摘要:

The drag coefficients for cylinders normal to the flow have been determined experimentally at Mach ∼2, Mach ∼4, and Mach ∼6 with Knudsen numbers extending from continuum conditions to free‐molecule‐flow conditions. The results indicate a smooth transition from inviscid values at low Knudsen numbers to free‐molecule‐flow predictions for diffuse reflection at high Knudsen number. Small departure theories which are applicable to the ``near free molecule flow'' regime are compared to the experimental data.

ISSN:0031-9171    

DOI:10.1063/1.1706736

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The stability of a liquid layer flowing down an inclined plane is investigated. A new perturbation method is used to furnish information regarding stability of surface waves for three cases: the case of small wavenumbers, of small Reynolds numbers, and of large wavenumbers. The results for small wavenumbers agree with Benjamin's result obtained by the use of power series expansion, and the results for the two other cases are new. The results for large wavenumbers, zero surface tension, and vertical plate contradict the tentative assertion of Benjamin. The three cases are then re‐examined for shear‐wave stability, and the results compared with those for confined plane Poiseuille flow. The comparison serves to indicate the vestiges of shear waves in the free‐surface flow, and to give a sense of unity in the understanding of the stability of both flows. The case of large wavenumbers also serves as a new example of the dual role of viscosity in stability phenomena.The topological features of thecicurves for four cases (surface tension = 0 or ≠ 0 and angle of plate inclination = or <½&pgr;) are depicted. The effect of variability of surface tension is briefly assessed.

ISSN:0031-9171    

DOI:10.1063/1.1706737

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Transition reversal—the sometimes observed decrease in transition Reynolds number with surface cooling—has been thought to be other than a Tollmien—Schlichting instability phenomenon since it could not be reconciled with the results of the Dunn and Lin calculations of the temperatures required for complete stabilization of supersonic flat plate boundary layers. Recent theoretical developments in the stability of compressible boundary layers to Tollmien—Schlichting waves, however, point out the importance of considering in the analysis the hitherto neglected temperature fluctuations and thermal boundary condition. Accordingly, the temperatures required for complete stabilization of flat plate boundary layers to both two‐and three‐dimensional disturbances have been recomputed. The new required temperatures are all below the Dunn—Lin values. In the usual diagram of surface temperature vs stream Mach number there are two loops of complete stability. The trends suggested by this diagram tend to substantiate the experimentally observed transition reversal phenomenon. The results are compared with available wind tunnel and flight data.

ISSN:0031-9171    

DOI:10.1063/1.1706738

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The theory of a probe to measure local atom concentrations in hypersonic flows of a dissociated gas at low densities is presented. The probe operates on a principle of measuring the differential heat transfer between catalytic and noncatalytic gauges immediately adjacent to one another on the stagnation line of a cylindrical model. The theoretical performance of the probe in the free molecule, the viscous shock layer, and the boundary layer regimes, respectively, is considered. It is shown that the probe cannot be operated successfully in the free molecule regime, except under unusual circumstances. In continuum flow, it is shown that under those conditions necessary for the atoms in the free stream to reach the surface of the probe (chemically frozen shock layer and boundary layer), we are always working in the viscous shock layer regime. Accordingly, it is this flow regime in which the probe measurements can be interpreted readily. The results of detailed calculations which relate to the application of this probe to measure local atom concentrations in nonequilibrium, hypersonic nozzle flows are presented.

ISSN:0031-9171    

DOI:10.1063/1.1706739

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A solution to the problem of the flow at low Reynolds number of a dissociated gas about a catalytic probe has been obtained using the method of inner and outer expansions. The solution gives the atom concentration distribution about the probe as a function of the Reynolds number based on diffusion and the parameterK=kw′a/D, wherekw′ is the effective speed of the surface reaction,Dis the diffusion coefficient, andathe radius of the probe. It is shown that, from a measurement of the heat transfer to the probe and an independent measurement of the free stream atom concentration, one can establish the catalytic efficiency of the surface whenK« 1 and the diffusion coefficient whenK» 1. Conversely, knowing either the diffusion coefficient or the catalytic efficiency, the probe may be used to determine atom concentrations. The results of the theory are used to establish experimental conditions in a glow discharge facility under which the sought data may be obtained. Plots of valid operating regimes of this facility are presented as examples.

