irregularities and subcritical angles, larger ones persist in these situations and can regrow if the intersection angle changes to become more favorable. The experimental and numerical results show that although Mach stems occur only over a limited range of intersection angles and size scales, within these ranges they are relatively robust, and hence are a viable explanation for variable bright knots observed in Hubble Space Telescope images at the intersections of some bow shocks in stellar jets.
Gapcynski, John P; Carlson, Harry W
1955-01-01
The changes in the aerodynamic characteristics of a body of revolution with a fineness ratio of 8 have been determined at Mach numbers of 1.41 and 2.01, a Reynolds number, based on body length, of 4.54 x 10 to the 6th power, and angles of incidence of 0 degrees and plus or minus 3 degrees as the position of the body is varied with respect to a reflection plane. The data are compared with theoretical results.
Shock can be caused by any condition that reduces blood flow, including: Heart problems (such as heart attack or heart failure ) Low blood volume (as with heavy bleeding or dehydration ) Changes in blood vessels (as with infection ...
Jump Conditions of a Shock with Current in Cylindrical Non-Neutral Plasma
Institute of Scientific and Technical Information of China (English)
HE Yong; HU Xi-Wei; HU Ye-Min
2006-01-01
Jump conditions of the parameters (mass flow, momentum flow and energy Bow) of a shock with current (thereby, electric and magnetic field) in cylindrical non-neutral plasma are presented and derived from Maxwell's equations and two fluid equations for electron and ion fluid. The critical Mach number for the shock existence is calculated, which depends on the shock carried current, the ion charge, and the composition of the magnetic and thermal pressure. The numerical results show that both the strength and profiles of the downstream shock parameters will be affected obviously by the shock carried current, electric and magnetic field in the two-dimensional shock.
Experiments in hand-operated, hypersonic shock tunnel facility
Sudhiesh Kumar, Chintoo; Reddy, K. P. J.
2016-11-01
Experiments were conducted using the newly developed table-top, hand-operated hypersonic shock tunnel, otherwise known as the Reddy hypersonic shock tunnel. This novel instrument uses only manual force to generate the shock wave in the shock tube, and is designed to generate a freestream flow of Mach 6.5 in the test section. The flow was characterized using stagnation point pressure measurements made using fast-acting piezoelectric transducers. Schlieren visualization was also carried out to capture the bow shock in front of a hemispherical body placed in the flow. Freestream Mach numbers estimated at various points in the test section showed that for a minimum diameter of 46 mm within the test section, the value did not vary by more than 3 % along any cross-sectional plane. The results of the experiments presented here indicate that the device may be successfully employed for basic hypersonic research activities at the university level.
Wallskog, Harvey A.
1954-01-01
A 1/5-scale, rocket-propelled model of the Convair F-102 configuration was tested in free flight to determine zero-lift drag at Mach numbers up to 1.34 and at Reynolds numbers comparable to those of the full-scale airplane. This large-scale model corresponded to the prototype airplane and had air flow through the duct. Additional zero-lift drag tests involved a series of small equivalent bodies of revolution which were launched by means of a helium gun. The several small-scale models tested corresponded to: the basic configuration, the 1/5-scale rocket-propelled model configuration, a 2-foot (full-scale) fuselage-extension configuration, and a 7-foot (full-scale) fuselage-extension configuration. Models designed to correspond to the area distribution at a Mach number of 1.0 were flown for each of these 'shapes and, in addition, models designed to correspond to the area distribution at a Mach number of 1.2 were flown for the 1/5-scale rocket-propelled model and the 7-foot-fuselage-extension configuration. The value of external pressure drag coefficient (including base drag) obtained from the large-scale rocket model was 0.0190 at a Mach number of 1..05 and the corresponding values from the equivalent-body tests varied from 0.0183 for the rocket-propelled model shape to 0.0137 for the 7-foot-fuselage-extension configuration. From the results of tests of equivalent bodies designed to correspond to the area distribution at a Mach number of 1.0, it is evident that the small changes in shape incorporated in the basic and 2-foot-fuselage-extension configurations from that of the rocket-propelled model configuration will provide no significant change in pressure drag. On the other hand, the data from the 7-foot-fuselage-extension model indicate a substantial reduction in pressure drag at transonic speeds.
Vortex dynamics in 3D shock-bubble interaction
Hejazialhosseini, Babak; Rossinelli, Diego; Koumoutsakos, Petros
2013-11-01
The dynamics of shock-bubble interaction involve an interplay of vortex stretching, dilation, and baroclinic vorticity generation. Here, we quantify the interplay of these contributions through high resolution 3D simulations for several Mach and Atwood numbers. We present a volume rendering of density and vorticity magnitude fields of shock-bubble interaction at M = 3 and air/helium density ratio η = 7.25 to elucidate the evolution of the flow structures. We distinguish the vorticity growth rates due to baroclinicity, stretching, and dilatation at low and high Mach numbers as well as the late time evolution of the circulation. The results demonstrate that a number of analytical models need to be revised in order to predict the late time circulation of shock-bubble interactions at high Mach numbers. To this effect, we propose a simple model for the dependence of the circulation to Mach number and ambient to bubble density ratio for air/helium shock-bubble interactions.
Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
Pfrommer, C; Ensslin, T A; Jubelgas, M; Pfrommer, Christoph; Springel, Volker; Ensslin, Torsten A.; Jubelgas, Martin
2006-01-01
We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks not only play a decisive role for the thermalization of gas in virialising structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. Our formalism is applicable both to ordinary non-relativistic thermal gas, and to plasmas composed of CRs and thermal gas. To this end, we derive an analytical solution to the one-dimensional Riemann shock tube problem for a composite plasma of CRs and thermal gas. We apply our methods to study the properties of structure formation shocks in high-resolution hydrodynamic simulations of the LCDM model. We find that most of the energy is dissipated in weak internal shocks with Mach numbers M~2 which are predominantly central flow shocks or merger shock waves traversing halo centres. Collapsed cosmological structures are surrounded by external ...
Transition to Double Mach Stem for Nuclear Explosion at 104 ft Height of Burst.
1981-11-17
intersecting the ground. The initialization provides a strong shock with Mach number MI = 12. This speed and the need for restart capability led to the choice...a HOB of 104 ft (31.7m). A strong spherical shock is created in the surrounding air, and’ reflects from the grcund. 9 The outward-traveling airbiast...AIR FCIPCF SYST T’M CCvfvtANC NORTON" A!7, CA 9?40Pg (MIIJ’r’-MAN) QICY ATTN "INNYH "D IALAN5S<Y 0O1C Y ATTNJ MMN)) eHM kF-LVECCHir OICY ATTN fuNN w
Pioneer 10 studies of interplanetary shocks at large heliocentric distances
Mihalov, J. D.; Wolfe, J. H.
1979-01-01
Pioneer 10 Ames plasma analyzer data collected in the 6.1 to 12.6 AU range of heliocentric distances (November 1974 to April 1977) have been examined for interplanetary shock waves. Eighteen shock signatures have been identified, with four of these being of the reverse type and the remainder the forward type. Sonic Mach numbers in the range from 3 to 10 are estimated for these events.
Ion-acoustic shocks with self-regulated ion reflection and acceleration
Malkov, M. A.; Sagdeev, R. Z.; Dudnikova, G. I.; Liseykina, T. V.; Diamond, P. H.; Papadopoulos, K.; Liu, C.-S.; Su, J. J.
2016-04-01
An analytic solution describing an ion-acoustic collisionless shock, self-consistently with the evolution of shock-reflected ions, is obtained. The solution extends the classic soliton solution beyond a critical Mach number, where the soliton ceases to exist because of the upstream ion reflection. The reflection transforms the soliton into a shock with a trailing wave and a foot populated by the reflected ions. The solution relates parameters of the entire shock structure, such as the maximum and minimum of the potential in the trailing wave, the height of the foot, as well as the shock Mach number, to the number of reflected ions. This relation is resolvable for any given distribution of the upstream ions. In this paper, we have resolved it for a simple "box" distribution. Two separate models of electron interaction with the shock are considered. The first model corresponds to the standard Boltzmannian electron distribution in which case the critical shock Mach number only insignificantly increases from M ≈1.6 (no ion reflection) to M ≈1.8 (substantial reflection). The second model corresponds to adiabatically trapped electrons. They produce a stronger increase, from M ≈3.1 to M ≈4.5 . The shock foot that is supported by the reflected ions also accelerates them somewhat further. A self-similar foot expansion into the upstream medium is described analytically.
Foda, Khaled; Abdeldaeim, Hussein; Youssif, Mohamed; Assem, Akram
2013-11-01
To define the parameters that accompanied a successful extracorporeal shock wave lithotripsy (ESWL), namely the number of shock waves (SWs), expulsion time (ET), mean stone density (MSD), and the skin-to-stone distance (SSD). A total of 368 patients diagnosed with renal calculi using noncontrast computerized tomography had their MSD, diameter, and SSD recorded. All patients were treated using a Siemens lithotripter. ESWL success meant a stone-free status or presence of residual fragments 934 HUs and SSD >99 mm. The required number of SWs and the expected ET can be anticipated. Copyright © 2013 Elsevier Inc. All rights reserved.
Numerical simulation of Mach reflection of cellular detonations
Li, J.; Lee, J. H. S.
2016-09-01
The Mach reflection of cellular detonation waves on a wedge is investigated numerically in an attempt to elucidate the effect of cellular instabilities on Mach reflection, the dependence of self-similarity on the thickness of a detonation wave, and the initial development of the Mach stem near the wedge apex. A two-step chain-branching reaction model is used to give a thermally neutral induction zone followed by a chemical reaction zone for the detonation wave. A sufficiently large distance of travel of the Mach stem is computed to observe the asymptotic behavior in the far field. Depending on the scale at which the Mach reflection process occurs, it is found that the Mach reflection of a cellular detonation behaves essentially in the same way as a planar ZND detonation wave. The cellular instabilities, however, cause the triple-point trajectory to fluctuate. The fluctuations are due to interactions of the triple point of the Mach stem with the transverse waves of cellular instabilities. In the vicinity of the wedge apex, the Mach reflection is found to be self-similar and corresponds to that of a shock wave of the same strength, since the Mach stem is highly overdriven initially. In the far field, the triple-point trajectory approaches a straight line, indicating that the Mach reflection becomes self-similar asymptotically. The distance of the approach to self-similarity is found to decrease rapidly with decreasing thickness of the detonation front.
Mitchell, Glenn A; Campbell, Robert C
1957-01-01
Provided sufficient throat bleed was employed, maximum pressure recoveries of 0.87 to 0.88 at Mach number 2.0 were obtained for a fuselage-mounted 14 degrees ramp inlet regardless of the amount of fuselage boundary layer ingested. The addition of inlet side fairings yielded further increases in pressure recovery to 0.90 to 0.91, decreased critical drag coefficients, and increased critical mass-flow ratios. With throat bleed, peak pressure recoveries and calculated thrust-minus-drag values were comparable at two axial positions of the scoop and were highest with the greatest amount of fuselage boundary layer ingested.
Relativistic electrons produced by foreshock disturbances observed upstream of the Earth's bow shock
Wilson, Lynn Bruce, III; Sibeck, David G.; Turner, Drew L.; Osmane, Adnane; Caprioli, Damiano; Angelopoulos, Vassilis
2017-04-01
It has been known for years that charged particles can be accelerated by high Mach number collisionless shock waves. The accelerated particles can stream away upstream to form a foreshock region in communication with the shock. Due to differences in gyroradii, ions are more readily accelerated than electrons by collisionless shocks. These energetic, suprathermal ions stream against the incident flow providing free energy that can generate foreshock disturbances - large-scale (i.e., tens to thousands of thermal ion gyroradii), transient ( 5-10 per day) structures. They have recently been found to accelerate ions to energies of several keV [e.g., Wilson et al., 2013] and even produce their own mini foreshocks [e.g., Liu et al., 2016]. While the high Mach number (M > 40) Kronian bow shock can generate MeV electrons [e.g., Masters et al., 2013], the much weaker Earth's bow shock (1 ≤ M questions in heliospheric and astrophysical plasmas.
Energy Technology Data Exchange (ETDEWEB)
Sanna, G.; Tomassetti, G. [L`Aquila Univ. (Italy). Dipt. di Fisica
1998-02-01
The discontinuities in the flow fields (both tangential and shocks) are considered and the equations for the quantities conserved across them are written. The post-shock flow variables are expressed by the Mach number of the incident supersonic flow and its deflection angle operated by rigid wall. Normal and oblique shocks are considered and graphs and polar diagrams are introduced. Then the reflections of a shock wave operated by a rigid wall and by the boundary between a jet and a stagnating gas are analyzed. Finally, the interactions between two distinct shock waves are considered. [Italiano] Vengono considerate le discontinuita` (tangenziali e shocks) nei campi di flusso e sono scritte le equazioni per le quantita` che si conservano attraverso di esse. Le variabili del flusso oltre lo shock sono espresse in funzione del numero di Mach del flusso supersonico incidente e dell`angolo di deflessione di questo operato da una parete rigida. I casi di shock normale, obliquo e distaccato sono considerati e sono introdotti grafici vari e rappresentazioni polari. Sono quindi considerate le riflessioni di un fronte di shock da una parete rigida e dalla frontiera tra un gas in moto ed uno stagnante. Sono infine considerate le diverse interazioni tra due shock distinti.
A shock front at the radio relic of Abell 2744
Eckert, D.; Jauzac, M.; Vazza, F.; Owers, M. S.; Kneib, J.-P.; Tchernin, C.; Intema, H.; Knowles, K.
2016-09-01
Radio relics are Mpc-scale diffuse radio sources at the peripheries of galaxy clusters which are thought to trace outgoing merger shocks. We present XMM-Newton and Suzaku observations of the galaxy cluster Abell 2744 (z = 0.306), which reveal the presence of a shock front 1.5 Mpc east of the cluster core. The surface-brightness jump coincides with the position of a known radio relic. Although the surface-brightness jump indicates a weak shock with a Mach number M=1.7_{-0.3}^{+0.5}, the plasma in the post-shock region has been heated to a very high temperature (˜13 keV) by the passage of the shock wave. The low-acceleration efficiency expected from such a weak shock suggests that mildly relativistic electrons have been re-accelerated by the passage of the shock front.
Curved Radio Spectra of Weak Cluster Shocks
Kang, Hyesung
2015-01-01
We explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock impinges on a magnetized cloud of fossil relativistic electrons in the cluster periphery. Such a scenario could explain uniformity of the surface brightness and spectral curvature in the integrated spectra of thin arc-like radio relics. Toward this end, we perform DSA simulations of spherical shocks with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301, and calculate the ensuing radio synchrotron emission from re-accelerated electrons. The surface brightness profile of radio-emitting postshock region and the volume-integrated radio spectrum are calculated as well. We find that the observed width of the Sausage relic can be explained reasonably well by shocks with speed $u_s \\sim 3,000 \\kms$ and sonic Mach number $M_s \\sim 3$. These shocks produce curved radio spectra that steepen gradually over $(0.1-10) \
Simulations of Turbulent Flows with Strong Shocks and Density Variations
Energy Technology Data Exchange (ETDEWEB)
Zhong, Xiaolin
2012-12-13
In this report, we present the research efforts made by our group at UCLA in the SciDAC project Simulations of turbulent flows with strong shocks and density variations. We use shock-fitting methodologies as an alternative to shock-capturing schemes for the problems where a well defined shock is present. In past five years, we have focused on development of high-order shock-fitting Navier-Stokes solvers for perfect gas flow and thermochemical non-equilibrium flow and simulation of shock-turbulence interaction physics for very strong shocks. Such simulation has not been possible before because the limitation of conventional shock capturing methods. The limitation of shock Mach number is removed by using our high-order shock-fitting scheme. With the help of DOE and TeraGrid/XSEDE super computing resources, we have obtained new results which show new trends of turbulence statistics behind the shock which were not known before. Moreover, we are also developing tools to consider multi-species non-equilibrium flows. The main results are in three areas: (1) development of high-order shock-fitting scheme for perfect gas flow, (2) Direct Numerical Simulation (DNS) of interaction of realistic turbulence with moderate to very strong shocks using super computing resources, and (3) development and implementation of models for computation of mutli-species non-quilibrium flows with shock-fitting codes.
Experimental investigation of the shock-induced distortion of a spherical gas inhomogeneity
Ranjan, Devesh
In a high load capability vertical shock tube, a series of experiments have been carried out to characterize the interaction of a planar shock wave with discrete gas inhomogeneities. Eleven scenarios have been considered covering the Atwood (A) and Mach (M) number ranges -0.8 soap bubble. The shock wave strength, leading to a post-shock compressible regime, allows the study of instability development in an intermediary regime between low Mach number shock tube experiments and high Mach number laser-driven experiments that has not been investigated previously. Flow visualizations are obtained using planar laser diagnostics. The imaging technique used here takes advantage of the atomization of the liquid bubble film by the incident shock wave, and up to five shocked bubble images are captured per run, enhancing the investigation of the evolution of the instability during a single experiment. Quantitative analyses of the experimental data include the vortex velocity, and subsequent circulation calculations, along with a new set of relevant geometrical length scales. As the planar shock passes over the bubble, intense vortical and nonlinear acoustic phenomena are observed, including vortex ring formation, mixing, and growth of turbulence-like features. At late-times, experimental images show the presence of secondary features in the flow field at high Mach numbers, some of which were predicted previously but, until now, not confirmed experimentally. In the case of a low Atwood number, the late time flow field is dominated by coherent vortical structures while, in the case of a high Atwood number, the shocked bubble is effectively reduced to a small core of compressed fluid, which trails behind a plume-like structure indicative of a well-developed mixing region. Dimensionless analysis of trends in the bubble length scales and other features shows that no universal timescale exists, but for each feature, a unique velocity scale is appropriate as a basis for timescaling
Ernst Mach a deeper look : documents and new perspectives
1992-01-01
Ernst Mach -- A Deeper Look has been written to reveal to English-speaking readers the recent revival of interest in Ernst Mach in Europe and Japan. The book is a storehouse of new information on Mach as a philosopher, historian, scientist and person, containing a number of biographical and philosophical manuscripts publihsed for the first time, along with correspondence and other matters published for the first time in English. The book also provides English translations of Mach's controversies with leading physicists and psychologists, such as Max Planck and Carl Stumpf, and offers basic evidence for resolving Mach's position on atomism and Einstein's theory of relativity. Mach's scientific, philosophical and personal influence in a number of countries -- Austria, Germany, Bohemia and Yugoslavia among them -- has been carefully explored and many aspects detailed for the first time. All of the articles are eminently readable, especially those written by Mach's sister. They are deeply researched, new interpre...
Directory of Open Access Journals (Sweden)
Qian Wan
2015-04-01
Full Text Available Research on shock wave mitigation in channels has been a topic of much attention in the shock wave community. One approach to attenuate an incident shock wave is to use obstacles of various geometries arranged in different patterns. This work is inspired by the study from Chaudhuri et al. (2013, in which cylinders, squares and triangles placed in staggered and non-staggered subsequent columns were used to attenuate a planar incident shock wave. Here, we present numerical simulations using a different obstacle pattern. Instead of using a matrix of obstacles, an arrangement of square or cylindrical obstacles placed along a logarithmic spiral curve is investigated, which is motivated by our previous work on shock focusing using logarithmic spirals. Results show that obstacles placed along a logarithmic spiral can delay both the transmitted and the reflected shock wave. For different incident shock Mach numbers, away from the logarithmic spiral design Mach number, this shape is effective to either delay the transmitted or the reflected shock wave. Results also confirm that the degree of attenuation depends on the obstacle shape, effective flow area and obstacle arrangement, much like other obstacle configurations.
Ion-acoustic Shocks with Self-Regulated Ion Reflection and Acceleration
Malkov, M A; Dudnikova, G I; Liseykina, T V; Diamond, P H; Papadopoulos, K; Liu, C-S; Su, J-J
2015-01-01
An analytic solution describing an ion-acoustic collisionless shock, self-consistently with the evolution of shock-reflected ions, is obtained. The solution extends the classic soliton solution beyond a critical Mach number, where the soliton ceases to exist because of the upstream ion reflection. The reflection transforms the soliton into a shock with a trailing wave and a foot populated by the reflected ions. The solution relates parameters of the entire shock structure, such as the maximum and minimum of the potential in the trailing wave, the height of the foot, as well as the shock Mach number, to the number of reflected ions. This relation is resolvable for any given distribution of the upstream ions. In this paper, we have resolved it for a simple "box" distribution. Two separate models of electron interaction with the shock are considered. The first model corresponds to the standard Boltzmannian electron distribution in which case the critical shock Mach number only insignificantly increases from M=1....
Moes, Timothy R.; Whitmore, Stephen A.; Jordan, Frank L., Jr.
1993-01-01
A nonintrusive airdata-sensing system was calibrated in flight and wind-tunnel experiments to an angle of attack of 70 deg and to angles of sideslip of +/- 15 deg. Flight-calibration data have also been obtained to Mach 1.2. The sensor, known as the flush airdata sensor, was installed on the nosecap of an F-18 aircraft for flight tests and on a full-scale F-18 forebody for wind-tunnel tests. Flight tests occurred at the NASA Dryden Flight Research Facility, Edwards, California, using the F-18 High Alpha Research Vehicle. Wind-tunnel tests were conducted in the 30- by 60-ft wind tunnel at the NASA LaRC, Hampton, Virginia. The sensor consisted of 23 flush-mounted pressure ports arranged in concentric circles and located within 1.75 in. of the tip of the nosecap. An overdetermined mathematical model was used to relate the pressure measurements to the local airdata quantities. The mathematical model was based on potential flow over a sphere and was empirically adjusted based on flight and wind-tunnel data. For quasi-steady maneuvering, the mathematical model worked well throughout the subsonic, transonic, and low supersonic flight regimes. The model also worked well throughout the angles-of-attack and -sideslip regions studied.
Hunt, L. Roane; Notestine, Kristopher K.
1990-06-01
Surface and gap pressures and heating-rate distributions were obtained for simulated Thermal Protection System (TPS) tile arrays on the curved surface test apparatus of the Langley 8-Foot High Temperature Tunnel at Mach 6.6. The results indicated that the chine gap pressures varied inversely with gap width because larger gap widths allowed greater venting from the gap to the lower model side pressures. Lower gap pressures caused greater flow ingress from the surface and increased gap heating. Generally, gap heating was greater in the longitudinal gaps than in the circumferential gaps. Gap heating decreased with increasing gap depth. Circumferential gap heating at the mid-depth was generally less than about 10 percent of the external surface value. Gap heating was most severe at local T-gap junctions and tile-to-tile forward-facing steps that caused the greatest heating from flow impingement. The use of flow stoppers at discrete locations reduced heating from flow impingement. The use of flow stoppers at discrete locations reduced heating in most gaps but increased heating in others. Limited use of flow stoppers or gap filler in longitudinal gaps could reduce gap heating in open circumferential gaps in regions of high surface pressure gradients.
Viscous solution of the triple shock reflection problem
Lau-Chapdelaine, S She-Ming
2016-01-01
The reflection of a triple-shock configuration was studied numerically in two dimensions using the Navier-Stokes equations. The flow field was initialized using three shock theory, and the reflection of the triple point on a plane of symmetry was studied. The conditions simulated a stoichiometric methane-oxygen detonation cell at low pressure on time scales preceding ignition, when the gas was assumed to be thermodynamically inert. Viscosity was found to play an important role on some shock reflection mechanisms believed to accelerate reaction rates in detonations where time scales are small. A small wall jet was present in the double Mach reflection and increased in size with Reynolds number, eventually forming a small vortex. Kelvin-Helmholtz instabilities were absent and there was no Mach stem bifurcation at Reynolds numbers corresponding to and exceeding the induction length. Kelvin-Helmholtz instabilities are unlikely to be a source of rapid reactions in detonations at time scales commensurate with the i...
Subgrid-scale backscatter after the shock-turbulence interaction
Livescu, Daniel; Li, Zhaorui
2017-01-01
The statistics of the subgrid scales (SGS) are studied in the context of Large Eddy Simulations (LES) of turbulence after the interaction with a nominally normal shock wave. In general, in practical applications, the shock wave width is much smaller than the turbulence scales and the upstream turbulent Mach number is modest. In this case, recent high resolution shock-resolved Direct Numerical Simulations (DNS) (Ryu and Livescu, J. Fluid Mech., 756, R1, 2014) show that the interaction can be described by the Linear Interaction Approximation (LIA). By using LIA to alleviate the need to resolve the shock wave, DNS post-shock data can be generated at much higher Reynolds numbers than previously possible. Here, such results with Taylor Reynolds number ≈ 180 are used for an analysis of the SGS backscatter properties. In particular, it is shown that the interaction with the shock wave decreases the asymmetry of the SGS dissipation Probability Density Function (PDF) as the shock Mach number increases, with a significant enhancement in size of the regions and magnitude of backscatter.
Waves near interplanetary shocks observed by STEREO
Aguilar-Rodriguez, E.; Blanco-Cano, X.; Russell, C. T.; Luhmann, J. G.; Krauss-Varban, D.
2007-12-01
We investigate the properties of interplanetary shocks that form ahead of virtually all fast propagating coronal mass ejections (CMEs). Understanding the characteristics of these shocks and their surrounding regions is of great interest as they play a major role in the acceleration of solar energetic particles (SEPs). In this work we study low frequency waves upstream and downstream of interplanetary shocks (IP) observed by the twin spacecraft mission STEREO. In the upstream region waves can be generated by ion beams reflected or otherwise energized at the shock. Downstream the wave spectrum may be formed by both, waves generated locally and waves transmitted through the shock.The efficiency of wave generation and wave convection to the shock depends on the shock Mach number, and the angle between the IMF and the shock normal. Waves can disturb the shock and participate in ion acceleration processes. Multi-point STEREO measurements will allow us to study wave characteristics in different regions near IP shocks and determine the effects that these fluctuations have on particle energization.
Planar shock wave sliding over a water layer
Rodriguez, V.; Jourdan, G.; Marty, A.; Allou, A.; Parisse, J.-D.
2016-08-01
In this work, we conduct experiments to study the interaction between a horizontal free water layer and a planar shock wave that is sliding over it. Experiments are performed at atmospheric pressure in a shock tube with a square cross section (200× 200 mm^2) for depths of 10, 20, and 30 mm; a 1500-mm-long water layer; and two incident planar shock waves having Mach numbers of 1.11 and 1.43. We record the pressure histories and high-speed visualizations to study the flow patterns, surface waves, and spray layers behind the shock wave. We observe two different flow patterns with ripples formed at the air-water interface for the weaker shock wave and the dispersion of a droplet mist for the stronger shock wave. From the pressure signals, we extract the delay time between the arrival of the compression wave into water and the shock wave in air at the same location. We show that the delay time evolves with the distance traveled over the water layer, the depth of the water layer, and the Mach number of the shock wave.
Kamath, Pradeep S.; Holden, Michael S.; Mcclinton, Charles R.
1990-01-01
This paper presents results from a study conducted to investigate the effect of incident oblique shocks on the effectiveness of a coolant film at Mach numbers, typical of those expected in a scramjet combustor at Mach 15 to 20 flight. Computations with a parabolic code are in good agreement with the measured pressures and heat fluxes, after accounting for the influence of the shock upstream of its point of impingement on the plate, and the expansion from the trailing edge of the shock generator. The test data shows that, for the blowing rates tested, the film is rendered largely ineffective by the shock. Computations show that coolant blowing rates five to ten times those tested are required to protect against shock-induced heating. The implications of the results to scramjet combustor design are discussed.
Energy Technology Data Exchange (ETDEWEB)
Ansanay-Alex, G.
2009-06-17
The development of simulation codes aimed at a precise simulation of fires requires a precise approach of flame front phenomena by using very fine grids. The need to take different spatial scale into consideration leads to a local grid refinement and to a discretization with homogeneous grid for computing time and memory purposes. The author reports the approximation of the non-linear convection term, the scalar advection-diffusion in finite volumes, numerical simulations of a flow in a bent tube, of a three-dimensional laminar flame and of a low Mach number an-isotherm flow. Non conformal finite elements are also presented (Rannacher-Turek and Crouzeix-Raviart elements)
Capone, F. J.
1972-01-01
An exploratory investigation was conducted in the Langley 16-foot transonic tunnel at Mach numbers from 0.20 to 1.30 to determine the induced lift characteristics of a body and swept-wing configuration having a partial-span two-dimensional propulsive nozzle with exhaust exit in the notch of the swept-wing trailing edge. The Reynolds number per meter varied from 4,900,000 to 14,030,000. The effects on wing-body characteristics of deflecting the propulsive jet in the flap mode at nominal exhaust-nozzle deflection angles of 0 deg and 30 deg were studied for two nozzle designs with different geometry and wing spans.
A pneumatic driver for shock wave production
Leftwich, Megan; Mejila-Alvarez, R.; Prestridge, K.
2011-11-01
We are presenting a novel technique to generate shock waves in shock tube experiments. Typically this is done with a high pressure driver section that is separated from the low pressure driven section by a physical membrane. The membrane is burst at a specific pressure and a shock wave is formed. This process limits the repetition of experiments, and membrane particles must be removed from the shock tube after each experiment. The driver presented here does not contain a membrane. Instead, it uses a series of high pressure chambers and fast-acting pistons to create the pressure jump between the high pressure driver section and low pressure driven section. The entire system is controlled remotely and requires no insertion or cleanup of membranes between experiments. The system is designed to achieve shock waves exceeding Mach 3 with air as the working fluid (higher Mach numbers can be generated with other working fluids). It will allow high repetition rates, even in challenging experimental environments (such as a vertical shock tube configuration). We present results from the initial characterization of this driver system.
Quantification of initial-data uncertainty on a shock-accelerated gas cylinder
Energy Technology Data Exchange (ETDEWEB)
Tritschler, V. K., E-mail: volker.tritschler@aer.mw.tum.de; Avdonin, A.; Hickel, S.; Hu, X. Y.; Adams, N. A. [Institute of Aerodynamics and Fluid Mechanics, Technische Universität München, 85747 Garching (Germany)
2014-02-15
We quantify initial-data uncertainties on a shock accelerated heavy-gas cylinder by two-dimensional well-resolved direct numerical simulations. A high-resolution compressible multicomponent flow simulation model is coupled with a polynomial chaos expansion to propagate the initial-data uncertainties to the output quantities of interest. The initial flow configuration follows previous experimental and numerical works of the shock accelerated heavy-gas cylinder. We investigate three main initial-data uncertainties, (i) shock Mach number, (ii) contamination of SF{sub 6} with acetone, and (iii) initial deviations of the heavy-gas region from a perfect cylindrical shape. The impact of initial-data uncertainties on the mixing process is examined. The results suggest that the mixing process is highly sensitive to input variations of shock Mach number and acetone contamination. Additionally, our results indicate that the measured shock Mach number in the experiment of Tomkins et al. [“An experimental investigation of mixing mechanisms in shock-accelerated flow,” J. Fluid. Mech. 611, 131 (2008)] and the estimated contamination of the SF{sub 6} region with acetone [S. K. Shankar, S. Kawai, and S. K. Lele, “Two-dimensional viscous flow simulation of a shock accelerated heavy gas cylinder,” Phys. Fluids 23, 024102 (2011)] exhibit deviations from those that lead to best agreement between our simulations and the experiment in terms of overall flow evolution.
Shock finding on a moving-mesh - II. Hydrodynamic shocks in the Illustris universe
Schaal, Kevin; Springel, Volker; Pakmor, Rüdiger; Pfrommer, Christoph; Nelson, Dylan; Vogelsberger, Mark; Genel, Shy; Pillepich, Annalisa; Sijacki, Debora; Hernquist, Lars
2016-10-01
Hydrodynamical shocks are a manifestation of the non-linearity of the Euler equations and play a fundamental role in cosmological gas dynamics. In this work, we identify and analyse shocks in the Illustris simulation, and contrast the results with those of non-radiative runs. We show that simulations with more comprehensive physical models of galaxy formation pose new challenges for shock finding algorithms due to radiative cooling and star-forming processes, prompting us to develop a number of methodology improvements. We find in Illustris a total shock surface area which is about 1.4 times larger at the present epoch compared to non-radiative runs, and an energy dissipation rate at shocks which is higher by a factor of around 7. Remarkably, shocks with Mach numbers above and below mathcal {M}≈ 10 contribute about equally to the total dissipation across cosmic time. This is in sharp contrast to non-radiative simulations, and we demonstrate that a large part of the difference arises due to strong black hole radio-mode feedback in Illustris. We also provide an overview of the large diversity of shock morphologies, which includes complex networks of halo-internal shocks, shocks on to cosmic sheets, feedback shocks due to black holes and galactic winds, as well as ubiquitous accretion shocks. In high-redshift systems more massive than 1012 M⊙, we discover the existence of a double accretion shock pattern in haloes. They are created when gas streams along filaments without being shocked at the outer accretion shock, but then forms a second, roughly spherical accretion shock further inside.
On the electron-ion temperature ratio established by collisionless shocks
Vink, Jacco; Broersen, Sjors; Bykov, Andrei; Gabici, Stefano
2015-07-01
Astrophysical shocks are often collisionless shocks, in which the changes in plasma flow and temperatures across the shock are established not through Coulomb interactions, but through electric and magnetic fields. An open question about collisionless shocks is whether electrons and ions each establish their own post-shock temperature (non-equilibration of temperatures), or whether they quickly equilibrate in the shock region. Here we provide a simple, thermodynamic, relation for the minimum electron-ion temperature ratios that should be expected as a function of Mach number. The basic assumption is that the enthalpy-flux of the electrons is conserved separately, but that all particle species should undergo the same density jump across the shock, in order for the plasma to remain charge neutral. The only form of additional electron heating that we allow for is adiabatic heating, caused by the compression of the electron gas. These assumptions result in an analytic treatment of expected electron-ion temperature ratio that agrees with observations of collisionless shocks: at low sonic Mach numbers, Ms ≲ 2, the electron-ion temperature ratio is close to unity, whereas for Mach numbers above Ms ≈ 60 the electron-ion temperature ratio asymptotically approaches a temperature ratio of Te/Ti = me/ ⟨ mi ⟩. In the intermediate Mach number range the electron-ion temperature ratio scales as Te/Ti ∝ Ms-2. In addition, we calculate the electron-ion temperature ratios under the assumption of adiabatic heating of the electrons only, which results in a higher electron-ion temperature ratio, but preserves the Te/Ti ∝ Ms-2 scaling. We also show that for magnetised shocks the electron-ion temperature ratio approaches the asymptotic value Te/Ti = me/ ⟨ mi ⟩ for lower magnetosonic Mach numbers (Mms), mainly because for a strongly magnetised shock the sonic Mach number is larger than the magnetosonic Mach number (Mms ≤ Ms). The predicted scaling of the electron
INTERFERENCE OF COUNTERPROPAGATING SHOCK WAVES
Directory of Open Access Journals (Sweden)
P. V. Bulat
2015-03-01
Full Text Available The subject of study. We examined the interaction of counterpropagating shock waves. The necessity of counterpropagating shock waves studying occurs at designing of high Mach number modern internal compression air intakes, Ramjets with subsonic and supersonic combustion, in asymmetrical supersonic nozzles and in some other cases. In a sense, this problem is a generalization of the case of an oblique shock reflection from the wall or from the plane of symmetry. With the renewed vigor, the interest to this problem emerged at the end of the 90s. This was due to the start of the programs for flight study at hypersonic speeds. The first experiments performed with air intakes, which realized the interaction of counterpropagating shock waves have shown that the change in flow velocity is accompanied by abrupt alteration of shock-wave structure, the occurrence of nonstationary and oscillatory phenomena. With an increase of flow velocity these phenomena undesirable for aircraft structure became more marked. The reason is that there are two fundamentally different modes of interaction of counterpropagating shock waves: a four-wave regular and a five-wave irregular. The transition from one mode to another can be nonstationary abrupt or gradual, it can also be accompanied by hysteresis. Main results. Criteria for the transition from regular reflection of counterpropagating shock waves to irregular are described: the criterion of von Neumann and the stationary Mach configuration criterion. We described areas in which the transition from one reflection type to another is possible only in abrupt way, as well as areas of possible gradual transition. Intensity dependences of the reflected shock waves from the intensity of interacting counterpropagating shocks were given. Qualitative pictures of shock-wave structures arising from the interaction of counterpropagating shock waves were shown. Calculation results of the intensity of outgoing gas
Free Piston Double Diaphragm Shock Tube
OGURA, Eiji; FUNABIKI, Katsushi; SATO, Shunichi; Abe, Takashi; 小倉, 栄二; 船曳, 勝之; 佐藤, 俊逸; 安部, 隆士
1997-01-01
A free piston double diaphragm shock tube was newly developed for generation of high Mach number shock wave. Its characteristics was investigated for various operation parameters; such as a strength of the diaphragm at the end of the comparession tube, an initial pressure of low pressure tube, an initial pressure of medium pressure tube and the volume of compression tube. Under the restriction of fixed pressures for the driver high pressure tube (32×10^5Pa) and the low pressure tube (40Pa) in...
