Ssu

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 TEMPERATURE, °F

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 TEMPERATURE, °C

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 TEMPERATURE, °F

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 TEMPERATURE, °C

FIGURE 12 Viscosity characteristics for SAE oil grades.

Performance Curves Performance plots have been generated for the following types of bearings:

• Two-groove cylindrical bearings

• Symmetric three-lobe bearings: Each lobe is offset such that in the concentric position the minimum film thickness in the center of each lobed region is half the machined clearance c (see definition following). The pads are each 110° in the angular extent.

• Canted three-lobe bearing: The lobing is canted such that in the concentric position the leading edge clearance was twice the trailing edge and the trailing edge film thickness (minimum) in the concentric position was 0.5c where c equals the machined clearance. The pads are each 110° in the angular extent.

• Tilting-pad bearing: The tilting-pad bearing that information is obtained for is a five-pad bearing with a 60° pad and a preload ratio of 30 percent.

Two length/diameter ratios are examined for each type of bearing: L/D = 0.5 and 1.0.

The definition of the nondimensional parameters is as follows:

W = nondimensional load parameter = wc2/6/m«RL3 (28)

P = nondimensional viscous power loss parameter = 1100cp/m( oRL)2 (29)

Q = nondimensional flow parameter = 2q/0.26vRLc (30)

HM = nondimensional minimum film thickness = hM/c (31)

where w = bearing load capacity, lb (N) and c = reference clearance (machined clearance = radius of bearing — radius of shaft), in (mm) m = absolute viscosity, reyns (lb • s/in2) (cP) o) = shaft or journal rotational speed rad/s R = shaft radius, in (mm) L = bearing length, in (mm) p = viscous power loss, hp (kW) q = flow, gpm (m3/h)

LOAD PARAMETER W FIGURE 14 Performance characteristics for three-lobe bearings.

qi = inlet flow to the leading edge of bearing (for multipad bearings, equals the sum of inlet flow to each pad), gpm (m3/h) qs = side leakage flow or flow out of the bearing ends (for multipad bearings, equals the sum of side leakage flow of each pad), gpm (m3/h) hM = minimum film thickness in bearing, in (mm)

Performance curves are shown in Figures 13 through 17.

At times, the nondimensional data can be confusing and lead to erroneous judgments. For example, the nondimensional power loss P is greater for an LID equal to 0.5 than for an LID equal to 1.0. However, when the dimensional value of the power loss is being computed, the nondimensional value is multiplied by L2. Therefore, the power loss for the LID

LOAD PARAMETER W FIGURE 15 Performance characteristics for canted three-lobe bearings.
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