Hamed Shahmohamadi

Analytic Approximate Solutions for Unsteady Two-Dimensional and Axisymmetric Squeezing Flows between Parallel Plates

The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the plates is investigated. The unsteady Navier-Stokes equations are reduced to a nonlinear fourth-order differential equation by using similarity solutions. Homotopy analysis method (HAM) is used to solve this nonlinear equation analytically. The convergence of the obtained series solution is carefully analyzed. The validity of our solutions is verified by the numerical results obtained by fourth-order Runge-Kutta.

Thermo-Mixed Hydrodynamics of Piston Compression Ring Conjunction

A new method, comprising Navier–Stokes equations, Rayleigh–Plesset volume fraction equation, an analytical control-volume thermal-mixed approach and asperity interactions, is reported. The method is employed for prediction of lubricant flow and assessment of friction in the compression ring–cylinder liner conjunction. The results are compared with Reynolds-based laminar flow with Elrod cavitation algorithm. Good conformance is observed for medium load intensity part of the engine cycle. At lighter loads and higher sliding velocity, the new method shows more complex fluid flow, possessing layered flow characteristics on the account of pressure and temperature gradient into the depth of the lubricant film, which leads to a cavitation region with vapour content at varied volume fractions. Predictions also conform well to experimental measurements reported by other authors.

Glass capillary microfluidics for production of monodispersed poly (dl-lactic acid) and polycaprolactone microparticles: Experiments and numerical simulations

HYPOTHESIS Droplet size in microfluidic devices is affected by wettability of the microfluidic channels. Three-dimensional countercurrent flow focusing using assemblies of chemically inert glass capillaries is expected to minimize wetting of the channel walls by the organic solvent. EXPERIMENTS Monodispersed polycaprolactone and poly(lactic acid) particles with a diameter of 18-150 μm were produced by evaporation of solvent (dichloromethane or 1:2 mixture of chloroform and toluene) from oil-in-water or water-in-oil-in-water emulsions produced in three-dimensional flow focusing glass capillary devices. The drop generation behaviour was simulated numerically using the volume of fluid method. FINDINGS The numerical results showed good agreement with high-speed video recordings. Monodispersed droplets were produced in the dripping regime when the ratio of the continuous phase flow rate to dispersed phase flow rate was 5-20 and the Weber number of the dispersed phase was less than 0.01. The porosity of polycaprolactone particles increased from 8 to 62% when 30 wt% of the water phase was incorporated in the organic phase prior to emulsification. The inner water phase was loaded with 0.156 wt% lidocaine hydrochloride to achieve a sustained drug release. 26% of lidocaine was released after 1 h and more than 93% of the drug was released after 130 h.

Big End Bearing Losses with Thermal Cavitation Flow Under Cylinder Deactivation

The paper presents a mixed thermo-hydrodynamic analysis of elliptic bore bearings using combined solution of Navier–Stokes, continuity and energy equations for multi-phase flow conditions. A vapour transport equation is also included to ensure continuity of flow in the cavitation region for the multiple phases as well as Rayleigh–Plesset to take into account the growth and collapse of cavitation bubbles. This approach removes the need to impose artificial outlet boundary conditions in the form of various cavitation algorithms which are often employed to deal with lubricant film rupture and reformation. The predictions show closer conformance to experimental measurements than have hitherto been reported in the literature. The validated model is then used for the prediction of frictional power losses in big end bearings of modern engines under realistic urban driving conditions. In particular, the effect of cylinder deactivation (CDA) upon engine bearing efficiency is studied. It is shown that big-end bearings losses contribute to an increase in the brake specific fuel consumption with application of CDA contrary to the gains made in fuel pumping losses to the cylinders. The study concludes that implications arising from application of new technologies such as CDA should also include their effect on tribological performance.

A Novel Solution for the Glauert-Jet Problem by Variational Iteration Method-Padé Approximant

We will consider variational iteration method (VIM) and Pade approximant, for finding analytical solutions of the Glauert-jet (self-similar wall jet over an impermeable, resting plane surface) problem. The solutions are compared with the exact solution. The results illustrate that VIM is an attractive method in solving the systems of nonlinear equations. It is predicted that VIM can have a found wide application in engineering problems.

Cavitating flow in engine piston ring-cylinder liner conjunction

The main function of piston compression ring is to seal the space between the piston and the liner, acting as slider bearing, subjected to reciprocating motion. The compression ring-cylinder liner conjunction has been extensively studied and it is responsible for a significant part of the total frictional parasitic power losses of an engine. Paradoxically, the required sealing function of the compressions ring can result in increased friction. Therefore, in order to improve engine efficiency, it is important to fundamentally understand and subsequently palliate some of these losses. Another problem in any slider bearing-type contact is lubricant film rupture and cavitation in the conjunctional outlet zone, reducing load carrying capacity and potentially leading to erosion damage.A cavitation model presented in two-phase flow CFD analysis of the ring-bore contact under isothermal conditions. Liquid flow is modelled as a continuous phase and a dispersed phase, representing cavitation bubbles. Many of the fundamental physical processes assumed to take place in cavitating flows are incorporated into the model.Copyright

Thermal Analysis of an Oil Jet-Dry Sump Transmission Gear under Mixed-Elastohydrodynamic Conditions

mproved fuel efficiency and reduced emissions are key drivers for modern drivetrain systems. Therefore, in recent years, dry sumps with air–oil mist lubrication have been used for efficient transmission design in order to reduce the churning losses. With dry sumps, appropriate cooling measures should be implemented to dissipate the generated contact heat in an efficient manner. This paper integrates a tribological model with three-dimensional (3D) thermofluid analysis in order to predict the heat generated in the lubricated meshing gear contacts and its dissipation rate by an impinging oil jet in air–oil mist environment. Such an approach has not hitherto been reported in literature. The results show that the generated heat under realistic conditions cannot be entirely dissipated by the impinging oil jet in the air–oil mist transmission casing. Numerical results are used to derive extrapolated regressed equations for heat transfer purposes for time-efficient analysis. These conform well with the detailed numerical results.

Analytic Approximate Solution for Two-Dimensional Steady Slip Flow in Microchannels by Variational Iteration Method

In this paper, the two-dimensional steady slip flow in microchannels is investigated. Research on micro flow,especially on micro slip flow, is very important for designing and optimizing the micro electromechanical system (MEMS). The Navier–Stokes equations for 2-dimensional steady slip flow in microchannels are reduced to a nonlinear three-order differential equation by using similarity solution. Variational iteration method (VIM) is used to solve this nonlinear equation analytically.Comparison of the result obtained by the present method with numerical solution reveals that the accuracy and fast convergence of the new method. It is predicted that the VIM can have wide application in engineering problems.