摘要:

Some experimental phenomena associated with cavitation are examined. It is shown that these experimental results can be duplicated by the response of a single spherical bubble subjected to a suitable incident tension wave.

ISSN:0031-9171    

DOI:10.1063/1.864177

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Simultaneous top‐end view visualization studies of the flow behavior in the near‐wall region of a turbulent boundary layer have been done using hydrogen bubble wires and a dual‐camera, high‐speed video system. The studies show clearly that the low‐speed streaks formed in the near‐wall region are discrete regions of outward motion, with the degree of activity varying with distance from the wall. The visualizations also reveal the presence of significant streamwise rotation in the wall region fory+≳10, including frequent observation of counter‐rotating streamwise structures. An apparent interdependency between these counter‐rotating structures and low‐speed streak formation is observed, and appears to support the suggestions of several previous investigators.

ISSN:0031-9171    

DOI:10.1063/1.864178

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Some experimental results of intermittency in the near wake (X/D=2 and 4) of a circular cylinder at a Reynolds number of 52 300 are presented. Both conventional and phase‐averaged properties of the intermittency are given. From the conditional analysis of turbulent/nonturbulent events, some features of the phase control of the intermittency by the periodic motion due to the vortex shedding are emphasized.

ISSN:0031-9171    

DOI:10.1063/1.864179

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A problem of evaporation and condensation for a two‐phase system of a vapor gas and its cylindrical condensed phase is considered on the basis of the Boltzmann–Krook–Welander equation when the Knudsen number of the system is small. The analysis was carried out based on the nonlinear equation so that the results can be applied to the case where the Reynolds number of the flow field produced by the evaporation and condensation is finite. The distributions of pressure, temperature, and velocity of the gas are obtained together with the mass and energy flows for both evaporation and condensation cases. Even for very weak condensation, the linearized theory is invalid, and the present nonlinear analysis is required.

ISSN:0031-9171    

DOI:10.1063/1.864180

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A theory for low‐frequency electrostatic modes of a finite length pure electron plasma column is presented. The plasma is modeled as a cold uniform density cylinder with flat ends. An interesting result is that the diocotron mode can have an axial wavelength that is much larger than the plasma length. Also, for particular values of the plasma density, the axial magnetic field, and the dimensions of the plasma, the diocotron mode is degenerate with a plasma mode and this results in a strong mixing of the modes.

ISSN:0031-9171    

DOI:10.1063/1.864181

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The stability of the ion‐temperature gradient mode in a toroidal plasma is investigated. Using the ballooning‐mode formalism, an ordinary difference‐differential equation is derived which includes full kinetic effects. The equation is then examined in various limits where it reduces to an ordinary differential equation. Analytic and computational studies show that, for &eegr;i≡d ln Ti/d ln n≫1, toroidal effects further destabilize the mode. However, it is also found that toroidal effects give rise to higher &eegr;ithreshold compared to the slab case. Extensive numerical calculations over a wide range of parameters are carried out to delineate the regions of instability. It is concluded that the &eegr;iinstability is of relevance to present‐day beam‐heated tokamaks.

ISSN:0031-9171    

DOI:10.1063/1.864182

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The effect of spatial electron diffusion on the stability properties of the universal drift mode in a sheared magnetic field are studied using an initial value code, TEDIT. In previous studies of this problem Hirshman and Molvig relied on an approximation to the electron resonance function equivalent to making a Krook approximation for the spatial diffusion operator,D∂2/∂x2. The present work treats the diffusion operator precisely and also allows the treatment of a realistic parallel velocity dependence of the diffusion coefficient,D=D(v∥). For the case of a velocity‐independent diffusion coefficient, the qualitative features found by Hirshman and Molvig are observed. The modes withky&rgr;i>1 destabilize at small values of the diffusion coefficient and saturate at higher values, corresponding to several orders of magnitude inD. There are quantitive discrepancies with the previous work that, near the saturation point, can be accounted for reasonably well by a simple asymptotic theory. However, when the code uses a more realistic form,D=D0(ve/‖v∥‖) exp(−v2c/v2∥)+Dc, whereDccorresponds to the (small) collisional diffusion, andD0parametrizes the turbulence level, then a quantitative difference is observed. Instability persists down to zero turbulence levels,D0=0. This is essentially linear instability due to collisional diffusion alone.

ISSN:0031-9171    

DOI:10.1063/1.864183

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An integral representation of the geometric optics solutions for the field of dressed particles in inhomogeneous plasma is derived. The representation is a natural generalization of the Fourier integral used for homogeneous systems. The set of plane waves is replaced by a complete orthogonal set of ‘‘quasiplane waves’’ which in practice may be constructed by using the existing ray tracing codes.

ISSN:0031-9171    

DOI:10.1063/1.864184

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Electromagnetic effects on the self‐modulation of nonlinear lower hybrid waves in an inhomogeneous plasma are studied for both broad and narrow spectrum excitations. For broad spectrum excitation, the complex modified Korteweg–de Vries equation is modified by two additional terms due to the electromagnetic correction and inhomogeneity. Numerical solutions of this equation for typical tokamak parameters show that these terms suppress soliton formation. For narrow spectrum excitation, the electromagnetic correction produces an additional dispersive term in the differential equation governing the wave envelope. This term opposes thermal dispersion, resulting in significant self‐modulation. Numerical solutions show constriction and splitting of the envelope as well as spreading of the Fourier spectrum.

ISSN:0031-9171    

DOI:10.1063/1.864185

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The equations of quasilinear momentum and energy transport are studied to show that a suprathermal level of low‐frequency fluctuations can cause highly enhanced electron energy transport without effectively changing the plasma resistivity.

ISSN:0031-9171    

DOI:10.1063/1.864186

出版商:AIP    

年代:1983

数据来源: AIP