Overall relative thickness specifies the total thickness of all boundary layers combined, expressed as a proportion of the size of the surface mesh element adjacent to those boundary layers.
In simpler terms, it defines how thick the entire set of boundary layers is in relation to the size of the mesh elements that surround them on the surface. This is a crucial parameter in computational fluid dynamics (CFD) simulations using boundary layers.
Here's a breakdown:
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Boundary Layers: Thin layers of fluid near a solid surface where velocity gradients are significant due to viscous effects. Accurately resolving these layers is vital for accurate CFD results.
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Surface Mesh Element: The individual cells or elements that make up the mesh on the surface of the object being simulated. The size of these elements influences the overall accuracy and computational cost of the simulation.
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Overall Relative Thickness (Value): A dimensionless number (typically between 0 and 1) representing the ratio of the total boundary layer thickness to the size of the adjacent surface mesh element.
- A value of 0 indicates no boundary layer thickness.
- A value of 1 indicates the boundary layer thickness is equal to the size of the adjacent surface mesh element.
- Values greater than 1 are generally not used.
Why is this important?
- Mesh Quality: Choosing an appropriate overall relative thickness ensures that the boundary layer mesh is fine enough to capture the steep velocity gradients accurately.
- Accuracy of Simulation: Insufficient boundary layer resolution can lead to inaccurate predictions of drag, heat transfer, and other important flow characteristics.
- Computational Efficiency: Excessive boundary layer resolution can unnecessarily increase the computational cost of the simulation.
Example:
Imagine a wing with a surface mesh element size of 0.01 meters. If the overall relative thickness is set to 0.5, the total thickness of all the boundary layers combined would be 0.005 meters (0.5 * 0.01 meters).
In summary, overall relative thickness is a vital parameter controlling the size and resolution of the boundary layers in a CFD simulation. It represents the thickness of the boundary layer relative to the size of the adjacent surface mesh and directly influences the accuracy and computational cost of the simulation.
