STABILITY ANALYSIS OF MECHANICAL SEALS WITH 2 FLEXIBLY MOUNTED ROTORS

Dynamic stability is investigated for a mechanical seal configuration in which both seal elements are flexibly mounted to independently rota ting shafts. The analysis is applicable to systems with both counterro tating and corotating shafts. The fluid film effects are modeled using rotor dynamic coefficients, and the equations of motion are presented including the dynamic properties of the flexible support. A closed-fo rm solution for the stability criteria is presented for the simplified case in which the support damping is neglected. A method is presented for obtaining the stability threshold of the general case, including support damping. This method allows instant determination of the stabi lity threshold for a fully-defined seal design. A parametric study of an example seal is presented to illustrate the method and to examine t he effects of various parameters in the seal design upon the stability threshold. The fluid film properties in the example seal are shown to affect stability much more than the support properties. Rotors having the form of short disks are shown to benefit from gyroscopic effects which give them a larger range of stable operating speeds than long ro tors. For seals with on long rotor, counterrotating operation is shown to be superior because the increased fluid stiffness transfers restor ing moments from the short rotor to the long.