Optical response of a layer of a nematic liquid crystal to an air flow

A liquid crystal coating is used to measure the surface friction created when a flat plate is subjected to an air flow. Surface friction is determined from the optical response of the nematic liquid crystal coating to the flow. The proposed method does not require precise monitoring of the thickness of the coating or the angles of illumination and observation. This makes it possible to eventually progress to panoramic measurements of surface aerodynamic characteristics. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 4, pp. 102–109, July–August, 1998.     

Method of effective length for the boundary layer on a thin filament drawn out of a half-space

Heat transfer from a thin filament pulled from a half-space is considered. On the basis of the self-similar solution, obtained in the study, and using the method of effective length, the friction and heat transfer coefficients on the surface of a thin filament of varying radius and with distributed surface temperature and velocity are determined. The results obtained with this approximate method agree well with the results of a numerical solution of the boundary layer equations. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 23–28, January–February, 1994.     

On local perturbations of a boundary layer with small skin friction

This paper studies the effect of two-dimensional surface irregularities on the flow in a plane steady boundary layer with small skin friction in an incompressible fluid. A detailed analysis is carried out for the flow regime with a given pressure gradient determined on the scale of the small irregularity by its shape. It is shown that there is a critical value of the height (depth) of the irregularity at which the skin friction first becomes zero, and the nonuniqueness of the corresponding solution is established. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 87–97, November–December, 1998. The work was financially supported by the Russian Foundation for Basic Research (project No. 97-01-00354).     

Critical equilibrium state of a bushing in a contact pair with cracks possessing plastic tip zones

The problem of mechanics of contact fracture is considered for a bushing in a friction pair. It is assumed that multiple reciprocating motion of the plunger leads to fracture of the bushing material owing to friction caused by contact interaction and accompanied by the joint effect of loading and temperature. It is assumed that there are several arbitrarily located straight-line cracks with tip zones near the contact surface of the bushing. The stress state of the bushing is examined in the presence of regions where the crack faces (or some part of them) come into contact. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 145–156, September–October, 2006.     

Effect of local heat supply to a turbulent boundary layer on the friction

The results of calculating a supersonic turbulent boundary layer on a flat plate in the presence of thermal energy supply to the boundary layer are presented. Two methods of energy supply are considered: heating a local interval of the surface, which is otherwise thermally insulated and using a local volume heat source. It is shown that for the same amount of heat supplied to the gas volume heating leads, under certain conditions, to greater friction reduction than the surface heating. Localization of the energy supply zone leads to the intensification of the viscous drag reduction effect and to a greater decrease in the local friction coefficient, which extends a considerable distance downstream. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 48–56, January–February, 1997. The work was carried out with financial support from the Russian Foundation for Fundamental Research (project No. 93-013-17600).     

Friction and Heat Transfer in a Laminar Separated Flow behind a Rectangular Step with Porous Injection or Suction

Results of a numerical study of a laminar separated flow behind a rectangular step on a porous surface with uniform injection or suction are described. Two cases are considered: an unconfined flow past a step and flow evolution in a confined channel (duct). It is shown that mass transfer on the surface causes strong changes in the flow structure and substantially affects the position of the reattachment point, as well as friction and heat transfer. More intense injection leads first to an increase in the separation-zone length and then to its rapid vanishing due to boundary-layer displacement. Vice versa, suction at high Reynolds numbers Re _s > 100 reduces the separation-zone length. The duct flow has a complicated distribution of friction and heat-transfer coefficients along the porous surface owing to the coupled effect of the transverse flow of the substance and changes in the main flow velocity due to mass transfer. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 18–28, January–February, 2006.     

Effects of Viscous Dissipation on Unsteady Free Convection in a Fluid Past a Vertical Plate Immersed in a Porous Medium

The effects of viscous dissipation on unsteady free convection from an isothermal vertical flat plate in a fluid saturated porous medium are examined numerically. The Darcy–Brinkman–Forchheimer model is employed to describe the flow field. A new model of viscous dissipation is used for the Darcy–Brinkman–Forchheimer model of porous media. The simultaneous development of the momentum and thermal boundary layers are obtained by using a finite difference method. Boundary layer and Boussinesq approximation have been incorporated. Numerical calculations are carried out for various parameters entering into the problem. Velocity and temperature profiles as well as local friction factor and local Nusselt number are shown graphically. It is found that as time approaches infinity, the values of friction factor and heat transfer coefficient approach steady state.     

