摘要:

When Hagen–Poiseuille flow is naturally changed from laminar to turbulent, frequencies of pressure fluctuation in the transition region are measured by means of highly sensitive pressure transducers installed at the inner wall of the circular pipe. The frequency of the pressure wave at minimum transition Reynolds number nearly agrees with the frequency corresponding to the minimum critical Reynolds number for the neutral stability curve obtained experimentally by azimuthal disturbance.

ISSN:0031-9171    

DOI:10.1063/1.862567

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Theoretical and experimental results are presented describing viscous incompressible flow in spherical annuli. The character of the flow depends strongly upon the dimensionless frequency of oscillation and the amplitude ratio of the oscillations of the bounding spherical surfaces. The secondary flow can be either ’’inward’’ or ’’outward’’ centrifuging, depending on the values of the parameters.

ISSN:0031-9171    

DOI:10.1063/1.862568

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The propagation of internal gravity waves in shear is investigated theoretically. The known solution of the problem is modified by a technique based on characteristic surfaces. It consists of taking as a new independent variable a family of characteristics. The new solution shows that a tangential discontinuity appears below the critical level. The horizontal velocity and the density pertubation remain bounded up to the discontinuity.

ISSN:0031-9171    

DOI:10.1063/1.862569

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Axial flow in the core of a laminar steady trailing vortex from the tip of a semi‐infinite wing is analyzed assuming small departure of the axial velocity from the free‐stream velocity. It is further assumed that the axial pressure gradient is determined by the swirl velocities of an ideal infinite line vortex in which the radial and the associated axial velocity variations are neglected in the equation for the angular momentum. The axial and lateral variations of the axial velocity depend on the strength of the vortex and initial axial velocity distribution which must be specified at some station behind the wing except at the virtual origin of the vortex where a nonintegrable singularity exists. Numerical solutions for the axial velocity are obtained using the axial pressure gradient given by the line vortex and analytical solutions are obtained using an equivalent axial pressure gradient with good agreement between the two sets of axial velocity distributions. Resolution of the previous uncertainties in this field is given which were due to the unrecognized singularity at the virtual origin of the vortex. Using the calculated axial velocity the neglected radial and the associated axial fluxes of angular momentum are determined and the limits of validity of the theory presented here in terms of a suitably defined vortex Reynolds number and a nondimensional distance measured from the virtual origin of the vortex are given.

ISSN:0031-9171    

DOI:10.1063/1.862570

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

When a compressible laminar boundary layer encounters a corner, a viscous‐inviscid interaction occurs. The correct mathematical structure for such interactions at large Reynolds numbers is provided by the asymptotic triple‐deck theory. Within this framework, solutions of the energy equation for supersonic flow past compression and expansion corners are considered. The limiting structure for far upstream and downstream temperature profiles is examined and a linearized solution for wall heat transfer is derived for very small corner angles. For corners of larger angles, numerical solutions of the energy equation are presented, including cases with separation.

ISSN:0031-9171    

DOI:10.1063/1.862571

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The straightforward third perturbation solution is derived for a time harmonic disturbance applied at the nozzle. The problem formulation sets two boundary conditions at the nozzle and downstream radiation conditions. Numerical results are presented for parameters appropriate to ink‐jet printers that show the jet radius near the breakup point. In a certain frequency range good quantitiative agreement with experiment is obtained for satellite drop behavior as regards forward or backward merging with the main drops.

ISSN:0031-9171    

DOI:10.1063/1.862572

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The formation of stationary striations in an argon plasma due to the development of an instability is studied using the equations for the competing plasma population species. The nonlinear dynamic stability of the system is analyzed using a two‐time perturbation procedure. The unstable uniform steady state bifurcates to a new state with a sinusoidal density variation in space leading to the formation of balls of glowing plasma. This is analogous to phenomena of structure formation that appear in chemical reactions and biological processes.

ISSN:0031-9171    

DOI:10.1063/1.862573

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The addition of a weak toroidal magnetic field to a poloidal octupole field confining a collisional helium plasma,ne∼5×1011cm−3,Ti∼Te∼0.2 eV, was observed to damp the nonthermal vortex spectrum and associated anomalous diffusion previously observed with a purely poloidal field. As a result, the plasma was observed to diffuse across field lines solely by classical diffusion whenBt/Bp≳0.1.

ISSN:0031-9171    

DOI:10.1063/1.862574

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The turbulent behavior of a two‐dimensional dynamics of electrostatic drift‐wave turbulence, proposed by Hasegawa and Mima, is explored analytically and numerically. A dual‐cascade hypothesis leads to modal potential spectra which vary ask−14/3at lowerkandk−6at higherk.

ISSN:0031-9171    

DOI:10.1063/1.862565

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The problem of suppression of a plasma instability by the introduction of an externally controlled spectrum of turbulent electric fields is considered. The theory of strong turbulence is extended to include external fields, and is applied to the half‐cyclotron frequency instability occurring in counterstreaming, magnetically confined electron beams. Experimental results from such an electron beam system are presented which confirm that the suppression of the instability is due to resonance broadening.

ISSN:0031-9171    

DOI:10.1063/1.862566

出版商:AIP    

年代:1979

数据来源: AIP