摘要:

Differential filters for the large eddy numerical simulation of turbulent flows are defined and their properties are discussed. Their main advantages are that the correlations can be expressed exactly in the so‐called resolvable scale and the attenuation of the filtered function in the Fourier space can be carefully controlled

ISSN:0031-9171    

DOI:10.1063/1.865649

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Linear differential filters, i.e., filters in which the filtered functionf¯ and the original functionfare connected by a linear differential equation, are studied on a general basis concerning the elliptic operators of second order. In addition, a particular example of a parabolic filter depending on space and extended to past times is given, and its interest in the context of the large eddy simulation of turbulence is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865650

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An equation of the Korteweg–de Vries (KdV) type with variable coefficients in cylindrical coordinates for nonlinear wave propagation on water of variable depth is presented. The special case concerning water motion with cylindrical symmetry reduces to an equation of the KdV type obtained from approximate equations for long waves.

ISSN:0031-9171    

DOI:10.1063/1.865651

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The influence of resistivity on energetic trapped particle‐induced internal kink modes, dubbed ‘‘fishbones’’ in the literature, is explored. A general dispersion relation, which recovers the ideal theory in its appropriate limit, is derived and analyzed. An important implication of the theory for present generation fusion devices such as the Joint European Torus [PlasmaPhysicsandControlledNuclearFusionResearch(IAEA, London, 1984), Vol I, p.11] is that they will be stable to fishbone activity.

ISSN:0031-9171    

DOI:10.1063/1.865652

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Small particles in plasmas can form a coulomb lattice. The conditions for solidification in a laboratory plasma are discussed.

ISSN:0031-9171    

DOI:10.1063/1.865653

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The widely usedsvs &agr; stability diagram for ballooning modes is based on the assumption of circular flux surfaces with small shifts. (Heres=rq’/qand &agr;=−R0q2&bgr;’.) This analysis is extended to include finite shifts. There again results a universal stability diagram, although in this case it is parametrized by three quantitiess, &agr;, and &sgr;’, the differential shift between flux surfaces. The analysis shows that the inclusion of a finite shift leads to a significant further stabilization of the ballooning modes over that from the standard case.

ISSN:0031-9171    

DOI:10.1063/1.865654

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

There are many instances of hydrodynamic instability induced by a variation, or stratification, in either a fluid property or a flow property. In this article a new instability is presented. It is shown that when there is a variation in thermal conductivity in the fluid, instability can occur in the presence of a longitudinal gravitational field.

ISSN:0031-9171    

DOI:10.1063/1.865603

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The excitation of instabilities caused by the parametric coupling between an external source and the normal modes of bubbly flow is investigated. It is shown that the presence of two species of bubbles gives rise to two types of parametric excitations. In the first one the frequency of the external source is smaller than the larger of the natural frequencies of the species. As a result, the excited mode is nonoscillatory. In the second type the driving frequency is bigger than both natural frequencies and the resulting instability is oscillatory. The threshold amplitude of the external source is calculated as well as the growth rates and frequencies of the different types of instabilities.

ISSN:0031-9171    

DOI:10.1063/1.865604

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The modifications to the vertical velocity of a turbulent flow by the large‐eddy breakup devices (LEBU) were analyzed using linear three‐dimensional unsteady aerodynamics. A Fourier component of the input turbulence convected over these devices was considered and the modified vertical velocity in the far downstream wake was solved. It is shown that the amplitude of the vertical velocity behind the device is reduced, the effect increasing with increasing stream and spanwise wavenumber. Two plates placed far apart in series produce a reduction that is the square of that for a single plate. The presence of the ground plane decreases the effectiveness of the LEBU in reducing the amplitude of the vertical velocity in the far wake.

ISSN:0031-9171    

DOI:10.1063/1.865605

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An experimental investigation of large‐scale structural patterns in the similarity region of a two‐dimensional turbulent jet was performed. Two‐point correlation and coherence‐based measurements obtained from both longitudinal and lateral component velocity fluctuations are, in general, supportive of the existence of an antisymmetric array of counterrotating vortices in the similarity region. Particularly graphic evidence is obtained from detailed isocorrelation contour maps that are presented. A novel method of determining structural convective velocity is developed and indicates the structural array propagates at 60% of the local centerline mean velocity. Very limited structural two dimensionality is exhibited in the direction of mean flow homogeneity and it is suggested that this is likely to be related to the existence of multiple coherent modes in the flow.

ISSN:0031-9171    

DOI:10.1063/1.865606

出版商:AIP    

年代:1986

数据来源: AIP