Experimental evaluation of a metal-mesh bearing damper in a high speed test rig

Abstract

Metal mesh is a commercially available material used in many applications including seals, heat shields, filters, gaskets, aircraft engine mounts, and vibration absorbers. This material has been tested in the Turbomachinery Laboratory at Texas A&M University (TAMU) as a bearing damper in a rotordynamic test rig. The test facility was originally used to support the design of a turboprop engine at TAMU, developing squirrel cage bearing supports and squeeze film dampers for both the gas generator and power turbine rotors. To design the metal mesh damper, static stiffness and dynamic rap test measurements were first made on metal mesh samples in a specially designed non-rotating test fixture. These property tests were performed on samples of various densities and press fits. One sample was also tested in an Instron machine as an ancillary and redundant way to determine the stiffness. Using the stiffness test results and equations derived by a previous investigator, a spreadsheet program was written and used to size metal mesh donuts that have the radial stiffness value required to replace the squirrel cage in the power turbine. The squirrel cage and squeeze-film bearing damper developed for the power turbine rotor was then replaced by a metal mesh donut sized by the computer code. Coast-down tests were conducted through the first critical speed of the power turbine. The results of the metal mesh tests were compared with those obtained from previous testing with the squeeze film damper. The results show that the metal mesh damper has the same damping as the squeeze film at room temperature but does not lose its damping at elevated temperatures up to 210F̊. Experiments were run under several different conditions including balanced rotor hot oil soaked, unbalanced rotor hot oil soaked, balanced dry, and unbalanced dry. Over all, metal mesh dampers appear to be a viable and attractive substitute for squeeze film dampers in gas turbine engines. The advantages shown to date include less variation of damping with temperature, ability to handle large rotor unbalance, and the ability (if required) to operate effectively in an oil free environment.