Fluid mechanics
| Name | Symbol | Formula | Meaning |
|---|---|---|---|
| Reynolds | Re | ρvL / μ | Inertia / viscous — turbulence threshold |
| Mach | M | v / c | Flow / sound speed — compressibility |
| Froude | Fr | v / √(gL) | Inertia / gravity — waves |
| Weber | We | ρv²L / σ | Inertia / surface tension — droplets |
| Strouhal | St | fL / v | Oscillatory / flow — vortex shedding |
| Rossby | Ro | v / (fL) | Inertia / Coriolis — geophysical flows |
| Capillary | Ca | μv / σ | Viscous / surface tension |
| Knudsen | Kn | λ / L | Mean free path / length — rarefaction |
Heat transfer
| Name | Symbol | Formula | Meaning |
|---|---|---|---|
| Prandtl | Pr | ν / α = μc_p / k | Momentum / thermal diffusion |
| Nusselt | Nu | hL / k | Convective / conductive heat transfer |
| Biot | Bi | hL / k_solid | Surface / conduction resistance |
| Grashof | Gr | gβΔT·L³ / ν² | Buoyancy / viscous — natural convection |
| Rayleigh | Ra | Gr · Pr | Natural convection threshold |
| Stanton | St | Nu / (Re · Pr) = h / (ρ c_p v) | Convection / heat capacity flux |
| Peclet | Pe | Re · Pr = vL / α | Advection / thermal diffusion |
Mass transfer
| Name | Symbol | Formula |
|---|---|---|
| Schmidt | Sc | ν / D |
| Sherwood | Sh | k_c L / D |
| Lewis | Le | α / D = Sc / Pr |
Other
| Name | Symbol | Meaning |
|---|---|---|
| Drag coefficient | C_D | F_D / (½ ρ v² A) |
| Lift coefficient | C_L | F_L / (½ ρ v² A) |
| Poisson ratio | ν | Lateral / axial strain |
| Mach angle | μ | arcsin(1/M) — shock wave angle |
| Deborah | De | relaxation / observation time — viscoelastic |
Was this article helpful?