Showing papers on "Lubrication theory published in 2011"

Elastohydrodynamic Lubrication: A Gateway to Interfacial Mechanics—Review and Prospect

Abstract: Elastohydrodynamic Lubrication (EHL) is commonly known as a mode of fluid-film lubrication in which the mechanism of hydrodynamic film formation is enhanced by surface elastic deformation and lubricant viscosity increase due to high pressure. It has been an active and challenging field of research since the 1950s. Significant breakthroughs achieved in the last 10–15 years are largely in the area of mixed EHL, in which surface asperity contact and hydrodynamic lubricant film coexist. Mixed EHL is of the utmost importance not only because most power-transmitting components operate in this regime, but also due to its theoretical universality that dry contact and full-film lubrication are in fact its special cases under extreme conditions. In principle, mixed EHL has included the basic physical elements for modeling contact, or hydrodynamic lubrication, or both together. The unified mixed lubrication models that have recently been developed are now capable of simulating the entire transition of interfacial status from full-film and mixed lubrication down to dry contact with an integrated mathematic formulation and numerical approach. This has indeed bridged the two branches of engineering science, contact mechanics, and hydrodynamic lubrication theory, which have been traditionally separate since the 1880s mainly due to the lack of powerful analytical and numerical tools. The recent advancement in mixed EHL begins to bring contact and lubrication together, and thus an evolving concept of “Interfacial Mechanics” can be proposed in order to describe interfacial phenomena more precisely and collaborate with research in other related fields, such as interfacial physics and chemistry, more closely. This review paper briefly presents snapshots of the history of EHL research, and also expresses the authors’ opinions about its further development as a gateway to interfacial mechanics. [DOI: 10.1115/1.4004457]

The influence of the cohesive process zone in hydraulic fracturing modelling

Abstract: This paper studies the importance of the cohesive zone in the modelling of a fluid driven fracture under plain strain conditions. The fracture is driven by pumping of an incompressible viscous fluid at the fracture inlet. Rock deformation is modeled for linear elastic and poroelastic solids. Fluid flow in the fracture is modeled by lubrication theory. The cohesive zone approach is used as the fracture propagation criterion. Finite element analysis was used to compute the solution for the crack length, the fracture opening and propagation pressure as a function of the time and distance from the wellbore. It is demonstrated that the crack profiles and the propagation pressures are larger in the case of elastic-softening cohesive model compared to the results of the rigid-softening cohesive model for both elastic and poroelastic cohesive solids. It is found that the results are affected by the slope of the loading branch of the cohesive model and they are nearly unaffected from the exact form of the softening branch. Furthermore, the size of the process zone, the fracture geometry and the propagation pressure increase with increasing confining stresses. These results may explain partially the discrepancies in net-pressures between field measurements and conventional model predictions.

Peristaltic pumping of viscous fluid in an elastic tube

Abstract: A model is derived for long peristaltic waves propagating steadily down a fluid-filled, axisymmetric tube. The waves are driven by imposing a radial force of prescribed form on the tube. The resulting deformation of the tube wall is modelled using linear elasticity and the internal flow using the lubrication approximation. Numerical solutions for periodic wave trains and solitary waves are presented, along with asymptotic solutions at both small and large forcing amplitudes. Large-amplitude periodic waves are characterized by narrow blisters adjoining long occluded sections of the tube, whereas a solitary wave of strong contraction produces a long inflated bow wave that propels a large quantity of fluid. A measure of pumping efficacy is given by the ratio of the net fluid displacement to the power input, and is highest for a large-amplitude solitary wave.

Lubrication in soft rough contacts: A novel homogenized approach. Part I - Theory

Abstract: We study the lubricated steady sliding contact between rough surfaces of (elastically) soft solids. A novel mean field theory of mixed lubrication is presented, which takes into account the coupled effect of asperity–asperity and asperity–fluid interactions. We calculate the fluid flow factors, and discuss the nature of the transition from the boundary lubrication regime, where the normal load is supported by the asperity–asperity interactions (sometimes mediated by boundary films), to the hydrodynamic regime, where a thin fluid film prevents direct contact between the mating surfaces.

