摘要:

A simplified form of the stability equation appropriate for liquids of small viscosity undergoing nearly spherically symmetric flow is derived on the basis of earlier results. This equation is then applied to the analysis of the stability characteristics of the spherical shape for growing and collapsing cavitation bubbles. It is found that viscosity does not remove the well‐known instability associated wihth the collapse process, although it does delay the growth of higher order modes. This feature explains the relatively small number of microbubbles to which a cavitation bubble gives rise upon fragmentation.

ISSN:0031-9171    

DOI:10.1063/1.862408

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The problem of laminar, incompressible flow over a periodic wavy surface is treated as a first‐order perturbation to the boundary layer flow on a flat surface. The analysis demonstrates that some nonlinear terms in the disturbance boundary‐layer equations are first order if the wave amplitude and disturbance sublayer thickness are comparable in magnitude. Further, the theory predicts that the nonlinear effects are confined to the thin sublayer adjacent to the wavy surface. Computer‐generated, nonlinear solutions are presented for sinusoidal waves with a range of wave amplitudes, including cases with local separated flow regions.

ISSN:0031-9171    

DOI:10.1063/1.862409

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An axisymmetric air free shear layer was experimentally investigated in order to determine the effect of the initial peak fluctuation levelu′pe/Ueon the characteristic measures of the free shear layer. The shear layer width and the similarity parameter depend noticeably onu′pe/Ue. The asymptotic peak turbulence intensityu′p∞increases withu′pe/Uebut appears to have a limiting value of about 0.18. The location for achievement of self‐preservation progressively moves upstream with increasingu′pe/Ue, suggesting that higher initial fluctuations hasten the spectral evolution of the velocity fluctuations and development of the shear layer. The results show that the initial fluctuation level has a much more dramatic effect on the evolution and the average characteristic measures of the free shear layer than the initial momentum thickness has, and may have been the primary reason for discrepancies among results from different previous inverstigations.

ISSN:0031-9171    

DOI:10.1063/1.862410

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Constitutive equations appropriate to nearly extensional flows are derived. The main conclusion is that three functionals are required in contrast to the thirteen involved in the corresponding case of nearly viscometric flows.

ISSN:0031-9171    

DOI:10.1063/1.862411

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A theoretical model is presented for calculating the species velocity of a gas mixture expanding as a free jet through a sonic orifice into vacuum. Calculations were done for two systems (a) a binary gas mixture of argon seeded in helium, and (b) a ternary mixture of uranium hexafluoride isotopes seeded in helium. The results are compared with previous calculations and with experiments.

ISSN:0031-9171    

DOI:10.1063/1.862412

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The influence of metastable atoms on the equilibrium distribution function of an isotropic plasma is studied. It is shown that there is a quasi‐stationary solution to this problem resulting from the balance between electron‐electron interactions, inelastic and super‐elastic collisions. The distribution function is composed of thermal Maxwellian electrons and of a bump at the excitation energy potential of the metastables. Evaluation of the electronic density in this bump is made for the case of helium.

ISSN:0031-9171    

DOI:10.1063/1.862413

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The emissivity of spontaneous synchrotron radiation is computed for a plasma consisting of a background thermal plasma in addition to an energetic runaway electron component. The analysis is performed for both the ordinary and extraordinary modes, for frequencies in the vicinity of the electron plasma frequency and the higher harmonics of the electron gyrofrequency, and for &ohgr;e≲&OHgr;e(where &ohgr;eand &OHgr;eare the electron plasma and cyclotron frequencies, respectively). The relativistic gyroresonance with the runaway electrons is found to result in a level of spontaneous emission which, for frequencies in the neighborhood of &ohgr;e, is significantly enhanced over the thermal radiation.

ISSN:0031-9171    

DOI:10.1063/1.862414

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The relativistic corrections to the ponderomotive force for a general transverse plane wave of arbitrary polarization lead to an approximately twenty percent reduction in the single particle ponderomotive force for 10.6 &mgr;m CO2light at 1016W/cm2. The recent nonrelativistic derivation of laser‐induced plasma profiles is extended to the relativistic regime by including the relativistic corrections to the ponderomotive force in the fluid equations. Specifically, analytic results are obtained which facilitate relating the number densities and flow velocities to the electric field strength at the sonic point; in addition, these relations allow the complete self‐consistent steady state structure of the profile to be determined numerically. Several detailed comparisons of nonrelativistic and relativistic results are discussed.

ISSN:0031-9171    

DOI:10.1063/1.862415

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Previous calculations of the linear growth rate and two‐dimensional spatial structure of trapped‐electron modes are made more general and more accurate in several ways. First, an integral equation formulation of the eigenmode problem allows arbitrary values ofkr&rgr;i(wherekris the radial wavenumber and &rgr;iis the ion gyroradius) to be treated. Second, the ion response is generalized so that arbitrary ratios of the ion magnetic drift frequency to the mode frequency are allowed. Finally, the electron and ion collision operators have been improved to allow consideration of the plateau and Pfirsch–Schlu¨ter regimes in addition to the usual banana regime. It is therefore possible to follow the transition in toroidal geometry from the trapped‐electron mode to the collisionless and collisional drift modes. The method used involves expansion of the perturbed electrostatic potential in complete sets of radial and poloidal basis functions to convert the quasi‐neutrality integral equation into a matrix equation.

ISSN:0031-9171    

DOI:10.1063/1.862416

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An analysis and computer simulations of dissipative trapped electron modes in toroidal plasmas based on the electron drift‐kinetic equation Fourier transformed with respect to the poloidal and toroidal angles are presented.

ISSN:0031-9171    

DOI:10.1063/1.862400

出版商:AIP    

年代:1978

数据来源: AIP