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Int. J. Turbomach. Propuls. Power, Volume 9, Issue 3 (September 2024) – 6 articles

Cover Story (view full-size image): This study explores cost-effective methods to reduce the measurement samples needed in turbomachinery by employing Gaussian process (GP) modelling in the context of a data-driven hybrid technique. Three GP approaches—baseline, CFD experiments, and multi-fidelity—are evaluated for their ability to predict the mean flow characteristics and uncertainties in a low aspect ratio axial compressor stage. While the baseline GP shows strong accuracy, the CFD experiment GP introduces complexity and errors. The multi-fidelity GP, combining CFD and experimental data, enhances accuracy and robustness and reduces the need for extensive measurements and testing times. View this paper

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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

Viewed by 622

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 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

Viewed by 552

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 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

Viewed by 508

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 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

Viewed by 807

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 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

Viewed by 856

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 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

Viewed by 664

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. 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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