Dynamics of elastocapillary rise

Abstract: We present the results of a combined experimental and theoretical investigation of the surface-tension-driven coalescence of flexible structures. Specifically, we consider the dynamics of the rise of a wetting liquid between flexible sheets that are clamped at their upper ends. As the elasticity of the sheets is progressively increased, we observe a systematic deviation from the classical diffusive-like behaviour: the time to reach equilibrium increases dramatically and the departure from classical rise occurs sooner, trends that we elucidate via scaling analyses. Three distinct temporal regimes are identified and subsequently explored by developing a theoretical model based on lubrication theory and the linear theory of plates. The resulting free-boundary problem is solved numerically and good agreement is obtained with experiments.

Quasi-steady capillarity-driven flows in slender containers with interior edges

Abstract: In the absence of significant body forces the passive manipulation of fluid interfacial flows is naturally achieved by control of the specific geometry and wetting properties of the system. Numerous ‘microfluidic’ systems on Earth and ‘macrofluidic’ systems aboard spacecraft routinely exploit such methods and the term ‘capillary fluidics’ is used to describe both length-scale limits. In this work a collection of analytic solutions is offered for passive and weakly forced flows where a bulk capillary liquid is slowly drained or supplied by a faster capillary flow along at least one interior edge of the container. The solutions are enabled by an assumed known pressure (or known height) dynamical boundary condition. Following a series of assumptions this boundary condition can be in part determined a priori from the container dimensions and further quantitative experimental evidence, but not proof, is provided in support of its expanded use herein. In general, a small parameter arises in the scaling of the problems permitting a decoupling of the edge flow from the global bulk meniscus flow. The quasi-steady asymptotic system of equations that results may then be easily solved in closed form for a useful variety of geometries including uniform and tapered sections possessing at least one critically wetted interior edge. Draining, filling, bubble displacement and other imbibing flows are studied. Cursory terrestrial and drop tower experiments agree well with the solutions. The solutions are valued for the facility they provide in computing designs for selected capillary fluidics problems by way of passive transport rates and meniscus displacement. Because geometric permutations of any given design are myriad, such analytic tools are capable of efficiently identifying and comparing critical design criteria (i.e. shape and size) and the impact of various wetting conditions resulting from the fluid properties and surface conditions. Sample optimizations are performed to demonstrate the utility of the method.

A group invariant solution for a pre-existing fluid-driven fracture in permeable rock

Abstract: The propagation of a two-dimensional pre-existing fracture in permeable rock by the injection of a viscous, incompressible Newtonian fluid is considered. The fluid flow in the fracture is laminar. By the application of lubrication theory, a partial differential equation relating the half-width of the fracture to the fluid pressure and leak-off velocity is derived. The model is closed by the adoption of the PKN formulation in which the fluid pressure is proportional to the fracture half-width. The partial differential equation admits four Lie point symmetries provided the leak-off velocity satisfies a first order linear partial differential equation. The solution of this equation yields the leak-off velocity as a function of the distance along the fracture and time. The group invariant solution is derived by considering a linear combination of the Lie point symmetries. The boundary value problem is reformulated as a pair of initial value problems. The model in which the leak-off velocity is proportional to the fracture half-width is considered. The working condition of constant pressure at the fracture entry is analysed in detail.

Bubble entrapment during sphere impact onto quiescent liquid surfaces

Abstract: We report observations of air bubble entrapment when a solid sphere impacts a quiescent liquid surface. Using high-speed imaging, we show that a small amount of air is entrapped at the bottom tip of the impacting sphere. This phenomenon is examined across a broad range of impact Reynolds numbers, 0.2 ≤ Re = (DU0/νl) ≤ 1.2 × 105. Initially, a thin air pocket is formed due to the lubrication pressure in the air layer between the sphere and the liquid surface. As the liquid surface deforms, the liquid contacts the sphere at a finite radius, producing a thin sheet of air which usually contracts to a nearly hemispherical bubble at the bottom tip of the sphere depending on the impact parameters and liquid properties. When a bubble is formed, the final bubble size increases slightly with the sphere diameter, decreases with impact speed but appears independent of liquid viscosity. In contrast, for the largest viscosities tested herein, the entrapped air remains in the form of a sheet, which subsequently deforms upon close approach to the base of the tank. The initial contact diameter is found to conform to scalings based on the gas Reynolds number whilst the initial thickness of the air pocket or ‘dimple’ scales with a Stokes' number incorporating the influence of the air viscosity, sphere diameter and impact speed and liquid density.

