Boundary-layer separation from a smooth slip surface

Numerical results are presented for the streaming motion of an incompressible Newtonian fluid past axisymmetric ellipsoids of fixed shape, subject to the condition of zero tangential stress on the body surface. It is demonstrated that a substantial, closed-streamline wake appears behind the ellipsoid at moderate Reynolds numbers, O(20–50), when the ellipsoid is sufficiently nonspherical, and that this wake initially increases in size with increase of Reynolds number but then eventually decreases in size and disappears when the Reynolds number is sufficiently large, O(200–250) in our cases. The existence of streaming flow past a smooth, slip surface without separation is consistent with predictions from laminar boundary-layer theory. It is concluded that the recirculating wake that appears behind moderately deformed bubbles is strictly a finite Reynolds number phenomenon that cannot be predicted (or understood) via a boundary-layer analysis.