3.4 Water Tunnels
91
3.4 Water Tunnels
3.4.1 General Description
Although strictly speaking not an aerodynamic means, water tunnels have been and
are still widely used to study low velocity flows around aerodynamic objects. The
justification for their use is due to the fact that at low speeds air can be considered
as an incompressible fluid which is the case of water. Very low velocity water flows
(close to 1 m/s) lend themselves very well to visualisations by injections of dye or
fluid tracers, which make it possible to highlight separation and vortex formation.
These tracers can be injected either upstream of the model or through orifices at
the model wall. Other more sophisticated techniques can be used (see Sect. 7.3).
The main disadvantage of the water tunnel is the low Reynolds number achievable,
this inconveniency being secondary in the study of largely separated regions whose
formation and development do not depend much on the Reynolds number. Thus,
water tunnels have been extensively used for the study of vortex formations on delta
wings, base flows and three-dimensional separated structures in general. Three types
of arrangement exist:
The closed return circuit water tunnel has an architecture similar to that of a
closed return circuit wind tunnel, the circulation of water being ensured by a pump,
such as the ONERA Thales water tunnel (see Fig. 3.56). This type of facility is well
Fig. 3.56 Test section of the ONERA Thales water tunnel (© ONERA)
91
3.4 Water Tunnels
3.4.1 General Description
Although strictly speaking not an aerodynamic means, water tunnels have been and
are still widely used to study low velocity flows around aerodynamic objects. The
justification for their use is due to the fact that at low speeds air can be considered
as an incompressible fluid which is the case of water. Very low velocity water flows
(close to 1 m/s) lend themselves very well to visualisations by injections of dye or
fluid tracers, which make it possible to highlight separation and vortex formation.
These tracers can be injected either upstream of the model or through orifices at
the model wall. Other more sophisticated techniques can be used (see Sect. 7.3).
The main disadvantage of the water tunnel is the low Reynolds number achievable,
this inconveniency being secondary in the study of largely separated regions whose
formation and development do not depend much on the Reynolds number. Thus,
water tunnels have been extensively used for the study of vortex formations on delta
wings, base flows and three-dimensional separated structures in general. Three types
of arrangement exist:
The closed return circuit water tunnel has an architecture similar to that of a
closed return circuit wind tunnel, the circulation of water being ensured by a pump,
such as the ONERA Thales water tunnel (see Fig. 3.56). This type of facility is well
Fig. 3.56 Test section of the ONERA Thales water tunnel (© ONERA)