摘要:

A direct integration approach coupled with Newton’s iteration scheme was devised to determine the linear stability of a hydrodynamic system with general boundary conditions. A fundamental set of linearly independent solutions was constructed whose coefficients are to be determined by the boundary conditions. In order to assure the existence of nontrivial solutions for the coefficients, a secular equation must be solved whose solution determines the stability criteria to an arbitrary degree of accuracy. This method was applied to a two‐component liquid system with rigid‐rigid boundaries and an imposed temperature gradient. No approximation was made of the Soret‐effect term and of the primary‐state configuration. A slope discontinuity was found in the critical Rayleigh number as the Soret coefficient increases in the positive region. The frequency of the oscillatory mode was found to be very sensitive to the variation of the negative Soret coefficient near the bifurcation point, and to the variation of the concentration near zero or unity. Comparison with existing experiments is also discussed.

ISSN:0031-9171    

DOI:10.1063/1.861036

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Long nonlinear waves on a thin fluid layer flowing down an inclined plane are investigated. For the condition of the Weber number of order one, the equation for the free surface is computed to the third‐order accuracy of the shallow water parameter. The development of a long monochromatic wave is analyzed by use of this equation. Near the upper branch of the neutral curve, the original steady flow is found to be supercritically stable and the amplitude of the monochromatic wave is determined. The stretching of the eigenfrequency by nonlinearity has no definite sign. For a comparatively large wavenumber, the wave velocity can be smaller than that of the linear wave. The nonexistence of the periodic wave in the region far from the upper branch of the neutral curve is discussed in connection with the temporally growing solution of the equation in order to determine the second harmonic.

ISSN:0031-9171    

DOI:10.1063/1.861037

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Measurements of the marginal and joint probability density functions of the longitudinal and radial components of the velocity, and temperature at three different radial positions of an axisymmetric heated turbulent air jet are presented. The results are compared with normal distributions.

ISSN:0031-9171    

DOI:10.1063/1.861038

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The molar‐entropy change of a gas expansion in a free jet is analyzed. Relating the entropy change along the expansion process to the entropy change evaluated using the thermodynamic properties of the initial and final states, one finds that the Mach‐disk location is proportional to the square root of the pressure ratiop0/p∞in agreement with the empirical expression given by Ashkenas and Sherman. The analysis shows further that the Mach‐disk location is independent of the temperature ratioT0/T∞, and is only a weak function of the specific heat ratio &ggr;.

ISSN:0031-9171    

DOI:10.1063/1.861039

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A theory is developed to account for the variable nature of the specific heatCand the transport coefficients of thermal and mass diffusion, &lgr; andD, for the quasi‐steady equilibrium vaporization of a droplet in an unbounded, stagnant atmosphere. In the theoryC, &lgr;, andDare all temperature dependent whereasCand &lgr; are further concentration weighted. Results from the present theory are found to agree within 15% with existing numerical solutions.

ISSN:0031-9171    

DOI:10.1063/1.861040

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The techniques of fluid dynamics are applied to the passage of ionizing waves counter to strong electric fields. The wave is considered to be characterized by a weak discontinuity at its front, and a solution for the wave speed and structure has been found. The structure of the ionizing wave divides into two distinct regions: (1) a sheath region at the wavefront where the electric field, temperature, and velocity first attain maximum values and then the electric field decreases to zero as the electrons reach the same velocity as the ions, and (2) a quasi‐neutral region. The electrons possess a large temperature at the beginning of the quasi‐neutral region and ionization continues to take place until the electrons cool below the ionizing temperature. The dependence of the velocity of the ionizing wave upon the applied electric field has been found to agree well with experiment.

ISSN:0031-9171    

DOI:10.1063/1.861041

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The thickness of an ion shock embedded in a collisional shock propagating in an electron proton gas is calculated, using both the kinetic theory and the continuum approach, for the free stream Mach numbersM=3 toM→∞. It is found that the shock thickness predicted by the kinetic theory is 2–4 times the thickness obtained from the continuum approach. It is also found that the electric field, via which the electrons are compressed across the ion shock, although representing considerable dissipation of the ion kinetic energy, has very little effect on the ion shock broadening.

ISSN:0031-9171    

DOI:10.1063/1.861042

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Wakes at mesothermal conditions are studied in a plasma wind tunnel which simulates ionospheric flight conditions. The need for a very low pressure in the chamber, provided by a liquid‐helium trap, is shown. Wakes of bodies large with respect to the Debye length are investigated and the ratioTe/Ti(electron temperature/ion temperature) can be varied. ForTe/Ti≫1, an ion density peak arises in the midwake and ion waves propagate in the far wake. ForTe/Ti≈1, peaks and waves are entirely suppressed. A quantitative agreement with different theories is achieved.

ISSN:0031-9171    

DOI:10.1063/1.861043

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The evolution of thermally generated magnetic fields in a plasma undergoing a nearly spherically symmetric adiabatic compression or expansion is calculated. The analysis is applied to obtain approximate results for the development of magnetic fields in a laser‐driven compression and explosion of a pellet of nuclear fuel. Localized sources such as those occurring at composition boundaries in structured pellets or at shock fronts give stronger fields than those deriving from smoothly distributed asymmetries. Although these fields may approach 107G in the late stages of compression, this is not expected to present difficulties for the compression process. Assuming ignition of a nuclear explosion occurs, the sources become much stronger and values of ≈1010G are obtained at tamper boundaries assuming a 20% departure from spherical symmetry during the explosion.

ISSN:0031-9171    

DOI:10.1063/1.861044

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Space‐ and time‐resolved interferometric measurements of electron density in CO2‐laser produced plasmas in helium or hydrogen are made near the laser focal spot. Immediately after breakdown, a rapidly growing region of approximately uniform plasma density appears at the focal spot. After a few tens of nanoseconds, shock waves are formed, propagating both transverse and parallel to the incident laser beam direction. Behind the transverse propagating shock is an on‐axis density minimum, which results in laser‐beam self‐trapping. The shock wave propagating toward the focusing lens effectively shields the interior plasma from the incident beam because the lower plasma temperature and higher plasma density in the shock allow strong absorption of the incident beam energy. By arranging the laser radiation‐plasma interaction to begin at a plasma‐vacuum interface at the exit of a free‐expansion jet, this backward propagating shock wave is eliminated, thus permitting efficient energy deposition in the plasma interior.

ISSN:0031-9171    

DOI:10.1063/1.861045

出版商:AIP    

年代:1975

数据来源: AIP