Linear stability analysis of rotor-bearing system: couple stress fluid model

Based upon the Stokes micro-continuum theory, the problem of film instability threshold of a rotor-bearing system with couple stress fluids as lubricants is theoretically studied. To take into account the effects of couple stresses arising from a non-polar lubricant blended with additives, a non-Newtonian polar Reynolds-type equation is derived. The film pressure is solved and applied to evaluate the equilibrium solutions and vibrational stability boundary of a short journal bearing. According to the results presented, the presence of couple stresses provides an increase in the values of the KXX- and KXY-stiffness coefficients as well as the CXX-damping coefficient. For general applied load numbers (corresponding to the eccentricity ratio ϵs⩽0.7), the rotor-bearing system with a couple stress fluid under small disturbances is observed to be more stable than the conventional Newtonian-lubricant case.