Recurrent SI super plus -SI super minus impulse pairs and shock structure in M-region beams.
Worldwide positive-negative impulse pair observed on geomagnetic records found to be recurrent and associated with M-region disturbances
M-REGION↗
SEARCH · Engineering Papers
Results for “Shock structure”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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On the structure of shock waves
Structure of shock waves in gas with thermoconductivity and viscosity
GAS VISCOSITY↗
Shock drift acceleration
Basic aspects of shock drift acceleration at fast-mode collisionless shocks are reviewed. Recent modeling efforts that incorporate such effects as shock structure, shock curvature magnetic loops, rippled shocks, and magnetic turbulence are described. Theoretical and observational questions prompted by the models described are posed.
Decker, R. B.↗
Three dimensional particle simulation of high altitude rocket plumes
The interaction of two nozzles exhausting into vacuum generates a complex three-dimensional shock structure. The shock structure and resulting plume flowfield is characterized by the nozzle separation distance. For the appropriate range of penetration Knudsen numbers, the analysis of this shock structure can be suitably accomplished through a Monte Carlo simulation. This paper describes the application of a general three-dimensional Monte Carlo simulation on the Connection Machine CM-2 to the analysis of the plume self-interaction shock in the near field. Results are presented for two cases, corresponding to a small and a large nozzle separation distance. The results correctly reproduce the expected flow features and demonstrate the ability of this method to properly simulate the start of the plume self-interaction shock. This has significance not only for allowing analysis of the self-interacting plume in the near field, but also for allowing the subsequent simulation of the far field flow through the use of a continuation downstream exit boundary.
Dagum, Leonardo↗
Structures of Alfven shocks - S-shaped magnetic hodogram observed at the magnetopause
The Alfven shock structure is obtained by a two-fluid simulation code including dissipations due to resistivity, viscosity and heat conductivity. The hodogram of the tangential magnetic field component of the simulated Alfven shock is S-shaped with a 180-deg angular rotation. This is the first simulation result to show the S-shaped hodogram associated with Alfven shocks. The S-shaped hodograms have been observed at the magnetopause (Berchem and Russell, 1982). On the basis of this result, it is proposed that the magnetopause is an Alfven shock where and when the hodogram is S-shaped and rotates 180 deg.
Lyu, L. H.↗
Structure of perpendicular shocks in collisionless plasma
The macrostructure of perpendicular shocks in the supercritical regime is investigated theoretically. The coupling between the shock precursor (foot region) associated with reflected ions and the magnetic ramp associated with electron ohmic heating is analyzed using a model in which the ions are treated as a multifluid and the electrons as a massless fluid. The results are found to be in good agreement with a number of features exhibited by recent numerical simulations of perpendicular shocks, including the morphology of the reflected-gyrating ion stream, the presence of potential and magnetic field overshoots, and the Mach number dependence of the shock structure.
Leroy, M. M.↗
A viscous flow study of shock-boundary layer interaction, radial transport, and wake development in a transonic compressor
A numerical study based on the 3D Reynolds-averaged Navier-Stokes equation has been conducted to investigate the detailed flow physics inside a transonic compressor. 3D shock structure, shock-boundary layer interaction, flow separation, radial mixing, and wake development are all investigated at design and off-design conditions. Experimental data based on laser anemometer measurements are used to assess the overall quality of the numerical solution. An additional experimental study to investigate end-wall flow with a hot-film was conducted, and these results are compared with the numerical results. Detailed comparison with experimental data indicates that the overall features of the 3D shock structure, the shock-boundary layer interaction, and the wake development are all calculated very well in the numerical solution. The numerical results are further analyzed to examine the radial mixing phenomena in the transonic compressor. A thin sheet of particles is injected in the numerical solution upstream of the compressor. The movement of particles is traced with a 3D plotting package. This numerical survey of tracer concentration reveals the fundamental mechanisms of radial transport in this transonic compressor.
Hah, Chunill↗
Shock wave structure using nonlinear model Boltzmann equations
The structure of a strong plane shock wave in a monatomic rarefied perfect gas is one of the simplest problems able to be posed in kinetic theory, and one of the hardest to solve. Its simplicity lies in the absence of solid boundaries, geometrical complications, or internal molecular energy. Its difficulty arises from the great departure of the gas from equilibrium within the shock, which invalidates many of the techniques used successfully elsewhere in kinetic theory. In addition to this theoretical challenge, the modern development of ballistics and hypersonic flight has helped to stimulate extensive theoretical and experimental interest in the shock problem. The experimenters in turn have encountered great difficulties on account of the very small physical dimensions of shocks. In fact, until very recently indeed, any close comparisons of theoretical and experimental shock structure results have been rather unprofitable due to the inadequacies of both theory and experiment. During the last few years this situation has been appreciably improved by development of the Monte Carlo method. This allows idealized 'experiments' to be performed on large computers instead of in wind tunnels, using a known intermolecular force law. The most developed of these methods has been shown to be equivalent theoretically to the Boltzmann equation and to give results which agree extremely closely with measurements of high accuracy. Thus Monte Carlo results not only form the soundest basis for our present theoretical knowledge of shock wave structure, but, for purposes of developing other theories, can also be considered a very valuable experimental resource. However, such results remain very expensive to obtain. In this thesis we develop more economical kinetic theory methods for the approximate prediction of shock structure, and compare our results with those of the Monte Carlo method.
