摘要:

The effect of polyethyleneoxide (Polyox grade WSR 301) on grid‐generated turbulence was investigated using laser anemometry and flow‐visualization techniques. It was found that the polymer additive reduced both the turbulent intensity and the rate of decay behind the grid. At typical drag‐reducing concentrations, turbulent energy spectra were qualitatively the same as those in water, in agreement with the results of other investigations. However, at higher additive concentrations, the dissipation‐range spectra showed noticeable attenuation. This seemed to be a threshold effect with onset at a polymer concentration between 100 and 250 ppm. This result was supported by photographs of dye‐injection tracer but in this case the onset concentration for small‐eddy suppression was between 50 and 100 ppm.

ISSN:0031-9171    

DOI:10.1063/1.861977

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Thermodynamic coupling effects become important in such applications as injection of low molecular gases into boundary‐layer flows, ablative thermal protection processes, chemically reacting flows, and membrane transport processes which involve large gradients of temperature or concentrations. Thermodynamic couplings due to thermal diffusion, diffusion‐thermo andobaliamdiffusion effects in multicomponent compressible laminar boundary layers with nonequilibrium surface chemical reactions are analyzed and compared with other available analyses for simpler specific cases. A generalized mathematical description of the boundary conditions associated with surface reactions and thermodynamic coupling contributions to the various fluxes is also presented. The boundary conditions are transformed into total enthalpy‐concentration fields, and a new generalized Damkohler number for surface reactions is defined. The applicability of the present theory is demonstrated by new solutions to surface catalytic reactions with coupled heat and mass transfer at the stagnation region with and without blowing or suction. These results are then compared with Chung’s uncoupled solutions.

ISSN:0031-9171    

DOI:10.1063/1.861964

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The special class of quasi‐simple wave solutions is studied for the system of partial differential equations governing inviscid acoustic gravity waves. It is shown that these traveling wave solutions do not admit shocks. Periodic solutions are found to exist when there is no propagation in the vertical direction. The solutions for some particular cases are depicted graphically.

ISSN:0031-9171    

DOI:10.1063/1.861965

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A kinetic theory analysis is made of the flow of a rarefied monatomic gas through a two‐dimensional slot connecting two reservoirs. Numerical solutions are obtained by the moment and discrete ordinate methods. The former method portrays the transition regime characteristics well, but has limitations in the free molecule regime. The latter method gives accurate results in the free molecule and slip regime and bolsters confidence in the accuracy of the transition regime results. The numerical solution for the mass flux through the slot agrees well with an approximate analytic solution of the moment equations for length‐to‐width ratios from 6 to 0.5, pressure ratios from 0.8 to 0.1, and Knudsen numbers from 5 to 0.5.

ISSN:0031-9171    

DOI:10.1063/1.861966

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Scaling laws for field induced mixing of a semi‐insulating liquid of uniform viscosity &eegr; and permittivity &egr;, but of inhomogeneous conductivity, are deduced for motions with characteristic times long compared with viscous‐diffusion and charge relaxation times. In an electric field,E, time is shown to scale with electric‐viscous time &tgr;ev=&eegr;/&egr;E2. An experiment involving mixing of a highly conducting thin layer into a lesser conducting bulk region uses temporal current evolution to confirm scaling. A simple mixing model is shown to correlate with experimental results. Linear instability mechanisms underlying the mixing process are described by a bulk‐coupled model, with viscous diffusion effects included. Eigenfrequencies are determined as they depend on conductivity variation and ratio of viscous diffusion to electric‐viscous time. Static instabilities and overstabilities are predicted. Corresponding eigenfunctions and streamlines lend insights into the onset of instability leading to a turbulent mixing state.

ISSN:0031-9171    

DOI:10.1063/1.861967

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Surface‐coupled electrohydrodynamic instability at the interface between miscible fluid components with identical permittivity, mass density, and viscosity but disparate conductivities, as stressed by an equilibrium normal electric field, is described in the instantaneous relaxation limit. Long wave, inertia‐dominated and short wave, viscous‐dominated regimes of the dispersion relation are identified. Experimental studies, using freon 113 as a base liquid, compare observed interfacial displacements as functions of time with growth rates predicted by the model. Correlation varies from almost perfect to experimental growth only 0.1 as fast as predicted by theory, with all observed motions in the inertia‐dominated regime. Instability dynamics at the scale of interfacial conductivity distribution are documented by allowing diffusion before electric field application.

ISSN:0031-9171    

DOI:10.1063/1.861978

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The combined effects of resistivity and viscosity on a magnetohydrodynamically unstable plasma slab are shown to be responsible for the existence of a stationary (marginal) mode. This mode gives rise to plasma convection in a shear‐free situation when nonlinear effects are taken into account. In the case of a sheared magnetic field, it still extends over the entire width of the slab and is driven by what would be an interchange localized about the resonant (k⋅B(0)=0) surface in the absence of dissipation. The critical value of the plasma analog of the Rayleigh number in hydrodynamics is calculated as a function of shear, mode wavenumber, and dissipation (represented by the square of the Hartmann number).

ISSN:0031-9171    

DOI:10.1063/1.861979

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

The treatment of the magnetohydrodynamic problem of a sharp‐boundary theta pinch plasma column in the presence of perturbing magnetic fields is extended to include long wavelengthm=1 motion. The long wavelengthm=1 instability, which is a serious problem for fusion devices based on the theta pinch, is explained in a simple way. Plasma equations of motion which are suitable for modeling of complicated experimental situations are given. The high‐beta stellarator is discussed.

ISSN:0031-9171    

DOI:10.1063/1.861980

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

Numerical studies of various aspects of two‐dimensional Langmuir solitons, are made, viz., (i) instability and collapse of a planar soliton perturbed in the perpendicular direction, (ii) the effect of an approximate Landau damping on the collapse, and (iii) the generation and subsequent collapse of planar solitons by an external pump field. These computations verify the flow of energy from long wavelength pump fields, through soliton formation and collapse, to shorter wavelengths, where the energy is transferred to the electrons.

ISSN:0031-9171    

DOI:10.1063/1.861981

出版商:AIP    

年代:1977

数据来源: AIP

摘要:

A collisionless spatially nonuniform plasma is considered in a finite conducting cylinder in a uniform magnetic field. The magnetic field is increased by a small fractional amount over the critical value for onset of instability. A single mode grows and is saturated by nonlinear effects. Analytic expressions are obtained for the time‐asymptotic saturation amplitude and frequency shift. Indeterminate equations and singular functions are resolved by methods similar to those used earlier in the one‐dimensional bump‐on‐tail analysis, and the form of the modified equilibrium distribution and potential is obtained. A specific numerical example demonstrates that saturation is due to increased ion Landau damping, and that this saturated amplitude is unstable to small deviations. Hence, the onset of the instability is predicted to be of the ’’hard’’ variety. This result holds both in the ’’quasi‐linear’’ approximation and in the full nonlinear case.

ISSN:0031-9171    

DOI:10.1063/1.861982

出版商:AIP    

年代:1977

数据来源: AIP