摘要:

An energy transfer mechanism which has been explored by Miles and which produces growth of a wave on a fluid boundary is considered theoretically. A simple linear high Reynolds number shear flow model possessing similar energy transfer characteristics is formulated. Two terms in its energy balance equation are estimated using approximation techniques for cases when the location of the point where wavespeed equals shear flow velocity is either close to or distant from the boundary surface. Implications of the approximations for growth of the wave are discussed and are compared with conclusions of Miles, and the importance of the position of the above‐mentioned point with respect to the boundary is confirmed.

ISSN:0031-9171    

DOI:10.1063/1.1694347

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Correlations of the instantaneous velocity fluctuations on opposite sides of a subsonic plane jet have been measured. These indicate that there is a measurable flapping of the jet. The frequency of the flapping is estimated by taking the correlation with one signal delayed in time.

ISSN:0031-9171    

DOI:10.1063/1.1694348

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The equations developed by Prager for fully developed laminar flow with swirl in a porous pipe have been solved numerically. A complete description of the solutions is presented using graphs of the skin‐friction and the velocity profiles.

ISSN:0031-9171    

DOI:10.1063/1.1694349

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The initial‐value problem for small amplitude disturbances governed by the Navier‐Stokes equations is considered. This is shown to be governed by a system of Burgers and diffusion equations. The asymptotic solution of the finite amplitude initial‐value problem is obtained by the introduction of asymptotic initial data. The analysis is also applied to the solution of a semi‐infinite shock tube problem.

ISSN:0031-9171    

DOI:10.1063/1.1694350

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Shock‐tube experiments have been conducted to study the nonequilibrium gas‐surface interaction which occurs when a thick shock wave in argon reflects from a coplanar, heat‐conducting wall. Fast‐response instrumentation (rise time≲ 0.1 &mgr;sec) was used to monitor variations in temperature and normal stress on the surface of the shock‐tube end wall during and immediately following reflection of the incident shock wave. The laboratory observations are compared with computer predictions obtained by Deiwert using the direct‐simulation Monte Carlo method, and excellent agreement is obtained when a suitable average thermal accommodation coefficient is chosen for the wall surface. In the present case, with the wall surface probably covered with adsorbed gases, best agreement between laboratory and simulation results is found for an accommodation coefficient of 0.75.

ISSN:0031-9171    

DOI:10.1063/1.1694351

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Ionizing shock waves in helium and argon are structured by nonequilibrium radiative and inelastic collisional transitions. The model atom of the monatomic gas has three electronic energy levels. The monatomic gas is not in local equilibrium with respect to population, and local translational equilibrium between the heavy species present and the electron gas is not assumed either. For the flow conditions studied, the physics and morphology of the shock is further developed on a continuum basis from previous work, and the shock is found to consist of a far precursor due to radiative excitation, a near precursor due to radiative ionization, an embedded transport shock, an inelastic and thermal collisional relaxation zone, and an equilibrium radiating tail. Of particular interest in the results are (i) the heating of the electron gas in the precursor by the said radiative and the associated de‐exciting collisional mechanisms and (ii) the subsequent, electron‐triggered collisional relaxation zone which is optically transparent to radiation; thus, nonequilibrium radiative and collisional processes are locally uncoupled throughout the shock. A family of numerical examples is displayed diagrammatically for an upstream temperature of 300°K and an upstream pressure of 10−4. atm. Selected were those accompanying downstream temperatures giving nominal equilibrium degrees of ionization of either 0.8 or 0.95.

ISSN:0031-9171    

DOI:10.1063/1.1694352

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Collision‐dominated transverse magnetohydrodynamic shock structure is examined for the case where the magnetic fields are strong enough to make the plasma transport properties anisotropic. Different electron and ion temperatures are assumed. A singular perturbation approach is taken to obtain an analytic description of the steady shock structure. For very high Mach numbers (i.e.,us≫ai, upstream sound speed) the shock width is given by&Dgr;s≅2×10−2 us4n1  1 − 32 &ggr;+1&ggr;−1 bs2us2 (m)in hydrogen whereus, n1, b1, and&ggr;are the shock speed, upstream number density, Alfve´n speed, and ratio of specific heats, respectively, and where(us/b1)2≳ 12has been assumed. This shock width is at least an order of magnitude less than shock widths calculated at the same shock speeds with isotropic dissipation coefficients. The results agree reasonably well with previous computer simulations and experimental data.

ISSN:0031-9171    

DOI:10.1063/1.1694353

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Free‐surface gravity flows and capillary wicking provide examples of flow structures with fluid partially ducted at “free” surfaces by external forces. “Wall‐less” electromechanical flow structures are developed which have a similar nature, but with polarization forces providing the orientation at free surfaces. Like their mechanical counterparts, these have the ability to ingest liquid or expel vapor through their walls. The structures consist of electrodes running in the flow directionzwith slowly varying cross sections in a plane transverse to the flow. A formulation is given of the long‐wave nonlinear (principal mode) dynamics, with use made of energy functions to represent a broad class of possible mechanical and electrical structure geometries. Based on the considerable analogy shown between electromechanical and gravity flows, conservative flow transitions and shock conditions are described. The role played by gravity waves in conventional free‐surface flows is taken by polarization waves. Three types of experiments illustrate the significance of the model: (i) standing and traveling wave resonances, (ii) critical flow transition, and (iii) fluid pendulum oscillations. Quantitative checks on the small‐amplitude wave dynamics, and on the nonlinear steady dynamics as well as qualitative observations on the behavior of an electrohydraulic jump, are reported.

ISSN:0031-9171    

DOI:10.1063/1.1694354

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Simulation calculations and theory which show that a very strong electric field with a frequency near the plasma frequency parametrically excites electrostatic turbulence are presented. The plasma is strongly heated with the electrons receiving most of the energy. A simple electron trapping theory accounts for the saturation electric field. After the plasma becomes turbulent, the real part of the frequency of the ion mode is drastically changed from the linear value.

ISSN:0031-9171    

DOI:10.1063/1.1694355

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The diffusion of two and two and a half‐dimensional plasmas across magnetic fields have been studied theoretically and by numerical simulation. Only diffusion at thermal equilibrium is studied. It is found that there are three regions: for sufficiently weak magnetic fields the diffusion coefficient is the classical one withD⊥going likeB−2; for moderate magnetic fields(&ohgr;ce≈&ohgr;pe)the diffusion rate is enhanced andB−1is almost independent ofB; finally, for very large fields(&ohgr;ci>&ohgr;pi)the diffusion coefficient goes likeB−1. The enhanced diffusion at moderate and high magnetic fields is dominated by collective modes; i.e., by thermally excited convective modes. Theory and simulation are in good agreement. It is also shown that the diffusion coefficient behaves essentially the same way for a three‐dimensional plasma when the magnetic field lines are closed.

ISSN:0031-9171    

DOI:10.1063/1.1694356

出版商:AIP    

年代:1973

数据来源: AIP