摘要:

The quasilinear generation of current by rf wave fields is investigated in toroidal geometry. A general expression is derived for the amount of current generated for a given wave‐induced flux of particles. This expression should be of great practical value in assessing the various competing effects on current generation in toroidal geometry and is well‐suited for implementation in a toroidal ray tracing code.

ISSN:0031-9171    

DOI:10.1063/1.863906

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Numerical simulations of the instability, merger, and breaking of two piecewise‐constant finite‐area vortex regions (FAVR’s) are presented. An improved contour dynamical algorithm with node insertion‐and‐removal to maintain theaprioriaccuracy is used. Corotating ’’Vstates’’ (symmetric steady‐state FAVR’s) were found to be unstable when properly perturbed if their centroid‐effective radius ratio, x¯/R, is <1.6, thereby verifying an estimate of Saffman and Szeto. This causes the FAVR’s to approach at an exponential rate, merge, and reform into a stable perturbed elliptical structure with filamentary arms (to conserve angular momentum). For larger x¯/Rratios, regular perimeter oscillations were observed and estimates of an eigenfrequency of the perturbed stableVstates were obtained. When regions of different vorticity density merge, the larger‐density region is eventually entrained within the smaller‐density region. These simulations elucidate the self‐consistent close interactions of isolated vortex regions in two‐dimensional high Reynolds number flows.

ISSN:0031-9171    

DOI:10.1063/1.863907

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A theory is presented that gives an analytical solution to the kinematic interaction of a convergent (or divergent) mean flow and turbulence for spatially constant convergence and homogeneous turbulence of a specified type. The turbulence is characterized by its mean square velocity, ∼(v2), and by its Lagrangian autocorection function. The problem is formally that of the Langevin equation, and analytical solutions for the time dependence of the ensemble‐average variance of many fluid tracers are presented. These solutions are compared with numerical solutions obtained by calculating the Lagrangian motion of a large number of tracers.

ISSN:0031-9171    

DOI:10.1063/1.863908

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The stability characteristics of a Helmholtz velocity profile in a stably stratified, compressible fluid in the presence of a lower rigid boundary are studied. A jump in the Brunt–Va¨isa¨la¨ frequency at a level different from the shear zone is introduced and the variation of the Brunt–Va¨isa¨la¨ frequency with respect to the vertical coordinate in the middle layer of the three‐layered model is considered. An analytic solution in each of the layers is obtained, and the dispersion relation is solved numerically for parameters relevant to the model. The effect of shear in the lowermost layer of the three‐layered model for a Boussinesq fluid is discussed. The results are compared with the earlier studies of Lindzen and Rosenthal, and Sachdev and Satya Narayanan. In the present model, new unstable modes with larger growth rates are obtained and the most unstable gravity wave modes are found to agree closely with the observed ones at various heights.

ISSN:0031-9171    

DOI:10.1063/1.863909

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Wiener–Hermite expansion with a renormalized, time‐dependent moving base is used to calculate the evolution of the energy spectra of several homogeneous, isotropic flows. The results compare well with laboratory experiments and with numerical simulation experiments. Wiener– Hermite calculations have been done previously for high Reynolds numbers by Hogge and Meecham [J. Fluid Mech. 85, 325 (1978)]with some success. In this work moderate Reynolds numbers are treated.

ISSN:0031-9171    

DOI:10.1063/1.863910

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Lagrangian dispersion theory of Durbin is used to analyze experiments by Warhaft and Lumley [J. Fluid Mech. 88, 659 (1978)] and by Sreenivasanetal. [J. Fluid Mech. 100, 279 (1980)] on temperature fluctuations in grid‐generated turbulence. Both theory and experiment show that the decay exponentmdepends on the ratio of the initial length scales of velocity and temperature; although when this ratio is greater than 2.5 such dependence is negligible. The theory shows thatmis not truly constant, but within the range covered by the experiments it is nearly so. The agreement between theory and experiment lends credence to the idea that the decay of fluctuations is controlled largely by turbulent relative dispersion.

ISSN:0031-9171    

DOI:10.1063/1.863911

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Rayleigh scattering and laser Doppler velocimetry were used to study density and velocity statistics in a strongly heated turbulent boundary layer with free stream velocityU∞= 19 m/sec and wall temperatureTw= 1100 °K. Mean and rms fluctuation profiles of density and velocity were found to be self‐preserving, and the velocity profiles were not significantly affected by wall heating. Streamwise velocity profiles, and mean temperature profiles deduced from density data were compared with Townsend’s self‐preserving analysis. It was found that wall heating caused a reduction in Reynolds stress within the thermal layer. This phenomenon was explained with reference to the thermal layer structures observed in high speed schlieren movies.

ISSN:0031-9171    

DOI:10.1063/1.863912

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Previous treatments of relativistic Brillouin flow stability are extended to the case of nonzero anode resistivity, for the case of wave propagation across the equilibrium magnetic field. It is found that transverse magnetic (TM) waves are unstable at frequencies below the equilibrium cyclotron frequency, unlike the case for a perfectly conducting anode. Transverse electric (TE) waves, always oscillatory in the case of a perfectly conducting anode, are damped; an explicit expression for the damping rate, valid for large conductivities, is given.

ISSN:0031-9171    

DOI:10.1063/1.863913

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The effect of the translational temperature anisotropyT∥≳T⊥on the rotational distributionyj, temperatureTr, and collision numberZrof N2in the Ar free jet is studied at the lower density levelP0d= 15 Torr‐mm using the ellipsoidal velocity distribution and the rotational transition cross section of the power law. The effect ofT∥≳T⊥is appreciable. The overpopulation of the higher rotational levelsjabove the Boltzmann distribution fitted to the distribution of the lowerj, i.e., the degree of nonequilibrium for the caseT∥≳T⊥=Ti(i≡isentropic) is slightly less pronounced than for the caseT∥=T⊥=Tibut more pronounced than for the caseT∥=T⊥≳Ti. The ratioyj/y0,Tr, and the terminalZrforT∥≳T⊥=Tiare larger than forT∥=T⊥=Tibut smaller than forT∥=T⊥≳Ti.

ISSN:0031-9171    

DOI:10.1063/1.863914

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Using three single‐particle adiabatic invariants, we derive an energy principle which generalizes that for the usual guiding center plasma in order to describe the low‐frequency stability of a plasma containing an energetic nonhydromagnetic component (such as the annular electrons in an Elmo Bumpy Torus device).

ISSN:0031-9171    

DOI:10.1063/1.863898

出版商:AIP    

年代:1982

数据来源: AIP