International Journal of Turbomachinery, Propulsion and Power

24 pages, 5021 KB

Open AccessArticle

Droplet-Laden Flows in Multistage Compressors: An Overview of the Impact of Modeling Depth on Calculated Compressor Performance

by Silvio Geist and Markus Schatz

Int. J. Turbomach. Propuls. Power 2025, 10(4), 36; https://doi.org/10.3390/ijtpp10040036 - 2 Oct 2025

Abstract

There are various mechanisms through which water droplets can be present in compressor flows, e.g., rain ingestion in aeroengines or overspray fogging used in heavy-duty gas turbines to boost power output. For the latter, droplet evaporation within the compressor leads to a cooling [...] Read more.

There are various mechanisms through which water droplets can be present in compressor flows, e.g., rain ingestion in aeroengines or overspray fogging used in heavy-duty gas turbines to boost power output. For the latter, droplet evaporation within the compressor leads to a cooling of the flow as well as to a shift in the fluid properties, which is beneficial to the overall process. However, due to their inertia, the majority of droplets are deposited in the first stages of a multistage compressor. While this phenomenon is generally considered in CFD computations of droplet-laden flows, the subsequent re-entrainment of collected water, the formation of new droplets, and the impact on the overall evaporation are mostly neglected because of the additional computational effort required, especially with regard to the modeling of films formed by the deposited water. The work presented here shows an approach that allows for the integration of the process of droplet deposition and re-entrainment based on relatively simple correlations and experimental observations from the literature. Thus, the two-phase flow in multistage compressors can be modelled and analyzed very efficiently. In this paper, the models and assumptions used are described first, then the results of a study performed based on a generic multistage compressor are presented, whereby the various models are integrated step by step to allow an assessment of their impact on the droplet evaporation throughout the compressor and overall performance. It can be shown that evaporation becomes largely independent of droplet size when deposition on both rotor and stator and subsequent re-entrainment of collected water is considered. In addition, open issues with regard to the future improvement of models and correlations of two-phase flow phenomena are highlighted based on the results of the current investigation. Full article

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18 pages, 3783 KB

Open AccessArticle

Flutter Analysis of the ECL5 Open Fan Testcase Using Harmonic Balance

by Christian Frey, Stéphane Aubert, Pascal Ferrand and Anne-Lise Fiquet

Int. J. Turbomach. Propuls. Power 2025, 10(4), 35; https://doi.org/10.3390/ijtpp10040035 - 2 Oct 2025

Abstract

This paper presents a flutter analysis of the UHBR Open Fan Testcase ECL5 for an off-design point at part speed and focuses on the second eigenmode, which has a strong torsional character near the blade tip. Recent studies by Pagès et al., using [...] Read more.

This paper presents a flutter analysis of the UHBR Open Fan Testcase ECL5 for an off-design point at part speed and focuses on the second eigenmode, which has a strong torsional character near the blade tip. Recent studies by Pagès et al., using a time-linearized solver, showed strong negative damping for an operating point at 80% speed close to the maximal pressure ratio. This was identified as a phenomenon of convective resonance; for a certain nodal diameter and frequency, the blade vibration is in resonance with convective disturbances that are linearly unstable. In this work, a nonlinear frequency domain method (harmonic balance) is applied to the problem of aerodynamic damping prediction for this off-design operating point. It is shown that, to obtain plausible results, it is necessary to treat the turbulence model as unsteady. The impact of spurious reflections due to numerical boundary conditions is estimated for this case. While strong negative damping is not predicted by the analysis presented here, we observe particularly high sensitivity of the aerodynamic response with respect to turbulence model formulation and the frequency for certain nodal diameters. The combination of nodal diameter and frequency of maximal sensitivities are interpreted as points near resonance. We recover from these near-resonance points convective speeds and compare them to studies of the onset of nonsynchronous vibrations of the ECL5 fan at part-speed conditions. Full article

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18 pages, 7892 KB

Open AccessArticle

Validation of an Eddy-Viscosity-Based Roughness Model Using High-Fidelity Simulations

by Hendrik Seehausen, Kenan Cengiz and Lars Wein

Int. J. Turbomach. Propuls. Power 2025, 10(4), 34; https://doi.org/10.3390/ijtpp10040034 - 2 Oct 2025

Abstract

In this study, the modeling of rough surfaces by eddy-viscosity-based roughness models is investigated, specifically focusing on surfaces representative of deterioration in aero-engines. In order to test these models, experimental measurements from a rough T106C blade section at a Reynolds number of 400 [...] Read more.