Shock Wave Induced Separation Control by Streamwise Vortices
Institute of Scientific and Technical Information of China (English)
Ryszard SZWABA
2005-01-01
Control of shock wave and boundary layer interaction finds still a lot of attention. Methods of this interaction control have been especially investigated in recent decade. This research was mostly concerned with flows without separation. However, in many applications shock waves induce separation often leads to strong unsteady effects. In this context it is proposed to use streamwise vortices for the interaction control. The results of experimental investigations are presented here. The very promising results were obtained, meaning that the incipient separation was postponed and the separation size was reduced for the higher Mach numbers. The decrease of the RMS of average shock wave oscillation was also achieved.
Prandtl number effects in MRT lattice Boltzmann models for shocked and unshocked compressible fluids
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
This paper constructs a new multiple relaxation time lattice Boltzmann model which is not only for the shocked compressible fluids,but also for the unshocked compressible fluids.To make the model work for unshocked compressible fluids,a key step is to modify the collision operators of energy flux so that the viscous coefficient in momentum equation is consistent with that in energy equation even in the unshocked system.The unnecessity of the modification for systems under strong shock is analyzed.The model ...
Umeda, Takayuki; Matsukiyo, Shuichi; Yamazaki, Ryo
2012-01-01
A full particle simulation study is carried out for studying microinstabilities generated at the shock front of perpendicular collisionless shocks. The structure and dynamics of shock waves are determined by Alfven Mach number and plasma beta, while microinstabilities are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the plasma-to-cyclotron frequency. Thus, growth rates of microinstabilities are changed by the ion-to-electron mass ratio, even with the same Mach number and plasma beta. The present two-dimensional simulations show that the electron cyclotron drift instability is dominant for a lower mass ratio, and electrostatic electron cyclotron harmonic waves are excited. For a higher mass ratio, the modified two-stream instability is dominant and oblique electromagnetic whistler waves are excited, which can affect the structure and dynamics of collisionless shocks by modifying shock magnetic fields.
Chen, Chang-Hsin; Donzis, Diego
2016-11-01
Substantial efforts have been made to understand the canonical interaction between isotropic turbulence and a normal shock. Evidence from theories, experiments and simulations, however, has shown that the interaction is complex and that the outcome is determined not only by mean flow behavior, as suggested by early theories, but also by characteristics of turbulence fluctuations typically quantified by parameters such as the Reynolds (Rλ) and the turbulent Mach number (Mt). An important, yet unresolved, issue is the accurate determination of departures from Rankine-Hugoniot relations due to turbulent fluctuations upstream of the shock. We present an analytic study, based on the quasi-equilibrium assumption, that yield turbulent jumps that depend not only on the mean flow but also on turbulence characteristics. In particular, the focus will be on thermodynamic jumps. Our analytical results agree well with new shock-resolving simulations at a range of Reynolds and Mach numbers. In the context of these results we also present a comparison of previous theory on the dilatation at the shock with the new DNS data. This is further discussed in the context of the transition from wrinkled to broken regimes and the difficulties associated with identifying a shock for very vigorous turbulence. Support from AFOSR is gratefully acknowledged.
Unsteady flow with separation behind a shock wave diffracting over curved walls
Law, C.; Muritala, A. O.; Skews, B. W.
2014-05-01
The unsteady separation of the compressible flow field behind a diffracting shock wave was investigated along convex curved walls, using shock tube experimentation at large length and time scales, complemented by numerical computation. Tests were conducted at incident shock Mach numbers of 1.5 and 1.6 over a 100 mm radius wall over a dimensionless time range up to 6.45. The development of the near wall flow at 1.5 has been described in detail and is very similar to that observed for slightly lower 's at 1.6. Computations were performed at wall radii of 100 and 200 mm and for incident shock Mach numbers from 1.5 up to and including Mach 2.0. Comparing dimensionless times for different size walls shows that for a given value of the flow field is very similar for the various wall radii published to date and tested in this study. Previously published results that were examined alongside the results from this study had typical values of . At the later times presented here, flow features were observed that previously had only been observed at higher Mach numbers. The larger length scales allowed for a degree of Reynolds number independence in the results published here. The effect of turbulence on the numerical and experimental results could not be adequately examined due to limitations of the flow imaging system used and a number of questions remain unanswered.
Caprioli, Damiano
2014-01-01
We use large hybrid (kinetic ions-fluid electrons) simulations to study ion acceleration and generation of magnetic turbulence due to the streaming of energetic particles that are self-consistently accelerated at non-relativistic shocks. When acceleration is efficient (at quasi-parallel shocks), we find that the magnetic field develops transverse components and is significantly amplified in the pre-shock medium. The total amplification factor is larger than 10 for shocks with Mach number $M=100$, and scales with the square root of $M$. We find that in the shock precursor the energy spectral density of excited magnetic turbulence is proportional to spectral energy distribution of accelerated particles at corresponding resonant momenta, in good agreement with the predictions of quasilinear theory of diffusive shock acceleration. We discuss the role of Bell's instability, which is predicted and found to grow faster than resonant instability in shocks with $M\\gtrsim 30$. Ahead of these strong shocks we distinguis...
The properties and causes of rippling in quasi-perpendicular collisionless shock fronts
Directory of Open Access Journals (Sweden)
R. E. Lowe
Full Text Available The overall structure of quasi-perpendicular, high Mach number collisionless shocks is controlled to a large extent by ion reflection at the shock ramp. Departure from a strictly one-dimensional structure is indicated by simulation results showing that the surface of such shocks is rippled, with variations in the density and all field components. We present a detailed analysis of these shock ripples, using results from a two-dimensional hybrid (particle ions, electron fluid simulation. The process that generates the ripples is poorly understood, because the large gradients at the shock ramp make it difficult to identify instabilities. Our analysis reveals new features of the shock ripples, which suggest the presence of a surface wave mode dominating the shock normal magnetic field component of the ripples, as well as whistler waves excited by reflected ions.
Key words. Space plasma physics (numerical simulation studies; shock waves; waves and instabilities
Impact Angle Control of Interplanetary Shock Geoeffectiveness
Oliveira, D M
2015-01-01
We use OpenGGCM global MHD simulations to study the nightside magnetospheric, magnetotail, and ionospheric responses to interplanetary (IP) fa st forward shocks. Three cases are presented in this study: two inclined oblique shocks, here after IOS-1 and IOS-2, where the latter has a Mach number twice stronger than the former. Both shocks have impact angles of 30$^o$ in relation to the Sun-Earth line. Lastly, we choose a frontal perpendicular shock, FPS, whose shock normal is along the Sun-Earth line, with the same Mach number as IOS-1. We find that, in the IOS-1 case, due to the north-south asymmetry, the magnetotail is deflected southward, leading to a mild compression. The geomagnetic activity observed in the nightside ionosphere is then weak. On the other hand, in the head-on case, the FPS compresses the magnetotail from both sides symmetrically. This compression triggers a substorm allowing a larger amount of stored energy in the magnetotail to be released to the nightside ionosphere, resulting in stronger...
Zhao, X.
1992-01-01
We show that the 25 November 1978 shock pair was caused by the interaction of a fast steady flow with a slow coronal mass ejection in interplanetary space (ICME). It is suggested that the slow ICME may be disconnected from the sun. In addition, a new method to infer the shock angle and Mach number from the observed upstream plasma beta and the jump ratios of proton density and magnetic flux density across a shock is described.
Phillips, W. P.
1984-01-01
Aerodynamic characteristics at M=5.97 for the 140 A/B Space Shuttle Orbiter configuration and for the configuration modified by geometric changes in the wing planform fillet region and the fuselage forebody are presented. The modifications, designed to extend the orbiter's longitudinal trim capability to more forward center of gravity locations, include reshaping the baseline wing fillet, changing the fuselage forebody camber, and adding canards. The Langley 20 inch Mach 6 Tunnel at a Reynolds number of approximately 6 million based on fuselage reference length was used. The angle of attack range of the investigation varied from about 15 deg to 35 deg at 0 deg and -5 deg sideslip angles. Data are obtained with the elevators and body flap deflected at appropriate negative and positive conditions to assess the trim limits.
RADIO AND X-RAY SHOCKS IN CLUSTERS OF GALAXIES
Energy Technology Data Exchange (ETDEWEB)
Hong, Sungwook E. [School of Physics, Korea Institute for Advanced Study, Seoul 130-722 (Korea, Republic of); Kang, Hyesung [Department of Earth Sciences, Pusan National University, Busan 609-735 (Korea, Republic of); Ryu, Dongsu, E-mail: swhong@kias.re.kr, E-mail: hskang@pusan.ac.kr, E-mail: ryu@sirius.unist.ac.kr [Department of Physics, UNIST, Ulsan 689-798 (Korea, Republic of)
2015-10-10
Radio relics detected in the outskirts of galaxy clusters are thought to trace radio-emitting relativistic electrons accelerated at cosmological shocks. In this study, using the cosmological hydrodynamic simulation data for the large-scale structure formation and adopting a diffusive shock acceleration (DSA) model for the production of cosmic-ray (CR) electrons, we construct mock radio and X-ray maps of simulated galaxy clusters that are projected in the sky plane. Various properties of shocks and radio relics, including the shock Mach number, radio spectral index, and luminosity, are extracted from the synthetic maps and compared with observations. A substantial fraction of radio and X-ray shocks identified in these maps involve multiple shock surfaces along lines of sight (LOSs), and the morphology of shock distributions in the maps depends on the projection direction. Among multiple shocks in a given LOS, radio observations tend to pick up stronger shocks with flatter radio spectra, while X-ray observations preferentially select weaker shocks with larger kinetic energy flux. As a result, in some cases the shock Mach numbers and locations derived from radio and X-ray observations could differ from each other. We also find that the distributions of the spectral index and radio power of the synthetic radio relics are somewhat inconsistent with those of observed real relics; a bit more radio relics have been observed closer to the cluster core and with steeper spectral indices. We suggest that the inconsistency could be explained if very weak shocks with M{sub s} ≲ 2 accelerate CR electrons more efficiently, compared with the DSA model adopted here.
Jump Conditions of a Non-Neutral Plasma Shock with Current and Potential Difference
Institute of Scientific and Technical Information of China (English)
胡希伟
2002-01-01
Jump conditions about the total momentum flux and energy flux in a non-neutral plasma shock with electric current and field are given, which are derived from the double fluid equations and the Poisson equation for electron and ion fluids. Furthermore, we derive the relations between the upstream and downstream velocities and temperatures, and the minimum upstream Mach number for the plasma shock existence M1min, which depend on the current through the shock front J0, the electric potential difference between the upstream and downstream of shock △φ, and the ion charge Z.
A Theoretic Model for the Shock Observed in Geo-space
Institute of Scientific and Technical Information of China (English)
SHI Jian-Kui; WANG Xiao; ZHANG Tie-Long; Torkar Klaus; LIU Zhen-Xing
2005-01-01
An electrostatic model for the shock observed in the earth's polar region is established by deriving the "Sagdeev potential" from the magnetohydrodynamic equations in a cylindrical coordinate system. The results show that the shock can develop from the ion acoustic wave or ion cyclotron wave. in the polar region, and can exist when the Mach number M and the initial electric field E0 satisfy the condition of |(a/M2 - 1) E0| = 1. Also, some features of the shock wave are discussed. The result can interpret the electrostatic shock observed in the earth's polar region.
Anderson, B. H.; Bowditch, D. N.
1958-01-01
Investigation of the control parameters of an external-internal compression inlet indicates that the cowl-lip shock provides a signal to position the spike and to start the inlet over a Mach number range from 2.1 to 3.0. Use of a single fixed probe position to control the spike over the range of conditions resulted in a 3.7-count loss in total-pressure recovery at Mach 3.0 and 0 deg angle of attack. Three separate shock-sensing-probe positions were required to set the spike for peak recovery from Mach 2.1 to 3.0 and angles of attack from 0 deg to 6 deg. When the inlet was unstarted, an erroneous signal was obtained from the normal-shock control through most of the starting cycle that prevented the inlet from starting. Therefore, it was necessary to over-ride the normal-shock control signal and not allow the control to position the terminal shock until the spike was positioned.
A non-diaphragm type small shock tube for application to a molecular beam source.
Yoshimoto, Yuta; Osuka, Kenichi; Miyoshi, Nobuya; Kinefuchi, Ikuya; Takagi, Shu; Matsumoto, Yoichiro
2013-07-01
A non-diaphragm type small shock tube was developed for application to a molecular beam source, which can generate beams in the energy range from 1 to several electron volts and beams containing dissociated species such as atomic oxygen. Since repetitive high-frequency operation is indispensable for rapid signal acquisition in beam scattering experiments, the dimensions of the shock tube were miniaturized to reduce the evacuation time between shots. The designed shock tube is 2-4 mm in diameter and can operate at 0.5 Hz. Moreover, a high shock Mach number at the tube end is required for high-energy molecular beam generation. To reduce the shock attenuation caused by the wall boundary layer, which becomes significant in small-diameter tubes, we developed a high-speed response valve employing the current-loop mechanism. The response time of this mechanism is about 100 μs, which is shorter than the rupture time of conventional diaphragms. We show that the current-loop valve generates shock waves with shorter formation distances (about 200-300 mm) than those of conventional shock tubes. In addition, the converging geometry efficiently accelerates shock wave in the small-diameter tubes. The optimal geometry of the shock tube yields shock Mach number around 7, which indicates that the translation energy of molecular beams can exceed 1 eV even in the presence of the real gas effect.
Viscous solution of the triple-shock reflection problem
Lau-Chapdelaine, S. S.-M.; Radulescu, M. I.
2016-09-01
The reflection of a triple-shock configuration was studied numerically in two dimensions using the Navier-Stokes equations. The flow field was initialized using three shock theory, and the reflection of the triple point on a plane of symmetry was studied. The conditions simulated a stoichiometric methane-oxygen detonation cell at low pressure on time scales preceding ignition when the gas was assumed to be inert. Viscosity was found to play an important role on some shock reflection mechanisms believed to accelerate reaction rates in detonations when time scales are small. A small wall jet was present in the double Mach reflection and increased in size with Reynolds number, eventually forming a small vortex. Kelvin-Helmholtz instabilities were absent, and there was no Mach stem bifurcation at Reynolds numbers corresponding to when the Mach stem had travelled distances on the scale of the induction length. Kelvin-Helmholtz instabilities are found to not likely be a source of rapid reactions in detonations at time scales commensurate with the ignition delay behind the Mach stem.
Theoretical Investigation of 3-D Shock Wave Turbulent Boundary Layer Interactions.
1996-09-18
development of a Reynolds Stress Equation ( RSE ) model (including determination of all constants), and computation of 3-D asymmetric and symmetric...shock interactions at Mach 4 using Chien’s k - epsilon turbulence model, the RSE model and the k - epsilon model with the new low Reynolds number
Effect of air jet vortex generators on a shock wave boundary layer interaction
Souverein, L.J.; Debiève, J.-F.
2010-01-01
The effect of upstream injection by means of continuous air jet vortex generators (AJVGs) on a shock wave turbulent boundary layer interaction is experimentally investigated. The baseline interaction is of the impinging type, with a flow deflection angle of 9.5degrees and a Mach number Me = 2.3. Con
Effect on a shock wave boundary layer interaction of air jet vortex generators
Souverein, L.J.; Debieve, J.F.
2013-01-01
The effect of upstream injection by means of continuous Air Jet Vortex Generators (AJVGs) on a shock wave turbulent boundary layer interaction is experimentally investigated. The baseline interaction is of the impinging type, with a flow deflection angle of 9.5◦, a Mach number Me = 2.3, and a moment
Reflection of curved shock waves
Mölder, S.
2017-03-01
Shock curvatures are related to pressure gradients, streamline curvatures and vorticity in flows with planar and axial symmetry. Explicit expressions, in an influence coefficient format, are used to relate post-shock pressure gradient, streamline curvature and vorticity to pre-shock gradients and shock curvature in steady flow. Using higher order, von Neumann-type, compatibility conditions, curved shock theory is applied to calculate the flow near singly and doubly curved shocks on curved surfaces, in regular shock reflection and in Mach reflection. Theoretical curved shock shapes are in good agreement with computational fluid dynamics calculations and experiment.
Reflection of curved shock waves
Mölder, S.
2017-09-01
Shock curvatures are related to pressure gradients, streamline curvatures and vorticity in flows with planar and axial symmetry. Explicit expressions, in an influence coefficient format, are used to relate post-shock pressure gradient, streamline curvature and vorticity to pre-shock gradients and shock curvature in steady flow. Using higher order, von Neumann-type, compatibility conditions, curved shock theory is applied to calculate the flow near singly and doubly curved shocks on curved surfaces, in regular shock reflection and in Mach reflection. Theoretical curved shock shapes are in good agreement with computational fluid dynamics calculations and experiment.
Shock Wave-Boundary Layer Interaction in Forced Shock Oscillations
Institute of Scientific and Technical Information of China (English)
Piotr Doerffer; Oskar Szulc; Franco Magagnato
2003-01-01
The flow in transonic diffusers as well as in supersonic air intakes becomes often unsteady due to shock wave boundary layer interaction. The oscillations may be induced by natural separation unsteadiness or may be forced by boundary conditions. Significant improvement of CFD tools, increase of computer resources as well as development of experimental methods have again.drawn the attention of researchers to this topic.To investigate the problem forced oscillations of transonic turbulent flow in asymmetric two-dimensional Laval nozzle were considered. A viscous, perfect gas flow, was numerically simulated using the Reynolds-averaged compressible Navier-Stokes solver SPARC, employing a two-equation, eddy viscosity, turbulence closure in the URANS approach.For time-dependent and stationary flow simulations, Mach numbers upstream of the shock between 1.2 and 1.4 were considered. Comparison of computed and experimental data for steady states generally gave acceptable agreement. In the case of forced oscillations, a harmonic pressure variation was prescribed at the exit plane resulting in shock wave motion. Excitation frequencies between 0 Hz and 1024 Hz were investigated at the same pressure amplitude.The main result of the work carried out is the relation between the amplitude of the shock wave motion and the excitation frequency in the investigated range. Increasing excitation frequency resulted in decreasing amplitude of the shock movement. At high frequencies a natural mode of shock oscillation (of small amplitude) was observed which is not sensitive to forced excitement.
Pfyl, Frank A.; Presley, Leroy L.
1961-01-01
The local recovery factor was determined experimentally along the surface of a thin-walled 20 deg included angle cone for Mach numbers near 6.0 at stagnation temperatures between 1200 deg R and 2600 deg R. In addition, a similar cone configuration was tested at Mach numbers near 4.5 at stagnation temperatures of approximately 612 deg R. The local Reynolds number based on flow properties at the edge of the boundary layer ranged between 0.1 x 10(exp 4) and 3.5 x 10(exp 4) for tests at temperatures above 1200 deg R and between 6 x 10(exp 4) and 25 x 10(exp 4) for tests at temperatures near 612 deg R. The results indicated, generally, that the recovery factor can be predicted satisfactorily using the square root of the Prandtl number. No conclusion could be made as to the necessity of evaluating the Prandtl number at a reference temperature given by an empirical equation, as opposed to evaluating the Prandtl number at the wall temperature or static temperature of the gas at the cone surface. For the tests at temperatures above 1200 deg R (indicated herein as the tests conducted in the slip-flow region), two definite trends in the recovery data were observed - one of increasing recovery factor with decreasing stagnation pressure, which was associated with slip-flow effects and one of decreasing recovery factor with increasing temperature. The true cause of the latter trend could not be ascertained, but it was shown that this trend was not appreciably altered by the sources of error of the magnitude considered herein. The real-gas equations of state were used to determine accurately the local stream properties at the outer edge of the boundary layer of the cone. Included in the report, therefore, is a general solution for the conical flow of a real gas using the Beattie-Bridgeman equation of state. The largest effect of temperature was seen to be in the terms which were dependent upon the internal energy of the gas. The pressure and hence the pressure drag terms were
McMIllin, S. Naomi; Byrd, James E.; Parmar, Devendra S.; Bezos-O'Connor, Gaudy M.; Forrest, Dana K.; Bowen, Susan
1996-01-01
An experimental investigation of the effect of leading-edge radius, camber, Reynolds number, and boundary-layer state on the incipient separation of a delta wing at supersonic speeds was conducted at the Langley Unitary Plan Wind Tunnel at Mach number of 1.60 over a free-stream Reynolds number range of 1 x 106 to 5 x 106 ft-1. The three delta wing models examined had a 65 deg swept leading edge and varied in cross-sectional shape: a sharp wedge, a 20:1 ellipse, and a 20:1 ellipse with a -9.750 circular camber imposed across the span. The wings were tested with and without transition grit applied. Surface-pressure coefficient data and flow-visualization data are electronically stored on the CD-ROM. The data indicated that by rounding the wing leading edge or cambering the wing in the spanwise direction, the onset of leading-edge separation on a delta wing can be raised to a higher angle of attack than that observed on a sharp-edged delta wing. The data also showed that the onset of leading-edge separation can be raised to a higher angle of attack by forcing boundary-layer transition to occur closer to the wing leading edge by the application of grit or the increase in free-stream Reynolds number.
An Investigation of Transonic Resonance in a Mach 2.2 Round Convergent-Divergent Nozzle
Dippold, Vance F., III; Zaman, Khairul B. M. Q.
2015-01-01
Hot-wire and acoustic measurements were taken for a round convergent nozzle and a round convergent-divergent (C-D) nozzle at a jet Mach number of 0.61. The C-D nozzle had a design Mach number of 2.2. Compared to the convergent nozzle jet flow, the Mach 2.2 nozzle jet flow produced excess broadband noise (EBBN). It also produced a transonic resonance tone at 1200 Herz. Computational simulations were performed for both nozzle flows. A steady Reynolds-Averaged Navier-Stokes simulation was performed for the convergent nozzle jet flow. For the Mach 2.2 nozzle flow, a steady RANS simulation, an unsteady RANS (URANS) simulation, and an unsteady Detached Eddy Simulation (DES) were performed. The RANS simulation of the convergent nozzle showed good agreement with the hot-wire velocity and turbulence measurements, though the decay of the potential core was over-predicted. The RANS simulation of the Mach 2.2 nozzle showed poor agreement with the experimental data, and more closely resembled an ideally-expanded jet. The URANS simulation also showed qualitative agreement with the hot-wire data, but predicted a transonic resonance at 1145 Herz. The DES showed good agreement with the hot-wire velocity and turbulence data. The DES also produced a transonic tone at 1135 Herz. The DES solution showed that the destabilization of the shock-induced separation region inside the nozzle produced increased levels of turbulence intensity. This is likely the source of the EBBN.
Relativistic Electrons Produced by Foreshock Disturbances Observed Upstream of Earth's Bow Shock
Wilson, L. B.; Sibeck, D. G.; Turner, D. L.; Osmane, A.; Caprioli, D.; Angelopoulos, V.
2016-11-01
Charged particles can be reflected and accelerated by strong (i.e., high Mach number) astrophysical collisionless shock waves, streaming away to form a foreshock region in communication with the shock. Foreshocks are primarily populated by suprathermal ions that can generate foreshock disturbances—large-scale (i.e., tens to thousands of thermal ion Larmor radii), transient (˜5 - 10 per day ) structures. They have recently been found to accelerate ions to energies of several keV. Although electrons in Saturn's high Mach number (M >40 ) bow shock can be accelerated to relativistic energies (nearly 1000 keV), it has hitherto been thought impossible to accelerate electrons beyond a few tens of keV at Earth's low Mach number (1 ≤M events. These relativistic electrons are not associated with any solar or magnetospheric activity. Further, due to their relatively small Larmor radii (compared to magnetic gradient scale lengths) and large thermal speeds (compared to shock speeds), no known shock acceleration mechanism can energize thermal electrons up to relativistic energies. The discovery of relativistic electrons associated with foreshock structures commonly generated in astrophysical shocks could provide a new paradigm for electron injections and acceleration in collisionless plasmas.
Brown, C. A., Jr.; Campbell, J. F.; Tudor, D. H.
1971-01-01
An investigation was conducted to obtain flow properties in the wake of the Viking '75 entry vehicle at Mach numbers from 1.60 to 3.95 and at angles of attack of 0 deg and 5 deg. The wake flow properties were calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.0 to 8.39 body diameters and lateral stations varying from -0.42 to 3.0 body diameters. These measurements showed a a consistent trend throughout the range of Mach numbers and longitudinal distances and an increase in dynamic pressure with increasing downstream position.
Indian Academy of Sciences (India)
Balla Venukumar; K P J Reddy
2007-02-01
Substantial aerodynamic drag, while ﬂying at hypersonic Mach number, due to the presence of strong standing shock wave ahead of a large-angle bluntcone conﬁguration, is a matter of great design concern. Preliminary experimental results for the drag reduction by a forward-facing supersonic air jet for a 60° apex-angle blunt cone at a ﬂow Mach number of 8 are presented in this paper. The measurements are carried out using an accelerometer-based balance system in the hypersonic shock tunnel HST2 of the Indian Institute of Science, Bangalore. About 29% reduction in the drag coefﬁcient has been observed with the injection of a supersonic gas jet.
An experimental study of shock wave propagation through a polyester film
Eliasson, Veronica; Jeon, Hongjoo
2016-11-01
A polyester film is available in a variety of uses such as packaging, protective overlay, barrier protection, and other industrial applications. In the current study, shock tube experiments are performed to study the influence of a polyester film on the propagation of a planar shock wave. A conventional shock tube is used to create incident shock Mach numbers of Ms = 1.34 and 1.46. A test section of the shock tube is designed to hold a 0.009 mm, 0.127 mm, 0.254 mm, or 0.508 mm thick polyester film (Dura-Lar). High-temporal resolution schlieren photography is used to visualize the shock wave mitigation caused by the polyester film. In addition, four pressure transducers are used to measure the elapsed time of arrival and overpressure of the shock wave both upstream and downstream of the test section. Results show that the transmitted shock wave in the polyester film is clearly observed and the transmitted shock Mach number is decreased by increasing film thickness. This study is supported by the National Science Foundation under Grant No. CBET-1437412.
Cosmological shock waves: clues to the formation history of haloes
Planelles, Susana
2012-01-01
Shock waves developed during the formation and evolution of cosmic structures encode crucial information on the hierarchical formation of the Universe. We analyze an Eulerian AMR hydro + N-body simulation in a $\\Lambda$CDM cosmology focused on the study of cosmological shock waves. The combination of a shock-capturing algorithm together with the use of a halo finder allows us to study the morphological structures of the shock patterns, the statistical properties of shocked cells, and the correlations between the cosmological shock waves appearing at different scales and the properties of the haloes harbouring them. The shocks in the simulation can be split into two broad classes: internal weak shocks related with evolutionary events within haloes, and external strong shocks associated with large-scale events. The shock distribution function contains information on the abundances and strength of the different shocks, and it can be fitted by a double power law with a break in the slope around a Mach number of 2...
Shock wave interactions with liquid sheets
Jeon, H.; Eliasson, V.
2017-04-01
Shock wave interactions with a liquid sheet are investigated by impacting planar liquid sheets of varying thicknesses with a planar shock wave. A square frame was designed to hold a rectangular liquid sheet, with a thickness of 5 or 10 mm, using plastic membranes and cotton wires to maintain the planar shape and minimize bulge. The flat liquid sheet, consisting of either water or a cornstarch and water mixture, was suspended in the test section of a shock tube. Incident shock waves with Mach numbers of M_s = 1.34 and 1.46 were considered. A schlieren technique with a high-speed camera was used to visualize the shock wave interaction with the liquid sheets. High-frequency pressure sensors were used to measure wave speed, overpressure, and impulse both upstream and downstream of the liquid sheet. Results showed that no transmitted shock wave could be observed through the liquid sheets, but compression waves induced by the shock-accelerated liquid coalesced into a shock wave farther downstream. A thicker liquid sheet resulted in a lower peak overpressure and impulse, and a cornstarch suspension sheet showed a higher attenuation factor compared to a water sheet.
Flat plate heat transfer for laminar transition and turbulent boundary layers using a shock tube
Brostmeyer, J. D.; Nagamatsu, H. T.
1984-01-01
Heat transfer results are presented for laminar, transition, and turbulent boundary layers for a Mach number of 0.12 with gas temperatures of 425 K and 1000 K over a flat plate at room temperature. The measurements were made in air for a Reynolds number range of 600 to 6 million. The heat transfer measurements were conducted in a 70-ft long, 4 in. diameter shock tube. Reflecting wedges were used to reflect the incident shock wave to produce a flow Mach number of 0.12 behind the reflected shock wave. Thin film platinum heat gages were mounted on the plate surface to measure the local heat flux. The laminar results for gas temperatures of 425 K to 1000 K agree well with theory. The turbulent results are also close to incompressible theory, with the 1000 K flow case being slightly higher. The transition results lie between the laminar and turbulent predictions.
Electron acceleration to relativistic energies at a strong quasi-parallel shock wave
Masters, A; Fujimoto, M; Schwartz, S J; Sergis, N; Thomsen, M F; Retinò, A; Hasegawa, H; Lewis, G R; Coates, A J; Canu, P; Dougherty, M K
2013-01-01
Electrons can be accelerated to ultrarelativistic energies at strong (high-Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron accele...
Plane shock wave structure in a dilute granular gas
Reddy, M. H. Lakshminarayana; Alam, Meheboob
2016-11-01
We analyse the early time evolution of the Riemann problem of planar shock wave structures for a dilute granular gas by solving Navier-Stokes equations numerically. The one-dimensional reduced Navier-Stokes equations for plane shock wave problem are solved numerically using a relaxation-type numerical scheme. The results on the shock structures in granular gases are presented for different Mach numbers and restitution coefficients. Based on our analysis on early time shock dynamics we conclude that the density and temperature profiles are "asymmetric"; the density maximum and the temperature maximum occur within the shock layer; the absolute magnitudes of longitudinal stress and heat flux which are initially zero at both end states attain maxima in a very short time and thereafter decrease with time.
A shock at the radio relic position in Abell 115
Botteon, A; Brunetti, G; Dallacasa, D
2016-01-01
We analyzed a deep Chandra observation (334 ks) of the galaxy cluster Abell 115 and detected a shock co-spatial with the radio relic. The X-ray surface brightness profile across the shock region presents a discontinuity, corresponding to a density compression factor $\\mathcal{C}=2.0\\pm0.1$ leading to a Mach number $\\mathcal{M}=1.7\\pm0.1$ ($\\mathcal{M}=1.4-2$ including systematics). Temperatures measured in the upstream and downstream regions are consistent with what expected for such a shock: $T_u=4.3^{+1.0}_{-0.6}\\:\\rm{keV}$ and $T_d=7.9^{+1.4}_{-1.1}\\:\\rm{keV}$ respectively, implying a Mach number $\\mathcal{M}=1.8^{+0.5}_{-0.4}$. So far, only few other shocks discovered in galaxy clusters are consistently detected from both density and temperature jumps. The spatial coincidence between this discontinuity and the radio relic edge strongly supports the view that shocks play a crucial role in powering these synchrotron sources. We suggest that the relic is originated by shock re-acceleration of relativistic el...
Interplanetary shocks and foreshocks observed by STEREO during 2007-2010
Blanco-Cano, X.; Kajdič, P.; Aguilar-Rodríguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.
2016-02-01
Interplanetary shocks in the heliosphere modify the solar wind through which they pass. In particular, shocks play an important role in particle acceleration. During the extended solar minimum (2007-2010) STEREO observed 65 forward shocks driven by stream interactions (SI), with magnetosonic Mach numbers Mms ≈ 1.1-4.0 and shock normal angles θBN ~ 20-87°. We analyze the waves associated with these shocks and find that the region upstream can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) waves (f ~ 10-2-10-1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is most probably associated with local kinetic ion instabilities. We find that when the Mach number (Mms) is low and the shock is quasi-perpendicular (θBN > 45°) whistler waves remain close to the shock. As Mms increases, the shock profile changes and can develop a foot and overshoot associated with ion reflection and gyration. Whistler precursors can be superposed on the foot region, so that some quasi-perpendicular shocks have characteristics of both subcritical and supercritical shocks. When the shock is quasi-parallel (θBN modified probably by reflected and/or leaked ions and by almost circularly polarized waves at lower frequencies that may be locally generated by ion instabilities. In contrast with planetary bow shocks, most of the upstream waves studied here are mainly transverse and no steepening occurs. Some quasi-perpendicular shocks (45° Earth's orbit and have been accelerating ions for a shorter interval of time.
Reynolds, Robert M; Samonds, Robert I; Walker, John H
1957-01-01
An investigation has been made to determine the aerodynamic characteristics of the NACA 4-(5)(05)-041 four-blade, single-relation propeller and the NACA 4-(5)(05)-037 six- and eight-blade, dual-rotation propellers in combination with various spinners and NACA d-type spinner-cowling combinations at Mach numbers up to 0.84. Propeller force characteristics, local velocity distributions in the propeller planes, inlet pressure recoveries, and static-pressure distributions on the cowling surfaces were measured for a wide range of blade angles, advance ratios, and inlet-velocity ratios. Included are data showing: (a) the effect of extended cylindrical spinners on the characteristics of the single-rotation propeller, (b) the effect of variation of the difference in blade angle setting between the front and rear components of the dual-rotation propellers, (c) the negative- and static-thrust characteristics of the propellers with 1 series spinners, and (d) the effects of ideal- and platform-type propeller-spinner junctures on the pressure-recovery characteristics of the single-rotation propeller-spinner-cowling combination.
