bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Fidelity Simulations and RANS Analysis of a Low-Pressure Turbine Cascade in a Spanwise-Diverging Gas Path - End-Wall Flow Analysis and Loss Generation Mechanisms
Authors: Rosenzweig Marco , Kozul Melissa , Sandberg Richard , Marconcini Michele , Pacciani Roberto
Published: September 2023

In order to increase the impact of cascade tests on the design of low-pressure turbines (LPT), the end-wall geometry must be taken into account. Even if, given the high aspect ratio of LPT bladings, profile loss is expected to be the major loss source, the evolving secondary flow phenomena in the end-wall region can contribute up to 40% of loss generation. In addition, the growth of end-wall boundary layers introduces blockage effects on the otherwise undisturbed, free-stream flow away from the end-walls. Scale-resolving computational fluid dynamics have in the past been able to shed light on the mechanisms driving the evolution of vorticity and loss generation in the end-wall region. The majority of those past studies, however, have been conducted with spanwise-parallel end-walls. The present paper considers the MTU-T161 LPT cascade with spanwise-diverging end-walls, which feature in many real engines. The diverging gas path adds another layer of complexity to the flow field. To study the aerodynamic performance of this cascade, wall-resolved large-eddy simulations (LES) and Reynolds-Averaged Navier-Stokes (RANS) analyses are performed at engine-relevant conditions of isentropic exit Reynolds number of 90,000 and isentropic exit Mach number of 0.6 with proven computational fluid dynamic solvers. Firstly, the LES results are validated against experimental data. Then, in separate simulations, the momentum thickness of the incoming boundary layers is systematically varied, as the resulting end-wall flow downstream of the blade is highly dependent on the state of the incoming end-wall flow. The data-rich results are used to perform a detailed decomposition of the various contributions to loss, to deepen the understanding of loss generation mechanisms in LPT flows in an engine-like, spanwise-divergent gas path. Lastly, a rigorous comparison between the results from LES and RANS shows there is scope for improvement in the capability of standard transition/turbulence closures in accurately reproducing three-dimensional flow features. This is needed if lower-order numerical tools are to be effective in driving the design of next-generation aeronautical LPTs.
A Study of Unsteady Aerodynamic Forces on Last Stage Blades in a Low-Pressure Model Steam Turbine at Very Low Operating Conditions
Authors: Tanuma Tadashi , Okuda Hiroshi , Haraguchi Taiga , Okuno Kenichi , Shibukawa Naoki
Published: September 2023

The relatively higher vibration stress of steam turbine last stage blade which appears at very low load operating condition is investigated in this paper. An unsteady Computational Structural Mechanics (CSM) analysis was conducted using the unsteady Computational Fluid Dynamics (CFD) result as the blade surface Boundary Conditions (BC) of traction in order to reveal the relationship between the aerodynamic unsteady forces and the abrupt increase of the blade vibration stresses. The present FEA model contains the same structures of lacing wires for blade vibration damping as the model steam turbine.

A series of calculations were performed in accordance with a sub-scale test model turbine that precisely simulated an actual large steam turbine. The CFD calculation results were evaluated compared with test data. CFD results for two representative cases explained that under the extremely small flow rate condition where vibration stress increases, several reverse flow cells are generated near the tip of the blades and rotate at a speed slower than the rotational speed. The causal relationship between the aerodynamic excitation force due to this phenomenon and the vibration mode of the long blade and the magnitude of the stress was discussed. It was confirmed that the characteristic vibration mode obtained in the analysis was the same as the vibration mode measured by the test turbine, and the validity of the analysis was confirmed.
Comparison of Equivalence Ratio Fluctuations in a Lean Premixed Combustor for Kerosene and Natural Gas
Authors: Vogel Manuel , Kaufmann Jan , Völkl Vinzenz , Hirsch Christoph , Sattelmayer Thomas
Published: September 2023

Equivalence ratio fluctuations have been identified as a major driving mechanism for thermoacoustic instabilities in lean premixed combustion. In the present study, equivalence ratio fluctuations are determined experimentally from flame chemiluminescence in a lean premixed combustor at atmospheric conditions for kerosene and natural gas combustion. The phase-resolved CH* and CO2* chemiluminescence signals of acoustically excited flames are acquired with an intensified camera equipped with an image doubler and bandpass filters. A calibration chart derived from stationary operation provides the correlation between the global CH*/CO2* ratio and the equivalence ratio for both fuels. Equivalence ratio fluctuations are found to be particularly dominant as long as the convective wavelength of the equivalence ratio wave exceeds the distance between fuel injection and flame. The fluctuations decrease significantly with increasing frequencies and finally become almost negligible. The more complex mixture preparation for liquid fuels compared to gaseous fuels is shown to significantly influence the generation and propagation of equivalence ratio fluctuations. The applied measurement method is validated by investigating externally premixed natural gas combustion, where no equivalence ratio fluctuations are detected. A one-dimensional transport model is employed to analyze the generation and propagation of the equivalence ratio wave. A comparison with the experimental results reveals that the propagation of the equivalence ratio wave can be approximated quite accurately by the model. However, the model fails to predict important features attributed to an interaction of the equivalence ratio wave with swirl fluctuations.
Efficient Unsteady Simulations of Multistage Turbines Using a Flexible Frequency-Domain Approach
Authors: Tartinville Benoît , Vilmin Stéphane
Published: September 2023

Predicting the unsteady nature of the flow within a multistage turbine is of crucial importance for modern design. Indeed, such unsteady interactions can not only affect the turbine global efficiency but also the level of tonal noise and the structural and thermal integrity of the blades. Thermal stresses are of particular importance for turbine blades since the hot streaks coming out of the combustion chamber can severely reduce the blade lifetime.