In this study, the modeling of rough surfaces by eddy-viscosity-based roughness models is investigated, specifically focusing on surfaces representative of deterioration in aero-engines. In order to test these models, experimental measurements from a rough T106C blade section at a Reynolds number of 400 K are adopted. The modeling framework is based on the k-ω-SST with Dassler’s roughness transition model. The roughness model is recalibrated for the k-ω-SST model. As a complement to the available experimental data, a high-fidelity test rig designed for scale-resolving simulations is built. This allows us to examine the local flow phenomenon in detail, enabling the identification and rectification of shortcomings in the current RANS models. The scale-resolving simulations feature a high-order flux-reconstruction scheme, which enables the use of curved element faces to match the roughness geometry. The wake-loss predictions, as well as blade pressure profiles, show good agreement, especially between LES and the model-based RANS. The slight deviation from the experimental measurements can be attributed to the inherent uncertainties in the experiment, such as the end-wall effects. The outcomes of this study lend credibility to the roughness models proposed. In fact, these models have the potential to quantify the influence of roughness on the aerodynamics and the aero-acoustics of aero-engines, an area that remains an open question in the maintenance, repair, and overhaul (MRO) of aero-engines. Full article

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20 pages, 4517 KB

Open AccessArticle

An Investigation of the Laminar–Turbulent Transition Mechanisms of Low-Pressure Turbine Boundary Layers with Linear Stability Theories

by Alice Fischer and Frank Eulitz

Int. J. Turbomach. Propuls. Power 2025, 10(4), 33; https://doi.org/10.3390/ijtpp10040033 - 2 Oct 2025

Abstract

Stability theory offers a practical method on parametric studies that encompass scales in the boundary layer typically not captured in Large Eddy (LES) or Reynolds-Averaged Navier–Stokes (RANS) simulations. We investigated the transition modes of a Low-Pressure Turbine (LPT) with Linear Stability Theory (LST) [...] Read more.

Stability theory offers a practical method on parametric studies that encompass scales in the boundary layer typically not captured in Large Eddy (LES) or Reynolds-Averaged Navier–Stokes (RANS) simulations. We investigated the transition modes of a Low-Pressure Turbine (LPT) with Linear Stability Theory (LST) and Linear Parabolized Stability Equations (LPSEs) over a wider parametric space. A parametric study was done to examine the wall-shear stress, shape factor, momentum thickness, as well as the growth rate and N-factor envelope. Additionally, the methodology was applied to active control techniques like suction and blowing. The results are consistent with the expected physical behavior and initial observations, while also offering a quantitative description of trends in frequencies, amplitude growth, and wavelengths. This confirms the suitability of the two stability theories, laying the base for their future validation to ensure accuracy and reliability. Full article

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12 pages, 765 KB

Open AccessArticle

Optimising Ventilation System Preplanning: Duct Sizing and Fan Layout Using Mixed-Integer Programming

by Julius H. P. Breuer and Peter F. Pelz

Int. J. Turbomach. Propuls. Power 2025, 10(4), 32; https://doi.org/10.3390/ijtpp10040032 - 1 Oct 2025

Abstract

Traditionally, duct sizing in ventilation systems is based on balancing pressure losses across all branches, with fan selection performed subsequently. However, this sequential approach is inadequate for systems with distributed fans in the central duct network, where pressure losses can vary significantly. Consequently, [...] Read more.

Traditionally, duct sizing in ventilation systems is based on balancing pressure losses across all branches, with fan selection performed subsequently. However, this sequential approach is inadequate for systems with distributed fans in the central duct network, where pressure losses can vary significantly. Consequently, when designing the system topology, fan placement and duct sizing must be considered together. Recent research has demonstrated that discrete optimisation methods can account for multiple load cases and produce ventilation layouts that are both cost- and energy-efficient. However, existing approaches usually concentrate on component placement and assume that duct sizing has already been finalised. While this is sufficient for later design stages, it is unsuitable for the early stages of planning, when numerous system configurations must be evaluated quickly. In this work, we present a novel methodology that simultaneously optimises duct sizing, fan placement, and volume flow controller configuration to minimise life-cycle costs. To achieve this, we exploit the structure of the problem and formulate a mixed-integer linear program (MILP), which, unlike existing non-linear models, significantly reduces computation time while introducing only minor approximation errors. The resulting model enables fast and robust early-stage planning, providing optimal solutions in a matter of seconds to minutes, as demonstrated by a case study. The methodology is demonstrated on a case study, yielding an optimal configuration with distributed fans in the central fan station and achieving a 5% reduction in life-cycle costs compared to conventional central designs. The MILP formulation achieves these results within seconds, with linearisation errors in electrical power consumption below 1.4%, confirming the approach’s accuracy and suitability for early-stage planning. Full article

