CAVITATION MODELLING IN DIFFERENT DESIGNS OF MICRO KAPLAN HYDRO-TURBINE

The paper investigates the cavitation in micro-turbomachinery, using a small-sized water system. Unsteady numerical model is architected to predict cavitating flows through a 7.5 cm axial hydro-turbine working at 2.8 m water head. Based on the validated simulations, specific turbine designs (regular design and rim-drive turbines) are simulated with cavitating flow conditions including different rotation speeds (1000-5000 rpm) and outlet pressures (0,-24,-48,-96, kPa gage). Phase change interactions (liquid water and vapor) were considered by adding the physics models of Volume of Fluid (VOF) multiphase, cavitation, and Large Eddy Simulation (LES) turbulence. Records featured spatial variation in the cavitation pattern between the two designs. Rim-drive turbine stands against cavitation along the rim integration lines, but it starts the hub cavitation earlier than the regular turbine. The proposed rim-drive bests the regular geometry before cavitation, and the relative efficiency gap increased to be 16% at extreme cavitation condition.