An engineering approach for the fast simulation of radial inflow turbines with vaneless spiral casing by single-channel CFD models

The basic RANS-CFD analysis of the simplest radial-inflow turbine configuration is the subject of this paper. An original technique is here proposed to model the effect of the vaneless spiral casing using single-channel CFD calculations and providing an effective alternative to the more complex simulation of the 360-degree domain otherwise required to simulate this turbine configuration. The aim of the paper is to verify the effectiveness of the proposed modelling technique as a reliable engineering approach conceived to support the preliminary design phase of radial-inflow turbines with time-effective CFD calculations. To this end, the open-source CFD code MULTALL has been used to predict the aerodynamic performance of optimal designs of radial-inflow turbines with different specific speed and diameter and working with air as ideal gas. The MULTALL predictions are compared with the corresponding steady-state results obtained by calculations suited to the preliminary assessment of radial turbines designs performed on fully 360-degree turbine domains using the commercial code Star CCM+®. The investigation is conducted on two turbines that are designed in accordance with a widely validated method. The results show that the proposed CFD approach predicts well the trends and values of the aerodynamic performance of both the turbine designs: a 5% overestimation of the performance predicted by the fully 360-degree CFD models was never exceeded. The suggested turbine modelling approach implemented in MULTALL requires a three times lower computation time than the corresponding traditional 360-degree model.