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Numerical Study of the Velocity Decay of Offset Jet in a Narrow and Deep Pool

Li, Xin, Zhou, Maolin, Zhang, Jianmin, Xu, Weilin
Water 2018 v.11 no.1
model validation, simulation models, velocity, water flow
The present study examines the configuration of an offset jet issuing into a narrow and deep pool. The standard k-&epsilon; model with volume-of-fluid (VOF) method was used to simulate the offset jet for three exit offset ratios (OR = 1, 2 and 3), three expansion ratios (ER = 3, 4 and 4.8), and different jet exits (circular and rectangular). The results clearly show significant effects of the circumference of jet exits (L<inf>exit</inf>) in the early region of flow development, and a fitted formula is presented to estimate the length of the potential core zone (L<inf>PC</inf>). Analysis of the flow field for OR = 1 showed that the decay of cross-sectional streamwise maximum mean velocity (U<inf>m</inf>) in the transition zone could be fitted by power law with the decay rate n decreased from 1.768 to 1.197 as the ER increased, while the decay of U<inf>m</inf> for OR = 2 or 3 was observed accurately estimated by linear fit. Analysis of the flow field of circular offset jet showed that U<inf>m</inf> for OR = 2 decayed fastest due to the fact that the main flow could be spread evenly in floor-normal direction. For circular jets, the offset ratio and expansion ratio do not affect the spread of streamwise velocity in the early region of flow development. It was also observed that the absence of sudden expansion of offset jet is analogous to that of a plane offset jet, and the flow pattern is different.