Differences between mean value and fixed value in Pressure Outlet boundary condition in SimScale

 In SimScale, when defining a pressure outlet boundary condition for your fluid flow simulations, you get to choose the "pressure type." This determines how the pressure is calculated at the outlet boundary. Here's a breakdown of the two main options in a simple way:

1. Mean Value:

• Imagine a group of people exiting a crowded room. The "mean value" represents the average pressure experienced by all the fluid particles leaving the domain through the outlet.
• Think of it like this: Even though individual fluid particles might have slightly different pressures as they leave, the average pressure across the entire outlet boundary is what matters.

2. Fixed Value:

• Picture a specific pressure setting on a water valve at the outlet. This type dictates a constant pressure value for the entire outlet boundary.
• Think of it like this: No matter where a fluid particle exits through the boundary, it will experience the same exact pressure.

Choosing the Right Pressure Type:

The choice depends on the specific scenario you're simulating:

• For most outlet conditions: Use "Mean Value." This allows SimScale to calculate the pressure based on the flow behavior within the domain, leading to a more natural and realistic flow simulation.
• For specific situations: Use "Fixed Value" only if you know for sure that the pressure at the outlet needs to be a constant value throughout the entire boundary. This might be the case if the outlet is connected to another fixed-pressure system.

Remember: "Mean Value" is the more common and versatile option for most outlet simulations. It allows the flow to adjust the pressure at the outlet naturally based on the overall flow behavior within the domain.