bluuebunny/crossref_metadata_2025 huggingface dataset:
Possibilities of Applying Machine Learning Techniques for Probabilistic Analysis in a Turbine Blade-Disk Interface
Authors: Emmrich Elmira , Islam Md Tarekul , Voigt Matthias , Bruder Lukas , von Lautz Julian , Mailach Ronald
Published: August 2024

The design of the blade-disk interface in a jet engine is crucial, as the stresses on both disk and blade directly affect the engine’s service life and potentially lead to catastrophic failure. In particular, any variation in design parameters can have a significant impact on the life of the components. While finite element (FE) analysis is commonly used to analyze the effects of each variation on the geometry separately, surrogate models can be a much more efficient alternative to explore these effects and thus the design space, as long as they can describe the system behavior well.

This paper addresses the challenge of surrogate modeling a high-dimensional parameterized FE model of a turbine blade-disk interface using deep neural networks (DNNs) to describe the system behavior. Sampling methods as a part of Monte Carlo simulation (MCS), are used for training to evaluate the efficiency of using DNNs.

In applications such as FE analysis, where interactions between neighboring nodes are essential, DNNs are advantageous due to their ability to account for these interactions and to process a large amount of data simultaneously and for all nodes in an FE model, so that there is only one DNN model for the entire FE model. They can adapt to different mesh topologies, eliminating the need for topologically identical positions, unlike conventional approaches such as node-based least squares. This advantage of DNNs is demonstrated in this work by a comparative analysis of geometry variation due to manufacturing tolerances and its impact on stress values using an in-house probabilistic tool MetamodelGUI. With this tool, the FE results of an MCS can be visualized in a much easier and faster way and the components can be preliminary designed using surrogate models. In addition, the ability of using DNNs to perform sensitivity analyses is evaluated. Furthermore, the robustness of DNN models for describing the system behavior is discussed, as well as the feasibility of using this method for robust optimization and failure probability estimation.
Effusion Cooling Characteristics of Effusion-Cooled Combustor Liners With Different Hole Configurations Under Swirl Impact
Authors: Xiang Lu , Yuliang Jia , Yongbin Ji , Bing Ge , Shusheng Zang
Published: August 2024

The conjugate cooling characteristics of effusion-cooled n-shaped holes, were compared with the combustor widely used cooling air pressure drop (ΔPcool) ranging from 0.08% to 1.90%. All plates were covered by a thermal barrier coating. The cooling effectiveness distribution correlates closely to the swirl impact. In specific, there appear two low-effectiveness regions due to the swirl impact. The area of the regions for the cylindrical holes account for 37.52% to 13.77% of the plate as the cooling air pressure drop increases, and the fan-shaped and laidback fan-shaped holes have gradually smaller area. The lowest effectiveness for the cylindrical holes is 27.5% to 14.3% lower than the average, and for the fan-shaped and laidback fan-shaped holes the value increases, meaning greater disuniformity of cooling effectiveness. In terms of the cooling performance, the laidback fan-shaped holes are the best, 0.05 higher than the worst cylindrical holes in cooling effectiveness. The points that are lowest in cooling effectiveness, migrate along the center line of the regions forward as the pressure drop increases and downstream as the hole outlet expands since the increasing of outlet velocity of cooling holes is significant for the resistance of swirl impact.
An Aerodynamic Investigation of a High-Pressure Turbine Using Rotor Casing Static Pressure Measurements at Engine Representative Conditions With Different Tip Designs, Tip Gaps and Inlet Temperature Profiles
Authors: Singh Deepanshu , Beard Paul F. , Cardwell David , Staelens Vianney , Bahulekar Pratik , Stokes Mark , Bather Simon , Chana Kam S.
Published: August 2024

A rotating High-Pressure (HP) turbine, in modern aircraft engines, is subjected to high cyclic thermal and mechanical loads. Shroudless turbines experience high heat loads on the rotor tip and casing, which makes them one of the life-limiting components for an engine. If the rotor tip starts to erode, then the tip clearance increases which increases the over-tip leakage flow, resulting in reduced stage efficiency and ultimately, the engine lifetime. Since the 1970s, extensive research has been undertaken to understand the over-tip leakage flow, and develop mitigation strategies such as novel tip designs, to minimize the losses and heat load. However, the majority of the present findings are based on linear cascade or low-speed rotational studies, due to the high cost of the experiments and difficulty in instrumentation at engine conditions. Recent studies (mostly numerical) have shown the importance of testing at engine representative conditions, specifically targeting the transonic tip flow in a high-speed rotational environment, which is essential for an accurate understanding.