(This article belongs to the Special Issue Advances in Industrial Fan Technologies)

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24 pages, 4357 KB

Open AccessArticle

Experimental and Numerical Investigation of Suction-Side Fences for Turbine NGVs

by Virginia Bologna, Daniele Petronio, Francesca Satta, Luca De Vincentiis, Matteo Giovannini, Gabriele Cattoli, Monica Gily and Andrea Notaristefano

Int. J. Turbomach. Propuls. Power 2025, 10(4), 31; https://doi.org/10.3390/ijtpp10040031 - 1 Oct 2025

Abstract

This work presents an extensive experimental and numerical analysis, aimed at investigating the impact of shelf-like fences applied on the suction side of a turbine nozzle guide vane. The cascade is constituted of vanes characterized by long chord and low aspect ratio, which [...] Read more.

This work presents an extensive experimental and numerical analysis, aimed at investigating the impact of shelf-like fences applied on the suction side of a turbine nozzle guide vane. The cascade is constituted of vanes characterized by long chord and low aspect ratio, which are typical features of some LPT first stages directly downstream of an HPT, hence presenting high channel diffusion, especially near the tip. In particular, the present study complements existing literature by highlighting how blade fences positioned on the suction side can reduce the penetration of the large passage vortex. This is particularly effective in applications where flow turning is limited, the blades are lightly loaded at the front, and the horseshoe vortex is weak. The benefits of the present fence design in terms of losses and flow uniformity at the cascade exit plane have been demonstrated by means of a detailed experimental campaign carried out on a large-scale linear cascade in the low-speed wind tunnel installed in the Aerodynamics and Turbomachinery Laboratory of the University of Genova. Measurements mainly focused on the characterization of the flow field upstream and downstream of straight and fenced vane cascades using a five-hole pressure probe, to evaluate the impact of the device in reducing secondary flows. Furthermore, experiments were also adopted to validate both low-fidelity (RANS) and high-fidelity (LES) simulations and revealed the capability of both simulation approaches to accurately predict losses and flow deviation. Moreover, the accuracy in high-fidelity simulations has enabled an in-depth investigation of how fences act mitigating the effects of the passage vortex along the blade channel. By comparing the flow fields of the configurations with and without fences, it is possible to highlight the mitigation of secondary flows within the channel. Full article

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2 pages, 137 KB

Open AccessEditorial

Fans: Noise, Aerodynamics, Applications and Systems—The Best of the International Conference FAN2025

by Thomas Helmut Carolus and Massimo Masi

Int. J. Turbomach. Propuls. Power 2025, 10(3), 30; https://doi.org/10.3390/ijtpp10030030 - 19 Sep 2025

Abstract

Industrial fans are indispensable components in modern engineering systems [...] Full article

(This article belongs to the Special Issue Advances in Industrial Fan Technologies)

24 pages, 19377 KB

Open AccessFeature PaperArticle

ECL5/CATANA: Comparative Analysis of Advanced Blade Vibration Measurement Techniques

by Christoph Brandstetter, Alexandra P. Schneider, Anne-Lise Fiquet, Benoit Paoletti, Kevin Billon and Xavier Ottavy

Int. J. Turbomach. Propuls. Power 2025, 10(3), 29; https://doi.org/10.3390/ijtpp10030029 - 4 Sep 2025

Abstract

A comprehensive understanding of aerodynamic instabilities, such as flutter, non-synchronous vibration (NSV), rotating stall, and forced response, is crucial for the safe and efficient operation of turbomachinery, particularly fans and compressors. These instabilities impose significant limitations on the operating envelope, necessitating precise monitoring [...] Read more.