Segal, Ben Maurice↗
Structure of the terrestrial bow shock
Preliminary results of a bow shock study which isolates various parameters are reported. The main findings are successful isolation of shock structures by parameter set, and correlated diagnostic behavior. Conventional shock structural nomenclature is first modified to suit the results of spacecraft observations and to provide the terminology needed in the remainder of the paper. Several examples of shock morphology for a wide range of plasma states are then displayed, as seen with various diagnostics. The bow shock is described as a system in the solar wind. Advantages of the bow shock as an object of shock investigation are pointed out, and a few aims of future study are outlined.
Greenstadt, E. W.↗
Shock transmission in coupled beams and rib stiffened structures
Shock transmission in a simple coupled beam structure and in a ring-stringer stiffened cylinder is investigated experimentally and analytically using wave transmission and statistical energy analysis concepts. The use of the response spectrum to characterize the excitation provided to a simple beam by a force pulse is studied. Analysis of the transmission of a dilatation wave in a periodically stiffened plate indicates that the stiffeners are fairly transparent to the wave, but some of the dilatational energy is scattered into bending at each support.
Pope, L. D.↗
Computational Analyses in Support of Sub-scale Diffuser Testing for the A-3 Facility: Unsteady Analyses and Risk Assessment - Part 2
Simulation technology can play an important role in rocket engine test facility design and development by assessing risks, providing analysis of dynamic pressure and thermal loads, identifying failure modes and predicting anomalous behavior of critical systems. This is especially true for facilities such as the proposed A-3 facility at NASA SSC because of a challenging operating envelope linked to variable throttle conditions at relatively low chamber pressures. Design Support of the feasibility of operating conditions and procedures is critical in such cases due to the possibility of startup/shutdown transients, moving shock structures, unsteady shock-boundary layer interactions and engine and diffuser unstart modes that can result in catastrophic failure. Analyses of such systems is difficult due to resolution requirements needed to accurately capture moving shock structures, shock-boundary layer interactions, two-phase flow regimes and engine unstart modes. In a companion paper, we will demonstrate with the use of CFD, steady analyses advanced capability to evaluate supersonic diffuser and steam ejector performance in the sub-scale A-3 facility. In this paper we will address transient issues with the operation of the facility especially at startup and shutdown, and assess risks related to afterburning due to the interaction of a fuel rich plume with oxygen that is a by-product of the steam ejectors. The primary areas that will be addressed in this paper are: (1) analyses of unstart modes due to flow transients especially during startup/ignition, (2) engine safety during the shutdown process (3) interaction of steam ejectors with the primary plume i.e. flow transients as well as probability of afterburning. In this abstract we discuss unsteady analyses of the engine shutdown process. However, the final paper will include analyses of a staged startup, drawdown of the engine test cell pressure, and risk assessment of potential afterburning in the facility. Unsteady simulations have been carried out to study the engine shutdown process in the facility and understand the physics behind the interactions between the steam ejectors, the test cell and the supersonic diffuser. As a first approximation, to understand the dominant unsteady mechanisms in the engine test cell and the supersonic diffuser, the turning duct in the facility was removed. As the engine loses power a rarefaction wave travels downstream that disrupts the shock cell structure in the supersonic diffuser. Flow from the test cell is seen to expand into the supersonic diffuser section and re-pressurizes the area around the nozzle along with a upstream traveling compression wave that emanates from near the first stage ejectors. Flow from the first stage ejector expands to the center of the duct and a new shock train is formed between the first and second stage ejectors. Both stage ejectors keep the facility pressurized and prevent any large amplitude pressure fluctuations from affecting the engine nozzle. The resultant pressure loads the nozzle experiences in the shutdown process are small.