The Oxford Turbine Research Facility (OTRF) is a highspeed rotating transient test facility that allows unsteady aerodynamics and heat transfer measurements, at engine representative conditions. This paper presents an experimental investigation, of the HP turbine rotor casing aerodynamics, performed in the OTRF. Steady and unsteady casing static pressure measurements were acquired, using pneumatic lines and high-frequency response (∼100 kHz) Kulite pressure transducers respectively. The single-stage HP turbine consisted of cooled vanes (featuring film and trailing edge slot cooling), and uncooled rotor blades. Three different tip designs (two squealers and one flat) were tested, at two tip gaps, and with two inlet temperature profiles that included a spatially uniform total temperature profile and an engine representative HP turbine inlet total temperature profile. In parallel, a numerical investigation of the experimental test cases is presented using unsteady Computational Fluid Dynamics (CFD) predictions. The experimental results from this study provide a unique dataset to validate numerical models.
Advancing Airfoil Design: A Physics-Inspired Neural Network Model
Authors: Unlusoy Can , Maier Bill , Al Handawi Khalil , Varghese Mathew Tittu , Srinivasan Ravichandra , Salz Mathieu , Kokkolaras Michael
Published: August 2024

Turbomachines are an integral part of the energy and industrial landscapes, and improvements to their efficiency benefit the environment, profitability of operation, and in turn, society at large. Therefore, the application of advanced methods for rapid design and development of high-performance turbomachinery components is of significant interest. In the past decade, the use of optimization methods has made inroads in improving turbomachinery aerodynamics. Recent advances in machine learning (ML) methods have the potential to augment design systems by providing the ability to explore larger design spaces and generate high-quality initial designs. Physics Informed Neural Networks (PINNs), based on the Navier-Stokes equations, are used to incorporate physical laws into the design process. This approach leverages the power of deep learning while ensuring that the designs conform to fundamental principles of fluid dynamics. The use of Physics Informed Neural Networks (PINNs) not only accelerates the design process by reducing the need for extensive simulations but also improves the accuracy of the designs by ensuring physical consistency as opposed to designs made using Generative Artificial Intelligence (AI) models. However, combining PINNs with Generative AI for airfoil optimization could provide a fruitful avenue in improving compressor blade designs.
Heat Transfer Enhancement for Gas Turbine Blade Internal Cooling With Lattice Structured Rib
Authors: Kim Sangmin , Park Yong Gap , Yoon Sang Youl , Ha Man Yeong , Min June Kee
Published: August 2024

A higher turbine inlet temperature is crucial for enhancing efficiency in gas turbines. However, this increase can reduce the lifetime of turbine blades due to thermal deformation in the solid material. To address this challenge, this study numerically explores the use of lattice-structured ribs within the internal cooling channels of gas turbine blades to improve heat transfer performance. Conjugate heat transfer analysis evaluates the effectiveness of these ribs. The methodology’s accuracy was affirmed by comparing the results with those of a channel featuring fully-filled ribs under thermal performance factor tests. A constant temperature boundary condition was applied to the channel’s bottom wall in the middle section. The k-ω and SST turbulence models were utilized for their precise prediction of flow separation near wall regions. The results indicate that the flow through the lattice structure mixes with bypass flow downstream, significantly enhancing heat transfer compared to the fully-filled rib model. This enhancement is attributed to the combined effects of flow mixing and increased surface area.
Scaling Heat Transfer and Pressure Losses of Novel Additively Manufactured Rib Designs
Authors: Corbett Thomas M. , Thole Karen A.
Published: August 2024