A comprehensive understanding of aerodynamic instabilities, such as flutter, non-synchronous vibration (NSV), rotating stall, and forced response, is crucial for the safe and efficient operation of turbomachinery, particularly fans and compressors. These instabilities impose significant limitations on the operating envelope, necessitating precise monitoring and accurate quantification of vibration amplitudes during experimental investigations. This study addresses the challenge of measuring these amplitudes by comparing multiple measurement systems applied to the open-test case of the ultra-high bypass ratio (UHBR) fan ECL5. During part-speed operation, the fan exhibited a complex aeromechanical phenomenon, where an initial NSV of the second blade eigenmode near peak pressure transitioned to a dominant first-mode vibration. This mode shift was accompanied by substantial variations in blade vibration patterns, as evidenced by strain gauge data and unsteady wall pressure measurements. These operating conditions provided an optimal test environment for evaluating measurement systems. A comprehensive and redundant experimental setup was employed, comprising telemetry-based strain gauges, capacitive tip timing sensors, and a high-speed camera, to capture detailed aeroelastic behaviour. This paper presents a comparative analysis of these measurement systems, emphasizing their ability to capture high-resolution, accurate data in aeroelastic experiments. The results highlight the critical role of rigorous calibration procedures and the complementary use of multiple measurement technologies in advancing the understanding of turbomachinery instabilities. The insights derived from this investigation shed light on a complex evolution of instability mechanisms and offer valuable recommendations for future experimental studies. The open-test case has been made accessible to the research community, and the presented data can be used directly to validate coupled aeroelastic simulations under challenging operating conditions, including non-linear blade deflections. Full article

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21 pages, 6049 KB

Open AccessArticle

Goals and Strategies for Open Fan Design

by Carola Rovira Sala, Thomas Dygutsch, Christian Frey, Rainer Schnell and Raul Martinez Luque

Int. J. Turbomach. Propuls. Power 2025, 10(3), 28; https://doi.org/10.3390/ijtpp10030028 - 4 Sep 2025

Abstract

This paper highlights recent activities associated with the design of an uninstalled open fan propulsor for next-generation civil aircraft in the high-subsonic flight regime. The concept comprises a transonic propeller–rotor and a subsequent guide vane, which are both subject to pitch-variability in order [...] Read more.

This paper highlights recent activities associated with the design of an uninstalled open fan propulsor for next-generation civil aircraft in the high-subsonic flight regime. The concept comprises a transonic propeller–rotor and a subsequent guide vane, which are both subject to pitch-variability in order to account for the strong variations in flight conditions over the entire mission profile. The engine-scale design aimed for high technological maturity and to comply with a high number of industrially relevant requirements to ensure a competitive design, meeting performance requirements in terms of high efficiency levels at cruise and maximum climb conditions, operability in terms of stability margins, good acoustic characteristics, and structural integrity. During the design iterations, rapid 3D-RANS-based optimisations were only used as a conceptual design tool to derive sensitivities, which were used to support and justify major design choices in addition to established relations from propeller theory and common design practice. These design-driven optimisation efforts were complemented with more sophisticated CFD analysis focusing on rotor tip vortex trajectories and resulting in unsteady blade row interaction to optimise the guide vane clipping, as well as investigations of the entire propulsor under angle-of-attack conditions. The resulting open fan design will be the very basis for wind tunnel experiments of a downscaled version at low and high speed. Full article

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18 pages, 5980 KB

Open AccessArticle

Effect of Solidity on the Leakage Flow and Related Noise in Axial-Flow Fans with Rotating Shroud Operating at Fixed Performance

by Tayyab Akhtar, Edward Canepa, Andrea Cattanei, Matteo Dellacasagrande and Alessandro Nilberto

Int. J. Turbomach. Propuls. Power 2025, 10(3), 27; https://doi.org/10.3390/ijtpp10030027 - 2 Sep 2025

Abstract

This work presents an experimental study of the effect of blade count on the flow field and the radiated noise in a low-speed axial fan with a rotating shroud. A two-component Laser Doppler Velocimetry (LDV) system and Particle Image Velocimetry (PIV) instrumentation have [...] Read more.

This work presents an experimental study of the effect of blade count on the flow field and the radiated noise in a low-speed axial fan with a rotating shroud. A two-component Laser Doppler Velocimetry (LDV) system and Particle Image Velocimetry (PIV) instrumentation have been employed to investigate the flow in the gap region and in front of the rotor blades. Additionally, the fan has been installed in a hemi-anechoic chamber and far-field acoustic measurements have been taken with a microphone mounted on-axis upstream of the rotor to show changes in the spectral features of the radiated noise. The tested rotor is a variable-geometry one that has allowed for studying rotor configurations with different numbers of blades of the same chord and shape, i.e., of the same geometry but different solidity. Rotor pressure rise and flow rate are average quantities that have a relevant effect on the leakage flow. Keeping them fixed while varying solidity allows us to highlight the local effects of circumferential pressure non-uniformity caused by differing blade loading. The results show that, at low solidity, the flow leaving the gap is mainly directed radially outward and follows a longer path before being ingested by the rotor, thus losing strength due to mixing with the main flow. As solidity increases, the flow becomes less radial and is more rapidly ingested by the rotor. In all cases, the sound pressure level spectrum shows marked subharmonic humps and peaks originating from the interaction between the leakage flow and rotor. The departure of such peaks from the blade passing frequency increases with the solidity, while the associated energy increases up to seven blades and then decreases. Full article

