Widely used in power and automotive industry, the fluid film journal bearing is critical to a machine’s overall reliability. Fluid film bearings reduce friction by maintaining a thin layer of liquid or gas between the rotating parts. The rotating loads are completely supported by the pressure force induced in the thin film. Because of simple construction, fluid film bearings are suitable in high load, high speed or high precision applications where ordinary ball bearings would have short life or cause high noise and vibration. Therefore, fluid film bearings are commonly used in IC engines, pumps, compressors, gas turbines, turbo chargers, hydro turbines, electric generators, marine propeller shaft, hard disc drive and many other forms of rotating equipment. They are also used increasingly to reduce cost. For example, hard disk drive motor fluid film bearings are both quieter and cheaper than the ball bearings they replace.
Fluid film bearing characterization is a complex but fairly understood discipline. Static as well as dynamic bearing characteristics (such as load capacity, pad temperature, power loss, oil consumption, stiffness and damping coefficients) are a complex function of clearance, speed, load and fluid viscosity. While the basic fluid dynamics of film bearings are well understood, secondary effects such as elastic deformations, heat transfer to solids and turbulence are less understood and also impact performance. However, desire for improved reliability and performance is constantly forcing a better understanding of secondary effects.
Conventionally, engineers characterizing fluid film bearings use simplified modeling approaches, such as reduced Reynolds equation based tools. These tools assume the flow film is purely two dimensional and only approximate the modeling of cavitation. They may approximate the thermal interaction between the film and solid components such as shaft, bearings but they are not likely to account the elastic deformation in the components. The advantage of such simplified simulation is fast turnaround time.
Fluid pressure and bearing deformation predicted using coupled fluid-structural simulation
These simplified analysis methods are falling short as innovation introduces new designs that demand the accurate and detailed prediction of bearing performance. Accurate modeling of elasticity is one of the most difficult tasks in a bearing analysis since the poor evaluation of journal and shell deformation can introduce a large error in the modeling prediction. Full 3-D coupled fluid- thermal-structural analysis eliminates the error associated with simplified, approximate approaches. Fortunately, huge improvements in computational capabilities have made full 3-D CFD analysis, coupled thermal analysis and coupled fluid-structural analysis possible.
ANSYS has developed and validated a new simulation method that not only addresses this complex problem but also makes it simple to solve. This methodology actually opens detailed full 3-D, coupled solution arena for fluid film bearing designers which could not use 3-D simulation before because of the complex nature of this problem. If you would like to hear more about this topic, please join us for one of the upcoming webinars.
Analyzing Fluid Film Bearings and Rotordynamics with ANSYS
Thursday, April 9 at 10:30 am IST
Thursday, April 9 at 4 pm ET
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