bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Experiments of Magnetohydrodynamic Shocks and the Stability of Switch-On Shocks
Authors: Chu C. K. , Taussig Robert T.
Published: December 2004

Numerical experiments are performed on a variety of magnetohydrodynamic shock waves to determine their behavior in a dissipative fluid. The Lundquist equations are integrated with Lax's finite difference scheme in which physical dissipation is imitiated by numerical dissipation. Fast and slow magnetohydrodynamic shocks respond to small disturbances just as predicted by linear nondissipative theory. The disintegration of an intermediate (nonevolutionary) shock is followed in time to its final (stable) flow pattern. In this case, the disturbance builds up inside the shock structure to a maximum, and the shock splits into two shocks (e.g., a switch-on and a switch-off shock) separated by a uniform region. This analysis gives the qualitatively correct time behavior of the splitting which, for small times, agrees with previous linearized dissipative results. The magnetohydrodynamic switch-on shock is examined using the same techniques. Small transverse disturbances, which might split the shock according to a linear analysis, merely rotate the magnetic field in the plane of the shock (repolarize the shock) and leave an Alfvén wave tail behind it. The fluid dynamic properties of the shock are not changed, the shock does not split, and therefore the switch-on shock is stable. In short, this approach overcomes the insufficiencies of linear, nondissipative analyses and gives physically realistic and reasonable answers to the long unresolved questions of magnetohydrodynamic shock stability.
Kinetic Models for a Gas with Internal Structure
Authors: Hanson F. B. , Morse T. F.
Published: December 2004

Kinetic model equations for a polyatomic gas have been obtained by employing a diagonal approximation in the truncation of the linearized operator of the Wang Chang-Uhlenbeck equation. These models possess an H theorem, and a Chapman-Enskog analysis of these equations yields the correct transport coefficients, such as bulk viscosity, viscosity, and thermal conductivity for translational and internal degrees of freedom. The restrictions of the Wang Chang-Uhlenbeck equation are discussed, and it is believed that these model equations should be most useful in the study of those kinetic problems involving scalar transport phenomena, in particular, sound propagation, heat transfer, and shock structure.
Convective Instabilities Driven by Electromagnetic Waves
Authors: Lindman E. L.
Published: December 2004

A description of destabilizing effects present in a plasma due to the radio frequency motion of the two species is obtained by expanding the fluid equations and the electromagnetic wave equations in an asymptotic series in 1/ωrf. Equations for the high-frequency and low-frequency motion are separated, linearized, and solved for a plasma with a density gradient perpendicular to a magnetic field. An electromagnetic wave propagating in a direction parallel to the density gradient at a frequency near the lower hybrid is considered. A convenient method of description of the interaction between the electromagnetic wave and the unstable density perturbation involving the simultaneous introduction of more than one phase operator (i) is given. It is found that time average vrf·∇vrf¯ terms which contain the effects of radio frequency gradient forces lead to instability in qualitative agreement with experiments on electrodeless radio frequency discharges.
Hot Plasma in a Cylindrical Waveguide
Authors: Swanson D. Gary
Published: December 2004

An approximate theory for the propagation of waves in a hot plasma in a cylindrical waveguide with an arbitrary axial magnetic field is presented. The boundary value problem is treated by a perturbation expansion in the smallness of the Larmor radius compared to the transverse wavelength. In the limit of zero Larmor radius, only the electromagnetic boundary conditions are important, while acoustic and higher-order boundary conditions appear as corrections. The results to zero order in Larmor radius are found to be formally identical to the cold plasma equations. Mode orthogonality and some limiting cases are also discussed.
Approximate Calculation of the Kolmogorov-Obukhov Constant
Authors: Orszag Steven A.
Published: December 2004

Approximate calculations of the Kolmogorov-Obukhov constant are made on the basis of a simple analytical transfer formula. It is found that the result is insensitive to the functional form assumed for the Kolmogorov relaxation times which appear in the formula.
Summation of Series for Cyclotron Harmonic Wave Dispersion
Authors: Diament Paul
Published: December 2004

The slowly convergent series previously quoted for cyclotron harmonic wave dispersion relations are converted into more rapidly convergent forms, convenient for numerical and analytic work.
Linear Stability of Symmetrical Parabolic Flows
Authors: Potter Merle C.
Published: December 2004

The linear stability of a symmetrical two-dimensional parabolic flow is investigated. A parameter is included so that the primary flow can be varied from the parabolic Poiseuille flow with zero-velocity gradient at the centerline to the linear symmetrical flow. The results show that all flows for which this parameter exceeds a critical value are stable at all finite Reynolds numbers.
Higher-Order Correlations in a Turbulent Field
Authors: Frenkiel François N. , Klebanoff Philip S.
Published: December 2004

Higher-order time-correlations and the associated skewnesses and flatnesses were measured in a turbulent field downstream of a grid using high-speed computing techniques. The results were obtained using samples of 160 020 digitized data recorded at time intervals of 1/12 800 sec during time periods of approximately 12.5 sec. Comparison is made between the measured correlations and the higher-order correlation curves corresponding to a Gaussian probability density distribution of turbulent velocities. The departures from Gaussianity are shown, and non-Gaussian probability distributions are proposed which correspond considerably better to experimental reality. Several relations between correlation coefficients of different orders are obtained for the non-Gaussian probability distributions and confirmed by comparison with the measured correlations, skewnesses, and flatnesses.
Temperature and Density Measurements in Free Jets and Shock Waves
Authors: Marrone Paul V.
Published: December 2004

