摘要:

A sequential‐spark schlieren system with cylindrical‐lens camera was used to trace the history of transition from laminar to turbulent flow on a cylindrical model in a Mach number 1.96 air stream. Both smooth and rough models were tested at several Reynolds numbers per unit length. The results showed that transition in a supersonic stream starts with high‐frequency disturbances in the laminar boundary layer which degenerate into areas of turbulent flow. These spots erupt independently near the trailing face of the turbulent‐flow region which is always moving downstream. The addition of the newly turbulent areas of finite size to the trailing face of the turbulent‐flow region causes it to jump upstream discontinuously. Spots are traveling at a very low velocity when they first become visible and accelerate to continue downstream at a velocity of about 0.7 times free‐stream speed at their trailing face. The origin of the fresh areas of breakdown to turbulence is apparently in amplified Tollmien‐Schlichting waves. The frequency of spot production lies within the region where stability theory predicts that disturbances within the boundary layer will be amplified. It is concluded that transition mechanisms in supersonic flow are similar to those in a subsonic air stream.

ISSN:0031-9171    

DOI:10.1063/1.1706110

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The earlier theory of the growth of vapor bubbles in superheated liquids is extended to the situation in which the rate of temperature rise of the liquid is large. Numerical solutions are presented for the early stages of bubble growth for various rates of liquid temperature rise. The asymptotic behavior of a bubble is found explicitly for a temperature rise of the liquid which is linear in time. In this case the bubble radius grows initially ast½, as in asymptotic solutions found previously for small rates of temperature rise, but then deviates toward a latet32variation.

ISSN:0031-9171    

DOI:10.1063/1.1706111

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The classical theories of condensation and coagulation are considered as limiting cases of a general theory of new phase formation. By making several assumptions concerning the nature of the vapor and of the cooling process, it is shown that the equation of condensation can be written in a simplified dimensionless form. The embryo size spectrum function at the end of the condensation process is a function of a number of dimensionless groups; hence, condensation can be modeled in the sense that particle size can be controlled by varying certain scale factors. An application to condensation by mixing of a hot vapor with cool air is proposed.

ISSN:0031-9171    

DOI:10.1063/1.1706112

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The relativistic Rankine‐Hugoniot shock wave conditions of Taub are extended to include radiation pressure and energy density. Specialization to the situation of a nonrelativistic ambient gas gives strong shocks, and solutions are obtained separately for the cases of a pure material gas and a pure radiation gas behind the shock. The material gas is considered to have a constant adiabatic exponent &ggr; ≤ 2, or to be itself relativistic, and the value&ggr;=43gives the radiation gas results. The rest density compression increases above its nonrelativistic strong shock limit (&ggr; + 1)/(&ggr; − 1), by a term proportional to &bgr;2in the lowest order, where &bgr; is the ratio of shock velocity to light velocity. As &bgr; → 1 (extreme relativistic strong shock) the rest density compression goes as 1/(1 − &bgr;2)½, but there is no setting‐in of degeneracy in the shocked gas. In shock coordinates, the flow velocity ratio across the shock (front to back) decreases monotonically from its nonrelativistic limit and approaches the value 1/(&ggr; − 1) as &bgr; → 1. An expression is also obtained for the velocity of relativistic sound wave propagation in a mixture of a thermally perfect material gas and a radiation gas.

ISSN:0031-9171    

DOI:10.1063/1.1706113

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A steady planar detonation wave, considered to be a shock wave followed by a reaction zone, is studied with both irreversible and reversible first‐order reaction kinetics. A perturbation solution with first‐order transport effects, valid in the reaction zone for those cases where the ratio of the characteristic collision time to the characteristic chemical time is small compared to one, is presented with sample calculations of temperature and concentration distributions for typical irreversible and reversible reaction cases. Analysis of the solution shows that simple series solutions and hence the given perturbation solutions do not hold near the hot boundary for all possible final Mach numbers. In the irreversible reaction case, the perturbation solution is a valid approximation for final Mach numbers less than (1 −B)½, whereBis the ratio of characteristic times, the approximation becoming less accurate as the Mach numbers tend toward this limiting value. In the reversible reaction case, the perturbation solution is a valid approximation for final Mach numbers up to the Chapman‐Jouguet value of unity, if the Mach number is based on the equilibrium speed of sound.

