Combined influence of the Reynolds number and localised wall suction on a turbulent boundary layer

This paper considers the effect the Reynolds number has on a turbulent boundary layer that is subjected to concentrated suction, applied through a short porous wall strip. The response of the skin friction coefficient to suction is strongly modulated by the momentum thickness Reynolds number R ₀. The magnitude and wavelength of the variation of the skin friction decrease as R ₀ increases. Measurements clearly show that it is the combination of R ₀ and the suction rate that controls the boundary layer response. Relaminarisation of the near-wall flow, which occurs just downstream of the suction strip when =5.5 and R ₀=660, could not be achieved at higher Reynolds numbers. It is suggested that the ratio R ₀/ should not exceed a (as yet undetermined) critical value if pseudo-relaminarisation is to occur. The mean velocity profiles differ from the undisturbed profile for all the values of R ₀ and considered here. Although the redistribution of the turbulent kinetic energy among the normal Reynolds stresses is affected by , a variation in R ₀ does not appear to alter the effect of on this redistribution.     

Stress concentration around a spheroidal crack caused by a harmonic wave incident at an arbitrary angle

A method is proposed to study the stress concentration around a shallow spheroidal crack in an infinite elastic body. The stress concentration is due to the diffraction of a low-frequency plane longitudinal wave by the crack. The direction of wave propagation is established in which the combined concentration of mode I and mode II stresses is maximum __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 1, pp. 70–77, January 2006.     

Dynamic analysis of interacting coplanar cracks in a half space with a clamped boundary condition using boundary integral equations

The three-dimensional dynamic problem of coplanar circular cracks in an elastic half-space with a clamped boundary condition is considered. The crack faces are subjected to harmonic loads. The problem is reduced to a system of two-dimensional boundary integral equations of the type of the Helmholtz potential for unknown discontinuities in the displacements of the opposite faces of the cracks. The stress intensity factors at the crack contours are obtained and discussed.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 153–159, January–February, 2005     

Effect of the Geometry of the Working Chamber of a Cylindrical-Conical Hydrocyclone on the Non-Newtonian Fluid Dynamics

Numerical simulation is used to study the dynamics of non-Newtonian free-surface flow in a cylindrical-conical hydrocyclone. For different angles of taper of the conical section of the hydrocyclone, the pressure and velocity distributions are calculated, together with the dependence of the fluid film thickness on the axial coordinate. The effect of the rheological properties of the fluid and the controlling similarity parameters on the flow dynamics is studied.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 102–112.Original Russian Text Copyright © 2005 by Yablonskii.     

On convective stability of suspensions

Convective flow onset in a dilute suspension filling a horizontal layer heated from below is studied analytically. It is shown that at a certain concentration of the suspension, instead of Rayleigh cells, lower-scale eddies surrounding each of the dispersed-phase particles may appear in the system.Perm. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 44–47, May–June, 1996.     

Thermal cracking in railroad vehicle wheels subjected to high performance stop braking

An investigation of thermal cracks observed in the wheels of certain electric multiple unit (EMU) locomotives in North American commuter rail service is summarized. The cause is found to be partial reversal of the wheel rim residual hoop stress, which is initially compressive from the manufacturer's quench treatment. The residual stress reversal is caused by thermal stresses during high performance stop braking. Crack propagation and failure mechanisms are summarized. Measures for prevention are discussed.     

Delta wing in a subsonic flow

On the basis of experimental wind tunnel research, a topological classification of possible delta wing flow regimes is given and a diagram in angle of attack-sweep angle coordinates is constructed. A regime with two pairs of symmetrically disposed whirlwind like vortices formed on the surface of the wing is detected. The effect of the V-shape of the wing is considered. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 161–164, March–April, 1994.     

Dilute polymeric solutions close to bounding surfaces: Shear stresses in equilibrium

The problem of a dilute polymer solution in equilibrium close to a wall, an edge, and a corner, respectively, is studied theoretically. Detailed knowledge of the rheology in these regions is needed in order to obtain the proper boundary conditions for bulk variables. It is interesting to see that shear stresses are predicted, whose origin is based on the intramolecular (elastic) interaction between the beads.     

Interaction forces of particles dispersed in an electrolyte

Expressions are derived for the forces acting in a disperse medium in the presence of interaction of the double layers surrounding particles or drops of the dispersed phase when the potential of the dispersed particles is small. It is found that the force produced by the presence of double layers is proportional to the concentration gradient of the dispersed particles. It is shown that this force is comparable with the force produced by Brownian motion of the particles and may even exceed it. The equations of motion for the dispersed phase are derived with allowance for the convective terms, the pressure gradient, and the forces caused by Brownian motion and the presence of the double layers. A generalized Fick's law is obtained with effective diffusion coefficient. The equilibrium distribution of the particle concentration in a uniformly rotating cylinder is found with allowance for the interaction of the double layers.Translated from Izvestiya Akademii Nauk SSSR, Meklianika Zhidkosti i Gaza, No. 5, pp. 98–102, September–October, 1984.     

Screw dislocation pile-ups in two phase materials of finite rigidity

The arrangement of discrete screw dislocations piled-up under the action of a uniform applied stress against the welded interface between different elastically isotropic half-spaces has been determined by representing the pile-up as a continuous distribution of infinitesimal dislocations. The dislocation slip plane is inclined at an arbitrary angle $\text{1}\text{2}\text{aπ}$ to the normal to the interface, assuming a to be a rational number. The singular integral equation expressing the condition for static equilibrium of the dislocations under a constant applied stress is solved by a method based on the Wiener-Hoph technique with the Mellin transform, and from this solution the mean density of dislocations and the stress field of the pile-up are determined.