International Journal of Turbomachinery, Propulsion and Power

18 pages, 4952 KB

Open AccessFeature PaperArticle

Detached Eddy Simulation of a Radial Turbine Operated with Supercritical Carbon Dioxide

by Benedikt Lea, Federico Lo Presti, Wojciech Sadowski and Francesca di Mare

Int. J. Turbomach. Propuls. Power 2025, 10(4), 43; https://doi.org/10.3390/ijtpp10040043 (registering DOI) - 4 Nov 2025

Abstract

This paper presents the first-of-its-kind full-crown Detached Eddy Simulation (DES) of a radial turbine designed for operation in a transcritical CO2-based power cycle. The simulation domain contains not only the main blade passage but also the exhaust diffuser and the rotor disk cavities. [...] Read more.

This paper presents the first-of-its-kind full-crown Detached Eddy Simulation (DES) of a radial turbine designed for operation in a transcritical CO2-based power cycle. The simulation domain contains not only the main blade passage but also the exhaust diffuser and the rotor disk cavities. To ensure accurate simulation of the turbine, two hybrid RANS/LES models, using the Improved Delayed Detached Eddy Simulation (IDDES) approach, are validated in a flow around a circular cylinder at

Re = 3900

, obtaining excellent agreement with other experimental and numerical studies. The turbine simulation was performed using the k-

ω

-SST-based IDDES model, which was identified as the most appropriate approach for accurately capturing all relevant flow dynamics. Thermophysical properties of CO2 are modeled with the Span–Wagner reference equation, which was evaluated by a highly efficient spline-based table look-up method. A preliminary assessment of the grid quality in the context of DES is performed for the full-crown simulation, and characteristic flow features of the main passage and cavity flow are highlighted and discussed. Full article

23 pages, 7318 KB

Open AccessFeature PaperArticle

A Comparative Study of Varying Incidence Angle Effects on a Low-Reynolds-Number Compressor Cascade Based on Experiments and Low-Fidelity and High-Fidelity Numerical Simulations

by Michael Bergmann, Christian Morsbach, Felix M. Möller, Björn F. Klose, Alexander Hergt and Georgios Goinis

Int. J. Turbomach. Propuls. Power 2025, 10(4), 42; https://doi.org/10.3390/ijtpp10040042 - 4 Nov 2025

Abstract

The trend towards higher bypass ratios and downsized cores in modern compressors leads to locally reduced Reynolds numbers, intensifying flow separation and unsteadiness, which limits the reliability of RANS models and motivates the use of LES as a feasible and attractive high-fidelity approach [...] Read more.

The trend towards higher bypass ratios and downsized cores in modern compressors leads to locally reduced Reynolds numbers, intensifying flow separation and unsteadiness, which limits the reliability of RANS models and motivates the use of LES as a feasible and attractive high-fidelity approach for these conditions. In this paper, we assess the capabilities of low- and high-fidelity numerical tools for predicting the effects of varying incidence angles for a linear compressor cascade at a Reynolds number of 150,000 and a Mach number of 0.6 based on the inflow conditions. The comparison is supported by experiments carried out at the Transonic Cascade Wind Tunnel at the DLR in Cologne, which feature an incidence angle variation of plus/minus 5 degrees. Particular emphasis is put on the numerical setup to reproduce the cascade experiment, discussing the effects of spanwise domain size, axial-velocity density ratio and inflow turbulence. The effects of the incidence angle variation are studied on the basis of instantaneous and mean flow quantities with a focus on separation, transition and loss mechanisms. Full article

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21 pages, 3316 KB

Open AccessArticle

Toward the Detection of Flow Separation for Operating Airfoils Using Machine Learning

by Kathrin Stahl, Arnaud Le Floc’h, Britta Pester, Paul L. Ebert, Alexandre Suryadi, Nan Hu and Michaela Herr

Int. J. Turbomach. Propuls. Power 2025, 10(4), 41; https://doi.org/10.3390/ijtpp10040041 - 3 Nov 2025

Abstract

Turbulent flow separation over lifting surfaces impacts high-lift systems such as aircraft, wind turbines, and turbomachinery, and contributes to noise, lift loss, and vibrations. Accurate detection of flow separation is therefore essential to enable active control strategies and to mitigate its adverse effects. [...] Read more.

