摘要:

A simple expression for the aeroydynamic lift on an elliptical cylinder in a nonuniform, inviscid, free stream is derived. The derivation is exact for a flow with uniform vorticity and directed perpendicular to the axis of the cylinder. The derivation is approximate for a general large scale flow, for which the force is calculated to first order in the derivatives of the initial free‐stream velocityUi(x,y,z).

ISSN:0031-9171    

DOI:10.1063/1.862488

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The hierarchy of turbulence equations is closed by several methods, but good results for higher Reynolds numbers are obtained only for a closure by specification of initial conditions. Four terms of an exponential series, which is an iterative solution of the Navier–Stokes equation, are used in the closure. A complete solution, in the sense that the evolution of all of the initially specified spectra can be calculated, is obtained. This cannot be done by using a Taylor series, regardless of how many terms are retained. The results indicate that purely viscous decay becomes negligible compared with inertial decay as Reynolds number becomes large.

ISSN:0031-9171    

DOI:10.1063/1.862489

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Measurements in a two‐dimensional helium jet discharging into a moving airstream establish that entrainment at the upstream edges of turbulent structures is dominant with the consequence that the velocity and helium concentration are lower at these edges. These results are consistent with earlier data showing preferential entrainment at the downstream edges of turbulent structures in both boundary layers and wakes, since in all cases entrainment at leeward edges predominates.

ISSN:0031-9171    

DOI:10.1063/1.862490

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The problem of local internal waves is studied within an infinite medium with a mean density profile described by a periodic Brunt–Va¨isa¨la¨ frequencyN(z). This appears to be the analog of the quantum‐mechanical problem for a particle in a unidimensional lattice potential. Explicit calculations and detailed analysis are carried out for a delta shapedN2(z) profile, paralleling the so‐called Dirac‐comb model for the quantum crystal. The analysis of this rather special case was motivated by recent oceanographical observations in the Mediterranean showing a sort of periodic behavior in the fine structure of density profiles. The selection of Brillouin zones for the wavenumbers of internal waves and the existence of frequency gaps appear to be the most interesting issues of the study of the dispersion relation. Corrections for a finite depth of the ocean and for a finite extent of the density gradients are also suggested.

ISSN:0031-9171    

DOI:10.1063/1.862491

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An efficient numerical scheme to compute steep gravity waves in water of shallow uniform depth is described. The problem is formulated as a system of integrodifferential equations for the free surface. A numerical procedure based on Newton’s iterations is devised to solve these equations. Solutions of high accuracy for depth as small as 1/120 of a wavelength are presented. Numerical confirmation is obtained for the existence of maxima of the potential and kinetic energies of the waves as functions of the steepness.

ISSN:0031-9171    

DOI:10.1063/1.862492

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The evolution equations describing the interaction of long and short waves when they are resonantly coupled are discussed. Envelope‐pulse soliton solutions of these equations are constructed using the method of Hirota and the existence of a breather state is shown. The wavetrain modulational characteristics and envelope‐hole solitary wave solutions are also presented.

ISSN:0031-9171    

DOI:10.1063/1.862493

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The flow fields of supersonic, nonequilibrium corner expansion flows of ionized gases have been solved numerically, for three different gases, using the method of characteristics. Special attention has been given to the effect that the gas mass and its ionization potential have upon the solution obtained. It was found that the ratio between the atomic mass of the element considered and its ionization potentialma/&Vthgr;I, plays an important role in establishing thermal equilibrium. Gases having a small value ofma/&Vthgr;Iwill approach thermal equilibrium at a faster rate than those having a larger value ofma/&Vthgr;I. On the other hand, the approach to chemical equilibrium is controlled by the recombination rate which is strongly temperature dependent. Therefore, fast reduction in temperature, in the expansion field, promotes a rapid approach to chemical equilibrium. The effect of the electron‐atom collision cross section &sgr;ea, on the numerical results obtained, is also studied. It is shown that accurate knowledge of &sgr;eais required to evaluate the plasma electronic properties (Teand &agr;), but even a rough estimate of &sgr;eais sufficient for the evaluation of the gross properties of the plasma (p, &rgr;, andT).

ISSN:0031-9171    

DOI:10.1063/1.862494

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Numerical solutions of the exact relativistic nonlinear Boltzmann equation have been obtained which describe the structure of relativistic shock transitions in dilute one‐component simple gases. When the speed of the shock wave is near the speed of light, the calculated velocity profiles, as viewed in the rest frame of the shock wave, are similar to the velocity profiles of weak nonrelativistic shock waves. Starting from this observation an analytic theory for the velocity profile is derived which is accurate for all relativistic energies and may be used to study relativistic shock waves in nonideal fluids where the Boltzmann equation is not valid.

ISSN:0031-9171    

DOI:10.1063/1.862495

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The stability of a one‐dimensional cylindrically symmetric quasi‐steady ablation flow near a solid hydrogen pellet is investigated. The gas‐dynamic conservation equations describing the flow are linearized in order to look for growing perturbations of the helical type. The problem is treated both analytically and numerically and comparisons are made between both approaches. The analysis reveals that the ablation process itself has no significant instabilities.

ISSN:0031-9171    

DOI:10.1063/1.862477

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Plasma diffusion due to magnetic field fluctuations has been studied in two dimensions for a plasma near thermal equilibrium and when the fluctuations are suprathermal. It is found that near thermal equilibrium, electron diffusion varies asB−2when the collisionless skin depth is greater than the thermal electron gyroradius and is generally smaller than the diffusion due to collisions or electrostatic fluctuations for a low‐&bgr; plasma. When the suprathermal magnetic fluctuation exists because of macroscopic plasma currents, electron diffusion is enhanced due to the coalescence of current filaments and magnetic islands. Magnetic field energy is found to condense to the longest wavelength available in the system and stays there longer than the electron diffusion time scale.

ISSN:0031-9171    

DOI:10.1063/1.862478

出版商:AIP    

年代:1979

数据来源: AIP