Couple stress fluids in squeeze film flows

Abstract

The thesis attempts to theoretically analyse the axisymmetric laminar squeezing flow of an incompressible couple stress fluid between parallel disks in curved circular, annular, porous circular and porous annular geometries. In order to increase the accuracy of hydrodynamic lubrication, the study considers some of the usually neglected forces like the local and convective fluid inertia and non-linear couple stresses. The squeeze film flow problem in a curved circular geometry is analysed using modified lubrication theory and energy integral method. The thesis also analyses the squeeze film flow problem in an annular geometry using modified lubrication theory and studies the individual and combined effects of inertia forces and couple stresses on the squeeze film characteristics. The analytical expressions for the squeeze film pressure and force are obtained in each case and numerical results are presented in the form of graphs using MATLAB. From the various squeeze film problems considered in the thesis, it is observed that the fluid inertia forces and couple stresses play a significant role in squeeze film mechanisms. It is also observed that the viscosity dependence on pressure strongly influence the squeeze film behaviour. In the case a of curved circular geometry, use of a concave disk is highly recommended due to better squeeze film performance when compared to flat and convex disks. Use of porous facings reduces the wear and tear on the moving parts without the necessity for frequent replacement of the lubricant fluid and thus many machines include porous facings for longer life of the parts and the lubricants. Although the load carrying capacity is not significantly high in porous squeeze films, the same is enhanced by the use of suitable couple stress fluids as lubricants. On the whole, the couple stress fluid model is found to be well suited for hydrodynamic lubrication and the effects of couple stresses improve the performance of lubrication processes. newline newline newline