摘要:

The phenomenon of vortex merging in a two‐dimensional mixing layer is treated statistically by introducing the probability density of spacings between neighboring vortices. The rate of merging is the other statistical variable and is a function of the spacing. The mixing layer is assumed to be statistically uniform along the streamwise coordinate and not to change with time. The following further assumptions were made: no correlation between adjacent spacings, similarity of the probability density, etc., to all times, and that the rate of merging for a single pair of vortices is inversely proportional to the square of their distance. The probability density was obtained by solving the governing equation. The result agrees well with that data measured by Brown and Roshko.

ISSN:0031-9171    

DOI:10.1063/1.862208

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An experimental investigation of a developed plane turbulent wake has been carried out to gain some insight into the spanwise structure of the large scale intermittent turbulent bulges. The results indicate that these bulges are three dimensional, and that their extent in the spanwise direction is less than in the streamwise direction and greater than in the lateral direction. No evidence of periodicity was found.

ISSN:0031-9171    

DOI:10.1063/1.862209

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A statistical analysis is performed of various low‐order truncations of the two‐dimensional inviscid Navier–Stokes equations. The behavior of the time‐averaged enstrophy and time‐correlation function of each Fourier mode is analyzed and compared to the behavior expected in a random dynamical system. Empirical evidence is presented for the randomness of all isotropically truncated models for which the wavenumber cutoff is large enough to insure that every mode is involved in nontrivial interactions. This evidence is contrasted with the apparent nonrandomness found in other special truncations. The results strengthen the evidence for the validity of statistical descriptions of two‐dimensional turbulence.

ISSN:0031-9171    

DOI:10.1063/1.862210

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A model of turbulence including a Reynolds‐stress‐mean velocity relation is developed. The functional nature of this relationship is presented and expressions are given for the unknown terms that can be derived from spectral information. With some modifications, inhomogeneous turbulent fields in which shear effects prevail can be pretty well predicted.

ISSN:0031-9171    

DOI:10.1063/1.862211

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A search for the eigenvalue spectrum of the Orr–Sommerfeld equation for the Blasius boundary layer is conducted. The investigation is numerical involving two different numerical methods. The resulting spectrum is found to depend on the finite interval of integration chosen for the numerical scheme. This spectrum is shown to be infinite and discrete whenever it is identified with the aid of numerical integrations. The spectrum belonging to the exact semi‐infinite problem is inferred from the asymptotic behavior of the same spectrum. This is shown to be comprised of a finite discrete set and a continuous portion.

ISSN:0031-9171    

DOI:10.1063/1.862212

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The problem of the instability of an incompressible viscous liquid jet is considered within the context of one‐dimensional Cosserat equations. Linear stability analyses are performed for both the infinite and semi‐infinite jets. The results obtained for the inviscid case are compared with the corresponding results derived from ideal fluid equations. They are also compared with recent results by other authors obtained from a different set of one‐dimensional jet equations. Solutions are also obtained, within the framework of the linearized theory, to the jet break‐up problems formulated as an initial‐value problem for the infinite jet and as a boundary‐value problem for the semi‐infinite jet.

ISSN:0031-9171    

DOI:10.1063/1.862213

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

It has recently been observed that the dissipative nonlinearities for a variety of transport processes can be written in a formally identical fashion. This ’’canonical form’’ expresses the spontaneous changes of extensive variables in terms of exponentials of intensive variables and depends on the molecular processes causing the dissipation. It is shown here that the dissipative terms in Newtonian fluid mechanics can be written in canonical form. Using a postulated relationship between these dissipative terms and fluctuations, the canonical form is used to describe the molecular fluctuations in the flow of Newtonian fluids. The theory describes the effect of nonlinearities, including the streaming terms, and is consistent whenever the phenomenological equations are valid. Close to equilibrium the theory reduces to the Fox–Uhlenbeck theory of hydrodynamic fluctuations, and away from equilibrium it gives an unambiguous generalization of the Landau–Lifshitz theory.

ISSN:0031-9171    

DOI:10.1063/1.862214

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Models of the collision integral are developed for polyatomic structureless molecules subject to certain classes of phenomenological energy exchange between internal and translational energy modes in binary collisions. The exchange is described either by a model differential cross section for energy scattering or equivalently by a set of pair pseudo‐internal coordinates which correlate pre‐ and post‐ collision values of the particle energies. Restrictions placed on admissible models of the exchange process are identified and one recently proposed special model is reformulated under these conditions. Chapman–Enskog type transport properties for this model are evaluated and its behavior in the context of the Monte‐Carlo direct simulation method is discussed briefly.

ISSN:0031-9171    

DOI:10.1063/1.862215

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The effect of the disturbances behind a strong shock moving in a medium of nonuniform density is considered. The similarity solution is used to find the strength of the overtaking disturbance which modifies Chisnell’s approximation to become an exact theory.

ISSN:0031-9171    

DOI:10.1063/1.862216

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A general dispersion relation and quasi‐linear diffusion operator for electrostatic turbulence in strongly magnetized but inhomogeneous plasmas are derived. Wave induced particle transport rates across the gradients and criteria for their applicability are then deduced. The theory is applied to assess enhanced transport associated with high‐power lower‐hybrid heating of toroidally confined plasmas.

ISSN:0031-9171    

DOI:10.1063/1.862194

出版商:AIP    

年代:1978

数据来源: AIP