摘要:

Using point vortices, the interaction of a single vortex, as well as patterns of vortices, with a corner is examined; comparisons are made with corresponding experiments. Trajectories of a vortex swept past the corner can be well‐approximated, provided that a sufficiently weak strength of the vortex is specified. Calculations show that the dimensionless amplitude of the pressure fluctuation at the corner is very sensitive to small variations of the initial position of the vortex, and relatively insensitive to variations in strength; this finding has important consequences for recently observed amplitude modulation of pressure at, and velocity near, impingement. In fact, by prescribing transversely staggered patterns of vortices upstream of the corner, determined from experimental flow visualization, the form of the time‐averaged pressure and velocity spectra can be approximated. The most critical feature of these spectra, a well‐defined low‐frequency component(s), confirms the hypothesized mechanism associated with low‐frequency modulation observed in experiments. In addition, shortcomings of this method, primarily due to distributed vorticity inherent in laboratory vortices, are pointed out.

ISSN:0031-9171    

DOI:10.1063/1.863327

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An approximate similarity solution, derived by Raizer, of a concentrated impact (or intense explosion) at the boundary of a semi‐infinite volume of a perfect gas is used to determine the propagation velocity of the shock front as a function of its position. This velocity function is then used to obtain the shape of the propagating shock wave. It is shown that dish‐shaped shock fronts are formed when the movement of the gas at the surface is into the gas region and that cup‐shaped shock fronts are formed when the movement is out of the gas region. Comparison of these results with the shapes of explosions and meteorite craters are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863328

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A finite‐difference computer code is used to calculate the time development of an explosion on a gas‐vacuum interface. An analytic theory of the shape of the shock wave produced in the explosion is compared with the results of the computer simulation. The assumptions used in obtaining this analytic solution are verified, and the degree to which the variables describing the explosion are self‐similar is examined. Finally, certain consistency relations among the similarity exponents are tested.

ISSN:0031-9171    

DOI:10.1063/1.863329

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The strong evaporation problem in half‐space for the one‐dimensional Bhatnagar–Gross–Krook model is considered, and it is shown that highly accurate results in the lowest approximation can be obtained by a judicious use of two different integral transport methods. Extensions of the work to higher order kinetic models is discussed, and some comments regarding obtaining accurate results for the Boltzmann equation by use of the generalized Maxwell method are also included.

ISSN:0031-9171    

DOI:10.1063/1.863330

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The uniform density region that develops behind a rarefaction shock in planar geometry (and attaches downstream to the outer expansion flow) is shown to be modified by geometric divergence into a region of self‐similar flow with nonvanishing gradients. A single set of equations is derived that describes both shock and similarity flow. The longest gradient scale length in the transition region is shown to vary linearly with the radius at the shock.

ISSN:0031-9171    

DOI:10.1063/1.863331

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The boundary layer of a weakly ionized rare gas discharge is treated using kinetic theory. A self‐consistent two‐scale analysis is performed and the exact presheath and sheath solutions are constructed for the following model: A plasma consisting of Boltzmann distributed electrons and singly charged atomic ions is in contact with a negative absorbing wall. The ion kinetics is dominated by charge exchange with cold neutrals (T0≪T−). The mean‐free‐path &lgr; is constant and large compared with the electron Debye length &lgr;D. This model represents a collision‐dominated counterpart to the well known Tonks–Langmuir model of the collision‐free plasma.

ISSN:0031-9171    

DOI:10.1063/1.863332

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A theory of electron motion in a spatially sinusoidal wave of slowly varying amplitude is presented. On the basis of a reformulation of classical conservative motion, a set of approximate analytical, adiabatic solutions for the case of a temporally varying amplitude is derived. The set can describe electron transitions from trapped to untrapped conditions, or vice versa, and provides a formally unified description of both kinds of motion through Jacobi’s real transformation.

ISSN:0031-9171    

DOI:10.1063/1.863333

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A self‐consistent calculation of the damping of an electron plasma wave is presented including, for the first time, the contribution of all electrons (untrapped, detrapped, and trapped). The effect of the detrapped electrons, which is strong at the higher damping rates, is to lower the first minimum of the amplitude after the initial stage of Landau damping and the general level of its oscillation afterward. At &ggr;L&tgr;0≊−0.75, a qualitative change is observed from amplitude oscillation to near‐plateau behavior. The existence of an important secularity in the Vlasov–Poisson system is pointed out.

ISSN:0031-9171    

DOI:10.1063/1.863334

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An eigenmode equation for drift waves in low‐aspect‐ratio spheromak geometry is derived and solved numerically. In contrast to the large‐aspect‐ratio tokamak limit, the strong equilibrium variation involved here, allows partially localized modes at more than one value of the poloidal angle.

ISSN:0031-9171    

DOI:10.1063/1.863335

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The dielectric tensor of a weakly relativistic magnetized plasma is discussed for wave frequencies very close to the fundamental or higher harmonics of the electron or ion cyclotron frequency. Since in real situations the plasmas of interest are often in nonequilibrium states, the present paper generalizes Shkarofsky’s result to include three nonequilibrium features; namely, a loss‐cone distribution, anisotropic temperatures, and a field‐aligned drift. The discussion is motivated by current interest in the study of absorption and emission of radiation near the electron cyclotron harmonics.

ISSN:0031-9171    

DOI:10.1063/1.863324

出版商:AIP    

年代:1981

数据来源: AIP