Experimental Investigation of the Effects of Squeeze Film Damper Design on Highspeed Rotor System

Squeeze film dampers (SFDs) are used in highspeed rotordynamics systems, such as aircraft engines, to mitigate vibrations while traversing critical speeds. SFDs are critical in dissipating large amplitude motions and dynamic loading transferred from the rotor to the bearing supports during highspeed operation. SFDs also act to stabilize the rotor and isolate the rotor from the rest of the engine and the engine supports. Very little testing on the effect of SFDs on rotor shafts under realistic operating conditions is available in the literature. Thus, an SFD-rotor test rig has been designed and built to study the effect of various operating conditions on the response of a Jeffcott rotor. The rotor is supported on either end by an SFD and is connected to a 10 HP motor with variable frequency drive that can run the rotor up to a maximum speed of 20,000 rpm. Unbalance is added to the system at the central disk with the test rig instrumentation measuring the oil pressure and temperature within the squeeze film land along with the displacements at the two supporting SFDs and the central disk. Test parameters that are varied include: unbalance, oil supply temperature, oil supply pressure, oil inlet orientation/number, SFD clearance, and sealed/open-ended configurations.

In this paper, the calibration of the test rig through static and dynamic testing is outlined and the effect of the SFD on the rotor response under different highspeed operating conditions is demonstrated. The calibration is carried out in order to recreate idealized conditions for the purpose of calibrating previously developed nonlinear SFD models. Thus, the effect of support structure, coupling, and bearing loading were investigated and their effect on the rotor response was minimized. Guided by modal tap testing, the stiffness of the support structure of the test rig was modified in order to avoid asymmetric rotor response in the vertical and horizontal directions. Loads applied to the bearing to stabilize the rotor during operation were also established through modal testing. Runout correction and unbalance sensitivity studies were also performed where test masses were added to compensate for rotor bow. Dynamic testing was carried out by performing runup, rundown, and dwell tests with and without SFDs to establish a baseline rotor response. Modal tap testing and runup/rundown tests show similar locations for critical speed and rotor natural frequency. These values also agreed with dynamic finite element simulations of the rotordynamics test rig. Initial test results from the limit cases for each test parameter are also presented and compared with results from combined rotordynamic-SFD modeling showing good agreement once calibration of the test rig was completed.