The rotary-type energy recovery device (RERD) is a promising energy recovery device which can significantly reduce the energy consumption of the Reverse Osmosis system in seawater desalination. A two-dimensional particle image velocimetry (PIV) measurement has been carried out in our previous study to visualize and understand the flow dynamics in the duct of the RERD. Based on the PR/experimental results, a computational fluid dynamics (CFD) method was applied to study flow characteristics and mixing process in the RERD. Three different turbulence modeling approaches (standard k-epsilon, RNG k-epsilon, and Realizable k-epsilon) were compared and validated by PIV experimental data. As a result, the simulation method was able to capture major features of the flow characteristic in the duct, such as the jet flow and the vortex structure. The Realizable k-epsilon turbulence model, presenting a good agreement with the experimental data, was recommended for analyzing the detailed information of flow characteristics. The simulation results revealed a swirling flow formed in the duct. This three-dimensional flow structure caused high flow turbulence and significant mass transfer in the mixing zone. These results would be beneficial to researchers in better understanding the mixing process in the duct of the RERD.