ISSN:0031-9171    

DOI:10.1063/1.1706114

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The integrals required for the calculation of transport properties for gases are carefully examined, assuming that the intermolecular potentials vary inversely as a power of the separation, &PHgr; = −c/rn. When the potential corresponds to mutual attraction, the behavior at the origin, corresponding to the centers of the two molecules colliding, must be prescribed because some trajectories of the relative motion reach the origin. Calculations are made on the basis of three models: (a) A rigid core corresponding to the Sutherland potential in the limit that the rigid core approaches zero (for spherical models this is the most realistic model); (b) a transparent core model which corresponds to the limiting behavior of a well‐shaped potential; and (c) a random‐scattering core model which is an appropriate idealization for molecules without spherical symmetry. The behavior of the collision integrals is considered for the full range of potentials asngoes from one to infinity (or from the Coulomb to the rigid‐sphere potential).

ISSN:0031-9171    

DOI:10.1063/1.1706115

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

If −cr−nis the intermolecular potential for separationr, bthe classical collision parameter, &mgr; the reduced mass,gthe relative velocity before collision, and &khgr; the angle of deflection of the relative velocity due to collision, it is found that&khgr;=−t=1∞&Ggr;(12nt+12)&Ggr;(12)t!&Ggr;(12nt−t+1)2c&mgr;g2bnt,the series converging only forb>b0, where &mgr;g2b0n= ½nn/2(n− 2)1−n/2, this being true both forcpositive (attractive potentials) andcnegative (repulsive potential). This result makes it possible to calculate, by analytic integrations, the contributions to the elementary collision integrals from the rangeb>b0. It also simplifies greatly the calculation of the collision integrals for both attractive and repulsive inverse power potentials which can be evaluated entirely by analytic means, forn> 2.

ISSN:0031-9171    

DOI:10.1063/1.1706116

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A fluid of rigid spheres in equilibrium is considered from a viewpoint which allows the deduced equation of state to reflect very sensitively the accuracy of two approximations to the triplet distribution function. Specifically, these approximations are: (1) the usual Kirkwood superposition scheme, and (2) assumption that the correlation of excess particles near a fixed particle pair is additively composed of the excesses induced individually by each member of the pair (linear correlation field hypothesis). Granted only these hypotheses, each in turn, the rigorous statistical mechanical relations between rigid‐sphere distribution functions and the thermodynamic pressure and compressibility lead unambiguously to nonlinear first‐order differential equations for the pressure as a function of density. The simply obtained numerical solutions clearly demonstrate that assumption (1) is considerably superior to (2).

ISSN:0031-9171    

DOI:10.1063/1.1706117

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The methods of Mott‐Smith and Rosen for the shock structure problem are correlated. It is found that the application of Rosen's restricted variational technique to the Boltzmann equation yields the transport equation used by Mott‐Smith, and in addition determines a transport function. The expression for the average translational temperature profile, as derived by Mott‐Smith, is examined for the existence of relative minima or maxima. For a monatomic gas the temperature profiles have no relative extrema inside the shock wave for any Mach number. For a diatomic gas the temperature profiles are smooth for Mach numbers below 1.89, but above that a hump appears.

ISSN:0031-9171    

DOI:10.1063/1.1706118

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The thermal conductivity of liquid He II in the interstices of a column of packed jeweler's rouge (Fe2O3powder) has been found to have a temperature dependence:k∝Tn, wherenfalls monotonically from a value of 13 at 1.5°K to possibly zero at the lambda point. The value of the thermal conductivity at the lambda point is 0.60 ± 0.03 w/cm°K. From the flow of helium, nitrogen, and water at room temperature it is estimated that a typical rouge column provides the equivalent of about 1.4 × 109parallel channels having an average diameter of 0.18 ± 0.02&mgr;. The viscosity of the normal component of He II, computed from the measured conductivity on the basis of the two‐fluid model, follows a temperature dependence very similar to that observed for the bulk liquid and for 52‐and 108‐&mgr; capillaries above 1.9°K. The magnitude of the values, however, is lower, but in agreement with that obtained in Leiden with 0.7‐&mgr; slits. Empirical values of a correcting slip coefficient are smaller in magnitude (0.007&mgr;) and less temperature dependent (−0.018&mgr;/°K) than theoretical values calculated at Oxford. It was not possible, though, to rule out a phonon mean free path effect of the order of magnitude calculated by Atkins. Points on the lambda line have been determined from the fountain effect for pressures below 0.4 atm. The slope of the line is approximately −70 atm/°K, in agreement with the slope determined at higher pressures by other means.

ISSN:0031-9171    

DOI:10.1063/1.1706119

出版商:AIP    

年代:1960

数据来源: AIP