Pendergraft, O. C., Jr.; Schmeer, J. W.
1972-01-01
Twin-jet afterbody models were investigated by using two balances to measure the thrust-minus-total drag and the afterbody drag, separately, at static conditions and at Mach numbers up to 2.2 for an angle of attack of 0 deg. Hinged-flap convergent-divergent nozzles were tested at subsonic-cruise- and maximum-afterburning-power settings with a high-pressure air system used to provide jet-total-pressure ratios up to 20. Two nozzle lateral spacings were studied, using afterbodies with similar interfairing shapes but with different longitudinal cross-sectional area distributions. Alternate, blunter, interfairings with different shapes for the two spacings, which produced afterbodies having identical cross-sectional area progressions corresponding to an axisymmetric minimum wave-drag configuration, were also tested. The results indicate that the wide-spaced configurations improved the flow field around the nozzles, thereby reducing drag on the cruise nozzles; however, the increased surface and projected cross-sectional areas caused an increase in afterbody drag. Except for a slight advantage with cruise nozzles at subsonic speeds, the wide-spaced configurations had the higher total drag at all other test conditions.
The Role of Momentum Interpolation Mechanism of the Roe Scheme in the Shock Instability
Li, Xue-song
2015-01-01
The shock instability phenomenon is a famous problem for the shock-capturing scheme. By subdividing the numerical dissipation of the Roe scheme, the term of pressure-difference-driven modification for the cell face velocity is regarded as a version of the momentum interpolation method (MIM), which is necessary for incompressible flows to suppress the pressure checkerboard problem. Through the analysis and odd-even decoupling test, it is discovered that MIM plays the most important role on the shock instability. In fact, for non-linear flows MIM should be completely removed, but unexpected MIM is activated on the cell face nearly parallel to the flow for high Mach number flows or low Mach number flows in shock. For such conditions, two coefficients are designed based on local Mach number and a shock detector, respectively, and then the improved Roe scheme is proposed, which gives consideration to requirement of MIM for incompressible and compressible flows and is validated for good performance of avoiding odd-...
Magnetosheath Filamentary Structures Formed by Ion Acceleration at the Quasi-Parallel Bow Shock
Omidi, N.; Sibeck, D.; Gutynska, O.; Trattner, K. J.
2014-01-01
Results from 2.5-D electromagnetic hybrid simulations show the formation of field-aligned, filamentary plasma structures in the magnetosheath. They begin at the quasi-parallel bow shock and extend far into the magnetosheath. These structures exhibit anticorrelated, spatial oscillations in plasma density and ion temperature. Closer to the bow shock, magnetic field variations associated with density and temperature oscillations may also be present. Magnetosheath filamentary structures (MFS) form primarily in the quasi-parallel sheath; however, they may extend to the quasi-perpendicular magnetosheath. They occur over a wide range of solar wind Alfvénic Mach numbers and interplanetary magnetic field directions. At lower Mach numbers with lower levels of magnetosheath turbulence, MFS remain highly coherent over large distances. At higher Mach numbers, magnetosheath turbulence decreases the level of coherence. Magnetosheath filamentary structures result from localized ion acceleration at the quasi-parallel bow shock and the injection of energetic ions into the magnetosheath. The localized nature of ion acceleration is tied to the generation of fast magnetosonic waves at and upstream of the quasi-parallel shock. The increased pressure in flux tubes containing the shock accelerated ions results in the depletion of the thermal plasma in these flux tubes and the enhancement of density in flux tubes void of energetic ions. This results in the observed anticorrelation between ion temperature and plasma density.
Interplanetary double-shock ensembles with anomalous electrical conductivity
Dryer, M.
1972-01-01
Similarity theory is applied to the case of constant velocity, piston-driven, shock waves. This family of solutions, incorporating the interplanetary magnetic field for the case of infinite electric conductivity, represents one class of experimentally observed, flare-generated shock waves. This paper discusses the theoretical extension to flows with finite conductivity (presumably caused by unspecified modes of wave-particle interactions). Solutions, including reverse shocks, are found for a wide range of magnetic Reynolds numbers from one to infinity. Consideration of a zero and nonzero ambient flowing solar wind (together with removal of magnetic considerations) enables the recovery of earlier similarity solutions as well as numerical simulations. A limited comparison with observations suggests that flare energetics can be reasonably estimated once the shock velocity, ambient solar wind velocity and density, and ambient azimuthal Alfven Mach number are known.
Batterton, P. G.; Arpasi, D. J.; Baumbick, R. J.
1974-01-01
A digitally implemented integrated inlet-engine control system was designed and tested on a mixed-compression, axisymmetric, Mach 2.5, supersonic inlet with 45 percent internal supersonic area contraction and a TF30-P-3 augmented turbofan engine. The control matched engine airflow to available inlet airflow. By monitoring inlet terminal shock position and over-board bypass door command, the control adjusted engine speed so that in steady state, the shock would be at the desired location and the overboard bypass doors would be closed. During engine-induced transients, such as augmentor light-off and cutoff, the inlet operating point was momentarily changed to a more supercritical point to minimize unstarts. The digital control also provided automatic inlet restart. A variable inlet throat bleed control, based on throat Mach number, provided additional inlet stability margin.
Directory of Open Access Journals (Sweden)
Tiago Cavalcanti Rolim
2011-05-01
Full Text Available This paper presents a research in the development of the 14-X hypersonic airspace vehicle at Institute for Advanced Studies (IEAv from Department of Science and Aerospace Technology (DCTA of the Brazilian Air Force (FAB. The 14-X project objective is to develop a higher efficient satellite launch alternative, using a Supersonic Combustion Ramjet (SCRAMJET engine and waverider aerodynamics. For this development, the waverider technology is under investigation in Prof. Henry T. Nagamatsu Aerothermodynamics and Hypersonics Laboratory (LHTN, in IEAv/DCTA. The investigation has been conducted through ground test campaigns in Hypersonic Shock Tunnel T3. The 14-X Waverider Vehicle characteristic was verified in shock tunnel T3 where surface static pressures and pitot pressure for Mach number 10 were measured and, using Schlieren photographs Diagnostic Method, it was possible to identify a leading-edge attached shock wave in 14-X lower surface.
Liu, S.; Marsch, E.; Schwenn, R.; Rosenbauer, H.
1995-01-01
A new method to determine and classify shocks from in situ measurements is developed, using normalized velocities up- and down-stream in a velocity V(sub 1)-V(sub 2) diagram. With this method one can show how the shock solutions vary with different time averages over the data from the up- and down-stream region. For stable fast forward shocks the solutions are confined well in the 1 to 2 region, and for slow shocks most of the solutions are confined in the 3 to 4 region. A candidate for an intermediate shock was observed by Helios and with our method clearly identified. We found perhaps the first shock with parameters in the 2 to 3 region (with C(sub F1) greater than V(sub 1) greater than C(sub I1), and C(sub I2) greater than V(sub 2) greater than C(sub SL2) and a 180 deg rotation of the tangential magnetic field), which is interpreted as an intermediate shock with B(sub perpendicular 1) being less than B(sub perpendicular 2). The different shock solutions are somewhat distributed in the normalized V(sub 1)-V(sub 2) diagram, but only the intermediate shock solutions are consistent with the Rankine-Hugoniot relations for this particular shock. The Mach number M(sub I1) equals 1.067, a figure in good agreement with the Kennel et al. (1989) theoretical values.
Study of astrophysical collisionless shocks at NIF
Park, Hye-Sook; Higginson, D. P.; Huntington, C. M.; Pollock, B. B.; Remington, B. A.; Rinderknecht, H.; Ross, J. S.; Ryutov, D. D.; Swadling, G. F.; Wilks, S. C.; Sakawa, Y.; Spitkovsky, A.; Petrasso, R.; Li, C. K.; Zylstra, A. B.; Lamb, D.; Tzeferacos, P.; Gregori, G.; Meinecke, J.; Manuel, M.; Froula, D.; Fiuza, F.
2016-10-01
High Mach number astrophysical plasmas can create collisionless shocks via plasma instabilities and turbulence that are responsible for magnetic field generations and cosmic ray acceleration. Recently, many laboratory experiments were successful to observe the Weibel instabilities and self-generated magnetic fields using high-power lasers that generated interpenetrating plasma flows. In order to create a fully formed shock, a series of NIF experiments have begun. The characteristics of flow interaction have been diagnosed by the neutrons and protons generated via beam-beam deuteron interactions, the x-ray emission from the hot plasmas and proton probe generated by imploding DHe3 capsules. This paper will present the latest results from the NIF collisionless shock experiments. Prepared by LLNL under Contract DE-AC52-07NA27344.
Aeroacoustic computation of low mach number flow
Energy Technology Data Exchange (ETDEWEB)
Skriver Dahl, K. [Risoe National Laboratory, Roskilde (Denmark)
1997-12-31
The possibilities of applying a recently developed numerical technique to predict aerodynamically generated sound from wind turbines is explored. The technique is a perturbation technique that has the advantage that the underlying flow field and the sound field are computed separately. Solution of the incompressible, time dependent flow field yields a hydrodynamic density correction to the incompressible constant density. The sound field is calculated from a set of equations governing the inviscid perturbations about the corrected flow field. Here, the emphasis is placed on the computation of the sound field. The nonlinear partial differential equations governing the sound fields are solved numerically using an explicit MacCormack scheme. Two types of non-reflecting boundary conditions are applied; one based on the asymptotic solution of the governing equations and the other based on a characteristic analysis of the governing equations. The former condition is easy to use and it performs slightly better than the charcteristic based condition. The technique is applied to the problems of the sound generation of a co-rotating vortex pair, which is a quadrupole, and the viscous flow over a circular cylinder, which is a dipole. Numerical results agree very well with the analytical solution for the problem of the co-rotating vortex pair. Numerical results for the viscous flow over a cylinder are presented and evaluated qualitatively. (au)
Pietersen, CY; Bosker, FJ; Posterna, F; den Boer, JA
2006-01-01
Many fear conditioning studies use electric shock as the aversive stimulus. The intensity of shocks varies throughout the literature. In this study, shock intensities ranging from 0 to 1.5 mA were used, and the effects on the rats assessed by both behavioural and biochemical stress parameters. Resul
Pietersen, C.Y.; Bosker, F.J; Posterna, F.; Den Boer, J.A.
2006-01-01
Many fear conditioning studies use electric shock as the aversive stimulus. The intensity of shocks varies throughout the literature. In this study, shock intensities ranging from 0 to 1.5 mA were used, and the effects on the rats assessed by both behavioural and biochemical stress parameters. Resul
Shock finding on a moving-mesh: II. Hydrodynamic shocks in the Illustris universe
Schaal, Kevin; Pakmor, Rüdiger; Pfrommer, Christoph; Nelson, Dylan; Vogelsberger, Mark; Genel, Shy; Pillepich, Annalisa; Sijacki, Debora; Hernquist, Lars
2016-01-01
Hydrodynamical shocks are a manifestation of the non-linearity of the Euler equations and play a fundamental role in cosmological gas dynamics. In this work, we identify and analyse shocks in the Illustris simulation, and contrast the results with those of non-radiative runs. We show that simulations with more comprehensive physical models of galaxy formation pose new challenges for shock finding algorithms due to radiative cooling and star forming processes, prompting us to develop a number of methodology improvements that robustly suppress spurious shock detections. We find in Illustris a total shock surface area which is about 1.4 times larger at the present epoch compared to non-radiative runs, and an energy dissipation rate at shocks which is higher by a factor of around 7. Remarkably, shocks with Mach numbers above and below $\\mathcal{M} \\approx 10$ contribute about equally to the total dissipation across cosmic time. This is in strong contrast to non-radiative simulations, and we demonstrate that a lar...
Shock formation induced by poloidal flow and its effects on the edge stability in tokamaks
Seol, Jaechun; Shaing, Kerchung; Aydemir, Ahmet
2016-10-01
In the high confinement mode of tokamaks, magnitude of the radial electric field increases at the edge. Thus, the poloidal flow inside the transport barrier can be sonic when the edge pressure gradient is not steep enough to make the poloidal flow subsonic. When the poloidal Mach number is close to unity, a shock appears in the low field side and causes a large density perturbation. In this study, we describe a shock induced by the sonic poloidal plasma flow. Then, an entropy production across the shock is calculated. Finally, we introduce a simple model for Type III edge localized modes using the poloidal density variation driven by the sonic poloidal flow.
Shock jump relations for a dusty gas atmosphere
Anand, R. K.
2014-01-01
This paper presents simplified forms of jump relations for one dimensional shock waves propagating in a dusty gas. The dusty gas is assumed to be a mixture of a perfect gas and spherically small solid particles, in which solid particles are continuously distributed. The simplified jump relations for the pressure, the temperature, the density, the velocity of the mixture and the speed of sound have been derived in terms of the upstream Mach number. The expressions for the adiabatic compressibility of the mixture and the change-in-entropy across the shock front have also been derived in terms of the upstream Mach number. Further, the handy forms of shock jump relations have been obtained in terms of the initial volume fraction of small solid particles and the ratio of specific heats of the mixture, simultaneously for the two cases viz., (i) when the shock is weak and, (ii) when it is strong. The simplified shock jump relations reduce to the Rankine-Hugoniot conditions for shock waves in an ideal gas when the mass fraction (concentration) of solid particles in the mixture becomes zero. Finally, the effects due to the mass fraction of solid particles in the mixture, and the ratio of the density of solid particles to the initial density of the gas are studied on the pressure, the temperature, the density, the velocity of the mixture, the speed of sound, the adiabatic compressibility of the mixture and the change-in-entropy across the shock front. The results provided a clear picture of whether and how the presence of dust particles affects the flow field behind the shock front. The aim of this paper is to contribute to the understanding of how the shock waves behave in the gas-solid particle two-phase flows.
A comparison of shock-cloud and wind-cloud interactions: the longer survival of clouds in winds
Goldsmith, K. J. A.; Pittard, J. M.
2017-09-01
The interaction of a hot, high-velocity wind with a cold, dense molecular cloud has often been assumed to resemble the evolution of a cloud embedded in a post-shock flow. However, no direct comparative study of these two processes currently exists in the literature. We present 2D adiabatic hydrodynamical simulations of the interaction of a Mach 10 shock with a cloud of density contrast χ = 10 and compare our results with those of a commensurate wind-cloud simulation. We then investigate the effect of varying the wind velocity, effectively altering the wind Mach number Mwind, on the cloud's evolution. We find that there are significant differences between the two processes: 1) the transmitted shock is much flatter in the shock-cloud interaction; 2) a low-pressure region in the wind-cloud case deflects the flow around the edge of the cloud in a different manner to the shock-cloud case; 3) there is far more axial compression of the cloud in the case of the shock. As Mwind increases, the normalized rate of mixing is reduced. Clouds in winds with higher Mwind also do not experience a transmitted shock through the cloud's rear and are more compressed axially. In contrast with shock-cloud simulations, the cloud mixing time normalized by the cloud-crushing time-scale tcc increases for increasing Mwind until it plateaus (at tmix ≃ 25 tcc) at high Mwind, thus demonstrating the expected Mach scaling. In addition, clouds in high Mach number winds are able to survive for long durations and are capable of being moved considerable distances.
Energy Technology Data Exchange (ETDEWEB)
Handa, T.; Miyazato, Y.; Maasuda, M.; Matsuo, K. [Kyushu Univaersity, Fukuoka (Japan)
2000-05-25
Concerning the self-excited shock oscillation in a transonic diffuser flow, the response of a normal shock wave to a 'white' pressure disturbance, that is, a small pressure disturbance having the same power spectral density over every frequency, is analyzed by solving the equation representing shock displacement due to the disturbance. According to the present analysis, the spectral density distribution and peak frequency of the shock oscillation depend on Mach number just upstream of the shock wave and a non-dimensional parameter determined from the diffuser geometry at the time-mean shock location. The shock displacement power spectral density distributions obtained by the analysis agree very well with those measured in our experiment. A non-dimensional relationship between the peak frequency of the shock oscillation and diffuser geometry at the shock location, Eq. (18), is obtained, and this equation agrees well with the present and previous experimental results. (author)
Institute of Scientific and Technical Information of China (English)
金志伟; 杨兴锐; 苏北辰
2016-01-01
It is hard to use precise mechanism to describe system dynamic feature of 2.4 m transonic wind tunnel. Put forwards wind tunnel Mach number predictive control strategy based on neural network. Combine the advanteges of model predictive control and nueral network modeling, it is good at processing control parameter unkown, unlinear system and time varing system. Use dynamic response of nueral network based on radial basis function and nonlinear neural network to capture system dynamic feature, apply nerual nwork model in MPC structure. The simulation results show that the control strtegy has a good control effect and trace performance.%针对2.4 m跨声速风洞很难用精确的机理模型表示系统的动态特性的问题,提出了基于神经网络模型的风洞马赫数预测控制策略.综合了模型预测控制和神经网络建模的优点,对于控制参数未知、非线性和时变系统具有很好的处理效果.利用基于径向基函数的神经网络模型预测系统的动态响应、非线性神经网络模型可以在训练过程中捕获系统的动态特性等措施,实现了将神经网络模型应用到MPC结构中.仿真结果表明,该控制策略具有很好的跟踪性能和控制效果.
Electromagnetic Structure and Electron Acceleration in Shock–Shock Interaction
Nakanotani, Masaru; Matsukiyo, Shuichi; Hada, Tohru; Mazelle, Christian X.
2017-09-01
A shock–shock interaction is investigated by using a one-dimensional full particle-in-cell simulation. The simulation reproduces the collision of two symmetrical high Mach number quasi-perpendicular shocks. The basic structure of the shocks and ion dynamics is similar to that obtained by previous hybrid simulations. The new aspects obtained here are as follows. Electrons are already strongly accelerated before the two shocks collide through multiple reflection. The reflected electrons self-generate waves upstream between the two shocks before they collide. The waves far upstream are generated through the right-hand resonant instability with the anomalous Doppler effect. The waves generated near the shock are due to firehose instability and have much larger amplitudes than those due to the resonant instability. The high-energy electrons are efficiently scattered by the waves so that some of them gain large pitch angles. Those electrons can be easily reflected at the shock of the other side. The accelerated electrons form a power-law energy spectrum. Due to the accelerated electrons, the pressure of upstream electrons increases with time. This appears to cause the deceleration of the approaching shock speed. The accelerated electrons having sufficiently large Larmor radii are further accelerated through the similar mechanism working for ions when the two shocks are colliding.
Cosmological structure formation shocks and cosmic rays in hydrodynamical simulations
Pfrommer, C; Ensslin, T A; Jubelgas, M; Pfrommer, Christoph; Springel, Volker; Ensslin, Torsten A.; Jubelgas, Martin
2006-01-01
Cosmological shock waves during structure formation not only play a decisive role for the thermalization of gas in virializing structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. We discuss a novel numerical treatment of the physics of cosmic rays in combination with a formalism for identifying and measuring the shock strength on-the-fly during a smoothed particle hydrodynamics simulation. In our methodology, the non-thermal CR population is treated self-consistently in order to assess its dynamical impact on the thermal gas as well as other implications on cosmological observables. Using this formalism, we study the history of the thermalization process in high-resolution hydrodynamic simulations of the Lambda cold dark matter model. Collapsed cosmological structures are surrounded by shocks with high Mach numbers up to 1000, but they play only a minor role in the energy balance of thermalization. However, this finding has important consequences fo...
Chandra observation of two shock fronts in the merging galaxy cluster Abell 2146
Russell, H R; Fabian, A C; Baum, S A; Donahue, M; Edge, A C; McNamara, B R; O'Dea, C P
2010-01-01
We present a new Chandra observation of the galaxy cluster Abell 2146 which has revealed a complex merging system with a gas structure that is remarkably similar to the Bullet cluster (eg. Markevitch et al. 2002). The X-ray image and temperature map show a cool 2-3 keV subcluster with a ram pressure stripped tail of gas just exiting the disrupted 6-7 keV primary cluster. From the sharp jump in the temperature and density of the gas, we determine that the subcluster is preceded by a bow shock with a Mach number M=2.2+/-0.8, corresponding to a velocity v=2200^{+1000}_{-900} km/s relative to the main cluster. We estimate that the subcluster passed through the primary core only 0.1-0.3 Gyr ago. In addition, we observe a slower upstream shock propagating through the outer region of the primary cluster and calculate a Mach number M=1.7+/-0.3. Based on the measured shock Mach numbers M~2 and the strength of the upstream shock, we argue that the mass ratio between the two merging clusters is between 3 and 4 to one. B...
A Strong Merger Shock in Abell 665
Dasadia, S.; Sun, M.; Sarazin, C.; Morandi, A.; Markevitch, M.; Wik, D.; Feretti, L.; Giovannini, G.; Govoni, F.; Vacca, V.
2016-03-01
Deep (103 ks) Chandra observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of M = 3.0 ± 0.6, propagating in front of a cold disrupted cloud. This makes Abell 665 the second cluster, after the Bullet cluster, where a strong merger shock of M ≈ 3 has been detected. The shock velocity from jump conditions is consistent with (2.7 ± 0.7) × 103 km s-1. The new data also reveal a prominent southern cold front with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined.
A Strong Merger Shock in Abell 665
Dasadia, Sarthak; Sarazin, Craig; Morandi, Andrea; Markevitch, Maxim; Wik, Daniel; Feretti, Luigina; Giovannini, Gabriele; Govoni, Federica; Vacca, Valentina
2016-01-01
Deep (103 ks) \\chandra\\ observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of $M$ = 3.0 $\\pm$ 0.6, propagating in front of a cold disrupted cloud. This makes Abell~665 the second cluster where a strong merger shock of $M \\approx$ 3 has been detected, after the Bullet cluster. The shock velocity from jump conditions is consistent with (2.7 $\\pm$ 0.7) $\\times$ 10$^3$ km sec$^{-1}$. The new data also reveal a prominent southern cold front, with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the re-acceleration model with the X-ray and radio data combined.
Phillips, W. P.; Fournier, R. H.
1985-01-01
Wind-tunnel tests were conducted at Mach 1.5 to 2.5 to determine the effect of modifications designed to extend the forward center-of-gravity trim capability on the static longitudal and lateral directional characteristics of a Space shuttle 140 A/B orbiter model (0.01 scale). The modifications consisted of a forward-extended wing fillet, a flat plate canard, and a blended canard. The investigation was conducted in the low Mach number test section of the Langley unitary plan wind tunnel at a Reynolds number of approximately 2.15 million based on the fuselage reference length. The test angle of attack range was -1 deg to 32 deg and the sideslip angles were 0 deg and 5 deg.
Shock wave profiles in the burnett approximation
Uribe; Velasco; Garcia-Colin; Diaz-Herrera
2000-11-01
This paper is devoted to a discussion of the profiles of shock waves using the full nonlinear Burnett equations of hydrodynamics as they appear from the Chapman-Enskog solution to the Boltzmann equation. The system considered is a dilute gas composed of rigid spheres. The numerical analysis is carried out by transforming the hydrodynamic equations into a set of four first-order equations in four dimensions. We compare the numerical solutions of the Burnett equations, obtained using Adam's method, with the well known direct simulation Monte Carlo method for different Mach numbers. An exhaustive mathematical analysis of the results offered here has been done mainly in connection with the existence of heteroclinic trajectories between the two stationary points located upflow and downflow. The main result of this study is that such a trajectory exists for the Burnett equations for Mach numbers greater than 1. Our numerical calculations suggest that heteroclinic trajectories exist up to a critical Mach number ( approximately 2.69) where local mathematical analysis and numerical computations reveal a saddle-node-Hopf bifurcation. This upper limit for the existence of heteroclinic trajectories deserves further clarification.
Relaminarization of the boundary layer over a flat plate in shock tube experiments
Hinckel, J. N.; Nagamatsu, H. T.
1986-01-01
The relaminarization of the boundary layer over a flat plate in the shock tube was investigated by using the partially reflected shock wave technique. The flow Mach number was approximately 0.14, which corresponds to the inleft flow Mach number for the first row of vanes in a gas turbine. The thin film platinum heat gauges were used to measure the heat transfer rate and the Stanton number was calculated from the oscilloscope voltage traces. The Reynolds number was varied by changing the operation pressure of the shock tube and the values varied from 2.3 x 10 to the 4th to 5.3 x 10 to the 5th. For a Reynolds number range of 7 x 10 to the 4th to 3.5 x 10 to the 5th, the relaminarization of the boundary layer was observed. This phenomenon is due to the decay of the turbulence level in the flow as the reflected shock wave moves upstream from the flat plate. As the Reynolds number increased, the relaminarization was delayed and the delay was related to the turbulence generated by the reflected shock wave.
Umeda, Takayuki; Matsukiyo, Shuichi; Yamazaki, Ryo
2014-01-01
Large-scale two-dimensional (2D) full particle-in-cell simulations are carried out for studying the relationship between the dynamics of a perpendicular shock and microinstabilities generated at the shock foot. The structure and dynamics of collisionless shocks are generally determined by Alfven Mach number and plasma beta, while microinstabilities at the shock foot are controlled by the ratio of the upstream bulk velocity to the electron thermal velocity and the ratio of the plasma-to-cyclotron frequency. With a fixed Alfven Mach number and plasma beta, the ratio of the upstream bulk velocity to the electron thermal velocity is given as a function of the ion-to-electron mass ratio. The present 2D full PIC simulations with a relatively low Alfven Mach number (M_A ~ 6) show that the modified two-stream instability is dominant with higher ion-to-electron mass ratios. It is also confirmed that waves propagating downstream are more enhanced at the shock foot near the shock ramp as the mass ratio becomes higher. T...
Converging shocks in elastic-plastic solids.
Ortega, A López; Lombardini, M; Hill, D J
2011-11-01
We present an approximate description of the behavior of an elastic-plastic material processed by a cylindrically or spherically symmetric converging shock, following Whitham's shock dynamics theory. Originally applied with success to various gas dynamics problems, this theory is presently derived for solid media, in both elastic and plastic regimes. The exact solutions of the shock dynamics equations obtained reproduce well the results obtained by high-resolution numerical simulations. The examined constitutive laws share a compressible neo-Hookean structure for the internal energy e=e(s)(I(1))+e(h)(ρ,ς), where e(s) accounts for shear through the first invariant of the Cauchy-Green tensor, and e(h) represents the hydrostatic contribution as a function of the density ρ and entropy ς. In the strong-shock limit, reached as the shock approaches the axis or origin r=0, we show that compression effects are dominant over shear deformations. For an isothermal constitutive law, i.e., e(h)=e(h)(ρ), with a power-law dependence e(h) is proportional to ρ(α), shock dynamics predicts that for a converging shock located at r=R(t) at time t, the Mach number increases as M is proportional to [log(1/R)](α), independently of the space index s, where s=2 in cylindrical geometry and 3 in spherical geometry. An alternative isothermal constitutive law with p(ρ) of the arctanh type, which enforces a finite density in the strong-shock limit, leads to M is proportional to R(-(s-1)) for strong shocks. A nonisothermal constitutive law, whose hydrostatic part e(h) is that of an ideal gas, is also tested, recovering the strong-shock limit M is proportional to R(-(s-1)/n(γ)) originally derived by Whitham for perfect gases, where γ is inherently related to the maximum compression ratio that the material can reach, (γ+1)/(γ-1). From these strong-shock limits, we also estimate analytically the density, radial velocity, pressure, and sound speed immediately behind the shock. While the
Converging shocks in elastic-plastic solids
López Ortega, A.; Lombardini, M.; Hill, D. J.
2011-11-01
We present an approximate description of the behavior of an elastic-plastic material processed by a cylindrically or spherically symmetric converging shock, following Whitham's shock dynamics theory. Originally applied with success to various gas dynamics problems, this theory is presently derived for solid media, in both elastic and plastic regimes. The exact solutions of the shock dynamics equations obtained reproduce well the results obtained by high-resolution numerical simulations. The examined constitutive laws share a compressible neo-Hookean structure for the internal energy e=es(I1)+eh(ρ,ς), where es accounts for shear through the first invariant of the Cauchy-Green tensor, and eh represents the hydrostatic contribution as a function of the density ρ and entropy ς. In the strong-shock limit, reached as the shock approaches the axis or origin r=0, we show that compression effects are dominant over shear deformations. For an isothermal constitutive law, i.e., eh=eh(ρ), with a power-law dependence eh∝ρα, shock dynamics predicts that for a converging shock located at r=R(t) at time t, the Mach number increases as M∝[log(1/R)]α, independently of the space index s, where s=2 in cylindrical geometry and 3 in spherical geometry. An alternative isothermal constitutive law with p(ρ) of the arctanh type, which enforces a finite density in the strong-shock limit, leads to M∝R-(s-1) for strong shocks. A nonisothermal constitutive law, whose hydrostatic part eh is that of an ideal gas, is also tested, recovering the strong-shock limit M∝R-(s-1)/n(γ) originally derived by Whitham for perfect gases, where γ is inherently related to the maximum compression ratio that the material can reach, (γ+1)/(γ-1). From these strong-shock limits, we also estimate analytically the density, radial velocity, pressure, and sound speed immediately behind the shock. While the hydrostatic part of the energy essentially commands the strong-shock behavior, the shear
Ju, Wenhua; Stone, James M.; Zhu, Zhaohuan
2017-05-01
We perform global three-dimensional MHD simulations of unstratified accretion disks in cataclysmic variables (CVs). By including mass inflow via an accretion stream, we are able to evolve the disk to a steady state. We investigate the relative importance of spiral shocks and the magnetorotational instability (MRI) in driving angular momentum transport and how each depend on the geometry and strength of the seed magnetic field and the Mach number of the disk (where Mach number is the ratio of the azimuthal velocity and the sound speed of gas). We use a locally isothermal equation of state and adopt temperature profiles that are consistent with CV disk observations. Our results indicate that the relative importance of spiral shocks and MRI in driving angular momentum transport is controlled by the gas Mach number and the seed magnetic field strength. MRI and spiral shocks provide comparable efficiency of angular momentum transport when the disk Mach number is around 10 and the seed magnetic field has plasma β =400 (where β is the ratio of gas pressure and magnetic pressure). The MRI dominates whenever the seed field strength, or the disk Mach number, is increased. Among all of our simulations, the effective viscosity parameter {α }{eff}˜ 0.016{--}0.1 after MRI saturates and the disk reaches steady state. Larger values of {α }{eff} are favored when the seed magnetic field has vertical components or the flow has stronger magnetization (1/β ). Our models all indicate that the role of MRI in driving angular momentum transport thus mass accretion in CV disks is indispensable, especially in cool disks with weak spiral shocks.
Brown, C. A., Jr.; Campbell, J. F.
1973-01-01
An investigation was conducted to obtain flow properties in the wake of a preliminary configuration of the Viking '75 Entry Vehicle at Mach numbers from 0.20 to 1.20 and at angles of attack of 0 deg, 5 deg, and 10 deg. The wake flow properties were calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.50 to 11.00 body diameters, and are presented in tabulated and plotted form. The wake properties were essentially symmetrical about the X-axis at alpha = 0 deg and the profiles were shifted away from the X-axis at angles of attack. An unexpected reduction in wake property ratios occurred as the Mach number increased from 0.60 to 1.00; these ratios then increased as the Mach number increased to 1.20. The reduction was present for all the longitudinal stations of the tests and decreased with increased longitudinal distance.
Schrenk, Markus
2011-01-01
In his Contributions to the Analysis of the Sensations (Mach 1885) the phenomenalist philosopher Ernst Mach confronts us with a difficulty: “If we regard the Ego as a real unity, we become involved in the following dilemma: either we must set over against the Ego a world of unknowable entities […] or we must regard the whole world, the Egos of other people included, as comprised in our own Ego.” (Mach 1885: 21) In other words, if we start from a phenomenalist viewpoint, i.e., if we believ...
Velocity Measurement of Induced Flow by a Laser Focusing Shock Wave
Institute of Scientific and Technical Information of China (English)
Hiroyuki HIRAHARA; Masaru FUJINAMI; Masaaki KAWAHASHI
2006-01-01
The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave,a non-stationary flow was induced in the small space between the parallel plates. The spherical and cylindrical shock propagations were observed with schlieren method. The shock Mach number decreases with time and approaches to unity. As reported in the previous investigations, the shock speed was attenuated in a short distance and time. In the present experiment, It was not found a remarkable difference in the shock speed between the spherical and cylindrical shock experiments. Subsequently, the flow induced by the cylindrical shock wave was studied using PIV technique. A smoke tracer was used in the experiment and its velocity was measured within 100 μs. A numerical simulation was carried out to investigate the momentum relaxation between the gas and smoke particle. A suitable shock initiation model was introduced in the simulation. The experimental results show that a wide acceleration and deceleration zone exist behind the shock wave. Also,the relaxation distance in the experimental data is much longer than that in numerical simulation.
Blasi, P; Bandiera, R; Amato, E; Caprioli, D
2012-01-01
A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, that we refer to as "the neutral return flux", is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge exchange interaction lengths of fast neutrals moving towards upstream infinity. In the case of a shock propagating in the interstellar m...
Energy Technology Data Exchange (ETDEWEB)
Fortin, T
2006-05-15
This work deals with the discretization of Navier-Stokes equations using different finite element methods adapted to the problem of two-phase flows. These methods must be of high order to limit the presence of spurious flows (which contradict the establishment of a physical equilibrium) and to verify energy conservation properties. Several solutions are proposed which seem to fulfill these expectations. A reformulation of the six-equation system adapted to low Mach two-phase flows has been also proposed. These methods have been implemented into the Trio-U code of CEA Grenoble, but have been tested only on simple 'academic' configurations. (J.S.)
Institute of Scientific and Technical Information of China (English)
Dorine; Houston
1998-01-01
Dear Xiao Lan, You remember the pain of culture and reentry shock; humor me please; let mereview the facts for the sake of the students you are sending here in greater numbers.Culture shock is the emotional pain that people experience when they visit a newcountry and find customs, experiences, smells, and non-verbal communication stylesto be different from their own country.
Clumpy shocks and the clump mass function
Clark, P C; Bonnell, Ian A.; Clark, Paul C.
2006-01-01
In this paper, we examine whether clumpy, colliding, flows could be responsible for the clump mass functions that have been observed in several regions of embedded star formation, which have been shown to be described by a Salpeter type slope. The flows presented here, which comprise a population of initially identical clumps and the calculations are performed with and without the inclusion of self-gravity. When the shock region is at its densest, we find that the clump mass spectrum is always well modelled by a Salpeter type slope. This is true regardless of whether the self-gravity is included in the simulations or not. In the non-self-gravitating simulations, this slope is retained at lower Mach numbers (Mach 5 and 10) as the simulations progress past the densest phase. In the simulations which include self-gravity, we find that low Mach number runs yield a flatter mass function after the densest phase. This is simply a result of increased coagulation due to gravitational collapse of the flows. In the high...