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19 pages, 12119 KB

Open AccessArticle

Multi-Disciplinary Optimization of Mixed-Flow Turbine for Additive Manufacturing

by Victor Loir, Bayindir H. Saracoglu and Tom Verstraete

Int. J. Turbomach. Propuls. Power 2025, 10(3), 26; https://doi.org/10.3390/ijtpp10030026 - 2 Sep 2025

Abstract

Additive manufacturing offers new perspectives for creating complex geometries with improved design features at lower cost and with reduced manufacturing time. It may even become possible to print a micro-turbojet engine in one single print, but then unconventional geometrical constraints on compressor and [...] Read more.

Additive manufacturing offers new perspectives for creating complex geometries with improved design features at lower cost and with reduced manufacturing time. It may even become possible to print a micro-turbojet engine in one single print, but then unconventional geometrical constraints on compressor and turbine designs are inevitable. If a radial machine were printed through additive manufacturing as a standalone component, the most logical print direction would be from the radial outlet/inlet to the axial inlet/outlet to ease the process and limit the supports, with limited additional constraints compared to traditional manufacturing methods. If the rotor comprising a radial compressor and turbine needs to be printed in one single print, one of the components will be printed in a direction that is not favorable. In the present work, the radial turbine is considered to be printed in the unfavorable direction, namely, from the axial outlet to the radial inlet. These geometrical constraints orient the geometry towards a mixed-flow configuration with a trailing-edge cutback. Such design features reduce the available design space for improvement and will clearly have an unfavorable impact on performance. Therefore, a multi-disciplinary gradient-based adjoint optimization of the mixed-flow turbine is performed, striving to limit the adverse impact on total-to-total efficiency while respecting the mass flow rate and power matching with the upstream compressor. The structural constraint limits the p-Norm von Mises stress to a maximum threshold based on the material yield strength at the operating temperature. The results show that a satisfactory compromise can be found between manufacturability constraints, material limits and aerodynamic performance. Full article

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21 pages, 9867 KB

Open AccessArticle

Time, Space, and Dynamic Split of Loss Sources in LPT by Means of Phase-Locked Proper Orthogonal Decomposition

by Matteo Russo, Matteo Dellacasagrande, Francesca Satta, Davide Lengani, Daniele Simoni, Juri Bellucci, Matteo Giovannini, Angelo Alberto Granata and Monica Gily

Int. J. Turbomach. Propuls. Power 2025, 10(3), 25; https://doi.org/10.3390/ijtpp10030025 - 2 Sep 2025

Abstract

In this study, a procedure based on Phase-locked Proper Orthogonal Decomposition (PPOD) was applied to Large Eddy Simulations (LESs) of two low-pressure turbine blades operating with unsteady inflow. This decomposition allows the inspection of the effect of blade loading on loss generation mechanisms, [...] Read more.

In this study, a procedure based on Phase-locked Proper Orthogonal Decomposition (PPOD) was applied to Large Eddy Simulations (LESs) of two low-pressure turbine blades operating with unsteady inflow. This decomposition allows the inspection of the effect of blade loading on loss generation mechanisms, focusing especially on their variation throughout the incoming wake period. After sorting snapshots based on their phase within the wake cycle using temporal POD coefficients associated with wake migration, POD was reapplied to each sub-ensemble of snapshots at a given phase, providing an optimal representation of the dynamics at fixed wake locations. This highlighted the effects of the migration, bowing, tilting, and reorientation of the incoming wake filaments, as well as the breakup of streaky structures in the blade boundary layer and the formation of Von Karman vortices at the blade trailing edge. PPOD offered us the opportunity to observe how all these processes are modulated and change throughout the wake period. The comparison between the two analyzed blades showed that overall loss generation follows similar temporal patterns during the wake-passing cycle, increasing with the propagation of the upstream wake and reaching its maximum value when the wake is in the peak suction position. According to the specific blade loading distribution, the production of TKE was observed in different regions of the computational domain. The described procedure may contribute to the development of advanced design processes based on physically informed strategies. Full article

