摘要:

This letter provides an analysis for the correct behavior of the dissipation tensor in the Reynolds‐stress transport equation in the limit as a wall is approached. This differs from what is used conventionally, and hence is important for turbulence models that include the near‐wall region.

ISSN:0031-9171    

DOI:10.1063/1.864274

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An experiment is conducted in which plate vibration is used to successfully cancel a sound‐excited Tollmien–Schlichting wave. With sound excitation, transition to turbulence in the boundary layer occurs at a streamwise Reynolds number (Rx) of 1.2×106. The addition of plate vibration delays the transition toRx=1.8×106. In the laminar region of the boundary layer (atRx=0.97×106) the addition of plate vibration reduces the level of streamwise velocity fluctuations from more than 100 times to only two times the particle velocity of the sound excitation.

ISSN:0031-9171    

DOI:10.1063/1.864275

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The smoke wire technique was used to initial formation and growth of turbulent spots in a laminar boundary layer. The spots were observed to result not from the breakdown of wave packets arising at the spot generator but from longitudinal structures which preceded the wave packets. The original wave packet in turn was observed to ultimately take the form of oblique waves trailing the spot. These waves had little apparent involvement in the growth of the spot and did not appear to be associated with the formation of new spots within the region visualized.

ISSN:0031-9171    

DOI:10.1063/1.864276

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A kinetic theory analysis of the problem described in the title indicates that the disagreement with the continuum solution of Plesset can be less severe than it is usually assumed.

ISSN:0031-9171    

DOI:10.1063/1.864277

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The nonlinear self‐similar tearing‐mode solution of Rutherford is revisited. The steam function for the plasma flow including inertia, convection, and viscosity is explicitly computed. In all cases, Rutherford’s solution is asymptotically valid.

ISSN:0031-9171    

DOI:10.1063/1.864278

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A comparison of experimental data and theoretical results is presented that may help to explain the underlying causes of the flux regeneration mechanism (‘‘dynamo’’) in the reversed‐field pinch (RFP). Discrete events are seen on many diagnostic measurements which are coincident with observable increases in toroidal magnetic flux in discharges where the pinch parameter &thgr; (&thgr;≡B&thgr;wall/⟨B&fgr;⟩) exceeds the value 1.6. By observing the relative timing and the &thgr; dependence of these events as the discharge is returned to lower values of &thgr;, a case may be made for associating them=1 tearing mode with the RFP dynamo.

ISSN:0031-9171    

DOI:10.1063/1.864279

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The collisionless flow of a laser‐produced barium plasma through low‐pressure photoionized xenon in the presence of a uniform, transverse magnetic field is studied. Deceleration of the barium is observed, and attributed to magnetically induced instabilities. Interaction close (4 cm) to the target is observed. The front thickness is observed to vary inversely with field strength. Spontaneous emission of 4554.03 A˚ radiation increases by more than an order of magnitude when theBfield and background gas are both present, indicating significant electron heating. Theory shows that these observations can be explained by the modified two‐stream instability and the magnetized ion–ion instability.

ISSN:0031-9171    

DOI:10.1063/1.864280

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Experimental and theoretical results are presented for two‐dimensional creeping flow in a rotating circular tank that has stationary barriers against its wall. The type of flow pattern obtained depends on the number and size of the barriers.

ISSN:0031-9171    

DOI:10.1063/1.864281

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A study is made of flows of viscous fluids when viscosity varies with temperature according to an Arrhenius law, and when viscous dissipation is taken into account. It is shown that for fluids with highly temperature‐sensitive viscosity the graph of shear rate against shear stress is an S‐shaped curve, with either one or three values of shear rate for given shear stress. In this situation hysteresis can occur if steady unidirectional flow is maintained. The velocity and temperature profiles are calculated, and the manner in which the temperature‐sensitivity parameter affects the conclusions is discussed. The calculations serve as criteria for evaluating the importance of viscous‐heating effects in applications.

ISSN:0031-9171    

DOI:10.1063/1.864265

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The focus of this paper is on the fundamentals of the transient mechanism responsible for the establishment of natural convection in a two‐dimensional porous layer confined between isothermal vertical walls and insulated horizontal walls. In the first part of the paper, pure scaling arguments are used to identify the characteristic time scales of the phenomenon and, based on these scales, the evolution of the porous system to steady state. The type of steady state is shown to depend on the relative order of magnitude of the characteristic time scales. Distinct vertical boundary layers are shown to be possible if (L/H)Ra1/2>1, and distinct horizontal layers if (H/L)1/2 Ra1/4>1. In the second part of the paper, these and other scaling laws of the transient evolution to steady state are successfully tested against a series of transient numerical experiments conducted in the rangeH/L=0.2–5 and Ra=10–50.

ISSN:0031-9171    

DOI:10.1063/1.864266

出版商:AIP    

年代:1983

数据来源: AIP