33 research outputs found
Parametric and Optimization Study of Rectangular-Rounded, Hydraulic, Elastomeric, Reciprocating Seals at Temperatures between −54 and +135 °C
No full textHydraulic, reciprocating, polymeric seals are met in many engineering applications and are critical components for mechanism and machine reliability in industries including the automotive, marine, and aerospace industries. A parametric and optimization study of rectangular-rounded, hydraulic, reciprocating, elastomeric rod seals at −54, +23, and +135 °C is presented, which is particularly relevant to hydraulic actuators in aircraft landing gear. Parametric optimization not only improves performance, but also helps avoid sealing failures. The calculations were based on a physically based, deterministic mathematical model of such seals, experimentally validated at the aforementioned temperatures and recently published by the author. The parameters varied were the seal axial width and corner radius, seal elastic modulus, sealed pressure, stroking velocity, operating temperature, rod surface roughness, seal radial interference, and seal swelling by fluid uptake. Their influence was established based on the following performance variables: leakage rate, frictional force, coefficient of friction, temperature rise in the sealing contact, lambda ratio (proportional to the average film thickness in the contact), and ratio of the asperity friction force to the total friction force. The parametric study greatly facilitates the selection of optimal values of the analyzed parameters to minimize leakage, friction, and wear, either concurrently as a set or individually, depending on application priorities
Single droplet impacts onto deposited drops. Numerical analysis and comparison
No full textThe impact of a spherical water droplet onto a stationary sessile droplet lying on a solid wall is studied numerically using the volume-of-fluid methodology. The governing Navier-Stokes equations are solved both for the gas and liquid phase coupled with an additional equation for the transport of the liquid interface. An unstructured numerical grid is used along with an adaptive local grid refinement technique, which enhances the accuracy of the numerical results along the liquid-gas interface and decreases the computational cost. The stationary sessile droplet has been created from the prior impact of one or two water droplets falling onto the solid wall, while two solid walls have been studied−an aluminum substrate and a glass substrate. The material of the wall plays an important role because it has an impact on the droplet's wetting behavior. The numerical model is validated against corresponding experimental data presented in the first part of the present work (Nikolopoulos et al., 2010), showing good agreement. Furthermore, the numerical investigation sheds light on the governing physics of the phenomenon
Particle Entrapment in Line Elastohydrodynamic Contacts and the Influence of Intermolecular (van der Waals) Forces
No full textA metallic particle passing through concentrated rolling-sliding contacts is often linked to surface damage for particles larger than the available gap. At the instant of particle pinching, force balancing dictates particle entrapment and passing through the contact or rejection. It is vital to include all major forces in this process. This study revisits the analytical entrapment model previously published by the author for spherical micro-particles by incorporating a force so far overlooked in related studies, namely the van der Waals intermolecular force and, additionally, surface roughness effects. In conjunction with particle mechanical and fluid forces, this provides an almost complete set to use for correct force balancing. A parametric analysis shows the effect of several geometrical, mechanical, rheological, and surface parameters on spherical particle entrapment and reveals the significance of the van der Waals force for particles smaller than about 5–10 μm in diameter
Experimental investigation of a single droplet impact onto a sessile drop
No full textThis paper presents an experimental study of the impact of a single water droplet onto a stationary liquid bulk built by the previous impact of one or two droplets. The experiments were performed with two different film thicknesses, three different Weber (We) numbers, and two surface contact angles. In both cases we have hydrophilic conditions, which do not allow for a good investigation of this parameter. The morphology of the drop impact was studied using a chargecoupled device (CCD) camera, and the corresponding qualitative and quantitative characteristics regarding the time evolution of the phenomena, such as the diameter and height of the evolving crown, were obtained by image analysis. Analysis of the experimental data evidences that the phenomenon has a strong similarity to the impact of a single drop on shallow films, although the effect of the surface wetting characteristics plays, in this case, a negligible role. The regimes of deposition and splashing are identified as a function of theWe number and the maximum thickness of the steady film, which is affected by the surface wettability properties</p
An experimentally validated numerical model of indentation and abrasion by debris particles in machine-element contacts considering micro-hardness effects
No full textProfile Optimization of Hydraulic, Polymeric, Sliding Seals by Minimizing an Objective Function of Leakage, Friction and Abrasive Wear
No full textHydraulic dynamic seals for reciprocating or alternating motion are machine elements with widespread applications in the automotive, aerospace, marine, pharmaceutical and several other industrial sectors. They have been under commercial development for many decades, and are often met in critical positions, consuming a considerable amount of energy during operation. An objective function of mass leakage rate, friction force and an abrasive-wear representative term is proposed in the present study to evaluate the performance of hydraulic, polymeric sliding seals under suitable constraints. Using Variational Calculus, analytical and numerical techniques, the objective function is minimized, resulting in an optimal seal profile that maximizes sealing performance for given, steady-state operating conditions, in additional consideration of the structural integrity and manufacturability of the modified seal. The obtained seal shape and related pressure distribution are reminiscent of those for U-cup and step seals, designs that dominate the industry. In the course of the mathematical analysis, some major obstacles are documented that show how sensitive and complicated sealing performance really is
Particle extrusion in elastohydrodynamic line contacts: Dynamic forces and energy consumption
No full text The author’s model of particle entrapment and thermoviscoplastic indentation built and experimentally validated in recent publications is utilised to calculate the contact forces on ductile, isolated interference particles passing through elastohydrodynamic, rolling–sliding, line contacts. The model is detailed and enriched by supplementary equations. A parametric study deals with the effects of particle size and cold hardness, kinetic friction coefficient, rolling velocity and slide-to-roll ratio of the contact on the particle contact forces, mean friction coefficient, temperature, plastic work and power required to deform a particle, as well as on dent volume and plastic strain rates of the indented contact surfaces. A factual selection of optimal conditions and parameter values that minimise the disruption of a contaminated contact is thus greatly facilitated. </jats:p
Strain-rate effects on the plastic indentation and abrasion of elastohydrodynamic contacts by debris particles
No full textMiscalculation of film thickness, friction and contact efficiency by ignoring tangential tractions in elastohydrodynamic contacts
No full textParticle Entrainment in Elastohydrodynamic Point Contacts and Related Risks of Oil Starvation and Surface Indentation
No full textThis theoretical study concentrates on the mathematical analysis of the motion of small (5–50 μm) spherical solid particles in the inlet zone of elastohydrodynamic point contacts, found in various machine elements as, for example, in ball bearings, in order to compute the particle trajectories in the fluid flow. Particles may collide on a moving element of the contact (e.g., a ball in a bearing) or bypass it. For those particles that collide on another element, a fluid and mechanical force analysis reveals if they will be entrapped and, possibly, cause surface damage, or temporarily or finally expelled. Particle rejection is associated with the risk of inlet blockage and fluid starvation, which may further cause film collapse and scuffing. The study gives useful evidence of the probabilities of particle entrapment or rejection, extending the concept to evaluate the probabilities of oil starvation, surface indentation, or both, under various operating conditions.</jats:p