Rib turbulators are a key cooling feature that enable increased heat transfer on the interior of gas turbine components. As metal additive manufacturing becomes available for developing turbine parts, it is becoming increasingly important to understand how the surface roughness intrinsic to this manufacturing method impacts the performance of rib turbulators. To explore what impact roughness has on rib turbulator performance, several relevant scale test coupons were manufactured on two different additive machines out of IN718. Additionally, several coupons were built at large scales to effectively reduce the relative roughness size impacts and determine scale effects. A range of different wavy broken rib designs, varying both rib wavelength and orientation within a channel were evaluated. Coupon geometry and surface roughness were characterized using both computed tomography scans and optical profilometry. Variations between the print methods were found to have limited impact on the surface roughness, but significant impact on the accuracy to meet the design intent with rib heights varying by 30%. Following characterization, coupons were flow tested and it was found that the ribs that more regularly disturbed the flow as a function of their geometry most significantly enhanced heat transfer and pressure drop. The performance index of the broken wavy ribs was similar to other advanced rib designs, such as broken or V shaped ribs, but augmentations to heat transfer and pressure drop were generally lower. The rib performance was compared as a function of relative roughness, and it was found that increases in relative roughness resulted in increased friction factor and heat transfer, especially at higher Reynolds numbers.
Numerical Investigation on a Baseline Shaped Film Cooling Hole: One- and Two-Dimensional Cooling Performance
Authors: Jin Yejia , Dong Xuezhi , Sun Wenchao , Tan Chunqing
Published: August 2024

A recently proposed baseline shaped film cooling hole is numerically investigated on a flat plate at four blowing ratios (M), 0.5, 1.0, 2.0 and 3.0 and two density ratios (DR), 1.2 and 1.5. Results show that there exists an optimal blowing ratio and a best coolant operating condition in the current simulation set. The cooling effectiveness shows insensitivity to changes in density ratio for the same blowing ratio no higher than 1.0. A high density ratio effectively compensates for the negative impacts brought by a higher blowing ratio coolant than the optimal. It is also summarised that a velocity ratio (VR) around 1 should be a division point where the coolant flow behaviour differentiates and thus decides the cooling performance characteristics. Specifically, this paper proposes the idea of the quantification of two-dimensional film cooling performance, through three additional parameters: area-averaged adiabatic cooling effectiveness, standard deviation of adiabatic cooling effectiveness distribution and a defined distortion factor measuring the uniformity of adiabatic cooling effectiveness distribution. Different conclusions concerning the optimal coolant operating condition are drawn based on whether these two-dimensional cooling performance parameters or the commonly employed one-dimensional parameters, centreline and lateral-averaged adiabatic cooling effectiveness, are applied for evaluation. When using one-dimensional parameters, the DR = 1.5 M = 2.0 case is the best coolant operating condition, while using the two-dimensional parameters, the optimal condition changes to DR = 1.5 M = 1.0 and the optimal blowing ratio also changes from 2.0 to 1.0. Besides, the DR = 1.2 M = 3.0 case becomes the worst cooling performance working condition instead of the two M = 0.5 cases. In addition, VR is found to better scale and predict area-averaged cooling effectiveness. Some new information on the uniformity and the variation level of cooling effectiveness distribution under various coolant operating conditions is also revealed. Visualisation of the flow field structures shows that the two-dimensional cooling performance is decided by the offsetting results of the negative and positive influences from the counter-rotating vortex development in lateral, spanwise and streamwise directions.
Flow and Heat Transfer in Rotating Compressor Cavities With Inverted Shroud-Throughflow Temperature Differences
Authors: Pernak Mikolaj J. , Nicholas Tom E. W. , Carnevale Mauro , Lock Gary D. , Tang Hui , Scobie James A.
Published: August 2024

