INSTABILITY PHENOMENA IN DIFFERENTIALLY R OTATING CHANNEL-CAVITY SYSTEMS WITH A SUPERPOSED AXIAL THROUGHFLOW

Unsteady flows developing in a Taylor-Couette-like configuration (exhi biting an axi-symmetric square hump on the external cylinder) with a s uperposed axial throughflow are studied. For small values of the diffe rential rotation rate, a group of swirls moves downstream of the cavit y with velocity about the maximum velocity of the forced flow. This be haviour is interpreted as the convective Taylor instability. For highe r-values of the differential rotation rate, the instability becomes ab solute and the perturbations affect the whole channel. Ne noted that S quire's criterion, which is necessary for the onset of vortex breakdow n, is satisfied by the observed phenomenon.