CAVITATION
Cavitation risk assessment using CFD simulations
Traditionally, cavitation assessments rely on time-consuming flow loop tests or complex multiphase CFD simulations. This article presents a more efficient alternative: using single-phase
CFD simulations with pressure field correction to calculate key cavitation risk indicators like the incipient cavitation index( σ I
) and liquid pressure recovery factor( F L).
By Praveen Kumar Ramachandran, Centre for Computational
Technologies
About the author Praveen is a seasoned Product Marketing Manager at simulationHub, with over 15 years of experience in the field of Computational Fluid Dynamics( CFD). He has played a key role in the development of Autonomous Valve CFD( AVC)- the virtual flow loop testing application that predicts valve performance parameters, such as Cv, Cdt, σ, and FL, at the design stage. His expertise spans a wide range of applications, including Valves, HVAC, and more. As a Mechanical Engineer, Praveen has a solid technical foundation, complemented by a post-graduate certification in Product Management from IIM Indore. His extensive background allows him to bridge the gap between technical intricacies and market needs, helping businesses drive innovation and deliver impactful solutions.
The hidden cost of cavitation
Cavitation in control valves can lead to noise, vibration, reduced performance, material damage, and shortened service life. It occurs when pressure drops below the vapour pressure, forming vapour bubbles that collapse downstream, generating destructive microjets and shock waves. These forces can severely damage the valve surface, causing pitting and erosion. Cavitation risk is particularly high in control valves operating under severe service conditions, characterised by high pressure drops.
Methods to combat cavitation
Strategies to address cavitation include:
• Avoid cavitation: Elevating operating pressure to maintain flow pressure above vapour pressure.
• Robustness: Using high-strength materials to withstand erosive forces.
• Isolate cavitation: Directing collapsing bubbles toward the centre of the flow, to minimise surface damage.
• Eliminating cavitation: Designing the valve to drop the pressure in stages using an anti-cavitation cage or inserts, to prevent the formation of vapour bubbles.
The last two methods require careful valve flow path design, with staging the pressure drop involving gradual pressure reduction through the valve trim. These approaches often require multiple design iterations to optimise pressure conditions. Specific parameters are needed to assess cavitation intensity, allowing designers to evaluate and compare design solutions for the most effective outcome.
Parameters to assess cavitation
To assess the cavitation risk in control valves, two key parameters are commonly used: the
Cavitation Index( σ) and the Liquid Pressure Recovery Factor( F L
).
Cavitation Index( σ)- Three terms are commonly used to classify cavitation in valves according to the International Society of Automation( ISA- RP75.23-1995): 1. Incipient cavitation: The start of steady cavitation, indicated by an intermittent popping sound in the flow stream.
2. Constant cavitation: Indicated by a continuous popping similar to the sound of gravel flowing through the pipe
3. Choking cavitation: Occurs when the valve is passing the maximum flow possible for a given upstream pressure
The cavitation index is typically used to predict cavitation level and is calculated as follows( International Society of Automation, ISA- RP75.23-1995):
The operating cavitation index can be compared against the published cavitation indices( incipient, constant, or choking) to predict the level of cavitation. A valve’ s cavitation indices for incipient, constant, and choked levels can be determined from flow loop tests conducted in accordance with ANSI / ISA 75.02.01. Cavitation can be observed using a hydrophone or accelerometer during the test. A graph of the logarithmic accelerometer output versus flow rate or cavitation index is plotted. The slope of this curve normally changes at the points of incipient, constant, and choking cavitation, as shown in the image. The lower the calculated operating cavitation index value is, the greater the likelihood of cavitation damage.
52 Valve World August 2025 www. valve-world. net