Hydraulic performances of a bulb turbine with full field reservoir model based on entropy production analysis

Abstract

Bulb turbines are used to generate electric power, usually in low-head hydropower as a renewable source of energy. Flows in the turbines are typically characterized by low Froude number, so the pressure fields are more governed by the hydrostatic pressure gradient relative to the turbine head. As a result, the head loss mechanism is difficult to be identified by comparing local pressure characteristics, especially for vertical distributions. Furthermore, turbine flows are more sensitive to flows in reservoirs, due to shorter penstock lengths and larger runner diameters. In practice, the performances of each turbine obviously differ in a low-head hydropower station. The present paper analyzes hydraulic performance of a bulb turbine prototype, based on the entropy production theory. The full field reservoir modeling is conducted based on the two-phase flow simulation method and the geometric and environmental factors during multi turbine operation (5 units). The results showed the usefulness of the entropy production analysis for analyzing flow interactions between turbine and reservoir flows but also between each turbine unit. And, it showed that the flow interaction could play a noticeably strong role in determining operating conditions as well as the entire available energy in low-head hydropower stations.