Tilting Pad Journal Bearing

Tilting Pad Journal Bearing

For high speed and lightly loaded rotating machines, the bearings with fixed geometry are prone to self-excited vibration. Tilting pad (pivoted-pad) journal bearings are widely used in high-speed machinery because of their stability characteristics even though they are more expensive than fixed profile bearings. The bearing is made up of a number of pads (shoes) which are supported on pivots. The pads are free to tilt about the pivot points to accommodate the journal motion. Dynamic effects from each individual pad are assembled to obtain the full bearing performance.

Under Tilting-Pad menu, there are analysis and postprocessor for dimensional and non-dimensional analyses. The bearing stiffness and damping coefficients calculated from dimensional analysis can be saved as a bearing file to be readily used by DyRoBeS©_Rotor. All the input and output data can be viewed from the Text Output option, while only the key output parameters are summarized in the Tabulated List and can be displayed in the graphic forms.

Tilting Pad Bearing Geometry

Parameters used to describe the bearing geometry are defined in this section.

Tilting Pad Dimensional Analysis

The dimensional analysis includes Constant Viscosity analysis and Heat Balance analysis. For Constant Viscosity analysis, user must input a lubricant dynamic viscosity and no temperature rise will be calculated. For Heat Balance analysis, user must select a lubricant type and input the lubricant inlet temperature. Supplied oil flow rate can also be entered if it is known. Otherwise, the side leakage flow will be used in the heat balance calculation. The operating and maximum film temperatures will be calculated based on the heat balance method.

For heat balance calculation, the heat generated in the bearing is removed by the effective oil flow. The effective oil flow rate depends on many factors, such as the bearing construction, the specified oil flow rate, side leakage, total circumferential inlet flow, ways to supply the oil, and ways to drain the oil flow, etc. Several cases are considered:

1.When the supplied oil flow rate is NOT specified (i.e., Qsupplied = 0), the side leakage will be used as the effective oil flow. This is the default option and is commonly required in the bearing design process to determine the minimum required flow rate.

Qsupplied = 0, => Qeffective = Qside

2. When the specified oil flow rate is less than and equal to the side leakage (i.e., Qsupplied <= Qside ), the specified flow rate will be used as the effective flow rate. Note, this starvation will result in overheated bearing and is not desirable.

Qsupplied <= Qside, => Qeffective = Qsupplied

When the specified oil flow rate is greater than the side leakage (i.e., Qsupplied > Qside), the effective flow rate is estimated using the empirical expression. Q Integration factor is a parameter used in the flow integration. Typical value for this Q integration factor from many test data shows that the value is between 0.2 and 0.4 with an average of 0.25 to 0.3. This parameter heavily depends on the bearing construction, pad shape and design, the orifice configuration, ways of supply oil, ways of drain oil, etc.

Tilting Pad Non-Dimensional Analysis

The non-dimensional analysis is performed based on the given bearing eccentricity ratios.