Micropolar squeeze films between rough rectangular plates

In this paper, the lubrication theory for squeezing with micropolar fluids in smooth surfaces has been advanced to analyze the effects arising from roughness considerations using the stochastic approach. This theory is subsequently applied to the problem of squeezing between rough rectangular plates. It is observed that the roughness effects are more pronounced for micropolar fluids as compared to the Newtonian fluids.Nomenclature a x-dimension of rectangular plate - A area of rectangular plate - b z-dimension of rectangular plate - B non-dimensional roughness parameter, c/h _n (for load capacity), c/h _n1 (for squeeze time) - c maximum asperity deviation from nominal film height - E expectancy operator - f(N, l, h) defined by equation (4) - F(N, L, H) defined by equation (31) - F ₁(N, L, B) defined by equation (29) - F ₂(N, L, B) defined by equation (30) - F ₃(N, L, H _n , B) defined by equation (34) - F ₄(N, L, H _n , B) defined by equation (35) - g probability density distribution function - h film height, h=h _n +h _s - h _n nominal film height - h _s deviation of film height from nominal level - h _n1 initial (nominal) film height - H, H _n , H _s non-dimensional forms of h, h _n , h _s respectively - l characteristic material length, (/4)^1/2 - L length ratio, h _n /l (for load capacity), h _n1/l (for squeeze time) - n integer - N coupling number, (/(2+))^1/2 - p pressure - q _x , q _z flow components in x- and z-directions, respectively - t time - T non-dimensional time - w load capacity - W non-dimensional load capacity - x, z cartesian coordinates - angular coordinate - Newtonian viscosity - , micropolar viscosity coefficients - aspect ratio, b/a - standard deviation - /h _n - random variable - defined by equation (19) - defined in equation (28) - defined in equation (33)     

Derivation of two-dimensional couple-stress hydromagnetic squeeze film Reynolds equation and application to wide parallel rectangular plates

On the basis of Stokes couple-stress fluid model together with the hydromagnetic flow equations, a two-dimensional curved squeeze-film Reynolds equation has been derived. This equation can be applied to the study of squeeze film characteristics including the non-Newtonian hydromagnetic effects, in which the general film shape is h=h(x,z,t). To guide the application of the equation, an example of one-dimensional parallel rectangular plates lubricated with a non-Newtonian couple-stress, electrically conducting lubricant is illustrated. According to the results, the effects of couple stresses and external magnetic fields provide an increase in the load capacity and the response time as compared to the classical Newtonian hydrodynamic rectangular squeeze-film plates.     

Combined natural and forced convection hydromagnetic flow between electrically conducting walls

Summary The combined natural- and forced convection flow of a viscous, electrically conducting liquid between parallel electrically conducting walls, in the presence of a transverse magnetic field is analysed. The walls are taken to be at temperatures linearly varying along their lengths. The resulting nonlinear differential equations are solved in terms of even and odd functions depending on the Hartmann number and a modified Rayleigh number, so that solutions for a variety of conditions may be easily computed from their values. The cumulative effect of dissipative and Joule heating are found to be negligible. The Nusselt numbers and viscous drag are found to diminish with increase of the conductivities of the walls.On study leave from Coimbatore Institute of Technology, Coimbatore, India     

Performance of conical entrance orifice plates at low Reynolds numbers

Results are presented of an experimental investigation into the performance of conical entrance orifice plates manufactured according to BS 1042. Three plates, with diameter ratios of 0.247, 0.360 and 0.448, were tested in the region 100 < Re_D ? 1000 and in both the concentric and the fully eccentric position. The discharge coefficient, C_z, of the orifice was found to agree with that specified in BS 1042 for a diameter ratio of 0.247. For other diameter ratios, the discharge coefficient increased with the diameter ratio, as observed by other workers for the Kent plates. The eccentricity has no appreciable effect on the discharge coefficient, probably due to the effect of viscous action on the flow being more or less the same for the concentric and eccentric position of the orifice at low Reynolds numbers     

Plane strain compression between rough inclined plates

Summary The normal pressure distribution on rough plates, inclined at various angles, and the mean vertical pressure to effect a sideways expulsion of metal in terms of the plane-strain compressive yield stress of the material have been calculated using slip-line field solutions and conventional technological theory; the results are plotted for immediate use. A comparison of the results afforded by both these approaches is also made.     

