bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbomachinery Transient Dynamics of Radial Rotor-Stator Contact Occurrences With Friction
Authors: Jacobs Coline , Legrand Mathias , Thouverez Fabrice , Almeida Patricio
Published: September 2023

The present paper focuses on the numerical investigation of the transient response of a rotorshaft affected by unilateral contact occurrences with friction mechanisms. Rotor-stator contact is initiated radially at the shaft level. The components are modeled under the rigid bodies assumption and the rotor dynamical response is investigated in the time domain. The turbomachine is assumed to be driven by two torques: the first one is prescribed while the second one is induced by friction using Coulomb’s model. Particular attention is paid to the accurate prediction of the unknown rotational speed transient. The proposed methodologies are grounded on the Carpenter and Moreau-Jean time-marching algorithms, implying the use of Lagrange multipliers to solve the frictional and unilateral contact conditions. The simplest procedure considers only sliding friction while the most sophisticated one involves convex analysis in order to deal with normal and friction forces independently is case of stiction. The solutions predicted by the algorithms are compared and show good agreement. The sensitivity study on the stator properties and friction coefficient allows the identification of the conditions affecting the rotational speed limitation. Based on the response post-processing in the time and frequency domains, it is found that a higher friction coefficient, a stiffer stator support or a lighter stator leads to a decrease of the rotational speed maximum value.
On the Impact of Core Flow Inlet-Guide-Vanes on the Tonal Noise Signature of a Turbofan Engine
Authors: Blazquez-Navarro Ricardo , Node-Langlois Thomas , Thisse Johan , Nybelen Laurent , Cunha Guilherme , Yannic Baptiste , Chirico Giulia , Altuna Villanueva Gorka
Published: September 2023

Fan noise is one of the major aircraft noise sources at most operating conditions, featuring broadband and tonal contents. Tone noise is typically caused by the periodic interaction between the fan wakes and the outlet-guide-vanes (OGV). Additionally, a fraction of the wakes enter the primary flow. These impinge on the inlet-guide-vanes (IGV), leading as well to sound generation. Nevertheless, this noise mechanism is usually neglected due to the smaller size of the IGV compared to the OGV. This study numerically assesses the contribution of the IGV to the tone noise footprint on the ACAT1 test vehicle, a modern scaled-down fan, experimentally analysed in 2018 within the TurboNoiseBB project. The noise prediction methodology consists of the use of an extensively validated uRANS solver, chained to an acoustic post-processing to extract the acoustics. A vast number of simulations have been performed, at different operating points, and working lines, to provide a complete assessment of this phenomenon. For each operating condition, three configurations have been simulated: the complete assembly with the fan rotor, OGV and IGV, a configuration without IGV and a configuration without OGV. The noise footprints of those three computations have been compared to derive the contribution of the IGV. Surprisingly, the IGV lead to high noise levels and result in the dominant source of noise at most operating conditions, in the forward and rearward arcs. The strong hub secondary flows and an in-phase impact of the wakes on the IGV seem to be responsible for such an efficient noise radiation. These results cannot be compared with experimental data because the blade count of the OGV and the IGV of this test vehicle is the same, making it not possible to isolate the contribution of both components. Nonetheless, this work signals a potential risk of parasitic tone noise levels that could arise in current and future engines. There is a need for further research on this topic to confirm whether these conclusions are generalisable or not to real engines.
Scaling Overall Effectiveness in Low Temperature Experiments
Authors: Bryant Carol E. , Rutledge James L.
Published: September 2023

The design of film cooled engine components requires an understanding of the expected temperature distributions while in service, thus requiring accurate predictions through low-temperature testing. Overall effectiveness, ϕ, is the integrated indicator of overall cooling performance. An experiment to measure ϕ at low temperature requires appropriate scaling through careful selection of not only the coolant and freestream gases but also the model material itself. Matching ϕ requires that the experiment has matched values of the adiabatic effectiveness, Biot number, coolant warming factor, and ratio of external to internal heat transfer coefficient. Previous research has shown the requirements to match each of those four parameters individually. However, matching all those parameters simultaneously presents an over-constrained problem and no comprehensive recommendations exist for the practical experimentalist who wishes to conduct an appropriately scaled, low-temperature experiment truly suitable for determining ϕ. Four fluidic parameters are identified which in an experiment must be as close as possible to their values at engine conditions. A normalized root mean square difference (NRMSD) of the residuals of those parameters is proposed to quantify how well a proposed wind tunnel experiment is likely to yield engine relevant ϕ values. We show that this process may be used by any experimentalist to identify the appropriate fluids, conditions, and materials for a matched ϕ experiment. Several case studies were performed using computational fluid dynamics (CFD) to show the utility of this process. Of the common experimental techniques examined here, a matched Biot number experiment with 500 K freestream air and 250 K coolant appears to be particularly adept at simulating engine conditions, even better than experiments that make use of CO2 coolant.
GLDAN: Global and Local Domain Adaptation Network for Cross-Wind Turbine Fault Diagnosis
Authors: Peng Dandan , Desmet Wim , Gryllias Konstantinos
Published: September 2023

