Effect of Blade Scalloping on Performance of Inward Radial Flow Supercritical CO2 Turbines

Abstract The interest in cutting-edge technologies like supercritical CO2 (sCO2)-based power systems has gained traction during the past decade. A key practical challenge encountered in an inward flow radial (IFR) turbine impeller is the substantial axial thrust resulting from the large pressure differential between the blade flow passage and the backface. Axial thrust due to a large pressure differential (∼100 bar) can result in a significantly high net force varying between 2–8 kN in kW scale IFR turbines. Additionally, the high-pressure fluid trapped between the backface of the impeller and casing causes disk friction loss, adversely impacting turbine efficiency. These factors coupled with high operating speeds (10–30 krpm) further aggravate the situation resulting in high centrifugal stresses. In this paper, the effect of scalloping the blade on the aerodynamic performance and structural integrity of radial rotors is investigated. The exercise is undertaken for three power scales of 100 kW, 1 MW, and 5 MW, all of which capture the practical operating range of IFR turbines. In this study, axial thrust was found to decrease to 35–57% of the un-scalloped case for the kW scale and 37–65% for the MW scale. Additionally, scallops were observed to reduce the leakage flow rate to 10–35% of the un-scalloped case for kW scale and 20–38% for MW scale. Scalloping reduces total-to-static turbine efficiency by a 3–6% across all power scales. Structural analysis revealed the critical scallop depth which lead to maximum stress generation in the impeller. Furthermore, modal analysis revealed that the torsional natural frequency was more sensitive to scallops compared to the bending natural frequency across all configurations.