International Journal of Turbomachinery, Propulsion and Power

30 pages, 5923 KiB

Open AccessFeature PaperArticle

Experimental Investigation of Synchronous-Flow-Induced Blade Vibrations on a Radial Turbine

by Marios Sasakaros, Markus Schafferus, Manfred Wirsum, Arthur Zobel, Damian Vogt, Alex Nakos and Bernd Beirow

Int. J. Turbomach. Propuls. Power 2024, 9(4), 35; https://doi.org/10.3390/ijtpp9040035 - 8 Nov 2024

Abstract

In this study, a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed for different IGV configurations. First, the blade modes are measured experimentally and calculated numerically. Subsequently, the vibrations are recorded with two redundant measurement systems during [...] Read more.

In this study, a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed for different IGV configurations. First, the blade modes are measured experimentally and calculated numerically. Subsequently, the vibrations are recorded with two redundant measurement systems during real operation. Strain gauges were applied on certain blades, while a commercial blade-tip-timing system is used for the measurement of blade deflections. The experimentally determined vibration properties are compared with numerical estimations. Initially, the vibrations recorded with the “nominal” IGV were presented. This IGV primarily generates nodal diameter (ND) 0 vibrations. Subsequently, the impact of two different IGV configurations is examined. First, a mistuned IGV, which has the same number of vanes as the “nominal” IGV is examined. By intentionally varying the distance between the vanes, additional low engine order excitations are generated. Moreover, an IGV with a higher number of vanes is employed to induce excitations at higher frequency modes and ND6 vibrations. Certain vibrations are consistently measured across all IGV configurations, which cannot be attributed to the spiral turbine casing. In addition, a turbine–compressor interaction has been observed. Full article

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28 pages, 49508 KiB

Open AccessArticle

Rotationally Induced Local Heat Transfer Features in a Two-Pass Cooling Channel: Experimental–Numerical Investigation

by David Gutiérrez de Arcos, Christian Waidmann, Rico Poser, Jens von Wolfersdorf and Michael Göhring

Int. J. Turbomach. Propuls. Power 2024, 9(4), 34; https://doi.org/10.3390/ijtpp9040034 - 4 Nov 2024

Abstract

Turbine blades for modern turbomachinery applications often exhibit complex twisted designs that aim to reduce aerodynamic losses, thereby improving the overall machine performance. This results in intricate internal cooling configurations that change their spanwise orientation with respect to the rotational axis. In the [...] Read more.

Turbine blades for modern turbomachinery applications often exhibit complex twisted designs that aim to reduce aerodynamic losses, thereby improving the overall machine performance. This results in intricate internal cooling configurations that change their spanwise orientation with respect to the rotational axis. In the present study, the local heat transfer in a generic two-pass turbine cooling channel is investigated under engine-similar rotating conditions (

R o = {0 \dots 0.50}

) through the transient Thermochromic Liquid Crystal (TLC) measurement technique. Three different angles of attack (

α = {- {18.5}^{°}; + 8^{°}; + {46.5}^{°}}

) are investigated to emulate the heat transfer characteristics in an internal cooling channel of a real turbine blade application at different spanwise positions. A numerical approach based on steady-state Reynolds-averaged Navier–Stokes (RANS) simulations in ANSYS CFX is validated against the experimental method, showing generally good agreement and, thus, qualifying for future heat transfer predictions. Experimental and numerical data clearly demonstrate the substantial impact of the angle of attack on the local heat transfer structure, especially for the radially outward flow of the first passage, owing to the particular Coriolis force direction at each angle of attack. Furthermore, results underscore the strong influence of the rotational speed on the overall heat transfer level, with an enhancement effect for the radially outward flow (first passage) and a reduction effect for the radially inward flow (second passage). Full article

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13 pages, 3568 KiB

Open AccessArticle

Predictive Modeling of NOx Emissions from Lean Direct Injection of Hydrogen and Hydrogen/Natural Gas Blends Using Flame Imaging and Machine Learning

by Iker Gomez Escudero and Vincent McDonell

Int. J. Turbomach. Propuls. Power 2024, 9(4), 33; https://doi.org/10.3390/ijtpp9040033 - 3 Oct 2024

Abstract

This research paper explores the use of machine learning to relate images of flame structure and luminosity to measured NOx emissions. Images of reactions produced by 16 aero-engine derived injectors for a ground-based turbine operated on a range of fuel compositions, air pressure [...] Read more.