Prediction of Shock Wave Structure in Weakly Ionized Gas Flow by Solving MGD Equation
Deng, Z. T.; Oviedo-Rojas, Ruben; Chow, Alan; Litchford, Ron J.; Cook, Stephen (Technical Monitor)
2002-01-01
This paper reports the recent research results of shockwave structure predictions using a new developed code. The modified Rankine-Hugoniot relations across a standing normal shock wave are discussed and adopted to obtain jump conditions. Coupling a electrostatic body force to the Burnett equations, the weakly ionized flow field across the shock wave was solved. Results indicated that the Modified Rankine-Hugoniot equations for shock wave are valid for a wide range of ionization fraction. However, this model breaks down with small free stream Mach number and with large ionization fraction. The jump conditions also depend on the value of free stream pressure, temperature and density. The computed shock wave structure with ionization provides results, which indicated that shock wave strength may be reduced by existence of weakly ionized gas.
Thermodynamic and Kinetic Properties of Shocks in Two-Dimensional Yukawa Systems
Marciante, M.; Murillo, M. S.
2017-01-01
Particle-level simulations of shocked plasmas are carried out to examine kinetic properties not captured by hydrodynamic models. In particular, molecular dynamics simulations of 2D Yukawa plasmas with variable couplings and screening lengths are used to examine shock features unique to plasmas, including the presence of dispersive shock structures for weak shocks. A phase-space analysis reveals several kinetic properties, including anisotropic velocity distributions, non-Maxwellian tails, and the presence of fast particles ahead of the shock, even for moderately low Mach numbers. We also examine the thermodynamics (Rankine-Hugoniot relations) of recent experiments [Phys. Rev. Lett. 111, 015002 (2013), 10.1103/PhysRevLett.111.015002] and find no anomalies in their equations of state.
A Study of the Weak Shock Wave Propagating over a Porous Wall/Cavity System
Institute of Scientific and Technical Information of China (English)
H.D.KIM; S.J.JUNG; T.AOKI; T.SETOGUCHI
2005-01-01
The present computational study addresses the attenuation of the shock wave propagating in a duct, using a porous wall/cavity system. In the present study, a weak shock wave propagating over the porous wall/cavity system is investigated with computational fluid dynamics. A total variation diminishing scheme is employed to solve the unsteady, two-dimensional, compressible, Navier-Stokes equations. The Mach number of an initial shock wave is changed in the range from 1.02 to 1.12. Several different types of porous wall/cavity systems are tested to investigate the passive control effects. The results show that wall pressure strongly fluctuates due to diffraction and reflection processes of the shock waves behind the incident shock wave. From the results, it is understood that for effective alleviation of tunnel impulse waves, the length of the perforated region should be sufficiently long.
Manually operated piston-driven shock tube
Reddy, KPJ; Sharath, N
2013-01-01
A simple hand-operated shock tube capable of producing Mach 2 shock waves is described. Performance of this miniature shock tube using compressed high pressure air created by a manually operated piston in the driver section of the shock tube as driver gas with air at 1 atm pressure as the test gas in the driven tube is presented. The performance of the shock tube is found to match well with the theoretically estimated values using normal shock relations. Applications of this shock tube named ...
Experimental and numerical investigation of reactive shock-accelerated flows
Energy Technology Data Exchange (ETDEWEB)
Bonazza, Riccardo [Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
2016-12-20
The main goal of this program was to establish a qualitative and quantitative connection, based on the appropriate dimensionless parameters and scaling laws, between shock-induced distortion of astrophysical plasma density clumps and their earthbound analog in a shock tube. These objectives were pursued by carrying out laboratory experiments and numerical simulations to study the evolution of two gas bubbles accelerated by planar shock waves and compare the results to available astrophysical observations. The experiments were carried out in an vertical, downward-firing shock tube, 9.2 m long, with square internal cross section (25×25 cm^{2}). Specific goals were to quantify the effect of the shock strength (Mach number, M) and the density contrast between the bubble gas and its surroundings (usually quantified by the Atwood number, i.e. the dimensionless density difference between the two gases) upon some of the most important flow features (e.g. macroscopic properties; turbulence and mixing rates). The computational component of the work performed through this program was aimed at (a) studying the physics of multi-phase compressible flows in the context of astrophysics plasmas and (b) providing a computational connection between laboratory experiments and the astrophysical application of shock-bubble interactions. Throughout the study, we used the FLASH4.2 code to run hydrodynamical and magnetohydrodynamical simulations of shock bubble interactions on an adaptive mesh.
High-Energy Molecular Beam Source Using a Non-Diaphragm Type Small Shock Tube
Yoshimoto, Yuta; Miyoshi, Nobuya; Kinefuchi, Ikuya; Shimizu, Kazuya; Takagi, Shu; Matsumoto, Yoichiro
2010-11-01
The molecular beam technique is one of the powerful tools to analyze gas-surface interactions. In order to generate high-energy molecular beam in a range of 1 - 5 eV, which corresponds to the typical activation energy of surface reactions, we are developing a beam source using a non-diaphragm type shock tube, which can operate at a repetition rate high enough for efficient data acquisition. We made the volume of a tube much smaller than that of conventional ones so that the evacuation time between each shot becomes as short as possible. Our measurement of shock Mach numbers showed that even small diameter (2 or 4 mm) tubes, in which the wall boundary layer has a large influence on the propagation of shock waves, could generate molecular beam with the translational energy of more than 1 eV. This is because the reduction of shock formation distance by rapid opening of the valve, which separates a high pressure room from a low pressure room, weakened the effect of viscous damping on the accelerating shock wave. In addition, the convergent shock tubes of which diameters linearly decrease from 4 to 2 mm exhibited higher Mach numbers than straight ones. This indicates that the application of the convergent tube with the optimized geometry would be promising for generating high-energy molecular beam.
The Efficiency of B-Field Amplification at Shocks by Turbulence
Ji, Suoqing; Ruszkowski, Mateusz; Markevitch, Maxim
2016-01-01
Turbulent dynamo field amplification has often been invoked to explain the strong field strengths in thin rims in supernova shocks ($\\sim 100 \\, \\mu$G) and in radio relics in galaxy clusters ($\\sim \\mu$G). We present high resolution MHD simulations of the interaction between pre-shock turbulence, clumping and shocks, to quantify the conditions under which turbulent dynamo amplification can be significant. We demonstrate numerically converged field amplification which scales with Alfv\\'en Mach number, $B/B_0 \\propto {\\mathcal M}_{\\rm A}$, up to ${\\mathcal M}_{\\rm A} \\sim 150$. Amplification is dominated by compression at low ${\\mathcal M}_{\\rm A}$, and stretching (turbulent amplification) at high ${\\mathcal M}_{\\rm A}$. For the high Mach numbers characteristic of supernova shocks, the B-field grows exponentially and saturates at equipartition with turbulence, while the vorticity jumps sharply at the shock and subsequently decays; the resulting field is orientated predominately along the shock normal (an effect...
STUDY ON THE FUEL AIR MIXING INDUCED BY A SHOCK WAVE PROPAGATING INTO A H2-AIR INTERFACE
Institute of Scientific and Technical Information of China (English)
徐胜利; 岳朋涛; 韩肇元
2001-01-01
2 nd-order upwind TVD scheme was used to solve the laminar, fully Navier Stokes equations. The numerical simulations were done on the propagation of a shock wave with la 8 ＝ 2 and 4 into a hydrogen and air mixture in a duct and a duct with a rearward step. The results indicate that a swirling vortex may be generated in the lopsided interface behind the moving shock. Meanwhile, the complex shock system is also formed in this shear flow region. A large swirling vortex is produced and the fuel mixing can be enhanced by a shock wave at lov Mach number. But in a duct with a rearward step, the shock almost disappears in hydrogen for Mas = 2. The shock in hydrogen will become strong if Mas is large. Similar to the condition ofa shock moving in a duct full of hydrogen and air, a large vortex can be formed in the shear flow region. The large swirling vortex even gets through the reflected shock and impacts on the lower wall. Then, the distribution of hydrogen behind the rearward step is divided into two regions. The transition from regular reflection to Mach reflection vas observed as well in case Mas = 4 .
Comparison of geometrical shock dynamics and kinematic models for shock-wave propagation
Ridoux, J.; Lardjane, N.; Monasse, L.; Coulouvrat, F.
2017-09-01
Geometrical shock dynamics (GSD) is a simplified model for nonlinear shock-wave propagation, based on the decomposition of the shock front into elementary ray tubes. Assuming small changes in the ray tube area, and neglecting the effect of the post-shock flow, a simple relation linking the local curvature and velocity of the front, known as the A{-}M rule, is obtained. More recently, a new simplified model, referred to as the kinematic model, was proposed. This model is obtained by combining the three-dimensional Euler equations and the Rankine-Hugoniot relations at the front, which leads to an equation for the normal variation of the shock Mach number at the wave front. In the same way as GSD, the kinematic model is closed by neglecting the post-shock flow effects. Although each model's approach is different, we prove their structural equivalence: the kinematic model can be rewritten under the form of GSD with a specific A{-}M relation. Both models are then compared through a wide variety of examples including experimental data or Eulerian simulation results when available. Attention is drawn to the simple cases of compression ramps and diffraction over convex corners. The analysis is completed by the more complex cases of the diffraction over a cylinder, a sphere, a mound, and a trough.
Jernell, Lloyd S.
1961-01-01
An investigation w a s made i n the Langley Unitary Plan wind tunnel o determine the effects of fin area and the effects of antennas and w iring tunnels on the static longitudinal and lateral stability of a 0 .10- scale model of a three- stage configuration of the Scout vehicle. The tests were performed at Mach numbers of 2.29, 2.96, 3.96, and 4. 65 6 and at Reynolds numbers of about 3.5 X 10 per foot.
Slow light Mach-Zehnder fiber interferometer
Institute of Scientific and Technical Information of China (English)
Yundong Zhang; Jinfang Wang; Xuenan Zhang; Hao Wu; Yuanxue Cai; Jing Zhang; Ping Yuan
2012-01-01
A slow light structure Mach-Zehnder fiber interferometer is theoretically demonstrated.The sensitivity of the interferometer is significantly enhanced by the dispersion of the slow light structure.The numerical results show that the sensitivity enhancement factor varies with the coupling coefficient and reaches its maximum under critical coupling conditions.Interferometers have been investigated in relation to their applications in fields such as metrology[1],optical sensing[2],optical communication[3,4],quantum information processing[5],and biomedical engineering[6].A number of schemes have been proposed to improve the performance of interferometers[7],such as using photonic crystal structures to minimize the size of on-chip devices[8],utilizing the dispersive property of semiconductor to enhance the spectral sensitivity of interferometers[9,10],utilizing slow light medium to enhance the resolution of Fourier transform interferometer[11],exploiting fast light medium or slow light structure to increase the rotation sensitivity of a Sagnac interferometer[12,13],enhancing the transmittance of the Mach-Zehnder interferometer (MZI) in the slow light region by gratings[14],and using liquid crystal light valve to derive high sensitivity interferometers[15].%A slow light structure Mach-Zehnder fiber interferometer is theoretically demonstrated. The sensitivity of the interferometer is significantly enhanced by the dispersion of the slow light structure. The numerical results show that the sensitivity enhancement factor varies with the coupling coefficient and reaches its maximum under critical coupling conditions.
Energy Technology Data Exchange (ETDEWEB)
Kegalj, Martin
2013-11-01
In axial turbines tip leakage forms a large portion of the overall losses. Applying a shroud is very aerodynamically useful, but the higher mechanical loads of the revolving rotor blading exposed to a high thermal load and the higher costs suggest a shroudless configuration is better. The main parameter in the tip leakage loss is the tip gap height, which cannot be reduced arbitrarily as a running gap is necessary due to thermal expansion and vibration of the jet engine. The pressure ratio between pressure and suction of the rotor blade forces the fluid over the blade tip and leads to the formation of the tip leakage vortex. Reduced turning and losses caused by vortices and subsequent mixing are responsible for the reduced efficiency. Using a squealer cavity on the flat blade tip is a feasible way to reduce the aerodynamic losses. A portion of the kinetic energy of the tip leakage flow is dissipated while entering the cavity; the flow exiting the cavity enters the passage with reduced momentum and reduced tip gap mass flow. A 1(1)/(2) stage low mach number turbine was used to investigate the influence of tip geometry. Aerodynamic measurements, performed with five-hole probes, two-component hot-wire anemometer, unsteady wall pressure sensors, stereo and borescopic particle-image-velocimetry setups and oil and dye flow visualization, found small differences in the flow velocities and angles between the flat and squealer tip configuration in the measurement planes downstream of the rotor. The measurement uncertainty proves the difficulty of determining the influence of the squealer cavity on the blade row outflow with global measurement data. To gather information on the flow close to the casing inside the rotor passage is only possible with non-intrusive laser measurement techniques. Comparison of the different tip geometries is still difficult due to the small differences in the absolute flow data. The use of the {lambda}{sub 2} vortex criterion enables an objective
Reflection of a converging cylindrical shock wave segment by a straight wedge
Gray, B.; Skews, B.
2017-01-01
As a converging cylindrical shock wave propagates over a wedge, the shock wave accelerates and the angle between the shock wave and the wedge decreases. This causes the conditions at the reflection point to move from what would be the irregular reflection domain for a straight shock wave into the regular reflection domain. This paper covers a largely qualitative study of the reflection of converging shock wave segments with Mach numbers between 1.2 and 2.1 by wedges inclined at angles between 15° and 60° from experimental and numerical results. The sonic condition conventionally used for predicting the type of reflection of straight shock waves was found to also be suitable for predicting the initial reflection of a curved shock wave. Initially regular reflections persisted until the shock was completely reflected by the wedge, whereas the triple point of initially irregular reflections was observed to return to the wedge surface, forming transitioned regular reflection. After the incident shock wave was completely reflected by the wedge, a shock wave focusing mechanism was observed to amplify the pressure on the surface of the wedge by a factor of up to 100 for low wedge angles.
Relationship of Interplanetary Shock Micro and Macro Characteristics: A Wind Study
Szabo, Adam; Koval, A
2008-01-01
The non-linear least squared MHD fitting technique of Szabo 11 9941 has been recently further refined to provide realistic confidence regions for interplanetary shock normal directions and speeds. Analyzing Wind observed interplanetary shocks from 1995 to 200 1, macro characteristics such as shock strength, Theta Bn and Mach numbers can be compared to the details of shock micro or kinetic structures. The now commonly available very high time resolution (1 1 or 22 vectors/sec) Wind magnetic field data allows the precise characterization of shock kinetic structures, such as the size of the foot, ramp, overshoot and the duration of damped oscillations on either side of the shock. Detailed comparison of the shock micro and macro characteristics will be given. This enables the elucidation of shock kinetic features, relevant for particle energization processes, for observations where high time resolution data is not available. Moreover, establishing a quantitative relationship between the shock micro and macro structures will improve the confidence level of shock fitting techniques during disturbed solar wind conditions.
Numerical study of shock waves propagating through right angled multiple elbows
Kage, Kazuyuki; Shiroyama, Mihoko; Ishimatsu, Katsuya
2005-09-01
The details of the shock propagated through the right angled multiple elbows (mainly double elbow and fourfold elbow) are investigated by the numerical study. Computations were carried out by solving the two-dimensional compressible Navier-Stokes equations by using the total variation diminishing (TVD) scheme. Computations were performed for six types of elbow (two types of double elbow and four types of fourfold elbow) and two incident shock Mach numbers (Ms=1.5, 2.3). The effects of the direction and number of the bends in the stabilizing, merging and attenuating processes of the shock are numerically explored by various diagrams such as pressure contours, pressure distributions on the walls and time histories of the pressure contours, and the strength of the shock front at the location of about 20 times the length for each type of elbows was displayed.
Numerical Study of Shock Waves Propagating through Right Angled Multiple Elbows
Institute of Scientific and Technical Information of China (English)
Kazuyuki KAGE; Mihoko SHIROYAMA; Katsuya ISHIMATSU
2005-01-01
The details of the shock propagated through the right angled multiple elbows (mainly double elbow and fourfold elbow) are investigated by the numerical study. Computations were carried out by solving the two-dimensional compressible Navier-Stokes equations by using the total variation diminishing (TVD) scheme. Computations were performed for six types of elbow (two types of double elbow and four types of fourfold elbow) and two incident shock Mach numbers (Ms=1.5, 2.3). The effects of the direction and number of the bends in the stabilizing, merging and attenuating processes of the shock are numerically explored by various diagrams such as pressure contours, pressure distributions on the walls and time histories of the pressure contours, and the strength of the shock front at the location of about 20 times the length for each type of elbows was displayed.
Gasdynamic characteristics of toroidal shock and detonation wave converging
Institute of Scientific and Technical Information of China (English)
TENG; Honghui; JIANG; Zonglin
2005-01-01
The modified CCW relation is applied to analyzing the shock, detonation wave converging and the role of chemical reactions in the process. Results indicate that the shock wave is strengthened faster than the detonation wave in the converging at the same initial Mach number. Euler equations implemented with a detailed chemical reaction model are solved to simulate toroidal shock and detonation wave converging. Gasdynamic characteristics of the converging are investigated, including wave interaction patterns, observable discrepancies and physical phenomena behind them. By comparing wave diffractions, converging processes and pressure evolutions in the focusing area, the different effects of chemical reactions on diffracting and converging processes are discussed and the analytic conclusion is demonstrated through the observation of numerical simulations.
Ion streaming instabilities with application to collisionless shock wave structure
Golden, K. I.; Linson, L. M.; Mani, S. A.
1973-01-01
The electromagnetic dispersion relation for two counterstreaming ion beams of arbitrary relative strength flowing parallel to a dc magnetic field is derived. The beams flow through a stationary electron background and the dispersion relation in the fluid approximation is unaffected by the electron thermal pressure. Magnetic effects on the ion beams are included, but the electrons are treated as a magnetized fluid. The dispersion relation is solved with a zero net current condition applied and the regions of instability in the k-U space (U is the relative velocity between the two ion beams) are presented. These results are extensions of Kovner's analysis for weak beams. The parameters are then chosen to be applicable for parallel shocks. It is found that unstable waves with zero group velocity in the shock frame can exist near the leading edge of the shock for upstream Alfven Mach numbers greater than 5.5.
Cross-scale coupling at a perpendicular collisionless shock
Umeda, Takayuki; Yamazaki, Ryo; 10.1016/j.pss.2010.01.007
2011-01-01
A full particle simulation study is carried out on a perpendicular collisionless shock with a relatively low Alfven Mach number (M_A=5). In the present study, we have performed a two-dimensional (2D) electromagnetic full particle simulation with a "shock-rest-frame model". The simulation domain is taken to be larger than the ion inertial length in order to include full kinetics of both electrons and ions. The present simulation result has confirmed the transition of shock structures from the cyclic self-reformation to the quasi-stationary shock front. During the transition, electrons and ions are thermalized in the direction parallel to the shock magnetic field. Ions are thermalized by low-frequency electromagnetic waves (or rippled structures) excited by strong ion temperature anisotropy at the shock foot, while electrons are thermalized by high-frequency electromagnetic waves (or whistler mode waves) excited by electron temperature anisotropy at the shock overshoot. Ion acoustic waves are also excited at th...
Electron Weibel Instability Mediated Laser Driven Electromagnetic Collisionless Shock
Jia, Qing; Mima, Kunioki; Cai, Hong-Bo; Taguchi, Toshihiro; Nagatomo, Hideo; He, X. T.
2015-11-01
As a fundamental nonlinear structure, collisionless shock is widely studied in astrophysics. Recently, the rapidly-developing laser technology provides a good test-bed to study such shock physics in laboratory. In addition, the laser driven shock ion acceleration is also interested due to its potential applications. We explore the effect of external parallel magnetic field on the collisionless shock formation and resultant particle acceleration by using the 2D3V PIC simulations. We show that unlike the electrostatic shock generated in the unmagnetized plasma, the shock generated in the weakly-magnetized laser-driven plasma is mostly electromagnetic (EM)-like with higher Mach number. The generation mechanism is due to the stronger transverse magnetic field self-generated at the nonlinear stage of the electron Weibel instability which drastically scatters particles and leads to higher energy dissipation. Simulation results also suggest more ions are reflected by this EM shock and results in larger energy transfer rate from the laser to ions, which is of advantage for applications such as neutron production and ion fast ignition.
Energy Technology Data Exchange (ETDEWEB)
Tamborra, Irene; Raffelt, Georg G. [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, D-80805 München (Germany); Hanke, Florian; Janka, Hans-Thomas; Müller, Bernhard [Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); Marek, Andreas [Rechenzentrum der Max-Planck-Gesellschaft, Boltzmannstr. 2, D-85741 Garching (Germany)
2014-09-10
During the stalled-shock phase of our three-dimensional, hydrodynamical core-collapse simulations with energy-dependent, three-flavor neutrino transport, the lepton-number flux (ν {sub e} minus ν-bar {sub e}) emerges predominantly in one hemisphere. This novel, spherical-symmetry breaking neutrino-hydrodynamical instability is termed LESA for 'Lepton-number Emission Self-sustained Asymmetry'. While the individual ν {sub e} and ν-bar {sub e} fluxes show a pronounced dipole pattern, the heavy-flavor neutrino fluxes and the overall luminosity are almost spherically symmetric. Initially, LESA seems to develop stochastically from convective fluctuations. It exists for hundreds of milliseconds or more and persists during violent shock sloshing associated with the standing accretion shock instability. The ν {sub e} minus ν-bar {sub e} flux asymmetry originates predominantly below the neutrinosphere in a region of pronounced proto-neutron star (PNS) convection, which is stronger in the hemisphere of enhanced lepton-number flux. On this side of the PNS, the mass accretion rate of lepton-rich matter is larger, amplifying the lepton-emission asymmetry, because the spherical stellar infall deflects on a dipolar deformation of the stalled shock. The increased shock radius in the hemisphere of less mass accretion and minimal lepton-number flux ( ν-bar {sub e} flux maximum) is sustained by stronger convection on this side, which is boosted by stronger neutrino heating due to 〈ϵ{sub ν-bar{sub e}}〉>〈ϵ{sub ν{sub e}}〉. Asymmetric heating thus supports the global deformation despite extremely nonstationary convective overturn behind the shock. While these different elements of the LESA phenomenon form a consistent picture, a full understanding remains elusive at present. There may be important implications for neutrino-flavor oscillations, the neutron-to-proton ratio in the neutrino-heated supernova ejecta, and neutron-star kicks, which remain to be
Research status of key techniques for shock-induced combustion ramjet(shcramjet) engine
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
As one of the most promising propulsion systems in the future,shock-induced combustion ramjet engine can remedy the disadvantages in the integrated design of scramjet engine and airframe.It can shorten the length of the combustor,lighten the structure weight of the engine and keep better performance in a broad range of flight Mach number.The elementary principle of shock-induced combustion ramjet engine is introduced.The key technologies of this kind of propulsion system are described,while their research status is presented in detail.Suggestion on the development of shcramjet engine in China is put forward.
Numerical Study of Shock Waves Propagating in an Elbow : A Double Elbow
1999-01-01
In this paper, the attenuation and the nonuniformity regarding the strength and the shape of the shock wave front propagating through a double elbow were explored by numerical simulation. Computations were carried out by solving the two-dimensional compressible Navier-Stokes equations by using the total variation diminishing (TVD) scheme. Computations were performed for six types of elbow and two incident shock Mach numbers (M_s=1.3, 2.0). The flow field were numerically visualized by the pre...
A second-order shock-expansion method applicable to bodies of revolution near zero lift
1957-01-01
A second-order shock-expansion method applicable to bodies of revolution is developed by the use of the predictions of the generalized shock-expansion method in combination with characteristics theory. Equations defining the zero-lift pressure distributions and the normal-force and pitching-moment derivatives are derived. Comparisons with experimental results show that the method is applicable at values of the similarity parameter, the ratio of free-stream Mach number to nose fineness ratio, from about 0.4 to 2.
Effects of laser polarization on electrostatic shock ion acceleration in near-critical plasmas
Kim, Young-Kuk; Kang, Teyoun; Hur, Min Sup
2016-10-01
Collisionless electrostatic shock ion acceleration has become a major regime of laser-driven ion acceleration owing to generation of quasi-monoenergetic ion beams from moderate parametric conditions of lasers and plasmas in comparison with target-normal-sheath-acceleration or radiation pressure acceleration. In order to construct the shock, plasma heating is an essential condition for satisfying Mach number condition 1.5 Weibel instability. This work was supported by the Basic Science Research Program (NRF- 2013R1A1A2006353) and the Creative Allied Project (CAP-15-06-ETRI).
Directory of Open Access Journals (Sweden)
Mihai Leonida NICULESCU
2015-09-01
Full Text Available The temperature in the nose region of a hypersonic vehicle can be extremely high, for example, reaching approximately 11 000 K at a Mach number of 36 (Apollo reentry. The bow shock wave is normal, or nearly normal, in the nose region of a blunt body, and the gas temperature behind this shock wave can be enormous at hypersonic speeds. In this case, the assumption of a calorically perfect nonreacting gas with the ratio of specific heats of 1.4 gives an unrealistically high value of temperature. Therefore, the proper inclusion of chemically reacting effects is vital to the calculation of an accurate normal shock wave temperature.
Propagation of a Strong Shock Over a Random Bed of Spherical Particles
Energy Technology Data Exchange (ETDEWEB)
Mehta, Y. [Univ. of Florida, Gainesville, FL (United States); Neal, C. [Univ. of Florida, Gainesville, FL (United States); Salari, K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Jackson, T. L. [Univ. of Florida, Gainesville, FL (United States); Balachandar, S. [Univ. of Florida, Gainesville, FL (United States); Thakur, S. [Univ. of Florida, Gainesville, FL (United States)
2017-04-11
Propagation of a strong shock through a bed of particles results in complex wave dynamics such as a reflected shock, a transmitted shock, and highly unsteady flow inside the particle bed. In this paper we present three-dimensional numerical simulations of shock propagation in air over a random bed of particles. We assume the flow is inviscid and governed by the Euler equations of gas dynamics. Simulations are carried out by varying the volume fraction of the particle bed at a fixed shock Mach number. We compute the unsteady inviscid streamwise and transverse drag coefficients as a function of time for each particle in the random bed as a function of volume fraction. We show that (i) there are significant variations in the peak drag for the particles in the bed, (ii) the mean peak drag as a function of streamwise distance through the bed decreases with a slope that increases as the volume fraction increases, and (iii) the deviation from the mean peak drag does not correlate with local volume fraction. We also present the local Mach number and pressure contours for the different volume fractions to explain the various observed complex physical mechanisms occurring during the shock-particle interactions. Since the shock interaction with the random bed of particles leads to transmitted and reflected waves, we compute the average flow properties to characterize the strength of the transmitted and reflected shock waves and quantify the energy dissipation inside the particle bed. Finally, to better understand the complex wave dynamics in a random bed, we consider a simpler approximation of a planar shock propagating in a duct with a sudden area change. We obtain Riemann solutions to this problem, which are used to compare with fully resolved numerical simulations.
Fluid dynamics of the shock wave reactor
Masse, Robert Kenneth
2000-10-01
High commercial incentives have driven conventional olefin production technologies to near their material limits, leaving the possibility of further efficiency improvements only in the development of entirely new techniques. One strategy known as the Shock Wave Reactor, which employs gas dynamic processes to circumvent limitations of conventional reactors, has been demonstrated effective at the University of Washington. Preheated hydrocarbon feedstock and a high enthalpy carrier gas (steam) are supersonically mixed at a temperature below that required for thermal cracking. Temperature recovery is then effected via shock recompression to initiate pyrolysis. The evolution to proof-of-concept and analysis of experiments employing ethane and propane feedstocks are presented. The Shock Wave Reactor's high enthalpy steam and ethane flows severely limit diagnostic capability in the proof-of-concept experiment. Thus, a preliminary blow down supersonic air tunnel of similar geometry has been constructed to investigate recompression stability and (especially) rapid supersonic mixing necessary for successful operation of the Shock Wave Reactor. The mixing capabilities of blade nozzle arrays are therefore studied in the air experiment and compared with analytical models. Mixing is visualized through Schlieren imaging and direct photography of condensation in carbon dioxide injection, and interpretation of visual data is supported by pressure measurement and flow sampling. The influence of convective Mach number is addressed. Additionally, thermal behavior of a blade nozzle array is analyzed for comparison to data obtained in the course of succeeding proof-of-concept experiments. Proof-of-concept is naturally succeeded by interest in industrial adaptation of the Shock Wave Reactor, particularly with regard to issues involving the scaling and refinement of the shock recompression. Hence, an additional, variable geometry air tunnel has been constructed to study the parameter
Ball, J. W.; Lindahl, R. H.
1976-01-01
The purpose of the test was to investigate the nature of the Orbiter boundary layer characteristics at angles of attack from -4 to 32 degrees at a Mach number of 4.6. The effect of large grit, employed as transition strips, on both the nature of the boundary layer and the force and moment characteristics were investigated along with the effects of large negative elevon deflection on lee side separation. In addition, laminar and turbulent boundary layer separation phenomena which could cause asymmetric flow separation were investigated.
Magnetohydrodynamic Fast Shocks and Their Relation to Solar Energetic Particle Event Intensities
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Kan Liou
2013-01-01
Full Text Available Gradual solar energetic particles (SEPs are associated with interplanetary (IP shock driven by coronal mass ejections. Testing theories/models that are built around shock acceleration mechanisms is difficult due to the complexity of SEP fluxes acquired by single-point measurements. To circumvent this, we correlate fast-forward shock Mach numbers derived from a 1.5D magnetohydrodynamics simulation with the intensity of solar energetic oxygen (O and helium-4 (4He particles acquired by instruments aboard the ACE spacecraft during a series of coronal mass ejections in 2003 (October 28 - 31. A good correlation at the 5% significance level is found for O and 4He with energy (E > ~10 MeV n-1, with the peak correlation coefficient r = 0.82 for O (E = 63.8 - 89.8 MeV n-1 and r = 0.77 for 4He (E = 18.0 - 29.4 MeV n-1, respectively, for hourly averaged data. This result not only bolsters the causal relationship between IP fast shocks and SEPs, but also suggests that the Mach number of IP shocks is one of the major controlling parameters for the intensity of SEPs measured in the near-Earth space.
ALMA-SZ Detection of a Galaxy Cluster Merger Shock at Half the Age of the Universe
Basu, K.; Sommer, M.; Erler, J.; Eckert, D.; Vazza, F.; Magnelli, B.; Bertoldi, F.; Tozzi, P.
2016-10-01
We present ALMA measurements of a merger shock using the thermal Sunyaev-Zel’dovich (SZ) effect signal, at the location of a radio relic in the famous El Gordo galaxy cluster at z≈ 0.9. Multi-wavelength analysis in combination with the archival Chandra data and a high-resolution radio image provides a consistent picture of the thermal and non-thermal signal variation across the shock front and helps to put robust constraints on the shock Mach number as well as the relic magnetic field. We employ a Bayesian analysis technique for modeling the SZ and X-ray data self-consistently, illustrating respective parameter degeneracies. Combined results indicate a shock with Mach number { M }={2.4}-0.6+1.3, which in turn suggests a high value of the magnetic field (of the order of 4-10 μ {{G}}) to account for the observed relic width at 2 GHz. At roughly half the current age of the universe, this is the highest-redshift direct detection of a cluster shock to date, and one of the first instances of an ALMA-SZ observation in a galaxy cluster. It shows the tremendous potential for future ALMA-SZ observations to detect merger shocks and other cluster substructures out to the highest redshifts.
Nonrelativistic grey Sn-transport radiative-shock solutions
Ferguson, J. M.; Morel, J. E.; Lowrie, R. B.
2017-06-01
We present semi-analytic radiative-shock solutions in which grey Sn-transport is used to model the radiation, and we include both constant cross sections and cross sections that depend on temperature and density. These new solutions solve for a variable Eddington factor (VEF) across the shock domain, which allows for interesting physics not seen before in radiative-shock solutions. Comparisons are made with the grey nonequilibrium-diffusion radiative-shock solutions of Lowrie and Edwards [1], which assumed that the Eddington factor is constant across the shock domain. It is our experience that the local Mach number is monotonic when producing nonequilibrium-diffusion solutions, but that this monotonicity may disappear while integrating the precursor region to produce Sn-transport solutions. For temperature- and density-dependent cross sections we show evidence of a spike in the VEF in the far upstream portion of the radiative-shock precursor. We show evidence of an adaptation zone in the precursor region, adjacent to the embedded hydrodynamic shock, as conjectured by Drake [2,3], and also confirm his expectation that the precursor temperatures adjacent to the Zel'dovich spike take values that are greater than the downstream post-shock equilibrium temperature. We also show evidence that the radiation energy density can be nonmonotonic under the Zel'dovich spike, which is indicative of anti-diffusive radiation flow as predicted by McClarren and Drake [4]. We compare the angle dependence of the radiation flow for the Sn-transport and nonequilibrium-diffusion radiation solutions, and show that there are considerable differences in the radiation flow between these models across the shock structure. Finally, we analyze the radiation flow to understand the cause of the adaptation zone, as well as the structure of the Sn-transport radiation-intensity solutions across the shock structure.
Different variants of R13 moment equations applied to the shock-wave structure
Timokhin, M. Yu.; Struchtrup, H.; Kokhanchik, A. A.; Bondar, Ye. A.
2017-03-01
Various versions of the regularized 13-moment system (R13) are applied to the problem of the shock wave structure in a monatomic Maxwell gas for Mach numbers up to M = 10. Numerical solutions are compared to direct simulation Monte Carlo results computed by the SMILE++ software system, in order to identify applicability and limitations of the variants. Over time, several versions of the R13 equations were presented, which differ in non-linear contributions for high-order moments but agree in asymptotic expansion to the third order in the Knudsen number. All variants describe typical subsonic microflows well, for which the non-linear contributions only play a minor role. The challenge of the present study is to determine the real boundaries of applicability of each variant of the moment equations as applied to non-equilibrium supersonic flows, depending on the Mach number and local Knudsen number.
Non-ideal compressible-fluid effects in oblique shock waves
Gori, G.; Vimercati, D.; Guardone, A.
2017-03-01
The non-monotone dependence of the speed of sound along adiabatic transformations is demonstrated to result in the admissibility of non-ideal increase of the flow Mach number across oblique shock waves, for pre-shock states in close proximity of the liquid-vapour saturation curve. This non-ideal behaviour is primarily associated with a less-than-unity value of the fundamental derivative of gasdynamics and, therefore, non-ideal shock waves are expected to be observed in flows of fluids with moderate molecular complexity. The simple yet qualitatively sound van der Waals model is used to confirm the present findings and to provide exemplary non-ideal shock waves.
The 'toothbrush-cluster': probing particle acceleration by merger induced shock waves
van Weeren, Reinout
2012-09-01
We have discovered a spectacular merging galaxy cluster hosting a 2-Mpc elongated radio source, suggesting particle acceleration at merger shocks. The large straight extent is however very difficult to explain with current merger scenarios and a very high Mach number of 4.5 is required to explain the radio spectral index. We therefore argue that this cluster is a key object to test current models of shock acceleration and cluster formation. The proposed Chandra+EVLA observations will address the following: (i) is there a compelling need for a more sophisticated particle acceleration mechanism than standard diffusive shock acceleration? And (ii) are we witnessing a very special configuration consisting of multiple merger events that collectively conspire to yield such a linear shock?
An LDA investigation of the normal shock wave boundary layer interaction
Chriss, R. M.; Hingst, W. R.; Strazisar, A. J.; Keith, T. G.
