Bearing Oil Whirl & Oil Whip Stability Calculator

Q: What is the physical difference between oil whirl and oil whip?

Oil whirl is a fluid-driven subharmonic instability that precesses at ~43%–48% of rotor speed. Oil whip occurs when the whirl frequency coincides with the rotor’s first natural critical speed, locking into violent destructive resonance.

Q: Why are lightly loaded bearings especially prone to oil whirl?

Light unit loads force the journal to run at very low eccentricity ratios (ε < 0.3), near the center of the bearing. This promotes uniform annular fluid shear and maximizes destabilizing cross-coupled stiffness (Kxy).

Q: Why do tilting pad journal bearings (TPJB) eliminate oil whirl?

Because each pad is free to tilt, the fluid pressure profile on each pad is symmetrical about its pivot, destroying the non-conservative cross-coupled stiffness (Kxy ≈ 0) and driving the whirl frequency ratio (WFR) to zero.

Estimate rotordynamic oil whirl onset speed, whirl frequency ratio (WFR), and critical threshold velocity to avoid destructive subharmonic instability.

Rotor Dynamics & Bearing Type

First Rotor Critical Speed N_cr (RPM):

Normal Operating Speed N_op (RPM):

Bearing Bore Geometry:

Eccentricity Ratio ε at Op Speed: Lightly loaded (ε < 0.35) = high whirl risk

Rotor Modal Mass per Bearing (kg):

Modal Damping Ratio ζ:

Rotordynamic Stability Assessment

Whirl Threshold Speed:

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Whirl Frequency Ratio (WFR):

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Subharmonic Whirl Freq:

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Oil Whip Lock-In Speed:

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Dynamic Stability Verdict:

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Frequently Asked Questions

What is the physical difference between oil whirl and oil whip?

Oil whirl is a fluid-driven subharmonic instability that precesses at ~43%–48% of rotor speed. Oil whip occurs when the whirl frequency coincides with the rotor’s first natural critical speed, locking into violent destructive resonance.

Why are lightly loaded bearings especially prone to oil whirl?

Light unit loads force the journal to run at very low eccentricity ratios (ε < 0.3), near the center of the bearing. This promotes uniform annular fluid shear and maximizes destabilizing cross-coupled stiffness (Kxy).

Why do tilting pad journal bearings (TPJB) eliminate oil whirl?

Because each pad is free to tilt, the fluid pressure profile on each pad is symmetrical about its pivot, destroying the non-conservative cross-coupled stiffness (Kxy ≈ 0) and driving the whirl frequency ratio (WFR) to zero.