摘要:

The problem of centrifugal instability of the laminar boundary layer over a concave wall is posed as one of convective instability penetrating in neutrally stable fluid. It is found that the perturbations have a finite wavenumber; the mechanism of penetration is therefore essential for the selection of the shape of the perturbations. The critical conditions for a number of boundary‐layer‐like profiles are computed and compared with the experimental results. It is found that the stability characteristics of the boundary layer depend on the presence of points of inflection in the velocity profile.

ISSN:0031-9171    

DOI:10.1063/1.1693501

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The finite‐amplitude Be´nard convection problem is investigated by numerical integration of the rigid‐boundary Boussinesq equations in two and three space dimensions. Solutions are obtained for a wide range of Prandtl numbers and at moderate Rayleigh numbers for which the flow is observed to approach a two‐dimensional steady state. Detailed quantitative comparisons are made with experimental data in an effort to explain the observed increase of cell wavelength with Rayleigh number and to determine the effect of changing cell size on the heat transport. The three‐dimensional model shows good evidence of being able to yield realistic values of the cell wavelength, while the two‐dimensional models yield wavelengths that are much too short. These results strongly suggest that the increase in wavelength is determined by a three‐dimensional transient process, while the convection tends to a two‐dimensional steady state. The increase in cell size is shown to be responsible for a substantial part of the discrepancy between previous theoretical‐numerical and experimental determinations of Nusselt number. It also provides a plausible explanation for the experimentally observed dependence of heat transport on Prandtl number.

ISSN:0031-9171    

DOI:10.1063/1.1693502

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The stability of a flow consisting of solid body rotation superposed on an entrance‐type pipe flow profile is investigated experimentally. Increasing the swirl ratios from zero to four reduced the axial Reynolds number at which laminar flow breaks down from 2500 to 900.

ISSN:0031-9171    

DOI:10.1063/1.1693503

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A method, which was originally developed for predicting the pressure field on the walls of a two‐dimensional venturi in a mild cavitating flow, has been extended to predict the pressure distribution on the surface of a sphere. The method takes into account the effects of many cavitating bubbles. Several postulates based on the experimental observations of others, make it possible to obtain a formula for the pressure on the surface of the sphere resulting from the cavitating bubbles. A statistical approach is used which bears resemblance to techniques utilized in the kinetic theory of gases. The pressure on the surface of the sphere is taken to be an expected value and, therefore, requires the evaluation of an integral. However, before the integral can be evaluated, the one‐bubble distribution function must be specified. The objective of the work is to develop an approach to the problem of predicting the pressure distribution on a submerged body in a low‐degree cavitating flow.

ISSN:0031-9171    

DOI:10.1063/1.1693504

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements of the density and rotational temperature profiles about a disk normal to a cold nitrogen flow are presented for three free‐stream conditions:M∞=4.2, Re∞D=210; M∞=6.2, Re∞D=125;andM∞=9.6, Re∞D=150. The bow region was surveyed using the electron beam method. Disk support was by four free molecular wires oriented at 45° to the beam and optical axes. The shock regions are found to be diffuse and of a form closer to the free molecular solution than to the continuum limit. Essentially full rotational temperature recovery is observed at the stagnation point whereas the maximum shock layer density is slightly below the Rankine‐Hugoniot value. It appears that the viscous interaction parameter provides a useful measure of transition flow effects.

ISSN:0031-9171    

DOI:10.1063/1.1693505

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effect of an applied magnetic field on the instability of a laminar, free boundary layer formed between two parallel streams of semi‐infinite extent has been studied. It is shown that the stabilizing effect of the magnetic field does not give rise to any minimum critical Reynolds number. The fluid is assumed to have infinite electrical conductivity.

ISSN:0031-9171    

DOI:10.1063/1.1693506

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Solutions representing axially symmetric hydromagnetic equilibria with spherical plasma‐vacuum interfaces are extended from a low‐pressure paramagnetic regime to a high‐pressure diamagnetic regime.

ISSN:0031-9171    

DOI:10.1063/1.1693507

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Some similarities between ion waves in plasmas and gravity waves in incompressible fluids are investigated. It is shown that for zero ion temperature the ion‐wave dispersion relation is similar to that of gravity waves in a stratified liquid between rigid, horizontal walls; for large wavelength the ion waves behave as the surface gravity waves of shallow‐water theory. The general character of the pattern of ion waves arising in steady plasma flows is analyzed for arbitrary ion temperature, wavelength, and acoustic Mach number (which is based on the ion‐acoustic speed), and is compared to the pattern of surface gravity waves in steady water flows when surface tension is taken into account.

ISSN:0031-9171    

DOI:10.1063/1.1693508

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

It is shown that a high‐frequency field, with a frequency close to the electron plasma frequency and a strengthlessthan that required to excite parametric instabilities, can be used to externally control, in a very significant way, the frequency and damping of ion waves in a plasma.

ISSN:0031-9171    

DOI:10.1063/1.1693509

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The expansion of a semi‐infinite, uniform plasma into a vacuum is studied by computer simulation. The solution resembles an analytic similarity solution except for a discontinuous front that precedes the plasma at a velocity of about3(kT /mi)1/2. Thus, previous speculation that the initial burst of ions would be accelerated to velocities comparable to that of the thermal velocity of the plasma electrons on the basis of a fluid model alone is found to benotvalid.

ISSN:0031-9171    

DOI:10.1063/1.1693510

出版商:AIP    

年代:1971

数据来源: AIP