Static and dynamic characteristics for a two-axial-groove bearing and a pressure-dam bearing

Abstract

This thesis compares experimental static and dynamic force characteristics for a two-axial-groove bearing and a pressure-dam bearing without a relief track. The thesis also compares experimental results to predictions from a numerical analysis. The tested pressure-dam bearing has s θ= 130°, ' k =3.4~4.2, and d L − =0.75. The test results show that eccentricity for both bearings decreases as Sommerfeld number increases. However, the pressure-dam bearing maintains a minimum eccentricity of about 0.5 at high speeds. The results also show that the attitude angle for both bearings increases as Sommerfeld number increases. The maximum attitude angle for the axial-groove bearing is 90° at noload. However, the attitude angle for the pressure-dam bearing increases above 90° at no-load as speed increases. A dynamic test shows that the pressure-dam bearing has higher direct stiffness and damping at high Sommerfeld number because of the increase in eccentricity. However, as Sommerfeld number decreases, the difference between stiffness and damping coefficients of both bearings diminishes. The dynamic test also shows that both bearings have significant added mass coefficients in the laminar flow region that decrease as eccentricity increases. The estimated axial-groove bearing whirlfrequency ratio (WFR) from experimental results is 0.45. The WFR of the pressure-dam bearing reduces to 0.41 at high Sommerfeld numbers. Numerical analysis shows that the pressure-dam bearing can have lower WFR if the dam arc length is increased to 150°. Numerical analysis also shows that stability can be improved further by adding a relief track. Generally, the numerical analysis under predicts the bearings’ eccentricity and dynamic force coefficients with better agreement at low Sommerfeld numbers.