摘要:

A modification of the Korteweg‐deVries equation is found to describe weak dissipation in long waves in a swirling fluid. General features of solutions are discussed, and the solution for the damping of solitary waves is presented.

ISSN:0031-9171    

DOI:10.1063/1.1693373

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The anomalous laws of wave reflection from a rigid plane surface in an inviscid, rotating, stratified Boussinesq fluid are due to the anisotropic feature of the wave motion. The singularity of the reflection process in the inviscid linear analysis, where the reflected wave amplitude becomes very large when the ray of the reflected wave is nearly parallel to the reflection boundary, is studied for the limiting cases by considering viscous boundary effect on wave motion. As the angle that the reflected wave (ray) makes with the wall becomes very small, the effect of boundary layer on wave reflection becomes significant. In the nonsingular case, the boundary layer thickness is∼R−1/2whereR ( = n/&ngr;&kgr;2)is the wave Reynolds number. A thicker boundary layer,R−1/3is needed for the critical wave reflection and only within this layer is singularity removed. Two‐dimensional waves were generated in the laboratory by vertically oscillating a small wave‐making flap inside a clear Plexiglas container. The wave properties are determined by observing the motions of aluminum particles suspended in the working fluid. Some predictions have been tested and confirmed.

ISSN:0031-9171    

DOI:10.1063/1.1693374

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements of spatial absorption coefficients in shallow water are presented. The smallest depth was 2.3 times the thickness of the boundary layer. Basset's determinant was evaluated exactly. From the resulting equation, the spatial coefficient was found directly. This direct approach made it possible to calculate theoretical values for small depths. The measured values agreed with the theoretical values within the rather large experimental error.

ISSN:0031-9171    

DOI:10.1063/1.1693375

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Convection, production, diffusion, and dissipation of temperature fluctuations have been measured in the dynamically similar turbulent wake behind a headed circular cylinder 1140 diameters downstream from the cylinder at a Reynolds number of 960. The measurements show strong production and dissipation and moderate convection and diffusion. In addition, the dependence of one‐dimensional spectra of temperature fluctuations on wake parameters and the skewness of the temperature derivative have been measured for the Reynolds number range 440‐69 000. All measurements are consistent with the assumption of local isotropy except for the skewness of the temperature derivative.

ISSN:0031-9171    

DOI:10.1063/1.1693376

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The structure of a turbulent gas flow may be probed by analyzing scintillations of a laser beam which has traversed the turbulent medium. This technique is used to measure the spectrum of neutral gas turbulence in a pipe flow where the gas is nonuniformly heated and weakly ionized by an electrical discharge. First, the usual isotropic analysis relating the spectrum of light scintillations to the fluid turbulence is extended to include strong anisotropy as is appropriate in the present case. Second, the gas turbulence spectrum revealed by the scintillation, as well as by a hot film anemometer, is compared with the spectrum of plasma density fluctuations. It is found that the scale size of the neutral gas turbulence is larger than the scale size of the plasma density fluctuations by a factor of 2 for a case in which the plasma column is constricted to a considerably smaller diameter than the pipe. This indicates that whenever the plasma production process is constricted to dimensions smaller than the gas turbulence scale size, then the spectrum of wind‐driven plasma fluctuations will not be representative of the background gas turbulence.

ISSN:0031-9171    

DOI:10.1063/1.1693377

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The results of an experiment, conducted to determine the turbulent structure of the flow due to a rotating disk, are presented. Mean velocities, turbulent intensities, and one Reynolds stress component are measured. A scalar eddy viscosity coefficient is calculated from the measurements and used to determine the other Reynolds stress components using Boussinesq's model. This coefficient will also permit the numerical integration of two boundary‐layer‐type equations describing this flow. It is shown that the eddy viscosity in the turbulent boundary layer generated by the disk rotation is substantially larger than that of the turbulent boundary layer over a flat plate.

ISSN:0031-9171    

DOI:10.1063/1.1693378

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The model neutral exosphere with a uniformly rotating exobase is generalized by allowing variations in exobase density and temperature which characterize the thermosphere just below the base. The corresponding velocity distribution function, satisfying the collisionless Boltzmann equation, is constructed and used to form a general expression for the velocity moments. Resulting density profiles of rotating exospheres with nonuniform densities and temperatures on the exobase are compared with corresponding nonrotating exospheres. Density enhancements due to rotation are found to be greatest above regions of exobase density or temperature minima. Equatorial density enhancements of terrestrial hydrogen, resulting from rotation, are estimated to be 15%‐17% at altitudes of 10‐20 earth radii. Corresponding increases in terrestrial helium are 30%‐50% on the equator at altitudes of 0.7 to 1 earth radii even when there is a polar density bulge in the barosphere.

ISSN:0031-9171    

DOI:10.1063/1.1693379

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Simple and accurate expressions for the velocity slip coefficient and the diffusion slip velocity are obtained by applying a variational technique to the linearized Boltzmann equation for a multicomponent gas mixture.

ISSN:0031-9171    

DOI:10.1063/1.1693380

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The axial rotational temperature distribution in an underexpanded nitrogen jet emitted from a sonic orifice has been investigated. The expansion is from room temperature and the gas possesses negligible vibrational energy. The observed difference between the rotational temperature measured with an electronbeam probe and the isentropic value can be described by a rotational relaxation analysis. The governing flow equations were integrated numerically by the classical fourth‐order Runge‐Kutta method. The rotational relaxation time developed by Lordi using Wang Chang and Uhlenbeck's formal kinetic theory and Parker's molecular model was employed. Both the easy and difficult energy transfer cases were investigated and the easy case was shown to underestimate nonequilibrium affects. The numerical solutions were very sensitive to the separation between the repulsive force centers, for both energy transfer cases. The rotational temperature distributions obtained in this study are in general agreement with existing experimental data for nitrogen.

ISSN:0031-9171    

DOI:10.1063/1.1693381

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A combined analytical and experimental investigation of rapidly expanded CO2laser mixtures is described. Study of the vibrational kinetics indicates that population inversions with high vibrational energy density can be produced at high pressures by utilizing low (starved) concentrations of CO2. Scaling laws for predicting the gain of starved systems are developed. A description is given of gain measurements carried out using a CO2laser to probe the flow in a nozzle at the point where the Mach number is approximately four. Population inversions at static pressures as high as about 1 atm have been observed and found to be in reasonable agreement with predictions.

ISSN:0031-9171    

DOI:10.1063/1.1693382

出版商:AIP    

年代:1971

数据来源: AIP