摘要:

Simultaneous velocity and temperature measurements in the thermal mixing layer downstream of a partially heated turbulence grid are reported. The temperature data are in good agreement with earlier results. The velocity‐temperature correlations are new and permit a systematic assessment of an earlier similarity theory for the region far downstream of the grid. By selecting the virtual origin appropriately and by reconsidering the role of scalar dissipation in that region, agreement between measurement and prediction with respect to temperature intensity and two mean lateral fluxes, that of temperature and of temperature intensity, is achieved.

ISSN:0031-9171    

DOI:10.1063/1.863288

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An algorithm to enumerate the number of independent scalars that determine the general tensor formed fromnvelocity gradients at a point in homogeneous‐isotropic turbulence is elaborated forn= 4. The physical content of the invariants that result as well as their determination from experiment is discussed.

ISSN:0031-9171    

DOI:10.1063/1.863289

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Experiments have been performed in a two‐layer stably stratified flow where the mean velocity surpasses the phase speed of all internal waves of mode one. Results show the existence of two wave trains propagating in the direction of the mean flow (excited by a two‐dimensional wave maker), which are identified by the modulation of the amplitude of the linearly superposed wave trains. Measurements of the composite wave speed and dispersion relation are presented. Wave speeds are shown to be very near the mean. The qualitative behavior of composite wave trains is shown to appear similar to that of unstable Kelvin–Helmholtz waves where spatial growth is dominant, leading to possible misinterpretation.

ISSN:0031-9171    

DOI:10.1063/1.863290

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The structure of a two‐phase shock wave in a gas‐particulate fluidized bed is investigated. The present study gives (i) the jump relation across the two‐phase shock, (ii) the critical condition beyond which the stable two‐phase shock breaks up, and (iii) the distribution of the dependent variables through the two‐phase shock and the two‐phase shock thickness.

ISSN:0031-9171    

DOI:10.1063/1.863291

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The thermalization of a large energy fluxWin a medium of density &rgr; leads to heat waves consisting of compression and expansion fronts, associated with substantial bulk motion. Particles can enter or leave the thermalization front at subsonic, sonic, or supersonic speed, allowing for a wide variety of wave modes. The wave mode depends on power input, thermodynamic response of the medium, and the boundary conditions. The intake Mach number mainly determines the degree of compression achieved across the front. Using macroscopic conservation equations the thermodynamic properties of the wave fronts are discussed in a pressure–density diagram and compared to other thermodynamic processes. The fluid dynamic properties are shown as a function of the absorbed power inputW/&rgr;. Finally, the hydrodynamic properties of the entire two front heat wave are presented for specified boundary conditions in the response planeh–W/&rgr;, showing the enthalpyhof the heated target material as a function of an external energy fluxW/&rgr;. Examples of the boundary conditions of free and retarded flow and heat transport due to inverse bremsstrahlung are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863292

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The shape of an axisymmetric dielectric drop in a uniform electric field is computed numerically. The problem is formulated as a nonlinear integro‐differential system of equations. They are discretized and the resulting algebraic system is solved by Newton’s method. The results show that when the dielectric constant &egr; is larger than a critical value &egr;c, the drop develops two obtuse‐angled conical points at its ends for a certain field strength. For &egr;<&egr;c, the drop elongates and retains its original nearly prolate spheroidal shape without developing conical points as the field is increased. The numerical results are in good agreement with the moment and two‐point approximations. The energy, volume, and area of the drop are computed, and the two‐dimensional case is also treated.

ISSN:0031-9171    

DOI:10.1063/1.863293

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The scope and limitations of elementary methods for establishing qualitative properties of solutions of the nonlinear Schro¨dinger equation are discussed and clarified. The concept of recurrence is shown to be related to Lagrange and Poisson stability of the system. Lagrange stable motions in any number of spatial dimensions are shown to be recurrent in general.

ISSN:0031-9171    

DOI:10.1063/1.863294

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The nonlinear Schro¨dinger equation with linear growth and damping is truncated to three waves. The resulting system of nonlinear ordinary differential equations describes the excitation of linearly damped waves by the oscillating two‐stream instability driven by a linearly unstable pump wave. This system represents a simple model for the nonlinear saturation of a linearly unstable wave. The model is examined analytically and numerically as a function of the dimensionless parameters of the system. It is found that the model can exhibit a wealth of characteristic dynamical behavior including stationary equilibria, Hopf bifurcations to periodic orbits, period doubling bifurcations, chaotic solutions characteristic of a strange attractor, tangent bifurcations from chaotic to periodic solutions, transient chaos, and hysteresis. Many of these features are shown to be explainable on the basis of one‐dimensional maps. In the case of chaotic solutions, evidence for the presence of a strange attractor is provided by demonstrating Cantor set‐like structure (i.e., scale invariance) in the surface of section.

ISSN:0031-9171    

DOI:10.1063/1.863295

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Stability equations for axisymmetric compact toroidal configurations without a toroidal magnetic field are derived in a variational form. The application of a particular ordering procedure gives equations which include the coupling of geometry to finite Larmor radius as well as including resonant ion effects. The equations are readily obtained by applying the ordering assumptions to a variational dispersion functional form of the Vlasov‐fluid equations. Application of the dispersion functional to find necessary and sufficient conditions for stability are made for the case of small, but finite Larmor radius and for the case of zero Larmor radius. The mathematical result that the zero Larmor radius case is more optimistic is physically understood in the context of an interesting stabilizing mechanism involving parallel kinetic effects.

ISSN:0031-9171    

DOI:10.1063/1.863296

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The self‐consistent classical plasma equilibrium with diffusion is studied in a toroidal geometry having a sheared magnetic field. Near each rational surface it is found that the pressure gradient is zero unless the Fourier component of 1/B2, which resonates with that surface, vanishes. Despite the resonances, the overall plasma confinement is, in practice, only slightly modified by the rational surfaces.

ISSN:0031-9171    

DOI:10.1063/1.863297

出版商:AIP    

年代:1981

数据来源: AIP