Investigation on the 1-kW Francis turbine elbow type draft tube performance by numerical and optimisation approach

In this study, the performance of a 1-kW Francis turbine elbow-type draft tube is examined. Three geometric factors related to the draft tube, namely, the hose length, diffuser length, and exit diameter of the draft tube, are considered for improving the pressure recovery factor. The Taguchi method is applied to derive a regression equation related to these three parameters. The geometric factors of the draft tube are altered using a genetic algorithm (GA). The optimised draft tube is fabricated for the experimental investigation. The results indicate that using the optimised draft tube increases the overall efficiency. Moreover, it leads to an increase in the pressure recovery factor from 0.75 to 0.88. The pressure, velocity and kinetic energy flow fields were obtained using computational fluid dynamics (CFD) simulation. The shear stress transport k-omega model is applied for CFD simulation. The computed pressure recovery factor obtained from the CFD analysis is compared with that obtained from the experimental results. An acceptable range of accuracy is obtained in this study.