摘要:

Steady evaporation from a spherical and heterogeneous condensed body into vacuum is considered. Inert solid particles, initially embedded in the condensed phase, are liberated and collisionally accelerated by the evaporating gas molecules. A simple mathematical model for the flow is proposed and executed by the Direct Simulation Monte Carlo (DSMC) method. For small Knudsen numbers, the results are compared with a continuum solution including Knudsen layer corrections obtained by a moment method, demonstrating that these corrections are leading order effects in the treatment. ©1997 American Institute of Physics.

ISSN:1070-6631    

DOI:10.1063/1.869163

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Temperature and number density fields of a binary gas mixture over a plane solid wall kept at a constant temperature have been studied analytically on the basis of the linearized version of the Boltzmann equation of BGK type subject to the boundary condition of Maxwell’s type (specular‐diffusive reflection). An analysis within the Knudsen layer in the vicinity of the wall has been carried out by solving the set of equations accurately, which has enabled us to obtain the distributions of the temperature and number density explicitly over the entire flow field. Fictitious gas mixtures have been taken up, in addition to the mixtures of real gases such as helium–neon, helium–argon, neon–argon and so on, in order to see the effects of the molecular mass ratio, the concentration ratio and the accommodation coefficients of the component gases on the temperature and number density fields by suppressing the effects associated with the transport coefficients. The macroscopic jump coefficients in temperature at the wall have also been given for making a comparison with the other results available. The comparison with the theoretical results by other authors for a helium–argon mixture case shows a reasonably good agreement. The experimental data, however, seem to be too large compared with the present results, which may partly be attributable to some ambiguities in the definitions of some quantities involved in the experiment. ©1997 American Institute of Physics.

ISSN:1070-6631    

DOI:10.1063/1.869164

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In the early 1970s, Maxworthy [J. Fluid. Mech.51, 15 (1972)] and Oshimaetal. [J. Phys. Soc. Jpn.38, 1159 (1975)] attempted to produce leapfrogging between two coaxial vortex rings at low Reynolds numbers in their laboratories. However, the rings failed to undergo the classical leapfrogging behavior and merged to form a single ring. In a recent numerical study, Shariffetal. (NASA Tech. Memo. 102257, 1989) attributed the failure partly to the effect of core distortion. They pointed out that vortex cores at low Reynolds numbers are thicker and therefore more susceptible to distortion during the leapfrogging. In this Brief Communication, it is shown through a systematic investigation thattheinitialgeneratingconditionalso plays an important role in determining the success or failure of leapfrogging. The common belief that leapfrogging can be achieved simply by generating two vortex rings in quick succession may not be true for all flow conditions, especially when the Reynolds number is low. This finding may help to explain the results of Maxworthy and Oshimaetal. ©1997 American Institute of Physics.

ISSN:1070-6631    

DOI:10.1063/1.869160

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Evidence is presented for what appears to have been nonmodal disturbance growth in a pipe‐flow experiment performed by Kaskel [Technical Report No. 32‐138, Jet Propulsion Laboratory, California Institute of Technology, 1961], based on a comparison of the experimental traces of disturbance amplitude with predictions of transient amplitude growth calculated from the underlying linear stability operator. Owing to the geometry of the experimental disturbance generator, modes having azimuthal wavenumbersn=0, 6 and 12 are expected to contribute the bulk of the disturbance energy, and numerically predicted amplitude growth versus downstream distance is in good agreement with the experiment. ©1997 American Institute of Physics.

ISSN:1070-6631    

DOI:10.1063/1.869167

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An apparent contradiction between the results of Yang and Akylas [Phys. Fluids8, 1506 (1996)] and those of Vanden‐Broeck [Phys. Fluids3, 2669 (1991)] is clarified by comparing the cnoidal and solitary waves predicted by the Korteweg–de Vries theory. In particular the rate at which the cnoidal waves approach a solitary wave as the wavelength is increased, is discussed. ©1997 American Institute of Physics.

ISSN:1070-6631    

DOI:10.1063/1.869166

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:1070-6631    

DOI:10.1063/1.869521

出版商:AIP    

年代:1997

数据来源: AIP