Operating under harsh conditions and exposed to fluctuating loads for extended periods, wind turbines experience a heightened vulnerability in their key components. Early fault detection is crucial to enhance the reliability of wind turbines, minimize downtime, and optimize power generation efficiency. Although deep learning techniques have been widely applied to fault diagnosis tasks, yielding remarkable performance, practical implementations frequently confront the obstacle of acquiring a substantial quantity of labeled data to train an effective deep learning model. Consequently, this paper introduces an unsupervised Global and Local Domain Adaptation Network (GLDAN) for fault diagnosis across wind turbines, enabling the model to efficiently transfer acquired knowledge to the target domain in the absence of labeled data. This feature makes GLDAN an appropriate solution for situations with limited labeled data availability. Employing adversarial training, GLDAN aligns global domain distributions, diminishing the overall discrepancy between source and target domains, and local domain distributions within a single fault category for both domains, capturing more intricate and specific fault features. The proposed approach is corroborated using actual wind farm data, and comprehensive experimental results demonstrate that GLDAN surpasses deep global domain adaptation methods in cross-wind turbine fault diagnosis, underlining its practical value in the field.
Computational Fluid Dynamics Analysis and Experimental Results for the Dynamic Performance of Two Long Smooth Surface Annular Seals Operating With a Liquid in Air Mixture
Authors: Yang Jing , Tran Dung L. , San Andrés Luis
Published: September 2023

Compressors in subsea oil and gas production must handle wet gases to reliably operate for extended periods of time. Annular clearance seals contribute to compressor performance and do affect system rotordynamic stability. Prior experimental work with two smooth surface, uniform clearance seals supplied with a light oil in air mixture and undergoing similar operating conditions produced direct stiffnesses (K) with distinct trends as the liquid content increased to 8% in volume. Both seals differ in length and diameter albeit having similar radial clearance. Other force coefficients for both seals, namely cross-coupled stiffness (k) and direct damping (C) increase as the inlet liquid volume fraction (LVF) grows. Rationale for the peculiar differences in centering stiffness (K) is missing. Hence, a computational fluid dynamics (CFD) model and its predictions, the thrust of this paper, unveil flow field details (pressure, velocity fields, and liquid content evolution) for the oil in air mixture. Besides the CFD model, an enhanced bulk-flow model (BFM) also predicts the seals’ leakage and dynamic force coefficients. Both models predict through flows agreeing well with the measured ones, the maximum difference is less than 16%. The BFM direct stiffness (K) does reproduce closely the experimental K whereas the direct damping coefficient (C) is up to ∼ 41% lower than the test result. The CFD model captures the variation trend of K vs. inlet LVF for the first seal, albeit its magnitude is thrice the experimental stiffness. The CFD C agrees well with the test data for both seals, the largest difference is less than 10%. In spite of the complexity of the CFD model, significant differences with the experimental results persist, in particular for K. When considering the seal inlet corner as round, the CFD model produces a significant reduction in K to better approach the test result for a seal supplied with air. Attention to the seal geometry is paramount to produce accurate predictions.
Comparison Between Gradient-Free and Gradient-Based Optimizations of the SRV2 Radial Compressor
Authors: Châtel Arnaud , Verstraete Tom
Published: September 2023

This paper investigates the potential multimodality of a radial compressor optimization problem by comparing gradient-free and gradient-based methods in terms of results and computational cost. The turbomachinery application consists in a multipoint optimization of the well-known SRV2 radial compressor. The objective of the optimization is to maximize the total-to-total efficiency of the compressor at peak efficiency while maintaining the operating range of the original impeller. The geometry of the compressor is parametrized using 44 design variables and the fluid domain is automatically discretized using a multi-block structured mesh. The evaluation of the aerodynamic performance is performed using a steady-state RANS CFD solver with the Spalart-Allmaras turbulence model. Gradients of the cost functions with respect to the design variables are, when needed, efficiently evaluated with a discrete adjoint solver.

