Instead of a 3D colored foil mesh seen through a camera, this view plots the same pressure-coefficient physics two ways that are native to 2D:
Cavitation number: σ = (p∞ − pv) / (½ρV²)
Ambient pressure: p∞ = p_atm + ρgh
Vapor pressure: pv(T) (Antoine equation, water)
Inception criterion: σ ≤ −Cp,min ⇔ p∞ + Cp,min·½ρV² ≤ pv
Cp,min(α) ≈ −(0.42 + 0.09|α| + 0.012α²)
Top strip — Cp vs chord chart: a line graph of the local pressure margin Cp(x/c) + σ along the suction (upper, cyan) and pressure (lower, orange) surfaces, using the exact same chordwise suction-peak shape as the 3D sim. The zero line is the vapor-pressure threshold: wherever a curve dips below it the surface is cavitating, shaded white, and vapor bubbles are spawned rising out of exactly that x/c range — the same cavitatingExtent rule the 3D sim uses to seed its bubble field.
Bottom strip — speed/angle phase diagram: a heatmap over foil speed V (x-axis) and angle of attack α (y-axis) at the current depth and temperature, colouring every point cavitating or safe by the same σ ≤ −Cp,min test. The live inception-speed curve Vi(α) is traced on top, and a crosshair marks your current (V, α) — drag inside this panel to set both sliders at once and see directly how close you are to the boundary, something no single camera angle on the 3D mesh can show at a glance.
- Speed V — raises ½ρV², lowering σ toward the vapor threshold.
- Angle of attack α — steepens Cp,min, lowering the inception speed needed.
- Depth h — adds hydrostatic head ρgh to p∞; shallow running is far more cavitation-prone.
- Temperature T — raises the vapor pressure pv, shrinking the margin and lowering inception speed.
Real-world relevance: this is why hydrofoil craft, ship propellers and pump impellers are speed- and depth-limited — once σ drops below −Cp,min, the suction side erupts in vapor, killing lift/thrust and eroding the metal as the bubbles collapse downstream.