Published online by Cambridge University Press: 29 March 2006
Theoretical solutions exist for the flow about aerofoils in various modes of unsteady motion. This is also true for aerofoils whose lift is augmented by a jet flap. A common feature of these theories is the assumption of small amplitude displacements from the mean path and the generation of a continuous vortex sheet wake. However, in practice when the motion is oscillatory and of finite amplitude, an alternating trail of individual vortices is often found. The present visual investigation includes the measurement of some vortex street parameters associated with heaving aerofoils. The results are compared with those of conventional thin aerofoil theory in order to assess the significance of this departure from the conventional small displacement flow model.