This paper proposes to demonstrate the capabilities of the nonlinear harmonic method to solve in an accurate and efficient way the unsteady interactions between successive rows, and the propagation of hot streaks from the combustion chamber down to the exit of the low pressure turbine. This frequency-domain approach has been extended to allow for more flexibility in the choice of harmonics, in particular the way the perturbations are propagated through the whole multistage configuration. A special attention has also been paid to reduce the computing time and produce a better parallel efficiency. The high and low-pressure turbines of the KJ66 micro aero-engine have been selected as reference test case.
Full-Scale Demonstration and Validation of a 35 MW Transcritical CO2 Heat Pump
Authors: Wolscht Leonhard , Somaini Reto , Jacquemoud Emmanuel , Jenny Philipp
Published: September 2023

Large-scale industrial heat pumps are an emerging solution for the decarbonization of the district heating sector and its coupling with other thermal (heating or cooling) applications. Hermetically sealed compressors with integrated motors and magnetic bearings secure refrigerant confinement and eliminate thermal losses making them advantageous in large scale heat pump applications. This work presents the thermodynamic and rotordynamic specifics of a large-scale heat pump of 35 MW thermal duty operating with a transcritical CO2 cycle in a full scale testbed setup. Experimental data encompass different operating points at nominal, maximum and part load. Furthermore, fast load changes of more than 66% electrical input power variation prove the suitability of the presented heat pump concept for fast grid stabilisation. The paper discusses the operations’ impact on both the thermodynamic process cycle as well as the rotordynamic key figures. The testbed results show an overall cycle performance with a Lorenz efficiency of 43% and low mechanical unbalance at one third of the allowed vibration limit by ISO. While experiencing unfamiliar pipe vibration patterns the HPU casing vibrations remain well below common limits. This demonstration ensures the technical maturity of industrial-scale heat pumps ready for on-field installation. The experimental data gathered from the test campaign was employed for the successful validation of a dynamic model, that allows for further heat pump transient operation prediction in the future.
Mineral Composition Effects on Dust Deposition at Realistic Engine Conditions
Authors: Wendel Nathanael J. , Subasic Noah P. , Mizer Andrew E. , Bons Jeffrey P.
Published: September 2023

In this paper the role of mineral composition was assessed for Air Force Research Laboratory test dust (AFRL), for deposition in a realistic gas turbine engine environment. Experiments were performed on an effusion cooling test article with a coolant flow temperature of 894K and surface temperature of 1144K. Aerosolized dust with a 0–10 μm particle size distribution was delivered to the test article. The mineral recipe of AFRL was altered such that the presence of each of the five components ranged from 0% to 100%, and capture efficiency, hole capture efficiency, blockage per gram, and normalized deposit height were reported. Results are compared to a previous study of the inter-mineral synergies in an impingement cooling jet at the same temperature conditions. Despite differences in experimental facility flow geometry, overall agreement was found between the trends in deposition behavior of the dust blends. The strong deposition effects that were observed were shown to be related to adhesion forces of particles, mechanical properties, and chemical properties of the dust minerals. Supplemental testing was performed in a high-temperature (1425–1650 K) impinging jet (200–260 m/s) to evaluate mineral effects at hot gas path conditions. Capture efficiency and morphology of dust deposits are reported. The capture efficiency in this regime was shown to correlate well with temperature, with chemical effects being secondary. An attempt was made to predict capture efficiency using chemical assessments such as ratio of bases to acids, Ca:Si ratio, and optical basicity with only modest success.
Analysis of C-Spec Particle Breakage in a Turbine Engine Particle Ingestion Test Cell
Authors: Vlach Tomas , Olshefski Kristopher T. , Bunin David J. , Ehlers Alix M. , Caddick Mark J. , Lowe K. Todd , Ng Wing F.
Published: September 2023