This research paper explores the use of machine learning to relate images of flame structure and luminosity to measured NOx emissions. Images of reactions produced by 16 aero-engine derived injectors for a ground-based turbine operated on a range of fuel compositions, air pressure drops, preheat temperatures and adiabatic flame temperatures were captured and postprocessed. The experimental investigations were conducted under atmospheric conditions, capturing CO, NO and NOx emissions data and OH* chemiluminescence images from 27 test conditions. The injector geometry and test conditions were based on a statistically designed test plan. These results were first analyzed using the traditional analysis approach of analysis of variance (ANOVA). The statistically based test plan yielded 432 data points, leading to a correlation for NOx emissions as a function of injector geometry, test conditions and imaging responses, with 70.2% accuracy. As an alternative approach to predicting emissions using imaging diagnostics as well as injector geometry and test conditions, a random forest machine learning algorithm was also applied to the data and was able to achieve an accuracy of 82.6%. This study offers insights into the factors influencing emissions in ground-based turbines while emphasizing the potential of machine learning algorithms in constructing predictive models for complex systems. Full article

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20 pages, 4974 KiB

Open AccessFeature PaperArticle

Prediction of Fan Array Performance with Polynomial and Support Vector Regression Models

by Philipp Ostmann, Martin Rätz, Martin Kremer and Dirk Müller

Int. J. Turbomach. Propuls. Power 2024, 9(4), 32; https://doi.org/10.3390/ijtpp9040032 - 3 Oct 2024

Abstract

The increasing utilisation of demand-controlled ventilation strategies leads to the frequent operation of fans under part-load conditions. To accurately predict the energy demand of a ventilation system with a fan array in the early design stages, models that calculate reliable results across the [...] Read more.

The increasing utilisation of demand-controlled ventilation strategies leads to the frequent operation of fans under part-load conditions. To accurately predict the energy demand of a ventilation system with a fan array in the early design stages, models that calculate reliable results across the whole operating range are required. We present the comparison of a polynomial and a machine learning approach through support vector regression (SVR) to predict the fan performance over a wide range of typical operating points. For fitting and validation, we use experimental data. We investigate the extrapolation performance of both approaches. The SVR model achieves a slightly better representation of the experimental data with a lower error, especially when only sparse data are available. Both approaches yield similar results when the evaluation is conducted within the experimentally captured domain but deviates outside the domain. At operating points that are far from the experimentally captured domain, the polynomial models yield fan efficiencies that are physically plausible, while the SVR models drastically overpredict the fan efficiency. To rate the influence of such deviations towards modelling the actual energy demand, both approaches are applied to an operation simulation of a simplified office building. Both approaches yield similar results despite differing extrapolation capabilities. Full article

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Graphical abstract

12 pages, 6000 KiB

Open AccessFeature PaperArticle

Development and Design Validation of an Inflow-Settling Chamber for Turbomachinery Test-Benches

by Michael Henke, Stefan Gärling, Lena Junge, Lars Wein and Hans-Ulrich Fleige

Int. J. Turbomach. Propuls. Power 2024, 9(4), 31; https://doi.org/10.3390/ijtpp9040031 - 24 Sep 2024

Abstract

At Leibniz University of Hannover, Germany, a new turbomachinery test facility has been built over the last few years. A major part of this facility is a new 6 MW compressor station, which is connected to a large piping system, both designed and [...] Read more.

