Question

For a symmetry boundary, which is correct?

(a) Vn≠0, τnn=0

(b) Vn≠0, τnn≠0

(c) Vn=0, τnn≠0

(d) Vn=0, τnn=0

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Asked question is from Boundary Conditions in division Boundary Conditions of Computational Fluid Dynamics

Answer 1

The correct answer is:

(d) Vn = 0, τnn = 0

Explanation: For a symmetry boundary condition in fluid dynamics, the normal velocity component (VnVn​) is zero, meaning there is no flow normal to the boundary. The shear stress (τnnτnn​) is also zero, as there is no shear acting in the direction normal to the boundary. This is because a symmetry boundary represents a condition where the fluid flow is mirrored along the boundary, so there is no motion or force in the normal direction to the surface.

Thus, both the normal velocity and the normal stress are zero at a symmetry boundary.