摘要:

The Orr‐Sommerfeld equation was used to estimate the influence of free‐stream vorticity on the stability of incompressible boundary‐layer flow. The primary flow velocity profiles were obtained using second‐order boundary‐layer theory. Self‐similar flows with positive and negative pressure gradients and free‐stream vorticities were considered. The results show that positive vorticity at the edge of the boundary layer is stabilizing. The free‐stream vorticity influences the critical Reynolds numbers significantly when the pressure gradient is small, and influences the range of unstable wave lengths when the pressure gradient is large. The present results indicate that small amounts of vorticity in the free stream might have a large influence on transition.

ISSN:0031-9171    

DOI:10.1063/1.1694366

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The dynamical behavior of a system of parallel line vortices with the vorticity vector of some of the vortices being parallel to theZaxis while that of the rest of the vortices is antiparallel, is investigated numerically. It has been shown that a vortex system where some of the vortices are antiparallel to the rest evolves to a state of low vortex density. Therefore, it is unlikely to be produced in the experiments involving rotation of liquid helium II.

ISSN:0031-9171    

DOI:10.1063/1.1694367

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The problem of nonlinear rarefied Couette flow with heat transfer has been studied for both monatomic and diatomic gases using the Boltzmann equation with the Bhatnagar‐Gross‐Krook type models as the governing equation and the method of discrete ordinates as a tool. The calculated results have been compared with the existing experimental data in order to test the accuracy and the applicability of the statistical models for this one‐dimensional problem. The calculated density results are found to be in good agreement with available experimental data; the calculated heat flux solution for the linear case are found to always be lower than the experimental data of Teagan and Springer. There seems to be insufficient published experimental data available to draw rigid conclusions. However, the comparisons made here indicate that the statistical models are indeed reasonably accurate so that their use is justified in the type of problems investigated.

ISSN:0031-9171    

DOI:10.1063/1.1694368

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An approximate analytical solution for free molecule flow in a right circular cylinder has been derived, and the results are compared with those of the exact numerical solution for the free molecule flow problem. The agreement is well within 1% of the exact value. The results of this work are compared with those of earlier work.

ISSN:0031-9171    

DOI:10.1063/1.1694369

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The propagation of shock waves in atmospheres with spatially dependent density and temperature fields is considered. Assuming the medium to be an ideal polytropic gas, and representing the shock wave as a propagating singular surface, an expression is given for the variation in the shock strength in terms of the density gradient behind the wave and a critical density gradient. An example of shock wave propagation in the near‐earth atmosphere is presented.

ISSN:0031-9171    

DOI:10.1063/1.1694370

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The streaming flow of a weakly conducting viscous fluid past a nonconducting sphere in the presence of an aligned uniform magnetic field is investigated for low Hartmann numbers using a Galerkin method. If convection effects are neglected, it is found that eddies occur symmetrically fore and aft of the sphere when the Hartmann number exceeds 2.9.

ISSN:0031-9171    

DOI:10.1063/1.1694371

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Calculations are presented for the transport properties of a two‐temperature argon plasma based on the Chapman‐Enskog and perturbed‐Lorentzian solutions of the Boltzmann equations. The convergence problems known to exist in the Chapman‐Enskog solution for the properties of a one‐temperature argon plasma also occur here; this difficulty is removed by using the perturbed Lorentzian solution at low and moderate degrees of ionization. Also, it is found that the lowest order perturbed Lorentzian and Chapman‐Enskog approximate solutions provide upper and lower bounds to the actual solution at low and moderate degrees of ionization. Finally, owing to the Ramsauer minimum in the electron‐atom cross section, the electrical conductivity of the two‐temperature argon plasma is found to decrease with increasing electron temperature (at fixed heavy particle temperature and electron density) at low degrees of ionization, and increase with increasing electron temperature at higher degrees of ionization.

ISSN:0031-9171    

DOI:10.1063/1.1694372

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Nonlinear coupling among small amplitude electromagnetic and electrostatic waves in a cylindrical plasma‐column waveguide is analyzed theoretically. The warm plasma equations of motion, in the displacement/polarization format, are combined with the wave equation for guided transverse magnetic waves to derive the system dispersion relation and the coupled‐mode equations for this configuration. The coupling coefficients predict the strength of a given multiwave interaction from the intrinsic properties of the plasma waveguide. When the frequency selection rule is satisfied, for wave numbers consistent with the system dispersion relation, off‐resonance excitation will occur if the interaction is confined to a finite length of the waveguide. Typical interaction resonances are illustrated on the system dispersion diagram by an experimentally useful graphical construction. Numerical estimates of the coupling strengths of selected three‐wave “scattering” and “radiation” interactions are made from data obtained with the aid of this diagram. The analytical results are then illustrated and interpreted.

ISSN:0031-9171    

DOI:10.1063/1.1694373

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The spectrum of the synchrotron radiation emitted by the hot‐electron plasma produced in the University of Maryland pulsed magnetic mirror compression experiment has been measured in the 3.0‐cm to 0.3 mm wavelength region. The measured spectra are compared with those calculated using a theoretical model for the electron distribution function that conserves the magnetic moments of the trapped electrons during magnetic compression of the hot electron plasma.

ISSN:0031-9171    

DOI:10.1063/1.1694374

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The hot‐electron plasma produced in a single‐stage magnetic mirror compression experiment using a deuterated titanium washer stack source is compared with the nonneutral hot‐electron plasma produced using a thermionic electron gun source. Both plasmas contain approximately 5 × 1011electrons with 0.3‐MeV mean energy and 0.3‐MeV temperature at the peak magnetic field of 18.5 kG, and both remain trapped for more than 20 msec. These plasmas are similar because deuterated titanium washer stack sources are electron sources during the first few&mgr;secof operation and because the electron dynamics during compression is not strongly affected by the ion dynamics. The effect of the plasma self fields upon synchrotron radiation is investigated. The properties of these plasmas are compared with three other pulse compression hot electron plasmas obtained using a washer stack source.

ISSN:0031-9171    

DOI:10.1063/1.1694375

出版商:AIP    

年代:1973

数据来源: AIP