摘要:

The two‐dimensional trajectories of an ideal vortex pair near an orifice are calculated. Three geometries are examined, and the criteria for the vortices to travel away from the orifice are determined.

ISSN:0031-9171    

DOI:10.1063/1.861909

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Local equilibrium solutions for a stress‐transport turbulence model are given for the general case of turbulent plane flow. Turbulence is assumed to be in local equilibrium where the production balances the dissipation. The three‐dimensional fluctuations are induced by a two‐dimensional mean flow. The solution specifies the principal Reynolds stresses as well as the principal coordinate system as functions of the model coefficients and the mean velocity gradients. A hypothesis of a maximum third invariant is made and used to derive the model coefficients. A possible application of the solution as boundary conditions for the calculation of developing boundary layers is also outlined.

ISSN:0031-9171    

DOI:10.1063/1.861910

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

It is shown that the various moments of a one‐ (multi‐) dimensional variable must obey special inequalities, where the random variable can be taken as the turbulent fluctuation of either velocity components or temperature or pollutant density. These inequalities called realizability inequalities, are derived from the well‐known problem of moments. The inequalities are specified for the case of the quasi‐normal approximation (vanishing of fourth‐order cumulants) or of other approximations (vanishing of cumulants of orderk, 4⩽k?2n, wherenis an integer). An example of the use of such inequalities is given for the case of the quasi‐normal approximation.

ISSN:0031-9171    

DOI:10.1063/1.861911

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Turbulent Couette flow between parallel plates is studied utilizing a model equation, similar to the Boltzmann equation of kinetic theory, which was developed by Lundgren for the velocity distribution of fluid elements. Solutions to this equation are obtained numerically, employing the discrete ordinate method and finite differences. Two types of boundary conditions on the distribution function are considered, and the results of the calculations are compared with available experimental data. This study establishes that Lundgren’s equation provides a very good description of turbulence for the flow situation considered, and that it offers an analytical tool for further study of more complex turbulent flows. Further, the discrete ordinate method is shown to be an effective method for direct solution for the probability distribution, thus avoiding recourse to assuming,apriori, approximate forms for this function.

ISSN:0031-9171    

DOI:10.1063/1.861912

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

When treating a two‐phase system, the need to account for the fact that the phases of the mixture sharing the same space are mutually exclusive gives rise to the formulation with each phase following its own center‐of‐mass frame of reference together with inertial coupling. The lack of detailed knowledge of the virtual mass effect limits the formulation to a dilute suspension of the disconnected phase. The significance of the inertial coupling term due to the choice of frame of reference is noted.

ISSN:0031-9171    

DOI:10.1063/1.861913

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The asymptotic behavior (for small Knudsen number) of the steady flow of a rarefied gas over a specularly reflecting body with arbitrary but smooth shape is investigated on the basis of the linearized Boltzmann–Krook–Welander equation. As applications of the theory, a sphere in a uniform flow of gas and that in a gas at rest with a uniform temperature gradient are considered. The velocity and temperature fields around the spheres and the drag and thermal forces acting on the sphere are obtained. The formulae of the forces are compared with those given by various approximate methods and those for other types of boundary conditions.

ISSN:0031-9171    

DOI:10.1063/1.861914

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The theory of the electron distribution functions in a laser‐pellet plasma is developed taking advantage of the dominance of collisions with high charge number ions. For the thermal electrons the results is a description in terms of transport coefficients given in closed form. For the superthermal electrons, which are isotropic in velocity, the description is via a reduced kinetic equation. The adaptation of the scheme to numerical computation is discussed briefly.

ISSN:0031-9171    

DOI:10.1063/1.861915

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The possibility of a new type of laser has been investigated by computer simulation using a fully relativistic electromagnetic particle code which has one spatial and three velocity dimensions. By passing a relativistic electron beam over a rippled static magnetic field, high frequency electromagnetic radiation is generated. If the ripple wavelength is &lgr;0, the lasing wavelength is roughly &lgr;0/2&ggr;2. Thus, such a laser is continuously tunable by varying &ggr;. It has been observed in simulation that as much as 35% of the beam energy can be converted into radiation, of which as much as nearly 90% can be in the most rapidly growing mode. A theory of the coupling between the negative energy plasma wave and the electromagnetic radiation by means of the rippled magnetic field is presented. Good agreements have been obtained between the simulation and the theory. The saturation mechanism is found to be the trapping of the beam by the unstable plasma wave. A theoretical estimate of the amount of energy that can be converted into radiation from the electron beam is also given.

ISSN:0031-9171    

DOI:10.1063/1.861916

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The classical parallel friction coefficients, which relate the collisional friction forces to the flow of particles and heat along the magnetic field, are calculated for a multiple ion species plasma. In the short mean‐free‐path regime, the neoclassical Pfirsch–Schlu¨ter transport coefficients for a toroidally confined multispecies plasma are computed in terms of the classical friction coefficients. The dependence of the neoclassical cross‐field transport on the equilibration of the parallel ion temperature profiles is determined.

ISSN:0031-9171    

DOI:10.1063/1.861917

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The resonance cone structure in a warm bounded slab magnetoplasma has been obtained in the electrostatic approximation for small electron and ion temperatures and a large magnetic field. It is found that the conducting boundaries act as perfect mirrors as in the cold plasma case; the cones reflect off the boundaries without any distortion of shape. The thermal effects produce the shifting of the maximum of the potential and the appearance of an interference structure inside each cone as in unbounded plasma theory. The amount of the shift is a uniformly increasing function of the axial distance from the source of each cone, while the spatial frequency is a uniformly decreasing function of that distance. Because of the spreading, there is significant interference between nearby cones, so the total potential is more complicated than in the unbounded case. The solution is first obtained for a homogeneous plasma and studied, and then extended to the inhomogeneous plasma. The effects of Landau and collisional damping are included.

ISSN:0031-9171    

DOI:10.1063/1.861918

出版商:AIP    

年代:1977

数据来源: AIP