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21 pages, 44343 KB

Open AccessArticle

The Effect of a Variable Cantilevered Stator on 1.5-Stage Transonic Compressor Performance

by Benedikt Radermacher, Fabian Sebastian Klausmann, Felix Jung, Jonas Bargon, Heinz-Peter Schiffer, Bernd Becker and Patrick Grothe

Int. J. Turbomach. Propuls. Power 2025, 10(3), 24; https://doi.org/10.3390/ijtpp10030024 - 2 Sep 2025

Abstract

Future aero engine designs must address environmental challenges and meet noise and emissions regulations. To increase efficiency and reduce size, axial compressors require higher pressure ratios and a more compact design, leading to necessary modifications in the variable stator vanes, especially in the [...] Read more.

Future aero engine designs must address environmental challenges and meet noise and emissions regulations. To increase efficiency and reduce size, axial compressors require higher pressure ratios and a more compact design, leading to necessary modifications in the variable stator vanes, especially in the stator hub region. This study examines the impact of a variable cantilevered stator on the performance and aerodynamics of a 1.5-stage transonic compressor, representative of a high-pressure compressor front stage. Experimental tests at the transonic compressor test rig at Technical University of Darmstadt involved two variable stators with identical airfoil designs but different hub configurations, using the same inlet guide vane and rotor. Detailed aerodynamic analysis was conducted using steady and unsteady instrumentation. The cantilevered stator achieved a 2% increase in efficiency and a 1% increase in total pressure ratio, due to higher aerodynamic loading and reduced pressure losses. The primary performance gain comes from the reduction of the hub blockage area. The cantilevered stator also performed well at near stall conditions, unlike the shrouded stator. Time-resolved measurements indicated that loss mechanisms are closely linked to the rotor wake phase. Overall, variable cantilevered stators outperformed shrouded stators in this compressor stage. Full article

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23 pages, 4602 KB

Open AccessArticle

Trailing Edge Loss of Choked Organic Vapor Turbine Blades

by Leander Hake and Stefan aus der Wiesche

Int. J. Turbomach. Propuls. Power 2025, 10(3), 23; https://doi.org/10.3390/ijtpp10030023 - 8 Aug 2025

Abstract

The present study reports the outcome of an experimental study of organic vapor trailing edge flows. As a working fluid, the organic vapor Novec 649 was used under representative pressure and temperature conditions for organic Rankine cycle (ORC) turbine applications characterized by values [...] Read more.

The present study reports the outcome of an experimental study of organic vapor trailing edge flows. As a working fluid, the organic vapor Novec 649 was used under representative pressure and temperature conditions for organic Rankine cycle (ORC) turbine applications characterized by values of the fundamental derivative of gas dynamics below unity. An idealized vane configuration was placed in the test section of a closed-loop organic vapor wind tunnel. The effect of the Reynolds number was assessed independently from the Mach number by charging the closed wind tunnel. The airfoil surface roughness and the trailing edge shape were evaluated by experimenting with different test blades. The flow and the loss behavior were obtained using Pitot probes, static wall pressure taps, and background-oriented schlieren (BOS) optics. Isentropic exit Mach numbers up to 1.5 were investigated. Features predicted via a simple flow model proposed by Denton and Xu in 1989 were observed for organic vapor flows. Still, roughness affected the downstream loss behavior significantly due to shockwave boundary-layer interactions and flow separation. The new experimental results obtained for this organic vapor are compared with correlations from the literature and available loss data. Full article

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22 pages, 18501 KB

Open AccessFeature PaperArticle

ECL5/CATANA: Transition from Non-Synchronous Vibration to Rotating Stall at Transonic Speed

by Alexandra P. Schneider, Anne-Lise Fiquet, Nathalie Grosjean, Benoit Paoletti, Xavier Ottavy and Christoph Brandstetter

Int. J. Turbomach. Propuls. Power 2025, 10(3), 22; https://doi.org/10.3390/ijtpp10030022 - 7 Aug 2025

Cited by 1

Abstract

Non-synchronous vibration (NSV), flutter, or rotating stall can cause severe blade vibrations and limit the operating range of compressors and fans. To enhance the understanding of these phenomena, this study investigated the corresponding mechanisms in modern composite ultra-high-bypass-ratio (UHBR) fans based on the [...] Read more.

