Session: 23-11 Seal Rotordynamics

Paper Number: 154180

An Experimental Investigation of the Effects of Air Ingestion on Subsynchronous Damping Coefficients in an Open Ends SFD 

Squeeze film dampers (SFDs) are implemented in many turbomachinery applications to improve stability while crossing critical speeds and for maintaining acceptable stability margins. Previous SFD research shows that air ingestion leads to a reduction in damping coefficients; however, this research has only been performed for circular, centered orbits (CCO). This experiment uses a dual-frequency excitation with a synchronous frequency having a larger magnitude than the subsynchronous frequency. The synchronous frequency is tested at various amplitudes to induce a range of air ingestion levels while damping coefficients are extracted from the subsynchronous frequency to examine the effects of the air ingestion on the subsynchronous component. A first data set uses CCO orbits with a range of amplitudes to provide pressure profiles for determining the onset and severity of air ingestion for the synchronous amplitude range. A second data set includes both synchronous and subsynchronous excitations with a small, constant subsynchronous amplitude. The synchronous amplitude range is the same as the first data set to provide the same levels of air ingestion. A final data set applies equal amplitudes to both frequency components.  All testing is performed using an open ends configuration with a large clearance to promote air ingestion. Squeeze velocity, a function of both frequency and amplitude, is an effective indicator for air ingestion levels, so an additional analysis is provided by plotting subsynchronous damping coefficients against the squeeze velocity. This analysis requires an alternative calculation method for damping coefficients, requiring frequency specific coefficients rather than coefficients calculated from a linear curve fit. The results show that as the synchronous amplitude increases, the subsynchronous damping increases as well despite the onset of air ingestion, showing that the large squeeze velocities provided by the synchronous frequency at high amplitudes have a greater effect than air ingestion on the subsynchronous damping. Increasing the subsynchronous frequencies shows incremental gains in squeeze velocity with a decreasing damping trend. However, increasing the synchronous amplitude causes a rise in subsynchronous damping, overshadowing the damping reduction due to increased subsynchronous frequency. An additional analysis compares the damping coefficient corresponding to the synchronous component to the damping coefficients for the circular tests. This analysis shows no significant variation between the circular coefficients and synchronous coefficients, showing that the behavior of the synchronous damping is not affected by the subsynchronous excitation.

Presenting Author: Nicolas Grigat Texas A&M University

Presenting Author Biography: M.S. Student at Texas A&M University in Mechanical Engineering
Graduate Researcher at Texas A&M Turbomachinery Lab Focusing on Squeeze Film Dampers
B.S. from Texas A&M University in Mechanical Engineering (2023)

Authors:

Nicolas Grigat Texas A&M University
Edoardo Gheller Politecnico di Milano
Adolfo Delgado Texas A&M University
Paolo Pennacchi Politecnico di Milano