摘要:

The structure of turbulence in an axisymmetric jet at the nozzle exit Reynolds number of 4×104was examined at several streamwise stations (1.0≤x/D≤40), by measuring, for a few fixed radial positions, two‐point correlation functions of the streamwise velocity and temperature fluctuations with azimuthal separation. By an orthogonal Fourier decomposition of the azimuthal correlation functions, an interpretation of these correlations and of the large‐scale evolution is provided.

ISSN:0031-9171    

DOI:10.1063/1.864691

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The theory of evaporation and condensation is considered from a kinetic theory approach with a particular interest in the continuum limit. The moment method of Lees is used to solve the problem of the steady flow of vapor between a hot liquid surface and a cold liquid surface. By incorporating the singular nature of the problem, the forms of the continuum flow profiles found by Plesset are recovered. The expression for mass flux has the form of the Hertz–Knudsen formula but is larger by a factor of 1.665. A result of the theory is that the temperature profile in the vapor for the continuum problem is inverted from what would seem physically reasonable. This paradox is significant in that it casts a shadow of doubt on the fundamental theory.

ISSN:0031-9171    

DOI:10.1063/1.864716

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The formation and structure of normal shock waves in compressible, polytropic gases is investigated using the continuum gas dynamical equations. A phenomenological model for temperature‐dependent viscosity and thermal conductivity is preassumed. The fundamental resulting nonlinear differential equation is solved exactly, and the complete structure of the shock wave is determined. It is found that the flow quantities and characteristics depend upon one parameter, the upstream Prandtl number Pr1, which satisfies the inequality 3&ggr;/(&ggr;+1)≤2Pr1<3, where &ggr; is the ratio of specific heats. For smaller values of Pr1, the strength and compression ratio of the shock increase. Special cases of interest cannot be obtained from this solution and are to be treated independently. Numerical results are given and discussed.

ISSN:0031-9171    

DOI:10.1063/1.864717

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Reduced magnetohydrodynamics (RMHD) is a principal tool for understanding nonlinear processes, including disruptions, in tokamak plasmas. Although analytical studies of RMHD turbulence are useful, the model’s impressive ability to simulate tokamak fluid behavior has been revealed primarily by numerical solution. A new analytical approach, not restricted to turbulent regimes, based on Hamiltonian field theory is described. It is shown that the nonlinear (ideal) RMHD system, in both its high‐beta and low‐beta versions, can be expressed in Hamiltonian form. Thus a Poisson bracket, {  ,  }, is constructed such that each RMHD field quantity &xgr;ievolves according to &xgr;˙i={&xgr;i,H}, whereHis the total field energy. The new formulation makes RMHD accessible to the methodology of Hamiltonian mechanics; it has lead, in particular, to the recognition of new RMHD invariants and even exact, nonlinear RMHD solutions. A canonical version of the Poisson bracket, which requires the introduction of additional fields, leads to a nonlinear variational principle for time‐dependent RMHD.

ISSN:0031-9171    

DOI:10.1063/1.864718

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Nonlinear reduced fluid equations are derived for studying resistive instabilities in large‐aspect‐ ratio, low‐beta toroidal plasmas. An ordering is developed in which plasma compressibility as well as the poloidal curvature are retained. The nonlinear equations can be linearized and used to reproduce the Mercier criterion in the large‐aspect‐ratio, low‐beta limit. A second set of reduced equations is derived from the Braginskii fluid equations. These equations, which are very similar to the reduced magnetohydrodynamic equations, contain diamagnetic effects as well as parallel transport associated with magnetic fluctuations. Both sets of equations conserve energy exactly.

ISSN:0031-9171    

DOI:10.1063/1.864680

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The tokamak disruption model based on the nonlinear interaction of multiple helicity tearing modes is extended to include diamagnetic effects. This introduces mode rotation and time‐varying phases during the nonlinear interaction. The basic nonlinear destabilization mechanism associated with plasma disruptions remains unaffected by diamagnetic effects.

ISSN:0031-9171    

DOI:10.1063/1.864681

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Drift modes in toroidal geometry are destabilized by trapped electron inverse dissipation and evolve to a nonlinearly saturated state. Using renormalized one‐point turbulence theory for the nonlinear gyrokinetic equation in the ballooning representation, it is shown that ion Compton scattering is an effective saturation mechanism. Ion Compton scattering transfers wave energy from short to long perpendicular wavelength, where it is absorbed by ion resonance with extended, linearly stable, long‐wavelength modes. The fluctuation spectrum and fluctuation levels are calculated using the condition of nonlinear saturation. Transport coefficients and energy confinement time scalings are determined for several regimes. Specifically, the predicted confinement time density scaling for an Ohmically heated discharge increases fromn3/8in the collisionless regime ton9/8in the dissipative trapped electron regime.

ISSN:0031-9171    

DOI:10.1063/1.864682

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An analytical investigation is made of the development of the thermonuclear magneto‐acoustic cone instability in a tokamak reactor. The excitation mechanism for the instability is the anisotropy in the &agr;‐particle distribution function resulting from either direct orbit losses or ripple losses. Explicit expressions are obtained describing the time evolution of the magneto‐acoustic wave energy density as well as the distribution function, the anomalous particle loss, and the density of the &agr; particles. The results show that the quasilinear evolution of the instability causes rapid and severe &agr;‐particle losses and saturates at a high level of turbulence for the magneto‐acoustic waves. It is also shown that the quasilinear diffusion of the &agr; particles caused by the cone instabilities may result in the generation of a significant toroidal current in the plasma.

ISSN:0031-9171    

DOI:10.1063/1.864683

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

In the low‐collisionality nonresonant regime in a bumpy torus the transitional particles can make a large contribution to neoclassical transport. This contribution can be moderated by the toroidally induced radial drift which causes transitional particles to detrap and retrap in the mirror sectors. This effect leads to diffusion coefficients which are linear in the collision frequency and scale with the inverse aspect ratio instead of the more usual square of the inverse aspect ratio.

ISSN:0031-9171    

DOI:10.1063/1.864684

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The ion neoclassical transport coefficient in a multiple ion species plasma in a bumpy torus are calculated in the low‐collisionality regime. The poloidal electric field is calculated self‐consistently with collisional electrons. Both pitch angle and energy scattering are included in the collision operator.

ISSN:0031-9171    

DOI:10.1063/1.864685

出版商:AIP    

年代:1984

数据来源: AIP