The fluorescence stimulated by a 17.5-kV electron beam probe was used to obtain measurements of rotational temperature and gas density in supersonic nitrogen jets expanding from room temperature. The parameter P0d (where P0 is the stagnation pressure in Torricelli and d is the orifice exit diameter in millimeters) was varied from 15 to 480 Torr-mm. Density measurements were made using an interference filter-photomultiplier combination. The experimental density data follow the axial isentropic density distribution in regions of rotational nonequilibrium. Rotational temperature measurements were obtained from rotational spectra of the 0–0 band of the N2+ first negative system. The experimentally determined rotational temperatures, which initially follow the axial isentropic temperature distribution in a free jet, depart from the isentropic curve at low temperatures and freeze at a constant value, indicating a substantial degree of nonequilibrium in the expansion. A shock holder was inserted in the jet and a number of shock waves in the range M = 4 to M = 15 were investigated. Rotational spectra indicate a large departure from a Boltzmann distribution in the rotational levels in the center of a shock front. An apparent non-Boltzmann rotational distribution in the jet expansion was also observed.
Turbulent Shock Waves in Plasmas
Authors: Tidman D. A.
Published: December 2004

A model for a turbulent shock wave with a structure determined by ion wave instabilities is discussed. Quasi-linear theory for spatially growing waves is used to examine the spatial buildup of the turbulent spectrum in the leading edge of the shock transition. Although the principal calculations are made for an electrostatic shock, the response of a weak magnetic field in the plasma to such a thin ion-wave shock is also discussed. It is suggested that the earth's bow shock in the supersonic solar wind may sometimes have a structure of the type described here and a comparison with satellite data for this shock wave is made.
Third-Order Oscillations in a Maxwellian Plasma
Authors: Gary S. Peter
Published: December 2004

Nonlinear plasma oscillations in a classical, nonrelativistic, collisionless, Maxwellian electron gas are considered. There is assumed a small, sinusoidal variation in the spatial part of the initial distribution function, corresponding to excitation of wavenumber modes ±k0. The nonlinear Vlasov equation is solved to third order in the long time limit via the Montgomery-Gorman perturbation expansion, where the expansion parameter is ε, the amplitude of the initial perturbation. The linear, first-order k0 mode of the electric field is dominated by the Landau solution with (negative) damping decrement γL. The third-order k0 mode is modified, however, by singling out the spatially uniform part of the distribution function for special treatment, much in the manner of the quasi-linear theory. A nonlinear damping decrement results such that, for many values of k0 and ε, γL < γN. Thus at sufficiently long times, the modified third-order mode dominates the solution. For certain ε and k0 this behavior resembles the results of Knorr and Armstrong, obtained by numerical integration of the nonlinear Vlasov equation.
Oblique Incidence of an Electromagnetic Wave on Plasma Half-Space
Authors: Weston Vaughan H.
Published: December 2004

A radio frequency electromagnetic wave, polarized in the plane of incidence is incident obliquely upon a plasma half-space, where the equilibrium plasma is taken to be homogeneous and isotropic. Employing the specular boundary condition, an exact solution of the coupled Maxwell-Vlasov equations is derived, yielding both transverse and longitudinal waves in the plasma region. The reflection coefficient is derived, and approximately evaluated.
Application of the Hot-Film Technique on Flow of High-Polymer Solutions
Authors: Lindgren E. Rune , Chao Junn-Ling
Published: December 2004

Exploratory measurements have been made to evaluate the hot-film technique for flows of water with high molecular weight additives. Even a minute amount of additives considerably influence the heat transfer characteristics of the hot-film probe.
Shear Attainable in Stellarator Systems
Authors: Bickerton R. J. , Gibson A.
Published: December 2004

An estimate is made of the maximum shear attainable in a toroidal l = 3 stellarator. The loss of plasma due to universal instabilities in such a sheared system is compared with the Bohm loss rate. The maximum shear is compared with that obtained in other toroidal systems.
Instability of the Steady State of a Plasma in a Uniform Electric Field
Authors: Reiter George F.
Published: December 2004

The Bhatnagar-Gross-Krook equations are used to obtain the steady-state velocity distribution for a uniform, fully ionized plasma in a dc electric field. The Joule heating of the plasma is assumed to be compensated by volume heat losses such as bremstrahlung. The distribution obtained is far from Maxwellian if the drift velocity is comparable to the thermal velocity of the electrons. Longitudinal oscillations with wave vector in the direction of the field are introduced as a perturbation and their dispersion relation obtained. The stability of the steady state is investigated numerically, and it is found to be unstable for sufficiently high drift velocities, the instability being due to the familiar electron ion two stream interaction. The instability is impeded but not prevented by collisions. We find that the critical drift velocity exceeds that calculated in the collisionless theory by at about 20% in the limit that the electric field and collision frequency approach zero. This difference is attributable to the modification of the velocity distribution function.
Stability of Relativistic Magnetohydrodynamic Shock Waves
Authors: Lessen Martin , Deshpande Narayan V.
Published: December 2004

