Effects of bearing deadbands on bearing loads and rotor stability

Abstract

The Jeffcott model of a turbopump which was modified by adding deadband (clearance) effects along with fluid seal forces are currently understood. Equations of motion for the model were written in polar coordinates, and a constant side force was added to the model to account for the likely misalignment between bearings and seals. The force models and system equations of motion are described as well as limit cycle, and stability analyses. Studies of systems with rotor imbalance and with or without side effects were studied for three types of motion. Results show that: (1) deadband does not affect stability-in-the-large; (2) stability-in-the small is enhanced by deadband and side force; (3) bearings loads are highest for motion with synchronous or nonsynchronous periodic enclosing origin; (4) side force acting in concert with deadband effects may either increase or decrease bearing loads; and (5) bearing loads in a stable pump are determined primarily by rotor imbalance and side forces