At Leibniz University of Hannover, Germany, a new turbomachinery test facility has been built over the last few years. A major part of this facility is a new 6 MW compressor station, which is connected to a large piping system, both designed and built by AERZEN. This system provides air supply to several wind tunnel and turbomachinery test rigs, e.g., axial turbines and axial compressors. These test rigs are designed to conduct high-quality aerodynamic, aeroelastic, and aeroacoustic measurements to increase physical understanding of steady and unsteady effects in turbomachines. One primary purpose of these investigations is the validation of aerodynamic and aeroacoustic numerical methods. To provide precise boundary conditions for the validation process, extremely high homogeneity of the inflow to the investigated experimental setup is imminent. Thus, customized settling chambers have been developed using analytical and numerical design methods. The authors have chosen to follow basic aerodynamic design steps, using analytical assumptions for the inlet section, the “mixing” area of a settling chamber, and the outlet nozzle in combination with state-of-the-art numerical investigations. In early 2020, the first settling chamber was brought into operation for the acceptance tests. In order to collect high-resolution flow field data during the tests, Leibniz University and AERZEN have designed a unique measurement device for robust and fast in-line flow field measurements. For this measurement device, total pressure and total-temperature rake probes, as well as traversing multi-hole probes, have been used in combination to receive high-resolution flow field data at the outlet section of the settling chamber. The paper provides information about the design process of the settling chamber, the developed measurement device, and measurement data gained from the acceptance tests. Full article

(This article belongs to the Special Issue Selected Papers from the 10th EVI-GTI International Conference on Gas Turbine Instrumentation)

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9 pages, 2124 KiB

Open AccessTechnical Note

Verification of the Gage Factor of a High-Temperature Strain Gage for the Dynamic Testing of Gas Turbines

by Oleksii Podobied, Ihor Vernyhora and Oleksii Kulikov

Int. J. Turbomach. Propuls. Power 2024, 9(3), 30; https://doi.org/10.3390/ijtpp9030030 - 20 Sep 2024

Abstract

This paper presents an analysis of factors causing the change in the real gage factor of high-temperature strain gages installed with ceramic cements. A calibration tool to mimic the load on the strain gage during the testing of gas turbines and to determine [...] Read more.

This paper presents an analysis of factors causing the change in the real gage factor of high-temperature strain gages installed with ceramic cements. A calibration tool to mimic the load on the strain gage during the testing of gas turbines and to determine the real gage factor is described. Calibration data obtained for two samples of nickel–chromium strain gages and two samples of iron–chromium–aluminum strain gages are given and analyzed. Full article

(This article belongs to the Special Issue Selected Papers from the 10th EVI-GTI International Conference on Gas Turbine Instrumentation)

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20 pages, 7537 KiB

Open AccessArticle

Analysis and Prediction of the Stability Limit for Centrifugal Compressors with Vaneless Diffusers

by Xavier Flete, Nicolas Binder, Yannick Bousquet, Viviane Ciais, Sandrine Cros and Nicolas Poujol

Int. J. Turbomach. Propuls. Power 2024, 9(3), 29; https://doi.org/10.3390/ijtpp9030029 - 5 Aug 2024

Abstract

A numerical study was conducted to identify the mechanisms involved in the destabilisation of centrifugal compressors with vaneless diffusers. A stability analysis—carried out on the rotating and fixed parts of the studied machines—showed that the vaneless diffuser is a limiting component at a [...] Read more.