The stability of relativistic shock waves in an infinitely conducting plasma containing an applied magnetic field parallel to the plane of the shock wave is studied with respect to a disturbance with a wavenumber vector perpendicular to the magnetic field. It is concluded that such disturbances are stable.
Boundary Layer over a Thin Needle
Authors: Lee Lawrence L.
Published: December 2004

An equation governing the motion of an incompressible fluid flowing axially over a thin paraboloid of revolution is derived. The asymptotic behaviors and an approximate solution are discussed, and numerical solutions computed. From the numerical solutions, an extrapolation towards vanishing boundary thickness is made. It is found that for progressively thin needles, the displacement thickness and drag per unit length diminish very slowly, but eventually become zero as the needle vanishes.
Light Emission from Hydrodynamic Cavitation
Authors: Peterson Frank B. , Anderson Thomas P.
Published: December 2004

The characteristics of light emission from hydrodynamic cavitation are given. Changes were examined for small variations in water temperature, pressure, and gas content. Using oxygen, nitrogen, and xenon dissolved in water, the shapes, intensities, and pulse height spectra for individual light pulses were determined. With this information, combined with time integrated spectrophotometric data, the validity of some current theories is considered.
Effect of Transport Properties on Supersonic Expansion around a Corner
Authors: Adamson T. C.
Published: December 2004

The compressible flow of a viscous, heat-conducting gas around a corner is considered; in particular, the viscous corrections in the expansion region are calculated. The solutions are written in terms of asymptotic expansions, valid in the region far, compared to a viscous length, from the corner, so that the zeroth-order solutions are the classical Prandtl-Meyer solutions. The method of inner and outer expansions is used where the inner region encloses the first Mach line emanating from the corner. It is shown that the first effect of the transport properties in the expansion region is to generate terms either of order Re−1 (inverse Reynolds number) or of order Re−1 log Re, depending on the dependent variable considered.
Probability Density Measurements in a Curved Mixing Layer
Authors: Snyder William H. , Margolis David P.
Published: December 2004

Probability density measurements of the turbulent velocities were made at several positions in a curved mixing layer. The probability densities reveal the intermittent nature of the flow, which is fully turbulent in the center of the mixing layer but nonturbulent far away from the mixing layer. By using an ``intermittency analyzer'' in combination with a pulse height analyser, the statistical properties of the ``fully turbulent'' flow were obtained. An important result of this study is that the ``apparent'' transfer of energy, which appeared to be up the energy gradient, is actually due to a difference in mean velocity between the fully turbulent and nonturbulent fluid. The nonturbulent fluid contained within the convex bulges of turbulent fluid fluctuates wildly in velocity, but is almost free of vorticity.
Distribution Functions in the Statistical Theory of Turbulence
Authors: Lundgren T. S.
Published: December 2004

A hierarchy of coupled equations for multipoint turbulent velocity distribution functions is derived. These equations resemble the Bogoliubov-Born-Green-Kirkwood-Yvon equations of kinetic gas theory. The properties of the distribution functions and the equations are discussed and compared with kinetic theory.
Arc Measurement of High-Temperature Gas Transport Properties
Authors: Emmons Howard W.
Published: December 2004

A confined electric arc for the determination of gas transport properties is developed to the point that the resultant properties are found within a few percent. The measurements include the arc electrical gradient characteristic, the flow pressure drop, the radiative heat transfer, the spectral temperature distribution, and microwave resonance characteristics. Values of the electrical and thermal conductivity of equilibrium argon are tabulated for the temperature range from 7500 to 13 750°K. Helium in the confined arc at atmospheric pressure up to 400 A is shown not to be in thermodynamic equilibrium and hence its equilibrium properties cannot be determined by use of this experimental arrangement.
Laser-Driven Detonation Waves in Gases
Authors: Daiber J. W. , Thompson H. M.
Published: December 2004

The plasma created by the output of a 2 to 10 J Q-switched ruby laser focused into air, argon, helium and hydrogen at pressures from 15 to 1000 psi has been photographically recorded during and after the laser heating pulse. The growth of the luminous plasma front during laser irradiation was in accordance with a prediction based on a radiatively supported detonation-wave model in which a Gaussian pulse shape was used for the instantaneous energy addition. With hydrogen at atmospheric pressure an appreciable fraction of the laser energy was transmitted. Consequently, the detonation-wave model had to include only partial absorption of the incident laser beam. This was done by using the inverse bremsstrahlung absorption coefficient and a constant depth of energy addition. The shock wave created by this sudden energy addition was observed by using a Schlieren system. The growth of the shock wave was not in accordance with that predicted by spherical-blast-wave theory. The shock-wave position from the initial point of breakdown varied as time from breakdown to the (0.20 ± 20%) power independent of gas species or operating condition.
Schwarzschild's Criterion for Instability
Authors: Kaniel Shmuel , Kovetz Attay
Published: December 2004