On unsteady hydromagnetic flows of a dusty fluid between two oscillating plates

An initial value investigation is made of the motion of an incompressible viscous conducting fluid with embedded small spherical particles bounded by two infinite rigid non-conducting plates. The flow is generated in the fluid-particle system due to rectilinear oscillations of given frequencies superimposed on the plates in presence of an external transverse magnetic field. The operational method is used to derive exact solutions for the fluid and the particle velocities and the wall shear stress. It is shown that the effect of the dust particles on the fluid velocity depends on the time periods of the oscillating plates. When the time-periods are small, i.e., when the plates oscillate with high frequency, the fluid motion is found to be retarded by the particles. However, when the plates oscillate with larger time periods (smaller frequencies), the fluid velocity is increased by the presence of the particles at the early stage of the motion, and this effect persists until the equilibrium is reached when the particles exert their influence to resist the flow.     

Compression of a viscoelastic layer between rough parallel plates

If the maximal friction law is applied, then some generalizations of the Prandtl solution for the compression of a plastic layer between rough plates do not exist. In particular, this pertains to the viscoplastic solutions obtained earlier. In the present paper, we show that these solutions do not exist because of the properties of the model material and introduce a model for which this solution can be constructed. The obtained solution is singular. In particular, the equivalent strain rate tends to infinity as the friction surface is approached, and its asymptotic behavior exactly coincides with that arising in the classical solution. The obtained solution is illustrated by numerical examples, which, in particular, show that an extremely thin boundary layer may arise near the friction surfaces.     

Non-isothermal and viscoelastic effects in the squeeze flow between infinite plates

We investigate the early development of the squeeze flow for a finite amount of fluid material between two infinite plates. Finite element simulations are performed, and allow to capture complex features. In particular, we focus on the development of temperature boundary layers as well as of viscoelastic effects. Furthermore, we evaluate the required squeezing force when a constant squeezing velocity is applied.     

Large deformations of viscoelastic squeeze films

The large deformation behavior of a viscoelastic squeeze film being compressed or extended between two parallel circular plates is studied from a Lagrangian viewpoint. A single integro-differential equation is shown to govern the flow of a rubberlike liquid in this geometry, and the solution is compared with results for a Newtonian squeeze film. Instantaneous solid-like response, small amplitude oscillations, and creep-recovery calculations are presented.     

Compression of a plastic porous material between rotating plates

The problem of a plane flow of a rigid-plastic porous material between two rotating rough plates with no material flux through the point of their rotation and with a uniform distribution of porosity at the initial instant is considered under the assumption that the material behavior follows the cylindrical yield condition and the associated flow rule. The solution reduces to consecutive calculation of several ordinary integrals. It is demonstrated that the solution behavior depends on the angle between the plates, and the value of porosity at a certain stage of the deformation process can be equal to zero. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 128–135, July–August, 2009.     

Elastic indentation of a rough surface by a conical punch

In the contact of a cone with a rough plane the mean pressure in the contact area is constant. In particular, above a critical ratio of the opening angle of the cone with respect to the rms gradient of surface roughness, the mean pressure is the same of that for nominally flat contact, no matter how large is the normal load. We introduce a new variable, namely, the local density of contact area, whose integral over the smooth nominal contact domain gives the real contact area. The results given by the theoretical model agree with the numerical simulations of the same problem presented in the paper.     

