High-speed rotor dynamics - An assessment of current technology for small turboshaft engines

Abstract

An extensive study was made to determine current needs for research in rotor dynamics to solve problems encountered in small high-speed turboshaft engines for helicopter and aircraft propulsion. The purpose of this paper is to report the state-of-the-art for this area as completely and concisely as possible. The present and past philosophy of rotor-bearing system design including the impact of the demand for front drives, is discussed. Methods for critical speed prediction and high-speed balancing are reviewed. The trend to higher speeds is seen to require consideration of new approaches to balancing through flexural modes. The major parameters available for control by the designer are shown to be the bearing support properties, and recommendations are made for improving the accuracy of prediction of these properties. Nonsynchronous excitation is categorized according to the mechanisms producing the forces, and a need is shown for better methods to identify the resulting whirling and vibration, since several of these motions are potentially unstable. Finally, reasons are given for the predominant use of rolling-element bearings in these engines, and the potential for special applications of oil-film and gas bearings is discussed.