Multimodality, i.e. the existence of multiple local optima within the design space, is currently widely debated and plays an important role in the selection of the optimization method. The present study shows that both optimization algorithms converge to the same solution which seems to suggest that the design space is unimodal for the considered optimization problem.
Investigation of Fuel and Load Flexibility of an Atmospheric Single Nozzle Jet-Stabilized FLOX® Combustor With Hydrogen/Methane-Air Mixtures
Authors: Petry Niklas , Mannazhi Manu , Yin Zhiyao , Lammel Oliver , Geigle Klaus Peter , Huber Andreas
Published: September 2023

In this work, an existing single nozzle FLOX® [1] burner was modified with a fuel nozzle that was installed concentrically inside the outer air nozzle and was arranged in two different configurations. In the first, non-premixed case, the fuel and air nozzles were flush at the nozzle exit. In the second, technically premixed case, the fuel nozzle terminated 50 mm below the air nozzle exit. A third, fully premixed case was also achieved by injecting fuel into the air delivery line via an inline-mixer upstream of the nozzle exit. Additionally, measurements were performed using fuel nozzles with two different sizes. For all these cases, hydrogen volume fraction in the fuel was varied from 0 to 100 % at a constant equivalence ratio and thermal power. The resulting flames were characterized using 2D OH-chemiluminescence measurements. In addition, load-flexibility was investigated on the 100 vol.% H2 case by varying the equivalence ratio. Some selected conditions were further investigated using particle imaging velocimetry (PIV) to obtain velocity fields. The experimental results demonstrated a strong influence of nozzle configurations (mixedness), equivalence ratio and H2-content on flame shapes. First of all, increasing H2-content reduced the flame lift-off height above the nozzle exit for all three configurations. Secondly, for the cases with 100 vol.% H2 and independent of the nozzle configuration, the lift-off height increased drastically when Φ was reduced to below 0.3 while the flame became visibly unstable. Overall, increasing level of mixedness generally caused the flame to stabilize closer to the nozzle exit. A remarkable decrease in the lift-off height was observed for the technically premixed case compared to the non-premixed case. Increasing H2-content from 0 to 100 vol. % also increased the measured NOx emission by nearly a factor of 4, which was also strongly affected by the level of mixedness. Experimental results from this work are being used in a joint effort to validate numerical models for jet-stabilized hydrogen combustion.
Preliminary Design of Two-Phase Turbo-Expanders for Partial Evaporation Organic Rankine Cycle Power Systems
Authors: Tammone Carlotta , Parisi Simone , Haglind Fredrik
Published: September 2023

The partial evaporation organic Rankine cycle has been shown to be able to improve significantly the net power output of organic Rankine cycle power systems by expanding a fluid in two-phase conditions instead of a saturated or superheated vapor. However, the design of turbo-expanders for this application has not been undertaken yet, due to the complex fluid-dynamic modelling and the structural challenges posed by two-phase flows. This paper aims to provide a first insight into the preliminary design of two-phase axial turbines for partial evaporation organic Rankine cycle power systems by implementing two-phase flows features into a validated mean-line model for axial turbine design. The most important phenomena caused by the presence of a two-phase flow in the cascades are modelled based on the results from previous work conducted on wet steam turbines and on particulate flows in turbomachinery. The modelled phenomena include the deposition of droplets on the blades with the subsequent generation of a liquid film and the mixing between the bulk flow and the generated liquid film downstream the blade trailing edge. The effect of the presence on the two-phase flow on various losses is discussed in the work and the influence of the liquid film is investigated. The results suggest that the impact of the mixing loss on the designed geometries and their performance is significant. However, the decrease in efficiency is significantly mitigated by the reduction of droplets deposition. Therefore, the results from this paper will serve as a basis for future more fundamental research work on the deposition phenomenon and liquid film motion.
Experimental Analysis of Additive Manufactured Latticework Coupons
Authors: Castelli Niccolò , Sandri Umberto , Picchi Alessio , Facchini Bruno , Morante Francesco , Cubeda Simone
Published: September 2023

The capabilities and the precision of additive manufacturing processes have been tremendously increased in the last years, and this trend is not expected to be close to an end. Researchers, in the gas turbine industry, are focusing on the technology implementation on cooling systems. The aim of the present work is to investigate the performances of eight different geometries in order to exploit the cooling potential of some challenging latticework schemes with respect to traditional ones such as smooth channel, dimples and pin fins. Test coupons consisting of those cooling structures embedded inside a rectangular cooling channel with dimensions of 56mm width, 5mm height and 68mm length were fabricated by means of Direct Metal Laser Melting (DMLM) technique.

Since an aim of the present work is to evaluate the shape deformation associated with this additive process, the results of CT scan imaging technique are presented. The performances are characterized both in terms of averaged heat transfer and friction factor values inside the test coupons by means of steady-state technique with a constant wall temperature boundary condition. The investigated flow Reynolds numbers range from 18000 to 40000. These values allow the authors to provide a deeper understanding of the latticework structures performances at Reynolds numbers beyond the range typically investigated in the literature. An efficiency index is employed to compare the performances of each geometry. Although the obtained results reveal that none of the tested geometries outperforms the other ones, the latticework arrangements show a heat transfer enhancement with respect to a porosity decrease. In addition, the good capability in terms of heat transfer of the lattice structures measured in the present work suggests the use of such technologies for twofold optimization process based on mechanical resistance and heat transfer characteristics.
Advantages of Machine Learning Methods in Aerodynamic Blade Optimization
Authors: Beqiraj Klajdi , Perrone Andrea , Sanguineti Marco , Ricci Gianluca
Published: September 2023

The present paper describes the advantages of using Machine Learning methods within the aerodynamic optimization of blades, highlighting the benefits of such techniques in terms of both design time, and expected performance. The case study considered is the NASA Rotor 37.

