Simulation of macro and micro journal bearings: Using the Lattice Boltzmann Method

Numerical simulation of macro and micro journal bearings is investigated using Lattice Boltzmann Method. Bounce-back boundary condition is applied in macro flow simulation and a combination of diffuse scattering and bounce-back techniques is used in micro calculations. An approximation method which is called ghost boundary is employed to simulate the wall curvature of macro and micro bearings. The Lattice Boltzmann Method solutions of two classic configurations are compared with the numerical solution of the Reynolds equations. Bearing cavitation is approached in a simplified way for a macro journal bearing and the results are compared with a finite element solution. The Lattice Boltzmann Method results are satisfactory for the investigated problem. A computational analysis is also used to simulate the complicated behavior of the micro journal bearings in the slip flow regime with Knudsen number varying between 0.01 and 0.05. The working fluid in micro simulations is gas. In order to model the interaction between gas and solid walls, a local boundary condition which is derived from the kinetic theory of gases using multiple relaxation time method is employed and the static performance of the micro bearing is analyzed. Applying the second-order velocity boundary condition, the pressure distributions obtained from the Lattice Boltzmann Method are successfully compared with the results of spectral collocation method. Results indicate that by increasing Knudsen number the maximum of pressure decreases.