In the present work, hot-wire anemometry was employed for the characterization of the turbulent field at the inlet of a high-speed low-pressure turbine cascade, in terms of turbulence intensity and integral length scales. This work addresses two major topics relevant to the turbomachinery field: the application of hot-wire anemometry in transonic and rarefied flow regimes and the decoupling of the deterministic and the stochastic fluctuations when measuring unsteady phenomena. In compressible and rarefied flows, a hot-wire is strongly sensitive to both density and velocity fluctuations, and the commonly used Nusselt–Reynolds correlations are not valid. In this article, a nondimensional calibration methodology, based on Nusselt, Reynolds, and Knudsen numbers, was coupled with a sensitivity analysis and employed to postprocess the experimental dataset, allowing to decouple the fluctuations of density and velocity and to compute the turbulence parameters. In the presence of unsteady wakes generated upstream of the cascade, two different phase-locked averaging techniques were employed to distinguish the wake deterministic fluctuations from the background turbulence intensity.

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.