A turboshaft engine test rig based on a Rolls-Royce M250-C20B engine has been developed at Virginia Tech’s Advanced Propulsion and Power Laboratory in cooperation with its government and industry partners. The engine has been instrumented to allow measurement of the effects that dust particles have on the engine (power degradation) as well as the effects that the engine has on the particles (e.g., breakage). The work in this paper presents the first set of data collected from the engine tests and focuses on changes in the shape and size of C-Spec (quartz) dust after passage through the first five stages of the compressor and through the entire engine. Dust samples have been analyzed to determine particle size and shape distributions at the locations of interest and these have been compared with undigested material. These preliminary analyses suggest that average particle volume decreased to ∼5 % of the original size during transit through five stages of the axial compressor. No subsequent change in size and shape occurred, despite these particles then passing through one additional axial stage, the centrifugal stage, and four stages of the turbine section. Moreover, the apparent sphericity of the particles increased slightly in the axial compressor, hinting at the reduction of their erosion potential. The data presented here will assist communities interested in turbine engine environmental damage in understanding the deterioration processes and their prevention. Ultimately, the research will allow for pinpointing such degradation effects to a single compressor stage, resulting in a greater ability to predict engine damage and prevent subsequent loss of human life.
High-Dimensional Uncertainty Quantification of High-Pressure Turbine Vane Based on Multi-Fidelity Deep Neural Networks
Authors: Li Zhihui , Montomoli Francesco , Casari Nicola , Pinelli Michele
Published: September 2023

In this work a new multi-fidelity (MF) uncertainty quantification (UQ) framework is presented and applied to LS89 nozzle modified by fouling. Geometrical uncertainties significantly influence aerodynamic performance of gas turbines. One representative example is given by the airfoil shape modified by fouling deposition, as in turbine nozzle vanes, which generates high-dimensional input uncertainties. However, the traditional UQ approaches suffer from the curse of dimensionality phenomenon in predicting the influence of high-dimensional uncertainties. Thus, a new approach based on multi-fidelity deep neural networks (MF-DNN) was proposed in this paper to solve the high-dimensional UQ problem. The basic idea of MF-DNN is to ensure the approximation capability of neural networks based on abundant low-fidelity (LF) data and few high-fidelity (HF) data. The prediction accuracy of MF-DNN was first evaluated using a 15-dimensional benchmark function. An affordable turbomachinery UQ framework was then built based on the MF-DNN model, the sampling-, the parameterization- and the statistical processing modules. The impact of fouling deposition on LS89 nozzle vane flow was investigated using the proposed UQ framework. In detail, the MF-DNN was fine-tuned based on bi-level numerical simulation results: the 2D Euler flow field as low-fidelity data and the 3D Reynolds-Averaged Navier-Stokes (RANS) flow field as high-fidelity data. The UQ results show that the total pressure loss of LS89 vane is increased by at most 17.1 % or reduced by at most 4.3 %, while the mean value of loss is increased by 3.4 % compared to the baseline. The main reason for relative changes in turbine nozzle performance is that the geometric uncertainties induced by fouling deposition significantly alter the intensity of shock waves near the throat area and trailing edge. The developed UQ framework could provide a useful tool in the design and optimization of advanced turbomachinery considering high-dimensional input uncertainties.
Experimental Investigation of a Multi Tube Burner for Premixed Hydrogen and Natural Gas Low Emission Combustion
Authors: Jaeschke Alexander , Ćosić Bernhard , Wassmer Dominik , Paschereit Christian Oliver
Published: September 2023

Hydrogen as an essential part of future decarbonisation of the energy industry makes it a crucial necessity to replace conventional, natural gas based concepts in gas turbine combustion. This paper presents an experimental study of a multi tube jet flame burner. The study is carried out with natural gas and pure hydrogen fuel at gas turbine relevant conditions at atmospheric pressure. To identify key differences between hydrogen-air and natural gas-air flames on the overall robustness and flame flashback behaviour, air bulk velocity (80–120 m/s), adiabatic flame temperature (1235–2089 K) and air inlet temperature (623–673 K) are varied over a wide range, covering a range of Reynolds numbers of 10.000 to 20.000. Depending on flame temperature, two different flame shapes are observed for natural gas-air flames. The shape of the hydrogen-air flame changes less over the range of flame temperatures tested, but is generally more compact. The process of fuel-air mixing is further investigated by concentration distribution measurements in a water tunnel setup. Therefore, planar laser-induced fluorescence is utilized for visualization. The measured concentration distributions confirm the overall good mixing quality but also give an explanation on the observed flashback behaviour of the different burner designs at reacting tests. The findings of the study are composed in a flashback correlation combining the observed flashback drivers for the burner configurations investigated.
A Literature Review of NOx Emissions in Current and Future State-of-the-Art Gas Turbines
Authors: Dennis Richard , Long Henry A. , Jesionowski Gary
Published: September 2023

