Performance Comparison of NACA 6509 and 6712 on Pico Hydro Type Cross-Flow Turbine by Numerical Method

Abstract

Many Indonesian villages do not have access to electricity due to remote location and low income. Using pico hydro cross-flow turbines can provide them with energy. Cross-flow turbines are economical because their simple shape and construction allow for manufacturing in remote areas. This study examines the use of airfoils for cross-flow turbine blades to determine whether lift force can improve performance. Using numerical methods, this study compares two blade shapes: National Advisory Committee for Aeronautics (NACA) blades 6509 and 6712. The numerical results are compared with previous studies. The boundary conditions are two-dimensional transient domain, model turbulent using SST k-ω and 6-degree of freedom (6-DOF) function. From the results obtained, the maximum mechanical efficiencies of cross-flow turbine in NACA blades 6509 (47.6%) and 6712 (46.9%) are less efficient than standard blades at 77.8%. There are three possible reasons for this: adequate lift force is not produced by airfoil blades because the blade on the impeller resembles a straight shape, rotation and torque decrease in stage 2 as a result of pressure decrease at the bottom of the blade and energy absorption in stage 2 is not optimal due to the internal impeller occurrence of flow recirculation or vortex. There are three possible ways to optimise cross-flow turbine performance: standard blade shape should be used, flow recirculation or vortex should be minimised and the runner should be designed based on the ratio between turbine tangential velocity and water tangential velocity of 1.8 or the ratio of turbine velocity and inlet velocity of 0.53.