A review is presented of various rotordynamic problems which have been encountered and eliminated in developing the current flight engines and of continuing subsynchronous problems which are being encountered in developing a 109 percent power level engine. The basic model for the HPOTP, including the structural dynamic model for the rotor and housing and component models for the liquid and gas seals, turbine-clearance excitation forces, and impeller-diffuser forces, are discussed. Results from a linear model are used to examine the synchronous response and stability characteristics of the HPOTP, examining bearing load and stability problems associated with the second critical speed. Various seal modifications are examined and shown to have favorable consequences with respect to bearing reactions and stability. Differences between linear and nonlinear model results are discussed and explained in terms of simple models. The transient nonlinear model is used to demonstrate forced subsynchronous motion similar to that observed in test data for models which are lightly damped but stable. The subsynchronous motion results from bearing clearance nonlinearities. Simulation results indicates that synchronous bearing loads can be reduced but that sub-synchronous motion is not eliminated by seal modifications.

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