Non-synchronous vibration (NSV), flutter, or rotating stall can cause severe blade vibrations and limit the operating range of compressors and fans. To enhance the understanding of these phenomena, this study investigated the corresponding mechanisms in modern composite ultra-high-bypass-ratio (UHBR) fans based on the ECL5/CATANA test campaign. Extensive steady and unsteady instrumentation such as stereo-PIV, fast-response pressure probes, and rotor strain gauges were used to derive the aerodynamic and structural characteristics of the rotor at throttled operating conditions. The study focused on the analysis of the transition region from transonic to subsonic speeds where two distinct phenomena were observed. At transonic design speed, rotating stall was encountered, while NSV was observed at 90% speed. At the intermediate 95% speedline, a peculiar behavior involving a single stalled blade was observed. The results emphasize that rotating stall and NSV exhibit different wave characteristics: rotating stall comprises lower wave numbers and higher propagation speeds at around 78% rotor speed, while small-scale disturbances propagate at 57% rotor speed and lock-in with blade eigenmodes, causing NSV. Both phenomena were observed in a narrow range of operation and even simultaneously at specific conditions. The presented results contribute to the understanding of different types of operating range-limiting phenomena in modern UHBR fans and serve as a basis for the validation of numerical simulations. Full article

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17 pages, 8580 KB

Open AccessFeature PaperArticle

Assessment of Large-Eddy Simulations to Simulate a High-Speed Low-Pressure Turbine Cascade

by Florent Duchaine and Xavier Delon

Int. J. Turbomach. Propuls. Power 2025, 10(3), 21; https://doi.org/10.3390/ijtpp10030021 - 7 Aug 2025

Abstract

The development of compact high-speed low-pressure turbines with high efficiencies requires the characterization of the secondary flow structures and the interaction of cavity purge and leakage flows with the mainstream. During the SPLEEN project funded by the European Union’s Horizon 2020, the von [...] Read more.

The development of compact high-speed low-pressure turbines with high efficiencies requires the characterization of the secondary flow structures and the interaction of cavity purge and leakage flows with the mainstream. During the SPLEEN project funded by the European Union’s Horizon 2020, the von Karman Institute and Safran Aircraft Engines performed detailed measurements of low-pressure turbines in engine-realistic conditions (i.e., low Reynolds and high exit Mach numbers considering background turbulence, wakes, row interactions, and leakages). The SPLEEN project is thus a fundamental contribution to the progress of high-speed low-pressure turbines by delivering unique experimental databases, essential to characterize the time-resolved 3D turbine flow, and new critical knowledge to mature the design of 3D technological effects. Being able to simulate the flow and associated losses in such a configuration is both challenging and of paramount importance to help the understanding of the flow physics complementing experimental measurements. This paper focuses on the high-fidelity numerical simulation of one of the SPLEEN configuration consisting of a linear blade cascade. The objective is to provide a validated numerical setup in terms of computational domain, boundary conditions, mesh resolution and numerical scheme to reproduce the experimental results. By mean of wall-resolved large-eddy simulations, the design point characterized by an exit Mach number of 0.9 and an exit Reynolds number of 70,000 with a turbulence level of 2.4% is investigated for the baseline configuration without purge and without wake generator. The results show that the considered computational domain and the associated inlet total pressure profile play a critical role on the development of secondary flows. The isentropic Mach number distribution around the blade is shown to be robust to the mesh and numerical scheme. The development of the wake and secondary flow fields are drastically influenced by the mesh resolution and numerical scheme, impacting the resulting losses. Full article

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19 pages, 17392 KB

Open AccessArticle

Reducing Gas Accumulation in Horizontal Diffusers Under Two-Phase Flow Using Upstream Cross-Flow Steps

by Michael Mansour, Nicola Zanini, Mena Shenouda, Michele Pinelli, Alessio Suman and Dominique Thévenin

Int. J. Turbomach. Propuls. Power 2025, 10(3), 20; https://doi.org/10.3390/ijtpp10030020 - 7 Aug 2025

Abstract

In gas–liquid two-phase flows, diverging channels such as diffusers often develop low-pressure separation zones where gas can accumulate, hindering pressure recovery and reducing system performance. This issue is particularly critical in centrifugal pumps, where it leads to efficiency losses. Unlike pumps, diffusers without [...] Read more.

