Compute pipe flow velocity and pressure drop (Darcy-Weisbach).
根据达西-魏斯巴赫公式计算圆管流速、雷诺数、沿程阻力及压降，适用于常温清水。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Darcy-Weisbach equation | h_f = lambda · ( L / D ) · v^2 / ( 2 · g ), where lambda is the friction factor | Weisbach J. (1845), Lehrbuch der Ingenieur- und Maschinen-Mechanik |
| Mean velocity | v = Q / A = 4 · Q / ( pi · D^2 ) | ISO 80000-4:2019, Quantities and units - Part 4: Mechanics |
| Reynolds number | Re = v · D / nu, where nu is the kinematic viscosity | Reynolds O. (1883), An experimental investigation of the circumstances which determine... |
| Laminar friction factor | In laminar flow, lambda = 64 / Re | Hagen-Poiseuille law; Crane Co., Flow of Fluids Through Valves, Fittings, and Pipe (TP-410) |