[cfdblender]

Hello, this is my first post here.
I'm starting out in FLUENT with the classic Ahmed body exercise. I've done the geometry, a refined hybrid mesh, and got a solution. But when plotting velocity countours in the symmetry plane through the Ahmed body, I get strange artifacts, as if the fluid is somehow broken within the plane. (see attached 'artifacts.jpg'). It only happens for velocity, pressure contours look unbroken.

When I repeated using a simple, coarse mesh based only on FLUENT's default settings, the artifacts are not present in the solution. (see attached 'no_artifacts.jpg') But because the mesh is quite coarse, the quality of the results are poor.

Why do these artifacts happen? How do they affect the solution? How do I get rid of them?