What Is the Petroff Bearing Friction & Viscous Shear Power Loss Calculator?
Petroff’s law (1883) was the first successful mathematical treatment of hydrodynamic bearing friction, modeling the oil film as a thin laminar Couette shear flow.
It allows engineers to calculate the mechanical power turned into heat and size the oil lube coolers.
How Does the Petroff Bearing Friction & Viscous Shear Power Loss Calculator Work?
Viscous shear stress on the rotating surface is τ = μ · (ωR / C).
Integrating over surface area 2πRL yields the resisting friction torque T, which multiplied by rotational speed gives power loss P = T·ω.
Petroff Bearing Friction & Viscous Shear Power Loss Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Models Couette shear strain across the circumferential fluid gap to predict friction torque and thermal generation.
How to Use the Petroff Bearing Friction & Viscous Shear Power Loss Calculator
- Enter shaft dimensions, clearance, and rotational speed.
- Input the oil dynamic viscosity at operating sump temperature.
- Use the resulting power loss to size the oil cooling heat exchanger.
Step-by-Step Example Calculation
High-Speed 3600 RPM Generator Bearing
Input Values:
Understanding Your Result
Power loss scales quadratically with speed (ω²) and cubicly with radius (R³).
Petroff friction coefficient f allows easy mechanical efficiency comparisons.
Factors That Affect the Result
- Speed: Doubling RPM quadruples viscous power dissipation.
- Clearance: Tighter clearance increases shear rates, creating higher power loss.
When Should You Use This Calculator?
- Thermal balance calculations for turbomachinery lubrication skids.
- Mechanical drivetrain parasitic drag audits.
Assumptions & Limitations
- Assumes concentric shaft orientation; real eccentric loaded shafts have slightly higher friction (~10-20% higher).
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard baseline equation in machine design textbooks (Shigley, Norton).