ISSN:0031-9171    

DOI:10.1063/1.1706740

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The problem of spontaneous ionization (i.e., no externally applied electromagnetic fields, nor hard radiation) in the reaction zone behind strong normal shock waves in air has been treated concurrently with the problem of dissociation and vibrational relaxation. Through a comparison of specific ionization rates, one may conclude that up to a shock velocity of 9 km/sec (about 27 times the speed of sound at room temperature), the predominant electron production process would be atom—atom ionizing collisions. This would be followed in an approximately decreasing order of importance by photoionization, electron impact, atom—molecule collisions, and molecule—molecule collisions. The charge exchange reactions, while not contributing directly to the electron production process, were found to have a small but noticeable indirect effect on the resultant electron density distribution at some distance behind the shock due to their continuous shifting of the relative population between atomic and molecular ions (which recombine with the electrons at different rates). The specific rate constants for the atom—atom processes required to interpret all existing experimental results appear to be consistent with a simple extrapolation of the low‐temperature rate constants according to the crossing‐point model of Bates and Massey for atom—atom ionizing collisions.

ISSN:0031-9171    

DOI:10.1063/1.1706741

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The shock initiation of detonation in nitromethane, liquid TNT, and single‐crystal PETN has been studied using a numerical method for solving the reactive fluid‐dynamic equations. Agreement was obtained with previously reported experimental results.Studies were made which explain in detail the mechanism of initiation of detonation at hot spots created by the interaction of a shock with an inhomogeneity. Energy transfer is accomplished by shocks and rarefactions. It is shown how experimentally observed criticality in bubble size can be related to the divergence rate of the shock, and to other features of the fluid flow. The relation of these results to initiation of detonation in inhomogeneous explosives is discussed.

ISSN:0031-9171    

DOI:10.1063/1.1706742

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A weakly ionized plasma in a uniform magnetic field is considered. Application of a potential across the magnetic field results in a steady current flow, owing to the finite conductivity. It is shown that this steady state is unstable if the plasma density is nonuniform in the direction of the applied electric field and if the applied potential is large enough. It is necessary that the sign of the product of the electric field and the density gradient be positive.

ISSN:0031-9171    

DOI:10.1063/1.1706743

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The dispersive properties of a plasma with a generalized Cauchy equilibrium velocity distribution of the form (v2+a2)−3are derived for certain modes of propagation. The plasma dispersion function is found in a simple algebraic form which makes the solution of the dispersion equations readily accessible. A quartic dispersion relation which is obtained for right‐hand circularly polarized electromagnetic waves propagating along a uniform static magnetic field is solved for all frequencies including cyclotron resonance. The complex index of refraction for this mode is plotted for several values of the temperature and the plasma‐cyclotron frequency ratio. In general, thermal effects reduce the infinite discontinuity in phase at the cyclotron resonance to a finite value and cause thermal damping of the propagating wave below resonance. The results are compared with previous numerical analyses using the Maxwell distribution.

ISSN:0031-9171    

DOI:10.1063/1.1706744

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

In an earlier work the ac conductivity of a plasma was investigated by means of an elementary model. The validity of this model has been borne out by a rigorous treatment of plasma at thermal equilibrium. The elementary model is now extended to include the effects of ion correlations for arbitrary fixed ion distributions. For thermal equilibrium correlations it is found that the ion shielding reduces the maximum effective impact parameter by the factor (1 + Z)½(i.e., both ions and electrons contribute to the shielding) for frequencies low compared to the plasma frequency &ohgr;p. For frequencies high compared to &ohgr;p, the previous results obtain. The resistance due to the excitation of longitudinal waves at frequencies just in excess of &ohgr;pis reduced by the factor (1 + Z)−1. However, if large‐amplitude (nonthermal) ion fluctuations are present, the longitudinal wave contribution to the resistance may be greatly enhanced.

ISSN:0031-9171    

DOI:10.1063/1.1706745

出版商:AIP    

年代:1963

数据来源: AIP