摘要:

An experimental investigation of small‐scale atmospheric turbulence is presented. Airborne measurements were made in the vicinity of the meterological tower of Brookhaven National Laboratory. Hot‐wire probes mounted on the right wing tip of a Cherokee aircraft were used. The anemometer signals were recorded on an analog tape recorder in the aircraft after differentiation and filtering; they were digitized in the laboratory with a high‐speed analog‐to‐digital converter, and recorded on magnetic tape. All data were processed with an IBM‐360. A fast Fourier transform program was used to compute the spectra. The average Kolmogoroff constant computed from the small‐scale spectra was&agr; = 2.0. The cospectra and quadrature spectra of the small‐scale turbulence were virtually zero. The skewness and kurtosis of∂ui/∂x(the derivative of a velocity vector with respect to the coordinate in the direction of aircraft heading) ranged from ‐0.03 to ‐0.50 and from 4.5 to 14, respectively, at Reynolds number(R&lgr;)from 2280 to 5330. The spectra of(∂ui/∂x)2were found to exhibit a ‐0.3 power law in the inertial subrange. The probability distribution of(∂ui/∂x)2was nearly a straight line in log‐normal coordinates.

ISSN:0031-9171    

DOI:10.1063/1.1693416

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A two‐dimensional turbulent wake superimposed upon a linearly stratified main stream has been examined. The buoyancy forces were negligibly small and the temperature could be treated as a passive scalar contaminant. Mean and fluctuating temperature and velocity distributions were measured across the wake and a self‐preserving analysis was developed for the growth of the thermal wake in terms of a length and intensity scale. The results showed that the maximum temperature defect increases in the streamwise direction as the wake spreads laterally.

ISSN:0031-9171    

DOI:10.1063/1.1693417

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Turbulent pipe and channel flow and turbulent plane Couette flow are studied by means of turbulent model equations first proposed by Prandtl.

ISSN:0031-9171    

DOI:10.1063/1.1693418

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Prandtl's two‐dimensional, time‐dependent similarity solutions are corrected and extended to cases ofN‐branched vortex sheets possessing a certain central symmetry. For bothN = 1(Prandtl's case) andN = 2it is found that the similarity parametermis restricted to the rangem ≤ 0.5. WhenN = 1, multiple solutions are found for a given value ofmprovided|m|is sufficiently small compared with one. A property of these multiple solutions is that the tangential velocity to the concave side of a vortex sheet is0[exp( −4&pgr;)smaller than the tangential velocity to the convex side. All values ofmare found to be admissible for the caseN = 3. In all cases it is found that certain features of the flows resemble a classical (but time‐dependent) circular vortex. For example, it is found that the circulation in a disk of radiusris proportional tor2. There are also important differences. The flow fields forN = 1, 2, and 3 are described in some detail.

ISSN:0031-9171    

DOI:10.1063/1.1693419

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The time varying flow through a pipe is analyzed. Separation velocity profiles obtained under the influence of periodic pressure fluctuations were evaluated. These velocity profiles are compared with relaxed and unrelaxed separation concepts. It is found that a one parameter correlation is too limited to cover all possivle separation cases. In particular, the unsteady unrelaxed separation extends over a relatively wide range of velocity distributions.

ISSN:0031-9171    

DOI:10.1063/1.1693420

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Using linear perturbation theory, the effect of a slightly viscous gas on the stability of a viscous jet is estimated. The gas flows in the direction of the jet axis. The perturbation in the gas is supposed to be governed by the equations for an inviscid, incompressible fluid, but the gas viscosity is taken into account to a first approximation by means of an energy balance. The method is shown to give correct answers for a viscous jet in a vacuum. For the case of uniform gas velocity the results agree with those of earlier work by Weber and by Levich. In this case the effect of the gas viscosity is very small. For nonuniform gas flow, using a logarithmic velocity profile, solutions are found for the two limiting cases in which the gas velocity is either large or small compared with the wave velocity. The results for these two limiting cases do not differ greatly from each other and predict that the gas flow has a substantial stabilizing effect on the jet when the gas velocity is large.

ISSN:0031-9171    

DOI:10.1063/1.1693421

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The stability of a steady, axisymmetric, laminar, primary flow composed of two fluids flowing concentrically in a straight circular tube is investigated by the method of small perturbations. Both asymmetric and axisymmetric disturbances to the primary flow are considered. It is demonstrated that, regardless of the size of the Reynolds number, no situations are encountered for which the primary flow is stable to both types of disturbances, simultaneously. The primary cause of instability is found to be the difference in viscosities of the two fluids.

ISSN:0031-9171    

DOI:10.1063/1.1693422

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The profiles as well as the speeds of supercritically stable surface waves are obtained for various values of surface tension, Reynolds numbers, and the angle of inclination of a falling liquid layer. The calculated values of wave speeds are in good agreement with Kapitza's measurements and the theoretically obtained wave profiles seem to resemble those appearing in his photographs. Profiles of “generalized solitary waves” which propagated at speeds several times that of the kinematic speed are also found.

ISSN:0031-9171    

DOI:10.1063/1.1693423

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The interaction between viscous stress and diffusion is examined through the use of the Chapman and Cowling method, and the results for a general binary mixture of monatomic gases is obtained. It is demonstrated that the kinetic theory calculation provides a first iteration to the form predicted by statistical mechanics; it also produces a modification in the barodiffusion coefficient that is in more general agreement with the results of the 13‐moment method than has been shown previously. Finally, the general equations are modified to permit description of a dusty gas or aerosol of fine particles, and the result is found to differ significantly from a calculation based on the methods of stochastic processes.

ISSN:0031-9171    

DOI:10.1063/1.1693424

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Transport cross sections and collision integrals are calculated over a wide range of energies and temperatures for the attractive and repulsive screened Coulomb potentials. Results accurate to 1% over the whole range from classical to quantum‐mechanical behavior are given in the form of numerical tables. Results of lower accuracy are given as analytical expressions.

ISSN:0031-9171    

DOI:10.1063/1.1693425

出版商:AIP    

年代:1971

数据来源: AIP