Implementing Boundary Condition in CFD

Implementing boundary conditions in a CFD simulation using the finite volume method (FVM) involves several detailed steps:

1. Identify Physical and Geometric Boundaries

• Physical Boundaries: These include inlets, outlets, and walls. Each type has specific conditions like velocity, pressure, or temperature.
• Geometric Constraints: These include symmetry and periodicity, which help reduce the computational domain size.

2. Classify Boundary Conditions

• Specify the value of the variable at the boundary (e.g., temperature at a wall).
• Specify the flux of the variable at the boundary (e.g., heat flux).

3. Discretize Governing Equations

• Continuity Equation: Ensures mass conservation.
• Momentum Equation: Governs fluid motion.
• Energy Equation: Governs heat transfer.

4. Apply Boundary Conditions to Discretized Equations

• Inlet Boundary: Specify velocity and pressure or use a velocity profile.
• Outlet Boundary: Specify pressure or use a convective boundary condition.
• Wall Boundary: Apply no-slip condition for velocity and specify temperature or heat flux for thermal problems.

5. Modify Coefficients in Algebraic Equations

• Adjust coefficients in the discretized equations to incorporate boundary conditions. For example, at a no-slip wall, set the velocity to zero and adjust the pressure gradient.

6. Validate Boundary Conditions

• Use test cases to compare computed results with available numerical or experimental data to ensure accuracy.

7. Iterate and Solve

• Solve the system of equations iteratively, ensuring boundary conditions are correctly applied at each step.

8. Post-Processing

• Analyze the results to verify that boundary conditions have been correctly implemented and the solution is physically accurate.

This process ensures that the boundary conditions are accurately represented in the simulation, leading to reliable and robust results.