摘要:

Measurements of the three fluctuating components of the velocity and of the two components of the wall shear stress fluctuations have been made in a fully developed turbulent channel flow at Re=7700 using hot‐film probes. These measurements include rms values, skewness and flatness factors, and probability density functions. Although the wall region is emphasized here, information for the whole channel half‐width is also given.

ISSN:0031-9171    

DOI:10.1063/1.862737

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An experimental investigation of a two‐dimensional turbulent jet in a quiescent environment has been carried out to determine the structural characteristics of the outer, intermittent turbulent motion. An overall picture of this motion was deduced from the results which indicate that, on the average, the turbulent bulges are of the same order of magnitude in the three coordinate directions and are tilted backward at an angle of approximately 26° with respect to the lateral axis but have no spanwise yaw. Furthermore, it was found that there is no periodicity associated with the motion and that no correlation exists between bulges on opposite sides of the jet center line.

ISSN:0031-9171    

DOI:10.1063/1.862738

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Mutual slip‐through of two identical vortex rings, traveling along a common axis in the same direction, was experimentally achieved in air at various Reynolds numbers between 800 and 2000 and observed by using the smoke wire technique and cigarette smoke. The motions of a pair of vortices agree very well with an approximate potential theory based on the Biot–Savart law.

ISSN:0031-9171    

DOI:10.1063/1.862739

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Impulsively started spin‐up from an initial state of rest for incompressible fluid in a circular cylinder is examined from the viewpoint of the vorticity field. Existing theoretical models of this flow are thought to have implausible vorticity dynamics.

ISSN:0031-9171    

DOI:10.1063/1.862740

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The solution of the equations for two‐phase flow which models the steady sedimentation of a uniform distribution of particles in a liquid has been shown to be unstable to small perturbations. It is shown that when a diffusivity term (a force on the particles which is linear in the gradient of the particle concentration) with sufficiently large coefficient is included, the solution is stable and, furthermore, the equations are hyperbolic.

ISSN:0031-9171    

DOI:10.1063/1.862741

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A general analysis of thermodynamic coupling effects in flames and other nonequilibrium gas‐phase chemically reacting multicomponent boundary‐layer flows is presented. Changes in characteristic diffusion time relative to characteristic reaction time due to thermal‐diffusion, diffusion‐thermo‐ and multicomponent‐diffusion effects are considered and a new generalized gas‐phase Damkohler number which encompasses these effects is defined. Using a transformed total enthalpy‐concentration field and the newly defined Damkohler number, compressible laminar reacting boundary layers were analyzed and compared with other available analyses for simpler specific cases. The applicability of the present theory is demonstrated by new solutions for the problem of combustion of injected premixed fuel. Comparison between these results and uncoupled solutions reported in the literature indicate that thermodynamic coupling effects are significant, especially when Damkohler numbers are smaller than unity.

ISSN:0031-9171    

DOI:10.1063/1.862742

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The condensation of SF6in a dilute mixture with either Ar or He as a carrier gas when quickly expanded in a small, adjustable nozzle is investigated. Condensation is observed by monitoring the disappearance of individual rotational‐state lines in the SF6&ngr;4absorption band. For this, a diode‐laser spectroscopy system is employed, the nozzle is two dimensional, and the flows are short‐duration pulses. The gas density at which condensation onset occurs is measured as a function of local gas temperature (30°–100° K), local expansion rate, and SF6mole fraction (0.18%–3.4%). The onset density depends strongly on the local temperature and expansion rate and not at all on the mole fraction. For the SF6/Ar data, Ar co‐condensation appears to reduce the SF6onset density level at the lowest mole fractions, and SF6vibrational lag appears to increase the onset density level at the highest mole fractions. A simple ’’trimers‐critical’’ model for condensation onset is derived, and with this model reasonable correlation of much of the onset data is obtained. From this correlation, an effective dimer binding energy and trimer formation probability are extracted.

ISSN:0031-9171    

DOI:10.1063/1.862743

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

It is shown that in the calculation of the Spitzer function and the Pfirsch–Schlu¨ter transport coefficients for a multispecies tokamak plasma, a considerable analytic simplification occurs for the case of ions with multiple charge states. The number of coupled integrodifferential equations to be solved can be reduced from the total number of species (each charge state constitutes a distinct species) to the number of ions with different nuclei. The solutions are expressed in terms of quantities characterizing a system of interacting electrons and ion aggregates.

ISSN:0031-9171    

DOI:10.1063/1.862744

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A new class of resistive drift‐Alfve´n modes is discovered. The new modes are believed to be the generalization of shear‐Alfve´n waves to sheared magnetic fields. In addition, the finite &bgr; (plasma over magnetic pressure) corrections to the electrostatic dissipative drift wave are evaluated.

ISSN:0031-9171    

DOI:10.1063/1.862730

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The radial eigenmode problem for current‐driven drift modes in a plasma slab with sheared magnetic field is solved including the full electron dynamics and effects of electron temperature gradient and electron‐ion collisions. Particular attention is given to the eigenmode structure and comparisons with the universal drift mode are made. The threshold current for the onset of current‐driven drift mode is found to be close to that predicted by analytic theory and not greatly affected by electron temperature gradient or collisionality.

ISSN:0031-9171    

DOI:10.1063/1.862731

出版商:AIP    

年代:1979

数据来源: AIP