Learn how to use Ansys Discovery to assess valve performance, enabling engineers to design better products.
Understanding Valves
Valves are mechanical devices used to control the flow of fluids (liquids, gases, or slurries) in industrial processes. They play a crucial role in flow control in industrial processes, pressure regulation in pipelines, system isolation for maintenance, safety and overpressure protection and, direction control in hydraulic and pneumatic systems. The types and Classification are presented as follows:
- Gate Valves (On/off control, full bore)
- Globe Valves (Flow regulation)
- Ball Valves (Quick on/off, low pressure drop)
- Butterfly Valves (Large diameter applications)
- Check Valves (Prevent backflow)
- Pressure Relief Valves (Protect against overpressure)
The Key Valve Components are five:
- Body. Main structure that contains the internal parts and connects to the piping,
- Bonnet. Cover that provides access to internal parts.
- Seat. Sealing surface inside the valve body against which the disc closes.
- Disc. Movable part that controls flow by pressing against the seat.
- Stem. Rod or shaft that transmits motion to open/close the valve.
Performance
As the area of opening is variable, the friction loss depends on the flow going through the valve. Experimental testing has provided different correlations between flow and flow resistance, by measuring the pressure drop (Δp) and flow (Q), as well as by determining the fluid density (r) and the local acceleration of gravity (g). The most important correlations are the Pressure drop, the Resistance Coefficient (z) and the Flow Coefficient (Cv):
Where SG is the Specific Gravity equal to rg, and the velocity (V) is obtained from the continuity equation. The data is provided using the valve's standard size designation, rather than its exact internal dimensions. This practice simplifies valve selection and comparison across different manufacturers, though it may not always reflect the valve's precise performance. The performance is then presented in tables or graphs as shown below (dummy values):
Part I: Simulation in Explore Mode
Valve performance can be influenced by various factors, and simulation offers solutions to overcome these challenges. One of the main challenges is accurately predicting valve behavior under different operating conditions. By simulating the flow inside the valve, engineers can analyze how pressure drops can be minimized by changing areas of improvement and optimizing the valve design for efficient and reliable operation.
For this example, we use Ansys Discovery 2024R2. Ansys Discovery is a comprehensive tool that provides an immersive and interactive workspace for modeling, simulation design exploration, and solution analysis. It allows you to create and modify geometry using direct modeling technology, define simulations, and interact with results in real-time.
Description
The domain consists on a gate valve shown in the first image above. The simulations will be solved first in the Explore mode (Part I) and then in Refine Mode (Part II). The Pressure drop vs Flow rate and Resistance Coefficient vs Opening graphs are built using data found for four valve positions, four flow rates and, the valve size of D= 51 mm (2 in).
- Inlet: The four velocities are 0.5, 1.5, 2.5, 3.5 m/s.
- Outlet: Zero static pressure in Pa.
- Working fluid: Water at 20°C (68 F).
- Temperature: The simulations are isothermal at the given temperature.
Steps
- Geometry preparation
Group the components in the tree by creating different components (folders). Here, there is one for the housing, the stem/discs in different opening positions, and the connections. For the opening positions, depending on your geometry, there will be a total distance to close the valve. In this case, the minimum opening was defined as 10.4% to allow the flow to go through the valve.
- Fluid Domain
Disable and hide the components as shown below. Go to the 'Prepare' Tab > 'Volume Extract'. Follow the steps: 1) select the faces that enclosure the region, 2) select a face that lies within the volume and, 3) click on Complete. The picture on the right shows the section view. This is the Fluid Domain that will be cut by the different stem/disc positions. I renamed the volume as FluidDomain11.
- Model Setup
Now switch to the Explore Mode. Go to 'Simulation' Tab > 'Fluid Flow' > Flow. Select 'Inlet' and the right port, type the inlet velocity as 0.5 m/s and change the temperature to 20°C. Repeat the process but this time select 'Outlet' and the left port. Type the pressure and temperature. Follow the procedure.
Two materials can be seen on the tree: Structural Steel S275N for the solids (By default) and a fluid. Double click and verify that Liquid is selected. I changed the default density and viscosity to be in agreement with the values at 20°C. The thermal properties have values for 23°C as they are not used here, but if that is the case, change them accordingly. Moreover, change the initial temperature to 20°C and enable the gravity.
We need to cut the fluid domain by the initial stem/disc position to be simulated. This is accomplished by using the tool named "Cutting Bodies": 1) Right click on the fluid domain > 'Overlapping Bodies' > 'Set to be cutter bodies' (this allows the selected solid bodies on the tree to cut the fluid domain during the simulation), 2) right click on bodies/components to remove them as cutter bodies 3) except the stem/disc position 'Pos 4 (100%)' as it is the only body that will cut the fluid domain.
To make the simulations easier to run, we can also parametrize the inlet with the four velocities we established from the beginning: 1) click on 'Flow Inlet 1' located on the tree and select the Parametrization button, 2) open the parametrization table, 3) type the velocity values, 4) click on the button shown and finally, 5) update all design points. You can do something else while Discovery solves all the simulations.
- Solution
For each model you will see results of Velocity, Static pressure, Total pressure, temperature and Vortices Lambda 2 in different unit systems. In this Demo, we will check the first two of them. The following picture presents the 'Direction Field' aligned with the meridional plane. To get that visualization, go to the 'Results Arc' on the bottom-right part of the screen and select the first icon.
In the Explore Mode, the accuracy of the results and the simulation time depend on the Fidelity. Then, the results on the Parametrization Table shows four set of values for the same Fidelity. In this Demo, I worked with three Fidelity values to compare the results, which are presented in Table 1. The next picture shows the last set of results from Discovery and the general results. The above picture is for the 3.5 m/s of set #1.
Now you can build the curve 'Pressure Drop vs Flow Rate' from Table 1. There are two lines that connect the minimum and maximum points for each inlet velocity. If you repeat the same simulation procedure using the rest of the stem/disc positions (different openings) as cutter bodies, as well as the parametrization table, you can calculate easily the range of the Resistance Coefficient. The graphs are presented as follows. The main advantage is that the user knows the range in which the actual curve may be, but with results obtained in up to 2 minutes of processing time for each model.
This concludes the first part of the simulation of valve performance. In the second part, you will learn how to set up, solve and get results to build the same graphs more accurately in the Refine Mode. The files will be available for download.
Part II: Simulation in Refine Mode