The flow of swirling water through a convergentdivergent nozzle

Abstract

Experiments with Perspex nozzles, which were arranged to discharge vertically downwards and in which the convergent part was followed by a short divergency, showed that at low swirls the flow was unstable. When the swirl was sufficiently large for an air core to be established, its effective magnitude was estimated from measurements, at the throat, of the core diameter and of the wall pressure. The former were in closer accord with inviscid theory than the latter. The results are presented in terms of dimensionless discharge and swirl coefficients. Measurements of core diameter and wall pressure were also made throughout one of the nozzles and compared with the theory. Reversed axial flow in the upper part of the nozzles was easily produced, and the limits of its appearance were determined. Low pressure tests with the reservoir top alternately submerged and uncovered revealed that the top had a marked influence on the nature of the flow in the nozzle; and measurements of the tangential and axial velocities in the upper part of the nozzle proved the inviscid theory to be seriously in error at high swirls. For purposes of comparison, similar experiments were performed on a convergent nozzle.