A numerical study was conducted to identify the mechanisms involved in the destabilisation of centrifugal compressors with vaneless diffusers. A stability analysis—carried out on the rotating and fixed parts of the studied machines—showed that the vaneless diffuser is a limiting component at a low mass flow rate. It was demonstrated that the reorganisation of stall patterns into recirculation in the inducer stabilises the impellers’ flow fields. As the destabilisation of vaneless diffusers has been a recurrent topic in the literature, many models have shown that it is the inlet-flow angle that drives the loss of stability. Models from the literature have estimated critical angle values using the geometry of the diffuser. Thus, for a given stage, expressing the diffuser inlet-flow angle as a function of the mass flow rate allows one to estimate its stability limit. However, this law needs to be calibrated to consider each compressor’s geometrical and aerodynamic specificities. This calibration can be achieved through single-passage steady simulations performed at stable operating points with high mass flow rates. With this methodology, a designer can estimate the stability limit of a centrifugal compressor with a vaneless diffuser from single-passage RANS calculations. Full article

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18 pages, 9032 KiB

Open AccessFeature PaperArticle

Towards Improved Turbomachinery Measurements: A Comprehensive Analysis of Gaussian Process Modeling for a Data-Driven Bayesian Hybrid Measurement Technique

by Gonçalo G. Cruz, Xavier Ottavy and Fabrizio Fontaneto

Int. J. Turbomach. Propuls. Power 2024, 9(3), 28; https://doi.org/10.3390/ijtpp9030028 - 1 Aug 2024

Abstract

A cost-effective solution to address the challenges posed by sensitive instrumentation in next-gen turbomachinery components is to reduce the number of measurement samples required to assess complex flows. This study investigates Gaussian Process (GP) modeling approaches within the framework of a data-driven hybrid [...] Read more.

A cost-effective solution to address the challenges posed by sensitive instrumentation in next-gen turbomachinery components is to reduce the number of measurement samples required to assess complex flows. This study investigates Gaussian Process (GP) modeling approaches within the framework of a data-driven hybrid measurement technique for turbomachinery applications. Three different modeling approaches—Baseline GP, CFD to Experiments GP, and Multi-Fidelity GP—are evaluated, and their performance in predicting mean flow characteristics and associated uncertainties on a low aspect ratio axial compressor stage, representative of the last stage of a high-pressure compressor, are focused on. The Baseline GP demonstrates robust accuracy, while the integration of CFD data in CFD into Experiments GP introduces complexities and more errors. The Multi-Fidelity GP, leveraging both CFD and experimental data, emerges as a promising solution, exhibiting enhanced accuracy in critical flow features. A sensitivity analysis underscores its stability and accuracy, even with reduced measurements. The Multi-Fidelity GP, therefore, stands as a reliable data fusion method for the proposed hybrid measurement technique, offering a potential reduction in instrumentation effort and testing times. Full article

(This article belongs to the Special Issue Selected Papers from the XXVI Biennial Symposium on Measuring Techniques in Turbomachinery)

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20 pages, 2765 KiB

Open AccessArticle

Turbofan Performance Estimation Using Neural Network Component Maps and Genetic Algorithm-Least Squares Solvers

by Giuseppe Lombardo, Pierantonio Lo Greco and Ivano Benedetti

Int. J. Turbomach. Propuls. Power 2024, 9(3), 27; https://doi.org/10.3390/ijtpp9030027 - 23 Jul 2024

Abstract

Computational models of turbofans that are oriented to assist the design and testing of innovative components are of fundamental importance in order to reduce their environmental impact. In this paper, we present an effective method for developing numerical turbofan models that allows reliable [...] Read more.

Computational models of turbofans that are oriented to assist the design and testing of innovative components are of fundamental importance in order to reduce their environmental impact. In this paper, we present an effective method for developing numerical turbofan models that allows reliable steady-state turbofan performance calculations. The main difference between the proposed method and those used in various commercial algorithms, such as GasTurb, GSP 12 and NPSS, is the use of neural networks as a multidimensional interpolation method for rotational component maps instead of classical

β

parameter. An additional aspect of fundamental importance lies in the simplicity of implementing this method in Matlab and the high degree of customization of the turbofan components without performing any manipulation of variables for the purpose of reducing the dimensionality of the problem, which would normally lead to a high condition number of the Jacobian matrix associated with the nonlinear turbofan system (and, thus, to significant error). In the proposed methodology, the component behavior can be modeled by analytical relationships and through the use of neural networks trained from component bench test data or data obtained from CFD simulations. Generalization of rotational component maps by feedforward neural networks leads to an average interpolation error up to around