Ahuja, Vineet↗
Structure of steady state accretion shocks with several cooling functions: Closed integral-form solution
We present, for the first time, a closed integral-form solution to the accretion shock structures for the case where the cooling is due to optically thin bremsstrahlung emission and a series of power-law cooling functions of density and temperature. Our results can provide useful checks on numerical calculations and simple accurate estimates for valuable parameters such as the shock height. For the case where the cooling rate j = (2/3)Arho(exp 2)(P/rho)(exp 1/2)(1 + epsilon (sub s)(P/P(sub s)(exp alpha)(rho(sub s)/rho)(exp beta)), we find that a substantial amount of the accretion energy is released at the base of the accretion shock in the form of bremsstrahlung radiation. This implies that for a cyclotron-dominated shock (qualitatively given by alpha = 2.0, beta = 3.85, and epsilon(sub s) is much greater than 1), bremsstrahlung cooling still plays a crucial role in determining the shock structure. Our results are shown to be consistent with detailed numerical calculations.
Wu, Kinwah↗
The structure of shock wave in a gas consisting of ideally elastic, rigid spherical molecules
Principal approaches are examined to the theoretical study of the shock layer structure. The choice of a molecular model is discussed and three procedures are formulated. These include a numerical calculation method, solution of the kinetic relaxation equation, and solution of the Boltzmann equation.
Cheremisin, F. G.↗
SHOCK WAVES AND SHOCK-WAVE STRUCTURE IN MAGNETO-FLUID DYNAMICS
Shock waves and shock wave structure in magnetohydrodynamics
MAGNETOHYDRODYNAMICS↗
Shock-wave structure in a partially ionized gas
The structure of a steady plane shock in a partially ionized gas has been investigated using the Boltzmann equation with a kinetic model as the governing equation and the discrete ordinate method as a tool. The effects of the electric field induced by the charge separation on the shock structure have also been studied. Although the three species of an ionized gas travel with approximately the same macroscopic velocity, the individual distribution functions are found to be very different. In a strong shock the atom distribution function may have double peaks, while the ion distribution function has only one peak. Electrons are heated up much earlier than ions and atoms in a partially ionized gas. Because the interactions of electrons with atoms and with ions are different, the ion temperature can be different from the atom temperature.
Lu, C. S.↗
Shock associated noise reduction from inverted-velocity-profile coannular jets
Acoustic measurements show that the shock noise from the outer stream is virtually eliminated when the inner stream is operated at a Mach number just above unity, regardless of all the other jet operating conditions. At this optimum condition, the coannular jet provides the maximum noise reduction relative to the equivalent single jet. The shock noise reduction can be achieved at inverted-as well as normal-velocity-profile conditions, provided the coannular jet is operated with the inner stream just slightly supersonic. Analytical models for the shock structure and shock noise are developed indicate that a drastic change in the outer stream shock cell structure occurs when the inner stream increases its velocity from subsonic to supersonic. At this point, the almost periodic shock cell structure of the outer stream nearly completely disappears the noise radiated is minimum. Theoretically derive formulae for the peak frequencies and intensity scaling of shock associated noise are compared with the measured results, and good agreement is found for both subsonic and supersonic inner jet flows.
Tanna, H. K.↗
Screech Tones from Rectangular Jets with Spanwise Oblique Shock-Cell Structures
Understanding screech is especially important for the design of advanced aircraft because screech can cause sonic fatigue failure of aircraft structures. Although the connection between shock-cell spacing and screech frequency is well understood, the relation between non-uniformities in the shock-cell structures and the resulting amplitude, mode, and steadiness of screech have remained unexplored. This paper addresses the above issues by intentionally producing spanwise (larger nozzle dimension) variations in the shock-cell structures and studying the resulting spanwise screech mode. The spanwise oblique shock-cell structures were produced using imperfectly expanded convergent-divergent rectangular nozzles (aspect ratio = 5) with nonuniform exit geometries. Three geometries were studied: (a) a nozzle with a spanwise uniform edge, (b) a nozzle with a spanwise oblique (single bevelled) edge, and (c) a nozzle that had two spanwise oblique (double bevelled) cuts to form an arrowhead-shaped nozzle. For all nozzles considered, the screech mode was antisymmetric in the transverse (smaller nozzle dimension) direction allowing focus on changes in the spanwise direction. Three types of spanwise modes were observed: symmetric (1), antisymmetric (2), and oblique (3). The following significant results emerged: (1) for all cases the screech mode corresponds with the spanwise shock-cell structure, (2) when multiple screech modes are present, the technique presented here makes it possible to distinguish between coexisting and mutually exclusive modes, (3) the strength of shocks 3 and 4 influences the screech source amplitude and determines whether screech is unsteady. The results presented here offer hope for a better understanding of screech and for tailoring shock-containing jets to minimize fatigue failure of aircraft components.
Raman, Ganesh↗
OGO 5 observations of electrostatic turbulence in bow shock magnetic structures
Electrostatic turbulence in bow shock magnetic structures observed by OGO 5, explaining turbulence as ion acoustic or Buneman mode due to two stream instability
Coleman, P. J.↗