Schwarzschild's criterion states that a fluid layer in hydrostatic equilibrium in a gravitational field will become unstable if the rate of change of pressure with density exceeds the corresponding adiabatic derivative. The validity of the criterion is discussed. The initial-value problem for the hydrodynamic perturbation equations for adiabatic motion is reduced to a time-independent problem. The latter is solved by a systematic classification of the possible motions. The method uses the theory of symmetric, semibounded operators. The distinction between thermodynamic and general gravitational equilibrium follows naturally. In particular, it is proved that the density in a gravitating body cannot increase outwards.
Computer Study of Nonlinear Cross-Field Instability
Authors: Sato Tetsuya , Tsuda Takao
Published: December 2004

Evolution of a macroscopic cross-field instability in a weakly ionized plasma, first investigated by Simon on a linearized version, is studied numerically by solving a set of system equations. The dependent variables are replaced by spatial Fourier components. Calculations were carried out for two initial disturbances; i.e., a monochromatic disturbance and a white-noise-like disturbance. Results show that this instability explosively develops into a strong turbulence through wave-wave interactions between the excited Fourier modes. As far as the early stage of instability growth is concerned, it is found that machine calculations are in good agreement with linear analysis.
One-Dimensional Model of a Lorentz Plasma
Authors: Shanny Ramy , Dawson John M. , Greene John M.
Published: December 2004

A one-dimensional electron plasma model, in which electron sheets can scatter in three dimensions in velocity space through small-angle collisions with the stationary ions, has been constructed. Using the model, the dc conductivity of a Lorentz plasma is measured. The result agrees with the theoretical prediction, therefore confirming the validity of the model and exhibiting its capability for determining other transport coefficients. The decay rate of a standing wave when collisions are present is measured. The result verifies the theoretical result, in which the various decay increments are superimposed. The wavelength dependence of the collisional damping is observed.
Collisionless Electrostatic Shocks
Authors: Colgate Stirling A. , Hartman Charles W.
Published: December 2004

A one-dimensional computational model of counter-streaming plasmas exhibits enhanced dynamic friction created by electrostatic instabilities. Buneman and Dawson previously demonstrated the validity of the sheet charge model, and using this model, the collective electrostatic interactions of two contra-streaming plasmas were calculated for mass ratios mi/me = 1, 10, and 100. For initially cold plasma streams KTe = 7.5 × 10−3 (½mev02), KTi = 2.78 × 10−3 (½miv02) (where v0 is the stream velocity), electron oscillations grow to saturation in several electron plasma periods, creating a thermal electron distribution. Ion-electron oscillations then grow to saturation in several ion plasma periods (1/fpi) with mean potentials of approximately (½3miv02) (me/mi)½. These oscillations heat the electrons and thermalize the two ion streams in a time 13 (mi/me)½/fpi. Two nonlinear effects occur (adiabatic electron modulation heating and electron trapping) that maintain the ion-electron instability. A larger mass ratio problem was not calculated because of computational time limitations, but an extrapolation of these results predicts the existence of electrostatic shocks for mi/me = 1836.
Waves in Collisionless Plasmas. I: Transverse Waves
Authors: Levin Joel M.
Published: December 2004

Using the exact solution of the collisionless Boltzmann equation, Maxwell's equations are written in integro-differential form. For transverse waves in an infinite, nonrelativistic plasma, where the forces exerted by the induced magnetic fields are negligible, these equations can be solved without approximations; in this case the electric field, E(z, t), can be expressed for all − ∞ < z < ∞ and 0 < t < ∞ as the definite integral over all space of a Green's function operating on the initial fields, E(z, 0) and Ė(z, 0). The relation between the Fourier-Laplace transform of this Green's function and the dispersion relation is displayed, and the dispersion relation is solved in closed form for ω as a function of the complex phase velocity, ω/k. For an initially Maxwellian plasma ω is expressed in closed form as a function of k for all k. A rigorous proof is given that these waves cannot grow. Investigation of the spatial dependence of an externally driven field shows that in general the roots of the dispersion relation (when solved for k as a function of ω) cannot be identified as complex wave-numbers of a damped exponential. Discrepancies between these results and Enoch's earlier treatment of this problem are discussed.
Waves in Collisionless Plasmas. II: Longitudinal Waves
Authors: Levin Joel M.
Published: December 2004

The problem of longitudinal waves in an infinite one-dimensional plasma is treated by expressing the charge density in terms of the exact solution of the collisionless Boltzmann equation and then solving Poisson's equation. For an initially homogeneous plasma the electric field is determined exactly. For an initially inhomogeneous plasma an iterative procedure is developed which in principle determines the electric field for an arbitrary initial inhomogeneity. If the initial inhomogeneity is small with respect to the homogeneous part of the distribution function the problem can be treated by perturbation theory. To each order the field is found to obey a linear integral equation which is readily solved in terms of a Green's function, Γ(z, t), which maps the known nth-order source function into the nth-order field. For t ≠ 0, the Fourier transform of Γ(z, t) is a sum of damped oscillations whose complex frequencies are determined for all 0 < t < ∞ by the plasma-dispersion relation. A general procedure for solving this dispersion relation is developed. For a Maxwellian plasma an infinite number of frequencies are determined for large k in addition to the usual Landau results for small k. A physical interpretation of Landau damping is developed which explains the decrease of E with time in terms of the drifting dispersal of an initially localized inhomogeneity.
Double Spherical Electrostatic Probe Continuum Theory and Electron Temperature Measurement
Authors: Bradley D. , Matthews K. J.
Published: December 2004