1 %

, for all variables. The resulting nonlinear system is solved by a combined genetic algorithm and least squares algorithm approach, instead of the standard Newton’s method. The turbofan numerical model turns out to be convergent, and results suggest that the trend in overall turbofan performance, as flight conditions change, is in agreement with the outputs of the GSP 12 software. Full article

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13 pages, 12832 KiB

Open AccessArticle

Experimental Investigation of an Efficient and Lightweight Designed Counter-Rotating Shrouded Fan Stage

by Timea Lengyel-Kampmann, Jirair Karboujian, Guillaume Charroin and Peter Winkelmann

Int. J. Turbomach. Propuls. Power 2024, 9(3), 26; https://doi.org/10.3390/ijtpp9030026 - 3 Jul 2024

Cited by 1

Abstract

The German Aerospace Center designed, aero-mechanically optimized and experimentally investigated its own counter-rotating shrouded fan stage in the frame of the project CRISPmulti. Their target and the motivation of this work was, on the one hand, the generation of a highly accurate experimental [...] Read more.

The German Aerospace Center designed, aero-mechanically optimized and experimentally investigated its own counter-rotating shrouded fan stage in the frame of the project CRISPmulti. Their target and the motivation of this work was, on the one hand, the generation of a highly accurate experimental database for the validation of the modern numerical design and optimization processes, and on the other hand, the development of a new innovative technology for the manufacturing of 3D fan blades made of a lightweight CFRP material. The original CRISP-1m test rig designed by the MTU Aero Engines in the 1980s was reused with the new blading for experimental investigation in the Multistage Two-Shaft Compressor Test Facility (M2VP) of the DLR in Cologne. The evaluation of the steady measurement results and the validation of the numerical simulation based on the pressure and temperature measurement are presented in this paper. Full article

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14 pages, 3897 KiB

Open AccessArticle

Heat Load Development and Heat Map Sensitivity Analysis for Civil Aero-Engines

by Alireza Ebrahimi, Soheil Jafari and Theoklis Nikolaidis

Int. J. Turbomach. Propuls. Power 2024, 9(3), 25; https://doi.org/10.3390/ijtpp9030025 - 2 Jul 2024

Abstract

The design complexity of the new generation of civil aero-engines results in higher demands on engines’ components, higher component temperatures, higher heat generation, and, finally, critical thermal management issues. This paper will propose a methodological approach to creating physics-based models for heat loads [...] Read more.

The design complexity of the new generation of civil aero-engines results in higher demands on engines’ components, higher component temperatures, higher heat generation, and, finally, critical thermal management issues. This paper will propose a methodological approach to creating physics-based models for heat loads developed by sources, as well as a systematic sensitivity analysis to identify the effects of design parameters on the thermal behavior of civil aero-engines. The ranges and levels of heat loads generated by heat sources (e.g., accessory gearbox, bearing, pumps, etc.) and the heat absorption capacity of heat sinks (e.g., engine fuel, oil, and air) are discussed systematically. The practical research challenges for thermal management system design and development for the new and next generation of turbofan engines will then be addressed through a sensitivity analysis of the heat load values as well as the heat sink flow rates. The potential solutions for thermal performance enhancements of propulsion systems will be proposed and discussed accordingly. Full article

(This article belongs to the Special Issue Selected Papers from the 10th EVI-GTI International Conference on Gas Turbine Instrumentation)

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14 pages, 5033 KiB

Open AccessArticle

Experimental Investigation of the Sensitivity of Forced Response to Cold Streaks in an Axial Turbine

by Lennart Stania, Felix Ludeneit and Joerg R. Seume

Int. J. Turbomach. Propuls. Power 2024, 9(3), 24; https://doi.org/10.3390/ijtpp9030024 - 2 Jul 2024

Abstract

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. [...] Read more.

