The influence of splitter blades and meridional profiles on the performance of small-scale turbopumps for ORC applications; analysis, neural network modeling and optimization

This work presents the influence of splitters on the performance of small-scale turbopumps for organic Rankine cycle applications numerically. Different design parameters, such as impeller diameter at the outlet, number of blades, blade angle at the trailing edge, and the length and location of the splitter blades, are studied for both shrouded and unshrouded impellers at tip clearance ratios of 0.05 and 0.10 (relative to blade height). The results suggest that splitter blades can increase impeller head coefficient and slip factors up to 10%–24% depending on the blade outlet angle. At the same time, the total efficiency is not influenced significantly. The CFD calculations predict that the placement of splitters in the middle of the blade channel leads to the maximum head coefficient for shrouded impellers. In contrast, for the tip clearance ratio of 0.10, a higher head coefficient is observed for placement closer to the suction side of the main blade. After that, different meridional profiles are studied to investigate their influence on the performance characteristics and mitigation of tip clearance effects. Profiles with a sharper change of cross-section area at the inlet rather than a linear change are found more advantageous, as higher head rise, total efficiency, and static efficiency are observed. In the end, the splitter blade profiles are optimized through techniques of design of experiments, leading to a 2.43% improvement in total efficiency. In contrast, the head rise remains constant, and static efficiency decreases by 0.49% for an impeller with a tip clearance ratio of 0.05.