When a gas-liquid turbulent jet with hydroxyl free radicals is jetted into a ballast water discharge pipe to kill the invasive microbes, there is a challenge for hydroxyl free radicals to contact a large number of microbes in ballast water. In this paper, the Eulerian-Eulerian two-equation model is employed to simulate the mixing process of gas-liquid being jetted into the ballast water crossflow. The results show that the upstream wall-surface vortices lead to counter-rotating scarf vortex pairs (CVSPs) at downstream in confined crossflow, which enhance the mixing process. However, it is hard for the gas in the downstream wall-surface jet to diffuse due to the fact that the CVSPs have no influence on the downstream wall-surface jet. Therefore, the higher the momentum ratio is, the lower the value of weighted coefficient of variation of gas volume fraction at outlet is, however, when the momentum ratio is constant, the weighted coefficient of variation first drops and then goes up with increasing diameter ratio. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.