Experimental Force Coefficients of a Hydrostatic Thrust Bearing and Comparisons to Predictions

Reliable fluid film bearings for high-performance turbomachinery provide significantly extended operating life with controllable stiffness and damping force coefficients at low cost. Hydrostatic thrust bearings support thrust loads and control axial motions. This paper reports measurements and predictions of static and dynamic load characteristics of a hydrostatic thrust bearing fed with pressurized air. The current bearing model uses dynamic axial periodic motion amplitudes, that is, models as a function of the initial film thickness, to predict the dynamic force coefficients. Note that, presently, the recorded frequencies and their amplitudes of pneumatic hammer instability along the axial direction are implemented as an external excitation source. The measured and predicted static stiffnesses increase as the film thickness decrease and supply pressure into the bearing increase. The predicted dynamic force coefficients show a favorable agreement with the test data. Analysis reveals the negative damping coefficients and damping ratios as a distinctive onset condition of the present pneumatic hammer instability of the test bearing. A careful recess design and adequate operation conditions along with an accurate prediction can avoid or prevent undesirable pneumatic hammer instability in hydrostatic thrust bearings. This work extends the knowledge database of hydrostatic thrust bearings with pneumatic hammer instability and provides their design guideline for various operating conditions.