摘要:

Laminar flows past bodies under slip−boundary conditions are investigated theoretically within the framework of the Navier−Stokes equations. The numerical solutions to the equations are obtained using newly developed computer programs for incompressible fluid flows past elliptic cylinders and oblate spheroids. The influence of slippage on flow separation, vorticity, and vortex shedding, as well as on the force coefficients, is discussed.

ISSN:0031-9171    

DOI:10.1063/1.860987

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A novel perturbation technique originally proposed by Benjamin is applied to the study of surface waves in axisymmetric, swirling flow of an inviscid fluid. A first approximation to finite amplitude waves of large wavelength is obtained. The results are found to correspond to the classical solitary and conidial wave solutions given by Korteweg and deVries.

ISSN:0031-9171    

DOI:10.1063/1.861001

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The simple model used by Wang [C. P. Wang, Phys. Fluids 16, 744 (1973)] to describe the motion of a turbulent thermal in a uniform or a stably stratified atmosphere is modified and extended. A simple expression is derived which enables one to determine the entrainment coefficient from data on the rise and the size of a thermal. Analytical solutions are obtained for the maximum rise and the corresponding size of a thermal in a stable atmosphere. The model is applicable to thermals of all sizes, but comparisons with large thermals formed by strong explosions have been stressed. The results show good agreement between theory and observation and indicate that the entrainment coefficient for these thermals is of the same order of magnitude as those for other thermals (&agr; ≃ 0.25) reported in the literature. The numerical result reported by Wang is shown to be a special case of the more general analytical solution derived in the present work.

ISSN:0031-9171    

DOI:10.1063/1.860986

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A general hot−wire column type of experimental facility is described in its developed form for the unambiguous and accurate study of heat transfer from a heated wire to the surrounding gas. In particular, the measurements are reported for heated tungsten and platinum wires in neon for the temperature range 50° to 2450°C. The thermal conductivity values are determined from the heat transfer rate measurements in the continuum and temperature−jump regimes. The thermal conductivity values are compared with the conductivity and viscosity measurements of other workers, with the predictions based on the principle of corresponding states, and with the calculations based on kinetic theory in conjunction with the various spherically symmetric intermolecular potentials.

ISSN:0031-9171    

DOI:10.1063/1.860988

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The D’yakov work which deals with a shock that undergoes a slight disturbance is re−examined. Under a linear analysis the growth of perturbations is examined and this produces inequality restrictions for the shock to be stable. It is found that the shock is unstable forj2(dv/dp)H⟨−1 andj2(dv/dp)H⟩ 1 + 2M, whereMis the Mach number of the shock with respect to the material behind, and −j2is the slope of the Rayleigh line. These inequalities agree with those of D’yakov. It is also shown that these results are exactly the same as those derived by Erpenbeck by a different analysis. Some properties of general Hugoniot curves are also presented. It is demonstrated that the restriction toM<1, by itself, does not restrict the range of values for the slope of the Hugoniot curve.

ISSN:0031-9171    

DOI:10.1063/1.860989

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

An approximate solution of the Boltzmann equation for shock waves is obtained by a procedure which is an extension of the methods of Mott−Smith and of Salwen, Grosch, and Ziering. Shock thicknesses for the density, velocity, and temperature profiles are calculated for Mach numbers from 1.05 to infinity, and the numerical convergence of the results of the three methods is discussed.

ISSN:0031-9171    

DOI:10.1063/1.860990

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The problem of the two−dimensional, inviscid, infinitely−conducting hypersonic flow past nonconducting bodies, in the presence of near−aligned magnetic fields, is analyzed, the problem being solved by transforming from the physical plane to the stream function, magnetic stream function plane. The shock shapes and lift and drag coefficients are determined for some particular examples.

ISSN:0031-9171    

DOI:10.1063/1.860991

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Thomson scattering of ruby laser light at 90° was used to obtain electron temperature and density profiles for plasmas produced by strong collisional shock waves. Transverse (B1≠ 0) shocks of speed 3−25 cm/&mgr;sec in 50−100 mTorr deuterium were studied. Plasma created by reflecting a strong shock from a dielectric wall was also studied. It is found, in agreement with theoretical expectations, that the electron temperature (10−30 eV) is much lower than the ion temperature (100−500 eV) immediately after shock heating of the plasma. Temperature equilibration between ions and electrons, however, does not take place in the times of observation (2−4 &mgr;sec). It is shown that initial electron heating in the plasma is caused primarily by Ohmic dissipation of currents in the shock structure. For pure gas ionizing shocks (B1= 0), the measured electron temperature is in good agreement with theory.

ISSN:0031-9171    

DOI:10.1063/1.860992

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Stimulated Compton backscatter of incident Nd:glass laser photons (h&slash;&ohgr;≃ 1 eV) from free electrons (n<1019/cm3at &kgr;T≃ 103eV) in laser−induced fusion plasmas is investigated. The threshold for stimulated amplification of reflected radiation against spontaneous loss is 109W/cm2incident intensity while the low gain of the system determines the threshold effectively at 1015W/cm2. For 5×1018free electrons/cm2in the plasma, steady state reflectivities of 10−4are calculated for 1016W/cm2incident intensity. This results from the gain being driven to small values when stimulated photon scatter dominates particle collisions and thereby tends to level the resonant scattering interval of the electron momentum distribution. At lower incident intensities or on the time scales of the transients, interesting experiments might be designed to examine this phenomenon.

ISSN:0031-9171    

DOI:10.1063/1.860993

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Expressions are developed for the electron density fluctuation spectrum for monochromatic radiation incident upon a magnetized plasma in thermal equilibrium. The method is based upon the full−wave derivation of a formal relation between the autocorrelations of particle density and dielectric tensor. Collisions are introduced into the formulation via a BGK and a Fokker−Planck collision term in the Boltzmann equation. An enhancement of the scattered spectra due to the excitation of longitudinal slow−wave resonances is predicted when the differential scattering vector is aligned primarily perpendicular to the magnetic field, provided that the collision−to−cyclotron frequency ratio satisfies the relation &ngr;/&OHgr; ≪ 1 in the BGK model or &ngr;/&OHgr; ≪ &OHgr;2m/k2KTin the Fokker−Planck model.

ISSN:0031-9171    

DOI:10.1063/1.860994

出版商:AIP    

年代:1975

数据来源: AIP