Peristaltic Transport of a Rheological Fluid: Model for Movement of Food Bolus Through Esophagus

Abstract: Fluid mechanical peristaltic transport through esophagus has been of concern in the paper. A mathematical model has been developed with an aim to study the peristaltic transport of a rheological fluid for arbitrary wave shapes and tube lengths. The Ostwald-de Waele power law of viscous fluid is considered here to depict the non-Newtonian behaviour of the fluid. The model is formulated and analyzed with the specific aim of exploring some important information concerning the movement of food bolus through the esophagus. The analysis has been carried out by using lubrication theory. The study is particularly suitable for cases where the Reynolds number is small. The esophagus is treated as a circular tube through which the transport of food bolus takes places by periodic contraction of the esophageal wall. Variation of different variables concerned with the transport phenomena such as pressure, flow velocity, particle trajectory and reflux are investigated for a single wave as well as for a train of periodic peristaltic waves. Locally variable pressure is seen to be highly sensitive to the flow index `n'. The study clearly shows that continuous fluid transport for Newtonian/rheological fluids by wave train propagation is much more effective than widely spaced single wave propagation in the case of peristaltic movement of food bolus in the esophagus.

On the modelling of hybrid aerostatic-gas journal bearings:

Abstract: Gas journal bearings have been increasingly adopted in modern turbo-machinery applications as they meet the demands of operation at high rotational speeds, in clean environment, and with great efficiency. Due to the fact that gaseous lubricants, typically air, have much lower viscosity than more conventional oils, carrying capacity and dynamic characteristics of passive systems are generally poorer. In order to enhance these characteristics, one solution is used to combine the aerodynamic effect with the addition of external pressurization. This study presents a detailed mathematical model for hybrid lubrication of a compressible fluid-film journal bearing. Additional forces are generated by injecting pressurized air into the bearing gap through orifices located on the bearing walls. A modified form of the compressible Reynolds equation for active lubrication is derived. By solving this equation, stiffness and damping coefficients can be determined. A multibody dynamics model of a global system comprised ...

Impact of slippage on the morphology and stability of a dewetting rim.

Abstract: In this study lubrication theory is used to describe the stability and morphology of the rim that forms as a thin polymer film dewets from a hydrophobized silicon wafer. Thin film equations are derived from the governing hydrodynamic equations for the polymer to enable the systematic mathematical and numerical analysis of the properties of the solutions for different regimes of slippage and for a range of timescales. Dewetting rates and the cross sectional profiles of the evolving rims are derived for these models and compared to experimental results. Experiments also show that the rim is typically unstable in the spanwise direction and develops thicker and thinner parts that may grow into 'fingers'. Linear stability analysis as well as nonlinear numerical solutions are presented to investigate shape and growth rate of the rim instability. It is demonstrated that the difference in morphology and the rate at which the instability develops can be directly attributed to the magnitude of slippage. Finally, a derivation is given for the dominant wavelength of the bulges along the unstable rim.

Numerical modelling of hydraulic seals by inverse lubrication theory

Abstract: This article describes a methodology used to achieve a numerical analysis of hydraulic seals by the inverse hydrodynamic lubrication method. The main novelties consist of taking into account the in...

No-Slip Boundary Condition for Weak Solid−Liquid Interactions

Abstract: Lubrication forces between hydrophobized glass surfaces in alkane liquids have been measured using the atomic force microscopy colloid probe technique and compared to Reynolds lubrication theory with the aim of understanding the nature of the solid−liquid boundary condition for flow. Forces in n-hexadecane are consistent with the no-slip boundary condition. Forces in n-pentane and n-hexane are better fit when a small slip length of about 5−20 nm is included in the model. The error estimating slip length is about 10 nm, which is much greater than the error in measuring the deflection of an AFM cantilever. We rationalize the finite slip length for n-pentane and n-hexane using an activation model for shear-driven molecular motion, which predicts that only molecules with an activation energy less than about 5 kT will have their diffusion affected by applied shear. The difference in slip length between short (pentane) and long (hexadecane) molecules is then explained by the fact that the short alkanes experien...