Current U.S. government policy seeks to achieve a completely carbon-free economy by 2050, with a carbon-free electricity sector by 2035 (per executive orders #14008 and #14057). To address these goals, the U.S. Department of Energy is evaluating strategies and technologies that support the production, utilization, transport, and storage of hydrogen (via initiatives such as DOE’s Energy Earthshot – Hydrogen and various DOE funding opportunity announcements). A carbon-free fuel such as hydrogen cannot be overvalued in a dynamic electric energy sector seeking to decarbonize. One of the most important technologies needed to achieve the goal of a carbon-free electricity sector is a 100% hydrogen-fueled gas turbine. Accommodating hydrogen-based fuels has been a key goal for various original engine manufacturers (OEMs) for many years, but much more research and development (R&D) is needed. The purpose of this paper is to highlight the current state-of-the-art of hydrogen turbine technology, especially regarding nitrogen oxide (NOx) emissions compared to natural gas-fueled turbines. NOx is the primary criteria pollutant from thermally-driven combustion turbines and should be controlled to levels that are equivalent to or below existing standards (as reported “existing standards” for hydrogen-fueled gas turbines may need to be re-baselined). This paper will provide an overview of hydrogen as a fuel and various NOx emissions control techniques that are relevant for hydrogen-based fuels. A conclusion from this overview is that, with some level of R&D, NOx emissions from hydrogen-fueled gas turbines can be controlled to levels similar to those produced by state-of-the-art natural gas-fueled combustion turbines while remaining competitive in terms of performance and efficiency.
Numerical Investigation of Flow Characteristics in a Supercritical Carbon Dioxide Turbine for 20 Megawatt Brayton Cycle
Authors: Yang Guoying , Yang Rui , Deng Qinghua , Xu Bozhou , Li Jun , Feng Zhenping
Published: September 2023

Efficient and clean utilization of energy has become one of the themes of sustainable development. The closed Brayton cycle with supercritical carbon dioxide (SCO2) as working fluid has the advantages of compact structure, high efficiency and environmental friendliness, so it is widely concerned by scholars around the world. As the carrier of thermal power conversion in cycle system, the aerodynamic performance of CO2 turbines affects the cycle efficiency crucially. However, the research work about this topic is still relatively rare in open literature. In this paper, the flow characteristics and aerodynamic performance of a SCO2 axial-flow turbine are investigated by numerical method, and the enthalpy drop for each stage is optimized. The differences of flow characteristics under design conditions before and after optimization are compared. Finally, the off-design flow characteristics of the turbine are analyzed. The results show that compared with that before optimization, the total-to-total efficiency is increased by 0.79%, and the flow rate is increased by 4.30%. The leakage of clapboard seal and blade tip seal in the first stage is also significantly reduced. The leakage rate of the clapboard seal in the first stage reaches 3.13% of the total flow rate. The total-to-total efficiency of the turbine also decreases by 4.04% compared with that without seal clearance. In this paper, the flow characteristics of the main passage and the seal clearance of a SCO2 turbine are deeply analyzed. The reasons for the large leakage are revealed, and the relevant factors that have a negative impact on its efficiency are summarized. The research results can provide reference for the design of SCO2 axial flow turbines.
Sequential Performance Adaptation for a Turboprop Engine Model at Flight Condition
Authors: Kim Sangjo , Kwon Young-Min , Chun Youngju , Lee Chung-Ryeol , Yang Wonseck , Kim Youil
Published: September 2023

A performance adaptation method is proposed for a turboprop engine, to improve the prediction accuracy of an engine model based on measurement data on flight conditions. The corrected mass flow rate and efficiency of a high-pressure compressor (HPC) and the efficiency of a power turbine (PT) are adjusted by using adaptation factors to match the engine model and the measurements. Moreover, the calculated HPC exit pressure and high-pressure turbine (HPT) exit temperature from the engine model are adjusted by using additional adaptation factors. Shaft power from low-pressure (LP) spool, HPC exit pressure, HPT exit temperature, PT exit temperature, fuel mass flow rate, high-pressure shaft rotating speed, and LP shaft rotating speed are all measured at ten operating points. The proposed performance adaptation method is divided into several steps and proceeded sequentially. In the first step, the adaptation factors for adjusting component performance maps are calculated and generated empirical correlations. Then, the additional adaptation factors are calculated for adjusting the calculated HPC exit pressure and HPT exit temperature based on the revised engine model from the previous stage and the measurement data. Finally, the empirical correlations are applied to the original engine model and the prediction accuracy is compared to the measurement data. As a result, it is confirmed that the revised engine model reduced the error with the measured data in flight conditions, compared to the original engine model.
Radial Interference Fit and Centrifugal Force Effects on Lateral Rotordynamic Response
Authors: Kim Baik Jin , Oh Joseph , Palazzolo Alan
Published: September 2023

Interference fits or shrink fits are widely utilized in highspeed rotating machinery to secure impellers, bladed disks and couplings with high torque and thrust loadings. Shaft-disc locking assemblies (SDLA) are utilized to secure wheels on a shaft, via radially directed interference fits, in contrast butt joint, Hirth, and Curvic couplings have interface contacts in the axial direction. A conventional practice is to treat interference fits as continuous connections in rotordynamic shaft models. However, this may introduce significant inaccuracies by neglect of the local interface flexibilities at interference fits. A novel modeling approach incorporating 3D solid finite elements with a GW interface model at radial contact surfaces is presented. The approach is validated by benchmarking it with measured free-free natural mode and critical speed measurements. The test rig shaft has wheels attached by SDLAs, an industrial tilt pad bearing and a radial/deep groove ball bearing. Critical speeds are obtained from synchronous vibration measurements using relative shaft, eddy current sensors, attached to the bearing housing. The critical speeds are shown to be influenced by stress stiffening of the shaft resulting from centrifugal forces that increase circumferential (hoop) stress.
Optimization of a Fan-Shaped Film-Cooling Jet and Its Implementation in a High-Pressure Turbine Vane With Large-Eddy Simulations
Authors: Vincze Balazs , Agarwal Shubham , Odier Nicolas , Gicquel Laurent , Duchaine Florent
Published: September 2023

