摘要:

The problem of defining a proper measure for the size of disturbances that evolve spatially is assessed. A model problem serves as a demonstration that the disturbance energy, which is almost exclusively used in a temporal setting, is generally not sufficient as a measure of the disturbance size in the spatial case. It is shown that the specific form of the ‘‘energy’’ transferred between Fourier components in the spatial case is not unique, but rather depends on the formulation of the spatial evolution problem. In addition to the model problem, suggestions on how to evaluate spatial ‘‘energy’’ transfer in the Navier–Stokes equations are presented.

ISSN:1070-6631    

DOI:10.1063/1.868109

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The three‐dimensional long‐wave linear stability of a straight vortex, that runs down a circular tube, parallel with its axis but slightly displaced from it, is analyzed. The vortex flow is modeled by an infinite concentrated, potential vortex filament. The filament is immersed in an axial uniform flow, and autorotates around the tube axis due to its small eccentricity. The tube walls are modeled by a surface distribution of potential sources. Results show that the vortex develops a dynamic instability in a narrow range of wave numbers as a direct result of its small eccentricity. The vortex also tends to diverge statically at certain wave numbers, only when it is in a ‘‘subcritical’’ state. Finally, it is shown that a time‐dependent streamwise variation of the tube radius can be used as a controller to actively control the dynamic stability of an eccentric vortex in a tube.

ISSN:1070-6631    

DOI:10.1063/1.868110

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A method is presented whereby the fast chemistry reaction,Fuel+(r)Oxidizer→(1+r)Product, may be modeled in the context of a large eddy simulation (LES). The model is based on a presumed form for the subgrid‐scale probability density function (PDF) of a conserved scalar. The nature of the subgrid‐scale statistics is discussed and it is shown that a beta function representation of the subgrid‐scale PDF is appropriate. Data from both laboratory experiments and direct numerical simulations (DNS) are used to show that the predictions of the model are very accurate, given the exact values for the filtered scalar and its variance. A possible model for this variance is presented based on scale similarity.

ISSN:1070-6631    

DOI:10.1063/1.868111

出版商:AIP    

年代:1994

数据来源: AIP