Heat and mass transfer in laminar flow between parallel porous plates

Summary The problem of heat transfer in a two-dimensional porous channel has been discussed by Terrill [6] for small suction at the walls. In [6] the heat transfer problem of a discontinuous change in wall temperature was solved. In the present paper the solution of Terrill for small suction at the walls is revised and the whole problem is extended to the cases of large suction and large injection at the walls. It is found that, for all values of the Reynolds number R, the limiting Nusselt number Nu increases with increasing R.Nomenclature stream function - 2h channel width - x, y distances measured parallel and perpendicular to the channel walls respectively - U velocity of fluid at x=0 - V constant velocity of fluid at the wall - =y/h nondimensional distance perpendicular to the channel walls - f() function defined in equation (1) - coefficient of kinematic viscosity - R=Vh/ suction Reynolds number - density of fluid - C _p specific heat at constant pressure - K thermal conductivity - T temperature - x=x ₀ position where temperature of walls changes - T ₀, T ₁ temperature of walls for x<x ₀, x>x ₀ respectively - = (T – T ₁)/T ₀ – T ₁) nondimensional temperature - =x/h nondimensional distance along channel - R ^* = Uh/v channel Reynolds number - Pr = C _p/K Prandtl number - _n eigenvalues - B _n() eigenfunctions - B _n ⁽⁰⁾ , () eigenfunctions for R=0 - B ₀ ⁽ⁱ⁾ , B ₀ ⁽ⁱⁱ⁾ ... change in eigenfunctions when R0 and small - K _n constants given by equation (13) - h heat transfer coefficient - Nu Nusselt number - _m mean temperature - C _n constants given by equation (18) - perturbation parameter - B _0i () perturbation approximations to B ₀() - Q = B ₀/ ₀ derivative of eigenfunction with respect to eigenvalue - z nondimensional distance perpendicular to the channel walls - F(z) function defined by (54)     

Resistance of rough plates in a rotating fluid

Generalizing Navier’s partial slip condition, the flow due to a rough or striated plate moving in a rotating fluid is studied. It is found that the motion of the plate, the fluid surface velocity, and the shear stress are in general not in the same direction. The solution is extended to the case of finite depth, or Couette slip flow in a rotating system. In this case an optimum depth for minimum drag is found. The solutions are also closed form exact solutions of the Navier–Stokes equations. The results are fundamental to flows with Coriolis effects.     

Modelling of ER squeeze films at low amplitude oscillations

An experimental investigation of electrorheological squeeze film dynamics is presented for constant applied voltage and low strain amplitude. Both broadband random and sinusoidal motion are examined to explain complex film dynamics. Spectral results indicate a primarily elastic response with slip at the plate boundaries. By examining the evolution of an effective shear modulus over time, sinusoidal results show that slip at the boundaries is due to a solvent layer which may be modelled as a separate variable thickness squeeze film.     

Dynamic motion of a conical frustum over a rough horizontal plane

An analytical and numerical study of the dynamic motion of a conical frustum over a planar surface is presented resulting to a non-linear system of ordinary differential equations. Wobbling and rocking components of motion are discussed in detail concluding that, in general, the former component dominates the latter. For small inclination angles an asymptotic approximation of the angular velocities is possible, revealing the main characteristics of wobbling motion and its differences from rocking. Connection is made of the analysis with the behavior of the ancient classical columns, whose three dimensional dynamic response challenges the accuracy of the two dimensional models, usually applied in practice. The consideration of such discrete-blocky systems can benefit from the present study, through qualitative results and benchmarks for more complicated numerical methods, like the Distinct Element Method.     

Stagnation-point viscous flow of an incompressible fluid between porous plates with uniform blowing

The axially-symmetric laminar flow of an incompressible viscous fluid resulting from uniform injection through two parallel porous plates is analyzed. An exact numerical solution as well as asymptotic solutions for high and low Reynolds numbers are obtained. It is found that the velocity component normal to the porous plates is everywhere independent of radial position. This property of uniform accessibility may make this flow geometry a useful experimental tool analogous to the rotating disc. The analysis of high Peclet number mass transfer across the center plane of this geometry is presented as an example.