The continuum theory and numerical solutions of Su and Lam for single spherical probes are used to derive double probe current-voltage characteristics. These characteristics are used to test the validity of the expression for electron temperature derived by Johnson and Malter on the basis of collisionless theory. It is found that the expression gives reasonably accurate values of electron temperature for continuum conditions. Values of correction factor are presented to enable more accurate electron temperatures to be derived from the expression of Johnson and Malter.
Fluctuating Flow of an Elastico-Viscous Fluid Past a Porous Flat Plate
Authors: Kaloni P. N.
Published: December 2004

Stuart's solution for the incompressible viscous fluctuating flow over an infinite flat plate, with suction, is extended for an idealized elastico-viscous liquid. The effect of the presence of the elasticity of the fluid on the velocity field and the skin-friction is examined.
Note on Decay of Homogeneous Turbulence
Authors: Saffman P. G.
Published: December 2004

The assumption of self-similarity and the existence of an exact invariant are combined to predict the decay rate of homogeneous turbulence.
Turbulent Flow Measurements Utilizing the Doppler Shift of Scattered Laser Radiation
Authors: Goldstein R. J. , Hagen W. F.
Published: December 2004

The probability function for the turbulent velocity in a duct flow is determined from the frequency shift of laser illumination scattered by small particles contained in the flow. From this, the mean turbulent velocity and the intensity of turbulence are obtained.
Measurement of the Anisotropic Energy Distribution of Electrons in an Electron Cyclotron Resonance Plasma
Authors: Shohet J. L. , Gitomer S. J.
Published: December 2004

The anisotropy of the electrons in an electron cyclotron resonance plasma has been measured by means of the plasma diamagnetism and particle end flux out of a uniform magnetic field region. Measurements of x rays produced by the plasma were also made.
Exact Navier-Stokes Solutions Including Swirl and Cross Flow
Authors: Weinbaum Sheldon , O'Brien Vivian
Published: December 2004

A general analysis in curvilinear streamline coordinates is developed in order to investigate systematically the behavior of all possible two-dimensional and axially symmetric fluid motions with curl free convective accelerations that are exact solutions to the incompressible Navier-Stokes equation. The analysis includes: (a) all flows where the convective terms vanish, (b) irrotational flows, ω = 0, (c) Beltrami flows and (d) all other fluid motions that satisfy the kinematic constraint curl V×ω = 0. Specific solutions are referenced, derived or deduced by analogy with a related mechanical problem to give the reader a qualitative idea of the physical behavior of a class of motions. New exact solutions are presented for two-dimensional motions with cross flow and axially symmetric motions with swirl.
Boundary-Value Problems in Compressible Magnetohydrodynamics
Authors: Salathé Eric P. , Sirovich Lawrence
Published: December 2004

Linearized steady two-dimensional compressible magnetohydrodynamics is considered. No restriction on the gas law or on the field orientations is made. Thin-body flow problems are solved for all flow field regimes (e.g. doubly hyperbolic, hyperliptic). The method of solution is based on replacing material boundaries by surfaces of discontinuity. The discontinuous forms of the magnetohydrodynamic equations are derived in full generality. It is then shown that the solution to any problem may be represented in terms of the fundamental solution. The latter is obtained in closed form for all regimes. The final solution is then reduced to a single integral equation which may be solved in all cases.
Measurement of β, n, and Ti in High- and Low-Pressure Theta-Pinch Operation
Authors: Sawyer G. A. , Finlayson V. A. , Jahoda F. C. , Thomas K. S.
Published: December 2004

Three coordinated measurements on the Scylla III theta-pinch yield: β, which is the ratio of plasma pressure to external magnetic field pressure; n, which is the plasma density as a function of radius; and Ti, which is the ion temperature. The three measurements are (1) a differential magnetic loop-probe measurement that determines total flux excluded by the plasma, (2) side-on-measurement of the profile of light intensity emitted by the plasma that yields the relative density profile, and (3) a side-on gas-laser interferometer measurement that gives the absolute density integrated through the plasma. Electron temperature is measured separately by x-ray absorption and it is assumed that electron and ion temperatures are not a function of radius. In the low-pressure regime, (P initial = 20 mTorr) without bias magnetic field, typical measured values are β = 0.70 ± 0.15 and ne = ni = 3.0 × 1016/cm3 on axis, Ti = 2.2 keV, and the plasma density decreases monotonically with increasing radius from the axis, reaching zero at r = 1.1 cm. In the high-pressure regime, (P initial = 100 mTorr) with reverse-bias magnetic field, typical values are β = 0.85 ± 0.15 and ne = ni = 3.5 × 1016/cm3 on axis, Ti = 1.5 keV, and the plasma density has a central core of radius ∼0.8 cm of nearly constant density.
Proton Gyroresonance Observed in Incoherent Scattering from the Ionosphere
Authors: Farley Donald T.
Published: December 2004

