Author(s): Joseph H. W. Lee; H. W. Tang
Linked Author(s): Joseph Hun-Wei Lee
Keywords: Duckbill elastomer valves; Check valves; Outfall design; Sea water intrusion; Environmental hydraulics; Jets and plumes; Initial dilution; Elliptic jets; Jet in coflow; Turbulence; Mixing and transport; Environmental impact assessment
Abstract: In recent years duckbill-shaped elastomer check valves have been installed on many oceanic outfalls and diffusers to prevent sea water and sediment intrusion. Unlike fixed diameter ports, the duckbill valve jet velocity varies nonlinearly with port discharge flow, while the head-discharge relation is linear. The mixing of a duckbill valve jet in a coflow has been studied using Acoustic Doppler Velocimetry (ADV) and laser-induced fluorescence (LIF) techniques. The velocity field in the longitudinal centreline plane and various downstream cross-sections are measured. The measurements reveal a complicated near field flow extending up to about 12 jet diameters, within which the turbulence intensity is much higher than a round jet, and the jet spreading in the major and minor axes are distinctly different; the lip-shaped jet undergoes an‘axis-switching’in this region. Beyond the near field, however, the measurements show that the jet spreading characteristics are similar to an equivalent round jet in coflow.