Journal Bearings — validation & limitations

What it calculates

• Sommerfeld number and eccentricity ratio via the Raimondi-Boyd characteristic tables (L/D = 1, with Petroff asymptote blending) as tabulated in Shigley Ch. 12
• Film ratio Lambda = h_min / composite RMS roughness as the governing acceptance check — the criterion that says whether the oil film actually separates the surface asperities
• Dynamic viscosity derived automatically from your ISO VG grade at the MEAN FILM temperature (T_inlet + delta-T/2, solved iteratively) via the ASTM D341 Walther equation, so you never convert cSt to mPa.s by hand
• Minimum oil film thickness, eccentricity, attitude angle, friction coefficient, friction torque, power loss and oil flow
• Temperature rise with the Raimondi-Boyd side-flow correction (1 - Qs/2Q), which most simplified calculators omit
• Film-thickness and film-ratio sweep against speed, with the Trumpler floor drawn and the lowest speed the engine does not fail marked
• ASTM D341 viscosity-temperature curves for all nine ISO VG grades (VG 10 to VG 320) with a D.N speed-factor grade guide

Related standards — reference only, not implemented

• ISO 7902reference only — Journal-bearing analysis by the Raimondi-Boyd characteristic tables (L/D = 1) as tabulated in Shigley Ch. 12 — bearing characteristic number, eccentricity ratio, h_min, friction torque, power loss, oil flow and lubrication regime, with ISO VG viscosity selection and PDF report. Related to, but NOT computed as, ISO 7902 / DIN 31652: the displayed characteristic number is the reciprocal of their So, only the L/D = 1 column is read (ISO 7902-2 tabulates against ε and B/D), and the film-thickness limit is a house band rather than ISO 7902-3's h_lim.

Validation evidence — independent reference cases (2)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

• Journal bearing Sommerfeld number, film thickness and film ratio

  Agrees

  Source: Budynas & Nisbett, Shigley's Mechanical Engineering Design, 9th/10th ed., Ch. 12, Example 12-1; Trumpler criterion (Shigley Ch. 12, after Trumpler 1966); Raimondi & Boyd, Trans. ASLE 1958; Hamrock, Schmid & Jacobson, Fundamentals of Fluid Film Lubrication, Ch. 1/18

  Inputs: D = L 38.1 mm, c 0.0381 mm, W 2224.1 N, N 1800 rpm, mu 27.579 mPa·s, Ra 0.4 and 3.2 um

  Quantity	Reference value	Tolerance
  Sommerfeld number	0.1350 (book 0.135)	1e-6 relative
  minimum film thickness	0.015986 mm = 0.000629 in (book 0.00063 in)	1e-6 vs hand; 1 % vs book
  eccentricity ratio	0.5804 (book 0.58)	1e-6 vs hand; 1 % vs book
  film ratio Lambda at Ra 0.4 / 3.2 um	22.608 / 2.826	1e-6 relative

  tests/golden/REF-lubrication-journal-film.golden.test.ts

• Journal bearing friction, power loss, oil flow and temperature rise

  Conservative

  Source: Budynas & Nisbett, Shigley's Mechanical Engineering Design, 9th/10th ed., Ch. 12, Examples 12-1 to 12-3 and Eq. (12-15); Raimondi-Boyd l/d = 1 chart rows

  Inputs: D = L 38.1 mm, c 0.0381 mm, W 2224.1 N, N 1800 rpm, mu 27.579 mPa·s, S 0.135

  Quantity	Reference value	Engine	Tolerance
  temperature rise	15.46 K (book Eq. 12-15 on chart readings)	15.83 K	one-sided: -1 % to +4 % vs book; 1e-6 vs hand
  friction torque	2.62 lbf·in (book)	0.30342 N·m (2.6855 lbf·in)	-1 % to +4 % vs book
  power loss	494 lbf·in/s = 55.8 W (book)	57.19 W	-1 % to +4 % vs book
  oil flow	0.217 in3/s	0.21752 in3/s	1 % vs book

  Conservative simplification: The engine reads the friction variable on the higher side of the chart, so friction torque, power loss and temperature rise sit about 2.3 to 2.5 % above the book readings (oil flow +0.4 %).

  tests/golden/REF-lubrication-temperature-rise.golden.test.ts

Limitations

Conservative simplifications

• Journal bearing friction, power loss, oil flow and temperature rise — The engine reads the friction variable on the higher side of the chart, so friction torque, power loss and temperature rise sit about 2.3 to 2.5 % above the book readings (oil flow +0.4 %).

Not checked by this tool

• Shaft misalignment and journal deflection in the film — A rigid, aligned journal is assumed; check edge loading with the shaft slope from /shaft
• Rotor-bearing stability (oil whirl / whip) — Not assessed; check light-load, high-speed bearings with a stability analysis or the bearing maker
• Dynamic or rotating loads (e.g. crankshaft bearings) — Steady load only; dynamically loaded bearings need a mobility or transient analysis
• Oil supply: feed pressure, groove design and supply flow — Flow is read from the Raimondi-Boyd tables; design the feed groove and supply pressure with the bearing maker
• Turbulent film in fast, large bearings — A laminar film is assumed; apply turbulent-film corrections at high Reynolds numbers
• Bearing lining limits (specific load, babbitt temperature) — Check the specific load and peak film temperature against the lining maker's limits