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade’s lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade’s lifetime. Full article

(This article belongs to the Special Issue Selected Papers from the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16))

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29 pages, 22049 KiB

Open AccessArticle

Predicting Erosion Damage in a Centrifugal Fan

by Adel Ghenaiet

Int. J. Turbomach. Propuls. Power 2024, 9(2), 23; https://doi.org/10.3390/ijtpp9020023 - 17 Jun 2024

Abstract

Erosion damage can occur in fans and blowers during industrial processes, cooling, and mine ventilation. This study focuses on investigating erosion caused by particulate air flows in a centrifugal fan with forward-inclined blades. This type of fan is particularly vulnerable to erosion due [...] Read more.

Erosion damage can occur in fans and blowers during industrial processes, cooling, and mine ventilation. This study focuses on investigating erosion caused by particulate air flows in a centrifugal fan with forward-inclined blades. This type of fan is particularly vulnerable to erosion due to its radial flow component and flow recirculation. The flow field was solved separately, and the data transferred to the particle trajectory and erosion code. This in-house code implements the Lagrangian approach and the random walk algorithm, including statistical descriptions of particle sizes, release positions, and restitution factors. The study involved two types of dust particles, with a concentration between 100 and 500 μg/m³: The first type is the Saharan (North Africa) dust, which has a finer size between 0.1 and 100 microns. The second type is the Coarse Arizona Road Dust, also known as AC-coarse dust, which has a larger size ranging from 1 to 200 microns. The complex flow conditions within the impeller and scroll, as well as the concentration and size distribution of particles, are shown to affect the paths, impact conditions, and erosion patterns. The outer wall of the scroll is most heavily eroded due to high-impact velocities by particles exiting the impeller. Erosion is more pronounced on the pressure side of the full blades compared to the splitters and casing plate. The large non-uniformities of erosion patterns indicate a strong dependence with the blade position around the scroll. Therefore, the computed eroded mass is cumulated and averaged for all the surfaces of components. These results provide useful insights for monitoring erosion wear in centrifugal fans and selecting appropriate coatings to extend the lifespan. Full article

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21 pages, 23685 KiB

Open AccessFeature PaperArticle

Numerical Investigation of Forced Response in a Transonic Compressor Stage—Highlighting Challenges Using Experimental Validation

by Nicklas Kilian, Fabian Klausmann, Daniel Spieker, Heinz-Peter Schiffer and Mauricio Gutiérrez Salas

Int. J. Turbomach. Propuls. Power 2024, 9(2), 22; https://doi.org/10.3390/ijtpp9020022 - 6 Jun 2024

Abstract

An experiment-supported simulation process chain is set up to perform numerical forced response analyses on a transonic high-pressure compressor front stage at varying operating conditions. A wake generator is used upstream of the rotor to excite a specific resonance within the operating range [...] Read more.

An experiment-supported simulation process chain is set up to perform numerical forced response analyses on a transonic high-pressure compressor front stage at varying operating conditions. A wake generator is used upstream of the rotor to excite a specific resonance within the operating range of the compressor. Thereby, extensive aerodynamic and structural dynamic experimental data, obtained from state-of-the-art rig testing at the Transonic Compressor Darmstadt test facility at the Technical University of Darmstadt, are used to validate numerical results and ensure realistic boundary conditions. In the course of this, five-hole-probe measurements at steady operating conditions close to the investigated resonance enable a validation of the steady aerodynamics. Subsequently, numerically obtained aeroelastic quantities, such as resonance frequency, and damping, as well as maximum alternating blade stresses and tip deflections, are compared to experimental blade tip timing data. Experimental trends in damping can be confirmed and better explained by considering numerical results regarding the aerodynamic wall work density and secondary flow phenomena. The influence of varying loading conditions on the resonance frequency is not observed as distinctly in numerical, as in experimental results. Generally, alternating blade stresses and deflections appear to be significantly lower than in the experiments. However, similar to the aerodynamic damping, numerical results contribute to a better understanding of experimental trends. The successive experimental validation shows the capabilities of the numerical forced response analysis setup and enables the highlighting of challenges and identification of potential further adaptations. Full article

