Here i am doing proper CFD post-processing to experimentally verify the no-slip boundary condition using ParaView and the OpenFOAM elbow case. Let’s now interpret the screenshot from a CFD physics point of view.
Setup Summary
Case: OpenFOAM elbow (steady incompressible internal flow)
Tool: ParaView
Filter: Plot Over Line
Quantity: U_Magnitude (velocity magnitude)
X-axis: arc_length along the line (from one point inside the fluid to the wall)
Output: Velocity profile graph
What the Plot Shows
The graph on the right side shows:
X-axis: Distance along the probing line (arc_length)
Y-axis: Velocity magnitude (U_Magnitude)
The curve rises from a lower value, reaches a plateau around ~1.0 , and then drops sharply to near 0 at the right end of the line.
CFD Interpretation of the Image
1. Velocity Profile Inside the Fluid
The flat region (plateau around ~1.0) in the middle of the curve indicates uniform flow in the bulk of the fluid (away from walls).
This is expected in fully developed or near-uniform flow in a pipe elbow.
2. Sharp Drop in Velocity Near the Wall
On both ends (especially the right), the velocity drops rapidly to nearly 0.
This is exactly what we expect from the no-slip boundary condition :
This confirms that my line probe passed from:
Inside the fluid,
Through the boundary layer,
Up to the wall.
The no-slip condition is numerically satisfied in your simulation.
3. Boundary Layer Visualization
- The sharp decline in the graph represents the boundary layer — the thin region near the wall where velocity transitions from free-stream to 0.🔹
4. Numerical Observations
- The velocity doesn't drop instantly to zero, but over a few sample points — this is due to:
This is normal and expected in CFD.
CFD Physics Conclusion
| Observation | CFD Interpretation |
|---|---|
| Velocity ~0 at wall | ✔ No-slip boundary condition is respected |
| Plateau in middle | ✔ Uniform flow in the bulk |
| Sharp gradient near wall | ✔ Boundary layer captured |
| Small non-zero near-wall velocity | Acceptable due to mesh + numerical limits |
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