摘要:

A phenomenological theory is developed for Brownian motion in a flowing incompressible fluid. The Brownian particles are regarded as an ideal gas subject to a position‐ and time‐dependent force field that represents interactions with the host fluid. Ths approach immediately leads to deterministic partial differential equations of motion for the Brownian particles. These equations are then examined in the limit of large friction, in which they imply an expression for the diffusional mass flux of Brownian particles. This expression is a sum of terms representing concentration, forced, thermal, and pressure diffusion. Comparisons are made with earlier work, and with the corresponding expression for the molecular diffusion flux of one component in a binary ideal‐gas mixture. The Brownian and molecular diffusion fluxes are found to be identical in form, with the Brownian‐particle volume fraction corresponding to the molecular mole fraction.

ISSN:0031-9171    

DOI:10.1063/1.862818

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The behavior of small disturbances in a boundary layer flow is studied. The initial‐value problem is solved formally with Fourier–Laplace transforms, and an expression for the development of the velocity component normal to the wall is obtained. It is found that a disturbance evolves not only as discrete waves of the Tollmien–Schlichting type, but also has a portion described by a continuous spectrum. This portion is associated with a branch cut of the solution in the complex plane of the Laplace transform variable.

ISSN:0031-9171    

DOI:10.1063/1.862819

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An experimental comparison of grid turbulence performed in a wind tunnel and in a water tunnel is described. The measurements were made in the initial stage of decay with mesh Reynolds numbers ranging from 12 800 to 81 000. Hot‐wire and hot‐film instrumentation combining analog and digital computing methods were used to measure higher‐order correlations of the longitudinal component of turbulent velocity and higher‐order moments of longitudinal turbulent velocity gradients. A comparison of the latter is obtained for an increase in Reynolds number without having to alter the flow geometry. Apart from the intrinsic interest of such measurements in water, the results show the non‐Gaussian character of the turbulent fluctuation and compare the behavior of higher‐order moments of turbulent velocity gradients to theoretical considerations for the small scale turbulent structure.

ISSN:0031-9171    

DOI:10.1063/1.862820

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Converging shock waves generated by instantaneous energy release over cylindrical surfaces are investigated by an approximate method. The results agree with those of Bach and Lee when the shocks are near the cylindrical surfaces, while they are smoothly continued to Guderley’s solutions near the axis of the cylinder, thus appearing to represent the propagation of shock waves over a wide space in the intermediate region between the wall and the axis where neither Guderley’s solution nor Bach and Lee’s theory can be applied.

ISSN:0031-9171    

DOI:10.1063/1.862798

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A set of experiments has been performed which demonstrate that ’’hot spots’’ in an explosive control some aspects of the steady‐state detonation process. It is known, from experiments, that the relationship between explosive charge size and steady‐state detonation velocity (the ’’diameter‐effect curve’’) is qualitatively different for homogeneous and heterogeneous explosives. The experiments to be described strongly indicate that this qualitative difference is due to localized hot regions arising from flow modifications due to the presence of physical inhomogeneities. These local hot regions apparently produce an effective chemical reaction rate which allows a stable steady‐state flow at a much smaller charge size than is possible in an analogous homogeneous material. Detonation‐velocity measurements were carried out on cylindrical rate sticks at a number of radii thus generating diameter‐effect curves. The explosives studied were composed primarily of commercial‐grade nitromethane confined in Pyrex tubes. Silica impurities, with a known particle‐size distribution, were added to the nitromethane to produce a heterogeneous material. The silica impurities were held in suspension with a guar‐gum gelling agent. An attempt is made to interpret the new results by use of earlier numerical and experimental results concerning initiation of detonation at hot‐spots.

ISSN:0031-9171    

DOI:10.1063/1.862821

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The effect of massive blowing rates on the steady laminar hypersonic boundary‐layer flow of an electrically conducting fluid in the stagnation region of an axisymmetric body with an applied magnetic field has been studied. The governing equations have been solved numerically by combining the implicit finite‐difference scheme with the quasi‐linearization technique. It is observed that the effect of massive blowing rates is to remove the viscous layer away from the boundary, whereas the effect of the magnetic field is just the opposite. It is also found that the velocity overshoot increases with blowing rates and also with magnetic field. The effect of the variation of the density‐viscosity product across the boundary layer is strong only when the blowing rate is small, but for the massive blowing rate the effect is negligible.

ISSN:0031-9171    

DOI:10.1063/1.862822

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Similarity solutions for the propagation of cylindrical relativistic shock waves in the presence of a constant axial magnetic field for the medium, where the nucleon number density is uniform are obtained. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium or a cold gas.

ISSN:0031-9171    

DOI:10.1063/1.862823

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The Korteweg–de Vries equation is solved numerically by using the Fourier expansion method to clarify the recurrence of the initial state. A sufficiently accurate solution valid for large times as well as for small times is obtained. The solution does not show a clear recurrence.

ISSN:0031-9171    

DOI:10.1063/1.862824

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A model collision operator similar to the one first introduced by Chandrasekar is employed to obtain a kinetic equation for waves in a magnetized plasma that can be solved via a velocity Fourier transform technique.

ISSN:0031-9171    

DOI:10.1063/1.862825

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A formula is given for the energy of an arbitrary electrostatic or electromagnetic wave in a plasma which may be magnetized or unmagnetized, collisional or collisionless, and homogeneous or weakly inhomogeneous. The formula relates the energy of the wave to the magnitude of the electric and magnetic fields of the wave and derivatives of the frequency of the wave with respect to wavenumber and plasma parameters. This formula makes it possible to determine the energy of wave from its dispersion relation (and the magnitude of the fields). The derivation rests on a simple invariance property, related to dimensional analysis, of the Fokker–Planck equation, together with well‐known results from the theory of dispersive media.

ISSN:0031-9171    

DOI:10.1063/1.862799

出版商:AIP    

年代:1979

数据来源: AIP