For many years, ONERA has operated at its Chatillon Centre, near Pans, a laboratory devoted to the hydrodynamic visualization of the flow around a large variety of models These tests, carried out in water and therefore limited to incompressible flow, cover a very extensive Reynolds number domain (l03 = Re = 106) The results concern fundamental studies common to aerospatial and marine domains as well as specific applications to these two technologies.
The test possibilities of this laboratory, especially m the aeronautical and naval domains, were described in a recent paper (1, F1) Let us recall that it is equipped with three water tunnels of the same type, which are vertical, open circuit and operate by gravity. Their main characteristics are the following (2, F2) (The Table is available in full paper)
The main visualization methods are (3, F3)
Visualization by dyes with same density and viscosity as water and emitted by models in the form of streaks (Fig l(a)) or sheets (Fig 2(a)),
Use of small au bubbles suspended in water to bring out the shape of the flow in longtudinal sections (Fig l(b, d, f, h etc)) and cross-sections(Fig 3(f) and 4(g) etc) illuminated by a sheet of light.
These two complementary methods permit to compare dyes visualizations limited to the flow near the model (Fig l(a, c, e, g)) and au bubbles visualizations extended to all the(Figures are available in full paper) fluid (Fig l(b, d, f, h)) Under these conditions we can observe many fundamental phenomena In the unseparated and separated flows
The main phenomena recorded during the tests can be reviewed with a few examples
2D models
Flows around a NACA 0012 profile with incidence (4, F4) without separation (transition at leading edge, Fig l(a)), with separated leading edge bubble which ensures the transition (Fig l(b)) or with complete separation (Fig l(c, d))
Flow around a streamlined cylinder, which represents a Cousteau-Malavard turbine sail model (5, F5), with complete separation around the model without suction (Fig l(e, f)) and reduced separation obtained by controlled suction (Fig l(g, h))
Axisymmetrical models at zero angle of attack
Flow around a cylindrical pod without longitudinal pressure gradient in transitional regime (laminar flow on the left, full developed turbulence on the right Fig 2(a))
Flow along a cylindrical pod with a curved afterbody, without separation in turbulent regime (Fig 2(b)) and with rear separation m laminar regime (Fig 2(c, f)) (6, F6)
Complete reduction of the separation on a curved afterbody in laminar regime under the effect of an axial jet (Fig 2(d, e, g))
Vortex structures (Fig 2(h)) and induction effects (Fig 2(i)) observed along an isolated axial jet issued from the base of a cylinder
