Design optimisation factors for axial turbine stators in small-scale geo-solar powered Brayton applications

Small axial turbines for geo-solar Brayton cycles require stator designs that are efficient and robust, yet systematic guidance on how detailed stator airfoil geometry influences performance in this power range remains limited. This study quantifies the sensitivity of stator and stage performance to fourteen geometric parameters defining the stator airfoil and derives practical design guidance for small-scale geo-solar Brayton cycles in the 20–70 kW range. A reference axial turbine stage is first generated using mean-line design, followed by three-dimensional blade modelling and meshing using BladeGen and TurboGrid. Steady-state, three-dimensional compressible flow simulations are performed in ANSYS CFX employing the SST k-ω turbulence model. Each stator geometric parameter is varied individually within realistic bounds while all other parameters are held at baseline values. Stator losses, stator efficiency, and total-to-total stage efficiency are evaluated across a range of pressure ratios (PR = 2–4). Numerical accuracy is ensured through grid refinement, y-plus control, and comparison with independent experimental data from the literature. The results show a clear hierarchy of geometric influence. Four parameters, namely trailing edge wedge angle, trailing edge thickness, and two parameters governing the rear suction side contour, dominate performance, causing up to 5% variation in stator efficiency and about 2% variation in stage efficiency at higher pressure ratios. At PR = 3, the best configuration increased stator efficiency from 88.36% to 92.31% and total to total stage efficiency from 83.46% to 85.32%. Reducing the rear suction side parameter F13 from 50 to 20 mm increased stage efficiency from 82.70% to 85.76% at PR = 2 and reduced the nozzle loss coefficient from 0.757 to 0.377. Overall, most efficiency variation is governed by a small subset of geometric features, indicating that near optimal performance can be achieved with simplified stator geometries when these key parameters are selected carefully.