Triangular-flapped rotor blades

Fig. 1: Rotor with tri-flap blades, underwater

We just began running some experiments with these new blades in the stationary water tank. Beginning with an extremely clean tank full of fresh water, we began to pour a dense mixture of water and PIV seeding particles (15 micron silver-coated hollow glass spheres) into the tank, just above the rotor. We poured the mixture in while the rotor was in motion and the YAG laser was firing and our digital camera was recording images. The gray mixture sunk down toward the rotor and was nicely entrained in the inflow, and then the wake flow. The result was a rather nice set of images of the development of the tip and flap vortices in the wake of the rotor. Rather than commenting and speculating any further, I'll just show you the "video" (a series of bitmap images) of the experiment, as well as a single still image from the video and a nice close-up image of the region just downstream from the blades.

B&W image from the video of the experiment

Fig. 2: B&W image of PIV seeding particles mixture in the near-wake of the rotor, with YAG laser sheet illumination. The region shown is the upper half of the rotor plane, just downstrem of the rotor, and the blades are rotating out of the page, toward the viewer.

B&W image of PIV seeding particles mixture with YAG laser sheet illumination

Fig. 3: A close-up from the image above. The tip vortices are clearly visible, as is one of the triangular flap vortices as it gets "gobbled up" by the larger tip vortex.

In Fig. 3 above, there are two strong tip vortices clearly visible, as well as a one flap vortex being "gobbled up" by one of the tip vortices. But interestingly enough, the flap vortex is forming the dipole not with the tip vortex from the same rotor blade as it, but with the tip vortex from the blade immediately in front of it!

Again, I won't do any speculating on the images above, I'll just let them speak for themselves. Check back again sometime, though, for more updates on this work.