摘要:

Go¨rtler instability for boundary‐layer flows over generally curved walls is considered. The full‐linearized disturbance equations are obtained in an orthogonal curvilinear coordinate system. A perturbation procedure to account for second‐order effects is used to determine the effects of the displacement thickness and the variation of the streamline curvature on the neutral stability of the Blasius flow. The streamwise pressure gradient in the mean flow is accounted for by solving the nonsimilar boundary‐layer equations. Growth rates are obtained for the actual mean flow and compared with those for the Blasius flow and the Falkner–Skan flows. The results demonstrate the strong influence of the streamwise pressure gradient and the nonsimilarity of the basic flow on the stability characteristics.

ISSN:0031-9171    

DOI:10.1063/1.863557

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The three‐dimensional time‐dependence velocity of incompressible fluids satisfying linearized incompressible Navier–Stokes equations can often be expressed in terms of a singlehbyv=A∇h+B(lˆ×∇h)+Cl×(l×∇h), where l is a constant vector andA,B,Care scalar operators. ForB,C≠0,curl v≠0.

ISSN:0031-9171    

DOI:10.1063/1.863558

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The stability characteristics of a Helmholtz velocity profile in a stably stratified, compressible atmosphere in the presence of a lower boundary are studied. A jump in the Brunt–Va¨isa¨la¨ frequency is introduced and the level at which this jump occurs is assumed to be different from the shear zone, to simulate sharp temperature discontinuities in the atmosphere. The results are compared with those of Pellacani, Tebaldi, and Tosi and Lindzen and Rosenthal. In the present configuration, new unstable modes with larger growth rates are found. The wavelengths of the most unstable gravity waves for the parameters pertaining to observed cases of clear air turbulence agree quite closely with the experimental values.

ISSN:0031-9171    

DOI:10.1063/1.863559

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The effect of superimposed rigid body motions on the structure of two‐dimensional turbulence is examined. It is found that with regard to the fluctuation dynamics of the flow, the rotational behavior of two‐dimensional turbulence is quite different from its three‐dimensional counterpart. The implications that this has on turbulence modeling are discussed briefly.

ISSN:0031-9171    

DOI:10.1063/1.863560

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A derivation of the high wavenumber spectral transfer equation is given which indicates the wavenumber range of validity for this equation in terms of Re&lgr;. A similar treatment is given for the commonly used spectral approximation for the velocity derivative skewness and the analogous scalar spectral quantities.

ISSN:0031-9171    

DOI:10.1063/1.863561

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A variational method is developed to find approximate solutions to the Grad–Shafranov equation. The surfaces of the constant poloidal magnetic flux &psgr;(R,Z) are obtained by solving a few ordinary differential equations, which are moments of the Grad–Shafranov equation, for the Fourier amplitudes of the inverse mappingR(&psgr;, &Vthgr;) andZ(&psgr;, &Vthgr;). Analytic properties and solutions of the moment equations are considered. Specific calculations using the Impurity Study Experiment (ISX‐B) and the Engineering Test Facility (ETF)/International Tokamak Reactor (INTOR) geometries are performed numerically, and the results agree well with those calculated using standard two‐dimensional equilibrium codes. The main advantage of the variational moment method is that it significantly reduces the computational time required to determine two‐dimensional equilibria without sacrificing accuracy.

ISSN:0031-9171    

DOI:10.1063/1.863562

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Appendix to  Variational moment solutions to the Grad–Shafranov equation  (AIP)

ISSN:0031-9171    

DOI:10.1063/1.863563

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The thermal heat flux along a uniform magnetic field due to a temperature gradient is calculated using a Monte Carlo solution to the Fokker–Planck equation. This numerical solution, which is computed for a particular electron temperature profile, is valid for arbitrary mean‐free‐path, &lgr;mfp. The calculated heat flux makes a smooth transition between the analytic expressions for the short and long &lgr;mfplimits.

ISSN:0031-9171    

DOI:10.1063/1.863564

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Consider an unneutralized column of ions (a pure ion plasma) confined by an axial magnetic field. Because of space charge, there is a large radial electric field and a consequent rotation of the plasma column. For a multispecies ion plasma, the rotation tends to produce centrifugal separation of the plasma into its component species. Self‐consistent thermal equilibrium states which exhibit various degrees of separation are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863565

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Multiple electrostatic ion‐acoustic shock‐like density perturbations are observed experimentally to be launched from a large plate in a quiescent collisionless plasma. The formation of the fastest shock is due to ions expelled from the edge of the ’’transient sheath’’ surrounding the plate. The second shock then evolves as a result of the surrounding ions filling in the region of density depression created by the first shock. Reflected ions and turbulent ion‐acoustic noise at the shock front and amplitude modulation in the trailing dispersing oscillations are only observed for the leading shock.

ISSN:0031-9171    

DOI:10.1063/1.863566

出版商:AIP    

年代:1981

数据来源: AIP