The Role of Bearings in Rotating Machinery: Selection, Simulation, and Performance

In industrial turbomachinery, including steam turbines, compressors, pumps, and electric motors, bearings are critical components. They support shafts in rotating machinery, manage complex loads, and ensure smooth operation by minimizing friction between interacting surfaces. A bearing is a precision machine element that constrains relative motion to only the desired movement while reducing friction between interacting surfaces. Capable of carrying both radial and axial loads, bearings are typically classified based on the type of operation, allowed motions, and the direction of applied loads. Their performance directly influences machine reliability, efficiency, and service life, making the correct bearing selection a cornerstone of robust mechanical design. 

Overview of Bearing Types 

While there are many specialized bearings used in mechanical and structural applications, this article focuses on those most relevant to rotating machinery. 

Bearings are generally categorized into four main types based on their operating principles: 

• Sliding Liquid Film Bearings (Incl. Hydrodynamic and Hydrostatic): These bearings rely on a thin film of lubricant to generate a pressure field that separates the bearing surface and the rotating shaft. They are widely used in high-speed, heavy-load applications such as steam turbines and compressors due to their compact design and excellent damping capabilities. 

• Rolling Element Bearings: This group includes ball and roller bearings, which utilize  rolling elements to minimize friction and support  loads. They are easy to install and maintain, making them ideal for moderate-speed, moderate-load machines like gearboxes, motors, and pumps.

• Gas Bearings (Bump Foil and Herringbone Grooved Types): 

Ideal for oil-free, high-speed applications such as microturbines and turboexpanders: 

• • Gas Bump Foil Bearings: They utilize a compliant foil surface and a gas film (usually air) to support the shaft without physical contact.  
  • Herringbone (Spiral) Grooved Gas Bearings: A subtype of hydrodynamic bearings which use inclined-patterned grooves to generate pressure in the lubricant film even at low rotational speeds. This makes them self-acting and more stable under dynamic conditions. They are often used in small, high-speed machinery and environments where external lubrication pressure is undesirable or unavailable. 

Figure 2 Journal Gas Bump Foil Bearing [3]

Figure 3 Herringbone and Spiral Grooved Bearings [4]

• Magnetic Bearings (Active, Passive, and Combined): They use electromagnetic or magnetic forces to levitate the shaft, eliminating mechanical contact. Active Magnetic Bearings (AMBs) incorporate real-time control systems to center the shaft, making them ideal for ultra-high-speed machinery, vacuum environments, and advanced vibration management.

Comparison of Bearing Types 

Below is a comparative overview of common advanced bearing technologies—including gas/air foil, oil film, rolling element, and active magnetic bearings—highlighting their performance parameters and system requirements. 

Key Factors in Bearing Selection 

Choosing the right bearing requires aligning machine performance needs with design constraints. Critical factors include: 

• Load: Define the type (radial or axial), magnitude, and dynamics. Heavier or variable loads require more robust bearings. 

• Speed: High-speed applications benefit from low-friction designs like gas or magnetic bearings. 

• Temperature: Bearings must withstand thermal loads. Gas foil bearings and AMBs are ideal for high-temperature, oil-free systems. 

• Lubrication: Choose between oil, grease, or non-lubricated options to fit your system. Maintenance-free environments typically favor foil or magnetic types. 

• Damping and Stiffness: Critical for vibration-sensitive machinery. Hydrodynamic, herringbone grooved and bump foil designs offer good passive damping; AMBs provide active control. 

• Space and Weight: Compact and lightweight systems may benefit from rolling or herringbone grooved/bump foil bearings. 

• Maintenance: Consider ease of access and service intervals. Rolling bearings are replaceable; AMBs and foil bearings need less overall maintenance. 

Role of Simulation in Bearing Design 

A proper bearing selection balances performance, durability, and cost. Simulation tools help validate choices early, reducing risk and enhancing efficiency. Software such as AxSTREAM Bearing™ allows engineers to simulate a wide range of bearing types, including journal, thrust, oil/gas film, and rolling element configurations. These simulations incorporate detailed geometric properties, load conditions, lubrication regimes, and thermal effects—helping to ensure each bearing meets the operational demands of its specific application.

Figure 4 Example of Herringbone grove bearing model (a) and pressure distribution of fluid film calculated in AxSTREAM Bearing [5]

Ready to take the guesswork out of bearing selection?

With AxSTREAM Bearing, you can simulate real-world operating conditions, optimize your design for reliability and performance, and reduce development time and costs. To schedule a demo or learn how AxSTREAM can support your next project, click here.

References:  

[1] https://www.thb-bearings.com/products/plain-bearings/ 

[2] https://www.skf.com/ph/industries/automotive/cars-and-light-trucks/products-and-solutions/Rolling-element-bearings 

[3] Ying, M., Liu, X., Zhang, C., Wang, X., Liu, Y., & Zhang, Y. (2023). The Two-Pad: A novel gas foil bearing for fuel cell vehicles. Journal of Advanced Mechanical Engineering, 2023, Article 5521171. https://doi.org/10.1155/2023/5521171 

[4] https://en.wikipedia.org/wiki/Spiral_groove_bearing 

[5] Kochurov, R, Moroz, L, & Martynenko, V. “Nonlinear Response of the Rotor Supported by Gas Journal Bearings Considering Stationary and Rotating Herringbone Grooves.” Proceedings of the ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. Volume 11B: Structures and Dynamics — Emerging Methods in Engineering Design, Analysis, and Additive Manufacturing; Fatigue, Fracture, and Life Prediction; Probabilistic Methods; Rotordynamics; Structural Mechanics and Vibration. Boston, Massachusetts, USA. June 26–30, 2023. V11BT26A008. ASME. https://doi.org/10.1115/GT2023-102296