ADAPTION OF THE SINGLE-CHANNEL APPROACH TO USE THE CFD CODE MULTALL AS AN EFFECTIVE TOOL IN THE PRELIMINARY DESIGN OF RADIAL INFLOW TURBINES WITH VANELESS SPIRAL CASING

The preliminary design of radial-inflow turbines is commonly supported by CFD tools which require computation time and resources dependent on the model complexity. Single-channel CFD models allow for rapid and generally sufficiently accurate computations. However, they cannot be applied in non-periodic domains such the ones of turbines with vaneless spiral casing. To overcome this limitation, the present authors suggested in a previous publication a modelling approach which reduces the non-periodic domain of a spiral volute to a periodic one. Also, it was verified that such approach fits the capabilities of the open-source CFD code MULTALL. This code was chosen for its widely validated capabilities and basic physics modelling, which permit fast computations suited to support the preliminary design phase where the rapid check of a large set of designs is most important. In the present paper, the aerodynamic performance of a small-scale turbine with vaneless spiral casing as predicted by single-channel calculations performed with MULTALL, is compared with the prediction obtained using the state-of-the-art CFD code Star CCM+. The single-channel CFD solved with Star CCM+ was calculated on a non-periodic domain made of a turbine slice including only one runner passage, being the boundary conditions extracted from preliminary simulations of the full turbine domain. The results show that the turbine’s global performance as predicted in accordance with the periodic-domain approach implemented in MULTALL very well agrees with that obtained from the computations on the non-periodic single-channel domain using a state-of-the-art CFD code. These findings confirm the validity of the proposed modelling approach and demonstrate that MULTALL can be successfully used in the preliminary design of radial inflow turbines with vaneless spiral casing.