Flow Visualization

Flow visualization of a blade with penny-foot Copyright: © RWTH Aachen | IST

Flow visualization is used for qualitative representation. Flow patterns and especially vortex structures can be visualized. For this purpose, coating methods, thread method, paint injection or optical methods such as the Schlieren method are used, in which density gradients are represented by deflecting a light beam and thus shocks can be made visible.


In the oil flow visualization, a mixture of oil, color pigments and additives is applied to the walls of the test specimen to be examined. As soon as the flow hits the wall, a part of the oil mixture is carried by the flow near the wall, thus creating streamlines. Separation areas and vortices can also be made easily visible by the oil flow visualization. In preliminary tests, the viscosity of the oil mixture must be adapted to the respective boundary conditions of the flow.

The oil flow visualization is used, for example, in the institute's annular cascade wind tunnel to visualize leakage at the penny cavities of variable stator vanes. By using several colors, the outflow and inflow areas at the cavity can be identified. Corner stall and the present transitional separation bubble on the blade suction side can be determined in good agreement with the CFD.