A mathematical model for predicting spline coupling induced nonsynchronous rotor vibrations is developed, and the predictions are compared with data from a rotor dynamics test rig. The special feature of the spline model is the characterization of the friction forces that are produced at the mating spline teeth surfaces and subsequent calculation of the internal damping coefficients. The spline internal damping and the r esulting rotor instabilities are predicted for four different spline configurations and the solution results are correlated with measured data from a gas turbine rotor simulator test rig.

Throttle valves in steam turbines often operate at very small lift positions during turbine startup. The large pressure differentials across these valves, combined with the very small openings at the valve seat, result in large pressure drops across these valves and high local steam Mach numbers. A steam turbine throttle valve operated under these conditions was found to be undergoing self-excited vibration. Stress and structural dynamic finite element analyses (FEA) were performed to identify the structural mode for the valve oscillations. A three-dimensional transient computational fluid dynamics (CFD) analysis of the valve revealed an unsteady fluid dynamics phenomenon in the pressure balancing arrangement that served as a forcing function for this vibration. Valve modifications were implemented as a result of these analyses. The improved valve has performed successfully, and the design modifications have been incorporated in other production valves.

This paper is a companion to “Squeeze-Film Damper Technology, Part 1,” which covered an analytic approach and computer program for squeeze-film damper performance prediction. This paper describes a series of damper tests in which a controlled-orbit rig is used to explore squeeze-film damper behavior for representative gas turbine damper geometries and to verify and calibrate the damper analysis program. Test results for both locally end-sealed (hole fed and drained) and globally sealed (groove fed and drained) dampers are presented, along with performance predictions for those test points made using the software analysis. In particular, the effects of feeder hole flow resistance, feed groove geometry, and fluid inertia on damper performance are discussed and illustrated.

Squeeze-film dampers are commonly used in gas turbine engines and have been applied successfully in a great many new designs, and also as retrofits to older engines. Of the mechanical components in gas turbines, squeeze-film dampers are the least understood. Their behavior is nonlinear and strongly coupled to the dynamics of the rotor systems on which they are installed. The design of these dampers is still largely empirical, although they have been the subject of a large number of past investigations. To describe recent analytical and experimental work in squeeze-film damper technology, two papers are planned. This abstract outlines the first paper, Part 1, which concerns itself with squeeze-film damper analysis. This paper will describe an analysis method and boundary conditions which have been developed recently for modelling dampers, and in particular, will cover the treatment of finite length, feed and drain holes and fluid inertia effects, the latter having been shown recently to be of great importance in predicting rotor system behavior. A computer program that solves the Reynolds equation for the above conditions will be described and sample calculation results presented.

In this paper a novel, high-load chambered porous damper design, supporting analysis, and experimental results are presented. It was demonstrated that significant damping can be generated from the viscous discharge losses of capillary tubes arranged in chambered segments with large radial clearances and that the resulting damping is predictable and fairly constant with speed and eccentricity ratio. This design avoids the nonlinearities associated with high-eccentricity operation of conventional squeeze film dampers. Controlled orbit tests with a porous chambered configuration were completed and favorably compared with theoretical predictions. The ability to accommodate high steady-state and transient imbalance conditions makes this damper well suited to a wide range of rotating machinery, including aircraft gas turbine engines.