The automatic parameterization of entire datasets through the use of variational autoencoders, a specific type of Neural Network, is explained and discussed. The autoencoder latent parameters describe the blade 3D geometry and can be used as an alternative to the standard geometric parameters in describing the shape of each sample. The main advantage is that autoencoders enable an automatic parameterization of 3D geometries, thus overcoming the limits imposed by manual parameterization.

The performance prediction (efficiency, pressure ratio) is carried out through a specifically developed Neural Network, properly trained.

The aerodynamic optimization is performed using a Genetic Algorithm: by acting on the latent parameters, the algorithm generates new optimized blades, automatically meshed, verified through CFD simulation, and added to the starting database, with a re-train of the artificial intelligence algorithms. This loop is carried out several times until efficiency is maximized.

Finally, a comparison with a classical optimization based on standard geometric parameters is reported and the results are deeply discussed and analyzed.
Advanced Modelling of Flow and Heat Transfer in Rotating Disc Cavities Using Open-Source CFD
Authors: Wang Ruonan , Gao Feng , Chew John W. , Marxen Olaf , Sun Zixiang
Published: September 2023

Code_Saturne, an open-source computational fluid dynamics (CFD) code, has been applied to a range of problems related to turbomachinery internal air systems. These include a closed rotor-stator disc cavity, a co-rotating disc cavity with radial outflow and a co-rotating disc cavity with axial throughflow. Unsteady Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES) are compared with experimental data and previous direct numerical simulation (DNS) and LES results. The results demonstrate Code_Saturne’s capabilities for predicting flow and heat transfer inside rotating disc cavities. The Boussinesq approximation was implemented into the code for modelling centrifugally buoyant flow and heat transfer in the rotating cavity with axial throughflow. This is validated using recent experimental data and CFD results. Good agreement is found between LES and RANS modelling in some cases, but for the axial throughflow cases, advantages of LES compared to URANS are significant for a high Reynolds number condition. The wall-modelled large eddy simulation (WMLES) method is recommended for balancing computational accuracy and cost in engineering applications.
Experimental Investigation of the Effect of Superheated Liquid Fuel Injection on the Combustion Characteristics of Lean Premixed Flames
Authors: Izadi Saeed , Zanger Jan , Baggio Martina , Seliger-Ost Hannah , Kutne Peter , Aigner Manfred
Published: September 2023

The effect of superheated liquid fuel injection on the performance and emissions of a single nozzle combustor was investigated. Combustion of the lean premixed flames was achieved using a combination of jet and swirl as a stabilization method. In a non-reactive setup, the optimum transition temperature of Jet A-1 fuel from liquid to superheated vaporized state was analyzed. In a subsequent reactive setup, a series of tests were conducted with the liquid fuel at low and elevated temperatures. The experiments were conducted at ambient pressure and various air and fuel preheat temperatures, axial swirlers, thermal powers, adiabatic flame temperatures, and flame tube diameters. Concentrations of nitric oxide (NOx) and carbon monoxide (CO) in the flue gas were measured. The operating conditions were systematically selected according to the Design of Experiments (DOE) method. The results showed that the adiabatic flame temperature caused the most significant change in combustion emissions and the position and shape of the reaction zone, while the superheated fuel injection had only a minor effect because the liquid fuel droplets were largely vaporized before entering the reaction zone through the integration of a swirler and a prefilmer. The use of the axial swirler and prefilmer allowed the combustor to operate in both spray and fully vaporized fuel conditions. As a result, very low emission concentrations of NOx (≈ 5 ppm) and CO (≈ 6 ppm) were achieved. The median flame length and height above the burner of the characterized flames showed competitive values of 32 and 50 mm, respectively. Lean blowout limits of less than 1500 K were achieved. Two different flame modes were observed during the experiments. By increasing the bulk velocity of the combustor, its hysteresis was resolved, resulting in stable and reliable flames with a wide low-NOx operating range.
Investigation on Process Architectures for High-Temperature Heat Pumps Based on a Reversed Brayton Cycle
Authors: Kabat Nancy , Jende Enrico , Nicke Eberhard , Stathopoulos Panagiotis
Published: September 2023

