Model ship with firing laser during the measurement of the rudder flow.

At SVA Potsdam a submersible  stereoscopic PIV system has been in use for some years now that enables engineers to get insight into flow mechanics in a richness of details other techniques can hardly keep up with. With the help of this system  the acquisition of the three dimensional velocity field of large flow areas can reveal unknown flow structures with high accuracy, for example the flow around a semi balanced rudder.  Even the flow through the gaps between the  rudder blade and horn can be clearly identified (see left).

The modular design allows to apply the system under various conditions like in the towing tank as well as in the cavitation tunnel. The modules can be used even when taken apart completely, for many kinds of application.

The following animation shows the results of PIV measurements of a propeller wake flow in the cavitation tunnel: The measurement plane coincides with the vertical plane crossing the propeller axis. The cut through the helical wake of the propeller reveals the structure of the tip vortex propagating downstream.



Beside the classical wake field data of the velocity distribution along specific radii that can be extracted from the vector fields (in the case at hand behind a working propeller), even vorticity and turbulence fields can be retrieved from the PIV measurements.

Depending on the optical configuration (lenses used and distance to the area of interest) large fields of view up to 800x600 mm2 can be achieved (albeit for the cost of lower spatial resolution). As an example for the usefulness of large measurement areas like this the tracking and visualization of the unsteady decay of a vortex system behind a generic wing configuration may serve (see pictures gallery left).