SimScale's Velocity Symphony: Choosing the Right Note for Your Flow

In SimScale, when defining velocity boundary conditions for your fluid flow simulations, you need to specify the "velocity type." This determines how the velocity is applied at the boundary. Here's a breakdown of the most common velocity types and when to use them:

1. Fixed Value:

• Imagine a conductor setting a specific tempo for the orchestra. This type defines a constant velocity magnitude and direction at all points on the boundary. Think of setting a fixed inlet velocity for air flowing into a pipe.
• Use Cases: When you know the exact velocity profile you want at the boundary, perfect for simple, well-defined inlet flows.

2. Mean Value:

• Picture an orchestra slowly adjusting its tempo over time. This type calculates an average velocity based on specified values at different points on the boundary. Think of an inlet with a non-uniform velocity profile (e.g., higher velocity in the center).
• Use Cases: For situations where the velocity varies slightly across the boundary, allows you to define a representative average velocity.

3. Flow Rate:

• Imagine setting a target water flow rate for a pipe. This type specifies the total mass flow rate of fluid entering or exiting the domain. SimScale then calculates the velocity profile based on the specified flow rate and the geometry of the boundary.
• Use Cases: Useful when the total flow rate is known, but the exact velocity profile is not crucial. Think of analyzing pressure drop in a pipe with a known flow rate.

4. Freestream:

• Picture a steady wind blowing across an open field. This type defines a constant velocity and direction for the entire boundary, assuming the fluid approaches from a very large distance. Think of simulating airflow around a wing in a uniform wind tunnel.
• Use Cases: Ideal for external aerodynamics simulations where the flow can be considered "freestream" (uniform and undisturbed) at the inlet.

Choosing the Right Velocity Type:

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

• For simple, well-defined inlet flows: Use Fixed Value or Mean Value with a specified velocity profile.
• For simulations with a known total flow rate: Utilize Flow Rate.
• For external aerodynamics with a uniform incoming flow: Choose Freestream.

Additional Considerations:

• Some boundary condition types (like Velocity Profile Inlet) allow you to define a more complex velocity profile by specifying values at different points or using a mathematical formula.
• SimScale offers tutorials and documentation to help you choose the right velocity type for your specific needs.

By understanding these velocity types, you can fine-tune your inlet and outlet conditions in SimScale, setting the stage for accurate and insightful fluid flow simulations.