Axisymmetric nozzles with chamfered contraction

Abstract

Paper discusses experimental results obtained in measurements of essentially incompressible flows in axially symmetric nozzles with inlet entrance shaped as a 45° half-angle chamfering. Interest was concentrated on small, low Reynolds number conditions. Six differently behaving flow regimes, from A to F, were identified. Surprisingly, in the regimes B and C, of most importance for engineering applications, the nozzles exhibit lower hydraulic loss than comparable nozzles with smooth, rounded inlet. In the regime C were identified secondary invariants valid for the whole family of nozzles with different lengths. Most probably due to the de-stabilising effect of vortices, shed from the vortex rings formed at the sharp entrance edge made by the chamfering, at increasing Reynolds number the nozzles with chamfered inlet enter quite soon a transition into turbulence.