摘要:

The approach of axisymmetric, homogeneous turbulence to isotropy using the direct interaction approximation is investigated. The turbulence is characterized by two parameters, the spectral variance transverse and parallel to the direction of axisymmetry. The dependence of these energy components on wave vector orientation is developed into a spherical harmonic expansion, and only low order terms are examined in detail. In terms of this characterization of the theory, the general qualitative nature of the relaxation to isotropy is discussed and numerical results for the energy spectrum and transfer functions are presented. It is shown that the simplest characterization of the theory leads to an almost linear relaxation to isotropy. The numerical results at moderate Reynolds numbers are compared to the phenomenological theory of Rotta [J. C. Rotta, Z. Physik129,547 (1951)]. A simple analytic estimate of the Rotta relaxation rate is also presented.

ISSN:0031-9171    

DOI:10.1063/1.1694822

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An experimental investigation of the form of the temperature structure in the slightly heated plane wake and its relationship to the intermittency and interface structure is described. No evidence is found of periodic interface motion. Furthermore, it is shown that the large scale structures of the interface modulations with wavelengths greater than 10&percent; of the wake width are highly correlated with the large scale temperature structure within the wake and hence that the interface is related primarily to the large scale structure of the flow field.

ISSN:0031-9171    

DOI:10.1063/1.1694823

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Viscous linear stability analysis of half‐jet flows of superposed, immiscible fluids with small density difference is presented. For small values of wavenumber&agr;and Reynolds numbers, series solution is used to obtain the effect of density difference on the neutral stability curve.

ISSN:0031-9171    

DOI:10.1063/1.1694824

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The stability of the stably stratified Bickley jet to small disturbances in a viscous, heat conducting fluid is explored by numerical integration of the governing differential equation. Curves of neutral stability are presented in the&agr;‐Rplane and the parametric dependence of these curves upon Richardson number and Prandtl number is examined. The results show a curious bimodal behavior of the curve of neutral stability for small Richardson numbers. In addition, closed neutral curves are found for Richardson numbers in excess of the critical value for the inviscid flow. The unstable regions in the interior of these curves increase with decreasing Prandtl number. Energy balances are computed which show the relative magnitude of the Reynolds stress production, buoyancy dissipation, and viscous dissipation terms across the flow. As the thermal diffusivity becomes large compared with the kinematic viscosity, the buoyancy term is suppressed and the thermal stratification becomes irrelevant.

ISSN:0031-9171    

DOI:10.1063/1.1694825

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The linear instability of small but finite amplitude cnoidal waves on shallow water is examined. A new set of equations valid under the shallow water approximation is used to derive periodic wavetrains and to study the behavior of small perturbations. A resonance conditionk2 = k1 + 2k,similar to that used by other authors, is required to hold between the side‐band perturbations with wavenumbersk1andk2,and the main wave with wavenumberk.It is also necessary for the perturbations to have a specific nonzero frequency&OHgr;,measured with respect to the main wave which is stationary in a wave frame. In the region0 < F2 < 1,whereFis a Froude number of the flow underlying the cnoidal wave, all wavetrains are unstable to these side‐band perturbations. Like all other parametric instabilities, the instability is due to the resonant transfer of energy from the main wave to the perturbing waves.

ISSN:0031-9171    

DOI:10.1063/1.1694826

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Scaling laws are derived which define the source parameters (temperature, pressure, and nozzle size) of all those nozzle flows that show the same condensation effects for a given gas or gas mixture.

ISSN:0031-9171    

DOI:10.1063/1.1694827

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The problem of temperature jump in a multicomponent gas mixture is considered and a variational result valid for the Boltzmann equation and arbitrary gas surface interaction law is given. From this general result, a particularly useful expression for the monatomic binary gas mixtures and Maxwellian diffuse specular reflection is deduced. Explicit results for the He‐Ar mixture are given by using the Lennard‐Jones potential. Generalizations to the polyatomic gases are also discussed.

ISSN:0031-9171    

DOI:10.1063/1.1694828

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The behavior of the unsteady laminar boundary layer induced by the incident shock wave passing over a flat plate mounted in a shock tube has been experimentally studied for shock speeds ranging from 2.35 to 7.34 km/sec by measuring unsteady heat transfer rates to the plate using thin‐film heat‐flux gages. Theoretical heat‐transfer rates were predicted from analytical solutions in the literature which describe the unsteady flat plate boundary layer development for equilibrium real‐gas flows. Experimental results obtained for both air and nitrogen were found to be in good agreement with the theoretical predictions.

ISSN:0031-9171    

DOI:10.1063/1.1694829

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Hydrodynamic propagators of forces are formulated and studied in the following cases: for uniform temperature, neglecting convection or using Oseen's linearization, with or without compressibility, and also for nonuniform temperature. Discussions and comparisons are given wherever possible. Such a propagator formalism is useful in cases of hydrodynamic interactions among solid bodies, as well as thermodynamic fluctuation forces. It is found that the velocity correlation functions describe a source with time‐dependent or ‐independent Oseen propagators. The correlation of pressure fluctuations, which exists even in the absence of dissipation, agrees with the result derived from the relaxation function of the mechanical fluctuation‐dissipation theorem, as well as with the thermodynamic equilibrium correlation. The correlation of temperature fluctuations describes a diffusion process of the variance&kgr;/&rgr;0cpwhencp = c&ngr;. In accordance with Curie's principle of nonequilibrium thermodynamics, it is found that the transverse vector field is not coupled to the scalar fields. Finally, a possible comparison with a wind tunnel experiment on temperature fluctuations is indicated.

ISSN:0031-9171    

DOI:10.1063/1.1694830

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An equilibrium is called&sgr;stable if growth faster than exp(&sgr;t)does not occur. On the basis of this definition a modified energy principle is obtained by means of which the stability of plasma confinement systems can be tested for times of thermonuclear interest, instead of the infinitely long times which are pertinent to the usual stability analysis. The theory is applied to the diffuse linear pinch, a theorem for&sgr;stability is derived, and the connection with the normal‐mode analysis is shown to be given with the Sturmian property, which holds for the unstable side of the spectrum, whereas the stable side consists of Sturmian and anti‐Sturmian point spectra separated by continuous spectra. Growth rates and eigen‐functions of Suydam modes are numerically calculated, and it is shown that violation of Suydam's criterion in the high and intermediate shear case leads to nonlocalized rapidly growingm = 1modes. Consequently, this criterion obtains new relevance in the&sgr;‐stability analysis for this regime.

ISSN:0031-9171    

DOI:10.1063/1.1694831

出版商:AIP    

年代:1974

数据来源: AIP