(This article belongs to the Special Issue Selected Papers from the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16))

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15 pages, 4989 KiB

Open AccessFeature PaperArticle

Numerical Investigation of the Excitation Characteristics of Contaminated Nozzle Rings

by Michaela R. Beierl, Damian M. Vogt, Magnus Fischer, Tobias R. Müller and Kwok Kai So

Int. J. Turbomach. Propuls. Power 2024, 9(2), 21; https://doi.org/10.3390/ijtpp9020021 - 4 Jun 2024

Abstract

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation [...] Read more.

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient. Full article

(This article belongs to the Special Issue Selected Papers from the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16))

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14 pages, 5084 KiB

Open AccessArticle

Rotating Stall Inception Prediction Using an Eigenvalue-Based Global Instability Analysis Method

by Shenren Xu, Caijia Yuan, Chen He, Dongming Cao, Dakun Sun, Carlos Martel, Huihao Chen and Dingxi Wang

Int. J. Turbomach. Propuls. Power 2024, 9(2), 20; https://doi.org/10.3390/ijtpp9020020 - 4 Jun 2024

Abstract

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and [...] Read more.

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and experiments have partially confirmed it. As for the latter, recent computational and experimental findings have shown it to exhibit itself as a rapidly amplified flow perturbation. However, rigorous analysis has yet to be performed to prove that this is due to global linear instability. In this work, an eigenanalysis approach is used to investigate the rotating stall inception of a transonic annular cascade. Steady analyses were performed to compute the performance characteristics at a given rotational speed. A numerical stall boundary was first estimated based on the residual convergence behavior of the steady solver. Eigenanalyses were then performed for flow solutions at a few near-stall points to determine their global linear stability. Once the relevant unstable modes were identified according to the signs of real parts of eigenvalues, they were examined in detail to understand the flow destabilizing mechanism. Furthermore, time-accurate unsteady simulations were performed to verify the obtained eigenvalues and eigenvectors. The eigenanalysis results reveal that at the rotating stall inception condition, multiple unstable modes appear almost simultaneously with a leading mode that grows most rapidly. In addition, it was found that the unstable modes are continuous in their nodal diameters, and are members of a particular family of modes typical of a dynamic system with cyclic symmetries. This is the first time such an interesting structure of the unstable modes is found numerically, which to some extent explains the rich and complex results constantly observed from experiments but have never been consistently explained. The verified eigenanalysis method can be used to predict the onset of a rotating stall with a CPU time cost orders of magnitude lower than time-accurate simulations, thus making compressor stall onset prediction based on the global linear instability approach feasible in engineering practice. Full article

(This article belongs to the Special Issue Selected Papers from the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16))

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17 pages, 6793 KiB

Open AccessArticle

Physics of the Unsteady Response of Turbine Cascade to Pulsed Flow Conditions

by Pierre Bertojo, Nicolas Binder and Jeremie Gressier

Int. J. Turbomach. Propuls. Power 2024, 9(2), 19; https://doi.org/10.3390/ijtpp9020019 - 27 May 2024

Abstract

The present contribution is in direct continuation of previous work which aimed at demonstrating the possible benefit of the unsteady feeding of turbines. Some numerical analyses of the flow inside a skeletal cascade revealed that instantaneous overloading occurs on the blades. However, such [...] Read more.