In an aero-engine compressor, co-rotating discs form cavities that interact with an axial throughflow of secondary air at low radius. In the high-pressure (HP) compressor the shroud is hotter than the throughflow (directed downstream to the turbine) and the radial temperature gradient creates buoyancy-induced flow at Grashof numbers ∼ 1013. Such flows can be unstable and typically take the form of counter-rotating vortex pairs separated by radial hot and cold plumes. However, in low pressure (LP) and intermediate pressure (IP) compressors the secondary air is directed upstream. In this inverse scenario, the axial throughflow is hotter than the compressor discs, reversing the disc temperature gradient and eliminating the fundamental driver for buoyancy. Despite its practical application and importance, this inverse scenario has not been previously investigated. The University of Bath Compressor Cavity Rig has been uniquely designed to simulate such flows, measuring temperature and unsteady pressure in the frame of reference of the rotating discs. Bayesian and spectral analysis have determined the radial distribution of disc heat flux, as well as the asymmetry of the rotating vortex structures and their slip relative to the discs. Unexpectedly, the new data reveal the flow structure in cavities with positive and inverted temperature differences are fundamentally similar (albeit with reversed radial-temperature profiles). Isothermal cases identified a critical Rossby number (Ro), above which the flow structure in the cavity was dominated by a toroidal vortex. At sub-critical Ro, the flow structure for the inverted temperature gradient continued to be governed by buoyancy due to disc heat transfer. Momentum exchange with the axial throughflow and the gradient of circumferential pressure combine to vary the slip and vortex symmetry. This paper provides the first data and analysis of flow and heat transfer during inverse throughflow conditions in LP and IP compressors. The new insights are of importance for the determination of the thermal stresses in discs, engine life, compressor blade clearance and efficiency.
The Impact of Different Equilibrium Hypothesis on the Non-Linear Response of Bladed Disks
Authors: Zara Gianmarco , Berruti Teresa Maria , Zucca Stefano
Published: August 2024

Underplatform dampers (UPDs) are widely used in bladed disks to mitigate blades’ vibration amplitude. Such devices introduce localized nonlinearities, whose modelling requires nonlinear solution techniques. When the Harmonic Balance Method (HBM) is used to compute the nonlinear forced response of blades with UPDs, two different implementations are available: i) the uncoupled approach, where the static equilibrium is determined in advance and used as input to determine the dynamic equilibrium; ii) the coupled approach, where the static and dynamic equilibria are determined simultaneously. A common issue for both approaches is the variability in the static tangential contact forces, when the Coulomb friction model is used, that can result in multiple static equilibria and in multiple vibration levels. In this paper, the two approaches are used to determine the variability in the response levels of blades with UPDs and results are compared and discussed. Due to the large computation times associated with optimization algorithms implemented to compute the response limits, lumped parameter models are used, nevertheless the main findings of the paper can be considered general. In particular, results show that the coupled approach systematically overestimates the uncertainty with respect to the coupled approach and that UPDs geometry affects the range of variability of the response.
Development and Application of a High-Fidelity Numerical Tool for Dynamic Analysis of Bladed Disc Systems With Underplatform Dampers in Aircraft Engine Turbines
Authors: Tüfekci Mertol
Published: August 2024

This study presents VIBRANT: VIbration BehaviouR ANalysis Tool, a numerical tool developed for analysing the dynamic behaviour of complicated mechanical systems. The tool uses Python and Abaqus, employing time-marching algorithms to perform individual time domain simulations under harmonic excitation of certain frequencies until a steady state is reached to predict frequency domain behaviour. Hence, each monoharmonic excitation can be performed independently; the tool can parallelise the computations to shorten the computational time. This software enables the handling of various systems modelled by Abaqus, adeptly addressing numerous nonlinearities and conditions, expanding the capabilities of the software significantly. Properties of interest are measured for each frequency step of the simulation set. To validate and illustrate the capabilities of VIBRANT, two examples are presented. The first example is a beam with a dry friction contact element attached, and the second is a bladed disc system with underplatform dampers in aircraft engine turbines. Parametric studies evaluate the influence of the variation of parameters, such as excitation amplitudes and coefficient of friction, on the system’s dynamics. This research extends the scope of computational modelling in mechanical and aerospace engineering and provides a foundational tool that can be implemented to validate future aircraft engine designs.
Passage Secondary Flow Effects on Turbine Endwall Discrete Hole Film Cooling - A Review With Unique New Evidence
Authors: Chen Ting-Wei , Stinson Matthew , Simon Terrence
Published: August 2024

Film cooling effectiveness measurement results for gas turbine endwalls are discussed with emphasis on the effects that complex near-endwall flows in the passage have on them. The complexity comes from the secondary flows naturally occurring in a turbine passage. Important is their influence on coolant migration and film cooling effectiveness distributions downstream of coolant injection. Film cooling holes are typically distributed over the upstream portion of the endwall surface or over the entire surface in an attempt for full coverage.

