摘要:

The results of an investigation of the vibrational kinetics of carbon monoxide in a supersonic expansion are presented. In the experiments, arc‐heated argon was seeded with CO (5–20%) and expanded to Mach numbers of 4.0 to 4.2. The vibrational state of the gas was determined by obtaining individual vibrational populations from the CO overtone emission spectra. The vibrational distribution at the nozzle exit was observed to be non‐Boltzmann, in good quantitative agreement with the anharmonic model of vibrational relaxation.

ISSN:0031-9171    

DOI:10.1063/1.862345

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Condensation of water vapor via the rarefaction wave in a shock tube was investigated by measuring pressure as a function of time. At high temperature (260°K), condensation could be adequately explained by the classical nucleation theory combined with a small accommodation coefficient for particle growth. However, at low temperature (230°K), condensation was considerably faster than permitted by classical nucleation, and the classical theory of nucleation is therefore considered to be invalid. Condensation shocks due to the coupling of gasdynamics with condensation kinetics (heat release rate) were also observed.

ISSN:0031-9171    

DOI:10.1063/1.862346

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Thomson’s results concerning the stability of regular vortex polygons are generalized to include the case of the polygonal center being occupied by a vortex of arbitrary relative strength. Of most significance is the fact that a strong enough central vortex can stabilize a Thomson polygon consisting of arbitrarily many vortices. The efficacy of the free energy criterion for stability is demonstrated in showing that the Thomson heptagon is stable.

ISSN:0031-9171    

DOI:10.1063/1.862347

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An estimate is made of the accuracy in computing second‐, third‐, and fourth‐order time structure functions of temperature fluctuations on the axis of a slightly heated turbulent round jet. The estimate is based on a knowledge of higher‐order moments of the structure functions and of their integral time scales. For the particular data chosen, the root mean square error in computing second‐and fourth‐order moments is found to be small and effectively constant over a wide range of the temporal (or spatial) separation, which spans the inertial subrange. Comparison is made with some convergence trends observed in atmospheric boundary layer measurements.

ISSN:0031-9171    

DOI:10.1063/1.862348

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Spurred by large discrepancies among previous data on the free shear layer, effects of the initial condition on the characteristic measures of an axisymmetric air free shear layer were investigated experimentally. The initial, boundary layer state (i.e., laminar or turbulent), momentum thickness Reynolds numberR&Vthgr;e, and fluctuation intensityu″pe/Uehave been taken as three characteristic identifiers of the initial condition. The discrepancies among published data are reviewed, and data showing the effects of variations inR&Vthgr;e(at constantu″pe/Ue) for both initially laminar and tripped (turbulent) boundary layers are reported. It is found that the spread rate, similarity parameter, and peak turbulent intensity in the self‐preserving region are essentially independent ofR&Vthgr;e, but dependent on whether the initial boundary layer is laminar or tripped (turbulent). Initially, tripped shear layers manifest two stages of linear growth. The virtual origin as well as the distance required for attainment of self‐preservation depend noticeably and systematically onR&Vthgr;e. The mean velocity and turbulence intensity profiles appear to reach self‐similarity together when the initial boundary layer is laminar, but not when the initial boundary layer is turbulent.

ISSN:0031-9171    

DOI:10.1063/1.862349

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In a deep, turbulent flow with negligible advection, flowing over a surface roughened by regularly spaced, two‐dimensional roughness elements, measured Reynolds shear stress decreased as the surface was approached. The depth of the region of shear‐stress deficit was of the order of ten element spacings. Streamwise variations in mean velocities were unable to account for the magnitude of the shear‐stress deficit, and the log‐law estimate of surface shear disagreed with that measured directly by a drag balance. The data are presented as further information on a puzzling phenomenon.

ISSN:0031-9171    

DOI:10.1063/1.862350

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The potential for an oscillating ring source immersed in cold, magnetized, collisionless plasma in the resonance cone regime (K∥/K⊥<0) is evaluated exactly and asymptotically, giving insight into the gross spatial behavior of the focusing resonance cones. The nature of the singularity in potential is clarified by the introduction of a noninfinitesimal collision frequency. Thermal effects are considered numerically, revealing an interesting interference structure in potential as well as a density depression near the focus of the cone due to the ponderomotive force.

ISSN:0031-9171    

DOI:10.1063/1.862351

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Time‐dependent classical diffusion in large‐aspect toroidal plasmas with a circular section is studied for both low‐&bgr; and high‐&bgr; cases. In the low‐&bgr; case, both the fast and slow phases are examined and the difference between the slow phase and the quasi‐stationary theory is discussed.

ISSN:0031-9171    

DOI:10.1063/1.862352

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A nonlinear analysis of collisional drift instability is developed in a slab model based on the two fluid equations, where inhomogeneities in electron and ion temperatures and unperturbed current are included in addition to ion inertia, finite ion gyroradius, and viscosity. A systematic expansion is introduced by taking &egr;=‖&kgr;‖las a smallness parameter, where &kgr; is the degree of density gradient andlis the linear scale of the slab along the density gradient. The nonlinear development of the drift wave near marginal stability is studied on the basis of the model equations. A new feature, hard excitation, has been found, which is due to the effects of the nonlinear frequency shift and the electron temperature gradient. The saturation amplitude is calculated, and the expressions for wave‐associated particle and heat fluxes are obtained. A comparison of the expressions with the experimental results of a stellerator device is also made.

ISSN:0031-9171    

DOI:10.1063/1.862353

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A variational formulation of the radial eigenmode equations describing kink‐tearing modes, drift‐tearing modes, and drift modes, in slab geometry, is derived. The formalism is shown to provide accurate dispersion relations for a wide range of problems, with fewer approxmimations and less analytical effort than conventional methods require. Furthermore, derivation from a unified framework illuminates the relationships between different instabilities. The variational method is particularly well suited to the approximate solution of physically realistic problems, heretofore considered tractable only by numerical methods.

ISSN:0031-9171    

DOI:10.1063/1.862344

出版商:AIP    

年代:1978

数据来源: AIP