Effect of gas compressibility on the stability of a boundary layer above a permeable surface at subsonic velocities

In the present study we investigate the stability of a boundary layer for the condition that the velocity perturbations at the permeable surface are nonzero. The stability for the boundary layer of an incompressible liquid in such a formulation was considered in [1]. For the case of subsonic velocities the effect of compressibility on the flow inside the boundary layer is weak, and in the present article this effect was neglected. The unsteady flow in narrow pores of a permeable covering depends strongly on the compressibility of the gas. Therefore, in the derivation of the relation connecting the pressure oscillations at the permeable surface with the oscillations of the flow through it, the effect of the compressibility was taken into consideration. It is shown that the boundary conditions, and therefore also the stability of the boundary layer at the permeable surface, depend considerably on the Mach number, even for a subsonic exterior flow.     

Erratum to: “Giant Gamow-Teller Resonance in Neutron-Rich Nuclei”

Physics of Atomic Nuclei -     

Excitation by sound of Tollmien-Schlichting waves in a supersonic boundary layer

The interaction of sound with a supersonic boundary layer is considered. Because of the dependence of the main flow on the longitudinal coordinate, a sound wave generates unstable oscillations within the boundary layer. Calculations made for Mach number M = 2.0 and dimensionless frequency 2πfv_e/U_e ² = 0.91·10^?4 showed that near the lower branch of the curve of neutral stability a Tollmien—Schlichting wave can be excited with an intensity 2–3 times greater than that of the external acoustic wave.     

Investigation of the compositional changes of a Y-Ba-Cu-O HTSC target under ion sputtering

An Auger electron spectroscopy study is reported of the elemental depth profile of Y-Ba-Cu-O HTSC targets subjected to ion-plasma sputtering in a magnetron deposition system and ion-beam sputtering in the Auger spectrometer chamber. It has been established that the process consists in all cases of predominant copper sputtering accompanied by the formation of a modified surface layer and of a copper-depleted region. This region is assumed to originate from intense copper diffusion from the bulk to the modified surface layer driven by a concentration gradient.     

Interaction of hydrodynamic external disturbances with the boundary layer

Disturbances produced by external flow vorticity in a supersonic boundary layer are studied. It is shown that both vortical and nonvortical waves play an important role. The calculations are performed for subsonic and supersonic flows for a Mach number M=2.     

Synthesis of 4-styryl-2,3-dihydro-1H-1,5-benzodiazepin-2-ones

4-Styryl-2,3-dihydro-1H-1,5-benzodiazepin-2-ones were synthesized and their structure was established by means of PMR spectra and mass spectroscopy.Dnepropetrovsk State University Named in Honor of 300th Anniversary of the Reunion of Ukraina and Russia, Dnepropetrovsk 320625. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1560–1562, November, 1987.     

Efficiency of the invariant gradient criterion of stability for the flight conditions of the flow around axisymmetric bodies in the early stage of transition and relaminarization

Quantitative results of the study of the invariant gradient criterion of stability, which was theoretically obtained by N. N. Yanenko and S. A. Gaponov, for the flight conditions of the flow around the forebodies of aerophysical complexes in the laminar flow regions and in the early stage of the laminar-turbulent transition and relaminarization are presented. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 1, pp. 89–100, January–February, 1999.     

Three-wave interactions of disturbances in a hypersonic boundary layer on a porous surface

Interactions of disturbances in a hypersonic boundary layer on a porous surface are considered within the framework of the weakly nonlinear stability theory. Acoustic and vortex waves in resonant three-wave systems are found to interact in the weak redistribution mode, which leads to weak decay of the acoustic component and weak amplification of the vortex component. Three-dimensional vortex waves are demonstrated to interact more intensively than two-dimensional waves. The feature responsible for attenuation of nonlinearity is the presence of a porous coating on the surface, which absorbs acoustic disturbances and amplifies vortex disturbances at high Mach numbers. Vanishing of the pumping wave, which corresponds to a plane acoustic wave on a solid surface, is found to assist in increasing the length of the regions of linear growth of disturbances and the laminar flow regime. In this case, the low-frequency spectrum of vortex modes can be filled owing to nonlinear processes that occur in vortex triplets.