A radar directed nearly orthogonal to the geomagnetic field was used to measure the autocorrelation function of the scattered signal. Peaks were observed at the first three multiples of the proton gyroperiod, in excellent agreement with theory.
Two-Particle Correlation in a Static Plasma
Authors: Pinney Edmund
Published: December 2004

The two-particle correlation theory for a static plasma is developed by an inverse application of Poisson equation theory, a less cumbersome and restrictive method than the usual Fourier theory. The theory is developed in computable form for nonfrigid two-component plasmas, and completely for warm plasmas. In the latter case it is found that the two-particle correlation function has only a small effect, and that only in the sheath.
Stability of a Relativistic Half-Jet
Authors: Lessen Martin , Zien Hwa M.
Published: December 2004

The stability of an inviscid compressible relativistic half-jet is considered. Linearized disturbance equations are obtained for three-dimensional, infinitesimal, wavy disturbances superimposed on the main flow and the eigenvalue problem is investigated numerically for the case of two-dimensional disturbances. It is found that when the ratio of the ``relativistic'' speed of sound to the speed of light is small, the results do not differ appreciably from those for the nonrelativistic case. However, as the ratio increases the flow becomes less unstable with respect to small disturbances. Even when the disturbance wave speed becomes ``supersonic,'' the instability still exists.
Stability of a Relativistic Magneto-Gasdynamic Half-Jet
Authors: Lessen Martin , Zien Hwa M.
Published: December 2004

The stability of a relativistic half-jet of infinitely conducting, inviscid, compressible fluids with imbedded magnetic fields is considered. The general dispersion relation and eigenvalue equation are derived from the theory of special relativity. Numerical results show that the magnetic fields have a stabilizing effect and the effect is comparatively greater than that of an increase of the speed of sound. Moreover, disturbances in the vicinity of neutral oscillations correspond to supersonic, outgoing waves.
Precursor Infrared Radiation from Hypervelocity Ablating Bodies
Authors: Mermagen William H.
Published: December 2004

Infrared radiation has been observed in air as far as thirty body diameters ahead of ablating, hypervelocity bodies. This precursor is attributed to constituents of air such as CO2 and H2O, as well as C2 and CN contamination. The dominant mechanism for the precursor is thought to be resonance radiation due to photon flux absorption ahead of the shock. Precursor intensities were observed with infrared detectors and photomultipliers. Data from cylinders at velocities up to 5500 m/sec in air at from 20 to 75 mm Hg are presented. Some approximate formulas have been derived to account for precursor intensities. The data are compared with calculated estimates and fair agreement is observed. Water vapor is the most important contributor to the precursor while the effect of CO2 is small. The presence of C2 and CN as contaminants in the range apparatus is suggested.
Instabilities in Ternary Diffusion
Authors: Miller L. , Spurling T. H. , Mason E. A.
Published: December 2004

Two series of experiments on gaseous diffusion instabilities are reported. In one series the convection cells are made visible with ammonium chloride smoke; the observed behavior appears quite complex. In the other series the stability limits in osmotic diffusion are investigated as a function of pressure and composition for H2−CH4−CO2. Reasonable agreement is obtained with a stability theory based on Rayleigh's treatment of thermal convection.
Baro-Diffusion Effect on Diffusion Time
Authors: Kao Timothy W.
Published: December 2004

The evolution of the concentration distribution of a small quantity of a heavy gas diffusing in the steady flow field of a lighter gas is investigated. Two cases are treated: (1) the lighter parent gas is initially in rigid body rotation, (2) it is initially at rest under a strong body force. Under isothermal condition, baro-diffusion effect is the only physical factor causing separation of the two species. For small concentration of the heavy gas, the equation governing the diffusional process is decoupled from the flow equations. The resulting initial-boundary value problems are solved by eigenfunction expansions. Of special interest is the result that baro-diffusion effect reduces the time for the establishment of equilibrium profile for arbitrary nonuniform initial concentration distribution as compared to the time for ordinary mass diffusion.
Stability of Flow Induced by an Impulsively Started Rotating Cylinder
Authors: Chen C. F. , Christensen David K.
Published: December 2004

A Taylor-type instability has been found in the flow field of an impulsively started rotating cylinder in a large tank of water. Photographs showing the growth of the ``instability disks'' and the experimentally determined neutral stability curve are presented.
Evidence for Re-Reflected Shock Waves from Convergent Cylindrical Channels
Authors: Low W. , Shtricker J.
Published: December 2004

Microwave attenuation and optical emission spectra show that a secondary shock wave is set up when a shock wave passes through a cylindrical converging section. The secondary shock wave overtakes the primary shock wave, at a position when the Mach speed reaches a maximum.
Gladstone-Dale Constants for the Oxygen Atom and Molecule
Authors: Anderson J. H. B. , Osborne P. J. K. , Glass I. I.
Published: December 2004

