Abstract
Modern high performance turbomachinery providing increased power to weight ratios and larger efficiencies are designed to operate at higher speeds than prior designs. These machines are more sensitive to imbalance since they must traverse critical speeds. Adding damping to a rotor-bearing system reduces vibration amplitudes and provides isolation from the support structure. Squeeze film dampers (SFD), if properly employed, have been shown to effectively provide viscous damping and attenuate imbalance response. Present SFD modeling does not always provide reliable rotordynamic coefficient predictions due to omission of important phenomena or from a lack of experimental validation. The design, construction and operation of a rotordynamic SFD test rig is presented. The test rig consists of a massive rotor supported on two elastically supported SFDs. The SFDs, consistent with many current aircraft engine designs, are characterized by a slenderness ratio and a clearance to journal radius equal to 0.243 and 0.005, respectively. The rotor-bearing system is designed to have two rigid mode critical speeds (cylindrical and conical) below the 9,000 rpm maximum. All significant variables are measured and controlled during construction and testing. Impedance measurements (at zero rpm) and imbalance tests are performed to characterize the damping coefficients from the SFDs. System damping coefficients are extracted from the imbalance response results at the speed of maximum amplitude of motion. Amplification factors from 1.6 to 2.1 are found in the synchronous response to imbalance tests. Experimental damping and system variables are used in a linear rotordynamic model to predict the experimental imbalance responses. Experimental amplitudes of vibration and damping forces are proportional to the imbalance magnitude. Measured damping coefficients are lower than those predicted by a full film SFD model. The damping levels are also verified to be sensitive to the magnitude of lubricant viscosity.
Lubell, Daniel Roger (2000). Measurements of imbalance response for a rigid rotor fully supported on squeeze film dampers. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -L81.