LAUSR

Abstract A numerical model associated with preliminary design of a turbine for utilization of geothermal energy is developed. Considering the geothermal water flow at low/moderate temperature of the target area, Yilan (Taiwan), a radial-inflow turbine with a refrigerant, R134a, which has high density has been adopted in the study. A preliminary design method based on theoretical formulations, namely the mean-line approach, and an optimization scheme based on a genetic algorithm are used to create the optimal geometry of the turbine. This provides an input for three-dimensional (3-D) simulation of the flow field, in terms of the commercial software ANSYS CFX. The results of various physical features are compared with that of the preliminary design in order to identify the sources of some disagreement that have not been clarified for general 1-D analyses. Specifically, by changing the specific speed, we have found that there is a minimum value of total entropy increase throughout the passages. This enables us to conclude that the model of incidence loss in the preliminary analysis underestimates the loss that causes flow separation, which can be identified in the numerical simulation, therefore leading to their disagreement. The integration of the geometrical optimization via the preliminary design and the numerical simulation for the detailed flow properties can help us attain superior analysis and design. Consequently, it resulted in an increase of turbine power about 3.6% when the specific speed and blade shape were optimized in the tested ranges.