Turbulent flow separation over lifting surfaces impacts high-lift systems such as aircraft, wind turbines, and turbomachinery, and contributes to noise, lift loss, and vibrations. Accurate detection of flow separation is therefore essential to enable active control strategies and to mitigate its adverse effects. Several machine learning models are compared for detecting flow separation from surface pressure fluctuations. The models were trained on experimental data covering various airfoils, angles of attack (0°–23°), and Reynolds numbers, with

{Re}_{c} = 0.8 - - 4.5 \times 10^{6}

. For supervised learning, the ground-truth binary labels (attached or separated flow) were derived from static pressure distributions, lift coefficients, and the power spectral densities of surface pressure fluctuations. Three machine learning techniques (multilayer perceptron, support vector machine, logistic regression) were utilized with fine-tuned hyperparameters. Promising results are obtained, with the support vector machine achieving the highest performance (accuracy 0.985, Matthews correlation coefficient 0.975), comparable to other models, with advantages in runtime and model size. However, most misclassifications occur near separation onset due to gradual transition, suggesting areas for model refinement. Sensitivity to database parameters is discussed alongside flow physics and data quality. Full article

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

14 pages, 3560 KB

Open AccessArticle

An Experimental Investigation by Particle Image Velocimetry of the Active Flow Control of the Stall Inception of an Axial Compressor

by Olha Alekseik, Pierric Joseph, Olivier Roussette and Antoine Dazin

Int. J. Turbomach. Propuls. Power 2025, 10(4), 40; https://doi.org/10.3390/ijtpp10040040 - 3 Nov 2025

Abstract

This paper presents results from active flow control experiments carried out on a single stage axial compressor. The flow under various forced conditions has been investigated using 2D 2C particle image velocimetry (PIV) on three radial planes along the blades’ span and two [...] Read more.

This paper presents results from active flow control experiments carried out on a single stage axial compressor. The flow under various forced conditions has been investigated using 2D 2C particle image velocimetry (PIV) on three radial planes along the blades’ span and two different operating points corresponding to the minimum mass flow at which the compressor naturally stalls, and to the lower stability limit reached with the control system activated. In particular, a control strategy using continuous blowing is compared with a pulsed one using the same injected mass flow. Comparison is performed with the base flow without control (when available), or with each other, based on the PIV results in the form of relative velocity maps or inlet/outlet flow characteristics. Full article

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19 pages, 3351 KB

Open AccessArticle

A Multi-Point Preliminary Design Method for Centrifugal Compressor Stages of Fuel Cell-Based Propulsion Systems

by Alessandro Cappiello, Viviane Ciais and Matteo Pini

Int. J. Turbomach. Propuls. Power 2025, 10(4), 39; https://doi.org/10.3390/ijtpp10040039 - 3 Nov 2025

Abstract

The successful implementation of an airborne propulsion system based on hydrogen-powered fuel cell technology highly depends on the development of an efficient, lightweight and compact air supply compressor. Meeting these requirements by designing the compressor using conventional single-point preliminary design methods can be [...] Read more.

The successful implementation of an airborne propulsion system based on hydrogen-powered fuel cell technology highly depends on the development of an efficient, lightweight and compact air supply compressor. Meeting these requirements by designing the compressor using conventional single-point preliminary design methods can be challenging, due to the very wide range of corrected mass flow rate and pressure ratio values that the air supply compressor must be able to accommodate. This article presents a multi-point design methodology for the preliminary design of centrifugal compressors of air supply systems. The method is implemented in an in-house code, called TurboSim, and allows to perform single- and multi-objective constrained optimization of vaneless centrifugal compressors. Furthermore, an automatic design point selection method is also available. The accuracy of the compressor lumped-parameter model is validated against experimental data obtained on a high-pressure-ratio single-stage vaneless centrifugal compressor from the literature. Subsequently, the design methodology is applied to optimize the compressor of the air supply system of an actual fuel cell powertrain. The results, compared to those obtained with a more conventional single-point design method, show that the multi-point method provides compressor designs that feature superior performance and that better comply with the specified constraints at the target operating points. Full article

