Design of suction bay for balanced performance of a twin pump

Twin pumps are two vertical inline pumps in one casing. The direction of rotation of the two pumps is identical and the suction bays for the right and left sides of the twin pump naturally induce prerotation/preswirl to the flow approaching the impeller. It is observed from tests that the prerotation in the left side increases head and power while that on the right side decreases impeller head and power. During regular operation it is observed that the two sides no longer give the same performance for which they were designed. This fact is also verified during performance tests.

In this study an attempt is made to eliminate prerotation on either sides of the twin suction bay and equalize impeller power and head. Firstly the baseline design (vertical inline pump) is numerically studied using full pump simulation and the results are compared to that of experimental data. Evaluation of the traditional suction design is done using component simulation. Parametric design changes are carried out on the traditional suction bay to eliminate prerotation. Two selected redesigned versions are further analysed using full pump simulations and the results are compared with that of the baseline and the traditional designs.

From CFD simulation results for the baseline case its obeserved that the head and power near the design point is within 5% of that of the experiments with good trend wise agreement. The redesigns(over 7 configurations) undertaken shows that pump head and power on either side can be brought to within 1% of each other but the design would be difficult to cast. On foundry friendly designs its observed from full pump simulations that the head and power in the left and right sides can be brought to within 3% of each other.