Calculation of accelerated motion of fluid in a tube

The results of calculation of accelerated flow of a fluid in a tube are compared with known experiments [1] in the laminar regime. The difference method was used to obtain a solution for unsteady axisymmetric flow that becomes steady over the length of the tube; this case was calculated earlier by Gromeka in the form of a series. An expression is derived for the coefficient of friction as a function of the Reynolds number Re and the acceleration of the fluid. The comparison reveals agreement between the results with an error not worse than 37%. However, the calculation gives a coefficient of friction proportional to Re to the power –1.5, whereas the experiment [1] reveals a weaker dependence proportional to Re to the power –1.15.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 158–160, September–October, 1981.     

Boundary layer in the vicinity of the stagnation point of a body of axial symmetry in a turbulent stream

The flow in the boundary layer in the vicinity of the stagnation point of a flat plate is examined. The outer stream consists of turbulent flow of the jet type, directed normally to the plate. Assumptions concerning the connection between the pulsations in velocity and temperature in the boundary layer and the average parameters chosen on the basis of experimental data made it possible to obtain an isomorphic solution of the boundary layer equations. Equations are obtained for the friction and heat transfer at the wall in the region of gradient flow taking into account the effect of the turbulence of the impinging stream. It is shown that the friction at the wall is insensitive to the turbulence of the impinging stream, while the heat transfer is significantly increased with an increase in the pulsations of the outer flow. These properties are confirmed by the results of experimental studies [1–4].Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 83–87, September–October, 1973.     

Investigation of the mechanism of surface turbulent friction reduction by means of large-eddy breakup devices

The results of an experimental investigation of the mechanism of reducing surface friction by mounting thin plates — large-eddy break-up devices (LEBUs) — in a turbulent boundary layer parallel to the surface are given. The conditions under which the surface friction reduction is minimal are determined. It is shown that the presence of LEBUs in the turbulent boundary layer leads to a decrease in the frequency of decelerated-fluid ejection from the wall region into the outer region of the boundary layer.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 80–89, September–October, 1996.     

Effect of friction on motion of a piston driven by combustion products

In recent years the two-stage light gas ballistic apparatus with deformable plastic pistons has become widely used in experimental aerodynamics. The existing methods of calculating such devices either completely neglect friction of the piston on the channel wall [1–3] or use a schematization of the frictional forces [4–6], which does not have a satisfactory physical basis. In a number of studies [7, 8] the friction force was considered constant, and its value was specified not from physical considerations, but to produce the best agreement between calculated and experimental values of object velocity or driving gas pressure. Since friction is such a significant factor, its proper consideration in calculating piston motion parameters requires special study. In this connection, it is useful to consider the operation of only the first stage of the ballistic apparatus, which sets the piston in motion. Below we will consider the problem of the internal ballistics of a one-stage powder-driven apparatus in the column channel of which a piston made of polymer material moves, experiencing friction. The friction model is constructed on the basis of a series of experiments on the slow forcing of polymer specimens compressed in the longitudinal direction through a steel channel. An experimental study was made of the relationship between the gunpowder gas pressure and time within a constant volume chamber, allowing establishment of the true powder-burning law, and its deviation from the geometric law of [9]. Calculated and experimental values of maximum gas pressure and muzzle velocity of a polyethylene piston are compared.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 73–80, September–October, 1978.The authors express their gratitude to S. S. Grigoryan for his interest in the study and valuable advice, and to G. N. Suntsov for aid in performing the experimental studies.     

Investigation of the flow structure in a plane turbulent jet

Results of an experimental investigation of a plane, submerged air jet are elucidated. The distribution of the mean velocity, the longitudinal and transverse velocity component pulsations, the tangential friction stress, and the correlation coefficient in jet cross sections are presented. The results of measurements are compared with the data of other authors.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 176–179, July–August, 1970.     

Problem of a piston in a plastic medium with cultivation

The article discusses the self-similar problem of the motion of a spherical piston in a medium with dry friction and the differential connection between the first invariant of the stress tensor and the second invariant of the tensor of the deformation rates. For the case of flow with a shock wave, the method of a stationary wave is used to obtain the required relationships at a strong discontinuity. It is disclosed that the velocity of the piston, as well as the relationship between the cultivation coefficients and the dry friction, are determined by the smoothness of the friction.Translated from Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, 86–93, September–October, 1974.     

