Orbital Technologies announced on 8 Dec 2009 that it successfully static tested its big vortex hybrid rocket motor. What's a 'vortex hybrid'? It's a hybrid that controls the fuel regression rate and combustion stability by swirling or recirculating the oxygen that is injected into the cavity of the fuel grain.
The effect of swirling or recirculating the oxygen injection is seen in the photos below taken from this paper:
And here's a little CFD marketing snapshot taken from
Orbital's vortex hybrid data sheet:
And finally here's a nice photo of the test from the ORBITEC press release: