The engineer in me is still thriving - verifying the no-slip boundary condition of Fluid Mechanics using OpenFOAM and ParaView...

 

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:

  Velocity must be zero at the wall due to the viscous adhesion of the fluid.

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 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:

  • Finite resolution of the mesh,

  • Interpolation used in Plot Over Line,

  • Numerical diffusion (small artificial smearing due to discretization).

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