Film cooling technique is extensively used in turbine engines to protect the turbine components from the hot gases exiting the combustion chamber. With this approach, cold fluid effusing from holes along the surface of the turbine creates a protective film to prevent the ruin of the solid material composing the blade. As of today it is now known that the hole geometry is a key element which determines the thermal efficiency of film cooling. Their designs for optimal holes operating at conditions of high-pressure turbines are however a challenge for which several research groups and industrial companies have devoted intensive numerical and experimental campaigns. In this study, a Large-Eddy Simulation based approach is adopted to optimize the shape of a fan-shaped hole on an academic flat plate configuration in engine representative conditions. To do so, four of the most important geometrical parameters defining such a cooling hole shape, namely the depth of the expanded section, the hole inclination angle and the forward as well as the lateral expansion angles are selected as design variables to obtain an optimal hole shape. The Bayesian based Efficient Global Optimization method along with the Expected Improvement as the acquisition function are used to find the maximum surface averaged film cooling effectiveness as the objective function. After several database enrichment steps to reduce the overall model error, an optimal shape with the highest cooling performance for a given operating condition is obtained. The resulting hole geometry is then installed on an experimental high-pressure film-cooled turbine vane investigated in the TATEF2 European project for validation and assessment. In that case, Large-Eddy Simulations on a reduced span of the vane are conducted to compare the efficiencies of the original and optimized hole geometries. It is first shown that the simulation of the original geometry reproduces accurately the flow field around the vane and thermal efficiency. Then, the results illustrate the difficulties of integrating an optimal geometry obtained on a flat plate without group effects on a real geometry.
A Numerical Design Space Investigation of Low-Speed Axial Compressor Stages Using Single-Row and Tandem Bladings
Authors: von Jeinsen Philipp , Eckel Jannik , Giannini Samuele , Gümmer Volker
Published: September 2023

The present paper numerically investigates the design space of an axial, low-speed compressor stage using tandem- and single aerofoil configurations. The investigated rotor and stator designs follow a coupled throughflow and blade-to-blade design approach and will yield quasi-3D designed compressor stages with either single-rotor single-stator or tandem-rotor tandemstator configurations. In past studies, tandem aerofoil configurations have shown a potential for increasing stage working coefficients, while maintaining their efficiency compared to their single aerofoil reference configuration. However, it was also shown that tandem configurations are able to reduce efficiency due to an increase of secondary flow caused by the higher loading and introduction in the a second aerofoil. Currently, there is no clear design guideline on when tandem aerofoil configurations should be preferred over single ones, and under which circumstances they should be avoided. To answer this question, the present paper will attempt to create a “Smith-chart” for tandem aerofoil stages and compare them to their single aerofoil counterparts. Originally intended for use with turbine stages, the Smith-chart maps out the potential efficiencies of turbomachinery designs. It plots the working coefficient (Ψ) over the throughflow coefficient (φ), which gives a direct indication of the shape of velocity triangles in the stage. Whereas the Smith-chart has been well investigated for single aerofoil stages, both numerically and experimentally, as well as for low and high-speed applications, this is not the case so far for tandem configurations. The current work presents a fast Q3D design and analysis procedure, used on a low-speed axial compressor stage and will yield quasi-3D efficiencies for a large number of different design coefficients. The findings of this work will enable future research to identify preferred combinations of design coefficients for tandem aerofoil configurations, which can then be further analyzed in 3D investigations at a higher fidelity level.
Insights Into the Flow Field and Performance of a Boundary Layer Pump
Authors: Palaveev Kyril , Rajendran David John , Anselmi Eduardo , Santhanakrishnan Mani , Pachidis Vassilios
Published: September 2023

A flow field analysis of a realistic, integrated, multi-disc boundary layer pump as is necessary for investigating the reasons for typically quoted low efficiencies in such pumps is described. The study focuses on the 3D RANS solutions of a water boundary layer pump model created to replicate a design by Morris, 1973, which consists of 170 discs and a volute channel. A baseline study is performed to investigate the rotor-only performance after which a volute alone is separately simulated to identify the performance and losses in each as separate systems. Thereafter, an integrated model is characterized across mass flow rates and rotational speeds. The flow fields of all three models are discussed and the results of the integrated model are compared to the experimental data.