Heat pumps are a core technology for the decarbonization of industrial process heat. High-temperature heat pumps (HTHP) typically upgrade waste heat of industrial processes. This way they can simultaneously electrify process heat and reduce the respective primary energy consumption. The utilization of renewable electricity to drive HTHP additionally results in decarbonization of process heat supply. Commercial industrial heat pumps supply process heat at temperatures up to approximately 150°C. However, several studies have shown that process heat can be also supplied with HTHP at temperatures above 150°C. The economic and environmental performance of HTHPs depend strongly on their process architecture and their integration into the industrial process they supply with heat. This paper focuses on the investigation of high-temperature heat pump process architectures based on the reversed Brayton cycle with air as the working medium. The process architecture of the HTHP pilot plant at the Institute of Low-Carbon Industrial Processes of the German Aerospace Center (DLR) is presented and used as a reference. The current work investigates the heat source and heat sink integration in the heat pump cycle architecture and methods to effectively break down the compression and expansion processes to optimize performance for a heat sink temperature of 250°C. To analyze and compare the results, fixed boundary conditions valid for all architectures are made.
Optical Diagnostics for Aerospace and Turbomachinery Applications
Authors: Guimarães Bucalo Tamara , Ribarov Lubomir
Published: September 2023

Understanding the properties of complex reacting and non-reacting fluid flows is important for quantification and determination of parameters such as pressures, temperatures, velocities, and densities among many others. The use of conventional (intrusive) technologies, while sufficient in a limited way (and for simpler flows), may be overextended for more complex experimental flows (e.g., high-speed, high-temperature, etc.). The development and application of advanced non-intrusive (minimal/no-contact) optical diagnostics has offered the extended opportunities to successfully interrogate such complex flows. In this review paper, a broad consideration of some of the developed advanced optical diagnostics techniques is considered, including both seeded and unseeded methods. Applications to aerospace, combustion, and turbomachinery of the various optical diagnostics methods are discussed in an effort to summarize some of the advantages and challenges for each particular optical diagnostic method.
Study on Anti-Crossflows Characteristics of Jet Shape and Inclination in Multiple Jet Impingement Cooling
Authors: Hu Qingsong , Wang Yi , Yang Kefeng , Gao Shanghong , Wang Xiangyu , Feng Zhenping
Published: September 2023

Multiple jet impingement is one of the most efficient methods in the field of internal heat transfer enhancement. It provides a large heat transfer efficiency and a more uniform heat transfer distribution when cooling a large area of surface. This paper investigated the anti-crossflows characteristics of jet shape and inclination on multistage impingement channel. In order to reduce the adverse influence of upstream accumulative crossflow on downstream impingement heat transfer, two novel impingement jets, the Capsule and X-shape jets, were developed. On this basis, the flow and heat transfer characteristics of jet shape and inclination on multistage impingement channel were analyzed. The results indicated that with the development of the crossflow, the vortex and detached flow formed by the interaction of crossflow and impingement jet was a significant factor affecting the downstream impingement heat transfer. Once the intensity of the vortex developed to the point where it could pass through the downstream impingement core heat transfer region, the jet can no longer directly transfer heat with the target surface, resulting in the deterioration of downstream impingement heat transfer. The impingement jet hole with an inclination angle could offset the adverse influence of the crossflow on the downstream heat transfer and improve the heat transfer efficiency, due to the existence of the momentum component against the crossflow. Compared to the Circle and Capsule jet, the X-shape jet with jet inclination exhibits the best enhanced heat transfer performance and anti-crossflows characteristics. Considering the pressure drop and enhanced heat transfer effects comprehensively, the comprehensive performance of the X-shape jet with 0° inclination was the optimal, and its comprehensive heat transfer factor increased by 1.81% at a high Reynolds number compared with the reference case.
Multidisciplinary Assessment of Foreign Object Damage (FOD) Sensitive Regions on a Compressor Rotor Blade
Authors: Rocchi Simona , Roth Christian , Froebel Tobias , Hackenberg Hans-Peter , Gümmer Volker
Published: September 2023

During takeoff and landing, aero engines often ingest foreign objects which can damage the airfoils. These events can have a significant impact on the safety of the engine, particularly due to the operating load condition of gas turbines throughout their service life. In addition, the appearance of dents or cracks along the blade leads to surface damage, which in turn affects the structural mechanics integrity and the overall aerodynamic performance. In order to prevent safety concerns and high maintenance costs, blades with improved FOD robustness are being sought. In this prospect, the prediction of airfoil regions with high sensitivity to FOD plays a crucial role for later optimization. The aim of this work is to identify these areas, focusing on two aspects: the detection of airfoil regions with the highest probability of foreign object impact, and the evaluation of FOD critical areas through structural mechanics and aerodynamics evaluation. The first objective was achieved with the creation of a surface defect map obtained using a white light scanning technique. The structural mechanical investigation involved the numerical calculation of the stress concentration factor, which predicts the allowable stress increase caused by a local damage. From the aerodynamic perspective, the same assessment was carried out by placing a sample FOD at six positions along the airfoil edge. By comparing the compressor performance for the same damage at different heights, the most sensitive region was identified. Finally, the achieved multidisciplinary overview highlights potential regions to be optimized in future airfoil design in order to increase the overall robustness against FOD.
Condenser Retrofit in Leibstadt Nuclear Power Plant (BWR) - Far Beyond a Standard Modular Solution
Authors: Wolf Hartwig , Wettstein Arthur , Faltermeier Robert , Graf Peter , Schupp Daniel
Published: September 2023

The Leibstadt nuclear power plant (KKL) in Switzerland was originally commissioned in 1984 with a nominal power output of 1000 MWel. Since then, there have been several uprates of the boiling water reactor (BWR) which have increased the power to 1275 MWel.