New interferometric results give experimentally determined values for both the atomic and molecular Gladstone-Dale constants of oxygen with greater precision than has hitherto been reported.
Limits of Validity of Born Approximation in Microwave Scattering from Turbulent Plasma
Authors: Granatstein V. L. , Buchsbaum S. J.
Published: December 2004

Microwave scattering from a turbulent weakly ionized plasma column is studied. The scattering cross section is proportional to the mean-square plasma density fluctuation, 〈ñ2〉, as predicted in the Born approximation for 〈ñ2〉½ up to 5% of the critical density.
Electrical Conductivity of a Fully Ionized Plasma
Authors: Niu Keishiro
Published: December 2004

Using a Druyvesteyn distribution for the electrons and a Maxwellian distribution for the ions, the electrical conductivity of a fully ionized plasma is derived.
Viscous Sublayer and Adjacent Wall Region in Turbulent Pipe Flow
Authors: Bakewell Henry P. , Lumley John L.
Published: December 2004

The boundary-layer research facility utilizing the highly viscous fluid, glycerine, was constructed to permit detailed experimental investigation of the viscous sublayer. At a pipe Reynolds number of 8700 the sublayer thickness corresponding to a nondimensional distance from the wall of yuτ/ν = 5.00 was 0.110 in. Detailed measurements of the streamwise fluctuating velocities were obtained with hot-film anemometers within the viscous sublayer as well as in the transition region between the linear and logarithmic mean velocity profiles. These data were used to form the space-time correlation function of the streamwise fluctuating velocities. An eigenfunction decomposition of the streamwise fluctuating velocity into a sum of products of eigenfunctions in the inhomogeneous coordinate direction, with random coefficients dependent on the homogeneous and stationary variables, was obtained from the correlation data. One dominant eigenfunction with a structure nearly identical to the mean velocity in the wall region was found. The dominant large scale structure of the flow in the wall region, obtained with the aid of a mixing length approximation, consisted of randomly distributed counterrotating eddy pairs of elongated streamwise extent.
Aerodynamic Study of an Argon Plasma
Authors: Henderson Dale B.
Published: December 2004

An rf argon plasma generator has been built in combination with a ballistic range. Spheres are photographed in free flight (at about 2 km/sec) through the plasma with an imbedded magnetic field using an image converter camera. From a series of such photographs the stand-off distance of the bow shock wave is measured as a function of velocity. From this function the state of the neutral gas is deduced; from analysis of spectral data, the state of the electron gas is deduced. A model for the plasma is constructed from these data using a kinetic-theory approach. This model features a neutral gas temperature which is uniform over most of the plasma and an electron temperature which is elevated by 900°K in the outer skin depth. This model is not in agreement with previous studies of similar plasmas, these previous studies lacking any direct knowledge of the neutral gas state.
Volume Forces in Plasmas
Authors: Leiby C. C. , Oskam H. J.
Published: December 2004

A formula is derived for the force exerted by charged particles on neutral particles in a gaseous discharge. It is shown that (a) the discussions of Langmuir and Druyvesteyn with respect to the reaction force on the neutral gas particles resulting from the net rate of momentum transfer by the charged particles to the wall of the discharge tube are incomplete and (b) the expression for the force postulated by Leiby is a limiting case of a more general form of the force equation. The calculations also show that the presence of discharge container walls is not required for the existence of volume forces in contrast with the theories presented by Langmuir and Druyvesteyn.
Correlation Functions and Scattering of Electromagnetic Waves by Inhomogeneous and Nonstationary Plasmas
Authors: Weinstock Jerome
Published: December 2004

A rigorous formalism is given for interpreting the weak (Born) scattering of em waves by macroscopically inhomogeneous and nonstationary plasmas (plasmas whose macroscopic electron density varies within the scattering volume). This formalism does not resort to the heuristic, though useful, (coherent) assumption 〈|n(k, ω)|2〉 = |〈n(k, ω)〉|2, where n(k, ω) and 〈n(k, ω)〉 denote the (Fourier transformed) microscopic and macroscopic electron density, respectively. Rather, we determine criteria for the validity of this assumption. Generally, it is valid for only isolated regions of k and ω space—depending on the specific nature of 〈n(k, ω)〉. The derivation is based on the theorem relating space-time correlation functions to one-particle distribution functions. Correlation function and scattering divide into coherent (nonlinear) and incoherent parts. The coherent part |〈n(k, ω)〉|2, is due to macroscopic density variations. The incoherent part is due to (microscopic) fluctuations about the macroscopically varying density and is determined by solutions of the linearized Vlasov equation with space-time varying background. Examples are given for plasmas with time varying Gaussian density profiles, damped oscillations, and undamped oscillations.
Radial Pressure Gradient in Turbulent Pipe Flow
Authors: Patterson Gary K. , Ewbank Walter J. , Sandborn Virgil A.
Published: December 2004

Measurements made with a Prandtl static pressure probe have demonstrated that a radial pressure gradient does exist in turbulent pipe flow with approximately the magnitude predicted by Sandborn from hot-wire anemometry measurements.
Axisymmetric Free Turbulent Rotating Jets
Authors: Chigier N. A. , Lorenz D. H.
Published: December 2004