The results from the model with the rotor only confirm the typically made claim that the efficiency of the rotor in a boundary layer pump possesses relatively high values which in this case is 87% at the design point, reinforcing results from previous studies that the rotor assembly is not the cause of inefficiency. The volute on its own indicated a hydraulic efficiency of around 97%. However, the integrated model yielded a rotor efficiency of around 74% and an overall pump efficiency of 51% at the design point, clearly outlining the fact that the effect of the volute integrated with the rotor is the reason for both the rotor and pump efficiency degradataion. The reason for this drop in efficiency is discussed in detail by highlighting the change in the flow topologies. The insights into the flow field and the identification of the reason for inefficiencies using a separated component analysis approach provides directions for avenues in which design improvements would need to be attempted.
Acoustoelastic Modes in a Rotor-Cavity System With Superposed Through Flow
Authors: Unglaube Tina , Brillert Dieter
Published: September 2023

When increasing the pressure ratio in centrifugal compressors, understanding the fluid-structure interaction between the impeller and the surrounding fluid becomes increasingly important. It is crucial to know how critical frequencies shift when operating conditions vary. Therefore, this paper investigates acoustoelastic modes in a rotor-stator cavity, which serves as a simplified model of the side chambers of radial compressors for fundamental research purposes.

New experimental results gathered at the rotor-stator cavity test rig at the Chair of Turbomachinery at University Duisburg Essen (Germany) are presented. The measurements include such with a rotating disk and superimposed centrifugal and centripetal through flow. The mass flow of the superimposed through flow is varied, and results are compared to cases without added through flow. Results for structure dominant modes do not vary subject to a change in superposed mass flow, but acoustic dominant ones do. This agrees with the understanding that the flow structure in the cavity influences acoustic dominant modes but does not have a considerable effect on the structure dominant modes originating from the rotating disk. However, results for acoustic dominant modes do not show a consistent trend. While a centrifugal through flow appears to decrease the core rotation inside the cavity, results for centripetal through flow show a rather mixed picture. Also, measured acoustic dominant modes seem to be of mixed order, impeding the evaluation of possible coupling effects. Here, future research is expected to bring clarity. Ultimately, more evidence has been found that measured frequency shifts can be considered a summation of the frequency shifts due to a change in fluid properties and disk rotational speed, plus an additional frequency shift due to the superimposed through flow. This is an important contribution to a better understanding of acoustoelastic modes in rotor-stator cavities and efforts to avoid machine failure in highly loaded centrifugal compressors.
Investigation of the Applicability of Methods Approved for Steam to the Design of Labyrinth Seals in Turbines Operated With CO2 in Supercritical State
Authors: Tegethoff Katharina , Musch Christian , Glos Stefan , Schuster Sebastian , Brillert Dieter
Published: September 2023

This paper presents an approach for testing and adapting numerical models for the design and design optimisation of turbines operating with CO2 in supercritical condition (sCO2). Particular emphasis is put on the influence of the medium and its specific thermodynamic properties on the design process of labyrinth seals. In contrast to the medium steam, no comprehensive empirical values of power plants are available for CO2 in a supercritical state in the field of turbomachinery design. Therefore, the question arises whether the design rules established for steam turbines can also be used for the design of a sCO2 turbine and how any necessary adaptations for the medium CO2 can be introduced. This paper aims to contribute to answering this question by first identifying the labyrinth seal as one component in whose vicinity relevant effects, such as leakage and windage heating, as well as influences on the rotor dynamics are to be expected. The investigations carried out are based on mathematical modelling and computational fluid dynamics (CFD) calculations. Established methods and models are used, which are validated in a next step for the special requirements of the application in a sCO2 turbine and adapted if necessary. It can be shown that the properties of the fluid have an influence on the design of the components. A consideration of the material-specific properties as well as the thermodynamic state variables is therefore required. This is exemplified by the fact that the density of CO2 is about twice as high as that of the medium steam in classic steam turbine applications. The results presented have the potential to enable a turbine manufacturer to assess the confidence interval of known methods when applied to the particular challenges of sCO2 turbine design.
Feasibility of the Use of Thermal History Paints for Long Term Exposure of Low Temperature Life Critical Components
Authors: Araguas Rodriguez Silvia , Peral Jiménez David , Pilgrim Christopher C. , Scheibel John , Feist Jörg P.
Published: September 2023

Thermal History Paint (THP) is a new technique used to measure temperature in the harsh operating conditions inside gas turbines or other machinery. It is applied to the surface of a test component and upon heating, changes permanently according to the maximum temperature of exposure. After operation, the THP is read-out at many locations across the surface. Through calibration, the measurements are translated to temperature to deliver high-resolution thermal maps.

The technique has been recently demonstrated in short-term development tests for the validation of thermal models in the design phase. It has been shown that the THP has several advantages compared to traditional temperature measurement techniques. In comparison to thermocouples and thermal crystals the paint can acquire measurements at many locations without the challenging installation limitations. THP has been shown to have greater durability than thermochromic paints and can be applied to measure the temperature non-destructively.

