摘要:

The problem of a sphere moving in an infinite homogeneous incompressible liquid has been discussed by many writers. The corresponding problem for a semi‐infinite liquid with a free surface has not been treated earlier.It is shown that the surface wake of such a submerged sphere is approximately the same as that which would be caused by a traveling pressure disturbance in the atmosphere above the free surface. This is, essentially, a consequence of the Bernoulli theorem.If the motion is sufficiently slow, the surface reacts to this equivalent pressure as a barometer (equilibrium theory). For more rapid motions, dynamic effects reduce the response of the surface, but leave a wake in the region already traversed by the sphere. The calculation of this wake involves the usual distinction between incoming and outgoing waves, which is introduced in the Fourier transform of the solution. The resulting integrals are evaluated by Kelvin's approximate method of stationary phase.

ISSN:0031-9171    

DOI:10.1063/1.1724367

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The correlation between Fourier velocity components at the same wave numberkand two instants separated by a time &tgr; is investigated for a homogeneous, isotropic, and stationary turbulent field. Ensemble averages of four velocity components are related to second‐order averages as in a normal distribution. A power series in &tgr; for the time‐displaced kinetic energy spectrumE(k, &tgr;) is derived and the coefficient of &tgr;2evaluated explicitly using the Heisenberg spectrum for &tgr; = 0. The asymptotic behavior of this term for an infinite Reynolds numberRshows that the relaxation time associated with eddies of wave numberkvaries ask−1. These results were verified by numerical integrations for finite largeR. The resulting discrepancy with the dimensional result &tgr;k&agr;k−2/3is ascribed to the nonuniversality of the method of analysis followed. A general integrodifferential equation forE(k, &tgr;) is then derived and shown to admit solutions in similarity variables of the form &xgr; =k&tgr;1/&bgr;. The case &bgr; = 2/3 corresponds to the Kolmogoroff spectral law. Recent objections to the quasi‐normal approximation are criticized briefly in an appendix.

ISSN:0031-9171    

DOI:10.1063/1.1724368

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The development of a free molecule probe for use as an instrument in the investigation of two dimensional rarefied gas flow fields is described. The probe consists of a cross‐stream cylindrical wire of diameter small compared with the mean free path of the gas. Measurement of the probe temperature and heat transfer characteristics yields information that can be related theoretically to the state of the flowing gas. This paper describes the use of such information in the study of the qualitative nature of supersonic flow about sharp leading edges in regions where rarefaction, slip, and boundary layer‐shock wave interaction effects are important. The results showed clearly the effect of increasing density. Thus, at the lowest densities and Mach numbers, a clearly defined shock wave and boundary layer emerged from a region of mixed compressive and viscous action at the leading edge, while at the higher densities and Mach numbers there was a large region of strong boundary layer‐shock wave interaction and a considerable delay in the formation of clearly defined shock wave.

ISSN:0031-9171    

DOI:10.1063/1.1724369

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Atmospheric density measurements obtained with rocket‐borne ionization gauges are compared with U. S. A. and U. S. S. R. satellite‐drag density measurements. There is no significant disagreement between the results obtained by the two methods once atmospheric variations are taken into account.

ISSN:0031-9171    

DOI:10.1063/1.1724370

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The electrohydrodynamic phenomena associated with the high‐velocity motion of a charged body in a plasma are investigated with a view to applications to satellite motion in the ionosphere. It is shown that the effect of the electric field due to the charge on the body in inducing collective motion leads to similar results both for high‐ and low‐density gases. By using a linearized theory, formulas are obtained for the electrohydrodynamic drag and for the increased ionization in the Mach cone behind the body.

ISSN:0031-9171    

DOI:10.1063/1.1724371

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

In the conventional pinch effect an ionized gas is enclosed by a conducting cylinder, and a sufficiently large current passing through the gas and returning along the inner wall of the cylinder produces a magnetic field which compresses the gas into an axial filament. A device is described which produces an inverse pinch effect. Here the above conducting cylinder is replaced by an axial rod surrounded by the ionized gas. When a current passes through the gas and returns along the rod the magnetic field pushes the plasma outward, leaving a cylindrical vacuum region behind. The velocity and thickness of the expanding plasma front have been studied optically and by means of magnetic probes. Except at the highest gas densities, the velocity is in good agreement with the ``snow plow'' theory of Rosenbluth, and the thickness of the front is reasonably consistent with the ``snow plow'' model. At the higher densities it appears that diffusion of magnetic field into the plasma is significant. The advantages of the inverse pinch effect in studying plasma behavior and the idea of a magnetically stabilized inverse pinch are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1724372

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The effect of the neutral gas background on the formation of a thermonuclear plasma by highenergy injection is discussed. There ways of overcoming this barrier are detailed. The first is by sufficiently reducing the initial gas pressure; the second by injecting sufficient current so that plasma self‐shielding or ``burnout'' occurs; and the third by use of the ion pumping or ``gettering'' action of the trapped plasma. Numerical examples are given. In particular the requirements for ``burnout'' do not seem excessively difficult to attain.

ISSN:0031-9171    

DOI:10.1063/1.1724373

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The collective motions of a fully ionized cold plasma in a uniform external magnetic field are treated by standard small amplitude theory. Finite temperature and collision effects are neglected. Specializing the analysis to a neutral plasma of uniform unperturbed density containing electrons and ions of one species, one obtains a dielectric tensor and dispersion relation which is a special example of results previously given by Astro¨m. A detailed discussion of the exact dispersion relation is given for the entire frequency spectrum, and completeness theorems are presented with the aid of scalar potentials representing the electromagnetic field quantities. It is found that when the Alfve´n dielectric constant &agr; = 4&pgr;n(m + M)c2/B02becomes comparable in magnitude to the ion‐to‐electron mass ratio, the plasma space charge may play an important role in determining the nature of collective oscillations. In particular, if the axial wavelength of the perturbation is sufficiently large, the singularities of the effective dielectric constant become displaced from the neighborhood of the particle cyclotron frequencies to hybrid frequencies, which, in the limit of high plasma density, become equal to the geometric mean of the cyclotron frequencies and the plasma frequency, respectively. The last two sections discuss particle orbits in idealized oscillatory modes and simplified boundary value problems associated with plasma resonance.

ISSN:0031-9171    

DOI:10.1063/1.1724374

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Streak camera and oscillographic circuit‐damping data are presented for exploded copper wires varying in diameter from 3 to 8 mils. A maximum of specific shock‐wave energy in the induced flow is found at a wire diameter different from that of a minimum in the total damping time of the circuit. This displacement is shown to be caused by the presence of residual circuit resistance. The proof is based on a critical analysis of optimum damping conditions in the exploding wire circuit. A maximum of apparent energy within the contact surface appears at about the same wire diameter as the minimum of total damping time. Discussion of the implications of the Taylor‐Lin similarity theory indicates that lack of similarity of the flow is probably connected with the displacement of the maximum energies associated with shock‐wave and contact surface.

ISSN:0031-9171    

DOI:10.1063/1.1724375

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Measurement of the hydrodynamic state in an inert material adjacent to an interface with a detonating explosive yields a data point on the reflected shock Hugoniot of the explosive reaction products centered at the Chapman‐Jouguet state or on the isentrope below this state. Such measurements have been made, using various inert materials, for a range of shock impedances which yields pressures in the explosive reaction products from 515 000 bars down to 571 bars. The data fit a polytropic equation of state (P/&rgr;&ggr;= const. for the isentrope) with &ggr; = 2.77.

ISSN:0031-9171    

DOI:10.1063/1.1724376

出版商:AIP    

年代:1958

数据来源: AIP