Air-water multiphase turbulence flow in low rotation tub-type water wheel vessel (corrections on RANS model)

The demand for a small hydraulic power generator is increasing. For the spread of a small hydraulic power generator, lowering the initial and maintenance costs and increasing the tolerance for the flowing refuse are important. One of the water wheels meeting these requirements is a low rotation tub-type water wheel. In the tub-type water wheel, a flow from a water source enters a cylindrical vessel (a tub) from the side of the tub and leaves the tub from a bottom hole. Water induces a vortex in the tub. Placing the turbine blade from the top of the tub, we can generate the electricity. The low speed rotation and the simple instruments makes this water wheel robust. We take the low rotation tub-type water wheel as an object of this study. In this report, we focus on the flow without the turbine blade. The induced vortex in the tub is investigated. Air-water multiphase flow in a tub-type water wheel vessel is simulated with RANS turbulence models using OpenFOAM. A standard k-omega SST model with VOF method shows poor performance in reproducing the water surface structure and velocity profiles observed in our experiment. Corrections for rotation and density gradient were implemented. Turbulence models which are previously modified and made public and newly modified model are compared with the experimental result. The effects of the corrections were examined in detail. Buoyancy correction term which depends on the density gradient becomes large at the interface and suppresses the turbulence. Combining the both corrections increases the accuracy of k-Omega SST based model.