The increased durability opens the possibility that the THP could be applied to an operational component and operated through its lifetime and measured at maintenance intervals to monitor the maximum temperature of the component. This would improve run, repair and replace decisions, reducing life cycle costs. For example, rotor discs in industrial gas turbines are critical components that are expensive and time-consuming to replace and experience creep when exposed to excessive temperatures.

This paper provides the first investigation into the behaviour of the THP for extended operational exposures, with rotor discs as an example application. The objective was to understand whether the THP could be used for temperature measurements after such long exposures and, if so, how it would be calibrated. The results show that the THP exhibits good durability, enabling measurements up to 450°C after 7200 hours of exposure, covering the useful range for rotor disc applications. In addition, the behaviour of the THP allows the effect of time to be neglected for such long exposures, simplifying the calibration procedure and enabling practical use in this application. The results indicate the viability of this new technique to capture temperature information that is not currently possible to acquire.
Experimental Investigation of Transient Flow Phenomena in Rotating Compressor Cavities
Authors: Pernak Mikolaj J. , Nicholas Tom E. W. , Williams Jake T. , Jackson Richard W. , Tang Hui , Lock Gary D. , Scobie James A.
Published: September 2023

The clearance of compressor blade tips during aero-engine accelerations is an important design issue for next-generation engine architectures. The transient clearance depends on the radial expansion of the compressor discs, which is directly coupled to conjugate heat transfer in co-rotating discs governed by unsteady and unstable buoyancy-induced flow. This paper discusses an experimental and modelling study using the Bath Compressor Cavity Rig, which simulates a generic axial compressor at fluid-dynamically scaled conditions. The rig was specifically designed to generate heat transfer of practical interest to the engine designer and validate computational codes. This work presents the first study of the fundamental fluid dynamic and heat transfer phenomena under transient conditions. The rotating flow structure was seen to be characterised by coherent pairs of cyclonic/anti-cyclonic vortex pairs; the strength, rotational frequency, stability and number of these unsteady structures changed with changing rotational Reynolds and Grashof numbers during the transients. These structures, measured by unsteady pressure transducers in the rotating frame of reference, were only present when the flow in the rotating cavity was dominated by buoyancy. Experimental correlations of both Nusselt number and radial mass flow rate in the rotating core were correlated against Grashof number. Remarkably, the experiments revealed a consistent correlation for both steady-state and transient conditions over a wide range of Gr. The results have a practical application to thermo-mechanical models for engine design.
On the Secondary Flow System of an Aggressive Inter Compressor Duct
Authors: Fritz Stefan , Dygutsch T. , Kasper A. , Hergt A. , Grund S. , Flamm J. , Lejon M. , Sahota Harsimar
Published: September 2023

In the last decades much effort has been spent in optimizing the performance of the rotating components of the compression system of civil aircraft engines. While these components are highly optimized, further improvements are limited. In this light, the interfaces between these components are coming into focus of research. Especially the inter compressor duct (ICD) is offering a high potential. Due to a more aggressive design, the length of the whole engine can be reduced. Shorter and thus lighter engines are leading to further fuel savings for the next engine generation. The design of current ICDs is very conservative because of high uncertainties in design space. An extensive test campaign on two very aggressive ICD designs has been conducted at an annular cascade at German Aerospace Center (DLR) Cologne to explore these limitations and a vast amount of test data has been gathered. The test section is comprised of LPC-OGVs, struts and HPC-IGVs. To simulate the influence of the last rotor of the LPC and to vary the incidence of the OGV, a move-able swirler is placed in front of the OGV. This simplification results in differences relative to a real rotor outlet flow. Through geometrical restriction, the ability to move the swirler can only be achieved by adding partial gaps in the rear part of the swirler at hub and shroud. These gaps have a huge impact on the secondary flow structure of the swirler outflow and therefore, the inflow of the ICD. In this paper, the secondary flow system of an aggressive ICD is analyzed in detail by the means of experimentally validated CFD simulations. Attention is given to the impact of the stationary swirler on the secondary flow system. Furthermore, a recommendation for future experimental setups with respect to the described effects is concluded.
Effects of Downstream Vortex Generators on Film Cooling a Flat Plate Fed by Crossflow
Authors: Straub Douglas , Weber Justin , Roy Arnab , Lee Chien-Shing , Shih Tom I-P.
Published: September 2023

Counter-rotating vortices, formed by the interaction of film cooling jets and the hot gas flow, adversely affect performance of conventional film cooling designs. In two previous papers (GT2020-14317 and GT2022-82675), downstream vortex generators consisting of rectangular plates arranged in a V-shaped pattern were shown to improve cooling effectiveness by mitigating effects of the counter-rotating vortices and by deflecting the cooling jet laterally. In this study, computational and experimental methods were used to examine how cylindrical film cooling holes (D = 3.2mm, L/D = 6, p/D = 3, α = 30°) with and without downstream vortex generators perform when the flow in the coolant supply channel is perpendicular to the direction of the hot gas. For this study, the hot gas had a temperature of 650K, and an average Mach number of 0.23. The hot-gas-to-coolant temperature ratio was 1.9, and two blowing ratios (0.75 and 1.0) were studied. Results from the CFD study show how crossflow affects the interaction between the film cooling jet and hot gas flow with and without downstream vortex generators. The experimental measurements were based on infrared thermography in a conjugate heat transfer environment. Results were obtained for film cooling performance in terms of overall effectiveness, film effectiveness, and local heat transfer coefficients. The downstream vortex generators can increase the laterally averaged effectiveness by a factor of 1.5 relative to cylindrical holes, but this higher performance is restricted to low crossflow velocities and higher blowing ratios.
Parametric Reduced Order Model of a Gas Bearings Supported Rotor
Authors: Goutaudier Dimitri , Schiffmann Jürg , Nobile Fabio
Published: September 2023

