Opening your learning space
Starting the app …
Opening your learning space
Starting the app …
Cavitation number compares pressure margin above vapor pressure with flow dynamic pressure.
Free to browse · flashcards or a multiple-choice quiz · import from Essential
Formula
σ dimensionless; p and pv in Pa; ρ in kg/m3; v in m/s
| Symbol | Meaning | Unit |
|---|---|---|
| Cavitation number at a stated reference location | dimensionless | |
| Local absolute static pressure | Pa | |
| Vapor pressure at fluid temperature | Pa | |
| Fluid density | kg/m3 | |
| Characteristic flow speed | m/s |
\sigma=\frac{p-p_v}{\frac{1}{2}\rho v^2}The value depends on the chosen reference location, pressure and velocity. Lower values indicate less pressure margin relative to dynamic scale, but no universal critical threshold exists. Temperature, nuclei, geometry and turbulence affect cavitation and damage.
The value depends on the chosen reference location, pressure and velocity. Lower values indicate less pressure margin relative to dynamic scale, but no universal critical threshold exists. Temperature, nuclei, geometry and turbulence affect cavitation and damage.
Cavitation number compares pressure margin above vapor pressure with flow dynamic pressure.
Base equation for the target quantity
Preserve signs, boundary conditions and units when rearranging.
Work through the numerical example for “Cavitation number” and check its unit and magnitude.
For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94.
Substituting a related quantity that shares the same symbol.
Use variable definitions and check: σ dimensionless; p and pv in Pa; ρ in kg/m3; v in m/s.
Formula cluster
Cavitation number compares pressure margin above vapor pressure with flow dynamic pressure.
For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94.
Compare cavitation similarity in pumps, propellers and hydraulic components.
Here is how to work through a typical Cavitation number (σ = (p−pv)/(½ρv²)) task step by step:
Task
Work through the numerical example for “Cavitation number” and check its unit and magnitude.
Solution path
For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94.
Vapor pressure is an absolute thermodynamic pressure. Gauge pressure cannot be subtracted directly; convert it using ambient pressure. Otherwise the pressure margin and dimensionless value are physically wrong. Use absolute pressure and state the reference location and velocity convention. Application: Compare cavitation similarity in pumps, propellers and hydraulic components. The numerical example For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94 anchors the idea in a concrete measurement case. The corresponding units are σ dimensionless; p and pv in Pa; ρ in kg/m3; v in m/s. For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94. This checks that the reference quantities are compatible.
Local pressure is closer to vapor pressure relative to dynamic pressure, suggesting greater cavitation tendency. Without nuclei, temperature and geometry, it is not a definite threshold for bubbles or erosion. Use absolute pressure and state the reference location and velocity convention. The corresponding units are σ dimensionless; p and pv in Pa; ρ in kg/m3; v in m/s. For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94. This checks that the reference quantities are compatible. Scope: The value depends on the chosen reference location, pressure and velocity. Lower values indicate less pressure margin relative to dynamic scale, but no universal critical threshold exists. Temperature, nuclei, geometry and turbulence affect cavitation and damage. A practical application is Compare cavitation similarity in pumps, propellers and hydraulic components.
Use the characteristic velocity specified by the cavitation-number reference, such as mean approach speed or a local value. Different references yield different numbers. Document section and measurement point and compare consistently defined values. Use absolute pressure and state the reference location and velocity convention. Scope: The value depends on the chosen reference location, pressure and velocity. Lower values indicate less pressure margin relative to dynamic scale, but no universal critical threshold exists. Temperature, nuclei, geometry and turbulence affect cavitation and damage. A practical application is Compare cavitation similarity in pumps, propellers and hydraulic components.
Write the quantity and unit from the variable list next to every value: σ dimensionless; p and pv in Pa; ρ in kg/m3; v in m/s. Substitute only after converting to a consistent unit system, and state sign or reference direction explicitly. The example For p=150 kPa absolute, pv=3 kPa, ρ=1000 kg/m3 and v=10 m/s, σ≈2.94. is a calculation check: result, unit and order of magnitude must fit the described situation. Round after intermediate calculations so small contributions are not lost prematurely. Use absolute pressure and state the reference location and velocity convention.
The background states this starting condition: The value depends on the chosen reference location, pressure and velocity. Lower values indicate less pressure margin relative. That limits when the result is a valid model prediction. Compare the problem’s boundary conditions with this assumption before substituting values; real components, material properties or loads can introduce additional effects. The cited reference supports the relation used here but does not remove the need to check whether the specific case fits the model. Use absolute pressure and state the reference location and velocity convention.
Quanta exam set
Curated exam set for "Cavitation number":
Question (front)
Which formula describes Cavitation number?
Answer in your set
Question (front)
How do you rearrange Cavitation number for Base equation for the target quantity?
Answer in your set
Question (front)
Which common mistake happens with Cavitation number?
Answer in your set
+ 8 more cards: units, variables, derivation, example, exam task
The formula set contains 11 cards. After importing, review them and start practicing; your ratings determine later review intervals.
This list names subject references and further reading. A page or section number appears when it is part of the reference; these are not verbatim quotations.
Create a curated FSRS exam set for σ = (p−pv)/(½ρv²): formula recall, variables, derivation, rearrangement, worked example, common mistakes and exam context.
Curated formula set · LaTeX · FSRS spaced repetition · import from Essential