摘要:

The stability of the laminar mixing region between two uniform streams is investigated by numerically solving the linear sixth‐order equation for the disturbance amplitude function. This equation includes the effects of both viscosity and heat‐conduction and is, therefore, regular at the critical point, where the mean flow velocity and disturbance phase speed are equal. Both the neutral stability curve and curves of constant amplification rate are computed for various Richardson numbers. The results show that the damping effects of diffusion are quite small and, therefore, that the Richardson number is the dominant parameter governing the stability of the flow. Streamlines are computed for neutral disturbances and it is found that, in the inviscid limit for long waves, the flow pattern approaches the configuration obtained previously by Taylor in his study of a discontinuous three‐layer model.

ISSN:0031-9171    

DOI:10.1063/1.1693456

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The configurations of bubbles floating at a vapor‐liquid interface are investigated both analytically and experimentally. The differential equations governing the shape of a single bubble at rest in a liquid of infinite extent are deduced under the assumption of zero dome thickness, uniform surface tension, and equal gas densities within the bubble and above the interface. These equations show that nondimensional bubble shapes depend upon the value of a single parameter. An analytical solution, valid for small bubbles, is developed and shown to be in good agreement with the general numerical solution. Good agreement with theory is demonstrated for floating air bubbles, both stationary and translating, ranging in volume from 0.01 cc (in water) to 0.83 cc (in heavy mineral oil). Theoretical results over a dimensionless bubble volume (the ratio of volume to the cube of the capillary constant) range of from2.6 × 10−4to 5527 are given.

ISSN:0031-9171    

DOI:10.1063/1.1693457

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Doppler spectra in microwave scattering from wind waves have been measured at X band (3.2 cm) and K band (1.25 cm) in a short fetch wind wave tank. The scattering cross sections, mean frequency shifts, and bandwidths obtained are compared with results of measurements of the directional slope spectra, mean drift, and particle velocities of the wind waves. The scattering is attributed to low order Bragg scattering, the phase speeds of the wind waves are deduced and the dependence of the Doppler bandwidth on wind speed and Bragg wavenumber is given.

ISSN:0031-9171    

DOI:10.1063/1.1693458

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A linear stability analysis of the hydrodynamics of the isothermal two‐component reactive fluid(A2, A), confined between two infinite parallel plates, and involved in the surface catalyzed reaction(A2&lrhar2;2A)is performed. The existence of solutions to the eigenvalue problem governing the state of marginal instability corresponding to pure convection is established. A variational principle for the critical eigenvalue for instability is developed and used to show that the surface catalyzed reaction enhances the instability that would occur if the reaction were frozen.

ISSN:0031-9171    

DOI:10.1063/1.1693459

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The linear perturbation problem [D. J. Wollkind and H. L. Frisch, Phys. Fluids 14, 13 (1971)] is extended to include a nonlinear stability analysis of a horizontal layer of dissociating fluid, heated from above or below. This analysis deals with the simplest possible nonlinear problem, namely, a two‐dimensional situation in which material property variation with temperature is neglected. The results of this analysis show that there exist finite amplitude equilibrium rolls for both the case of heating from below (at a slight departure from the critical conditions for the Be´nard problem) and from above (the chemical instability). This problem having been solved, it can then be conjectured with some confidence what a fuller nonlinear analysis would reveal.

ISSN:0031-9171    

DOI:10.1063/1.1693460

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A calculation shows that amplification of acoustic waves by absorption of laser radiation should be measurable in the laboratory.

ISSN:0031-9171    

DOI:10.1063/1.1693461

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Using the Sonine polynomial expansion method the nonlinear Boltzmann equation for time‐dependent spatially uniform gases is solved to examine the relaxation of an initially nonequilibrium distribution toward the equilibrium. For an inverse‐fifth power law force, a simple analytical expression is presented for equations for expansion coefficients. As a result the higher‐order expansion coefficients as well as the lower‐order ones are obtained, so that the decay of larger initial departure of the distribution function from the equilibrium is dealt with. The resulting distribution function is compared with the corresponding one obtained on the basis of the Bhatnagar‐Gross‐Krook model. The latter model is shown to be adequate only when the departure of distribution function from the equilibrium becomes small.

ISSN:0031-9171    

DOI:10.1063/1.1693462

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The usual truncation procedure for coefficient equations is shown to be inconsistent for a certain class of initial‐value problems in that it retains terms of one magnitude while neglecting terms of the same or greater magnitude. Moreover, it predicts moments which are strongly dependent on the zero‐order function used in the expansion of the distribution function. A truncation procedure is developed for spatially homogeneous (time relaxation) problems which gives rise to moments which are independent of the particular zero‐order function used in the expansion; and which, for certain general initial distribution functions, are correct in value and first‐derivative both initially and in equilibrium. As an example, this procedure is used to solve the two‐temperature single‐gas mixture problem.

ISSN:0031-9171    

DOI:10.1063/1.1693463

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The phenomenon of transient condensation onto, or evaporation from, a liquid sheet in contact with its pure vapor is treated from a kinetic theory viewpoint. The Maxwell moment method is used to formulate the detailed transient problem. A steady surface mass flux rate exists for times large in comparison with the collision time, that is, in the continuum regime, and explicit formulas are given for this limit. The complete gasdynamic field, however, is nonsteady for all times. The calculations are carried out utilizing four moments, and the effects of incorporating additional moments are negligible. Finally, the analysis is extended to incorporate imperfect mass and temperature accommodation. Examination of the transient solution and a matched asymptotic “quasisteady” solution shows that the gasdynamic field consists of a diffusion process near the liquid surface coupled through an expansion or compression wave to the constant far field state.

ISSN:0031-9171    

DOI:10.1063/1.1693464

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A moment method for solving the Boltzmann equation for a gas of diatomic molecules in an external magnetic field and in cylindrical geometry is presented. It is found that the particular geometry is very important at all pressures while the specific form of the boundary conditions becomes dominant at low pressures. In the continuum region, the torque has the same features as a Burnett effect in being inversely proportional to the pressure while at lower pressures the Knudsen effect on the temperature distribution becomes the major contribution to the pressure dependence. In this case, an ansatz for a two‐sided distribution function is used in solving the heat flow and temperature distribution. A comparison is made with experimental results and other theoretical investigations.

ISSN:0031-9171    

DOI:10.1063/1.1693465

出版商:AIP    

年代:1971

数据来源: AIP