Endwall surface wall shear fields documented in the literature and the hole pattern design establish the angle between the near-wall flow approaching a selected coolant hole and the axis of the corresponding hole. Often, shear field data are not available; also, downstream injection would affect the shear field. Thus, approach flow directions can accurately be applied to only the most upstream rows of holes (particularly, upstream of any coolant injection).

Measurements of coolant coverage with discrete hole injection show migration of coolant on the endwall as it is affected by the momentum of injection, the passage main flow direction, and the effects of vortices in the vicinity of each hole. The latter provide some evidence regarding the effect of vortices near the endwall on coolant migration, giving a valuable description of vortex effects.

Results from recent studies in the literature that show interactions of emerging coolant flows and nearby vortices are applied to develop a description of the effects of passage vortices and other secondary flows on endwall coolant migration. One example is the discrete hole located under a vortex residing near the passage entrance where ejected coolant is swept by the vortex away from the endwall resulting in low local values of surface effectiveness. This leaves the upstream pressure and suction surfaces difficult regions to provide coolant coverage by discrete hole injection.

Cases discussed herein have no or low injection upstream of the passage inlet. Studies with high levels of injection upstream of the inlet (high ratios of passage inlet momentum flow near the endwall to passage average momentum flow) are not discussed herein. Such cases would have strong injection along the endwall immediately upstream of the passage inlet and, thus, would have a different passage secondary flow pattern, not discussed herein. Such a pattern is discussed in [21] as the “impingement vortex.”
Deep Learning Based Crack Detection in Inhomogeneous X-Ray Images for High Pressure Turbine Blades in Aviation
Authors: Kuhlgatz Timo , Ihler Sontje , Bonhage Marius , Seel Thomas
Published: August 2024

To ensure safety in aviation, there are stringent requirements for aircraft components, not only in design and manufacturing but also their maintenance. For economic reasons, the maintenance process is intended to be as efficient as possible while still meeting required safety standards. The increase in automation level contributes to enhancing the economic efficiency of the maintenance process. A highly time-consuming step involves the manual assessment of X-ray images. Advances in deep learning algorithms suggest a promising prospect for employing these algorithms to automatically inspect X-ray images. This paper introduces a deep learning-based approach to enhance the level of automation in the inspection of X-ray images of high-pressure turbine blades by automatically detecting the presence of internal axial cracks. We encountered challenges posed by the heterogeneous X-ray images with very small and variable damage patterns, along with the issue of limited available data. To address these challenges, we applied damage mapping to define a region of interest and used the concept of transfer learning. Three different model architectures of deep neural networks (Resnet18, Inception-V3 and Densenet161) were compared, and it is demonstrated that all three are well-suited (average AUPRC > 0.95 and average F2-Score > 0.93) for our task. We are therefore able to help increase the degree of automation of the HPT blade X-rays’ inspection process and thus make the maintenance process more efficient.
Experimental Characterization of a Bladeless Air Compressor
Authors: Tiwari Ravi Nath , Reggio Federico , Ferrari Mario Luigi , De Paepe Ward , Traverso Alberto
Published: August 2024

The Tesla compressor is an innovative technology that offers a unique approach to fluid compression. Unlike traditional compressors that use rotating blades, bladeless compressors utilize closely spaced disks to create compression. The purpose of this article is to design a prototype Tesla air compressor with optimal design parameters and investigate the performance and loss characteristics based on numerical analysis and experimental demonstration. The prototype model has been numerically investigated at different rotational speeds and the results have been compared with those obtained in experiments. CFD simulations indicate that the rotor-only efficiency is greater than 90% at very low mass flow rates, while the coupling of the rotor and volute leads to a total-to-static efficiency of approximately 58 % (without losses) at 14 g/s. At a nominal mass flow of 4 g/s, the highest total to static pressure ratio would be around 1.27.

