摘要:

The initial‐value problem of a forced Burgers equation is numerically solved by the Fourier expansion method. It is found that its solutions finally reach a steady state of ‘‘laminar flow’’ which has no randomness and is stable to disturbances. Hence, strictly speaking, the so‐called Burgers turbulence is not a turbulence. A new one‐dimensional model is proposed to simulate the Navier–Stokes turbulence. A series of numerical experiments on this one‐dimensional turbulence is made and is successful in obtaining Kolmogorov’sk−5/3inertial‐range spectrum. The (one‐dimensional) Kolmogorov constant ranges from 0.5 to 0.65.

ISSN:0031-9171    

DOI:10.1063/1.864850

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The periods of strong activity in the high‐frequency components of velocity and temperature fluctuations in a turbulent boundary layer are detected using digital data acquisition and processing by a method similar to that of Raoetal. [J. Fluid Mech.48, 339 (1971)]. These periods are identified with the fine structure of the flow. Conditional averages of temperature and especially velocity associated with the fine structure differ sufficiently from those determined using the variable interval time averaging (VITA) technique to question whether these two techniques trigger on the same events. The characteristic frequency of occurrence, duration and ensemble averages of the velocity and temperature fields associated with the fine structure scale on outer variables when the momentum thickness Reynolds number exceeds a value of about 2000.

ISSN:0031-9171    

DOI:10.1063/1.864851

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Scaling laws for turbulent channel flow were studied, with emphasis on the near‐wall region. The scaling behavior of power spectra and autocorrelations, as well as frequency of occurrence and duration of events detected with the variable‐interval time‐averaging (VITA) technique was investigated for Reynolds numbers ranging from 13 800 to 123 000 (based on centerline velocity and channel height). The governing time scale for the near wall region (of channel flow) was found to be a mixture (the geometric mean) of inner and outer time scales. This time scale collapsed data for different Reynolds numbers on, e.g., frequency of occurrence (cf. ‘‘bursting frequency’’) of VITA‐events detected in the near‐wall region. It is tentatively proposed that this behavior is due to interaction between the outer flow and the flow in the near‐wall region.

ISSN:0031-9171    

DOI:10.1063/1.864852

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

It is shown that the compatibility conditions for spontaneous splitting of a single shock into two shocks plus a contact discontinuity are satisfied whenever the instability limits derived by D’yakov, Kontorovich, and Erpenbeck are violated. They can be stated as −1<j2 (dV/dP)H<(1−M2−M2V0/V)(1−M2+M2V0/V)−1<1+2M, wherej2=( P−P0)/(v0−v),M=‖(D−u)/c‖, and the derivative is along the Hugoniot curve. One‐dimensional splitting can occur when the outer limits are exceeded. Violation of the intermediate upper limit (Kontorovich condition) admits spontaneous generation of steady transverse waves similar to those often observed in detonations.

ISSN:0031-9171    

DOI:10.1063/1.864853

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The effect of radiation on the appearance of an isothermal discontinuity in a relativistic shock wave is considered. When the postshock speed of sound is small compared to the speed of light, algebraic relations are found for the allowed ratios of radiation pressure to matter pressure and for the amplitude of the isothermal discontinuity.

ISSN:0031-9171    

DOI:10.1063/1.864854

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The relativistic ponderomotive Hamiltonian is derived under as general conditions as possible. Arbitraryk&rgr;,E∥/E⊥, &ohgr;/&OHgr;,v/c<1, wave polarization, spatial modulation of the wave, and nonuniformities in the background electric and magnetic fields are introduced in a systematic way. This calculation is a modification of guiding center theory, because in addition to averaging over gyration, there is also an averaging over rapid oscillations of the wave. Therefore, as a by‐product of our objective, a new formulation of the relativistic guiding center motion is derived.

ISSN:0031-9171    

DOI:10.1063/1.864855

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The resonant absorption of electromagnetic waves in an inhomogeneous plasma is studied at low intensity. Both fluid and particle models confirm the formation of solitons predicted by the Zakharov equations. The effects on the absorption coefficient and hot electron production are considered.

ISSN:0031-9171    

DOI:10.1063/1.864856

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The stability of a current‐carrying cylindrical plasma is studied by using the nonideal magnetohydrodynamic equations in a shearless magnetic field. It is shown that for eachmmode there are four marginal stationary states which, under some conditions, give rise to large scale stationary convection when nonlinear effects are taken into account.

ISSN:0031-9171    

DOI:10.1063/1.864857

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The energy balance of the collisional tearing mode is examined within linear theory. It is found that in an asymmetric case the quadratic form given by Furth for the net release of magnetic energy must be completed with a term connected with the current gradient in the resistive layer. The growth‐rate and the inner‐layer solution are calculated in the limit where viscosity dominates over inertia. The amounts of energy going into Joule heating and either kinetic energy or viscous dissipation are calculated analytically. In the inertial regime 1/4 of the net decrease in magnetic energy goes into kinetic energy and (3)/(4) into Joule heating, while, in viscous regime, (1)/(6) goes into viscous dissipation and (5)/(6) into Joule heating. The analytical results, based on the constant‐&psgr; approximation, are in good agreement with numerical simulations when the resistive layer is sufficiently narrow.

ISSN:0031-9171    

DOI:10.1063/1.864858

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The exact equations of motion for the oscillating two‐stream and parametric decay instabilities (OTSI and PDI) are derived in the reference system co‐moving with the ion‐acoustic disturbance and their physical interpretation in terms of wave pressure is presented. It is found that OTSI and PDI behave differently: whereas in the OTSI the ponderomotive force is shifted by −&pgr;/2 with respect to the disturbance, in the PDI case it is in phase with the propagating ion wave, as in stimulated Brillouin and Raman scattering. The decisive role of the pressure of an electrostatic wave is stressed.

ISSN:0031-9171    

DOI:10.1063/1.864859

出版商:AIP    

年代:1984

数据来源: AIP