Stability Characteristics of a Rigid Rotor Supported by a Gas-Lubricated Spiral-Groove Conical Bearing

Abstract

Five-degree-of-freedom (5-DOF) characterization of the stability of a gas-lubricated conical bearing of the spiral-groove design is presented for bearing numbers up to 500. Critical points in stability analysis are identified in impedance contour plots separately for axial, cylindrical, and conical modes. The stability thresholds with respect to each mode are graphed as functions of the bearing number. For axial and cylindrical modes, the threshold parameter is the rotor mass. For the conical mode, the threshold parameter is an equivalent mass that is dependent on both transverse and polar radii of gyration of the rotor. An application example illustrates a rational procedure to specify nominal bearing clearance and its allowable tolerance range.

Foil Bearing Design Guidelines for Improved Stability

“…This is carried out for X ranging from 0 to 3. It can be shown that, for higher whirl ratios, the bearing properties reach asymptotic values (Pan and Kim [19]). It is emphasized that, in this particular analysis, neither external vibrations nor seal forces have been considered.…”

“…The model is able to estimate the static load capacity and the dynamic stiffness and damping coefficients as a function of bearing geometry and operation conditions. Then, the foil bearing model is coupled with a linear, rigid body rotordynamic model, implementing an extension of the spectral analysis approach by Pan [18] and Pan and Kim [19]. The analysis estimates the whirl speed map and the corresponding stability map of a rotordynamic system where stiffness and damping are not only dependent on the rotational speed but also on the excitation frequency.…”

Enhanced Groove Geometry for Herringbone Grooved Journal Bearings

“…The bearing model is coupled with a linear, rigid body rotordynamic model, implementing an extension of the spectral analysis approach by Pan [9,10]. The technical approach is based on an integrated rotordynamic model for rotors supported on gaslubricated bearings.…”

“…The approach here is based on Pan's spectral analysis method [9] extended by Schiffmann and Favrat [7,8]. Pan shows that for higher whirl ratios the bearing properties reach asymptotic values (Pan [10]). 3 and described by , and location of the bearing midplanes relative to the rotor center of gravity (/", k).…”

“…The rigid-body rotordynamic system is shown in Fig. A compact description of stability was proposed by Pan [9,10] and Lund [15] by characterizing the stability threshold for cylindrical rotor motion through a nondimensional critical mass parameter. Equation (7) yields an eigenvalue problem with eigenvalues (8) where the imaginary part cu, = fi/CORot represents the damped natural frequency of the whirl motion and A, is the corresponding damping coefficient.…”