Aviation accounts for a significant share of global CO₂ emissions, necessitating efficient propulsion technologies to achieve net-zero emissions by 2050. Geared turbofan architectures offer a promising solution by enabling higher bypass ratios and improved fuel efficiency. However, geared turbofans introduce significant aerodynamic and structural challenges, particularly in the low-pressure turbine. Current understanding of high-speed low-pressure turbine behavior under engine-representative conditions is limited, especially regarding unsteady wake interactions, secondary flows, and compressibility effects. To address these gaps, this work presents a novel test case of high-speed low-pressure turbines, the SPLEEN C1. The test case and experimental methodology are depicted. The study includes the commissioning and characterization of a transonic low-density linear cascade capable of testing quasi-3D flows. The rig’s operational stability, periodicity, and inlet flow characterization are assessed in terms of loss and turbulence quantities to ensure an accurate representation of engine conditions. These findings provide a validated experimental platform for studying complex flow interactions in high-speed low-pressure turbines, supporting future turbine design and efficiency advancements.

High-speed, low-pressure turbines in geared turbofans operate at transonic exit Mach numbers and low Reynolds numbers. Engine-relevant data remain scarce. The SPLEEN C1 linear cascade was investigated at $M_{\mathrm{out}}=0.70–0.95$ and $R{e}_{\mathrm{out}}=\mathrm{65,000}–\mathrm{120,000}$ under steady inlet flow. Experiments were combined with 2D RANS and MISES, including transition modeling and inlet-turbulence decay calibrated to measurements. Results are consistent with conventional LPT behavior: loss decreased with increasing Mach and Reynolds numbers, except when shocks interacted with the blade boundary layer ($M\approx 0.95$). Profile loss dropped by $23\%$ from $M=0.70$ to $0.95$ at $Re=\mathrm{70,000}$, as well as by $19\%$ at $M=0.80$ when open separation is suppressed. Secondary loss decreased by up to $25\%$ at $Re=\mathrm{70,000}$ and showed weak sensitivity to the Reynolds number. A coupled loss model predicted profile loss with a root-mean square error of 4.7%. Secondary-loss modeling reproduced global trends: separating endwall dissipation from mixing kept errors within $\pm 10\%$ for most cases, but accuracy degraded near the shock–boundary layer interaction case and at the highest Reynolds number. Mixing dominated endwall loss (∼75%), with the passage vortex contributing ∼50% (±10%) of the mixing component.

High-speed low-pressure turbines in geared turbofans operate at transonic exit Mach numbers and low Reynolds numbers. Engine-relevant data remain scarce. The SPLEEN C1 linear cascade is investigated at Mout=0.70--0.95 and Reout=65,000--120,000 under steady inlet flow. Experiments are combined with 2D RANS and MISES, including transition modelling and inlet-turbulence decay calibrated to measurements. Results are consistent with conventional LPT behaviour: losses decrease with increasing Mach and Reynolds numbers, except when shocks interact with the blade boundary layer (M≈0.95). Profile loss drops by 23% from M=0.70 to 0.95 at Re=70,000, and by 19% at M=0.80 when open separation is suppressed. Secondary loss decreases by up to 25% at Re=70,000 and shows weak sensitivity to Reynolds number. A coupled loss model predicts profile loss with RMSE=4.7%. Secondary-loss modelling reproduces global trends: separating endwall dissipation from mixing keeps errors within ±10% for most cases, but accuracy degrades near the shock–boundary layer interaction case and at the highest Reynolds number. Mixing dominates endwall loss (∼75%), with the passage vortex contributing ∼50% (±10%) of the mixing component. This article is a revised and expanded version of “An Experimental Test Case for Transonic Low-Pressure Turbines—Part 2: Cascade Aerodynamics at On- and Off-Design Reynolds and Mach Numbers” presented at ASME Turbo Expo 2022, Rotterdam, June 13–17, 2022. All data and documentation are openly available at https://doi.org/10.5281/zenodo.7264761.