## Arguments against Prandtl’s Boundary Layer Theory

Prandtl explains drag (and also ultimately lift) as an effect of a thin boundary layer.We show that this is incorrect by computing solutions of the Navier-Stokes equations with slip boundary condition without boundary layers which gives drag in close correspondence with observation. Hence drag does not come from boundary layers.

We show that instead drag results from 3d rotational separation without the high pressure of zero-drag potential flow 2d separation.

## Large Effect from Small Cause: Tornado from Butterfly

Prandtl’s boundary layer theory is an example of **pseudo-science** in the sense that it explains a large effect (lift and drag) from a very small cause (vanishingly thin boundary layer), a cause which is so small that it is beyond analysis and thus has no explanatory function.

A theory stating that tornados in Texas are generated by butterflies in the Amazonas, cannot be refuted but then also is empty of predictive power.

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That is not true. The drag you computed is due to artificial dissipation in the solver. Use spectral type incompressible solver with slip. Then make a comment.

Yes, the simulation code includes a form of dissipation, but so does real turbulent flow.

A spectral solver without dissipation will blow up if the mesh is fine enough.