Nonsteady motion of a dropping compressible liquid in pipes under different laws of friction

Certain cases of nonsteady motion of a dropping compressible liquid with different laws of friction in conduits (in particular, in main oil pipelines) are considered. Results are presented of a solution of a number of problems of unsteady motion of a dropping liquid in pipes with a square law of resistance and for regimes characteristic of hydraulically smooth pipes, obtained numerically by the method of finite differences (method of nets). A comparison is made to results obtained by linearizing the term containing the square-law friction according to a previous [1] technique. Deviations of the parameters of nonsteady flows for given laws of resistance are studied.Translated from Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 87–94, January–February, 1976.     

Viscous sublayer in the neighborhood of a corner point in supersonic flow past a cooled body

The behavior of the flow functions at the upper edge of the viscous sublayer is subjected to an asymptotic analysis. The results obtained permit a more accurate formulation of the boundary-value problem and an improvement in the quality of numerical calculation of the flow in the viscous sublayer. The heat flux and friction distributions on the surface of the body are obtained for precritical and postcritical interaction regimes; for expansion flows the calculated results are presented in the form of the dependence of the maximum values of the friction and heat flux on the temperature factor and the angle of deflection of the flap; approximate expressions suitable for practical use are proposed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 142–147, November–December, 1989.     

Friction and heat transfer with simultaneous convection on a permeable surface

The velocity and heat transfer fields near a vertical permeable surface with simultaneous convection are investigated. A solution is found for the boundary layer equations with known laws of surface temperature and flow velocity change. The transformed boundary layer equations contain the parameter G/R², which determines the effect of free convection on friction and heat transfer for constrained motion. Calculations of friction and heat transfer as functions of draft (suction) with simultaneous convection are presented.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 96–100, March–April, 1973.     

Experimental investigation of the effect of longitudinal riblets on the friction drag of a flat plate

The results of a gravimetric investigation of the effect of longitudinal riblets on the friction drag of a flat plate are presented. The experiments were carried out with both natural and artificially thickened developed turbulent boundary layers in a zero-gradient flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 140–145, March–April, 1987.The authors wish to thank V. V. Mikhailov for his valuable assistance.     

Experimental study of the effect of riblets and LEBU-devices on the drag of a body of revolution

The effect of ribbed coatings and large-eddy-breakup devices (LEBUs) on the turbulent friction and total drag of a body-of-revolution model has been studied in a low-speed wind tunnel.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 154–157, May–June, 1996.     

Slow rotation of a sphere in a confined volume of a dilute gas

The axially symmetric motion of a gas in a volume confined between an external immobile surface of rotation and a coaxial surface of a rotating sphere is considered. A solution is obtained by the moment method based on the Boltzmann equation with a collision integral of Maxwellian molecules. The gas-velocity distribution and an expression for the friction torque exerted on the sphere are obtained for arbitrary Knudsen numbers and for an arbitrary shape of the outer surface. The proportionality of the gas slip velocity over the surface of the sphere to the friction strain is shown. The friction torque is investigated for specific shapes of the outer surface. The motion of a gas filling the space between concentric spheres, each of which rotates about an arbitrary axis, is treated. In the limiting case of small Knudsen numbers the expressions obtained are compared with the corresponding results for a continuous medium.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 117–124, July–August, 1978.The authors are grateful to the participants of the seminars guided by G. I. Petrov and A. M. Golovnyi for discussions concerning this work.     

Effect of the friction of a thrown piston on the internal ballistics of a one-stage unit

The present article gives a method for the direct measurement of the friction force of cylindrical samples strongly compressed along the axis at the wall of the bore of a gun with a small velocity of the motion, modelling the behavior of a piston in a ballistic unit. As an example, the article gives the results of measurements with a polymer material, i.e., caprolon. On the basis of an experimental investigation, a new friction model is constructed, which is used for the solution of the problem of the internal ballistics of a single stage powder unit with a piston made of caprolon. The laws of similarity of the processes under consideration are investigated. It is established that the value of the maximal pressure of the powder gases and velocity of the piston depend essentially on the value of the friction coefficient.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 76–83, May–June, 1978.     

