Flow and performance analyses of a partially-charged water retarder

Two-phase flow inside a water retarder is numerically studied to understand the water retarder performance and momentum dissipation mechanism for partially and fully-charged conditions at different rotational speeds, and the effects of external cooling flow into the water retarder. In order to accurately capture the flow interaction between the blades of different rotating speeds, the transient simulations are performed using unsteady turbulent flow assumption using a sliding mesh technique. The Realizable k-e turbulence model and the Volume of Fluid (VOF) method are adopted to simulate two-phase motion and interface of air and water mixture inside the retarder. A momentum index analysis is proposed for investigation of flow momentum and its dissipation. Results of partially-charged cases demonstrate that as a general trend, air is accumulated at the center of the hydraulic system forming a toroidal shape. At a low charged water volume flow, circulation inside the retarder and, hence, the retarding torque are trivial. Furthermore, it is observed that the retarding torque becomes very small for the charged water values lower than a special value. Finally, the simulations of the fully-charged open system with external cooling flow (through an inlet and an outlet) reveal that the retarding torque and also flow circulation between wheels decrease with the increase in flowrate.