After the nearly four decades of operation, the original condenser was impacted by advanced erosion corrosion and by progressive performance deterioration. In addition, the thermal power uprates required load reduction during hot summer periods to avoid high condenser back pressure.

Consequently, KKL asked GE to carry out a comprehensive retrofit study to identify potential improvements on both lifetime and performance. These included: robust material selection considering cycle chemistry and cobalt limitations; optimized extraction of non-condensable gases by means of a bespoke air cooler section of the condenser; and applying GE Steam Power’s latest innovative tube pattern design which is aligned to BWR requirements and simultaneously optimizes the condensation area together with the steam flow paths.

However, site constraints prevented the use of a typical modular condenser retrofit as both the local access in the machine house was very restricted and modifications of the concrete walls of the radiation shielding had to be avoided. Hence, working in a close cooperation between KKL and GE Steam Power, a customized retrofit concept was developed which used semi-prefabricated skeletal modules and an on-site rebuild of the condenser.

This paper provides details of the solution, particularly of the improvements which are specific to condensers operating in a BWR plant. Also described is the preparatory and complementary refurbishment work which was executed at the system interfaces. This includes replacement of strongly eroded condenser neck parts, an external reinforcement of the condenser walls, and modification of the continuous tube cleaning system. The construction site work itself is also described. This includes the required safety measures, the complex work logistics, the development of specific installation tools for handling and turning the skeletal modules, and the compliance with treatment rules for contaminated material.

In total, approximately 475 tons of old condenser material were dismantled, 24 new semi-prefabricated skeletal modules were installed, a condenser with 51’600 tubes was rebuilt on-site and 8 waterboxes were replaced with an improved design made of stainless steel. More than 350 professionals contributed to the successful retrofit with an overall site effort of 270’000 working hours — all without any major accident.

Key success factors for this retrofit have been the close and efficient cooperation between an experienced and knowledgeable customer with an OEM supplier bringing their expertise in engineering and construction during all project phases, and the very detailed planning and preparation phase.
Understanding the Effect of Three-Dimensional Design in Tandem Blade
Authors: Kumar Amit , Kumar Akshay , Chhugani Hitesh , More Shubhali , Pradeep A. M.
Published: September 2023

In order to maximize the pressure ratio and efficiency, compressor designers have tried several unconventional design approaches. Tandem blading is one such unconventional design that promises a higher-pressure ratio per stage through a higher diffusion factor. The nozzle shape created between the forward and aft blades of a tandem configuration acts as a passive boundary layer control mechanism. The boundary layer growth over the aft rotor is therefore effectively controlled with the help of this gap-nozzle flow. The flow complexity is likely to increase in the case of a tandem rotor due to the twin leakage vortices, twin wake regions, and their interaction with the hub and casing boundary layers. Modern compressor blades are often designed with three-dimensional blade techniques such as sweep, lean, dihedral, end bent, etc., to reduce the various losses and achieve optimum performance. However, to the best of the author’s knowledge, the effect of 3D blade designs on the performance of tandem rotors has not been fully explored so far. A comprehensive numerical investigation is undertaken to understand the effect of 3D designs on the performance of tandem blades. Axial sweep and dihedral failed to improve the performance of the tandem rotor. Significant improvement in the stall margin is observed for the forward chordwise-swept and negative lean tandem rotors and is largely attributed to lower tip incidence. The performance penalty of the forward-swept and negatively leaned cases can be reduced by integrating compound or variable lean and sweep into the design.
Investigations of the Unsteady Shock-Boundary Layer Interaction in a Transonic Compressor Cascade
Authors: Munoz Lopez Edwin J. , Hergt Alexander , Klinner Joachim , Grund Sebastian , Karboujian Jirair , Flamm Jasmin , Gümmer Volker
Published: September 2023

