Numerical investigation of flow separation in the lee side of transverse   dunes
  We investigate flow separation in the air flow over transverse sand dunes. CFD simulations of the air flow over differently shaped dunes are performed. The length of the recirculation region after the brink of the dune is found to depend strongly on the shape of the dune. A phenomenological expression for the separation length is presented. Suitably non-dimensionalised, it depends linearly on the angle of the dune at the slip face brink. We propose a fit for the shape of the separating streamline, which is well approximated by an ellipse. 
Volker Schatz and Hans J. Herrmann