Sonic Regime Research Articles

Turbulence, convection, and stability in accretion disks

Allowance for turbulent pressure pulsations, convection, and dependence of the turbulence along z in accretion disks results in turbulent scale length much less than the disk (semi) scale height, more effectiveness for the convectile energy transport against instability, and gas pressure dominance in the flow, even for sonic regimes. Solution for the convective disk exists only for beta (0) not less than 0.14 and forces instability to depend on the turbulence level of the disk. For the viscosity law adopted (and for the standard one), the disk will be stable up to alpha (turbulent Mach number) about 1 (sonic regime). When applied to Galactic and extragalactic X-ray sources, these results suggest that absence (presence) of fluctuations may indicate subsonic (supersonic) turbulent regime as well as confirm (refute) the assumed viscosity law, rather than be a clue for externally (internally) produced photons cooled by the thermal plasma.

Transonic wind tunnel wall interference minimization

Obtaining accurate predictions of aircraft aerodynamic coefficients from wind tunnel tests is a difficult task Wind tunnel users have struggled with the effects of wall interference, model support interference, subscale Reynolds number, etc for almost the entire history of powered flight Since wall interference is one of the principal problems this paper emphasizes the need to minimize it, especially in the near sonic test regime Practical ways of minimizing wall interference are identified This is best accomplished for near sonic testing by locally variable porosity with inclined hole perforations A number of porosity setting schemes are identified some of which are quite simple

Study of the Isakovich—Chaban Theory in Viscoelastic Relaxation

The recently proposed Isakovich—Chaban phenomenological theory for highly viscous liquids is examined, as it relates to the complex shear modulus for viscoelastic liquids, in the light of experimentation over the sonic frequency regime of liquid relaxation. Two butanediols, glycerol, and two chlorinated biphenyls are studied experimentally at atmospheric pressure to compare shear-relaxation spectra at various temperatures with the theoretical predictions. Similar comparison is made for one of the biphenyls at two temperatures but over a range of static pressure variation. Experimental spectra for polyisobutylene at atmospheric pressure are presented (reduced to a single temperature) to estimate applicability of the theory to polymeric materials. The findings generally indicate very good agreement between theory and experiment, except in a few instances for liquid shear rigidity over the upper frequency portion of the spectrum and for the maximum imaginary modulus component. Isakovich—Chaban theory does not appear to represent quite as well experimental results taken under static pressure variation at elevated temperature as it predicts relaxation spectra under temperature variation at ambient pressure. The theory may relate to certain polymers as well as to liquids, at least judging from the excellent comparison realized in the case of polyisobutylene at atmospheric pressure, where the analytical method even describes qualitatively the low-frequency behavior observed by other investigators.

UNSTEADY COMPRESSIBLE FLOW IN DUCTS

SUMMARY A rarefaction wave is produced in a two-dimensional channel by the impulsive retraction of a piston. In a finite section of the channel there is a slight variation in cross-section, and the effect of this variation on the rarefaction wave is considered. It is found that, after passing through the transition section, a perturbation is superimposed on the main wave which tends to decrease the flow velocity by a term which decreases inversely as the time for a point moving with the wave, but increases linearly with the time at a fixed point in the channel. In the transition section the disturbances accumulate and tend to increase the flow velocity if there is a throat, eventually producing a sonic regime. An attempt is made to describe the establishment of steady subsonic-supersonic flow in a converging-diverging nozzle.