Assessment of Turbulence Modelling for Numerical Simulations into Pico Hydro Turbine

Abstract

Currently the computational fluids dynamics (CFD) method is becoming an important subject of research in engineering, and pico hydro seems to be of particular interest. To increase accuracy using the CFD method, the assumptions made should be close to the actual conditions. However, there has been no comprehensive study that explains the characteristics and turbulent models that are considered suitable for use in in the pico hydro turbine. This study aims to explain flow characteristics to determine whether turbulent flow would occur and recommends a turbulent model that may be applied to a pico hydro turbine. To achieve the objectives of the study, several methods are used, including asymptotic invariance (Reynolds number analysis), local invariance, theoretical analysis and a literature study. This study found that the flow profile that occurs is irregular; the Reynolds number flow is 420,972, within the turbulent flow category; vorticity occurs with the prediction using isotropic assumptions; flow dissipation occurs; and is continuous because turbulent kinetic energy is supplied from the main flow. Thus, the category of water flow in a pico hydro turbine with power potential 1 kW is turbulent. The literature study reveals that the prediction of turbulent flow in the pico hydro turbine can be realized by three models: standard k-ε is recommended for the overshot waterwheel, RNG k-ε is recommended for the undershot waterwheel and cross-flow turbine, SST k-ω is recommended for propeller or openflume, Pelton, breastshot waterwheel and Turgo turbines. However, these recommendations do not constitute a final conclusion because a good turbulent model is based on actual conditions.