  The interaction between a laminar boundary layer and an open cavity is
investigated experimentally for Reynolds numbers between 860 and 32300. Flow
visualizations are carried out for different observation directions in order to
understand the spatial development of dynamical structures. The study is
conducted by changing the cavity length and height and the external flow
velocity, and therefore the flow patterns inside the cavity. The issue is to
emphasize the three-dimensional development of the flow. In particular, we show
that the cavity dynamical structures are not due to secondary shear layer
instabilities. G\"ortler-type vortices are developing inside the cavity for
some parameters and their properties are discussed. The existence diagram of
these instabilities is also provided.
