Near-field dilution of a turbulent jet discharged into coastal waters: Effect of regular waves

Abstract

The effect of regular waves on three-dimensional scalar structures of a vertical round jet in the wave-following-current environment is investigated. The wave effect is represented by two dimensionless parameters, i.e. the wave-to-current velocity ratio Rwc and Strouhal number St. The jet concentration distribution, including 13 cases in the wave-following-current environment and 1 case in the current-only environment, is obtained using the large eddy simulation method and validated by experimental data. The results show that the characteristics of the distinctive ‘effluent clouds’ phenomenon, namely the effluent cloud size and the distance between adjacent effluent clouds, are strongly dependent on Rwc and St. As a result, different structures of the time-averaged concentration distribution are found in the transverse planes, and they are classified into three types: one-peak type, two-peak type, and three-peak type. The area of the concentration contour of C =0.25Cm, where Cm is the time-averaged cross-sectional maximum concentration, is defined as the jet visual area that represents the jet dilution characteristic. It highlights the existence of an optimal wave-to-current velocity ratio (approximately 0.6 here) for the highest dilution of a jet in the wave-following-current environment, which provides useful guidelines for selecting the sites of wastewater or brine discharge projects.