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Int. J. Turbomach. Propuls. Power, Volume 10, Issue 1 (March 2025) – 5 articles

Cover Story (view full-size image): The SPLEEN C1 Cascade is a novel open access test case that enhances the understanding of high-speed low-pressure turbine (LPT) aerodynamics under engine-representative conditions. Developed by the von Karman Institute with Safran Aircraft Engines, it provides insights into unsteady wake interactions, secondary flows, and loss mechanisms in geared turbofan (GTF) LPTs. The transonic low-density linear cascade operates at Mach 0.70–0.95 and Reynolds 65,000–120,000, featuring high-fidelity measurements, a wake generator, and well-characterized inlet flow. This dataset aids CFD validation and turbine design improvement, supporting propulsion efficiency and sustainable aviation goals. View this paper

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20 pages, 5519 KiB

Open AccessArticle

Considerations for High-Fidelity Modeling of Unsteady Flows in a Multistage Axial Compressor

by Douglas R. Matthews and Nicole L. Key

Int. J. Turbomach. Propuls. Power 2025, 10(1), 5; https://doi.org/10.3390/ijtpp10010005 - 10 Mar 2025

Viewed by 569

Abstract

This paper presents the development and validation of a high-fidelity, unsteady, computational fluid dynamics (CFD) model of the Purdue 3-Stage Axial Research Compressor. A grid convergence study assesses the spatial discretization accuracy of the single-passage, steady-state computational model. Additionally, the periodic-unsteady convergence of the unsteady signals of a multiple-passage transient blade row model was explored. Computational predictions were compared with experimental measurements to evaluate the efficacy of the various modeling decisions. Notably, transient blade row model calculations employing the Scale-Adaptive Simulation (SAS) formulation of Menter’s Shear Stress Transport (SST) turbulence model exhibited a significantly improved agreement with experimental data compared to steady-state calculations. Particularly, in conjunction with the SAS-SST turbulence model, the transient calculations significantly improved the spanwise (radial) mixing characteristics of the transient-average stagewise total temperature profiles. Spectral analyses of the transient signals compared with unsteady pressure measurements showed fundamental and second harmonic blade-passing frequency amplitudes matching within 5–7% in the embedded stage. This research underscores the importance of including accurate geometry, practical minimization of modeling assumptions using higher-fidelity physics models, comprehensive convergence assessment, and the comparison and validation of computational predictions with experimental measurements. Full article

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37 pages, 2141 KiB

Open AccessFeature PaperArticle

Cavity Instabilities in a High-Speed Low-Pressure Turbine Stage

by Lorenzo Da Valle, Antonino Federico Maria Torre, Filippo Merli, Bogdan Cezar Cernat and Sergio Lavagnoli

Int. J. Turbomach. Propuls. Power 2025, 10(1), 4; https://doi.org/10.3390/ijtpp10010004 - 4 Mar 2025

Viewed by 635

Abstract

This study investigates the time-resolved aerodynamics in the cavity regions of a full-scale, high-speed, low-pressure turbine stage representative of geared turbofan engines. The turbine stage is tested in the von Karman Institute’s short-duration rotating facility at different purge rates (PR) injected through the upstream hub cavity. Spectra from the shroud and downstream hub cavity show perturbations linked to blade passing frequency and rotor speed. Asynchronous flow structures associated with ingress/egress mechanisms are observed in the rim seal of the purged cavity. At 0% PR, the ingress region extends to the entire rim seal, and pressure fluctuations are maximized. At 1% PR, the instability is suppressed and the cavity is sealed. At 0.5%, the rim-seal instability exhibits multiple peaks in the spectra, each corresponding to a state of the instability. Kelvin–Helmholtz instabilities are identified as trigger mechanisms. A novel technique based on the properties of the cross-power spectral density is developed to determine the speed and wavelength of the rotating structures, achieving higher precision than the commonly used cross-correlation method. Moreover, unlike the standard methodology, this approach allows researchers to calculate the structure characteristics for all the instability states. Spectral analysis at the turbine outlet shows that rim-seal-induced instabilities propagate into regions occupied by secondary flows. A methodology is proposed to quantify the magnitude of the induced fluctuations, showing that the interaction with secondary flows amplifies the instability at the stage outlet. Full article

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21 pages, 14831 KiB

Open AccessArticle

Panel Method for 3D Inviscid Flow Simulation of Low-Pressure Compressor Rotors with Tip-Leakage Flow

by Valentin Caries, Jérôme Boudet and Eric Lippinois

Int. J. Turbomach. Propuls. Power 2025, 10(1), 3; https://doi.org/10.3390/ijtpp10010003 - 6 Feb 2025

Viewed by 780

Abstract

This paper presents a low-order three-dimensional approach for predicting the inviscid flow around low-pressure compressors. The method is suitable for early design stages and allows a broad exploration of design possibilities at minimal cost. It combines the vortex lattice method with the panel method by using a mixed boundary condition. In addition, it models the tip-leakage flow using an iterative algorithm. First, the verification of the approach is carried out on a low-pressure compressor configuration. The wake length is a decisive parameter for ensuring correct flow deflection in ducted applications. A periodicity condition is introduced and validated, which reduces the computational and memory requirements. On average, the calculations take less than one minute in real time. The approach is validated on the same low-pressure compressor configuration. A good agreement is obtained with RANS concerning the mean flow and the tip-leakage flow characteristics. Sensitivity to the mass flow rate is also fairly well predicted, although discrepancies develop at lower mass flow rates. Full article

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31 pages, 7460 KiB

Open AccessFeature PaperArticle

An Open Test Case for High-Speed Low-Pressure Turbines: The SPLEEN C1 Cascade

by Gustavo Lopes, Loris Simonassi, Samuel Gendebien, Antonino Federico Maria Torre, Marios Patinios, Nicolas Zeller, Ludovic Pintat and Sergio Lavagnoli

Int. J. Turbomach. Propuls. Power 2025, 10(1), 2; https://doi.org/10.3390/ijtpp10010002 - 3 Feb 2025

Cited by 1 | Viewed by 1151

Abstract

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. Full article

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26 pages, 11358 KiB

Open AccessArticle

Computational Design of an Energy-Efficient Small Axial-Flow Fan Using Staggered Blades with Winglets

by Mustafa Tutar and Janset Betul Cam

Int. J. Turbomach. Propuls. Power 2025, 10(1), 1; https://doi.org/10.3390/ijtpp10010001 - 9 Jan 2025

Viewed by 1176

Abstract

The present study introduces a conceptual design of a small axial-flow fan. Both individual and combined effects of blade stagger angle and winglet on the performance of the fan design are investigated in design and off-design operating conditions using a computational flow methodology. A stepwise solution, in which a proper stagger angle adjustment of a specifically generated blade profile is followed by appending a winglet at the tip of the blade with consideration of different geometrical parameters, is proposed to improve the performance characteristics of the fan. The initial model comparison analysis demonstrates that a three-dimensional, Reynolds-averaged Navier–Stokes (RANS) equation-based renormalization group (RNG) k–ε turbulence modeling approach coupled with the multiple reference frame (MRF) technique which adapts multi-block topology generation meshing method successfully resolves the rotating flow around the fan. The results suggest that the use of a proper stagger angle with the winglet considerably increases the fan performance and the fan attains the best total efficiency with an additional stagger angle of +10° and a winglet, which has a curvature radius of 6.77 mm and a twist angle of −7° for the investigated dimensioning range. The present study also underlines the effectiveness of passive flow control mechanisms of the stagger angle and winglets for energy-efficient axial-flow fans. Full article

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