Determination of mechanical properties of fiber–matrix interface from pushout test

For ceramic matrix composites, the pushout test is the most widely used test for finding the two mechanical properties of the fiber–matrix interface – (1) the coefficient of friction and (2) the residual radial stress. Experimental measurements from the pushout test do not directly give the values of these two mechanical properties of the fiber–matrix interface, but need to be regressed to theoretical models. Currently, approximate theoretical models based on shear–lag analysis are used for regression. In this paper, the adequacy of the shear–lag analysis model in accurately finding the mechanical properties of the fiber–matrix interface is discussed. An elasticity solution of the pushout test based on boundary element method is developed. Regressing one set of available experimental data from a pushout test to both shear–lag analysis and boundary element method models gives values differing by 15% for the coefficient of friction but similar values for the residual radial stress. Parametric studies were also conducted to show the difference between the shear–lag analysis and boundary element method results for factors such as fiber to matrix elastic moduli ratios, coefficient of friction and fiber volume fractions.     

Interaction of wall turbulence with a compliant surface

The effect of various parameters of the compliant surface on the interaction with wall turbulence is analyzed using the monoharmonic approximation. It is shown that the interaction is resonant in character and that for certain values of the parameters a considerable reduction in turbulent skin friction is possible.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 67–72, July–August, 1990.     

Effect of longitudinal riblets on the aerodynamic characteristics of a straight wing

The results of balance aerodynamic tests on model straight wings with smooth and ribbed surfaces at an angle of attack =–4°–12°, Mach number M=0.15–0.63, and Reynolds number Re=2.4·10⁶–3.5·10⁶ are discussed. The nondimensional riblet spacings ⁺, which determines the effect of the riblets on the turbulent friction drag, and the effect of riblets on the upper and/or lower surface of a straight wing on its drag, lift, and moment characteristics are estimated.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 33–38, March–April, 1995.     

Dynamic Processes in a Spheroidal Seismic-Damping Mechanism

A mathematical model of a variable-structure system of solids with rolling friction and unilateral sliding friction bonds is described. The model can be applied to seismic isolation mechanisms. Conditions for transition between the possible structures of the equations of state are formulated. The behavior of the system with kinematically defined motion of the base is analyzed as an example__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 1, pp. 119–127, January 2005.     

Combined effect of longitudinal riblets and LEBU-devices on turbulent friction on a plate

The possibility of reducing turbulent friction with the help of large-eddy-breakup devices (LEBUs) and riblets is studied experimentally. The tests were conducted in a low-turbulence wind tunnel on a flat plate for 2·10⁶ Re 7·10⁶. The local friction coefficient was measured using internal strain-gauge balances, and the total drag was estimated by the momentum-transfer method. It is shown that a combination of LEBUs and riblets makes it possible to reduce the total turbulent friction drag of a flat plate 1800 mm long by 16%. The effects of the length of a ribbed surface on the efficiency of friction reduction and of LEBUs and riblets on the structure of a turbulent boundary layer are analyzed.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 39–46, May–June, 1995.     

Problem of a solid half-space melted by a hot rotating disk or ring

The sliding friction of solids at high speed and under heavy load may be accompanied by a transition to the plastic or fluid state in the friction contact zone [1]. The stage corresponding to a developed fluid layer is investigated without taking into account the plastic deformation of the rubbing bodies; it is assumed that all the heat released is expended exclusively on melting the solid. Previous attempts to investigate this stage theoretically have been based on the approximation of a fluid layer of constant thickness and the use of the heat balance equation [1, 2]. Here, the velocity and temperature profiles are approximated by relations quadratic in the transverse coordinate with coefficients that depend on the longitudinal coordinate. These are determined from the boundary conditions and the integral relations of boundary layer theory. The relations obtained are used to determine the rate at which a hot rotating ring melts through a block of ice.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 30–34, May–June, 1990.