1990-01-01
Nonintrusive measurements have been made of two normal shock wave-boundary layer interactions. Two-dimensional measurements were made throughout the interaction region while three-dimensional measurements were made in the vicinity of the shock wave. The measurements were made in the corner of the test section of a continuous flow supersonic wind tunnel in which a normal shock wave had been stabilized. LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The reported results define the flowfield structure in detail for each case.
Propagation of Spherical Magnetogasdynamic Shock in a Radiative Gas
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B.G. Verma
1977-07-01
Full Text Available In this paper the propagation of explosion waves, in a conducting gas, produced on account of a point explosion into inhomogeneous self-gravitating gas sphere is considered. Radiation effects have been taken into account and the density of the gas is assumed to vary as r/sup -alpha/, r being the distance from the point of explosion. In order that the mass and pressure be positive in the equilibrium state, the choice of alpha is restricted between 1 and 3. The variation of Mach number of the shock and energy of the wave with time have been taken into consideration.
First ALMA Detection of a Galaxy Cluster Merger Shock
Basu, K.; Sommer, M.; Erler, J.; Eckert, D.; Vazza, F.; Magnelli, B.; Bertoldi, F.; Tozzi, P.
2016-12-01
We report on the first ALMA measurement of a galaxy cluster merger shock, observed at the location of a radio relic in the famous El Gordo galaxy cluster at redshift z 0.9. Located at about half the current age of the Universe, this is also the most distant example of a directly measured astrophysical shock. ALMA Band 3 was utilised to measure the Sunyaev-Zel'dovich (SZ) effect signature that confirms a small-scale change in pressure as expected from the passage of a shock in the intracluster medium. The results support a previous radio-based estimate of the shock Mach number and display similarities, and also some mild tensions, with the X-ray based results. Most importantly, these results show the potential of ALMA to detect galaxy cluster shocks, observations that will advance our knowledge of cluster formation, non-thermal particle acceleration and amplification of magnetic fields across the entire observable Universe where such relic shocks can be found.
SHOCK HEATING OF THE MERGING GALAXY CLUSTER A521
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Bourdin, H.; Mazzotta, P. [Dipartimento di Fisica, Universita degli Studi di Roma ' Tor Vergata' , via della Ricerca Scientifica, 1, I-00133 Roma (Italy); Markevitch, M. [NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Giacintucci, S. [Joint Space-Science Institute, University of Maryland, College Park, MD 20742-2421 (United States); Brunetti, G., E-mail: herve.bourdin@roma2.infn.it [INAF-Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy)
2013-02-10
A521 is an interacting galaxy cluster located at z = 0.247, hosting a low-frequency radio halo connected to an eastern radio relic. Previous Chandra observations hinted at the presence of an X-ray brightness edge at the position of the relic, which may be a shock front. We analyze a deep observation of A521 recently performed with XMM-Newton in order to probe the cluster structure up to the outermost regions covered by the radio emission. The cluster atmosphere exhibits various brightness and temperature anisotropies. In particular, two cluster cores appear to be separated by two cold fronts. We find two shock fronts, one that was suggested by Chandra and that is propagating to the east, and another to the southwestern cluster outskirt. The two main interacting clusters appear to be separated by a shock-heated region, which exhibits a spatial correlation with the radio halo. The outer edge of the radio relic coincides spatially with a shock front, suggesting that this shock is responsible for the generation of cosmic-ray electrons in the relic. The propagation direction and Mach number of the shock front derived from the gas density jump, M = 2.4 {+-} 0.2, are consistent with expectations from the radio spectral index, under the assumption of Fermi I acceleration mechanism.
Shock Heating of the Merging Galaxy Cluster A521
Bourdin, H.; Mazzotta, P.; Markevitch, M.; Giacintucci, S.; Brunetti, G.
2013-01-01
A521 is an interacting galaxy cluster located at z = 0.247, hosting a low-frequency radio halo connected to an eastern radio relic. Previous Chandra observations hinted at the presence of an X-ray brightness edge at the position of the relic, which may be a shock front. We analyze a deep observation of A521 recently performed with XMM-Newton in order to probe the cluster structure up to the outermost regions covered by the radio emission. The cluster atmosphere exhibits various brightness and temperature anisotropies. In particular, two cluster cores appear to be separated by two cold fronts. We find two shock fronts, one that was suggested by Chandra and that is propagating to the east, and another to the southwestern cluster outskirt. The two main interacting clusters appear to be separated by a shock-heated region, which exhibits a spatial correlation with the radio halo. The outer edge of the radio relic coincides spatially with a shock front, suggesting that this shock is responsible for the generation of cosmic-ray electrons in the relic. The propagation direction and Mach number of the shock front derived from the gas density jump, M = 2.4 +/- 0.2, are consistent with expectations from the radio spectral index, under the assumption of Fermi I acceleration mechanism.
Cosmological Structure Formation Shocks and Cosmic Rays in Hydrodynamical Simulations
Pfrommer, C.; Springel, V.; Enβlin, T. A.; Jubelgas, M.
Cosmological shock waves during structure formation not only play a decisive role for the thermalization of gas in virializing structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. We discuss a novel numerical treatment of the physics of cosmic rays in combination with a formalism for identifying and measuring the shock strength on-the-fly during a smoothed particle hydrodynamics simulation. In our methodology, the non-thermal CR population is treated self-consistently in order to assess its dynamical impact on the thermal gas as well as other implications on cosmological observables. Using this formalism, we study the history of the thermalization process in high-resolution hydrodynamic simulations of the Lambda cold dark matter model. Collapsed cosmological structures are surrounded by shocks with high Mach numbers up to 1000, but they play only a minor role in the energy balance of thermalization. However, this finding has important consequences for our understanding of the spatial distribution of CRs in the large-scale structure. In high resolution simulations of galaxy clusters, we find a low contribution of the averaged CR pressure, due to the small acceleration efficiency of lower Mach numbers of flow shocks inside halos and the softer adiabatic index of CRs. These effects disfavour CRs when a composite of thermal gas and CRs is adiabatically compressed. However, within cool core regions, the CR pressure reaches equipartition with the thermal pressure leading, to a lower effective adiabatic index and thus to an enhanced compressibility of the central intracluster medium. This effect increases the central density and pressure of the cluster, and thus the resulting X-ray emission and the central Sunyaev-Zel'dovich flux decrement. The integrated Sunyaev-Zel'dovich effect, however, is only slightly changed.
Shock interaction with organized structures: Theory and computation
Ding, Zhong
Unsteady interactions between shocks and turbulence are important phenomena frequently encountered in high-speed flows. In this dissertation the problem of a shock interaction with an entropy spot is studied by means of both theoretical analysis and nonlinear computation. The main objective of the studies is to apply both theoretical and computational approaches to study the physics underlying such shock interaction process. The theoretical analysis is based on the Fourier decomposition of the upstream disturbance, the interaction of each Fourier mode with the shock, and the reconstruction of the downstream disturbance via the inverse Fourier transform. The theory is linear in that it assumes the principle of superposition and that the Rankine-Hugoniot relations are linearized about the mean position of the shock. The numerical simulation is carried out within the framework of the unsteady and compressible Euler equations, coupled with an equation for the shock motion, solved numerically by a sixth-order accurate spatial scheme and a fourth-order Runge-Kutta time-integration method. Analyses of the results are concentrated on the case of a Mach 2.0 shock interaction with an entropy spot that has a Gaussian density distribution. The theoretical analysis and the numerical simulation are verified with each other for small amplitude disturbances. The roles of the evanescent and the non-evanescent waves and the mechanisms for downstream disturbance generations are explored in details. In addition, the quasi three-dimensional interaction between a shock and a vortex ring is investigated computationally within the framework of the axisymmetric Euler equations. The vortex ring, which is based on Lamb's formula, has an upstream circulation Gamma = 0.01 and its aspect ratio R lies in the range 8 ≤ R ≤ 100. The shock Mach number varies in the range 1.1 ≤ M1 ≤ 1.8. The interaction results in the streamwise compression of the vortex core and the generation of a toroidal
Curved Radio Spectra of Weak Cluster Shocks
Kang, Hyesung; Ryu, Dongsu
2015-08-01
In order to understand certain observed features of arc-like giant radio relics such as the rareness, uniform surface brightness, and curved integrated spectra, we explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock impinges on a magnetized cloud containing fossil relativistic electrons. Toward this end, we perform DSA simulations of spherical shocks with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301, and calculate the ensuing radio synchrotron emission from re-accelerated electrons. Three types of fossil electron populations are considered: a delta-function like population with the shock injection momentum, a power-law distribution, and a power law with an exponential cutoff. The surface brightness profile of the radio-emitting postshock region and the volume-integrated radio spectrum are calculated and compared with observations. We find that the observed width of the Sausage relic can be explained reasonably well by shocks with speed {u}{{s}}˜ 3× {10}3 {km} {{{s}}}-1 and sonic Mach number {M}{{s}}˜ 3. These shocks produce curved radio spectra that steepen gradually over (0.1-10){ν }{br} with a break frequency {ν }{br}˜ 1 GHz if the duration of electron acceleration is ˜60-80 Myr. However, the abrupt increase in the spectral index above ˜1.5 GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons with {γ }{{e}}≳ {10}4.
Phillips, W. P.; Fournier, R. H.
1979-01-01
Supersonic aerodynamic characteristics are presented for the 140A/B space shuttle orbiter configuration (0.010 scale) and for the configuration modified to incorporate geometry changes in the wing planform fillet region. The modifications designed to extend the orbiter's longitudinal trim capability to more forward center-of-gravity locations, included reshaping of the baseline wing planform fillet and adding canards. The investigation was made in the high Mach number test section of the Langley Unitary Plan Wind Tunnel at a Reynolds number of approximately 2.2 million based on fuselage reference length. The angle-of-attack range for the investigation extended from -1 deg to 31 deg. Data were obtained with the elevators and body flap deflected at appropriate negative and positive conditions to assess the trim limits.
Energy Technology Data Exchange (ETDEWEB)
Weber, Christopher R. [Univ. of Wisconsin, Madison, WI (United States); Cook, Andrew W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bonazza, Riccardo [Univ. of Wisconsin, Madison, WI (United States)
2013-05-14
Here we derive a growth-rate model for the Richtmyer–Meshkov mixing layer, given arbitrary but known initial conditions. The initial growth rate is determined by the net mass flux through the centre plane of the perturbed interface immediately after shock passage. The net mass flux is determined by the correlation between the post-shock density and streamwise velocity. The post-shock density field is computed from the known initial perturbations and the shock jump conditions. The streamwise velocity is computed via Biot–Savart integration of the vorticity field. The vorticity deposited by the shock is obtained from the baroclinic torque with an impulsive acceleration. Using the initial growth rate and characteristic perturbation wavelength as scaling factors, the model collapses the growth-rate curves and, in most cases, predicts the peak growth rate over a range of Mach numbers (1.1 ≤M_{i}≤1.9), Atwood numbers (₋0.73 ≤ A ≤ ₋0.35 and 0.22 ≤ A ≤ 0.73), adiabatic indices (1.40/1.67≤γ_{1}/γ_{2}≤1.67/1.09) and narrow-band perturbation spectra. Lastly, the mixing layer at late times exhibits a power-law growth with an average exponent of θ=0.24.
Shock train generated turbulence inside a nozzle with a small opening angle
Energy Technology Data Exchange (ETDEWEB)
Grzona, A.; Olivier, H. [RWTH Aachen University, Shock Wave Laboratory, Aachen (Germany)
2011-09-15
The flow inside an over expanding rectangular nozzle with a small opening angle of 1.6 is investigated by means of high-speed schlieren and shadowgraph photography, pressure probes and hot-wire anemometry on the nozzle centre line in order to measure the turbulent fluctuations generated by the occurring shock wave/boundary layer interaction. Additionally, an optical shock capturing tool is deployed to measure the amplitude and frequency of the shock train oscillation. Varying the back pressure, the pre-shock Mach number is changed between Ma{sub 1} = 1.1 and 2.1. Two different modes of turbulence generation and distribution are detected. For a single normal shock and a normal shock train, the normal Reynolds stress u{sup '2} on the channel axis is only slightly increased compared to the free stream value, whereas for the cases of a lambda foot shock train and an x-type shock train, a strong intensification by forming a turbulent mixing zone can be observed. (orig.)
Shock-induced mixing of nonhomogeneous density turbulent jets
Hermanson, J. C.; Cetegen, B. M.
2000-05-01
An experimental study of the mixing enhancement and changes in flow structure arising from the interaction of weak normal shock waves with turbulent jets was conducted. The experimental configuration was an axisymmetric jet processed by weak normal shock waves propagating in a shock tube along the jet axis. Experiments involved three different jet gases: helium, air, and carbon dioxide, each in a coflowing air stream, with nominal jet fluid to ambient density ratios of 0.14, 1.00, and 1.52, respectively. The jet local Reynolds number was Reδ≈25 000 and the nominal oncoming shock Mach numbers were 1.23 and 1.45. Planar laser Mie light scattering from mineral oil smoke was utilized for flow visualization and for obtaining jet fluid concentration distributions across diametric planes of jets. Analysis of the spatial probability density function (pdf) of jet fluid concentration indicates that the average helium jet fluid concentration levels decrease and become more uniform in the regions processed by the shock waves. The degree of mixing enhancement increases with increasing shock strength, and amounts to nearly 30% for the stronger shock (M=1.45). The passage of a shock through low-density (helium) jets induces the formation of a flow structure that resembles a large-scale, toroidal vortex. The air and carbon dioxide jets exhibit neither a vortex-like structure or a significant change in mixing upon shock passage, unlike the helium jets. A comparison of the results for the helium and carbon dioxide jets indicates that the reversal of the density ratio between the jet and the surroundings, and the consequent change in the sign of baroclinic vorticity does not yield similar effects in terms of flow structure or mixing enhancement. The average concentration behind the shock wave decreases for both air and helium jets with increasing distance behind the shock. These features are explained qualitatively in terms of a simple characteristic time scale argument. The
Characteristics of Embedded-Shock-Free Compressible Vortex Rings: A Detailed Study Using PIV
Directory of Open Access Journals (Sweden)
C. Lakshmana Dora
2011-01-01
Full Text Available The present study focus on evolution of compressible vortex ring generated at the open end of a shock tube through accurate measurement of velocity field using Particle Image Velocimetry (PIV. To investigate the unsteady characteristics of embedded shock-free, low Mach number vortex rings, two cases (shock Mach numbers, M=1.27 and M=1.37 are considered for PIV measurements. Time-dependent variations of circulation, core and ring diameters, and ring velocity are calculated from the measured velocity field. Pinching-off process is investigated in detail for both cases. Formation time and the time of complete detachment of the vortex ring from the trailing jet are identified from the velocity and vorticity field. The ring formation is complete at about t*(=tUb/D=1.75 and 1.65 for M=1.27 and 1.37, respectively, where t is time, Ub is fluid velocity behind the shock at exit, and D is tube diameter. Complete detachment of the vortex ring from the trailing jet is observed at t∗=2 and 2.9 for M=1.27 and 1.37, respectively.
Experimental demonstration of bow-shock instability and its numerical analysis
Kikuchi, Y.; Ohnishi, N.; Ohtani, K.
2016-07-01
An experimental demonstration was carried out in a ballistic range at high Mach numbers with the low specific heat ratio gas hydrofluorocarbon HFC-134a to observe the unstable bow-shock wave generated in front of supersonic blunt objects. The shadowgraph images obtained from the experiments showed instability characteristics, in which the disturbances grow and flow downstream and the wake flow appears wavy because of the shock oscillation. Moreover, the influence of the body shape and specific heat ratio on the instability was investigated for various experimental conditions. Furthermore, the observed features, such as wave structure and disturbance amplitude, were captured by numerical simulations, and it was demonstrated that computational fluid dynamics could effectively simulate the physical instability. In addition, it was deduced that the shock instability is induced by sound emissions from the edge of the object. This inference supports the dependence of the instability on the specific heat ratio and Mach number because the shock stand-off distance is affected by these parameters and limits the sound wave propagation.
ALMA-SZ Detection of a Galaxy Cluster Merger Shock at Half the Age of the Universe
Basu, Kaustuv; Erler, Jens; Eckert, Dominique; Vazza, Franco; Magnelli, Benjamin; Bertoldi, Frank; Tozzi, Paolo
2016-01-01
We present ALMA measurement of a merger shock using the thermal Sunyaev-Zel'dovich (SZ) effect signal, at the location of a radio relic in the famous El Gordo galaxy cluster at $z \\approx 0.9$. Multi-wavelength analysis in combination with the archival Chandra data and a high-resolution radio image provides a consistent picture of the thermal and non-thermal signal variation across the shock front, and helps to put robust constraints on the shock Mach number as well as the relic magnetic field. We employ a Bayesian analysis technique for modeling the SZ and X-ray data self-consistently, illustrating respective parameter degeneracies. Combined results indicate a shock with Mach number ${\\cal M} = 2.4^{+1.3}_{-0.6}$, which in turn suggests a high value of the magnetic field (of the order $4-10 ~\\mu$G) to account for the observed relic width at 2 GHz. At roughly half the current age of the universe, this is the highest redshift direct detection of a cluster shock to-date, and one of the first instances of ALMA S...
A numerical investigation of shock propagation in three-dimensional microducts
Deshpande, A.; Puranik, B.
2017-07-01
In the present work, shock propagation and attenuation in three-dimensional microducts with rectangular cross-sections of differing aspect ratios are numerically investigated. The simulations are performed using the Navier-Stokes equations with no-slip wall boundary conditions. The post-shock flow in such microducts resembles a pipe flow, with the extent of the boundary layers comparable with the lateral dimension of the duct. The shock attenuation data are explained on the basis of the viscous dissipation characteristics in the post-shock flow-field, in addition to the behaviour of the boundary layers. It is shown that the three-dimensional effects are adequately modelled using a two-dimensional axisymmetric model or a two-dimensional model, depending on the aspect ratio of the microduct. The data for the shock attenuation are presented in the form of correlations involving the initial Mach number of the shock and a dimensionless parameter that includes the characteristic Reynolds number and the dimensionless shock travel.
Richtmyer-Meshkov instability on a low atwood number interface after reshock.
Energy Technology Data Exchange (ETDEWEB)
Weber, Chris (University of Wisconsin-Madison, Madison, WI)
2009-09-01
The Richtmyer-Meshkov instability after reshock is investigated in shock tube experiments at the Wisconsin Shock Tube Laboratory using planar laser imaging and a new high speed interface tracking technique. The interface is a 50-50% volume fraction mixture of helium and argon stratified over pure argon. This interface has an Atwood number of 0.29 and near single mode, two-dimensional, standing wave perturbation with an average amplitude of 0.35 cm and a wavelength of 19.4 cm. The incident shock wave of Mach number 1.92 accelerates the interface before it is reshocked by a reflected Mach 1.70 shock wave. The amplitude growth after reshock is reported for variations in this initial amplitude, and several amplitude growth rate models are compared to the experimental growth rate after reshock. A new growth model is introduced, based on a model of circulation deposition calculated from one-dimensional gas dynamics parameters. This model is shown to compare well with the amplitude growth rate after reshock and the circulation over a half-wavelength of the interface after the first shock wave and after reshock.
Shock wave reflection phenomena
Ben-dor, Gabi
2007-01-01
This book provides a comprehensive state-of-the-knowledge description of the shock wave reflection phenomena from a phenomenological point of view. The first part is a thorough introduction to oblique shock wave reflections, presenting the two major well-known reflection wave configurations, namely, regular (RR) and Mach (MR) reflections, the corresponding two- and three-shock theories, their analytical and graphical solution and the proposed transition boundaries between these two reflection-wave configurations. The second, third and fourth parts describe the reflection phenomena in steady, pseudo-steady and unsteady flows, respectively. Here, the possible specific types of reflection wave configurations are described, criteria for their formation and termination are presented and their governing equations are solved analytically and graphically and compared with experimental results. The resolution of the well-known von Neumann paradox and a detailed description of two new reflection-wave configurations - t...
Mach-like capillary-gravity wakes.
Moisy, Frédéric; Rabaud, Marc
2014-08-01
We determine experimentally the angle α of maximum wave amplitude in the far-field wake behind a vertical surface-piercing cylinder translated at constant velocity U for Bond numbers Bo(D)=D/λ(c) ranging between 0.1 and 4.2, where D is the cylinder diameter and λ(c) the capillary length. In all cases the wake angle is found to follow a Mach-like law at large velocity, α∼U(-1), but with different prefactors depending on the value of Bo(D). For small Bo(D) (large capillary effects), the wake angle approximately follows the law α≃c(g,min)/U, where c(g,min) is the minimum group velocity of capillary-gravity waves. For larger Bo(D) (weak capillary effects), we recover a law α∼√[gD]/U similar to that found for ship wakes at large velocity [Rabaud and Moisy, Phys. Rev. Lett. 110, 214503 (2013)]. Using the general property of dispersive waves that the characteristic wavelength of the wave packet emitted by a disturbance is of order of the disturbance size, we propose a simple model that describes the transition between these two Mach-like regimes as the Bond number is varied. We show that the new capillary law α≃c(g,min)/U originates from the presence of a capillary cusp angle (distinct from the usual gravity cusp angle), along which the energy radiated by the disturbance accumulates for Bond numbers of order of unity. This model, complemented by numerical simulations of the surface elevation induced by a moving Gaussian pressure disturbance, is in qualitative agreement with experimental measurements.
Chriss, R. M.; Hingst, W. R.; Strazisar, A. J.; Keith, T. G., Jr.
1989-01-01
Nonintrusive measurements were made of a normal shock wave/boundary layer interaction. Two dimensional measurements were made throughout the interaction region while 3-D measurements were made in the vicinity of the shock wave. The measurements were made in the corner of the test section of a continuous supersonic wind tunnel in which a normal shock wave had been stabilized. Laser Doppler Anemometry, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The results define the flow field structure in detail for each case.
Pressure-Sensitive Paint Measurements of Transient Shock Phenomena
Directory of Open Access Journals (Sweden)
Konstantinos Kontis
2013-04-01
Full Text Available Measurements of the global pressure field created by shock wave diffraction have been captured optically using a porous pressure-sensitive paint. The pressure field created by a diffracting shock wave shows large increases and decreases in pressure and can be reasonably accurately captured using CFD. The substrate, a thin-layer chromatography (TLC plate, has been dipped in a luminophore solution. TLC plates are readily available and easy to prepare. Illumination comes from two high-intensity broadband Xenon arc light sources with short-pass filters. The sample is imaged at 100 kHz using a Vision Research Phantom V710 in conjunction with a pair of long and short pass filters, creating a band. The PSP results are compared with numerical simulations of the flow using the commercial CFD package Fluent as part of ANSYS 13 for two Mach numbers.
Laser-driven shock acceleration of monoenergetic ion beams
Fiuza, F; Boella, E; Fonseca, R A; Silva, L O; Haberberger, D; Tochitsky, S; Gong, C; Mori, W B; Joshi, C
2012-01-01
We show that monoenergetic ion beams can be accelerated by moderate Mach number collisionless, electrostatic shocks propagating in a long scale-length exponentially decaying plasma profile. Strong plasma heating and density steepening produced by an intense laser pulse near the critical density can launch such shocks that propagate in the extended plasma at high velocities. The generation of a monoenergetic ion beam is possible due to the small and constant sheath electric field associated with the slowly decreasing density profile. The conditions for the acceleration of high-quality, energetic ion beams are identified through theory and multidimensional particle-in-cell simulations. The scaling of the ion energy with laser intensity shows that it is possible to generate $\\sim 200$ MeV proton beams with state-of-the-art 100 TW class laser systems.
Computational study of shock interaction with a vortex ring
Ding, Z.; Hussaini, M. Y.; Erlebacher, G.; Krothapalli, A.
2001-10-01
The problem of shock interaction with a vortex ring is investigated within the framework of axisymmetric Euler equations solved numerically by a shock-fitted sixth-order compact difference scheme. The vortex ring, which is based on Lamb's formula, has an upstream circulation Γ=0.01 and its aspect ratio R lies in the range 8⩽R⩽100. The shock Mach number varies in the range 1.1⩽M1⩽1.8. The vortex ring/shock interaction results in the streamwise compression of the vortex core by a factor proportional to the ratio of the upstream and downstream mean velocity U1/U2, and the generation of a toroidal acoustic wave and entropy disturbances. The toroidal acoustic wave propagates and interacts with itself on the symmetry axis of the vortex ring. This self-interaction engenders high amplitude rarefaction/compression pressure peaks upstream/downstream of the transmitted vortex core. This results in a significant increase in centerline sound pressure levels, especially near the shock (due to the upstream movement of the rarefaction peak) and in the far downstream (due to the downstream movement of the compression peak). The magnitude of the compression peak increases nonlinearly with M1. For a given M1, vortex rings with smaller aspect ratios (R40) generate pressure disturbances whose amplitudes are roughly independent of R.
Simulations of Shock Wave Interaction with a Particle Cloud
Koneru, Rahul; Rollin, Bertrand; Ouellet, Frederick; Annamalai, Subramanian; Balachandar, S.'Bala'
2016-11-01
Simulations of a shock wave interacting with a cloud of particles are performed in an attempt to understand similar phenomena observed in dispersal of solid particles under such extreme environment as an explosion. We conduct numerical experiments in which a particle curtain fills only 87% of the shock tube from bottom to top. As such, the particle curtain upon interaction with the shock wave is expected to experience Kelvin-Helmholtz (KH) and Richtmyer-Meshkov (RM) instabilities. In this study, the initial volume fraction profile matches with that of Sandia Multiphase Shock Tube experiments, and the shock Mach number is limited to M =1.66. In these simulations we use a Eulerian-Lagrangian approach along with state-of-the-art point-particle force and heat transfer models. Measurements of particle dispersion are made at different initial volume fractions of the particle cloud. A detailed analysis of the evolution of the particle curtain with respect to the initial conditions is presented. This work was supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science Academic Alliance Program, Contract No. DE-NA0002378.
A new facility for studying shock-wave passage over dust layers
Chowdhury, A. Y.; Marks, B. D.; Johnston, H. Greg; Mannan, M. Sam; Petersen, E. L.
2016-03-01
Dust explosion hazards in areas where coal and other flammable materials are found have caused unnecessary loss of life and halted business operations in some instances. The elimination of secondary dust explosion hazards, i.e., reducing dust dispersion, can be characterized in shock tubes to understand shock-dust interactions. For this reason, a new shock-tube test section was developed and integrated into an existing shock-tube facility. The test section has large windows to allow for the use of the shadowgraph technique to track dust-layer growth behind a passing normal shock wave, and it is designed to handle an initial pressure of 1 atm with an incident shock wave Mach number as high as 2 to mimic real-world conditions. The test section features an easily removable dust pan with inserts to allow for adjustment of the dust-layer thickness. The design also allows for changing the experimental variables such as initial pressure, shock Mach number (Ms), dust-layer thickness, and the characteristics of the dust itself. The characterization experiments presented herein demonstrate the advantages of the authors' test techniques toward providing new physical insights over a wider range of data than what have been available heretofore in the literature. Limestone dust with a layer thickness of 3.2 mm was subjected to Ms = 1.23, 1.32, and 1.6 shock waves, and dust-layer rise height was mapped with respect to time after shock passage. Dust particles subjected to a Ms = 1.6 shock wave rose more rapidly and to a greater height with respect to shock wave propagation than particles subjected to Ms = 1.23 and 1.32 shock waves. Although these results are in general agreement with the literature, the new data also highlight physical trends for dust-layer growth that have not been recorded previously, to the best of the authors' knowledge. For example, the dust-layer height rises linearly until a certain time where the growth rate is dramatically reduced, and in this second
Shock Acceleration Model for the Toothbrush Radio Relic
Kang, Hyesung; Ryu, Dongsu; Jones, T. W.
2017-05-01
Although many of the observed properties of giant radio relics detected in the outskirts of galaxy clusters can be explained by relativistic electrons accelerated at merger-driven shocks, significant puzzles remain. In the case of the so-called Toothbrush relic, the shock Mach number estimated from X-ray observations ({M}{{X}}≈ 1.2{--}1.5) is substantially weaker than that inferred from the radio spectral index ({M}{rad}≈ 2.8). Toward understanding such a discrepancy, we here consider the following diffusive shock acceleration (DSA) models: (1) weak-shock models with {M}{{s}}≲ 2 and a preexisting population of cosmic-ray electrons (CRe) with a flat energy spectrum, and (2) strong-shock models with {M}{{s}}≈ 3 and either shock-generated suprathermal electrons or preexisting fossil CRe. We calculate the synchrotron emission from the accelerated CRe, following the time evolution of the electron DSA, and the subsequent radiative cooling and postshock turbulent acceleration (TA). We find that both models could reproduce reasonably well the observed integrated radio spectrum of the Toothbrush relic, but the observed broad transverse profile requires the stochastic acceleration by downstream turbulence, which we label “turbulent acceleration” or TA to distinguish it from DSA. Moreover, to account for the almost uniform radio spectral index profile along the length of the relic, the weak-shock models require a preshock region over 400 kpc with a uniform population of preexisting CRe with a high cutoff energy (≳ 40 {GeV}). Due to the short cooling time, it is challenging to explain the origin of such energetic electrons. Therefore, we suggest the strong-shock models with low-energy seed CRe (≲ 150 {MeV}) are preferred for the radio observations of this relic.
Effects of shock structure on temperature field in compressible turbulence
Ni, Qionglin; Chen, Shiyi
2014-11-01
Effects of shock structure on temperature in compressible turbulence were investigated. The small-scale shocklets and large-scale shock waves were appeared in the flows driven by solenoidal and compressive forcings, i.e. SFT & CFT, respectively. In SFT the temperature had Kolmogorov spectrum and ramp-cliff structures, while in CFT it obeyed Burgers spectrum and was dominated by large-scale rarefaction and compression. The power-law exponents for the p.d.f. of large negative dilatation were -2.5 in SFT and -3.5 in CFT, approximately corresponded to model results. The isentropic approximation of thermodynamic variables showed that in SFT, the isentropic derivation was reinforced when turbulent Mach number increased. At similar turbulent Mach number, the variables in CFT exhibited more anisentropic. It showed that the transport of temperature was increased by the small-scale viscous dissipation and the large-scale pressure-dilatation. The distribution of positive and negative components of pressure-dilatation confirmed the mechanism of negligible pressure-dilatation at small scales. Further, the positive skewness of p.d.f.s of pressure-dilatation implied that the conversion from kinetic to internal energy by compression was more intense than the opposite process by rarefaction.
Budía Alba, A; López Acón, J D; Polo-Rodrigo, A; Bahílo-Mateu, P; Trassierra-Villa, M; Boronat-Tormo, F
2015-06-01
To assess the safety of increasing the number of waves per session in the treatment of urolithiasis using extracorporeal lithotripsy. Prospective, comparative, nonrandomized parallel study of patients with renoureteral lithiasis and an indication for extracorporeal lithotripsy who were consecutively enrolled between 2009 and 2010. We compared group I (160 patients) treated on schedule with a standard number of waves/session (mean 2858,3±302,8) using a Dornier lithotripter U/15/50 against group II (172 patients) treated with an expanded number of waves/session (mean, 6728,9±889,6) using a Siemens Modularis lithotripter. The study variables were age, sex, location, stone size, number of waves/session and total number of waves to resolution, stone-free rate (SFR) and rate of complications (Clavien-Dindo classification). Student's t-test and the chi-squared test were employed for the statistical analysis. The total rate of complications was 11.9% and 10.46% for groups I and II, respectively (P=.39). All complications were minor (Clavien-Dindo grade I). The most common complications were colic pain and hematuria in groups I and II, respectively, with a similar treatment intolerance rate (P>.05). The total number of waves necessary was lower in group II than in group I (P=.001), with SFRs of 96.5% and 71.5%, respectively (P=.001). Treatment with an expanded number of waves per session in extracorporeal lithotripsy does not increase the rate of complications or their severity. However, it could increase the overall effectiveness of the treatment. Copyright © 2014 AEU. Publicado por Elsevier España, S.L.U. All rights reserved.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
A study of Mach shocks generated by fast partonic jets propagating through the quark-gluon plasma (QGP) is reviewed briefly. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies compared to those created by a jet propagation through a static medium.Moreover, a new hydrodynamical study of jet energy loss is presented.
Converging cylindrical magnetohydrodynamic shock collapse onto a power-law-varying line current
Mostert, W.
2016-03-16
We investigate the convergence behaviour of a cylindrical, fast magnetohydrodynamic (MHD) shock wave in a neutrally ionized gas collapsing onto an axial line current that generates a power law in time, azimuthal magnetic field. The analysis is done within the framework of a modified version of ideal MHD for an inviscid, non-dissipative, neutrally ionized compressible gas. The time variation of the magnetic field is tuned such that it approaches zero at the instant that the shock reaches the axis. This configuration is motivated by the desire to produce a finite magnetic field at finite shock radius but a singular gas pressure and temperature at the instant of shock impact. Our main focus is on the variation with shock radius, as, of the shock Mach number and pressure behind the shock as a function of the magnetic field power-law exponent, where gives a constant-in-time line current. The flow problem is first formulated using an extension of geometrical shock dynamics (GSD) into the time domain to take account of the time-varying conditions ahead of the converging shock, coupled with appropriate shock-jump conditions for a fast, symmetric MHD shock. This provides a pair of ordinary differential equations describing both and the time evolution on the shock, as a function of, constrained by a collapse condition required to achieve tuned shock convergence. Asymptotic, analytical results for and are obtained over a range of for general, and for both small and large . In addition, numerical solutions of the GSD equations are performed over a large range of, for selected parameters using . The accuracy of the GSD model is verified for some cases using direct numerical solution of the full, radially symmetric MHD equations using a shock-capturing method. For the GSD solutions, it is found that the physical character of the shock convergence to the axis is a strong function of . For μ≤0.816, and both approach unity at shock impact owing to the dominance of the strong
Chao, J. K.; Wiskerchen, M. J.
1974-01-01
The empirical relationship between the standoff distance of a detached bow shock (generated by the flow of a supersonic gas past an impenetrable obstacle), the size of the obstacle, the Mach number of the gas, and the ratio of specific heats has been generalized to include the magnetic field. The value of the ratio of specific heats (gamma-prime) in the postshock plasma has been calculated in terms of the preshock Alfvenic and sonic Mach numbers and orientation of the magnetic field. The empirical relationship is further generalized by taking into consideration the normal momentum and energy flux due to waves and/or turbulence and/or heat flow in association with high Mach number shocks. The computed value of gamma prime is substantially modified in comparison with that given by the MHD or the gas dynamic model. For this generalized model the computed gamma prime can be considered to be a more precise thermodynamic quantity, since the macroscopic parameters of the plasma have been separated out. Application of this empirical relationship to the earth's bow shock has been given.
Experimental analysis of the shock dynamics on a transonic laminar airfoil
Brion, V.; Dandois, J.; Abart, J.-C.; Paillart, P.
