摘要:

The mechanics of collisions between molecules in front of a sphere moving at hypervelocity through a rarefied atmosphere are analyzed. The study is concerned with the ``transitional'' regime in which molecules emitted by the surface begin to shield the body from the oncoming Newtonian stream and the net drag decreases from its free‐molecular value. It is found that a simplified but physically significant model can be formulated, and that it leads to a dependence of the drag coefficient on two transition parameters. These can be interpreted as the Reynolds number and the surface‐to‐free stream temperature ratio. The predictions of this theory agree qualitatively and in order of magnitude with observations.

ISSN:0031-9171    

DOI:10.1063/1.1705880

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The interaction of cylindrical sound waves with a stationary shock is investigated by a method analogous to that used by H. Weyl in his treatment of the propagation of radio waves over the surface of a plane earth. The incident cylindrical sound wave is represented as a superposition of plane sound waves of varying direction. Each of the plane waves in this superposition interacts with the shock giving rise to a previously determined distortion of the shock front and reflected or refracted wave field; the cylindrical wave causes a disturbance which may be written in integral form as a superposition of these plane waves. The resulting interaction integrals are evaluated asymptotically to give explicit formulas for the distortion of the shock, the sound field, and the entropy‐vorticity wave.

ISSN:0031-9171    

DOI:10.1063/1.1705881

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A semiacoustic theory of blast energy propagation, incorporating Sachs' scaling modified for altitude of observation, gives excellent agreement with experiments, providing Hilliar's similarity principle is restricted to similar ambient (weather) conditions. Comparisons between this theory and experiments are made for free air (no reflections) blast pressures; ground‐level blast pressures in an isothermal, still atmosphere; and blast pressures under a linear temperature inversion.

ISSN:0031-9171    

DOI:10.1063/1.1705882

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The exact solution of the sixth‐order differential equation which governs the stability of a viscous fluid contained between two rigid walls and heated from below is briefly reviewed and extended to include detailed results on the curve of neutral stability and the cell pattern at the onset of instability. Two approximate methods of solution are then discussed which employ a Fourier or Fourier‐type expansion and which require the solution of only a fourth‐ or a second‐order differential equation. A comparison of these approximate results with the exact solution gives some insight into the relative accuracy of these methods when applied to other more general problems for which an exact solution cannot be obtained.

ISSN:0031-9171    

DOI:10.1063/1.1705871

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A three‐point correlation equation is used to obtain a relation for the triple correlations applicable at times before the final period. In this case the equation is made determinate by neglecting the quadruple correlations. Higher order approximations, valid at still earlier times, could be obtained by considering four‐ or five‐point correlation equations. In each case the set of equations is made determinate by neglecting the highest order correlation. Only two‐ and three‐point correlation equations are considered here. The correlation equations are converted to spectral form by taking their Fourier transforms. Expressions are obtained for the energy transfer function, which describes the transfer of energy from large to small eddies, and for the energy spectrum function which gives the contributions of the various eddy sizes to the total energy. By integrating the energy spectrum over all wave numbers (or eddy sizes), the following energy decay law is obtained:u2=A(t−t0)−5/2+B(t−t0)−7,whereu2is the mean square of the velocity fluctuation,tis the time, andA, B, andt0are constants determined by the initial conditions. For large times the last term becomes negligible leaving the well‐known −5/2 power decay law for the final period. Comparison of the decay law with experimental data indicates good agreement for times considerably before, as well as during, the final period.

ISSN:0031-9171    

DOI:10.1063/1.1705872

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A kinetic theory of moderately dense gases is developed. The theory is based on a modified Boltzmann equation, which takes into account the ``collisional transfer'' of momentum and energy. The theory applies to pure gases made up of spherical molecules, and the effect of multiple collisions is neglected. The Boltzmann equation is solved by a perturbation method which is applicable near equilibrium. Expressions for the flux coefficients, i.e., the thermal conductivity, bulk, and shear viscosity are obtained from this solution and these are in turn evaluated for a rigid sphere potential.

ISSN:0031-9171    

DOI:10.1063/1.1705873

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The customary density power series expansions of potentials of average force and distribution functions are converted into a new class of expansions, defined in terms of topological nodes. The physical meaning of the terms in the new expansions is discussed, and arguments are presented to show that the new expansions can be expected to converge considerably more rapidly than the customary density expansions. The probable occurrence of phase transitions is discussed. Possible further developments are suggested. The Kirkwood superposition approximation is shown to be valid for a large number of terms in the expansions of potentials of average force and distribution functions. The customary comparison of the exact value of the third virial coefficient with that obtained via the Kirkwood superposition approximation is shown to provide no proof of the validity or invalidity of the latter.

ISSN:0031-9171    

DOI:10.1063/1.1705874

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The flow field of a two‐dimensional Bunsen flame is examined by approximating the zone of combustion by a surface of discontinuity across which the density drops and normal velocity increases. Even though the flow of unburned gases is potential, the flow of the burned gases is always rotational and is therefore not amenable to complete analysis. Interaction of flame shape and flow field is obtained analytically and experimentally. The entire flow field of unburned and burned gases is mapped by taking stroboscopic photographs of small particles suspended in the combustible gases. The measured flow field is considered in the light of the above analysis.

ISSN:0031-9171    

DOI:10.1063/1.1705875

出版商:AIP    

年代:1958

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1705876

出版商:AIP    

年代:1958

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1705877

出版商:AIP    

年代:1958

数据来源: AIP