Radial variation of adiabatic and diabatic spiral vortex flow in a wide annular gap

Transitions occurring after the onset of spiral vortex flow in a wide concentric annular gap of radius ratio 0.8, formed by a stationary outer cylinder and a rotatable inner cylinder, have been studied experimentally. By isothermal heating of the annular surface, it was possible to consider diabatic as well as adiabatic conditions. At an axial Reynolds number of 500 and for a range of Taylor numbers up to 10⁷, power spectra and auto-correlograms were taken at two radial positions near to the inner and outer annular surfaces; these are compared with previous results taken at mid-gap under adiabatic conditions. Measurements of turbulence intensity across the gap were made also. Probability histograms and signal traces for diabatic flow near to the outer annular surface are presented. It has been shown that the vortex transitions affect the thermal boundary layer and, consequently, the heat transfer rates at the outer surface. A positive radial thermal gradient was seen to have little effect on the flow. The imposed axial flow was shown to be stabilising under adiabatic conditions but destabilising under diabatic conditions.