2017-06-01
This paper describes an experimental analysis of the buffet phenomenon on a two-dimensional (2D), transonic, and laminar airfoil at a Reynolds number around 3 · 106. Investigations are carried out in ONERA's S3Ch transonic wind tunnel. The experimental setup allows to vary the Mach number, the angle of attack, and the state of the boundary layer upstream of the shock which can be turbulent or laminar depending on the presence of artificial tripping. Buffet occurs when either the angle of attack or the Mach number is set above a given threshold, which depends upon the particular airfoil, and, as shown here, on the state of the boundary layer. Above the threshold, the boundary layer / shock interaction destabilizes, causing the oscillation of the entire flow field. In the turbulent case, the shock wave moves back and forth over a significant portion of the chord at a frequency of about 75 Hz corresponding to a chord based on Strouhal number St ≃ 0.07, in agreement with previous researches on this phenomenon. In the laminar case, a similar unsteady situation occurs but at a frequency much higher, about 1130 Hz, which corresponds to a Strouhal number of about St ≃ 1. Flow oscillations are limited to the shock foot, the shock itself moving only lightly. The turbulent and laminar bu¨et thresholds are provided. An attempt to apply the classical feedback loop scenario to explain the unsteadiness of the flow in the laminar case is carried out but shows a deceptive agreement with the experimental data. Two other mechanisms of unsteadiness are additionally explored, one based on vortex shedding behind the airfoil and the other on the possible breathing of the laminar separation bubble, which give valuable insights into the §ow physics.
Comparison of three methods for the estimation of cross-shock electric potential using Cluster data
Directory of Open Access Journals (Sweden)
Y. Hobara
2011-05-01
Full Text Available Cluster four point measurements provide a comprehensive dataset for the separation of temporal and spatial variations, which is crucial for the calculation of the cross shock electrostatic potential using electric field measurements. While Cluster is probably the most suited among present and past spacecraft missions to provide such a separation at the terrestrial bow shock, it is far from ideal for a study of the cross shock potential, since only 2 components of the electric field are measured in the spacecraft spin plane. The present paper is devoted to the comparison of 3 different techniques that can be used to estimate the potential with this limitation. The first technique is the estimate taking only into account the projection of the measured components onto the shock normal. The second uses the ideal MHD condition E·B = 0 to estimate the third electric field component. The last method is based on the structure of the electric field in the Normal Incidence Frame (NIF for which only the potential component along the shock normal and the motional electric field exist. All 3 approaches are used to estimate the potential for a single crossing of the terrestrial bow shock that took place on the 31 March 2001. Surprisingly all three methods lead to the same order of magnitude for the cross shock potential. It is argued that the third method must lead to more reliable results. The effect of the shock normal inaccuracy is investigated for this particular shock crossing. The resulting electrostatic potential appears too high in comparison with the theoretical results for low Mach number shocks. This shows the variability of the potential, interpreted in the frame of the non-stationary shock model.
A study of test section configuration for shock tube testing of transonic airfoils
Cook, W. J.
1978-01-01
Two methods are investigated for alleviating wall interference effects in a shock tube test section intended for testing two-dimensional transonic airfoils. The first method involves contouring the test section walls to match approximate streamlines in the flow. Contours are matched to each airfoil tested to produce results close to those obtained in a conventional wind tunnel. Data from a previous study and the present study for two different airfoils demonstrate that useful results are obtained in a shock tube using a test section with contoured walls. The second method involves use of a fixed-geometry slotted-wall test section to provide automatic flow compensation for various airfoils. The slotted-wall test section developed exhibited the desired performance characteristics in the approximate Mach number range 0.82 to 0.89, as evidenced by good agreement obtained between shock tube and wind tunnel results for several airfoil flows.
An experimental study on shock waves propagating through a dusty gas in a horizontal channel
Sugiyama, H.; Takimoto, A.; Shirota, T.; Hatanaka, H.
Experiments were run to characterize the propagation of shock fronts in a dusty gas shock tube. The 1 m long, 55 mm diam tube contained air and fly ash with a mean 3.3 micron diameter. The laser beam attenuation method was used to quantify the particle concentration and thereby the distribution of suspended particles and variations in the distribution over shock Mach numbers 1.38, 1.48 and 1.61. Among other results, it was found that the variations in particle concentration were affected by both the suspended particles and those which settled on the tube floor. When a vertical particle gradient was present, the shape of the particles was inclined in the flow direction.
Shocks, Ripples, and Bubbles: A Very Deep Observation of Abell 2052
Blanton, Elizabeth
2008-09-01
The cooling flow cluster A2052 has, arguably, the morphology most similar to the Perseus cluster as seen with Chandra. Two clear bubbles to the N and S of the center of A2052 are filled with the radio lobes associated with 3C 317. Surface brightness discontinuities consistent with shocks with Mach numbers of 1.8 and 1.2 are seen near the cluster center. These may be isothermal shocks. We propose to observe Abell 2052 much more deeply to study these shock features, ripple features due to sound waves that may be found at larger radii, possible ghost bubbles, cooling gas in the bright shells around the radio source that may link the X-ray and H-alpha emission, and possible hot gas within the X-ray holes. We will directly compare the star formation and cooling rates in the cluster center.
An LDA investigation of three-dimensional normal shock-boundary layer interactions in a corner
Chriss, R. M.; Keith, T. G., Jr.; Hingst, W. R.; Strazisar, A. J.; Porro, A. R.
1987-01-01
Nonintrusive, three-dimensional, measurements have been made of a normal shock wave-turbulent boundary layer interaction. The measurements were made in the corner of the test section of a continuous supersonic wind tunnel in which a normal shock wave had been stabilized. LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The reported results are believed to accurately define the flow physics of each case and may be used as benchmark data to verify three-dimensional computer codes.
The case for electron re-acceleration at galaxy cluster shocks
van Weeren, Reinout J.; Andrade-Santos, Felipe; Dawson, William A.; Golovich, Nathan; Lal, Dharam V.; Kang, Hyesung; Ryu, Dongsu; Brìggen, Marcus; Ogrean, Georgiana A.; Forman, William R.; Jones, Christine; Placco, Vinicius M.; Santucci, Rafael M.; Wittman, David; Jee, M. James; Kraft, Ralph P.; Sobral, David; Stroe, Andra; Fogarty, Kevin
2017-01-01
On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found1,2 . Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster-cluster merger events 3 . A long-standing problem is how low-Mach-number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411-3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. It also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.
A shock front in the merging galaxy cluster Abell 754: X-ray and radio observations
Macario, Giulia; Giacintucci, Simona; Brunetti, Gianfranco; Venturi, Tiziana; Murray, Stephen S
2010-01-01
We present new Chandra X-ray and Giant Meterwave Radio Telescope (GMRT) radio observations of the nearby merging galaxy cluster Abell 754. Our X-ray data confirm the presence of a shock front by obtaining the first direct measurement of a gas temperature jump across the X-ray brightness edge previously seen in the imaging data. A754 is only the fourth galaxy cluster with confirmed merger shock fronts, and it has the weakest shock of those, with a Mach number M=1.57+0.16-0.12. In our new GMRT observation at 330 MHz, we find that the previously-known centrally located radio halo extends eastward to the position of the shock. The X-ray shock front also coincides with the position of a radio relic previously observed at 74 MHz. The radio spectrum of the post-shock region, using our radio data and the earlier results at 74 MHz and 1.4 GHz, is very steep. We argue that acceleration of electrons at the shock front directly from thermal to ultrarelativistic energies is problematic due to energy arguments, while reacc...
Boundary-layer transition on blunt slender cones at Mach 10
Bell, R. L.
1984-08-01
Investigations of the effects of nose blunting on the location of boundary-layer transition on slender cones at supersonic or hypersonic speeds so back 25 years. For some time it was thought that the movement of the transition point was simply due to the reduction in local Reynolds number associated with the loss in total pressure through the bow shock. More recently, it has been shown that variations in the local transition Reynolds number also occur on a blunt cone and that both these effects must be taken into account in explaining the observed movement in transition along the cone frustum. The present investigation was carried out as a demonstration test for the development of a new capability in Hypervelocity Tunnel 9 at the Naval Surface Weapon Center. The objective of this development effort was to raise the Reynolds number at mach 10 from about 5 x 1000000 per foot to 20 x 1000000 per foot. This was done so that naturally turbulent boundary layers (i.e., without tripping) could be obtained on R/V models. Thus an investigation of boundary layer transition was an appropriate choice for the demonstration test.
Radiative Shock-Induced Collapse of Intergalactic Clouds
Fragile, P C; Anninos, P; Van Breugel, W; Murray, Stephen D.; Anninos, Peter; Breugel, Wil van
2004-01-01
Accumulating observational evidence for a number of radio galaxies suggests an association between their jets and regions of active star formation. The standard picture is that shocks generated by the jet propagate through an inhomogeneous medium and trigger the collapse of overdense clouds, which then become active star-forming regions. In this contribution, we report on recent hydrodynamic simulations of radiative shock-cloud interactions using two different cooling models: an equilibrium cooling-curve model assuming solar metallicities and a non-equilibrium chemistry model appropriate for primordial gas clouds. We consider a range of initial cloud densities and shock speeds in order to quantify the role of cooling in the evolution. Our results indicate that for moderate cloud densities (>1 cm^{-3}) and shock Mach numbers (0.01 and total H_2 mass fractions of >10^{-5} for the cloud gas. Finally, we compare our results with the observations of jet-induced star formation in ``Minkowski's Object.'' We conclude...
MACH: Fast Randomized Tensor Decompositions
Tsourakakis, Charalampos E
2009-01-01
Tensors naturally model many real world processes which generate multi-aspect data. Such processes appear in many different research disciplines, e.g, chemometrics, computer vision, psychometrics and neuroimaging analysis. Tensor decompositions such as the Tucker decomposition are used to analyze multi-aspect data and extract latent factors, which capture the multilinear data structure. Such decompositions are powerful mining tools, for extracting patterns from large data volumes. However, most frequently used algorithms for such decompositions involve the computationally expensive Singular Value Decomposition. In this paper we propose MACH, a new sampling algorithm to compute such decompositions. Our method is of significant practical value for tensor streams, such as environmental monitoring systems, IP traffic matrices over time, where large amounts of data are accumulated and the analysis is computationally intensive but also in "post-mortem" data analysis cases where the tensor does not fit in the availa...
Landrum, E. J.; Babb, C. D.
1979-01-01
Flow visualization and force data for a series of six bodies of revolution are presented without analysis. The data were obtained in the Langley Unitary Plan wind tunnel for angles of attack from -4 deg to 60 deg. The Reynolds number used for these tests was 6,600,000 per meter.
Experimental measurement of unsteady drag on shock accelerated micro-particles
Bordoloi, Ankur; Martinez, Adam; Prestridge, Katherine
2016-11-01
The unsteady drag history of shock accelerated micro-particles in air is investigated in the Horizontal Shock Tube (HST) facility at Los Alamos National laboratory. Drag forces are estimated based on particle size, particle density, and instantaneous velocity and acceleration measured on hundreds of post-shock particle tracks. We use previously implemented 8-frame Particle Tracking Velocimetry/Anemometry (PTVA) diagnostics to analyze particles in high spatiotemporal resolution from individual particle trajectories. We use a simultaneous LED based shadowgraph to register shock location with respect to a moving particle in each frame. To measure particle size accurately, we implement a Phase Doppler Particle Analyzer (PDPA) in synchronization with the PTVA. In this presentation, we will corroborate with more accuracy our earlier observation that post-shock unsteady drag coefficients (CD(t)) are manifold times higher than those predicted by theoretical models. Our results will also show that all CD(t) measurements collapse on a master-curve for a range of particle size, density, Mach number and Reynolds number when time is normalized by a shear velocity based time scale, t* = d/(uf-up) , where d is particle diameter, and uf and up are post-shock fluid and particle velocities.
Shock Train/Boundary-Layer Interaction in Rectangular Scramjet Isolators
Geerts, Jonathan Simon
Numerous studies of the dual-mode scramjet isolator, a critical component in preventing inlet unstart and/or vehicle loss by containing a collection of flow disturbances called a shock train, have been performed since the dual-mode propulsion cycle was introduced in the 1960s. Low momentum corner flow and other three-dimensional effects inherent to rectangular isolators have, however, been largely ignored in experimental studies of the boundary layer separation driven isolator shock train dynamics. Furthermore, the use of two dimensional diagnostic techniques in past works, be it single-perspective line-of-sight schlieren/shadowgraphy or single axis wall pressure measurements, have been unable to resolve the three-dimensional flow features inside the rectangular isolator. These flow characteristics need to be thoroughly understood if robust dual-mode scramjet designs are to be fielded. The work presented in this thesis is focused on experimentally analyzing shock train/boundary layer interactions from multiple perspectives in aspect ratio 1.0, 3.0, and 6.0 rectangular isolators with inflow Mach numbers ranging from 2.4 to 2.7. Secondary steady-state Computational Fluid Dynamics studies are performed to compare to the experimental results and to provide additional perspectives of the flow field. Specific issues that remain unresolved after decades of isolator shock train studies that are addressed in this work include the three-dimensional formation of the isolator shock train front, the spatial and temporal low momentum corner flow separation scales, the transient behavior of shock train/boundary layer interaction at specific coordinates along the isolator's lateral axis, and effects of the rectangular geometry on semi-empirical relations for shock train length prediction. (Abstract shortened by ProQuest.).
Studying astrophysical collisionless shocks with counterstreaming plasmas from high power lasers
Park, Hye-Sook; Ryutov, D. D.; Ross, J. S.; Kugland, N. L.; Glenzer, S. H.; Plechaty, C.; Pollaine, S. M.; Remington, B. A.; Spitkovsky, A.; Gargate, L.; Gregori, G.; Bell, A.; Murphy, C.; Sakawa, Y.; Kuramitsu, Y.; Morita, T.; Takabe, H.; Froula, D. H.; Fiksel, G.; Miniati, F.; Koenig, M.; Ravasio, A.; Pelka, A.; Liang, E.; Woolsey, N.; Kuranz, C. C.; Drake, R. P.; Grosskopf, M. J.
2012-03-01
Collisions of high Mach number flows occur frequently in astrophysics, and the resulting shock waves are responsible for the properties of many astrophysical phenomena, such as supernova remnants, Gamma Ray Bursts and jets from Active Galactic Nuclei. Because of the low density of astrophysical plasmas, the mean free path due to Coulomb collisions is typically very large. Therefore, most shock waves in astrophysics are "collisionless", since they form due to plasma instabilities and self-generated magnetic fields. Laboratory experiments at the laser facilities can achieve the conditions necessary for the formation of collisionless shocks, and will provide a unique avenue for studying the nonlinear physics of collisionless shock waves. We are performing a series of experiments at the Omega and Omega-EP lasers, in Rochester, NY, with the goal of generating collisionless shock conditions by the collision of two high-speed plasma flows resulting from laser ablation of solid targets using ˜1016 W/cm2 laser irradiation. The experiments will aim to answer several questions of relevance to collisionless shock physics: the importance of the electromagnetic filamentation (Weibel) instabilities in shock formation, the self-generation of magnetic fields in shocks, the influence of external magnetic fields on shock formation, and the signatures of particle acceleration in shocks. Our first experiments using Thomson scattering diagnostics studied the plasma state from a single foil and from double foils whose flows collide "head-on". Our data showed that the flow velocity and electron density were 108 cm/s and 1019 cm-3, respectively, where the Coulomb mean free path is much larger than the size of the interaction region. Simulations of our experimental conditions show that weak Weibel mediated current filamentation and magnetic field generation were likely starting to occur. This paper presents the results from these first Omega experiments.
Peterson, Victor L.; Menees, Gene P.
1961-01-01
Tabulated results of a wind-tunnel investigation of the aerodynamic loads on a canard airplane model with twin vertical tails are presented for Mach numbers from 0.70 to 2.22. The Reynolds number for the measurements was 2.9 x 10(exp 6) based on the wing mean aerodynamic chord. The results include local static-pressure coefficients measured on the wing, body, and one of the vertical tails for angles of attack from -4 degrees to 16 degree angles of sideslip of 0 degrees and 5.3 degrees, and nominal canard deflections of O degrees and 10 degrees. Also included are section force and moment coefficients obtained from integrations of the local pressures and model-component force and moment coefficients obtained from integrations of the section coefficients. Geometric details of the model are shown and the locations of the pressure orifices are shown. An index to the data contained herein is presented and definitions of nomenclature are given. Detailed descriptions of the model and experiments and a brief discussion of some of the results are given. Tabulated results of measurements of the aerodynamic loads on the same canard model but having a single vertical tail instead of twin vertical tails are presented.
Peterson, Victor L.; Menees, Gene P.
1961-01-01
Tabulated results of a wind-tunnel investigation of the aerodynamic loads on a canard airplane model with a single vertical tail are presented for Mach numbers from 0.70 to 2.22. The Reynolds number for the measurements was 2.9 x 10(exp 6) based on the wing mean aerodynamic chord. The results include local static pressure coefficients measured on the wing, body, and vertical tail for angles of attack from -4 deg to + 16 deg, angles of sideslip of 0 deg and 5.3 deg, vertical-tail settings of 0 deg and 5 deg, and nominal canard deflections of 0 deg and 10 deg. Also included are section force and moment coefficients obtained from integrations of the local pressures and model-component force and moment coefficients obtained from integrations of the section coefficients. Geometric details of the model and the locations of the pressure orifices are shown. An index to the data contained herein is presented and definitions of nomenclature are given.
The interaction of a magnetohydrodynamical shock with a filament
Goldsmith, K J A
2016-01-01
We present 3D magnetohydrodynamic numerical simulations of the adiabatic interaction of a shock with a dense, filamentary cloud. We investigate the effects of various filament lengths and orientations on the interaction using different orientations of the magnetic field, and vary the Mach number of the shock, the density contrast of the filament, and the plasma beta, in order to determine their effect on the evolution and lifetime of the filament. We find that in a parallel magnetic field filaments have longer lifetimes if they are orientated more 'broadside' to the shock front, and that an increase in the density contrast hastens the destruction of the cloud, in terms of the modified cloud-crushing time-scale, tcs. The combination of a mild shock and a perpendicular or oblique field provides the best condition for extending the life of the filament, with some filaments able to survive almost indefinitely since they are cocooned by the magnetic field. A high value for the density contrast does not initiate la...
PROMINENCE ACTIVATION BY CORONAL FAST MODE SHOCK
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Takahashi, Takuya [Department of Astronomy, Kyoto University, Sakyo, Kyoto, 606-8502 (Japan); Asai, Ayumi [Unit of Synergetic Studies for Space, Kyoto University, Yamashina, Kyoto 607-8471 (Japan); Shibata, Kazunari, E-mail: takahashi@kwasan.kyoto-u.ac.jp [Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471 (Japan)
2015-03-01
An X5.4 class flare occurred in active region NOAA11429 on 2012 March 7. The flare was associated with a very fast coronal mass ejection (CME) with a velocity of over 2500 km s{sup −1}. In the images taken with the Solar Terrestrial Relations Observatory-B/COR1, a dome-like disturbance was seen to detach from an expanding CME bubble and propagated further. A Type-II radio burst was also observed at the same time. On the other hand, in extreme ultraviolet images obtained by the Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA), the expanding dome-like structure and its footprint propagating to the north were observed. The footprint propagated with an average speed of about 670 km s{sup −1} and hit a prominence located at the north pole and activated it. During the activation, the prominence was strongly brightened. On the basis of some observational evidence, we concluded that the footprint in AIA images and the ones in COR1 images are the same, that is, the MHD fast mode shock front. With the help of a linear theory, the fast mode Mach number of the coronal shock is estimated to be between 1.11 and 1.29 using the initial velocity of the activated prominence. Also, the plasma compression ratio of the shock is enhanced to be between 1.18 and 2.11 in the prominence material, which we consider to be the reason for the strong brightening of the activated prominence. The applicability of linear theory to the shock problem is tested with a nonlinear MHD simulation.
Apperson, S.; Shende, R. V.; Subramanian, S.; Tappmeyer, D.; Gangopadhyay, S.; Chen, Z.; Gangopadhyay, K.; Redner, P.; Nicholich, S.; Kapoor, D.
2007-12-01
Nanothermite composites containing metallic fuel and inorganic oxidizer are gaining importance due to their outstanding combustion characteristics. In this paper, the combustion behaviors of copper oxide/aluminum nanothermites are discussed. CuO nanorods were synthesized using the surfactant-templating method, then mixed or self-assembled with Al nanoparticles. This nanoscale mixing resulted in a large interfacial contact area between fuel and oxidizer. As a result, the reaction of the low density nanothermite composite leads to a fast propagating combustion, generating shock waves with Mach numbers up to 3.
Detonation re-initiation mechanism following the Mach reflection of a quenched detonation
Bhattacharjee, Rohit; Maines, Geoffrey; Maley, Logan; Radulescu, Matei Ioan
2012-01-01
This experimental study addresses the re-initiation mechanism of detonation waves following the Mach reflection of a shock-flame complex. The detonation diffraction around a cylinder is used to reproducibly generate the shock-flame complex of interest. The experiments are performed in methane-oxygen. We use a novel experimental technique of coupling a two-in-line-spark flash system with a double-frame camera in order to obtain microsecond time resolution permitting accurate schlieren velocimetry. The first series of experiments compares the non-reactive sequence of shock reflections with the reflection over a rough wall under identical conditions. It was found that the hot reaction products generated along the rough wall are entrained by the wall jet into a large vortex structure behind the Mach stem. The second series of experiments performed in more sensitive mixtures addressed the sequence of events leading to the detonation establishment along the Mach and transverse waves. Following ignition and jet entr...
Effects of Initial Condition Spectral Content on Shock Driven Turbulent Mixing
Nelson, Nicholas J
2015-01-01
The mixing of materials due to the Richtmyer-Meshkov instability and the ensuing turbulent behavior is of intense interest in a variety of physical systems including inertial confinement fusion, combustion, and the final stages of stellar evolution. Extensive numerical and laboratory studies of shock-driven mixing have demonstrated the rich behavior associated with the onset of turbulence due to the shocks. Here we report on progress in understanding shock-driven mixing at interfaces between fluids of differing densities through 3D numerical simulations using the RAGE code in the implicit large eddy simulation context. We consider a shock tube configuration with a band of high density gas (SF$_6$) embedded in low density gas (air). Shocks with a Mach number of 1.26 are passed through SF$_6$ bands, resulting in transition to turbulence driven by the Richtmyer-Meshkov instability. The system is followed as a rarefaction wave and a reflected secondary shock from the back wall pass through the SF$_6$ band. We app...
Effects of laser polarization on electrostatic shock ion acceleration in near-critical plasmas
Kim, Young-Kuk; Kang, Teyoun; Hur, Min Sup
2016-10-01
Ion acceleration from laser-driven collisionless electrostatic shock (CES) is attracting much attention, as quasi-monoenergetic, tens of MeV ion beams are expected to be available from relatively moderate laser power and near-critical density plasmas. For generation of a high-speed shock by a laser pulse, it is important to compress a high-contrast density layer by hole-boring process, and to heat the electrons in the upstream, where the hole-boring speed should match the Mach number condition 1.5 boring speed is higher in lower density plasmas, we observed consistently higher speed of the shock and accelerated ion energy when driven by CP pulses. Interesting point is that the CP-shock generation is determined predominantly by the transmittance only, while the LP-shock formation depends on other parameters such as plasma scale length. In 2D simulations, we found that Weibel instability is less effective in CP than LP, which enables more stable shock formation for given conditions of the laser and plasma. This work was supported by the Basic Science Research Program (NRF-2013R1A1A2006353) and the Creative Allied Project (CAP-15-06-ETRI).
'GAIM' - Gas-addition, impedance-matched arc driver. [shock tube gas dynamics
Dannenberg, R. E.
1980-01-01
A conceptual view for a GAIM energy/driver system to maximize shock-tube performance through efficient interfacing of the energy source with the gas dynamics of the arc driver is presented. Electrical and arc-chamber requirements are evaluated utilizing two new computer codes. One code calculates the shock wave generated for a selected time rate and magnitude of arc-energy input; the other computes the values of external circuit elements required to produce the selected energy input, with the driver represented as the load element of the electrical discharge circuit. Results indicate that the energy-storage capability and the driver arrangement needed to produce the highest shock Mach number can be achieved by means of driver gas addition and by impedance matching (GAIM). Design criteria are presented for arc energy requirements necessary to produce given shock-wave speeds. Shock velocities as high as the 70 km/sec required for simulating Jovian entry now seem possible in shock-tube operation. Practical implementation of a GAIM system is discussed.
Suresh, K.; Shanmugaraju, A.; Syed Ibrahim, M.
2016-11-01
We have analyzed the propagation characteristics of four limb coronal mass ejections (CMEs) with their shocks. These CMEs were observed in 18 frames up to 18 solar radii using LASCO white light images. Gopalswamy and Yashiro (Astrophys. J. 736:L17, 2011) introduced the standoff distance method (SOD) to find the magnetic field in the corona using CME-driven shock. In this paper, we have used this technique to determine the magnetic field strength and to study the propagation/shock formation condition of these CMEs at 18 different locations. Since the thickness of shock sheath (standoff distance or SOD) is not constant around CME, we estimate the shock parameters and their variation in large and small SOD regions of the shock. The Mach number ranges from 1.7 to 2.8 and Alfvén speed varies from 197 to 857 km s^{-1}. Finally, we estimate the magnetic field variation in the corona. The magnetic field strength ranges from 4.9 to 26.2 mG from 8.3 to 17.5 solar radii. The estimated magnetic field strength in this study is consistent with the literature value (7.6 to 45.8 mG from Gopalswamy and Yashiro (Astrophys. J. 736:L17, 2011), and 6 to 105 mG from Kim et al. (Astrophys. J. 746:118, 2012)) and it smoothly follows the general coronal magnetic field profile.
Simulations of ion acceleration at non-relativistic shocks: i) Acceleration efficiency
Caprioli, Damiano
2013-01-01
We use 2D and 3D hybrid (kinetic ions - fluid electrons) simulations to investigate particle acceleration and magnetic field amplification at non-relativistic astrophysical shocks. We show that diffusive shock acceleration operates for quasi-parallel configurations (i.e., when the background magnetic field is almost aligned with the shock normal) and, for large sonic and Alfv\\'enic Mach numbers, produces universal power-law spectra proportional to p^(-4), where p is the particle momentum. The maximum energy of accelerated ions increases with time, and it is only limited by finite box size and run time. Acceleration is mainly efficient for parallel and quasi-parallel strong shocks, where 10-20% of the bulk kinetic energy can be converted to energetic particles, and becomes ineffective for quasi-perpendicular shocks. Also, the generation of magnetic turbulence correlates with efficient ion acceleration, and vanishes for quasi-perpendicular configurations. At very oblique shocks, ions can be accelerated via shoc...
A transport equation for the evolution of shock amplitudes along rays
Directory of Open Access Journals (Sweden)
Giovanni Russo
1991-05-01
Full Text Available A new asymptotic method is derived for the study of the evolution of weak shocks in several dimension. The method is based on the Generalized Wavefront Expansion derived in [1]. In that paper the propagation of a shock into a known background was studied under the assumption that shock is weak, i.e. Mach Number =1+O(ε, ε ≪ 1, and that the perturbation of the field varies over a length scale O(ε. To the lowest order, the shock surface evolves along the rays associated with the unperturbed state. An infinite system of compatibility relations was derived for the jump in the field and its normal derivatives along the shock, but no valid criterion was found for a truncation of the system. Here we show that the infinite hierarchy is equivalent to a single equation that describes the evolution of the shock along the rays. We show that this method gives equivalent results to those obtained by Weakly Nonlinear Geometrical Optics [2].
Interplay between Mach cone and radial expansion in jet events
Tachibana, Y.; Hirano, T.
2016-12-01
We study the hydrodynamic response to jet propagation in the expanding QGP and investigate how the particle spectra after the hydrodynamic evolution of the QGP reflect it. We perform simulations of the space-time evolution of the QGP in gamma-jet events by solving (3+1)-dimensional ideal hydrodynamic equations with source terms. Mach cone is induced by the jet energy deposition and pushes back the radial flow of the expanding background. Especially in the case when the jet passage is off-central one, the number of particles emitted in the direction of the push back decreases. This is the signal including the information about the formation of the Mach cone and the jet passage in the QGP fluid.
Interaction between a shock wave and a turbulent boundary layer in transonic flow
Adamson, T. C., Jr.; Feo, A.
1975-01-01
Interaction between a shock wave and an unseparated turbulent boundary layer is considered. The method of matched asymptotic expansions is used, with solutions valid in the double limit as Reynolds number tends to infinity and Mach number tends to unity. The shock is weak enough that interaction effects can be considered as perturbations to the undisturbed flow; the case considered is that where the sonic line is near the outer edge of the boundary layer. It is shown that, with order estimates for Reynolds stress perturbations, the induced wall pressure distribution can be calculated using only the two outer interaction regions, independent of a specific closure condition and that this solution is in fact a turbulent free interaction solution. A detailed analysis of the inner regions, for which an eddy viscosity model for the Reynolds shear stress is used, provides a description of the variations in velocity, temperature and density near and at the wall.
Swept shock/boundary-layer interactions: Scaling laws, flowfield structure, and experimental methods
Settles, Gary S.
1993-01-01
A general review is given of several decades of research on the scaling laws and flowfield structures of swept shock wave/turbulent boundary layer interactions. Attention is further restricted to the experimental study and physical understanding of the steady-state aspects of these flows. The interaction produced by a sharp, upright fin mounted on a flat plate is taken as an archetype. An overall framework of quasiconical symmetry describing such interactions is first developed. Boundary-layer separation, the interaction footprint, Mach number scaling, and Reynolds number scaling are then considered, followed by a discussion of the quasiconical similarity of interactions produced by geometrically-dissimilar shock generators. The detailed structure of these interaction flowfields is next reviewed, and is illustrated by both qualitative visualizations and quantitative flow images in the quasiconical framework. Finally, the experimental techniques used to investigate such flows are reviewed, with emphasis on modern non-intrusive optical flow diagnostics.
Soulard, Olivier; Griffond, Jérôme; Souffland, Denis
2012-02-01
In this work, a pseudocompressible approximation relevant for turbulent mixing flows encountered in shock tubes is derived. The asymptotic analysis used for this purpose puts forward the role played by four dimensionless numbers on the flow compressibility, namely, the turbulent, deformation, stratification, and buoyancy force Mach numbers. The existence of rapid distortion and diffusion-dissipation regimes is also accounted for in the analysis. Some consequences of the derived pseudocompressible approximation on statistical turbulence models are discussed. In particular, the evolutions of the density variance and flux are examined, as well as the turbulent transport of energy. The different aspects of this study are assessed by performing a direct numerical simulation of a shock tube flow configuration.
Mach, the Universe, and Foundations of Mechanics
Mashhoon, B
2011-01-01
Barbour's response to our recent paper on "Mach's principle and higher-dimensional dynamics" describes an approach to Mach's principle in which the universe as a whole is involved in the definition of inertial frames of reference. Moreover, Barbour's theoretical procedure is in agreement with general relativity for a finite universe that is spatially closed. However, we prefer an operational approach that relies ultimately on observational data.
Nagata, T.; Nonomura, T.; Takahashi, S.; Mizuno, Y.; Fukuda, K.
2016-05-01
In this study, analysis of flow properties around a sphere and its aerodynamic coefficients in the high-Mach-and-low-Reynolds-numbers conditions is carried out by direct numerical simulations solving the three-dimensional compressible Navier-Stokes equations. The calculation is performed on a boundary-fitted coordinate system with a high-order scheme of sufficient accuracy. The analysis is conducted by assuming a rigid sphere with a Reynolds number of between 50 and 300, based on the diameter of the sphere and the freestream velocity and a freestream Mach number of between 0.3 and 2.0, together with the adiabatic wall boundary condition. The calculation shows the following yields: (1) unsteady fluctuation of hydrodynamic forces become smaller as the Mach number increases under the same Reynolds number condition, (2) the drag coefficient increases with the Mach number due to an increase in the pressure drag by the shock wave, and (3) an accurate prediction of the drag coefficient in the supersonic regime using traditional models might be difficult.
LES of shock wave/turbulent boundary layer interaction affected by microramp vortex generators
Joly, Laurent; Grebert, Arnaud; Jamme, Stéphane; Bodart, Julien; Aerodynamics, Energetics; Propulsion Dep. Team
2016-11-01
At large Mach numbers, the interaction of an oblique shock wave with a turbulent boundary layer (SWTBLI) developing over a flat plate gives rise to a separation bubble known to exhibit low-frequency streamwise oscillations around StL = 0 . 03 (a Strouhal number based on the separated region length). Because these oscillations yield wall pressure or load fluctuations, efforts are made to reduce their amplitude. We perform large eddy simulations to reproduce the experiments by Wang etal (2012) where a rake of microramp vortex generators (MVGs) were inserted upstream the SWTBLI with consequences yet to be fully understood. There is no consensus on the flow structure downstream MVGs and this is first clarified in the case of MVGs protruding by 0 . 47 δ in a TBL at Mach number M = 2 . 7 and Reynolds number Reθ = 3600 . Large-scale vortices intermittently shed downstream the MVGs are characterized by a streamwise period close to twice the TBL thickness and a frequency f 0 . 5Ue / δ , two orders of magnitude higher than the one of the uncontrolled SWTBLI. We then characterize the interaction between the unsteady wake of the MVGs with the SWTBLI resulting in the reduction of the interaction length and the high-frequency modulation of the shock feet motions.
Energy Technology Data Exchange (ETDEWEB)
Blasi, P.; Morlino, G.; Bandiera, R.; Amato, E. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, I-50125 Firenze (Italy); Caprioli, D. [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08540 (United States)
2012-08-20
A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high-velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, which we refer to as the neutral return flux, is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge-exchange interaction lengths of fast neutrals moving toward upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion-neutral interactions are especially important for shock velocities <3000 km s{sup -1}. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test particles accelerated at the shock. We find that, for shocks slower than {approx}3000 km s{sup -1}, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely, {proportional_to}E{sup -2}.
Gopalswamy, Nat
2011-01-01
We determine the coronal magnetic field strength in the heliocentric distance range 6 to 23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection (CME) imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfven Mach number, and hence the Alfven speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from ~48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.
Institute of Scientific and Technical Information of China (English)
Ai-Feng Wang; Wei Zhao; Zong-Lin Jiang
2011-01-01
A simplified theoretic method and numerical simulations were carried out to investigate the characterization of propagation of transverse shock wave at wedge supported oblique detonation wave.After solution validation,a criterlon which is associated with the ratio φ (u2/ucJ) of existence or inexistence of the transverse shock wave at the region of the primary triple was deduced systematically by 38 cases.It is observed that for abrupt oblique shock wave (OSW)/oblique detonation wave (ODW) transition,a transverse shock wave is generated at the region of the primary triple when φ ＜ 1,however,such a transverse shock wave does not take place for the smooth OSW/ODW transition when φ ＞ 1.The parameter φ can be expressed as the Mach number behind the ODW front for stable CJ detonation.When 0.9 ＜ φ ＜ 1.0,the reflected shock wave can pass across the contact discontinuity and interact with transverse waves which are originating from the ODW front.When 0.8 ＜ φ ＜ 0.9,the reflected shock wave can not pass across the contact discontinuity and only reflects at the contact discontinuity.The condition (0.8 ＜ φ ＜ 0.9) agrees well with the ratio (Dave/DcJ) in the critical detonation.
