Abstract
Savonius Hydrokinetic Turbine (SHT) is a simple turbine in terms of construction and also has self-starting capability. The major problem of SHT is the lower power coefficient in comparison to other types of hydrokinetic turbines. Assuming a constant flow rate in an open channel, the mean velocity of the current hitting the rotor is a function of the free surface height, thus it can be considered as a parameter which is effective on the SHT performance. In this investigation, firstly, an experimental test is conducted on a SHT in an open channel with a certain free surface height. Experimental data of the turbine power coefficient at different tip speed ratios are applied for validation of the numerical method. Transient numerical simulation is conducted using ANSYS CFX 22.2 software. Two-phase flow simulation is done using Homogenous multiphase model. In a constant flow rate, runaway tests are conducted for evaluating free surface level at the channel inlet and outlet. The free surface heights at the channel inlet and outlet are applied as boundary conditions for numerical analysis. Numerical simulation at a constant volumetric flow rate and also constant tip speed ratio show that reducing free surface height, the turbine power increases up to 5.17 times the power produced by the turbine having the highest free surface level. The maximum power is generated when the free surface is tangent to the upper plate of the rotor and it is fully submerged. Also, the maximum power coefficient occurs when the free surface level location is somehow (About 25% of rotor total height) upper than the rotor.