The effectiveness of squeeze-film damper bearings supporting flexible rotors without a centralising spring

Abstract

An investigation has been carried out into the effectiveness of squeeze-film damper bearings incorporated into a flexible rotor system. A method has been devised for comparing the performance of squeeze-film damper bearings which operate without a parallel flexible support or centralising spring (squirrel cage). The model used in this investigation is a relatively simple one in which a rotor mass is lumped at the mid-point of a horizontal flexible shaft and separate rotor masses are lumped at each bearing position. The performance of the squeeze-film damper bearing is expressed in terms of six dimensionless system parameters. The squeeze-film damper bearing performance has been compared, in each case, against the excursion of the rotor centre and the maximum force transmitted to the bearing support, for an exactly similar system with rigid supports. This comparison has led to several interesting conclusions, for example, with a poorly designed squeeze-film damper bearing, the maximum force transmitted to the bearing support can be significantly greater than would have been the case if the damper had not been fitted. Similarly, the reduction in the transmitted force can be very large for certain ranges of parameters, with the squeeze-film damper response remaining constant for a wide range of frequency ratio either side of the (rigid support) critical speed. Further, this damper response is relatively insensitive to a wide variation of some of the system parameters, a trend which supports the past experiences of some aero-engine designers.