Propeller Cavitation Number - Inception
Cavitation number σ_n at a given depth and rpm compared to the empirical inception threshold - the first check before Burrill / Keller chart assessment.
Tip speed
35.7m/s
Cavitation number σ_n
0.221 -
Assessment
High - cavitation likely
Formula, assumptions, and limits
$$\sigma_n = \frac{p_a + \rho g h - p_v}{\tfrac{1}{2} \rho V_t^2}$$
First-order check; for design use Burrill or Keller charts with mean thrust loading coefficient $τ_c$. Back-cavitation occurs at $σ_n$ ≲ 0.3, sheet on face at $σ_n$ ≲ 0.15.
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 |
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