Numerical study of initial pulsed motion of a powder layer in a duct under the action of a compressed gas

One-dimensional plane pulsed joint motion of a gas phase and a disperse phase in the presence of friction of the latter against the duct walls are studied numerically using the model of a heterogeneous medium. It is established that two qualitatively different regimes of motion are possible, depending on the initial conditions in a high-pressure chamber and the value of the friction factor. It is found that the powder exit velocity is self-similar with respect to friction. Mozhaiskii Military Space Engineering Academy, St. Petersburg 197082. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 122–127, November–December, 1999.     

Reynolds analogy in a dusty laminar boundary layer

The nonisothermal Blasius problem for a gas suspension is considered on the basis of the equations of a quasiequilibrium two-phase laminar boundary layer [1–3]. Approximate analytical expressions are obtained for the friction and heat transfer coefficients and their region of applicability is estimated; the Reynolds analogy between friction and convective heat transfer processes [4] is extended to the case of a dusty quasiequilibrium laminar boundary layer. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 160–162, November–December, 1986.     

Modeling of heat transfer in a turbulent flow around a heat-conducting plate with local regions of heating

A solution of the coupled nonstationary boundary-value problem of turbulent flow around a flat heat-conducting plate of finite thickness having local regions with volume heat sources is given. For modeling the heat transfer in the boundary layer, thek-ε turbulence model is used. It is shown that the thermal conductivity of the plate material significantly affects the surface distributions of both temperature and local friction. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 79–86, November–December, 1998. The work received financial support from the International Scientific and Engineering Center (project No.199).     

Skin friction topology in a region enclosed by penetrable boundary

High-resolution skin friction fields in separated flows on a low-aspect-ratio rectangular wing are obtained by using quantitative global skin friction diagnostics based on surface luminescent oil visualizations. The topological features like the isolated singular points and the boundary switch points in regions enclosed by penetrable boundaries are identified. The conservation law given by the Poincare–Bendixson index formula for the numbers of the isolated singular points and the boundary switch points is used as a general approach to analyze the topological structure of a skin friction field in a singly connected region enclosed by a penetrable boundary in the separated flows.     

Soil Behavior at the Interface with a Rigid Projectile During Penetration

The motion and state of soil at the interface with a penetrating rigid projectile is studied by numerical solution of the problem of a cylindrical projectile which expands and at the same time moves translationally along its axis in soil. The soil behavior is described using the model of a compressible elastoplastic medium with transition to a plastic state depending on the pressure in it. It is shown that a thin layer of soil at the interface with the projectile nose should be set in motion and move together with the projectile without sliding. An analysis is performed of the validity of using the dry friction law to determine the shear stresses on the projectile surface during penetration. The heat release in the soil layer at the interface due to internal friction and its possible effect on the penetration are estimated. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 116–127, November–December, 2005.     

Experimental study on influence of microscale effects on liquid flow characteristic in microtubes

Using deioned water as a working fluid, the influence of the microscale effects on liquid flow resistance in microtubes with inner diameters of 19.6 and 44.2 μm, respectively, is experimentally studied. The temperature rise resulted from the microscale effects, such as viscous dissipation, electric double layer, wall rough on the wall surface, etc., is obtained by an IR camera with a special magnified lens adopting micro-area thermal image technology and the corresponding pressure drop and the flux are also measured, so the relationship among friction factor, temperature rise and Reynolds number is obtained. Investigation shows that experimental data are almost equal to those of Hagen–Poiseuille when Reynolds number is low. With the increase of Reynolds number, the values of the friction factor depart from that of classical theory due to the microscale effects. Moreover, the values of the experimental friction factor considering various microscale effects is the maximal 10–15% deviation from that of friction factor without considering various microscale effects with further increase of Reynolds number.     

