摘要:

Circular waves of a new type are observed in the disk boundary layer occurring on the end of a cylindrical cavity during impulsive spindown to rest. These waves occur aroundz(&OHgr;i/&ngr;)1/2≊3.6 and are reminiscent of Tollmien–Schlichting waves of an ordinary boundary layer. It is concluded that these waves are manifestations of the instabilities excited in the Bo¨dewadt‐type boundary layer developed over the disk.

ISSN:0031-9171    

DOI:10.1063/1.864124

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An exact equation for the Lagrangian two‐time velocity joint probability density function (pdf) is derived from the Navier–Stokes equation. The pdf equation contains as an unknown the conditional expectation of the fluid acceleration. A linear Markov model is proposed which leads to a modeled equation that is consistent both with Kolmogorov’s theory in the inertial subrange and with Reynolds‐stress models. The dissipation rate is obtained from the joint pdf in a way that is consistent with the modeled dissipation equation. A Monte Carlo method can be used to solve the modeled two‐time pdf equation for inhomogeneous turbulent flows.

ISSN:0031-9171    

DOI:10.1063/1.864125

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Breaking of nonuniform liquid films and threads is analyzed by means of a simple equation of motion. The results are applied to the bursting film between two merging gas bubbles in a liquid, to growing holes in liquid films on solid surfaces, and to the pinching off of a liquid jet. Two of the results are compared with exact hydrodynamic calculations.

ISSN:0031-9171    

DOI:10.1063/1.864126

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An experimental investigation of a two‐dimensional turbulent wake behind a spinning cylinder at Re=9000 is carried out to determine the influence of the rotation on the initial development of the flow. Spectral analysis of the velocity data measured in the near wake shows that for peripheral velocities up to the value of the free‐stream velocity, a distinct Ka´rma´n vortex activity exists within the wake, whereas for greater peripheral velocities, the Ka´rma´n activity deteriorates and disappears for values in excess of twice the free‐stream velocity.

ISSN:0031-9171    

DOI:10.1063/1.864127

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A method to solve the Liouville equation for an ensemble of two‐dimensional viscous flows that are driven by random forcing with arbitrary statistics is outlined. By appropriate transformations of both the dependent variable (probability distribution) and independent variables, and by expansion of the solution in eigenfunctions of the separable part of the Liouville operator, it is found possible to reduce the problem to that of solving a simultaneous system of nonhomogeneous linear algebraic equations. The equilibrium kinetic energy and energy‐transfer spectra can be calculated directly from the equilibrium probability distribution.

ISSN:0031-9171    

DOI:10.1063/1.864128

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Power series based on the Rankine–Hugoniot equation relate the states upstream and downstream of a shock. The usual forms for such series are limited to very weak shocks, e.g., to a shock Mach number approximately 1.1. Improvement is obtained by restricting the shock series to a form which is exact, for the special case of a perfect gas, with the lowest‐order term only. Series in this form show reasonable accuracy for real fluids up to shock Mach numbers of order 1.5.

ISSN:0031-9171    

DOI:10.1063/1.864129

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The effect on electron cyclotron current drive of the relativistic correction arising from the velocity dependence of the electron cyclotron frequency has been investigated. This correction is shown to be important, particularly for waves propagating close to perpendicular to the magnetic field, for plasmas in the keV range and above. The steady‐state current due to the asymmetric heating mechanism described by Fisch and Boozer has been calculated. The most striking effect of the relativistic correction is that the current driven in the plasma in response to a given wave amplitude is, in an inhomogeneous field, no longer antisymmetric about the cyclotron resonance layer. This means that it is possible to drive a nonzero total current without strong absorption, and also that the total current depends strongly on whether the wave is incident from the low‐field or the high‐field side.

ISSN:0031-9171    

DOI:10.1063/1.864130

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The stationary spectra of current‐driven ion‐acoustic turbulence in a magnetized plasma (with the electron drift velocityvdalongB0) are studied within the framework of quasilinear theory. In particular, a plasma with strongly magnetized electrons (&ohgr;ce>kdvTe) and unmagnetized ions (&ohgr;>&ohgr;ci) well above the threshold of instability (vd/vTe≫vs/vTe, &ngr;in/&ohgr;pi) is considered. It is found that the waves are mainly excited in a narrow angular region almost perpendicular tovd(i.e., cos &thgr;&bartil;vs/vd≪1), which is in agreement with experimental results by Gekelman and Stenzel [Phys. Fluids21, 2014 (1978)] and Batanovetal.

ISSN:0031-9171    

DOI:10.1063/1.864131

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The ponderomotive effects which arise in a single species plasma, i.e., a nonneutral plasma, are considered. The important difference from a neutral plasma is that quasineutral density cavities given by &dgr;n/n0&bartil;−‖E‖2/16&pgr;n0Tcannot arise in a single species plasma. Instead, it is found that the ponderomotive force is balanced by self‐consistent space charge fields, and results in &dgr;n&bartil;∇2‖E∥‖2/16&pgr;m&ohgr;2, where &ohgr; is the frequency andE∥refers to the wave electric field parallel to the confining magnetic field. In addition to the density rearrangement, the zero orderE×Brotation is modified. The self‐consistent nonlinear state has been found for a large‐amplitudel=0 axially standing Gould–Trivelpiece wave. The linear dispersion relation is modified by the presence of the large‐amplitude wave and results in a nonlinear frequency shift. This shift produces an interesting hysteresis effect in the nonlinear resonant response of the plasma when the frequency of the external driver is swept slowly.

ISSN:0031-9171    

DOI:10.1063/1.864132

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Synchrotron emission from a relativistic anti‐loss‐cone (runaway) distribution is investigated numerically and compared with various analytical approximations. The results are applied to recent measurements of enhanced emission during current‐drive experiments on the Princeton Large Torus (PLT) as well as to impulsive solar microwave bursts.

ISSN:0031-9171    

DOI:10.1063/1.864110

出版商:AIP    

年代:1983

数据来源: AIP