摘要:

The rate of spread of a plane, incompressible, turbulent shearlayer was determined experimentally. The velocity ratio was constant, while the actual velocities were altered. It was established that the divergence of the flow with downstream distance was not uniquely determined by the velocity ratio in the range of variables considered. It is believed that an instability is responsible for this behavior.

ISSN:0031-9171    

DOI:10.1063/1.863643

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The newly found time‐derivative‐dependent ponderomotive force and velocity modulation contributions in nonlinear whistler wave propagation are incorporated into the multidimensional stability analysis. It is shown by the Liapunov method that stable one‐dimensional whistler solitons exist. As a further result, it is demonstrated that the growth rate of the transverse bending instability, which is driven by the time‐derivative‐dependent ponderomotive force, is insignificant. This implies the observability of whistler solitons.

ISSN:0031-9171    

DOI:10.1063/1.863644

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Field‐reversed configurations are consistently formed at low filling pressures in the FRX‐C device, with decay time of the trapped flux after formation much larger than the stable period. This contrasts with previous experimental observations.

ISSN:0031-9171    

DOI:10.1063/1.863645

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Conducting properties of the target material are shown to affect both the penetration depth and lateral extent of hot electron transport in experiments with nsec‐CO2‐laser pulses incident on various planar layered targets. At an irradiance around 5×1013W/cm2on metal targets most hard x‐rays are emitted outside the focal spot. The hard x‐ray emission area is reduced by a factor of ten when the conducting target material is replaced by a dielectric of similarZ. The inward transport is likewise reduced. Strong electric fields produced by a local negative charge accumulation in a dielectric may explain the transport reductions.

ISSN:0031-9171    

DOI:10.1063/1.863646

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The dynamics of unbounded and bounded reduced density channels have been characterized by means of ruby laser schlieren photography. These channels are produced by CO2laser‐initiated discharges in clean atmospheric pressure air. Bounded channels exhibit a significant compression in width and earlier onset of fine scale turbulence. These results could impact proposed designs for inertial fusion reactors relying upon reduced density channels for particle transport through gas blankets.

ISSN:0031-9171    

DOI:10.1063/1.863647

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Experiments have been performed in a thermally stratified two‐layer shear flow with a nonzero mean velocity to observe the effects of artifically introduced low frequency internal waves on higher frequency, Kelvin–Helmholtz waves growing spatially on the density interface. Phillips’ model for wave‐induced shear across an interface is extended to the two first‐mode wave trains which can propagate in such a flow. It is shown that the Richardson number becomes a function of the phase of the internal composite waves and that its minimum value is either at the front or at the back face of the waveform depending on the sign of the background vorticity. Measurements are presented of the phase‐averaged temperature and velocity fields of generated internal waves and show the waves breaking down on the face where the Richardson number was found to be at a minimum. The breakdown is characterized by the rapid growth of high frequency waves which appear to be phase locked on the parent internal gravity wave. Possible instances where this type of breakdown could occur in nature are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863648

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The inviscid stability of Long’s vortex, which is believed to model tornado‐like flows, is investigated using a finite‐difference method. Flows of this type are found to be generally unstable to small, short‐wave, helical disturbances, while no instabilities to axisymmetric modes have been found using this method. This instability provides a possible mechanism for the development of ’’suction vortices’’ in tornadoes.

ISSN:0031-9171    

DOI:10.1063/1.863641

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Two fluid layers in fully‐saturated porous media are considered. The lighter fluid is above the heavier one so that in the absence of motion the arrangement is stable and the interface is flat. It is shown that when the fluids are moving parallel to each other at different velocities, the interface may become unstable (the Kelvin–Helmholtz instability). The corresponding conditions for marginal stability are derived for Darcian and non‐Darcian flows. In both cases, the velocities should exceed some critical values in order for the instability to manifest itself. In the case of Darcy’s flow, however, an additional condition, involving the fluids’ viscosity and density ratios, is required.

ISSN:0031-9171    

DOI:10.1063/1.863642

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The stability of a cylindrically symmetric plasma envelope driven outward by blast waves is considered. The plasma fluid is assumed to be a compressible, isentropic gas describable as an ideal gas ( p=a&rgr;&ggr;, &ggr;≳1). The stability problem of such an envelope undergoing self‐similar motion is solved by considering the initial‐value problem. It is shown that in the early phase of an expansion, the envelope is unstable to Rayleigh–Taylor modes which develop at the inner surface. In the later phase of the expansion, the Rayleigh–Taylor modes are weakened due to the geometrical divergence effect. The implications of the time‐dependent behavior of the Rayleigh–Taylor instability for plasma switches are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863649

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

In the atomization regime of a round liquid jet, a diverging spray is observed immediately at the nozzle exit. The mechanism that controls atomization has not yet been determined even though several have been proposed. Experiments are reported with constant liquid pressures from 500 psia (33 atm) to 2500 psia (166 atm) with five different mixtures of water and glycerol into nitrogen, helium, and xenon with gas pressures up to 600 psia (40 atm) at room temperature. Fourteen nozzles were used with length‐to‐diameter ratios ranging from 85 to 0.5 with sharp and rounded inlets, each with an exit diameter of about 340 &mgr;m. An evaluation of proposed jet atomization theories shows that aerodynamic effects, liquid turbulence, jet velocity profile rearrangement effects, and liquid supply pressure oscillations each cannot alone explain the experimental results. However, a mechanism that combines liquid–gas aerodynamic interaction with nozzle geometry effects would be compatible with our measurements but the specific process by which the nozzle geometry influences atomization remains to be identified.

ISSN:0031-9171    

DOI:10.1063/1.863650

出版商:AIP    

年代:1982

数据来源: AIP