Shock - cardiogenic ... electrical system of the heart (heart block) Cardiogenic shock occurs when the heart is unable to pump ... orthostatic hypotension) Weak (thready) pulse To diagnose cardiogenic shock, a catheter (tube) may be placed in the ...
Emergent gravity of fractons: Mach's principle revisited
Pretko, Michael
2017-07-01
Recent work has established the existence of stable quantum phases of matter described by symmetric tensor gauge fields, which naturally couple to particles of restricted mobility, such as fractons. We focus on a minimal toy model of a rank 2 tensor gauge field, consisting of fractons coupled to an emergent graviton (massless spin-2 excitation). We show how to reconcile the immobility of fractons with the expected gravitational behavior of the model. First, we reformulate the fracton phenomenon in terms of an emergent center of mass quantum number, and we show how an effective attraction arises from the principles of locality and conservation of center of mass. This interaction between fractons is always attractive and can be recast in geometric language, with a geodesiclike formulation, thereby satisfying the expected properties of a gravitational force. This force will generically be short-ranged, but we discuss how the power-law behavior of Newtonian gravity can arise under certain conditions. We then show that, while an isolated fracton is immobile, fractons are endowed with finite inertia by the presence of a large-scale distribution of other fractons, in a concrete manifestation of Mach's principle. Our formalism provides suggestive hints that matter plays a fundamental role, not only in perturbing, but in creating the background space in which it propagates.
The efficiency of magnetic field amplification at shocks by turbulence
Ji (), Suoqing; Oh, S. Peng; Ruszkowski, M.; Markevitch, M.
2016-12-01
Turbulent dynamo field amplification has often been invoked to explain the strong field strengths in thin rims in supernova shocks ( ˜ 100 μG) and in radio relics in galaxy clusters ( ˜ μG). We present high-resolution magnetohydrodynamic simulations of the interaction between pre-shock turbulence, clumping and shocks, to quantify the conditions under which turbulent dynamo amplification can be significant. We demonstrate numerically converged field amplification which scales with Alfvén Mach number, B/B_0 ∝ M_A, up to M_A ˜ 150. This implies that the post-shock field strength is relatively independent of the seed field. Amplification is dominated by compression at low M_A, and stretching (turbulent amplification) at high M_A. For high M_A, the B-field grows exponentially and saturates at equipartition with turbulence, while the vorticity jumps sharply at the shock and subsequently decays; the resulting field is orientated predominately along the shock normal (an effect only apparent in 3D and not 2D). This agrees with the radial field bias seen in supernova remnants. By contrast, for low M_A, field amplification is mostly compressional, relatively modest, and results in a predominantly perpendicular field. The latter is consistent with the polarization seen in radio relics. Our results are relatively robust to the assumed level of gas clumping. Our results imply that the turbulent dynamo may be important for supernovae, but is only consistent with the field strength, and not geometry, for cluster radio relics. For the latter, this implies strong pre-existing B-fields in the ambient cluster outskirts.
Shock Wave Diffraction Phenomena around Slotted Splitters
Directory of Open Access Journals (Sweden)
Francesca Gnani
2015-01-01
Full Text Available In the field of aerospace engineering, the study of the characteristics of vortical flows and their unsteady phenomena finds numerous engineering applications related to improvements in the design of tip devices, enhancement of combustor performance, and control of noise generation. A large amount of work has been carried out in the analysis of the shock wave diffraction around conventional geometries such as sharp and rounded corners, but the employment of splitters with lateral variation has hardly attracted the attention of researchers. The investigation of this phenomenon around two-dimensional wedges has allowed the understanding of the basic physical principles of the flow features. On the other hand, important aspects that appear in the third dimension due to the turbulent nature of the vortices are omitted. The lack of studies that use three-dimensional geometries has motivated the current work to experimentally investigate the evolution of the shock wave diffraction around two splitters with spike-shaped structures for Mach numbers of 1.31 and 1.59. Schlieren photography was used to obtain an insight into the sequential diffraction processes that take place in different planes. Interacting among them, these phenomena generate a complicated turbulent cloud with a vortical arrangement.
Fenomenologia e fenomenismo em Husserl e Mach
Directory of Open Access Journals (Sweden)
Denis Fisette
2009-12-01
Full Text Available Como conciliar as repetidas críticas ao fenomenismo de Mach, um pouco por toda a obra de Husserl, com o papel proeminente que Husserl parece nele reconhecer em seus últimos trabalhos, quanto à gênese de sua própria fenomenologia? Para responder a essa questão, examinaremos, primeiramente, a relação estreita que Husserl estabelece entre o método fenomenológico e o descritivismo de Mach à luz do debate que opõe nativismo e empirismo sobre a origem da percepção do espaço. Em seguida, examinaremos dois aspectos da crítica que Husserl faz ao positivismo de Mach: o primeiro se refere ao fenomenismo e sua doutrina dos elementos, enquanto o segundo, ao princípio de economia de pensamento, que Husserl associa a uma forma de psicologismo em Prolegômenos. A hipótese que nos guiará nesse estudo é que as opiniões aparentemente contraditórias de Husserl sobre o positivismo de Mach se explicam em parte pelo estatuto duplo que a fenomenologia recebe em seus últimos trabalhos: enquanto programa filosófico, ela se opõe explicitamente ao positivismo; enquanto método, ela se aparenta ao descritivismo de Mach. Concluiremos com a ideia de que esses dois filósofos de origem checa perseguiam o objetivo comum de apreender o sentido originário de positividade.How to conciliate the recurrent criticisms to Mach's phenomenism, a bit in all Husserl's work, with the outstanding role Husserl seems to recognise in phenomenism in his last works, as to the genesis of his own phenomenology? In order to answer this question, we examine, first, the close relationship stablished by Husserl between the phenomenological method and Mach's descriptivism in light of the debate that opposes nativism and empiricism regarding the origin of the perception of space. Next, we examine two features of Husserl's criticism to Mach's positivism: the first refers to phenomenism ans its doctrine of elements, and the second, to the principle of economy of thought, which
Plasma flow at a high Mach-number
Energy Technology Data Exchange (ETDEWEB)
Yu, Bing; Hameiri, Eliezer [Courant Institute of Mathematical Sciences, New York University New York, New York 10012 (United States)
2013-09-15
Unlike the case of static magnetohydrodynamic (MHD) equilibria, where an expansion in large aspect ratio of toroidal devices is common, cases of MHD equilibria with flow are rarely treated this way, and when this is done the expansion tends to be only partial. The main reason for the difference seems to be the difficulty of expanding the larger system of equilibrium equations with flow. Here, we use a recent expansion technique which employs a variational principle to simplify the process [E. Hameiri, Phys. Plasmas 20, 024504 (2013)]. We treat four cases of MHD equilibria with flow, developing their asymptotic expansions in full, and for an application consider the effect of the flow on the Shafranov shift.
Hydrocarbon-Fueled Scramjet Research at Hypersonic Mach Numbers
2005-03-31
hypersonic flow. Laser-induced fluorescence has the threefold advantages for combustion studies of being non- intrusive , species-specific and highly sensitive...Propulsion Conference and Exhibit, Seattle, WA. Griffiths, A. (2004), Development and Demonstration of a Diode Laser Based Temperature and Water Vapour
Test section configuration for aerodynamic testing in shock tubes
Cook, W. J.; Presley, L. L.; Chapman, G. T.
1980-01-01
This paper presents results of a study of the test section configuration required to minimize or alleviate interference effects on model flow produced by the presence of test section walls in the aerodynamic testing of two dimensional transonic airfoils in a shock tube. Tests at a nominal Mach number of 0.85 and a chord Reynolds number of 2,000,000 were carried out by means of schlieren photography and pressure measurements for several symmetric airfoil profiles using shock tube test sections with unmodified straight walls, contoured walls, and slotted walls with adjacent chambers. Results were compared with corresponding results from conventional wind tunnel tests of the airfoils. Results for the straight wall tests show major airfoil flow distortions. Results from contoured wall tests and those performed using a slotted wall test section developed in this study exhibit essential agreement with wind tunnel results. The collective results show that test sections for aerodynamic testing can be designed for shock tubes that will alleviate wall interference effects.
Directory of Open Access Journals (Sweden)
M. M. Ehsan
2012-01-01
Full Text Available In the study of wave propagation in the free atmosphere, it is desirable to obtain time measurements to an accuracy of microsecond level. An experiment has been conducted to measure the wave speed during the propagation in the free atmosphere by the present technique. Due to sudden rupture of the diaphragm for the chamber pressure of 4.2 kg/cm2 and a wave generating in a shock tube travels with subsonic speed and the measured incident wave Mach number is 0.8 which leaves the shock tube in the free atmosphere. The measured travelling time of the incident wave to travel 61.5 cm distance in the shock tube is 2200 μsec and the same technique can apply to measure the shock wave speed. Several trigger points are installed at the exit of the shock tube in the open atmosphere to measure the strength of the wave propagation. It is observed that the wave strength decreases during the wave propagation in free atmosphere. Due to spherical expansion behind the wave, the pressure across the wave decreases. A numerical simulation is also conducted on supersonic shock wave to determine the shock speed and the travelling time in the free atmosphere. The pressures across shock wave at different locations of the shock wave are determined by solving the Euler equations and the simulation results indicate that the shock speed decreases during the propagation in the free atmosphere. In both experimental and numerical results, it is observed that the strength of the wave propagation in the free atmosphere decreases continuously due to spherical expansion. The present technique can also be used to measure the supersonic jet velocity, the velocity of bullet and any particle velocity in subsonic or supersonic ranges.
Ju, Wenhua; Zhu, Zhaohuan
2016-01-01
We present results from the first global 3D MHD simulations of accretion disks in Cataclysmic Variable (CV) systems in order to investigate the relative importance of angular momentum transport via turbulence driven by the magnetorotational instability (MRI) compared to that driven by spiral shock waves. Remarkably, we find that even with vigorous MRI turbulence, spiral shocks are an important component to the overall angular momentum budget, at least when temperatures in the disk are high (so that Mach numbers are low). In order to understand the excitation, propagation, and damping of spiral density waves in our simulations more carefully, we perform a series of 2D global hydrodynamical simulations with various equation of states and both with and without mass inflow via the Lagrangian point (L1). Compared with previous similar studies, we find the following new results. 1) Linear wave dispersion relation fits the pitch angles of spiral density waves very well. 2) We demonstrate explicitly that mass accreti...
Oblique Ion Two-Stream Instability in the Foot Region of a Collisionless Shock
Ohira, Yutaka
2008-01-01
Electrostatic behavior of a collisionless plasma in the foot region of high Mach number perpendicular shocks is investigated through the two-dimensional linear analysis and electrostatic particle-in-cell (PIC) simulation. The simulations are double periodic and taken as a proxy for the situation in the foot. The linear analysis for relatively cold unmagnetized plasmas with a reflected proton beam shows that obliquely propagating Buneman instability is strongly excited. We also found that when the electron temperature is much higher than the proton temperature, the most unstable mode is the highly obliquely propagating ion two-stream instability excited through the resonance between ion plasma oscillations of the background protons and of the beam protons, rather than the ion acoustic instability that is dominant for parallel propagation. To investigate nonlinear behavior of the ion two-stream instability, we have made PIC simulations for the shock foot region in which the initial state satisfies the Buneman i...
Numerical investigation of 3D effects on a 2D-dominated shocked mixing layer
Reese, Daniel; Weber, Christopher
2016-11-01
A nominally two-dimensional interface, unstable to the Rayleigh-Taylor or Richtmyer-Meshkov instability, will become three-dimensional at high Reynolds numbers due to the growth of background noise and 3D effects like vortex stretching. This three-dimensionality changes macroscopic features, such as the perturbation growth rate and mixing, as it enhances turbulent dissipation. In this study, a 2D perturbation with small-scale, 3D fluctuations is modeled using the hydrodynamics code Miranda. A Mach 1.95 shockwave accelerates a helium-over-SF6 interface, similar to the experiments of Motl et al. ["Experimental validation of a Richtmyer-Meshkov scaling law over large density ratio and shock strength ranges," Phys. Fluids 21(12), 126102 (2009)], to explore the regime where a 2D dominated flow will experience 3D effects. We report on the structure, growth, and mixing of the post-shocked interface in 2D and 3D.
A conceptual design of shock-eliminating clover combustor for large scale scramjet engine
Sun, Ming-bo; Zhao, Yu-xin; Zhao, Guo-yan; Liu, Yuan
2017-01-01
A new concept of shock-eliminating clover combustor is proposed for large scale scramjet engine to fulfill the requirements of fuel penetration, total pressure recovery and cooling. To generate the circular-to-clover transition shape of the combustor, the streamline tracing technique is used based on an axisymmetric expansion parent flowfield calculated using the method of characteristics. The combustor is examined using inviscid and viscous numerical simulations and a pure circular shape is calculated for comparison. The results showed that the combustor avoids the shock wave generation and produces low total pressure losses in a wide range of flight condition with various Mach number. The flameholding device for this combustor is briefly discussed.
Atom-atom excitation in shock waves in argon-oxygen mixture
Energy Technology Data Exchange (ETDEWEB)
Ezumi, Hiromichi; Kawamura, Masahiko
1987-05-01
The slope constants of the excitational cross-section for atom-atom and atom-electron collisions were generally considered and that for the oxygen atom-atom collision S/sub 0-0/ was determined to be 3.14 x 10/sup -19/ cm/sup 2//eV. Using the newly determined value of S/sub 0-0/, the calculation of the ionizing shock structure of argon-oxygen mixture was made at shock Mach number M/sub S/ = 17.1 and the initial pressure P/sub 1/ = 2.85 Torr. From the comparison of the calculated value of relaxation length with the experimental one, it was proved that the experimental result can be explained well by the present determined value of S/sub 0-0/.
Shock-tube measurements of the excitational cross-section in xenon-hydrogen mixture
Energy Technology Data Exchange (ETDEWEB)
Ezumi, Hiromichi (Hiroshima Denki Inst. of Tech. (Japan)); Kawamura, Masahiko; Gohda, Noriaki
1984-02-01
The Ionization relaxation and radiative-cooling processes behind shock wave in xenon with or without a small amount of hydrogen have been investigated using a quadrature interferometer technique at shock Mach numbers Msub(s)--13 and the initial pressure P/sub 1/=2.0 Torr. By adding a small amount of hydrogen (--0.5% of the initial pressure) to xenon, the ionization relaxation time was drastically reduced to about one-third of its pure xenon value. From the comparison between theoretical values based on the two-step ionization model and experimental data, the slope constants of excitational cross-section against relative kinetic energy between xenon atom-atom collisions and xenon-hydrogen atom-atom collisions were determined to be 1.8x10/sup -19/ cm/sup 2//eV and 9.0x10/sup -19/ cm/sup 2//eV, respectively.
Zaliznyak, Yu A; Goedbloed, J P; Zaliznyak, Yu.
2003-01-01
We present a numerical study of an idealized magnetohydrodynamic (MHD) configuration consisting of a planar wake flow embedded into a three-dimensional (3D) sheared magnetic field. Our simulations investigate the possibility for in-situ development of large-scale compressive disturbances at cospatial current sheet -- velocity shear regions in the heliosphere. Using a linear MHD solver, we first systematically chart the destabilized wavenumbers, corresponding growth rates, and physical parameter ranges for dominant 3D sinuous-type instabilities in an equilibrium wake--current sheet system. Wakes bounded by sufficiently supersonic (Mach number $M_s > 2.6$) flow streams are found to support dominant fully 3D sinuous instabilities when the plasma beta is of order unity. Fully nonlinear, compressible 2.5D and 3D MHD simulations show the self-consistent formation of shock fronts of fast magnetosonic type. They carry density perturbations far away from the wake's center. Shock formation conditions are identified in ...
The influence of state-to-state kinetics on diffusion and heat transfer behind shock waves
Energy Technology Data Exchange (ETDEWEB)
Kunova, O.; Kustova, E.; Mekhonoshina, M.; Nagnibeda, E. [Saint Petersburg State University, 198504, Universitetskiy pr., 28, Saint Petersburg (Russian Federation)
2014-12-09
In the paper, the influence of vibrational and chemical kinetics on heat transfer and diffusion in hypersonic flows of N{sub 2}/N mixture in the relaxation zone behind shock waves is studied on the basis of the state-to-state kinetic theory approach. The results of calculations of vibrational level populations ni, gas temperature T, total energy flux q, diffusion velocities of molecules at different vibrational states V{sub i} and atoms V{sub a} in the relaxation zone behind a shock front are presented for the free stream Mach number M = 10, 15. The contribution of different dissipative processes to the total energy flux is estimated for various flow conditions. The impact of non-equilibrium vibrational distributions in the free stream on molecular level populations and transport properties in the relaxation zone is shown.
Kwon, Ryun Young; Vourlidas, Angelos
2017-08-01
We investigate the three-dimensional (3D) characteristics of coronal shocks associated with Coronal Mass Ejections (CMEs), in terms of geometry, kinematics, and density compression ratio, employing a new method we have developed. The method uses multi-viewpoint observations from the STEREO-A, -B and SOHO coronagraphs. The 3D structure and kinematics of coronal shock waves and the driving CMEs are derived separately using a forward modeling method. We analyze two CMEs that are observed as halos by the three spacecraft, and the peak speeds are over 2000 km s-1. From the 3D modeling, we find (1) the coronal shock waves are spherical apparently enclosing the Sun, in which the angular widths are much wider than those of CMEs (92° and 252° versus 58° and 91°), indicating shock waves are propagating away from the CMEs in the azimuthal directions, and (2) the speeds of the shock waves around the CME noses are comparable to those of the CME noses, but the speeds at the lateral flanks seem to be limited to the local fast magnetosonic speed. Applying our new method, we determine electron densities in the shock sheaths, the downstream-upstream density ratios, and the Mach numbers. We find (1) the sheath electron densities decrease with height in general but have the maximum near the CME noses, (2) the density ratios and Mach numbers also seem to depend on the position angle from the CME nose to the far-flank but are more or less constant in time, while the sheath electron densities and speeds decrease with time, because of the reduced local Alfven speed with height, and (3) the shocks could be supercritical in a wider spatial range, and it lasts longer, than those of what have been reported in the past. We conclude that the shock wave associated with an energetic CME is a phenomenon that is becoming a non-driven (blast-type), nearly freely propagating wave at the flank from a driven (bow- and/or piston-type) wave near the CME nose.
Shocks inside CMEs: A Survey of Properties from 1997 to 2006
Lugaz, N; Smith, C W; Paulson, K
2015-01-01
We report on 49 fast-mode forward shocks propagating inside coronal mass ejections (CMEs) as measured by Wind and ACE at 1 AU from 1997 to 2006. Compared to typical CME-driven shocks, these shocks propagate in different upstream conditions, where the median upstream Alfv{\\'e}n speed is 85 km s$^{-1}$, the proton $\\beta = 0.08$ and the magnetic field strength is 8 nT. These shocks are fast with a median speed of 590 km s$^{-1}$ but weak with a median Alfv{\\'e}nic Mach number of 1.9. They typically compress the magnetic field and density by a factor of 2-3. The most extreme upstream conditions found were a fast magnetosonic speed of 230 km s$^{-1}$, a plasma $\\beta$ of 0.02, upstream solar wind speed of 740 km s$^{-1}$ and density of 0.5 cm$^{-3}$. Nineteen of these complex events were associated with an intense geomagnetic storm (peak Dst under $-100$ nT) within 12 hours of the shock detection at Wind, and fifteen were associated with a drop of the storm-time Dst index of more than 50 nT between 3 and 9 hours ...
MINKOWSKI FUNCTIONALS FOR QUANTITATIVE ASSESSMENTS OF SHOCK-INDUCED MIXING FLOWS
Energy Technology Data Exchange (ETDEWEB)
STRELITZ, RICHARD A. [Los Alamos National Laboratory; KAMM, JAMES R. [Los Alamos National Laboratory
2007-01-22
We describe the morphological descriptors known as Minkowski Functionals (MFs) on a shock-induced mixing problem. MFs allow accurate and compact characterization of complex images. MFs characterize connectivity, size, and shape of disordered structures. They possess several desirable properties, such as additivity, smoothness, and a direct relationship to certain physical properties. The scalar MFs that we describe can be extended to a moment-based tensor form that allows more thorough image descriptions. We apply MFs to experimental data for shock-induced mixing experiments conducted at the LANL shock tube facility. Those experiments, using low Mach number shock waves in air to induce the Richtmyer-Meshkov instability on air-SF{sub 6} interfaces, provide high-resolution, quantitative planar laser-induced fluorescence (PLIF) images. We describe MFs and use them to quantify experimental PLIF images of shock-induced mixing. This method can be used as a tool fo r validation, i.e., the quantitative comparison of simulation results against experimental data.
A new compressibility modification k-ε turbulence model with shock unsteadiness effect
Institute of Scientific and Technical Information of China (English)
HAN XingSi; YE TaoHong; ZHU MinMing; CHEN YiLiang
2008-01-01
A new compressibility modification k-ε model, including shock unsteadiness effect and the previous compressibility modification of pressure dilatation and dilatational dissipation rate, was developed with a simple formulation for numerical simulation in supersonic complex turbulent flows. The shock unsteadiness effect was modeled by inhibiting turbulent kinetic energy production in the governing equations of turbulent kinetic energy and the turbulent kinetic energy dissipation rate. Sarkar's correction models were employed accounting for the dilatational compressibility effects in the new model.Two types of flows, the free supersonic mixing layers and complex supersonic flow with transverse injection were simulated with different flow conditions. Comparisons with experimental data of the free supersonic mixing layers showed that the new compressibility modification k-ε model significantly inhibited the excessive growth of turbulent kinetic energy and improved predictions. On the supersonic mixing layer flows, prediction results with the new model were in close agreement with experimental data, accurately predicting the decreasing trend of the mixing layer spreading rate with the increase of the convective Mach number. Due to the complicated flow field with flow separation, shock unsteadiness modification inhibited excessive growth of the turbulent kinetic energy in shock regions and wider shock regions are predicted, thereby significantly improving results of the flow with a strong separation forecast. The flow separation was stronger, which was the primary modification effect of the new model. Predictions accord with experimental results even in strong separation flows.
Exact solution of planar and nonplanar weak shock wave problem in gasdynamics
Energy Technology Data Exchange (ETDEWEB)
Singh, L.P. [Department of Applied Mathematics, Institute of Technology, Bananas Hindu University, Varanasi 221 005 (India); Ram, S.D., E-mail: sram.rs.apm@itbhu.ac.in [Department of Applied Mathematics, Institute of Technology, Bananas Hindu University, Varanasi 221 005 (India); Singh, D.B. [Department of Applied Mathematics, Institute of Technology, Bananas Hindu University, Varanasi 221 005 (India)
2011-11-15
Highlights: > An exact solution is derived for a problem of weak shock wave in adiabatic gas dynamics. > The density ahead of the shock is taken as a power of the position from the origin of the shock wave. > For a planar and non-planar motion, the total energy carried by the wave varies with respect to time. > The solution obtained for the planer, and cylindrically symmetric flow is new one. > The results obtained are also presented graphically for different Mach numbers. - Abstract: In the present paper, an analytical approach is used to determine a new exact solution of the problem of one dimensional unsteady adiabatic flow of planer and non-planer weak shock waves in an inviscid ideal fluid. Here it is assumed that the density ahead of the shock front varies according to the power law of the distance from the source of disturbance. The solution of the problem is presented in the form of a power in the distance and the time.
Laboratory studies of magnetized collisionless flows and shocks using accelerated plasmoids
Weber, T. E.; Smith, R. J.; Hsu, S. C.
2015-11-01
Magnetized collisionless shocks are thought to play a dominant role in the overall partition of energy throughout the universe, but have historically proven difficult to create in the laboratory. The Magnetized Shock Experiment (MSX) at LANL creates conditions similar to those found in both space and astrophysical shocks by accelerating hot (100s of eV during translation) dense (1022 - 1023 m-3) Field Reversed Configuration (FRC) plasmoids to high velocities (100s of km/s); resulting in β ~ 1, collisionless plasma flows with sonic and Alfvén Mach numbers of ~10. The FRC subsequently impacts a static target such as a strong parallel or anti-parallel (reconnection-wise) magnetic mirror, a solid obstacle, or neutral gas cloud to create shocks with characteristic length and time scales that are both large enough to observe yet small enough to fit within the experiment. This enables study of the complex interplay of kinetic and fluid processes that mediate cosmic shocks and can generate non-thermal distributions, produce density and magnetic field enhancements much greater than predicted by fluid theory, and accelerate particles. An overview of the experimental capabilities of MSX will be presented, including diagnostics, selected recent results, and future directions. Supported by the DOE Office of Fusion Energy Sciences under contract DE-AC52-06NA25369.
Numerical simulation of two-dimensional fluid flow with strong shocks
Energy Technology Data Exchange (ETDEWEB)
Woodward, P.; Colella, P.
1984-04-01
Results of an extensive comparison of numerical methods for simulating hydrodynamics are presented and discussed. This study focuses on the simulation of fluid flows with strong shocks in two dimensions. By ''strong shocks,'' we here refer to shocks in which there is substantial entropy production. For the case of shocks in air, we therefore refer to Mach numbers of three and greater. For flows containing such strong shocks we find that a careful treatment of flow discontinuities is of greatest importance in obtaining accurate numerical results. Three aproaches to treating discontinuities in the flow are discussed-artificial viscosity, blending of low- and high-order-accurate fluxes, and the use of nonlinear solutions to Riemann's problem. The advantages and disadvantages of each approach are discussed and illustrated by computed results for three test problems. In this comparison we have focused our attention entirely upon the performance of schemes for differencing the hydrodynamic equations. We have regarded the nature of the grid upon which such differencing schemes are applied as an independent issue outside the scope of this work. Therefore we have restricted our study to the case of uniform, square computational zones in Cartesian coordinates. For simplicity we have further restricted our attention to two-dimensional difference schemes which are built out of symmetrized products of one-dimensional difference operators.
Masters, A.; Sulaiman, A. H.; Stawarz, Ł.; Reville, B.; Sergis, N.; Fujimoto, M.; Burgess, D.; Coates, A. J.; Dougherty, M. K.
2017-07-01
A leading explanation for the origin of Galactic cosmic rays is acceleration at high-Mach number shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multi-wavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular) is debated. Cassini spacecraft observations at Saturn’s bow shock have revealed examples of electron acceleration under quasi-perpendicular conditions, and the first in situ evidence of electron acceleration at a quasi-parallel shock. Here we use Cassini data to make the first comparison between energy spectra of locally accelerated electrons under these differing upstream magnetic field regimes. We present data taken during a quasi-perpendicular shock crossing on 2008 March 8 and during a quasi-parallel shock crossing on 2007 February 3, highlighting that both were associated with electron acceleration to at least MeV energies. The magnetic signature of the quasi-perpendicular crossing has a relatively sharp upstream-downstream transition, and energetic electrons were detected close to the transition and immediately downstream. The magnetic transition at the quasi-parallel crossing is less clear, energetic electrons were encountered upstream and downstream, and the electron energy spectrum is harder above ˜100 keV. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and suggest that the quasi-parallel spectral break is due to an energy-dependent interaction between the electrons and short, large-amplitude magnetic structures.
Whistler damping at oblique propagation - Laminar shock precursors
Gary, S. P.; Mellott, M. M.
1985-01-01
This paper addresses the collisionless damping of whistlers observed as precursors standing upstream of oblique, low-Mach number terrestrial bow shocks. The linear theory of electromagnetic waves in a homogeneous Vlasov plasma with Maxwellian distribution functions and a magnetic field is considered. Numerical solutions of the full dispersion equation are presented for whistlers propagating at an arbitrary angle with respect to the magnetic field. It is demonstrated that electron Landau damping attenuates oblique whistlers and that the parameter which determines this damping is beta-e. In a well-defined range of parameters, this theory provides damping lengths which are the same order of magnitude as those observed. Thus electron Landau damping is a plausible process in the dissipation of upstream whistlers. Nonlinear plasma processes which may contribute to precursor damping are also discussed, and criteria for distinguishing among these are described.
High-speed flow visualization in hypersonic, transonic, and shock tube flows
Kleine, H.; Olivier, H.
2017-02-01
High-speed flow visualisation has played an important role in the investigations conducted at the Stoßwellenlabor of the RWTH Aachen University for many decades. In addition to applying the techniques of high-speed imaging, this laboratory has been actively developing new or enhanced visualisation techniques and approaches such as various schlieren methods or time-resolved Mach-Zehnder interferometry. The investigated high-speed flows are inherently highly transient, with flow Mach numbers ranging from about M = 0.7 to M = 8. The availability of modern high-speed cameras has allowed us to expand the investigations into problems where reduced reproducibility had so far limited the amount of information that could be extracted from a limited number of flow visualisation records. Following a brief historical overview, some examples of recent studies are given, which represent the breadth of applications in which high-speed imaging has been an essential diagnostic tool to uncover the physics of high-speed flows. Applications include the stability of hypersonic corner flows, the establishment of shock wave systems in transonic airfoil flow, and the complexities of the interactions of shock waves with obstacles of various shapes.
Effects of shock topology on temperature field in compressible turbulence
Ni, Qionglin
2015-01-01
Effects of two types of shock topology, namely, small-scale shocklet and large-scale shock wave, on the statistics of temperature in compressible turbulence were investigated by simulations. The shocklet and shock wave are caused by the solenoidal and compressive modes of driven forces, respectively. Hereafter, the related two flows are called as SFT and CFT, respectively. It shows that in SFT the temperature spectrum follows the k^-5/3 power law, and the temperature field has "ramp-cliff" structures. By contrast, in CFT the temperature spectrum obeys the k^-2 power law, and the temperature field is dominated by large-scale rarefaction and compression. The power-law exponents for the p.d.f. of large negative dilatation are -2.5 in SFT and -3.5 in CFT, close to theoretical values. For the isentropic assumption of thermodynamic variables, the derivation in SFT grows with the turbulent Mach number (Mt), and for same Mt, the variables in CFT are more anisentropic. The angle statistics shows that the temperature g...
Collisionless shock experiments with lasers and observation of Weibel instabilities
Energy Technology Data Exchange (ETDEWEB)
Park, H.-S., E-mail: park1@llnl.gov; Huntington, C. M.; Fiuza, F.; Levy, M. C.; Pollock, B. B.; Remington, B. A.; Ross, J. S.; Ryutov, D. D.; Turnbull, D. P.; Weber, S. V. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Drake, R. P.; Kuranz, C. C. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Froula, D. H.; Rosenberg, M. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14636 (United States); Gregori, G.; Meinecke, J. [University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Koenig, M. [LULI, Ecole Polytechnique, Palaiseau (France); Kugland, N. L. [Lam Research Corporation, Fremont, California 94538 (United States); Lamb, D. Q.; Tzeferacos, P. [University of Chicago, Chicago, California 94538 (United States); and others
2015-05-15
Astrophysical collisionless shocks are common in the universe, occurring in supernova remnants, gamma ray bursts, and protostellar jets. They appear in colliding plasma flows when the mean free path for ion-ion collisions is much larger than the system size. It is believed that such shocks could be mediated via the electromagnetic Weibel instability in astrophysical environments without pre-existing magnetic fields. Here, we present laboratory experiments using high-power lasers and investigate the dynamics of high-Mach-number collisionless shock formation in two interpenetrating plasma streams. Our recent proton-probe experiments on Omega show the characteristic filamentary structures of the Weibel instability that are electromagnetic in nature with an inferred magnetization level as high as ∼1% [C. M. Huntington et al., “Observation of magnetic field generation via the weibel instability in interpenetrating plasma flows,” Nat. Phys. 11, 173–176 (2015)]. These results imply that electromagnetic instabilities are significant in the interaction of astrophysical conditions.
Volpes, L
2015-01-01
We present an application of the stereoscopic self-similar-expansion model (SSSEM) to Solar Terrestrial Relations Observatory (STEREO)/Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) observations of the 03 April 2010 CME and its associated shock. The aim is to verify whether CME-driven shock parameters can be inferred from the analysis of j-maps. For this purpose we use the SSSEM to derive the CME and the shock kinematics. Arrival times and speeds, inferred assuming either propagation at constant speed or with uniform deceleration, show good agreement with Advanced Composition Explorer (ACE) measurements. The shock standoff distance $[\\Delta]$, the density compression $[\\frac{\\rho_d}{\\rho_u}]$ and the Mach number $[M]$ are calculated combining the results obtained for the CME and shock kinematics with models for the shock location. Their values are extrapolated to $\\textrm{L}_1$ and compared to in-situ data. The in-situ standoff distance is obtained from ACE solar-wind measurements, and t...
Nonstationarity of a two-dimensional perpendicular shock: Competing mechanisms
Lembège, Bertrand; Savoini, Philippe; Hellinger, Petr; Trávníček, Pavel M.
2009-03-01
Two-dimensional particle-in-cell (PIC) simulations are used for analyzing in detail different nonstationary behaviors of a perpendicular supercritical shock. A recent study by Hellinger et al. (2007) has shown that the front of a supercritical shock can be dominated by the emission of large-amplitude whistler waves. These waves inhibit the self-reformation driven by the reflected ions; then, the shock front appears almost ``quasi-stationary.'' The present study stresses new complementary results. First, for a fixed β i value, the whistler waves emission (WWE) persists for high M A above a critical Mach number (i.e., M A >= M A WWE). The quasi-stationarity is only apparent and disappears when considering the full 3-D field profiles. Second, for lower M A , the self-reformation is retrieved and becomes dominant as the amplitude of the whistler waves becomes negligible. Third, there exists a transition regime in M A within which both processes compete each other. Fourth, these results are observed for a strictly perpendicular shock only as B 0 is within the simulation plane. When B 0 is out of the simulation plane, no whistler waves emission is evidenced and only self-reformation is recovered. Fifth, the occurrence and disappearance of the nonlinear whistler waves are well recovered in both 2-D PIC and 2-D hybrid simulations. The impacts on the results of the mass ratio (2-D PIC simulations), of the resistivity and spatial resolution (2-D hybrid simulations), and of the size of the simulation box along the shock front are analyzed in detail.
Estimate of the maximum induced magnetic field in relativistic shocks
Ghorbanalilu, M.; Sadegzadeh, S.
2017-01-01
The proton-driven Weibel instability is a crucial process for amplifying the generated magnetic fields in gamma-ray bursts. An expression for the saturation level of magnetic fields is estimated in a relativistic shock consisting of electron-proton plasmas. Within the shock transition layer, the plasma is modelled with the waterbag and Maxwell-Jüttner distribution functions for asymmetric counter-propagating proton beams and isotropic background electrons, respectively. The proton-driven Weibel-type instability in the linear phase is investigated thoroughly and then the instability conditions and the stabilization mechanisms are considered in details just after the shutdown of the electron Weibel instability. The growth rate of the instability and the saturated magnetic field strength are obtained in terms of the effective proton beam Mach number, asymmetry parameter, and the background electron temperature. In this paper, fully relativistic kinetic treatment is used to formulate the dispersion relation for the proton Weibel-type instability. Then, by using the magnetic trapping criteria, the saturated magnetic field strength is computed. In the present scenario, the instability includes two stages: in the first stage the electron Weibel instability evolves very rapidly, but in the second one because of the free energy stored in the slow counter-propagating proton beams, the instability is further amplified in the context of electrons with an isotropic distribution function. Increment of the growth rate and saturated magnetic field by increasing (decreasing) the effective proton beam Mach number (the asymmetry parameter) is deduced from the results. It is shown that at the temperatures around 108 K a maximum magnetic field up to around 56 G can be detected by this mechanism after the saturation time.
