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Selected Papers from the 16th International Symposium on Unsteady Aerodynamics,...
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Selected Papers from the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16)

A special issue of International Journal of Turbomachinery, Propulsion and Power (ISSN 2504-186X).

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 12442

Special Issue Editors

Prof. Dr. Roque Corral

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Guest Editor
Department of Fluid Mechanics and Aerospace Propulsion, School of Aeronautics and Space, Universidad Politécnica de Madrid, 28040 Madrid, Spain
Interests: gas turbines aerodynamics; aeroelasticity and aeroacoustics in turbomachinery; computational fluid dynamics; reduced order methods
Prof. Dr. Damian Vogt

E-Mail Website
Guest Editor
Turbomachinery and Propulsion Group, Dipartimento di SM, ITSM—Institute of Thermal Turbomachinery and Machinery Laboratory, University of Stuttgart, 70569 Stuttgart, Germany
Interests: turbomachinery aerodynamics
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Special Issue Information

Dear Colleagues,

It is our pleasure and honor to organize and present this Special Issue of the International Journal of Turbomachinery, Propulsion and Power for the 16th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT16) held at Toledo, Spain, September 19–23, 2022.

The ISUAAAT conference series, which started more than 40 years ago, is held every two to three years, primarily in Europe and occasionally in the United States and Asia. The symposia provide a unique opportunity in a single session format to bring together researchers and engineers from academic institutions and engine manufacturers working in the field to share their latest findings and to exchange ideas. For ISUAAAT15, there were 55 accepted full conference papers, and 4 keynote lectures, with authors from 14 countries and 4 continents.

The 10 papers selected for this Special Issue on Aeroelasticity of Turbomachinery were first recommended for consideration by the members of the International Scientific Committee of ISUAAAT based on the full paper and the presentations and then peer-reviewed according to the IJTPP standards.

Prof. Dr. Roque Corral
Prof. Dr. Damian Vogt
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. International Journal of Turbomachinery, Propulsion and Power is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (8 papers)

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Research

14 pages, 5033 KiB  
Article
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 1089
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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21 pages, 23685 KiB  
Article
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
Viewed by 1210
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  
Article
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
Viewed by 1324
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  
Article
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
Viewed by 1140
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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20 pages, 2038 KiB  
Article
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
Viewed by 1866
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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17 pages, 10631 KiB  
Article
Relationship between Casing Pressure and Non-Synchronous Vibration in an Axial Compressor
by Valerie Hernley, Aleksandar Jemcov, Jeongseek Kang, Matthew Montgomery and Scott C. Morris
Int. J. Turbomach. Propuls. Power 2024, 9(2), 14; https://doi.org/10.3390/ijtpp9020014 - 2 Apr 2024
Cited by 2 | Viewed by 1526
Abstract
The relationship between aerodynamic forcing and non-synchronous vibration (NSV) in axial compressors remains difficult to ascertain from experimental measurements. In this work, the relationship between casing pressure and blade vibration was investigated using experimental observations from a 1.5-stage axial compressor under off-design conditions. [...] Read more.
The relationship between aerodynamic forcing and non-synchronous vibration (NSV) in axial compressors remains difficult to ascertain from experimental measurements. In this work, the relationship between casing pressure and blade vibration was investigated using experimental observations from a 1.5-stage axial compressor under off-design conditions. The wavenumber-dependent auto-spectral density (ASD) of casing pressure was introduced to aid in understanding the characteristics of pressure fluctuations that lead to the aeromechanical response. Specifically, the rotor blade’s natural frequencies and nodal diameters could be directly compared with the pressure spectra. This analysis indicated that the rotating disturbances coincided with the first bending (1B) and second bending (2B) vibration modes at certain frequencies and wavenumbers. The non-intrusive stress measurement system (NSMS) data showed elevated vibration amplitudes for the coincident nodal diameters. The amplitude of the wavenumber-dependent pressure spectra was projected onto the single-degree-of-freedom (SDOF) transfer function and was compared with the measured vibration amplitude. The results showed a near-linear relationship between the pressure and vibration data. 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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18 pages, 11703 KiB  
Article
Numerical and Experimental Study of Flutter in a Realistic Labyrinth Seal
by Oscar Bermejo, Juan Manuel Gallardo, Adrian Sotillo, Arnau Altuna, Roberto Alonso and Andoni Puente
Int. J. Turbomach. Propuls. Power 2024, 9(2), 13; https://doi.org/10.3390/ijtpp9020013 - 1 Apr 2024
Cited by 1 | Viewed by 1710
Abstract
Labyrinth seals are commonly used in turbomachinery in order to control leakage flows. Flutter is one of the most dangerous potential issues for them, leading to High Cycle Fatigue (HCF) life considerations or even mechanical failure. This phenomenon depends on the interaction between [...] Read more.
Labyrinth seals are commonly used in turbomachinery in order to control leakage flows. Flutter is one of the most dangerous potential issues for them, leading to High Cycle Fatigue (HCF) life considerations or even mechanical failure. This phenomenon depends on the interaction between aerodynamics and structural dynamics; mainly due to the very high uncertainties regarding the details of the fluid flow through the component, it is very hard to predict accurately. In 2014, as part of the E-Break research project funded by the European Union (EU), an experimental campaign regarding the flutter behaviour of labyrinth seals was conducted at “Centro de Tecnologias Aeronauticas” (CTA). During this campaign, three realistic seals were tested at different rotational speeds, and the pressure ratio where the flutter onset appeared was determined. The test was reproduced using a linearised uncoupled structural-fluid methodology of analysis based on Computational Fluid Dynamics (CFD) simulations, with results only in moderate agreement with experimental data. A procedure to adjust the CFD simulations to the steady flow measurements was developed. Once this method was applied, the matching between flutter predictions and the measured data improved, but some discrepancies could still be found. Finally, a set of simulations to retain the influence of the external cavities was run, which further improved the agreement with the testing data. 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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16 pages, 4744 KiB  
Article
Modelling Method for Aeroelastic Low Engine Order Excitation Originating from Upstream Vanes’ Geometrical Variability
by Marco Gambitta, Bernd Beirow and Sven Schrape
Int. J. Turbomach. Propuls. Power 2024, 9(2), 12; https://doi.org/10.3390/ijtpp9020012 - 1 Apr 2024
Viewed by 1368
Abstract
The manufacturing geometrical variability in axial compressors is a stochastic source of uncertainty, implying that the real geometry differs from the nominal design. This causes the real geometry to lose the ideal axial symmetry. Considering the aerofoils of a stator vane, the geometrical [...] Read more.
The manufacturing geometrical variability in axial compressors is a stochastic source of uncertainty, implying that the real geometry differs from the nominal design. This causes the real geometry to lose the ideal axial symmetry. Considering the aerofoils of a stator vane, the geometrical variability affects the flow traversing it. This impacts the downstream rotor, especially when considering the aeroelastic excitation forces. Optical surface scans coupled with a parametrisation method allow for acquiring the information relative to the real aerofoils geometries. The measured data are included in a multi-passage and multi-stage CFD setup to represent the mistuned flow. In particular, low excitation harmonics on the rotor vane are introduced due to the geometrical deviations of the upstream stator. The introduced low engine orders, as well as their amplitude, depend on the stator geometries and their order. A method is proposed to represent the phenomena in a reduced CFD domain, limiting the size and number of solutions required to probabilistically describe the rotor excitation forces. The resulting rotor excitation forces are reconstructed as a superposition of disturbances due to individual stator aerofoils geometries. This indicates that the problem is linear in the combination of disturbances from single passages. 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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