Solving the “Face is not laying on the boundary between the solid and fluid region” Error

When trying to validate a boundary condition in SOLIDWORKS Flow Simulation, we may get an error stating “Face is not laying on the boundary between the solid and fluid region”.

Typically, there are three main reasons the error message will appear, and the solutions are straightforward. The three most common reasons are invalid geometry, invalid contacts, and invalid fluid domain specification. Below, we detail additional information and steps to solve the error message.

What Causes The “Face is not laying on the boundary between the solid and fluid region” Error?

One of the simplest reasons for the error message to pop up is that we are correctly set up for an internal flow study, but the selected face is not in contact with the fluid domain. Selecting the outer face of a lid instead of the inner face to apply a boundary condition.

For example, we may have selected a face that entirely touches another solid body to apply a boundary condition. The solution in this case is simple: make sure you are picking the inside face of the lid that is in contact with the fluid domain, or select a face that is exposed to the fluid domain and not blocked by another body.

What If That Doesn’t Solve The Issue?

If the simplest explanation doesn’t solve the error message and let you solve the study, you need to investigate your study further. The other two common issues that prompt the error are invalid contacts between solids and incorrect geometry for the internal study.

Invalid Geometry For Invalid Flow Study

In this case, there are openings in the geometry that prevent SOLIDWORKS Flow from detecting an internal fluid domain that touches the selected face. For internal flow analysis, SOLIDWORKS Flow Simulation requires a fully closed model that contains an internal cavity.

If there are any gaps or holes in the external walls of the model, we will not be able to determine the fluid domain, which could result in this message being shown when adding boundary conditions.

Accessing the Leak Tracking command

The Leak Tracking tool can be used to detect leaks in the model by displaying the information graphically on screen based on two user-selected points: one on the inside and another on the outside. The connection drawn on screen between the points reveals a leak in the model.

Invalid Contact Between Solid Bodies

For internal flow analysis, SOLIDWORKS Flow Simulation requires a fully closed model that contains an internal cavity. Invalid contacts in the geometry prevent the software from detecting a cavity. This can cause a number of issues, one of them being the message that is the focus of this article.

Invalid contacts are typically linear and point contacts that occur between solid bodies. These conditions are created when we have a cylinder tangent to a planar face, a wedge or rectangle sitting with one edge touching a planar face, or a cone with the tip touching a planar face.

Examples of invalid contact between bodies

Invalid contacts are problematic for the following reasons:

• They prevent Boolean operations from succeeding.
• They represent unresolved geometry. SOLIDWORKS Flow Simulation cannot determine whether the geometry allows fluid to flow through or not.

Automatically Fixing Invalid Contacts

SOLIDWORKS Flow Simulation 2008 and later automatically heals many invalid contacts. It automatically adds small bodies to overlap the invalid contacts, such that you don’t need to modify the geometry in SOLIDWORKS.

• If you’re using SOLIDWORKS 2008 to 2022, you can activate the Improved Geometry Handling option from the Flow Simulation Analysis tree to resolve some invalid contacts automatically.
• If you’re using SOLIDWORKS Flow Simulation 2023 or later, you can activate the Preprocessor Boolean or the Mesh Boolean option to automatically resolve some geometric problems.

The automatic methods can resolve most invalid contacts, but some can remain if they involve complex faces. The Check Geometry tool can be used to find invalid contacts and determine if they have been successfully resolved. Any that cannot be resolved automatically will have to be resolved manually.

Additional SOLIDWORKS Flow Simulation Troubleshooting

The information provided should be sufficient to solve the “Face is not laying on the boundary between the solid and fluid region” error in SOLIDWORKS Flow Simulation. However, there may be additional issues that are causing instability in your simulation studies.

In those instances, the provided steps may not completely resolve the error, and you may need to contact our Technical Support team.

To contact our Technical Support team for additional troubleshooting, click here.