Cavitation number σ_n at a given depth and rpm compared to the empirical inception threshold - the first check before Burrill / Keller chart assessment.
Formula
$$ \sigma_n = \frac{p_a + \rho g h - p_v}{\tfrac{1}{2} \rho V_t^2} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $p_a$ | Atmospheric pressure | Pa | 101325 Pa |
| $h$ | Shaft depth | m | hydrostatic |
| $p_v$ | Water vapour pressure @ T | Pa | steam tables |
| $V_t$ | Tip speed | m/s | πDn |
Sources
- Burrill L.C. - RINA 1943.
- Keller J. - 1966.