Sharp Transition in the Lift Force of a Fluid Flowing Past Nonsymmetrical Obstacles: Evidence for a Lift Crisis in the Drag Crisis Regime

Patrick B. Bot (1) , Marc Rabaud (2) , Goulven Thomas (1) , Alessandro Lombardi (1) , Charles Lebret (1)

1 IRENAV - Institut de Recherche de l'Ecole Navale
2 FAST - Fluides, automatique, systèmes thermiques

Bluff bodies moving in a fluid experience a drag force which usually increases with velocity. However in a particular velocity range a drag crisis is observed, i.e., a sharp and strong decrease of the drag force. This counterintuitive result is well characterized for a sphere or a cylinder. Here we show that, for an object breaking the up-down symmetry, a lift crisis is observed simultaneously to the drag crisis. The term lift crisis refers to the fact that at constant incidence the time-averaged transverse force, which remains small or even negative at low velocity, transitions abruptly to large positive values above a critical flow velocity. This transition is characterized from direct force measurements as well as from change in the velocity field around the obstacle.

Mots clés: Lift Crisis; drag crisis; nonsymmetrical obstacles

Domaines: Dynamique des Fluides [physics.flu-dyn]; Mécanique des fluides [physics.class-ph]

Patrick B. Bot, Marc Rabaud, Goulven Thomas, Alessandro Lombardi, Charles Lebret. Sharp Transition in the Lift Force of a Fluid Flowing Past Nonsymmetrical Obstacles: Evidence for a Lift Crisis in the Drag Crisis Regime. Physical Review Letters, 2016, 117 (23), pp.234501. ⟨10.1103/PhysRevLett.117.234501⟩. ⟨hal-01410405⟩