Tilting pad journal bearings can operate under a wide range of conditions of speed, load, load angle, oil temperature, and oil viscosity. Each one of these variables has an effect on the oil film, and an influence on whether the film is laminar, turbulent, or in transition. Other parameters affect the film as well including geometry such as the bearing diameter, length, clearance, preload, the number of pads and their orientation.
A Reynolds Number (Re) of 1000 is typically used to distinguish whether the flow in the oil film is laminar or turbulent. A bearing behaves as expected in either of these flow regimes. For example, pad temperatures tend to increase with speed. Operation through the transition region, however, can lead to behavior that does not appear normal. This can be explained using the following graph which plots pad temperature data from recent tests conducted on Kingsbury's new tilting pad journal bearing test rig.
Referring to the 8 gpm [30 l/sec] data, pad temperatures are noticed to increase with speed from 100 to 200 ft/sec [30 to 60 m/sec] and from 250 to 350 ft/sec [75 to 105 m/sec]. These represent laminar and turbulent film flow, respectively. In the transition between 200 and 250 ft/sec [60 to 75 m/sec], however, pad temperatures decrease with speed. The decrease is attributed to the turbulent flow's capability to better remove heat from the pad surface.
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