摘要:

Taylor vortices caused by finite axisymmetric disturbances around the inner cylinder in a long apparatus with a resting outer cylinder have been studied. The forced Taylor vortices are unstable if their wavelengths are either too long or too short as compared with the critical wavelength of undisturbed Taylor vortex flow. It has also been found that axisymmetric Taylor vortices are stable to finite azimuthal disturbances over a large range in supercritical Taylor numbers in this apparatus with &eegr;=0.727.

ISSN:0031-9171    

DOI:10.1063/1.861181

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A photon correlation system employing a Bragg cell to frequency shift the incident laser light has been used to measure mean velocities and turbulence intensities in the separated flow behind a backward facing step. Theoretical relationships are derived relating the probability density of flow velocity to the count correlation, these results being applicable to the case of unseeded air flow. The method can be used for measuring in flow regions where there are very high local turbulence levels, outside the range of more conventional techniques. Good agreement was found with previous measurements recorded using hot‐wire anemometry.

ISSN:0031-9171    

DOI:10.1063/1.861182

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The stability of two‐phase flow in a vertical cylinder is considered. The liquid phase is assumed to flow past the cylinder surface in a thin layer, assuming no mixing with the core gas flow. The complete system of Navier–Stokes and continuity equations for both phases is treated analytically, using a perturbation procedure based on expansion in powers of small wavenumbers. The results of the first approximation determine the phase velocity of waves developed on the liquid‐gas interface. The second approximation reveals the complete pattern of hydrodynamical stability of two‐phase flow over the entire range of gas‐flow velocities. The topological features of stability curves are depicted. The effects of surface tension, cylinder radius, and interface curvature on the two‐phase flow stability are revealed.

ISSN:0031-9171    

DOI:10.1063/1.861183

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The mechanisms of penetration of single and multicomponent background gases into a free jet flowing into a stationary background are examined from theoretical and experimental points of view. The theoretical treatment is based on the asymptotic theory developed by Brook and Hamel for a spherically symmetric source flow expanding into a stationary rarefied atmosphere. Agreement between theory and experiment is reasonable; certain points of disagreement are identified for future study.

ISSN:0031-9171    

DOI:10.1063/1.861184

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Condensation of water vapor was studied in the expansion wave of the driver section of a shock tube by light scattering and pressure measurements. By arranging the onset of condensation to occur at the terminating characteristic of the unsteady expansion wave, the gasdynamic analysis could be simplified. The composition of the test gas was varied from pure vapor (steam) to small mole fractions of H2O in different carrier gases, yielding onset conditions in the temperature and pressure ranges of 225 to 282 °K and 2 to 62 Torr, respectivly. Steam condensation is well predicted by the classical rate expression for homogeneous nucleation, modified to account for nonisothermal effects and a variable amount of carrier gases. Results for the transition region from the pure vapor to small mole fractions of water vapor in argon, helium, and air reveal a dependence of the computed nucleation rates of several orders of magnitude on the mole fraction of the carrier gas, which is not explained by the nonisothermal theory. Possible reasons for this effect are discussed.

ISSN:0031-9171    

DOI:10.1063/1.861185

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A class of solutions of the ideal magnetohydrodynamic equilibrium equations of an axisymmetric magnetic configuration is derived. These solutions, besides including magnetic configurations with a large variety of cross sections and nonuniform current distributions, are exact solutions obtained without making any assumptions on the value of the aspect ratio. The stability of some of these configurations with respect to ideal localized modes has been numerically evaluated.

ISSN:0031-9171    

DOI:10.1063/1.861186

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A model representing the laser heating of a plasma in a straight solenoid magnetic field has been analyzed. The model incorporates an idealized plasma cross section, but otherwise appears to very accurately represent the real problem. The difficulty of unequal electron and ion temperatures is averted by considering only the equilibrium limit. The frozen ion limit is examined briefly and found to differ from this only by factors generally near one. The complicated exact solution of the model is approximated to good accuracy by simple expressions.

ISSN:0031-9171    

DOI:10.1063/1.861187

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A model of the plasma focus is considered, in which large axial electric fields are induced by the imploding current sheet during the final few nanoseconds of the collapse phase. This field provides a mechanism for creation of a beam of electrons of highly suprathermal energies. For such a beam, having a power‐law energy spectrum, the bremsstrahlung radiation above 100 keV to be expected from it, both from electron‐deuteron collisions in the focused plasma itself and when the beam reaches the walls of the device, is calculated. The expected radiation from the walls is found to be several orders of magnitude higher than that from the plasma. Thus, since experimental evidence indicates that little or no radiation above 100 keV originates in the walls, the conclusion is drawn that the electrons in the beam must be decelerated after leaving the plasma and before reaching the walls. Upon comparison with experimental results, qualitative agreement of the expected angular distribution of hard x rays with experiment is found. The total energy in accelerated electrons required to produce the observed total energy in hard x rays by this mechanism is also reasonable when compared with the total energy of the device.

ISSN:0031-9171    

DOI:10.1063/1.861188

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Theoretical and numerical methods now give a complete solution to the problem of finite‐&bgr; plasma equilibrium in mirror magnetic wells and toroidal devices. The equilibria can be made consistent on all of the progressively longer time scales of the guiding‐center fluid model, including the particle magnetic drifts and the Coulomb scattering equilibrium of a neutral injected plasma. The theory of equilibrium in the guiding‐center fluid model of a finite‐&bgr; plasma with an arbitrary, anisotropic pressure tensor can be formulated as a classical magnetostatic system: ∇⋅B = 0, ∇×H = 0, B = H + 4&pgr;M(B). The plasma magnetization is found explicitly in terms of three physically distinct components related to the laws of conservation of magnetic moment, of longitudinal invariant, and of the sign of the velocity along B of particles that do not undergo mirror reflection. A condition is derived upon the field geometry whereby a large class of special equilibria can be found in which all particles on a given line drift on the same surface, the omnigenous surface. Such systems allow a specially simple connection between particle and fluid models in the guiding‐center fluid theory. The usefulness of the theory is exemplified by application to the problem of a finite‐&bgr; plasma in a magnetic well. Finally, a brief treatment of stability in terms of the energy principle is given. The omnigenous equilibria have particularly simple stability criteria.

ISSN:0031-9171    

DOI:10.1063/1.861189

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The parametric decay of an incident lower hybrid pump wave to two lower frequency lower hybrid waves only occurs for a finite wavelength (nondipole) pump wave and can be an important process in lower hybrid resonance heating schemes. The growth rates and thresholds of this instability in homogeneous and inhomogeneous plasmas are obtained and discussed.

ISSN:0031-9171    

DOI:10.1063/1.861190

出版商:AIP    

年代:1975

数据来源: AIP