Gas bearings use pressurized gas as a lubricant to support and guide rotating machinery. These bearings have a number of advantages over traditional lubricated bearings, including higher efficiency in a variety of applications and reduced maintenance requirements. However, they are more complex to operate and exhibit nonlinear behaviors. This paper presents a parametric hyper Reduced Order Model (h-ROM) of a gas bearings supported rotor enabling to speed up the computations up to a factor 100 while preserving satisfactory accuracy. A Galerkin projection setting is employed to reduce the dimension of the governing equations and the nonlinear terms are efficiently tackled with a sparse sampling technique. The performances of the h-ROM are compared to a high fidelity model both in terms of accuracy and computation time, demonstrating the potential for future anomaly detection applications.
Experiments on Tuned UHBR Open-Test-Case Fan ECL5/CATANA: Stability Limit
Authors: Fiquet Anne-Lise , Schneider Alexandra P. , Paoletti Benoit , Ottavy Xavier , Brandstetter Christoph
Published: September 2023

Research of the past decades has shown that the operating range of modern fans and compressors is often limited by aeroelastic phenomena before the onset of pure aerodynamic instability. Prediction of these mechanisms is challenging for state-of-the-art numerical methods, particularly for configurations with flexible wide-chord blades. To provide a benchmark configuration for the community, the composite-material fan stage ECL5, representative of near future Ultra-High-Bypass Ratio architectures has been designed at Ecole Centrale de Lyon and recently shared as an open-test-case. In research program CATANA, different configurations with variable tuning and intake geometries are investigated experimentally, and here we present a comprehensive aeroelastic study of the tuned reference configuration. The study encompasses the investigation of the whole subsonic and transonic operating range using multi-physical instrumentation.

A characterization of structural properties under running conditions is analyzed in comparison to individual blade measurements and FEM-predictions. The stability limit is investigated at different speedlines. At transonic conditions, rotating stall occurred without aeroelastic precursors. Severe non-synchronous-vibrations were observed at subsonic speeds and limited the operating range before the onset of rotating stall. Through a detailed analysis of the aeroelastic coupling mechanism, a full characterization of interacting modes is presented. The challenging prediction of this coupled phenomenon and the discrepancy to aeroelastic simulations are discussed.

This paper is accompanied by a detailed aerodynamic study, and together a complete dataset including measurements of aerodynamic performance, radial flow profiles, blade-individual tip-clearance, stagger angle, vibration amplitudes and unsteady pressure fields at the rotor tip are provided. The results are a promising benchmark for future method development, particularly involving high-fidelity methods.
Spatially Resolved Modeling of the Nonlinear Dynamics of a Laminar Premixed Flame With a Multilayer Perceptron - Convolution Autoencoder Network
Authors: Rywik Marcin , Zimmermann Axel , Eder Alexander J. , Scoletta Edoardo , Polifke Wolfgang
Published: September 2023

This work presents a multilayer perceptron-convolutional autoencoder (MLP-CAE) neural network model, which accurately predicts the two-dimensional flame field dynamics of an acoustically excited premixed laminar flame. The obtained architecture maps the acoustic perturbation time series to a spatially distributed heat release rate field, capturing the flame lengths and shapes. This extends to previous neural network models, which predicted only the field-integrated value of the heat release rate. The MLP-CAE comprises two sub-models: a fully connected MLP and a CAE. The key idea behind the CAE network is to find a lower dimensional latent space representation of the heat release rate field. The MLP is responsible for modeling the flame dynamics by transforming the acoustic forcing signal into this latent space, enabling the decoder to produce the flow field distributions. To train the MLP-CAE, computational fluid dynamics (CFD) flame simulations with a broadband acoustic forcing were used. Its normalized amplitude was set to 0.5 and 1.0, resulting in a nonlinear flame response. The network was found to accurately predict the perturbed flame shapes — both under broadband and harmonic forcing. Additionally, it conserved the correct frequency response characteristics as verified by the global and local flame describing functions. The MLP-CAE provides a building block towards a potential shift away from a purely ‘0D’ analysis with the assumption of acoustic compactness of the flame. When combined with an acoustic network, the generated flame fields could provide more physical insight in the thermoacoustic dynamics of combustion chambers. Those capabilities do not come at an additional significant computational cost, as even the previous nonspatial flame models had to train on the CFD data, which readily included field distributions.