A Novel Bulk-Flow Model for Improved Predictions of Force Coefficients in Grooved Oil Seals Operating Eccentrically

Abstract: Oil seals in centrifugal compressors reduce leakage of the process gas into the support bearings and ambient. Under certain operating conditions of speed and pressure, oil seals lock, becoming a source of hydrodynamic instability due to excessively large cross coupled stiffness coefficients. It is a common practice to machine circumferential grooves, breaking the seal land, to isolate shear flow induced film pressures in contiguous lands, and hence reducing the seal cross coupled stiffnesses. Published tests results for oil seal rings shows that an inner land groove, shallow or deep, does not actually reduce the cross-stiffnesses as much as conventional models predict. In addition, the tested grooved oil seals evidenced large added mass coefficients; while predictive models, based on classical lubrication theory, neglect fluid inertia effects. This paper introduces a bulk-flow model for groove oil seals operating eccentrically and its solution via the finite element method. The analysis relies on an effective groove depth, different from the physical depth, which delimits the upper boundary for the squeeze film flow. Predictions of rotordynamic force coefficients are compared to published experimental force coefficients for a smooth land seal and a seal with a single inner groove with depth equaling 15 times the land clearance. The test data represent operation at 10 krpm and 70 bar supply pressure, and four journal eccentricity ratios (e/c = 0, 0.3, 0.5, 0.7). Predictions from the current model agree with the test data for operation at the lowest eccentricities (e/c = 0.3); discrepancies increasing at larger journal eccentricities. The new flow model is a significant improvement towards the accurate estimation of grooved seal cross-coupled stiffnesses and added mass coefficients; the later previously ignored or largely under predicted.Copyright © 2011 by ASME

The energetics of the breakup of a sheet and of a rivulet on a vertical substrate in the presence of a uniform surface shear stress

Abstract: We use the lubrication approximation to obtain a complete description of the energetics of the breakup both of a fluid sheet of uniform thickness into a periodic array of infinitely many identical thin rivulets and of a single thin rivulet into one or more identical sub-rivulets on a vertical substrate in the presence of a prescribed uniform longitudinal shear stress at the free surface of the fluid by comparing the total energies of the different states. For both problems the situation when the volume flux is positive is relatively straightforward (and, in particular, qualitatively the same as that in the case of no prescribed shear stress), but when the volume flux is negative it is more complicated. However, whatever the value of the prescribed shear stress, there is always a critical thickness below which it is energetically favourable for a sheet to break up into rivulets and a critical semi-width below which it is energetically favourable for a rivulet to remain as a single rivulet, and a critical thickness above which it is energetically favourable for a sheet to remain as a sheet and a critical semi-width above which it is energetically favourable for a rivulet to break up into sub-rivulets.

Highly transient squeeze-film flows

Abstract: The aim of this work was to investigate the flow evolution with time of fluid between two parallel disks and the corresponding pressure variations at the centre of the lower disk that occur subsequent to an impact-loading situation arising from dropping a mass onto the upper disk from a chosen height. During the event a fixed amount of energy is dissipated in the fluid between the disks through the action of friction. Therefore, this fundamental system may be regarded as a constant energy one, as distinct from one in which the upper disk is moving at a constant velocity, or is acted upon by a constant force. A test cell was set up to conduct the investigation, for which the separation between the disks was monitored, together with the pressure at the centre of the lower disk, over the duration of the experiment (about 8–10 ms). Glycerine was used as the test fluid. The equation of motion, based on a self-similarity approach, was reduced to a simpler (quasi-steady linear or QSL) form. Measured values of disk separation, velocity and acceleration were substituted as inputs into the full QSL model and two limiting cases, namely an inviscid and a viscous model. The QSL model provided excellent comparisons between the pressure measurements and data generated by a commercial computational fluid dynamics software package, throughout the duration of a typical experiment. The inviscid and viscous models achieved good correlations with measurements for the initial impact (during which disk accelerations exceeding 2 km s−2 occurred) and towards the end of the event, that were characterized by a small and much larger pressure rise, respectively. The former feature appears not to have been previously reported and is likely to typify that which would be observed in impact systems involving squeeze films.

Interface morphologies in Liquid/liquid dewetting

Abstract: The dynamics and morphology of a liquid polystyrene (PS) film with a thickness on the scale of a hundred nanometer dewetting from a liquid polymethylmethacrylate (PMMA) film is investigated experimentally and theoretically. The polymers considered here are both below their entanglement lengths and have negligible elastic properties. A theoretical model based on viscous Newtonian flow for both polymers is set up from which a system of coupled lubrication equations is derived and solved numerically. A direct comparison of the numerical solution with the experimental findings for the characteristic signatures of the cross-sections of liquid/air and liquid/liquid phase boundaries of the dewetting rims as well as the dewetting rates is performed and discussed for various viscosity ratios of the PS and PMMA layers.