Mach bands change asymmetrically during solar eclipses.
Ross, John; Diamond, Mark R; Badcock, David R
2003-01-01
Observations made during two partial eclipses of the Sun show that the Mach bands on shadows cast by the Sun disappear and reappear asymmetrically as an eclipse progresses. These changes can be explained as due to changes in the shape of the penumbras of shadows as the visible portion of the Sun forms crescents of different orientation.
Gopalswamy, Nat; Yashiro, Seiji
2011-07-01
We determine the coronal magnetic field strength in the heliocentric distance range 6-23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfvén Mach number, and hence the Alfvén speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from ~48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.
Gopalswamy, Nat; Yashiro, Seiji
2011-01-01
We determine the coronal magnetic field strength in the heliocentric distance range 6-23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfven Mach number, and hence the Alfven speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from approximately 48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.
The Numerical Simulation of the Flame Deformation Induced by Shock Wave%激波诱导火焰变形的数值模拟
Institute of Scientific and Technical Information of China (English)
谷壮志; 王超; 施红辉; 董若凌; 章利特; 贾会霞
2011-01-01
A numerical simulation of the process of shock wave and flame interaction in a shock tube, which is pre-filled with H2-air mixture, is performed. According to the calculated results, the paper shows the shock structure and the flame shape in the flow field, and the process of DDT induced by shock wave and flame interaction. The process of shock-flame interaction contains the generation of X structure and the region of twice induced by shock wave, if Mach number of the incident shock reached 2. 3, a stable detonation will be established.%在充满氢气空气混合气体的激波管中,对激波诱导火焰变形失稳的过程进行数值模拟.根据计算结果讨论流场中激波结构与火焰形状的变化情况,同时给出激波诱导火焰燃烧转爆轰的形式和发展过程.结果显示:激波与火焰作用过程中存在λ结构和二次激波诱导区域的形成,入射激波马赫数为2.3时形成爆轰.
Edge and divertor plasma measurements with ion sensitive and Mach probes in LHD
Energy Technology Data Exchange (ETDEWEB)
Hayashi, Y., E-mail: shihaya_uki884@yahoo.co.jp [Nagano National College of Technology, 716 Tokuma, Nagano 381-8550 (Japan); Ezumi, N. [Nagano National College of Technology, 716 Tokuma, Nagano 381-8550 (Japan); Masuzaki, S.; Tanaka, H.; Kobayashi, M. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Sawada, K. [Shinshu University, Wakasato, Nagano 380-8553 (Japan); Ohno, N. [Nagoya University, Furo-cho Chikusa-ku, Nagoya 464-8603 (Japan)
2013-07-15
Spatial profiles of plasma flow and Mach number in the stochastic magnetic boundary layer as well as ion temperature (T{sub i}) and electron temperature (T{sub e}) in the divertor region in Large Helical Device (LHD) have been studied by a movable multiple functions probe, which consists of Mach probes and an ion sensitive probe. The results of ion saturation current measurements indicated plasma flow direction is alternated in the stochastic magnetic boundary. Mach number profiles for different plasma densities have been evaluated experimentally which compared with 3-D transport code. T{sub i} and T{sub e} in the divertor region measured by the ion sensitive probe decreased with increasing line-averaged density. Although T{sub i} was higher than T{sub e} in the low density plasma, both temperatures became almost the same at higher density.
Investigation of Shock-Induced Laminar Separation Bubble in a Supersonic Boundary Layer
Sivasubramanian, Jayahar; Fasel, Hermann
2015-11-01
The interaction between an impinging oblique shock and a laminar boundary-layer on a flat plate is investigated using DNS. In particular, the two-dimensional separation bubble resulting from the shock/boundary-layer interaction (SBLI) at freestream Mach number of 2.0 is investigated in detail. The flow parameters used for the present investigation match the laboratory conditions in the experiments by Hakkinen et al. The skin friction and pressure distribution from the simulations are compared to the experimental measurements and numerical results available in the literature. Our results confirm the asymmetric nature of the separation bubble as reported in the literature. In addition to the steady flow field calculations, the response to low-amplitude disturbances is investigated in order to study the linear stability behavior of the separation bubble. For comparison, both the development of two-dimensional and three-dimensional (oblique) disturbances are studied with and without the impinging oblique shock. Furthermore, the effects of the shock incidence angle and Reynolds number are also investigated. Finally, three-dimensional simulations were performed in order to explore the laminar-turbulent transition process in the presence of a laminar separation bubble. Funded by the Air Force Office of Scientific Research under grant FA9550-14-1-0195.
Yamaguchi, Hiroya; Eriksen, Kristoffer A.; Badenes, Carles; Hughes, John P.; Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Petre, Robert; Slane, Patrick O.; Smith, Randall K.
2013-01-01
Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here, we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect K beta (3p yields 1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe K alpha (2p yields 1s) emission dominated by a relatively highly ionized component. Comparisons with our hydrodynamical simulations imply instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating and favors a cross-shock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using the Fe K alpha morphology from the Chandra observations. Since strong Fe K beta fluorescence is expected only from low-ionization plasma where Fe ions still have many 3p electrons, this feature is key to diagnosing the plasma state and distribution of the immediate postshock ejecta in a young SNR.
Time-dependent simulation of oblique MHD cosmic-ray shocks using the two-fluid model
Frank, Adam; Jones, T. W.; Ryu, Dongsu
1995-01-01
Using a new, second-order accurate numerical method we present dynamical simulations of oblique MHD cosmic-ray (CR)-modified plane shock evolution. Most of the calculations are done with a two-fluid model for diffusive shock acceleration, but we provide also comparisons between a typical shock computed that way against calculations carried out using the more complete, momentum-dependent, diffusion-advection equation. We also illustrate a test showing that these simulations evolve to dynamical equilibria consistent with previously published steady state analytic calculations for such shocks. In order to improve understanding of the dynamical role of magnetic fields in shocks modified by CR pressure we have explored for time asymptotic states the parameter space of upstream fast mode Mach number, M(sub f), and plasma beta. We compile the results into maps of dynamical steady state CR acceleration efficiency, epsilon(sub c). We have run simulations using constant, and nonisotropic, obliquity (and hence spatially) dependent forms of the diffusion coefficient kappa. Comparison of the results shows that while the final steady states achieved are the same in each case, the history of CR-MHD shocks can be strongly modified by variations in kappa and, therefore, in the acceleration timescale. Also, the coupling of CR and MHD in low beta, oblique shocks substantially influences the transient density spike that forms in strongly CR-modified shocks. We find that inside the density spike a MHD slow mode wave can be generated that eventually steepens into a shock. A strong layer develops within the density spike, driven by MHD stresses. We conjecture that currents in the shear layer could, in nonplanar flows, results in enhanced particle accretion through drift acceleration.
... thready Tests that may be done include: Blood chemistry, including kidney function tests and those tests looking ... severe shock. Severe hypovolemic shock may lead to death, even with immediate medical attention. Older adults are ...
Internal energy relaxation in shock wave structure
Josyula, Eswar; Suchyta, Casimir J.; Boyd, Iain D.; Vedula, Prakash
2013-12-01
The Wang Chang-Uhlenbeck (WCU) equation is numerically integrated to characterize the internal structure of Mach 3 and Mach 5 shock waves in a gas with excitation in the internal energy states for the treatment of inelastic collisions. Elastic collisions are modeled with the hard sphere collision model and the transition rates for the inelastic collisions modified appropriately using probabilities based on relative velocities of the colliding particles. The collision integral is evaluated by the conservative discrete ordinate method [F. Tcheremissine, "Solution of the Boltzmann kinetic equation for high-speed flows," Comput. Math. Math. Phys. 46, 315-329 (2006); F. Cheremisin, "Solution of the Wang Chang-Uhlenbeck equation," Dokl. Phys. 47, 487-490 (2002)] developed for the Boltzmann equation. For the treatment of the diatomic molecules, the internal energy modes in the Boltzmann equation are described quantum mechanically given by the WCU equation. As a first step in the treatment of the inelastic collisions by the WCU equation, a two- and three-quantum system is considered to study the effect of the varying of (1) the inelastic cross section and (2) the energy gap between the quantum energy states. An alternative method, the direct simulation Monte Carlo method, is used for the Mach 3 shock wave to ensure the consistency of implementation in the two methods and there is an excellent agreement between the two methods. The results from the WCU implementation showed consistent trends for the Mach 3 and Mach5 standing shock waves simulations. Inelastic contributions change the downstream equilibrium state and allow the flow to transition to the equilibrium state further upstream.
Interplanetary shocks and solar wind extremes
Vats, Hari
The interplanetary shocks have a very high correlation with the annual sunspot numbers during the solar cycle; however the correlation falls very low on shorter time scale. Thus poses questions and difficulty in the predictability. Space weather is largely controlled by these interplanetary shocks, solar energetic events and the extremes of solar wind. In fact most of the solar wind extremes are related to the solar energetic phenomena. It is quite well understood that the energetic events like flares, filament eruptions etc. occurring on the Sun produce high speed extremes both in terms of density and speed. There is also high speed solar wind steams associated with the coronal holes mainly because the magnetic field lines are open there and the solar plasma finds it easy to escape from there. These are relatively tenuous high speed streams and hence create low intensity geomagnetic storms of higher duration. The solar flares and/or filament eruptions usually release excess coronal mass into the interplanetary medium and thus these energetic events send out high density and high speed solar wind which statistically found to produce more intense storms. The other extremes of solar wind are those in which density and speed are much lower than the normal values. Several such events have been observed and are found to produce space weather consequences of different kind. It is found that such extremes are more common around the maximum of solar cycle 20 and 23. Most of these have significantly low Alfven Mach number. This article is intended to outline the interplanetary and geomagnetic consequences of observed by ground based and satellite systems for the solar wind extremes.
Mach-Zehnder interferometer for movement monitoring
Vasinek, Vladimir; Cubik, Jakub; Kepak, Stanislav; Doricak, Jan; Latal, Jan; Koudelka, Petr
2012-06-01
Fiber optical interferometers belong to highly sensitive equipments that are able to measure slight changes like distortion of shape, temperature and electric field variation and etc. Their great advantage is that they are insensitive on ageing component, from which they are composed of. It is in virtue of herewith, that there are evaluated no changes in optical signal intensity but number interference fringes. To monitor the movement of persons, eventually to analyze the changes in state of motion we developed method based on analysis the dynamic changes in interferometric pattern. We have used Mach- Zehnder interferometer with conventional SM fibers excited with the DFB laser at wavelength of 1550 nm. It was terminated with optical receiver containing InGaAs PIN photodiode. Its output was brought into measuring card module that performs on FFT of the received interferometer signal. The signal rises with the composition of two waves passing through single interferometer arm. The optical fiber SMF 28e in one arm is referential; the second one is positioned on measuring slab at dimensions of 1x2m. A movement of persons around the slab was monitored, signal processed with FFT and frequency spectra were evaluated. They rose owing to dynamic changes of interferometric pattern. The results reflect that the individual subjects passing through slab embody characteristic frequency spectra, which are individual for particular persons. The scope of measuring frequencies proceeded from zero to 10 kHz. It was also displayed in experiments that the experimental subjects, who walked around the slab and at the same time they have had changed their state of motion (knee joint fixation), embodied characteristic changes in their frequency spectra. At experiments the stability of interferometric patterns was evaluated as from time aspects, so from the view of repeated identical experiments. Two kinds of balls (tennis and ping-pong) were used to plot the repeatability measurements and
Directory of Open Access Journals (Sweden)
V. V. Lobzin
2008-09-01
Full Text Available A new method for remote sensing of the quasiperpendicular part of the bow shock surface is presented. The method is based on analysis of high frequency electric field fluctuations corresponding to Langmuir, upshifted, and downshifted oscillations in the electron foreshock. Langmuir waves usually have maximum intensity at the upstream boundary of this region. All these waves are generated by energetic electrons accelerated by quasiperpendicular zone of the shock front. Nonstationary behavior of the shock, in particular due to rippling, should result in modulation of energetic electron fluxes, thereby giving rise to variations of Langmuir waves intensity. For upshifted and downshifted oscillations, the variations of both intensity and central frequency can be observed. For the present study, WHISPER measurements of electric field spectra obtained aboard Cluster spacecraft are used to choose 48 crossings of the electron foreshock boundary with dominating Langmuir waves and to perform for the first time a statistical analysis of nonstationary behavior of quasiperpendicular zone of the Earth's bow shock. Analysis of hidden periodicities in plasma wave energy reveals shock front nonstationarity in the frequency range 0.33 f_{Bi}
On Mach's critique of Newton and Copernicus
Hartman, H I; Hartman, Herbert I.; Nissim-Sabat, Charles
2003-01-01
Maintaining the relativity of all motion, especially rotational motion, Mach denied the existence of absolute motion and absolute space. He maintained the equivalence of the Ptolemaic and the Copernican systems and the equivalence of a fixed bucket in a rotating universe with the converse. An analysis of the Foucault pendulum shows that there cannot be a fixed bucket in a rotating universe. Also, Mach's views violate the physics he espoused: non-inertial experiments, e.g. stellar aberration and electromagnetic effects, distinguish between a rotating bucket in a fixed universe and the converse, between the Copernican and the Ptolemaic systems, and establish that one cannot ascribe all observations solely to relative motion between a system and the universe.
Dynamics of compressional Mach cones in a strongly coupled complex plasma
Bandyopadhyay, P; Kadyan, Sangeeta; Sen, Abhijit
2016-01-01
Using a Generalised-Hydrodynamic (GH) fluid model we study the influence of strong coupling induced modification of the fluid compressibility on the dynamics of compressional Mach cones in a dusty plasma medium. A significant structural change of lateral wakes for a given Mach number and Epstein drag force is found in the strongly coupled regime. With the increase of fluid compressibility, the peak amplitude of the normalised perturbed dust density first increases and then decreases monotonically after reaching its maximum value. It is also noticed that the opening angle of the cone structure decreases with the increase of the compressibility of the medium and the arm of the Mach cone breaks up into small structures in the velocity vector profile when the coupling between the dust particles increases.
Ziborov, V. S.; Efremov, V. P.; Fortov, V. E.
2007-10-01
The propagation of shock waves in He and Ar containing 0.01% of molybdenum hexacarbonyl Mo(CO)6 as a heavy component of the mixture has been investigated with the use of the method of multichannel emission spectroscopy and an electrostatic probe with a spatial resolution of 0.2 mm placed in the core of a flow. The measurements have been carried out in incident shock waves with a high-vacuum shock tube in a Mach number range of 2.5 3.4. The equilibrium parameters behind the shock front are P 2 = 0.109 1.124 atm and T 2 = 853 1280 K, the concentration of Mo(CO)6 is specially controlled, and high-purity He and Ar are used. The experiments are carried out under conditions when collisions between heavy molecules can be disregarded. It has been found that a narrow conduction band with a carrier density of more than 105 cm-3 appears in the shock front. The carrier density and its time characteristics have been measured. A correlation has been found between the conduction band and peaks of the nonequilibrium radiation in the visible and ultraviolet spectral ranges. This radiation disappears when the equilibrium parameters are reached behind the shock wave. The arrival of the conduction band and radiation band in the shock front at the measurement section advances the arrival of the density gradient of the shock front in most regimes. It has been found that the maximum conduction increases as the square of the Mo(CO)6 concentration and decreases with increasing pressure. The effective threshold of the appearance of charges in the shock front has been determined as 1.35 ± 0.15 eV. A qualitative mechanism of the effect has been proposed with allowance for possible separation of charges in the shock front and with the inclusion of the “hot” wing of the energy distribution function of pair collisions.
Institute of Scientific and Technical Information of China (English)
履之
1994-01-01
Most engines compress air, add fuel and burn it, and then allow theheated gas to expand, creating power or thrust. A radical aircraft enginedevised by ONERA, France’s equivalent of NASA, does the opposite.The Priam inverse-cycle" engine is designed for hypersonic speedsabove Mach 4 (2, 650 mph). Conventional jets do not work at suchspeeds, because the air becomes so hot when it is rammed into the
Directory of Open Access Journals (Sweden)
Mojtaba Jafari
2016-02-01
Full Text Available Background and Objectives: The purpose of the present study was to investigate effects of various heat shock conditions and fast freezing and subsequent thawing on the viability and recovery of Bacillus coagulans and Bacillus subtilis as probiotic sporeformers, and also to compare spore plate and microscopic counts. Materials and Methods: After preparing the final suspensions of B. coagulans and Bacillus subtilis subsp. Natto spores, they were spread-plated before and after fast freezing treatment (-70°C for about 1 min. Heat shock treatments of the spores were carried out at 68oC for 15, 20, and 30 min as well as at 80oC for 10 and 15 min. Concentrations of the examined probiotic sporeformers were determined simultaneously by plate enumerations and microscopically determined counts. Student’s t-test and one-way analysis of variance (ANOVA of SPSS were used for statistical analysis of the data. Analysis of DoE results was carried out using Minitab. Results: The results presented here show that the highest recovery rates for B. coagulans (14.75 log CFU/mL and B. subtilis spores (14.80 log CFU/mL were under a heat shock condition of 68°C for 20 min in nutrient agar (p<0.05. In addition, the survival rates of B. coagulans and B. subtilis spores under the fast freezing and subsequent thawing condition were about 90% and 88%, respectively. Plate counts differed significantly from counts determined microscopically, with differences of almost 0.5 and 0.8 log for B. coagulans and B. subtilis spores, respectively (p<0.05. In addition, DoE results of the study revealed that both factors of spore count method and only freezing factor in fast freezing treatment have a significant effect on concentrations of the spores examined (p<0.05. Conclusions: Heat shock conditions, freezing and subsequent thawing circumstances, and plate counts or enumerations determined microscopically have significant influences on the viability of probiotic sporeformers and
Mach's Principle and Higher-Dimensional Dynamics
Mashhoon, B
2011-01-01
We briefly discuss the current status of Mach's principle in general relativity and point out that its last vestige, namely, the gravitomagnetic field associated with rotation, has recently been measured for the earth in the GP-B experiment. Furthermore, in his analysis of the foundations of Newtonian mechanics, Mach provided an operational definition for inertial mass and pointed out that time and space are conceptually distinct from their operational definitions by means of masses. Mach recognized that this circumstance is due to the lack of any a priori connection between the inertial mass of a body and its Newtonian state in space and time. One possible way to improve upon this situation in classical physics is to associate mass with an extra dimension. Indeed, Einstein's theory of gravitation can be locally embedded in a Ricci-flat 5D manifold such that the 4D energy-momentum tensor appears to originate from the existence of the extra dimension. An outline of such a 5D Machian extension of Einstein's gen...
Experimental Investigation of Shock Wave Surfing
Parziale, N J; Hornung, H G; Shepherd, J E
2010-01-01
Shock wave surfing is investigated experimentally in GALCIT's Mach 4.0 Ludwieg Tube. Shock wave surfing occurs when a secondary free-body follows the bow shock formed by a primary free-body; an example of shock wave surfing occurs during meteorite breakup. The free-bodies in the current investigation are nylon spheres. During each run in the Ludwieg tube a high speed camera is used to capture a series of schlieren images; edge tracking software is used to measure the position of each sphere. Velocity and acceleration are had from processing the position data. The radius ratio and initial orientation of the two spheres are varied in the test matrix. The variation of sphere radius ratio and initial angle between the centers of gravity are shown to have a significant effect on the dynamics of the system.
High-resolution PIV measurements of a transitional shock wave-boundary layer interaction
Giepman, R. H. M.; Schrijer, F. F. J.; van Oudheusden, B. W.
2015-06-01
This study investigates the effects of boundary layer transition on an oblique shock wave reflection. The Mach number was 1.7, the unit Reynolds number was 35 × 106 m-1, and the pressure ratio over the interaction was 1.35. Particle image velocimetry is used as the main flow diagnostics tool, supported by oil-flow and Schlieren visualizations. At these conditions, the thickness of the laminar boundary layer is only 0.2 mm, and seeding proved to be problematic as practically no seeding was recorded in the lower 40 % of the boundary layer. The top 60 % could, however, still be resolved with good accuracy and is found to be in good agreement with the compressible Blasius solution. Due to the effects of turbulent mixing, the near-wall seeding deficiency disappears when the boundary layer transitions to a turbulent state. This allowed the seeding distribution to be used as an indicator for the state of the boundary layer, permitting to obtain an approximate intermittency distribution for the boundary layer transition region. This knowledge was then used for positioning the oblique shock wave in the laminar, transitional (50 % intermittency) or turbulent region of the boundary layer. Separation is only recorded for the laminar and transitional interactions. For the laminar interaction, a large separation bubble is found, with a streamwise length of 96. The incoming boundary layer is lifted over the separation bubble and remains in a laminar state up to the impingement point of the shock wave. After the shock, transition starts and a turbulent profile is reached approximately 80-90 downstream of the shock. Under the same shock conditions, the transitional interaction displays a smaller separation bubble (43), and transition is found to be accelerated over the separation bubble.
Gas-grain energy transfer in solar nebula shock waves: Implications for the origin of chondrules
Hood, L. L.; Horanyi, M.
1993-01-01
Meteoritic chondrules provide evidence for the occurrence of rapid transient heating events in the protoplanetary nebula. Astronomical evidence suggests that gas dynamic shock waves are likely to be excited in protostellar accretion disks by processes such as protosolar mass ejections, nonaxisymmetric structures in an evolving disk, and impact on the nebula surface of infalling 'clumps' of circumstellar gas. Previous detailed calculations of gas-grain energy and momentum transfer have supported the possibility that such shock waves could have melted pre-existing chondrule-sized grains. The main requirement for grains to reach melting temperatures in shock waves with plausibly low Mach numbers is that grains existed in dust-rich zones (optical depth greater than 1) where radiative cooling of a given grain can be nearly balanced by radiation from surrounding grains. Localized dust-rich zones also provide a means of explaining the apparent small spatial scale of heating events. For example, the scale size of at least some optically thick dust-rich zones must have been relatively small (less than 10 kilometers) to be consistent with petrologic evidence for accretion of hot material onto cold chondrules. The implied number density of mm-sized grains for these zones would be greater than 30 m(exp -3). In this paper, we make several improvements of our earlier calculations to include radiation self-consistently in the shock jump conditions, and we include heating of grains due to radiation from the shocked gas. In addition, we estimate the importance of momentum feedback of dust concentrations onto the shocked gas which would tend to reduce the efficiency of gas dynamic heating of grains in the center of the dust cloud.
Shock wave configurations and reflection hysteresis outside a planar Laval nozzle
Institute of Scientific and Technical Information of China (English)
Wang Dan; Yu Yong
2015-01-01
When the pressure ratio increases from the perfectly expanded condition to the third lim-ited condition in which a normal shock is located on the exit plane, shock wave configurations out-side the nozzle can be further assorted as no shock wave on the perfectly expanded condition, weak oblique shock reflection in the regular reflection (RR) pressure ratio condition, shock reflection hys-teresis in the dual-solution domain of pressure ratio condition, Mach disk configurations in the Mach reflection (MR) pressure ratio condition, the strong oblique shock wave configurations in the corresponding condition, and a normal shock forms on the exit plane in the third limited con-dition. Every critical pressure ratio, especially under regular reflection and Mach reflection pressure ratio conditions, is deduced in the paper according to shock wave reflection theory. A hysteresis phenomenon is also theoretically possible in the dual-solution domain. For a planar Laval nozzle with the cross-section area ratio being 5, different critical pressure ratios are counted in these con-ditions, and numerical simulations are made to demonstrate these various shock wave configura-tions outside the nozzle. Theoretical analysis and numerical simulations are made to get a more detailed understanding about the shock wave structures outside a Laval nozzle and the RRMMR transition in the dual-solution domain.
Nath, G.; Sinha, A. K.
2017-01-01
The propagation of a cylindrical shock wave in an ideal gas in the presence of a constant azimuthal magnetic field with consideration for the axisymmetric rotational effects is investigated. The ambient medium is assumed to have the radial, axial, and azimuthal velocity components. The fluid velocities and density of the ambient medium are assumed to vary according to an exponential law. Nonsimilar solutions are obtained by taking into account the vorticity vector and its components. The dependences of the characteristics of the problem on the Alfven-Mach number and time are obtained. It is shown that the presence of a magnetic field has a decaying effect on the shock wave. The pressure and density are shown to vanish at the inner surface (piston), and hence a vacuum forms at the line of symmetry.
Modeling Shock Train Leading Edge Detection in Dual-Mode Scramjets
Ladeinde, Foluso; Lou, Zhipeng; Li, Wenhai
2016-11-01
The objective of this study is to accurately model the detection of shock train leading edge (STLE) in dual-mode scramjet (DMSJ) engines intended for hypersonic flight in air-breathing propulsion systems. The associated vehicles have applications in military warfare and intelligence, and there is commercial interest as well. Shock trains are of interest because they play a significant role in the inability of a DMSJ engine to develop the required propulsive force. The experimental approach to STLE detection has received some attention; as have numerical calculations. However, virtually all of the numerical work focus on mechanically- (i.e., pressure-) generated shock trains, which are much easier to model relative to the phenomenon in the real system where the shock trains are generated by combustion. A focus on combustion, as in the present studies, enables the investigation of the effects of equivalence ratio, which, together with the Mach number, constitutes an important parameter determining mode transition. The various numerical approaches implemented in our work will be reported, with result comparisons to experimental data. The development of an STLE detection procedure in an a priori manner will also be discussed.
Non-thermal Electrons at the Earth's Bow Shock: A `Gradual' Event
Oka, M; Fujimoto, M; Matsui, H; Kasaba, Y; Saitô, Y; Kojima, H; Matsumoto, H; Mukai, T
2008-01-01
Earth's bow shock is known to produce non-thermal electrons which are generally observed as a `spike' in their flux profile. Here, in this paper, we present an analysis of electron and whistler wave properties for a quasi-perpendicular shock crossing that is supercritical, but subcritical to the so-called whistler critical Mach number, M$^w_{\\rm crit}$, above which whistler waves cannot propagate upstream. We have found that the amplitudes of whistler waves increased exponentially as a function of time prior to the shock encounter, while the suprathermal ($>$ 2 keV) electron flux similarly increased with time, although with differing $e$-folding time scales. Comparison of the electron energy spectrum measured within the ramp with predictions from diffusive shock acceleration theory was poor, but the variation of pitch angle distribution showed scattering of non-thermal electrons in the upstream region. While not finding a specific mechanism to account for the electron diffusion, we suggest that the whistlers ...
Propagation of Shock on NREL Phase VI Wind Turbine Airfoil under Compressible Flow
Directory of Open Access Journals (Sweden)
Mohammad A. Hossain
2013-01-01
Full Text Available The work is focused on numeric analysis of compressible flow around National Renewable Energy Laboratory (NREL phase VI wind turbine blade airfoil S809. Although wind turbine airfoils are low Reynolds number airfoils, a reasonable investigation of compressible flow under extreme condition might be helpful. A subsonic flow (mach no. M=0.8 has been considered for this analysis and the impacts of this flow under seven different angles of attack have been determined. The results show that shock takes place just after the mid span at the top surface and just before the mid span at the bottom surface at zero angle of attack. Slowly the shock waves translate their positions as angle of attack increases. A relative translation of the shock waves in upper and lower face of the airfoil are presented. Variation of Turbulent viscosity ratio and surface Y+ have also been determined. A k-ω SST turbulent model is considered and the commercial CFD code ANSYS FLUENT is used to find the pressure coefficient (Cp as well as the lift (CL and drag coefficients (CD. A graphical comparison of shock propagation has been shown with different angle of attack. Flow separation and stream function are also determined.
Laser-driven, magnetized quasi-perpendicular collisionless shocks on the Large Plasma Device
Energy Technology Data Exchange (ETDEWEB)
Schaeffer, D. B., E-mail: dschaeffer@physics.ucla.edu; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Vincena, S.; Van Compernolle, B.; Tripathi, S. K. P.; Gekelman, W.; Niemann, C. [Department of Physics and Astronomy, University of California - Los Angeles, Los Angeles, California 90095 (United States); Winske, D. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2014-05-15
The interaction of a laser-driven super-Alfvénic magnetic piston with a large, preformed magnetized ambient plasma has been studied by utilizing a unique experimental platform that couples the Raptor kJ-class laser system [Niemann et al., J. Instrum. 7, P03010 (2012)] to the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. This platform provides experimental conditions of relevance to space and astrophysical magnetic collisionless shocks and, in particular, allows a detailed study of the microphysics of shock formation, including piston-ambient ion collisionless coupling. An overview of the platform and its capabilities is given, and recent experimental results on the coupling of energy between piston and ambient ions and the formation of collisionless shocks are presented and compared to theoretical and computational work. In particular, a magnetosonic pulse consistent with a low-Mach number collisionless shock is observed in a quasi-perpendicular geometry in both experiments and simulations.
Kink deformation of Weibel-mediated current filaments and onset of shock formation
Ruyer, Charles; Alves, E. Paulo; Fiuza, Frederico
2016-10-01
The Weibel instability is believed to mediate the interaction of high Mach number collisionless shocks in weakly magnetized astrophysical environments. Although the generation of current filaments and strong magnetic fields by this instability has now been demonstrated experimentally, it is still not clear what is the long-term evolution of these filaments and how they lead to shock formation. We have studied the stability of Weibel-mediated current filaments using 2D/3D Particle-In-Cell simulations and analytical theory. We show that these are prone to kink-like instabilities that we characterize in both the linear and non-linear stage for a single filament, leading to an efficient ion slowing down and isotropization. We then demonstrate that our results are relevant to the self-consistent counter-streaming plasma interaction. Our 3D simulations show that the kink deformation dominates the late-stage of the interaction, when the current filaments break and most of the flow dissipation occurs, leading to the onset of magnetic turbulence and shock formation. We will discuss the important implications of these results for the shock structure and its ability to accelerate particles. This work was supported by the DOE Office of Science, Fusion Energy Science (FWP 100182).
Turbulent Flow Physics and Noise in High Reynolds Number Compressible Jets
Glauser, Mark
2016-11-01
In this talk I will present a snapshot of our ongoing research in high Reynolds number turbulent compressible jets. The high speed axisymmetric jet work (Mach 0.6 - 1.1) has been jointly performed with Spectral Energies LLC through AFRL support and involves 10 kHz and large window PIV data extracted from the near field jet plume, simultaneously sampled with near field pressure and far field noise. We have learned from the simultaneously sampled 10 kHz PIV near field plume and far field noise data, using POD/OID and Wavelet filtering, that there are certain "loud" velocity modes that have low averaged turbulent kinetic energy content but strongly correlate with the far field noise. From the large window PIV data obtained at Mach 1.0 and 1.1, specific POD modes were found to contain important physics of the problem. For example, the large-scale structure of the jet, shock-related fluctuations, and turbulent mixing regions of the flow were isolated through POD. By computing cross correlations, particular POD modes were found to be related to particular noise spectra. I will conclude with a description of our complex nozzle work which uses the multi-stream supersonic single expansion rectangular nozzle (SERN) recently installed in our large anechoic chamber at SU. This work is funded from both AFOSR (joint with OSU with a primary focus on flow physics) and Spectral Energies LLC (via AFRL funds with a focus on noise). Particular emphasis will be on insight gained into this complex 3D flow field (and its relationship to the far field noise) from applications of POD, Wavelet filtering and DMD to various numerical (LES) and experimental (PIV, high speed schlieren, near and far field pressure) data sets, at a core nozzle Mach number of 1.6 and a second stream Mach number of 1.0.
Institute of Scientific and Technical Information of China (English)
T. Irie; T. Yasunobu; H. Kashimura; T. Setoguchi
2003-01-01
When the high-pressure gas is exhausted to the vacuum chamber from the nozzle, the underexpanded supersonic jet contained with the Mach disk is generally formed. The eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with time. The characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this paper. The sonic jet of the exit Mach number Me=1 is assumed and the axisymmetric conservational equation is solved by the TVD method in the numerical calculation.The diameter and position of the Mach disk differs with the results of a steady jet and the influence on the continuously changing of the back pressure is evidenced from the comparison with the case of steady supersonic jet.
Combustion-Powered Actuation for Dynamic Stall Suppression - Simulations and Low-Mach Experiments
Matalanis, Claude G.; Min, Byung-Young; Bowles, Patrick O.; Jee, Solkeun; Wake, Brian E.; Crittenden, Tom; Woo, George; Glezer, Ari
2014-01-01
An investigation on dynamic-stall suppression capabilities of combustion-powered actuation (COMPACT) applied to a tabbed VR-12 airfoil is presented. In the first section, results from computational fluid dynamics (CFD) simulations carried out at Mach numbers from 0.3 to 0.5 are presented. Several geometric parameters are varied including the slot chordwise location and angle. Actuation pulse amplitude, frequency, and timing are also varied. The simulations suggest that cycle-averaged lift increases of approximately 4% and 8% with respect to the baseline airfoil are possible at Mach numbers of 0.4 and 0.3 for deep and near-deep dynamic-stall conditions. In the second section, static-stall results from low-speed wind-tunnel experiments are presented. Low-speed experiments and high-speed CFD suggest that slots oriented tangential to the airfoil surface produce stronger benefits than slots oriented normal to the chordline. Low-speed experiments confirm that chordwise slot locations suitable for Mach 0.3-0.4 stall suppression (based on CFD) will also be effective at lower Mach numbers.
Houegnifioh, Komlanvi Kafui; Gfeller, Etienne; Garcia, Wenceslao; Ribordy, Vincent
2014-08-13
Cardiogenic shock, especially when it complicates a myocardial infarction, is still associated with high mortality rate. Emergency department or first care physicians are often the first providers to assess the cardiogenic shock patient, and plays thereby a key role in achieving a timely diagnosis and treatment. This review will detail the actual physiopathology understanding of the cardiogenic shock, its diagnosis and management focusing on the care within the emergency department.
Hejazialhosseini, Babak; Rossinelli, Diego; Koumoutsakos, Petros
2013-09-01
We present a simulation for the interactions of shockwaves with light spherical density inhomogeneities. Euler equations for two-phase compressible flows are solved in a 3D uniform resolution finite volume based solver using 5th order WENO reconstructions of the primitive quantities, HLL-type numerical fluxes and 3rd order TVD time stepping scheme. In this study, a normal Mach 3 shockwave in air is directed at a helium bubble with an interface Atwood number of -0.76. We employ 4 billion cells on a supercomputing cluster and demonstrate the development of this flow until relatively late times. Shock passage compresses the bubble and deposits baroclinic vorticity on the interface. Initial distribution of the vorticity and compressions lead to the formation of an air jet, interface roll-ups and the formation of a long lasting vortical core, the white core. Compressed upstream of the bubble turns into a mixing zone and as the vortex ring distances from this mixing zone, a plume-shaped region is formed and sustained. Close observations have been reported in previous experimental works. The visualization is presented in a fluid dynamics video.