Nonsimilar boundary-layer flow over a stationary permeable plate in a rotating fluid with a magnetic field

Summary  The nonsimilar boundary-layer flow and heat transfer over a stationary permeable surface in a rotating fluid in the presence of magnetic field, mass transfer and free stream velocity are studied. The parabolic partial differential equations governing the flow have been solved numerically by using a difference–differential method. For small streamwise distance, these partial differential equations are also solved by a perturbation technique with Shanks transformation. For uniform mass transfer, analytical solutions are obtained. The surface skin friction coefficients and the Nusselt number increase with the magnetic field, suction and streamwise distance from the leading edge of the plate except the skin friction coefficient in the y-direction which decreases with the increasing magnetic field. Received 4 December 2001; accepted for publication 24 September 2002     

Motion of a flexible finite-length filament in a flow of a viscous fluid

The two-dimensional problem of the configuration of a flexible filament of finite length in a deformable viscous fluid is solved. The flexuural stresses in the filament and the inertial and gravitational forces are not taken into account. The equilibrium equations are obtained. The friction force that acts on the filament surface from the side of the viscous fluid is proportional to the flow rate. The specific features of the evolution of a bent filament under the conditions of pure and simple shear of a fluid are studied numerically. Analytical solutions are obtained for the evolution of a rectilinear filament; in particular, the stretching force in the filament is found. For the indicated types of flow, the stability of a rectilinear filament against small perturbations is investigated. Volzhskii Polytechnical Institute at the Volgograd State Technical University, Volgograd 404121. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 144–153, March–April, 2000.     

Entropy generation of radiation effect on laminar-mixed convection along a wavy surface

The effects of thermal radiation on laminar-forced and free convection along the wavy surface are studied. The optically thick limit approximation for the radiation flux is assumed. A modified form for the entropy generation equation is derived. The effect of geometry (e.g. flat surface, wavy surface), fluid friction and heat transfer (e.g. convection and radiation effects) are all included in the modified entropy generation form. Prandtl’s transposition theorem is used to stretch the ordinary coordinate system in certain directions. The wavy surface can be transformed into a calculable planar coordinate system. The governing equations are derived from the complete Navier–Stokes equations. A simple transformation is proposed to transform the governing equations into boundary layer equations for solution by the cubic spline collocation method.     

Melting heat transfer in steady laminar flow over a moving surface

The steady laminar boundary layer flow and heat transfer from a warm, laminar liquid flow to a melting surface moving parallel to a constant free stream is studied in this paper. The continuity, momentum and energy equations, which are coupled nonlinear partial differential equations are reduced to a set of two nonlinear ordinary differential equations, before being solved numerically using the Runge–Kutta–Fehlberg method. Results for the skin friction coefficient, local Nusselt number, velocity profiles as well as temperature profiles are presented for different values of the governing parameters. Effects of the melting parameter, moving parameter and Prandtl number on the flow and heat transfer characteristics are thoroughly examined. It is found that the problem admits dual solutions.     

Radiation effect on MHD mixed convection flow about a permeable vertical plate

This study investigates mixed convection heat transfer about a permeable vertical plate in the presence of magneto and thermal radiation effects. The effects of the mixed convection parameter, the radiation–conduction parameter, the surface temperature parameter, the magnetic parameter and the suction/injection parameter on the local skin friction and local heat transfer parameters are presented and analyzed.     

Translation of a rigid body with gravity–friction seismic dampers

A refined mathematical dynamic model of a rigid body with a gravity–friction seismic damper moving inside a movable hemispherical rough depression is set up. This model describe the frequency and decrement properties of a rigid body undergoing translational vibrations on a gravity–friction seismic-isolation mechanism. The mechanism consists of two platforms. The lower (supporting) platform has spherical supports that contact with the upper (supported) platform within its hemispherical depressions. The equations of motion incorporate the nonideality of the unilateral constraints and the shock interaction of a material point with the sphere. It is shown how to join the models describing the free motion and the sliding motion of the point over a spherical surface     

Effect of pressure gradient of friction and heat transfer in a dusty boundary layer

Approximate analytic expressions for the local friction and heat transfer coefficients in a dusty laminar boundary layer are obtained and tested in the case of an incompressible carrier phase, power-law variation of the external gas flow velocity and small velocity and temperature phase disequilibrium. These expressions supplement the numerical analysis of the dusty boundary layer on a blunt body [1, 2] and the asymptotic calculation of the friction and heat transfer in a quasiequilibrium dusty gas boundary layer on a plate [3]. The combined effect of dustiness and pressure gradient on the friction and heat transfer coefficients is discussed. The results obtained can be used for the practical calculation of the friction and heat transfer in a quasiequilibrium dusty laminar boundary layer and for interpreting the corresponding experimental data. Tomsk. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 105–108, September–October, 1988.