Painting
The creation of paint pictures is a method for visualizing flows, which is used to represent "wall flow lines" on models in wind tunnels . In addition, the lines of flow separation and re-application as well as the transition from laminar to turbulent flow can also be seen on the model . The method is mainly used for air currents.
One approach to preparing paint images is to apply a suspension of a dye to the model surface. For this purpose, a suspension of fine-grain titanium white and petroleum can be sprayed onto a black surface as a thin layer for use in air currents . On the model then placed in the flow, the petroleum flows off the surface and evaporates, while the titanium white forms into lines. Strictly speaking, these “wall streamlines ” are not streamlines because the flow velocity is identical to zero on the surface of a body due to the sticking condition . Rather, these lines are the result of the effect of the shear stress on the model surface and can be interpreted as integral curves of the directional field of the wall shear stress . In addition, separation lines can be seen. The change from laminar to turbulent flow can be recognized by such a coating that, due to the increased exchange of substances in the turbulent area of the boundary layer, the petroleum evaporates faster and the titanium white is removed more quickly than in the area with laminar flow.
Suspensions of soot and petroleum can also be used for air currents on light surfaces.
For water currents, oil paints can be used to create painting pictures.
literature
- Helmut Eckelmann: Introduction to flow measurement technology. Teubner, Stuttgart 1997, ISBN 3519023792 , p. 256 ff.