摘要:

A rate equation is proposed to govern the variation of the effective turbulent viscosity. The effects of generation, convection, diffusion, and decay are each represented by appropriate terms leaving only two empirical constants to be determined by experiment. This rate equation together with the equations of motion form a closed system applicable to quasiparallel turbulent shear flows. For an incompressible turbulent boundary layer with zero pressure gradient, solutions were obtained by assuming local similarity and a linear growth of the boundary‐layer thickness. Another problem, the turbulent‐nonturbulent interface at the outer edge of the boundary layer was treated by using the further assumption that the large scale motion of the interface has no significant contribution to the Reynolds stress. It can be shown that for a nearly homogeneous domain, Prandtl's mixing length theory is a limiting case of the present theory.

ISSN:0031-9171    

DOI:10.1063/1.1692510

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The equation for the one‐point turbulent distribution function is closed by assuming a relaxation model for the pressure fluctuation term and several other less critical approximations. The resulting equation is solved for a class of rectilinear flows and for decay of a periodic wake. Good agreement with available experiments is found. A theory of turbulent transport coefficients is derived in a certain approximation.

ISSN:0031-9171    

DOI:10.1063/1.1692511

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The Navier‐Stokes equations for incompressible rotationally symmetric vortex flow at high swirl and large core Reynolds number are shown to approximate to the equation of inviscid rotating flow in regions where axial gradients are large. This equation becomes linear for flow originally near the axis, where rigid rotation results from viscous action. Series solutions at high supercritical swirl values near the critical one under the condition of flow retardation near the axis are found to exhibit the experimentally observed features of vortex breakdown flows: bulges of decelerated flow, or bubbles of recirculating fluid, with reversed axial and swirl velocities near the axis. It is concluded that the vortex breakdown in vortex tubes and on delta wings is neither due to hydrodynamic instability, nor is it a phenomenon akin to the hydraulic jump. Rather it is a regular feature of the solution of the equations of motion under the given conditions.

ISSN:0031-9171    

DOI:10.1063/1.1692512

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The onset of convection, in a water layer continuously formed by melting ice from above, has been obtained by the experimental determination of the water layer depthdat which the mode of heat transfer changes from conduction to convection. This was accomplished both by determining the time at which the temperature profile of the water layer started to deviate from linear distribution and by locating the inflection point in the curve relating water‐ice interface position and time. Experimental values ofd(either for melting from above or below) were found with a mean deviation of 14.1% from those by theoretical analysis of a similar problem. From the present and previous investigations [Phys. Fluids 11, 1263 (1968)], it can be concluded that the critical Rayleigh number for a horizontal layer of fluid with a density inversion is not a single value as for a normal fluid with a monotonic density‐temperature relationship, but varies with boundary temperatures.

ISSN:0031-9171    

DOI:10.1063/1.1692513

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Several new similarity solutions are presented for the laminar compressible boundary layer with reverse flow for Prandtl numbers of 1.0 and 0.723. New solutions without reverse flow are presented for Prandtl number equal 0.723. Wall‐to‐stagnation temperature ratios from 0 to 2 are considered. These solutions quantitatively show the effects of pressure gradient, and wall heat transfer on the wall shearing stress and enthalpy gradient.

ISSN:0031-9171    

DOI:10.1063/1.1692514

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The process of thermal choking of a subsonic flow of a grey, ideal gas by absorption of thermal radiation from an upstream source is analysed. The flow may be considered produced by a shock. Calculations for streamwise variation of flow properties are presented, and, for the radiation‐dominant case, an initial transparent process, a final Rosseland process and a matching solution are found analytically. A simple model is given for finding the radiation source temperature required to produce choking.

ISSN:0031-9171    

DOI:10.1063/1.1692515

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is found that the elasticity in the liquid cannot only destabilize the flow, but it can also stabilize the flow for certain values of depth ratio, viscosity ratio, and elasticity ratio. The stabilizing or destabilizing effect of the elasticity in liquid is absent in the absence of viscosity stratification, and is only brought about when the viscosity varies.

ISSN:0031-9171    

DOI:10.1063/1.1692516

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The phenomenological description of transport processes in a fluid composed of molecules or particles which are orientable is reformulated so as to render it capable of distinguishing between and determining the form of the distribution of orientation. With orientation variables playing the role of continuously distributed parameters suitable for tensorial labeling of multicomponent species, equations for the transport of mass, momentum, energy, and angular momentum in the position‐orientation hyperspace are independently derived by continuum and statistical mechanical arguments. The selection of the point of location of a particle is shown to have an important bearing upon the transport equations of physical space obtained by orientation averaging. Linear constitutive relations are established by means of thermodynamic arguments which suggest anisotropic thermal conductivity and viscosity as well as a coupling tensor each dependent for its anisotropy upon the polyadic (polarization) moments of the distributions. The rotational and translational diffusion fluxes are predicted to be governed by rotational, translational, and coupling multicomponent diffusion tensors, thermal diffusion tensors, and by the analogous shear diffusion tensors. The special case of dilute solution theory is examined and the thermodynamic predictions of generalized transport laws reaffirmed by appeal to component (orientation specific) balances of linear and angular momentum.

ISSN:0031-9171    

DOI:10.1063/1.1692517

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The linear Boltzmann equation for molecules with power‐law potentials is considered. The contribution of small scattering‐angle collisions is approximated by a Fokker‐Planck operator. Within this approximation, it is shown that the spectrum of the collision operator is discrete forp > 4/3and it contains a continuum forp ≤ 4/3, where p is the index of power‐law potentials.

ISSN:0031-9171    

DOI:10.1063/1.1692518

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The normal magnetic field configuration of aQdevice has been modified to obtain a “magnetic Laval nozzle.” Continuous supersonic plasma “winds” are obtained with March numbers∼3. The magnetic nozzle appears well suited for the study of the interaction of supersonic plasma “winds” with either material or magnetic obstacles.

ISSN:0031-9171    

DOI:10.1063/1.1692519

出版商:AIP    

年代:1969

数据来源: AIP