Governing equations for axisymmetric free turbulent rotating jets are reduced to a single differential equation, assuming self-preservation. Solutions are obtained for weak and moderate swirl by estimating orders of magnitude from experimental evidence.
Interaction of the Laminar Boundary Layer with Free-Stream Turbulence
Authors: Criminale William O.
Published: December 2004

A theory is presented which directs the investigation towards an understanding of the effect of the addition of small fluctuations to the free stream of the flow field caused by the laminar boundary layer over a flat plate. It is shown that this problem is no longer one of the eigenvalue variety and a response or impedance of the boundary layer must be computed in order to determine the fate of any perturbation. The system is very selective and indications are that it bears a strong analogy to the viscous sublayer of a fully turbulent boundary layer.
Structure of Turbulence in the Boundary Layer near the Wall
Authors: Willmarth W. W. , Tu Bo Jang
Published: December 2004

Previous measurements of space-time correlations of turbulent wall pressure and velocity in the boundary layer were extended to include space-time correlations between the wall pressure and all three velocity components in the vicinity of the wall. Additional measurements of space-time correlations between various velocity components have also been made. The velocity correlations include measurements of the spatial correlation of the streamwise component of the fluctuating wall shear stress. A qualitative model is proposed for the structure of that portion of the turbulent field near the wall that is correlated with the wall pressure. The model outlines the sequence of events that result in the production of intense pressure and velocity fluctuations by stretching of the vorticity produced by viscous stresses in the sublayer. All the measurements show that the shape and size of the contours of constant correlation and the sign of the measured correlations are in agreement with the proposed model for turbulent structure.
Structure of Velocity Space-Time Correlations in a Boundary Layer
Authors: Favre A. , Gaviglio J. , Dumas R.
Published: December 2004

Space-time correlations of longitudinal velocity fluctuations have been measured in a turbulent boundary layer, with and without frequency filtering. Celerities, relative to various fluctuations scales, are defined as partial derivatives of the isocorrelation curves with respect to both space separation and time delay. An example of the introduction of these celerities into the equations of motion is given for a simple case. The variation of these celerities with respect to fluid velocity is examined as a function of fluctuation scales and of distance to the wall. As a complement to the study of the effect of longitudinal space separation, the effect of space separation orthogonal to the wall resulting in a time delay corresponding to the maximum value of the correlation coefficient has been determined for various filtering frequencies.
Statistical Theory of Wall Turbulence
Authors: Ohji Michio
Published: December 2004

A steady fully developed turbulent shear flow of incompressible fluid between parallel walls is considered. The Fourier transforms of the spatial correlations are introduced with respect to the streamwise and the spanwise directions in particular, and then they are expanded in power series of the wall distances near the wall. From the dynamical equations certain relations are obtained between the expansion coefficients. It is shown that the Reynolds stress begins with the fourth-power of the wall distance at the wall in contrast with the usual assumption of the third-power-law.
Effect of Surface Roughness on the Velocity Defect Law
Authors: Furuya Yoshimasa , Fujita Hideomi
Published: December 2004

The logarithmic plot of the velocity defect law of rough-surface flat plates is slightly higher than that of smooth plates. This result is ascribed to the fact that the shear stress at the wall preserves its value at a larger distance from the wall.
Three-Dimensional Turbulent Boundary Layers with Heat Transfer at the Wall
Authors: Eichelbrenner E. A.
Published: December 2004

A method is developed which allows the calculation of characteristic parameters of three-dimensional turbulent boundary layers under the assumption of a third-degree polynomial for the temperature polar. This polar has a free parameter S which must be adjusted to satisfy the global energy equation. To determine the coefficients of this equation by a previous solution of the ``dynamic'' system, a first approximation of S is required. The final solution is then obtained by an iterative method, the convergence of which depends essentially on the quality of the first approximation for S. A simple formula for such an approximation is proposed.
Effect of Streamwise Wall Curvature on Compressible Turbulent Boundary Layers
Authors: Rotta J. C.
Published: December 2004

The mechanism of the turbulent motion is influenced by the density stratification, which is stable under the action of centrifugal acceleration in a boundary layer over a convex wall. On a concave wall the density stratification is unstable near the surface and stable farther away from it. The contribution of centrifugal and Coriolis forces to the turbulent energy production is discussed. The turbulent heat exchange is regarded as a transport of entropy fluctuations. Simple relations are proposed for shear stress and heat flux, which are applied to the flow in the vicinity of curved walls. The velocity profiles are more hollow on convex than on plane surfaces, and fuller shapes appear on concave surfaces.
Some Aspects of Boundary-Layer Turbulence over Land and Ocean
Authors: Lappe U. O. , Kirwan A. D. , Adelfang S. I.
Published: December 2004

A generalized vertical velocity spectrum representation is obtained from analysis of data from several turbulence measurement programs. These programs include observations from land towers, measurements to within 2m of the sea surface, and data obtained from sophisticated instrumentation aboard aircraft. The thermal stability conditions under which the data were obtained were predominately stable to slightly superadiabatic. Near the sea surface it is found that the vertical inclination angles (standard deviation divided by mean wind speed) are approximately linearly related to a stability factor consisting of the air-sea temperature difference divided by the square of the mean wind speed.