Identification of Dynamic Coefficients of a Five-Pad Tilting Pad Journal Bearing up to Highest Surface Speeds

Philipp Zemella* (zemella@itr.tu-clausthal.de; Phone: 0049-5323-723690)

Thomas Hagemann* (hagemann@itr.tu-clausthal.de; Phone: 0049-5323-722469)

Pfau, Bastian** (bastian.pfau@voith.com, Phone: 0049-7951-32795)

Hubert Schwarze* (schwarze@itr.tu-clausthal.de; Phone: 0049-5323-722465)

*Institute of Tribology and Energy Conversion Machinery, Clausthal University of Technology, Leibnizstr. 32

38678 Clausthal-Zellerfeld, Germany

**J. M. Voith SE & Co. KG, Voithstraße 1

74564 Crailsheim, Germany

Identification of dynamic coefficients of a five-pad tilting pad bearing up to highest surface speeds

Tilting-pad journal bearings are widely used in turbomachinery industry due to their positive dynamic properties at high rotor speeds. However, the exact description of this dynamic behavior is still part of current research. This paper presents measurement results for a five-pad tilting-pad journal bearing in load between pivot configuration. The bearing is characterized by a nominal diameter of 100 mm, a length of 90 mm and a pivot offset of 0.6. Investigations include results for surface speeds between 25 and 120 m/s and specific bearing loads ranging from 0.0 to 3.0 MPa.

Results of theoretical predictions are commonly derived from perturbation of stationary operation under static load. Therefore, experimental results for stationary operation including pad deflection under static load are presented first to characterize the investigated bearing. Measured results indicate considerable non-laminar flow in the upper region of the investigated range of rotor speeds. Second, dynamic excitation test are performed with excitation frequencies up to 400 Hz to evaluate dynamic coefficients of a stiffness (K) and damping (C) KC-model, and additionally, a KCM-model using additional virtual mass (M) coefficients. KCM-coefficients are obtained by fitting frequency dependent KC-characteristics to the KCM-model structure using least square approach. The wide range of rotating and excitation frequencies leads to subsynchronous as well as supersynchronous vibrations. Excitation forces are applied with multi-sinus and single-sinus characteristics. The latter one allows evaluation of KC-coefficients at the particular frequency ratio in the time domain. Different evaluation algorithms for dynamic coefficients are used in order to assess their special properties and quality. Results are compared to each other concerning values and uncertainties of the identified coefficients. General tendencies and findings are discussed in detail.

Finally, experimental results are compared to theoretical predictions. Here, a special emphasis exists on consideration of the combined pad and pivot elasticity and its impact on predicted results. Moreover, the analyses includes evaluation of speed and load dependent characteristics of deviations between measurement and predictions.