The performance of compressor blades in transonic flow conditions is heavily hampered by unsteady flow effects caused by the Shock-Boundary Layer Interaction (SBLI). Even though these effects have been subject to research for a long period of time, very little is still known about the physical mechanisms driving the unsteadiness. In order to help elucidate the nature of these interactions in turbomachines, the recently designed Transonic Cascade TEAMAero was tested at the DLR’s Transonic Cascade Wind Tunnel facility in Cologne. The cascade flow was measured with a unique high-speed Schlieren configuration capturing three adjacent passages simultaneously, along with unsteady total pressure measurements at the outlet, and unsteady acceleration measurements on the tunnel sidewalls. The results indicate that the main oscillation of the shocks is broadband at relatively low frequencies around 550 Hz for the aerodynamic design point, and 180 Hz for the off-design point. A further high-frequency tone is observed around 1140 Hz throughout. These frequencies were also observed with the different measurement devices employed. Cross-correlations between the signals indicate that there are different mechanisms at play between the passages that cause both upstream and downstream transmission of information. Because of this, the shock oscillations were not always in-phase between adjacent passages. The results help characterize the SBLI behavior of the cascade in the wind tunnel, aiding future numerical and experimental efforts aiming to decipher the inherent mechanisms causing it.
Integrally Bladed Rotor Modal Identification Under Traveling Wave Excitation With High Density Measurement Points
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L.
Published: September 2023

Vibration testing of an Integrally Bladed Rotor (IBR) is often completed through Traveling Wave Excitation (TWE) bench tests composed of multiple, simultaneously excited inputs. Often, each blade has many output locations. For IBRs with many blades, as often found in the high pressure compressor, the total number of outputs can be several orders of magnitude. Formulation of a full output spectral density matrix from all measurements will then contain an exponential number of values at each frequency bin that can be detrimental to computational resources during the spectral density matrix formulation as well as down-stream system identification algorithms. An online algorithm is proposed for collecting and analyzing TWE data to reduce the large, computationally burdensome data sets into a manageable number of subsets for subsequent system identification. Furthermore, a frequency domain decomposition technique is also proposed for system identification that also attempts to reduce the data size through singular value decomposition. Identified system poles can be averaged from each subset, but mode shapes require stitching each subset together to identify the full mode shape at all output locations. The developed approaches are tested on synthetic TWE data and compared to baseline system identification results obtained using the full spectral density matrix. Results indicate the data subsets accurately compare to the baseline without much loss in accuracy.
Predictions of the Wake of a Three-Bladed Wind Turbine Using Dynamic Mode Decomposition
Authors: Morales-Ramirez Carlos Mario , Benavides-Moran Aldo G.
Published: September 2023

The objective of this study is to develop a reduced order model (ROM) that accurately predicts the key features of the wake generated by a wind turbine, based on the results of a computational fluid dynamics (CFD) simulation with the actuator line model (ALM). The simulation of a three-bladed up-wind wind turbine was performed using Reynolds-averaged Navier-Stokes (RANS) equations and the finite volume method. The two-equation turbulence model K-ωSST was used to approximate the Reynolds stresses and the Actuator Line Method (ALM) was used to simulate the effect of the wind turbine rotor on the flow field, representing the rotor blades as a distribution of forces acting on the fluid. Data from the RANS simulation was collected to be used by the Dynamic Mode Decomposition (DMD) algorithm. Velocity field was defined as the object of study for the construction of the reduced order model (ROM). From the implementation of the DMD algorithm, the eigenvalues and energy content were obtained for the field of interest. From these results, the main modes and their spectrum were calculated. The velocity field reconstruction was performed using the DMD algorithm, and the RMSE was computed relative to the simulation and experimental data, yielding a good approximation. Due to the turbulence model used, very stable results were obtained in the reduced order model, showing great capability to predict the fields of interest in time.
Understanding the Role of Attractive Forces in Additively Manufactured Parts With Internal Particle Dampers
Authors: Kiracofe Daniel , Diaz Daniel , Postell Matthew , Celli Dino , Hollkamp John , Napper Lorean , Scott-Emuakpor Onome , George Tommy
Published: September 2023

Captured powder damping, creating a particle damper inside an additively manufactured part by leaving behind a pocket of unfused powder, is a technology that allows significant vibration reduction with no additional cost or weight. This is attractive for aerospace applications where weight is at a premium and high cycle fatigue issues are common. Previous work in this area has mostly been experimental, with some modeling, but the modeling has been primarily limited to a fixed excitation amplitude. Recent experimental work suggests the damping is strongly dependent on the excitation amplitude, with an order of magnitude change in quality factor possible as excitation is varied. Previous models of additively manufactured components with embedded internal particle dampers were unable to accurately capture this variation. This work advances beyond those models by incorporating attractive (van der Waals) forces. Upon introducing attractive forces into the model, the match with experiment is significantly improved. This is demonstrated on a real-world part (a wind tunnel rake) over three orders of magnitude of base excitation. This proves for the first time that particle dampers using fine powder can exhibit different behaviors than dampers using macro-sized particles (for which van der Waals forces are negligible). The improved model can be used to help optimize particle damper design for specific applications.
Modelling Ammonia-Hydrogen-Air Combustion and Emission Characteristics of a Generic Swirl Burner
Authors: Mazzotta Luca , D’Alessio Francesco , Meloni Roberto , Morris Steve , Goktepe Burak , Lamioni Rachele , Cerutti Matteo , Romano Christian , Galletti Chiara , Creta Francesco , Borello Domenico , Valera-Medina Agustin
Published: September 2023