In gas–liquid two-phase flows, diverging channels such as diffusers often develop low-pressure separation zones where gas can accumulate, hindering pressure recovery and reducing system performance. This issue is particularly critical in centrifugal pumps, where it leads to efficiency losses. Unlike pumps, diffusers without rotating components allow for more precise experimental studies. This research investigates a passive control method using upstream cross-flow steps to reduce gas accumulation in a horizontal diverging channel. Thin metallic sheets with toothed geometries of 2 mm, 5 mm, and 8 mm heights were installed upstream to interact with the flow. These features aim to enhance turbulence, break up larger gas pockets, and promote vertical bubble dispersion, all while minimizing additional flow separation. The diffuser was intentionally designed with an expanding angle to encourage flow separation and gas accumulation. The experiments covered various two-phase flow conditions (liquid Reynolds number 59,530–78,330; gas Reynolds number 3–9.25), and high-speed imaging captured detailed phase interactions. The results show that the steps significantly reduce gas accumulation, especially at higher water flow rates. These findings support the development of more accurate computational models and offer insights for optimizing centrifugal pump designs by minimizing gas buildup in separated flow regions. Full article

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25 pages, 8491 KB

Open AccessArticle

Application of a Novel Pseudo-Spectral Time-Marching Method to Turbomachinery

by Jesús Matesanz-García and Roque Corral

Int. J. Turbomach. Propuls. Power 2025, 10(3), 19; https://doi.org/10.3390/ijtpp10030019 - 6 Aug 2025

Cited by 1

Abstract

A novel efficient method to evaluate time-periodic flows is applied to turbomachinery configurations in this paper (PSpTM). The technique reduces the overall computational cost of unsteady CFD calculations relative to conventional implicit approaches. The method is based on a pseudo-spectral definition of the [...] Read more.

A novel efficient method to evaluate time-periodic flows is applied to turbomachinery configurations in this paper (PSpTM). The technique reduces the overall computational cost of unsteady CFD calculations relative to conventional implicit approaches. The method is based on a pseudo-spectral definition of the time derivative rearranged in a time-marching fashion. The key advantage of this novel formulation compared with classical harmonic methods is that it requires minor modifications in the CFD solver structure. The method was implemented into an existing unstructured edge-based, second-order, compressible RANS solver. To benchmark the method, a well-established implicit time scheme based on a second-order backward implicit approach (BDF2) is used. Sample unsteady turbomachinery configurations are used to determine the accuracy and efficiency of the method. The accuracy of the solution is highly linked to the number of harmonics prescribed for the solution. An adequate level of accuracy was obtained while retaining a reduced number of harmonics, with approximately twice the number of harmonics of the unsteady perturbation. Notable savings in computational cost were observed when the PSpTM method was used with speed-up factors of between 2 and 10 with respect to the BDF2, depending on the case. However, the PSpTM method exhibits a poor periodic convergence rate, leaving room for further improvements in efficiency. However, even in its current form and with the current understanding, the method has a remarkable performance. Full article

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19 pages, 15989 KB

Open AccessArticle

Influence of Radial Pressure Gradient on Secondary Flows: Numerical Study and Design Optimization for High-Speed Annular Sector Cascades

by Moritz Klappenberger, Christian Landfester, Robert Krewinkel and Martin Böhle

Int. J. Turbomach. Propuls. Power 2025, 10(3), 18; https://doi.org/10.3390/ijtpp10030018 - 5 Aug 2025

Abstract

Secondary flow phenomena have a significant influence on the generation of losses and the propagation of coolant on the turbine end walls. The majority of film cooling studies are carried out on linear rather than annular cascades due to the structural simplicity and [...] Read more.

Secondary flow phenomena have a significant influence on the generation of losses and the propagation of coolant on the turbine end walls. The majority of film cooling studies are carried out on linear rather than annular cascades due to the structural simplicity and ease of measurement integration of the former. This approach neglects the effects of the radial pressure gradient that is naturally imposed on the vortex flow in annular cascades. The first part of this paper numerically investigates the effect of the radial pressure gradient on the secondary flow under periodic flow conditions by comparing a linear and an annular case. It is shown that the radial pressure gradient has a significant influence on the propagation of the secondary flow induced vortices in the wake of the nozzle guide vanes (NGV). In the second part of the paper, a novel approach of a five-passage annular sector cascade is presented, which avoids the hub boundary layer separation, as is typical for this type of test rig. To increase the periodicity, a benchmark approach is introduced that includes multiple pointwise and integral flow quantities at different axial positions. Based on the optimized best-case design, general design guidelines are derived that allow a straightforward design process for annular sector cascades. Full article

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Journal Description

International Journal of Turbomachinery, Propulsion and Power

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