The present contribution is in direct continuation of previous work which aimed at demonstrating the possible benefit of the unsteady feeding of turbines. Some numerical analyses of the flow inside a skeletal cascade revealed that instantaneous overloading occurs on the blades. However, such an academic case is far from a realistic configuration. The present paper investigates the influence of a simplified thickness distribution to check whether the instantaneous benefit is still observed. Based on numerical simulations, an analysis of the physical origin of the overloading is proposed on a single blade. It results in the choice of a triangular thickness distribution, which should promote the physical phenomena responsible for the overloading. A parametric study of such a distribution demonstrates that it is possible to obtain instantaneous performance very close to the optimum of the flat plate. Conclusions drawn from the single-blade analysis are extended to cascades and stator–rotor configurations and show an increase in the complexity of physical phenomena. Ultimately, the aim is to optimize the geometric shape to obtain maximum overloading. Consequently, the same type of study was carried out for the expansion phase, and similar results were obtained. Full article

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18 pages, 11401 KiB

Open AccessArticle

Design and Characterization of Highly Diffusive Turbine Vanes Suitable for Transonic Rotating Detonation Combustors

by Sergio Grasa and Guillermo Paniagua

Int. J. Turbomach. Propuls. Power 2024, 9(2), 18; https://doi.org/10.3390/ijtpp9020018 - 9 May 2024

Abstract

In rotating detonation engines the turbine inlet conditions may be transonic with unprecedented unsteady fluctuations. To ensure an acceptable engine performance, the turbine passages must be suited to these conditions. This article focuses on designing and characterizing highly diffusive turbine vanes to operate [...] Read more.

In rotating detonation engines the turbine inlet conditions may be transonic with unprecedented unsteady fluctuations. To ensure an acceptable engine performance, the turbine passages must be suited to these conditions. This article focuses on designing and characterizing highly diffusive turbine vanes to operate at any inlet Mach number up to Mach 1. First, the effect of pressure loss on the starting limit is presented. Afterward, a multi-objective optimization with steady RANS simulations, including the endwall and 3D vane design is performed. Compared to previous research, significant reductions in pressure loss and stator-induced rotor forcing are obtained, with an extended operating range and preserving high flow turning. Finally, the influence of the inlet boundary layer thickness on the vane performance is evaluated, inducing remarkable increases in pressure loss and downstream pressure distortion. Employing an optimization with a thicker inlet boundary layer, specific endwall design recommendations are found, providing a notable improvement in both objective functions. Full article

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20 pages, 2038 KiB

Open AccessFeature PaperArticle

Simulation of Indexing and Clocking with a New Multidimensional Time Harmonic Balance Approach

by Laura Junge, Christian Frey, Graham Ashcroft and Edmund Kügeler

Int. J. Turbomach. Propuls. Power 2024, 9(2), 17; https://doi.org/10.3390/ijtpp9020017 - 8 May 2024

Abstract

Alongside the capability to simulate rotor–stator interactions, a central aspect within the development of frequency-domain methods for turbomachinery flows is the ability of the method to accurately predict rotor–rotor and stator–stator interactions on a single-passage domain. To simulate such interactions, state-of-the-art frequency-domain approaches [...] Read more.

Alongside the capability to simulate rotor–stator interactions, a central aspect within the development of frequency-domain methods for turbomachinery flows is the ability of the method to accurately predict rotor–rotor and stator–stator interactions on a single-passage domain. To simulate such interactions, state-of-the-art frequency-domain approaches require one fundamental interblade phase angle, and therefore it can be necessary to resort to multi-passage configurations. Other approaches neglect the cross-coupling of different harmonics. As a consequence, the influence of indexing on the propagation of the unsteady disturbances is not captured. To overcome these issues, the harmonic balance approach based on multidimensional Fourier transforms in time, recently introduced by the authors, is extended in this work to account for arbitrary interblade phase angle ratios on a single-passage domain. To assess the ability of the approach to simulate the influence of indexing on the steady, as well as on the unsteady, part of the flow, the proposed extension is applied to a modern low-pressure fan stage of a civil aero engine under the influence of an inhomogeneous inflow condition. The results are compared to unsteady simulations in the time-domain and to state-of-the-art frequency-domain methods based on one-dimensional discrete Fourier transforms. Full article

(This article belongs to the Special Issue Selected Papers from the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16))

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International Journal of Turbomachinery, Propulsion and Power

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