Calculated Rotordynamic Behaviour of a Twin Spool Engine and the Comparison With Test Results

Abstract

The new BR 700 series of twin spool engines, of the thrust class of 15,000 to 20,000 pounds, is being developed for business jets. In this paper the rotordynamic vibration analysis is performed with a detailed whole engine model including both rotors, bearings with oil squeeze film dampers and squirrel cages, the engine structure, the mounts and the fuselage. The analytical method is described and some calculated results are presented. The effectiveness of the oil squeeze film dampers on all main bearings will be demonstrated. The comparison of the analytical and the measured results gives a good agreement in the resonance frequencies and in the damping characteristics. It also shows that a linear analysis can describe with sufficient accuracy the dynamic behaviour of such a complex structure like a twin spool engine under normal operating conditions.