No-slip hydrodynamic boundary condition for hydrophilic particles

Abstract: We describe measurement and interpretation of the force acting on a smooth hydrophilic glass particle during rapid (1 - 100 mms -1) approach to, and separation from, a hydrophilic glass plate in viscous concentrated aqueous sucrose solutions (0:001 Pas

Interfacial thin films rupture and self-similarity

Abstract: Two superposed thin layers of fluids are prone to interfacial instabilities due to London-van der Waals forces. Evolution equations for the film thicknesses are derived using lubrication theory. Using the intrinsic scales, for a single layer, results in a system with parametric dependence of four ratios of the two layers: surface tension, Hamaker constant, viscosity, and film thickness. In contrast to the single layer case, the bilayer system has two unstable eigenmodes: squeezing and bending. For some particular parameter regimes, the system exhibits the avoided crossing behavior, where the two eigenmodes are interchanged. Based on numerical analysis, the system evolves into four different rupture states: basal layer rupture, upper layer rupture, double layer rupture, and mixed layer rupture. The ratio of Hamaker constants and the relative film thickness of the two layers control the system dynamics. Remarkably, the line of avoided crossing demarks the transition region of mode mixing and energy transfer...

Aeration in Lubrication With Application to Drag Torque Reduction

Abstract: The aeration of an oil film flowing between the faces of two closely spaced circular plates (one stationary, and one rotating) is examined experimentally, numerically, and with an improved lubrication model. The gap between the plates is small compared to their radii, making lubrication theory appropriate for modeling the flow. However, standard lubrication boundary conditions suggested by Reynolds (1886, "On the Theory of Lubrication and its Application to Mr. Beauchamp Tower’s Experiments, Including an Experimental Determination of the Viscosity of Olive Oil," Philos. Trans. R. Soc. London, 177 , pp. 157-234) of p = 0 and pn = 0 (Dirichlet and Neumann conditions on pressure) at the gas-liquid interface do not allow for the inclusion of a contact line model, a phenomenon that is important in the inception of aeration. Hence, the standard theory does not adequately predict the experimentally observed onset of aeration. In the present work, we modify the Neumann boundary condition to include both interfacial tension effects and the dynamics of the interface contact angle. The resulting one-dimensional Cartesian two-phase model is formulated to incorporate the prescribed contact line condition and tracks the interface shape and its motion. This model is then implemented in an axisymmetric, two-dimensional model of the rotating disk flow and used to predict the onset of aeration for varying surface tension and static contact angles. The results of the modified lubrication model are compared with experimental observations and with a numerical computation of the aerating flow using a volume of fluid method.

Electrified film flow over step topography at zero Reynolds number: an analytical and computational study

Abstract: The flow of a liquid film over step topography under the influence of an electric field is considered in the limit of zero Reynolds number. The particular topographies considered include a flat wall with a downward step or an upward step, or a flat wall which is indented with a rectangular trench. A uniform electric field is imposed at infinity in the direction normal to the flat wall. The air above the film is treated as a perfect dielectric. The liquid in the film is assumed to behave either as a perfect conductor or as a perfect dielectric whose dielectric constant in general differs from that in the air. Asymptotic results are derived on the assumption of small step height, and formulas are presented for the first-order correction to the free-surface deformation due to the topography. It is demonstrated that, in an appropriate long-wave limit, the solutions approach those obtained using the lubrication approximation. Finally, the small-step asymptotics are favourably compared with numerical solutions for Stokes flow over steps of arbitrary height computed using the boundary-element method. In summary, it is shown that asymptotic models based on small-amplitude step topography provide simple formulas which are effective in describing the flow even for moderate step amplitudes, making them an efficient analytical tool for solving practical film-flow problems.

