Numerical Model for the Unsteady Flow Behaviour Inside a Double Suction Pump

The fluid flow inside a single stage double aspirating pump has been studied using a three-dimensional unsteady numerical model. The main goal is the validation of the numerical procedure proposed and the flow-field analysis at the whole stage. The URANS equations have been solved using a sliding mesh unsteady model, which is able to model the real movement of the impeller inside the volute. The equations have been considered both in the rotating frame for the impeller and in the absolute reference frames, for the inlet and volute sections. Therefore, unsteady effects and dynamic interactions are captured. Mesh independency studies have been carried out and the usual turbomachinery boundary conditions have been imposed. Once the model was validated through performance curve comparison, the flow patterns in the impeller, volute and suction regions have been investigated. Particularly, the suction flow field is of special interest due to induced distortion of the axial and circumferential velocity fields. Besides that, the pressure evolution is also considered in order to study the different patterns at the inlet of the pump, where cavitation is likely to arise. The flow at the suction of this pump is characterized by the existence of a particular geometry that tries to force a uniform flow for nominal flow rate. However, this geometrical configuration produces a strong distortion for off-design conditions. This lack of uniformity produces an unsteady incidence that gives rise to strong loading variations. The study of the evolution of such unsteadiness of the inlet flow throughout the impeller and the volute was also carried out. Even at nominal flow rate, some non uniformities are detected in the pressure distribution at the inlet, that may be caused by the geometrical arrangement of this part of the inlet casing. Instantaneous and averaged pressure fields are studied.