Ammonia (NH3) is considered a valued alternative carbon-free fuel able to reduce greenhouse gas (GHG) emissions with respect to conventional fuel, therefore it has attracted the interest of gas turbine manufacturers over the last years. However, the use of ammonia in existing gas turbine combustors entails not yet resolved challenges: based on currently available studies, the simultaneous coexistence of high NOx emissions and poor flame stability is expected when typical lean premixed technologies are used. NOx containment strategies may lead to significant combustion architectural changes. The use of NH3/H2 blends is a valued way to improve the flame stability, even though in some cases it is obtained to the detriment of the emission performances. However, there is still a lack of knowledge and experimental data on the use of ammonia and hydrogen-ammonia blends under typical operating conditions of gas turbines. The combustion process of both pure NH3 and a NH3/H2 fuel blends is here analysed using two kinetics processors, i.e. CHEMKIN-PRO and CANTERA: detailed reaction mechanisms have been tested and compared in terms of laminar flame speed, ignition delay times and extinction strain rate with the aim to identifying the most suitable ones for the evaluation of NOx emissions. The generic swirl burner being used in Cardiff University’s Gas Turbine Research Centre has been considered as validation test case. Evaluations have been carried out by means of 2D axisymmetric RANS simulations leading to a significant reduction of the computational time. Different pressures and mass flow rates are evaluated to understand the correlation in the formation of NOx emissions for pollutants reduction purpose. A direct comparison between experimental and numerical results is carried out in terms of flow field, flame shape and NOx emissions. Results show that NOx emissions decrease significantly with increase in pressure, also indicating guidelines for using a simplified RANS analysis, which leads to improved computational efficiency, allowing wide sensitivity and optimisation analyses to support the design development of an industrial combustion system.
Asymptotic Evaluation of Nonlinear Friction Effects in Realistic LPT Rotors
Authors: Rodríguez-Blanco Salvador , González-Monge Javier , Martel Carlos
Published: September 2023

The study of the dynamical response of a bladed-disk usually requires finite element models with a very large number of degrees of freedom. In the case of the vibration produced by an external forcing, the dissipation associated with the nonlinear friction at the contact interfaces compensates the energy pumped into the structure and limits the growth of the vibration, producing a limit cycle oscillation. The small effect of nonlinear friction, which typically involves a very small subset of nodes, is therefore crucial for the calculation of the final response of the system. Friction laws are strongly nonlinear and can even show discontinuities, as a consequence, the equations of motion are numerically very stiff. On top of that, large integration times over many elastic cycles are typically needed to reach convergence. In the study of the forced response of a bladed-disk, this means that a quite significant computational effort goes into computing a single point of the resonance curve. Despite all these numerical difficulties, the resulting response is in most cases very similar to the one produced by a one dimensional nonlinear oscillator. In this work, we investigate the forced response of a realistic LPT rotor with 144 blades, and derive an asymptotically simplified model to directly capture this low dimensional dynamics. This asymptotic model is obtained using a multiple scales perturbation method, where the elastic time scale is filtered from the system, and only the evolution on the long time scale associated with the nonlinear friction is described. The resulting model consists of a single complex differential equation, and the computation of the resonance curve is reduced to just the evaluation of an analytical expression. The results of the asymptotic description show very good agreement with high fidelity time domain simulations of the full bladed-disk, and the computation times are reduced by several orders of magnitude.
Harmonic Response of Damped Fan Blades With Viscoelastic Patches Under Centrifugal Pre-Stress
Authors: Couet Matteo , Deü Jean-François , Rouleau Lucie , Thouverez Fabrice , Gruin Marion
Published: September 2023

Turboshaft engine fan blades are subject to high dynamic loads, particularly on new engine architectures such as Open Rotor. These loads can induce aeroelastic phenomena such as flutter or forced vibrations, which can lead to fatigue damage and potentially compromise the integrity of the engine. To reduce the fatigue stress experienced by these structures, external structural damping can be added to the blade with active or passive treatments. Constrained viscoelastic patches have been shown to be an effective passive damping treatment, relying on the energy dissipation capabilities of these materials while undergoing shear stresses.

In this paper, an in-house numerical model based on previous studies is developed to predict the dynamic behavior of a slender fan blade with a constrained viscoelastic patch. This numerical model is validated through a confrontation with experimental test data. A particular interest is given to the elastomer and its material non-linear behavior, which had not been previously studied. This allows a better quantification of the efficiency of the damping treatment under various operating conditions, such as rotation speed and temperature to permit future patch optimization.