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21 pages, 1219 KB

Open AccessArticle

Comparison of Different Strategies to Include Structural Mechanics in the Optimization Process of an Axial Turbine’s Runner Blade

by Stefan Fraas, Alexander Tismer and Stefan Riedelbauch

Int. J. Turbomach. Propuls. Power 2025, 10(4), 38; https://doi.org/10.3390/ijtpp10040038 - 3 Nov 2025

Abstract

Different strategies to include structural mechanical aspects in the design process of hydraulic machines are compared. Therefore, an axial turbine’s runner blade is optimized using evolutionary algorithms. Four different setups with a scalar objective function are investigated. In the first two setups, structural [...] Read more.

Different strategies to include structural mechanical aspects in the design process of hydraulic machines are compared. Therefore, an axial turbine’s runner blade is optimized using evolutionary algorithms. Four different setups with a scalar objective function are investigated. In the first two setups, structural mechanical aspects are added to the optimization process as a constraint, once with a penalty term and once with a modified selection operator. If structural mechanical aspects are considered as a constraint, the risk of a premature convergence increases. For this reason, additionally, two setups including the minimization of the maximum stress as an objective within a scalar objective function are analyzed. Furthermore, a multi-objective optimization with resolution of the Pareto front is performed. The differences in the results regarding fitness between the setups using a scalar objective function are small. However, the best result is found for a setup where the minimization of the stress is added as an objective. This demonstrates the risk of a premature convergence involved with constraint handling strategies. The worst result is found for the multi-objective optimization with resolution of the Pareto front, most likely due to a less directed search. Full article

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21 pages, 19839 KB

Open AccessArticle

Development of a Reduced Order Model for Turbine Blade Cooling Design

by Andrea Pinardi, Noraiz Mushtaq and Paolo Gaetani

Int. J. Turbomach. Propuls. Power 2025, 10(4), 37; https://doi.org/10.3390/ijtpp10040037 - 8 Oct 2025

Viewed by 475

Abstract

Rotating detonation engines (RDEs) are expected to have higher specific work and efficiency, but the high-temperature transonic flow delivered by the combustor poses relevant design and technological difficulties. This work proposes a 1D model for turbine internal cooling design which can be used [...] Read more.

Rotating detonation engines (RDEs) are expected to have higher specific work and efficiency, but the high-temperature transonic flow delivered by the combustor poses relevant design and technological difficulties. This work proposes a 1D model for turbine internal cooling design which can be used to explore multiple design options during the preliminary design of the cooling system. Being based on an energy balance applied to an infinitesimal control volume, the model is general and can be adapted to other applications. The model is applied to design a cooling system for a pre-existing stator blade geometry. Both the inputs and the outputs of the 1D simulation are in good agreement with the values found in the literature. Subsequently, 1D results are compared to a full conjugate heat transfer (CHT) simulation. The agreement on the internal heat transfer coefficient is excellent and is entirely within the uncertainty of the correlation. Despite some criticality in finding agreement with the thermal power distribution, the Mach number, the total pressure drop, and the coolant temperature increase in the cooling channels are accurately predicted by the 1D code, thus confirming its value as a preliminary design tool. To guarantee the integrity of the blade at the extremities, a cooling solution with coolant injection at the leading and trailing edge is studied. A finite element analysis of the cooled blade ensures the structural feasibility of the cooling system. The computational economy of the 1D code is then exploited to perform a global sensitivity analysis using a polynomial chaos expansion (PCE) surrogate model to compute Sobol’ indices. Full article

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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

Viewed by 361

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

Viewed by 357

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

Viewed by 405

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

Viewed by 751

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

Viewed by 345

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

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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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Int. J. Turbomach. Propuls. Power, Volume 10, Issue 4 (December 2025) – 13 articles

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