Two-fluid pressure-driven channel flow with wall deposition and ageing effects

Abstract: Two-fluid, stratified pressure-driven channel flow is studied in the limit of small viscosity ratios. Cases are considered in which the core fluid undergoes phase separation that results in the ‘precipitation’ of a distinct phase and the formation of a wall layer; these situations are common in the oil industry where ‘fouling’ deposits are formed during the flow. The thickness of this layer increases as a result of continual deposition through Stefan-like fluxes, which are related to the phase behaviour of the core fluid through a chemical equilibria model that treats the fluid as a bi-component mixture. The deposit also undergoes an ‘ageing’ process whereby its viscosity increases due to the build-up of internal structure; the latter is modelled here via a Coussot-type relation. Lubrication theory is used in the wall layer and an integral balance in the core fluid wherein inertial effects are important. By choosing appropriate semi-parabolic velocity and temperatures closures for the laminar flow in the channel core, and a closure relation for the wall layer rheology, evolution equations are derived that describe the flow dynamics. In the presence of ageing but absence of deposition, it is demonstrated how the time-varying deposit rheology alters the wave dynamics; for certain parameter ranges, these effects can give rise to the formation of steep waves and what appears to be finite-time ‘blow-up’. With both ageing and deposition, the spatio-temporal evolution of the deposit is shown together with the increase in the deposition rate with increasing temperature difference between the wall and the inlet.

Stokes flow of micro-polar fluids by peristaltic pumping through tube with slip boundary condition

Abstract: This paper studies the Stokes flow of micro-polar fluids by peristaltic pumping through the cylindrical tube under the effect of the slip boundary condition. The motion of the wall is governed by the sinusoidal wave equation. The analytical and numerical solutions for the axial velocity, the micro-polar vector, the stream function, the pressure gradient, the friction force, and the mechanical efficiency are obtained by using the lubrication theory under the low Reynolds number and long wavelength approximations. The impacts of the emerging parameters, such as the coupling number, the micro-polar parameter, the slip parameter on pumping characteristics, the friction force, the velocity profile, the mechanical efficiency, and the trapping phenomenon are depicted graphically. The numerical results infer that large pressure is required for peristaltic pumping when the coupling number is large, while opposite behaviors are found for the micro-polar parameter and the slip parameter. The size of the trapped bolus reduces with the increase in the coupling number and the micro-polar parameter, whereas it blows up with the increase in the slip parameter.

Theoretical Investigation of Couple Stress Squeeze Films in a Curved Circular Geometry

Abstract: A theoretical investigation of the laminar squeeze flow of a couple-stress fluid between a flat circular static disk and an axisymmetric curved circular moving disk has been carried out using modified lubrication theory and microcontinuum theory. The combined effects of fluid inertia forces, curvature of the disk and non-Newtonian couple stresses on the squeeze film behavior are investigated analytically. Each of these effects and their combinations show a significant enhancement in the squeeze film behavior, and these are studied through their effects on the squeeze film pressure and the load carrying capacity of the fluid film as a function of time. Two different forms of the gapwidth between the disks have been considered, and the results have been shown to be in good agreement with the existing literature.

Towards the efficient numerical solution of three-dimensional thin film flows on real surfaces: an evaluation of finite-difference-based schemes

Abstract: The comparative efficiency of time-splitting and multigrid schemes for the solution of lubrication models of three-dimensional (3D), thin film flow is demonstrated via detailed comparisons for benchmark gravity-driven continuous film and droplet spreading problems. Data are presented which show the effect of (1) problem formulation (either as a single fourth-order partial differential equation for the film thickness or two coupled second-order equations for film thickness and pressure) and (2) grid density on the choice of fixed time-step, CPU time per time-step and overall efficiency of each scheme. On the basis of these findings, recommendations are given as to the most efficient combination of problem formulation and numerical scheme for solving 3D thin film free surface flows over practical, engineering surfaces.

A Computational Leakage Model for Solid Oxide Fuel Cell Compressive Seals

Abstract: One of the key obstacles precluding the maturation and commercialization of planar solid oxide fuel cells has been the absence of a robust sealant. A computational model has been developed in conjunction with leakage experiments at Oak Ridge National Gaboratory. The aforementioned model consists of three components: a macroscopic model, a microscopic model, and a mixed lubrication model. The macroscopic model is a finite element representation of a preloaded metal-metal seal interface, which is used to ascertain macroscopic stresses and deformations. The microscale contact mechanics model accounts for the role of surface roughness in determining the mean interfacial gap at the sealing interface. In particular, a new multiscale fast Fourier transform-based model is used to determine the gap. An averaged Reynolds equation derived from mixed lubrication theory is then applied to approximate the leakage flow across the rough annular interface. The composite model is applied as a predictive tool for assessing how certain physical parameters (i.e., seal material composition, compressive applied stress, surface finish, and elastic thermophysical properties) affect seal leakage rates. The leakage results predicted by the aforementioned computational leakage model are then compared with experimental results.