Gas Journal Bearing Suite Calculator

Equations used

All pressure inputs are absolute. Positive load is radial capacity; eccentricity ε=e/c is positive toward the minimum-film side. SI units are used internally.

Partial porous surface and porous rings

Partially grooved, externally pressurized

Here Lₙ=L₁/L₀, Bₙ=B₁/B₀, N is groove-to-land film ratio, k is an even groove count, β is local pressure factor, M is total mass flow, η is dynamic viscosity, R is gas constant, and T is absolute temperature. The factor 2 represents the symmetric bearing halves.

Self-acting spiral and plain air bearings

S₁ and attitude angle β are linearly interpolated from the published Λ={0.5,1,5,10} and L/D={1,1.5} tables. The spiral table assumes groove angle 33°, groove/ridge width ratio 1, and depth ratio 1. Values with 10<Λ≤12 are extrapolations; values above 12 are rejected.

How to use

1. Select one of five modes. Partial porous, Porous rings, and Partial grooves are externally pressurized; the self-acting modes require shaft rotation.
2. Enter shaft diameter in mm and L/D. For self-acting tables, use 1≤L/D≤1.5.
3. For porous modes, enter absolute supply pressure, radial clearance, porous permeability, gas viscosity, specific gas constant, and temperature. Ambient pressure is fixed at 1 bar absolute.
4. For partial grooves, enter absolute supply and ambient pressures, c/R, even groove count, groove length/width/depth ratios, and signed eccentricity ratio 0≤ε<1.
5. For self-acting modes, enter radial clearance in µm, speed in krpm, and viscosity in µPa·s. A warning appears when Λ exceeds the tabulated limit of 10.
6. Select Calculate to update the canonical load or stiffness and secondary metrics. Correct any red warning before interpretation.
7. Read porous/grooved load as screening radial capacity; read self-acting stiffness as local radial stiffness. Re>500 and Λ>10 require special caution.
8. Select Reset example to restore the partial-porous demonstration. Do not use these models for contact, choked/turbulent supply, large thermal distortion, rotor-dynamic stability, manufacturing tolerance, or safety-critical qualification.

Worked example

1. Select Partial porous. 2. Enter L/D=1, D=50 mm, pₛ=6 bar absolute, c=10 µm, kₚ=2.5×10⁻¹⁵ m², η=18 µPa·s, R=287 J/(kg·K), and T=293 K. 3. Calculate. Expected results are 308.75 N load, F*=0.247, 61.75 N/µm stiffness, 3.5625 mm porous thickness, 4.3240×10⁻⁵ kg/s mass flow, and 2.1817 L/min ambient flow. This is a nominal screening point; verify permeability, clearance tolerance, deformation, and supply capacity.

Theory and method

Externally pressurized gas bearings develop load before rotation by throttling supply gas through porous material or grooves into a thin annular film. The porous correlations use a fixed centered pressure factor β=0.5 and ε=0.5 for stiffness scaling. The partially grooved model discretizes half the circumference and sums compressible-film pressure and flow contributions. Self-acting bearings instead generate pressure through journal motion; Λ captures the balance of viscous pumping, speed, clearance, and ambient pressure.

The models assume ideal isothermal gas, constant viscosity, rigid circular surfaces, symmetric geometry, small clearance, quasi-static response, and no slip, choking, inertia, turbulence, thermal growth, elastic distortion, or rotor dynamics. The partial-groove Reynolds output is a screening check: prefer Re<500 and treat 500–1000 cautiously. Results are unsuitable when surfaces can touch, geometry leaves the tabulated range, or stability and transient response govern.

References

• Anton van Beek, Advanced Engineering Design, gas-bearing chapters and published calculation tables.
• ISO 4378-1, Plain bearings—terms, definitions, classification and symbols.

Related aerostatic linear-bearing screening · Continue in TriboSolver to refine film pressure, deformation, and stability with higher-fidelity analysis.