Experimental results indicate leakage losses greatly reduce net mass flow, while pressure ratio values are in good agreement with CFD predictions. During this experiment, a maximum isentropic efficiency of 32.4% is measured. Indeed, the prototype included ventilation and leakage losses, which were not modelled in the CFD analysis. It is remarkable that the compressor does not show any unstable behavior down to zero mass flow (closed valve test), where the CFD and the experiment show consistent pressure ratios. An estimation of the losses from end wall friction and leakage flow is carried out using numerical simulations at different exit radial clearances. Increasing radial clearance results in an increase in leakage and end wall power loss, the latter being driven mainly by the axial clearance with the casing, which remained unchanged. To minimize leakage, a Teflon ring has been used as a first measure. Numerical calculations have indicated that the leakage rate is approximately 6 g/s at design speed. A brush seal-type solution can improve the sealing system to reduce leakage.
Experimental Study on Friction Coefficient and Heat Transfer Characteristics of Elliptical Pin Fin Channel at Rotating State
Authors: Zhang Xuejiao , You Ruquan , Chen Wenbin , Li Haiwang
Published: August 2024

In this study, an elliptical pin-fins array is proposed to enhance the heat transfer coefficient (HTC) of turbine blade trailing edge channel. The friction coefficient (f) and HTC are obtained at the condition where inlet Reynolds number (Re) ranges from 10,000 to 70,000, rotation number (Ro) ranges from 0 to 1.0, temperature ratio (TR) ranges from 0.04 to 0.22, and Buoyancy number (Bo) ranges from 0 to 2.55. The streamlined design of the elliptical pin-fins allows the fluid to enter and pass through the channel more smoothly, thereby reducing flow disturbances at the inlet and minimizing the loss of heat transfer efficiency. Under low Re conditions, the pin-fins enhances fluid mixing, making the TR a significant factor affecting HTC. Under high Res, due to the complexity of fluid flow, the influence of the TR is relatively diminished. Similarly, under rotational conditions, the Coriolis force alters fluid flow direction and velocity distribution, increasing heat transfer intensity and making the impact of the TR more pronounced. The relationship between f and TR variation is not evident. The f is relatively small at lower Ro (0.1–0.3), then significantly increases as the Ro reaches 0.35. Subsequently, there is a slight fluctuation with the increase in Ro, exhibiting an overall trend of first decreasing and then increasing.
Centrifugal Compressor Preliminary Design Optimization for a Hydrogen Pipeline Compression Station
Authors: Jottrand Samuel , Hendrick Patrick
Published: August 2024

As the demand for hydrogen is expected to increase in the coming years, infrastructure requirements for the transport and storage of hydrogen should follow this trend to reduce its cost for users. For example, the European Hydrogen Backbone (EHB) represents a milestone toward a more accessible hydrogen network of pipelines. New compressors will be necessary to feed those pipelines, and for the volumes of hydrogen considered, only centrifugal compressors would be an adequate solution. But centrifugal compressors for hydrogen are a complex matter. Many technical issues are still under ongoing research, such as leakage through bearings and seals or materials problems due to hydrogen embrittlement.

This work introduces a method to optimize the preliminary design of a centrifugal compressor for hydrogen applications. This optimization is based on the variation of geometrical parameters of the impeller to minimize the energy required to power the compressor. This optimization can be applied for a steady state operation or for an unsteady set of operation. Furthermore, this optimization process of a centrifugal compressor stage extends to the optimization of multiple stages compressors, but also for the optimization of the arrangement in series and/or in parallel. This method is then applied to different case studies of a possible compression station pre-design for a hydrogen pipeline application. The compression station is tested under steady state conditions for a pressure ratio of 1.2 and a mass flow rate of 2.8 kg/s. Then it is tested on a transient flow, with variations of the mass flow rate of up to 10 percent.
Centrifugal Compressor Instrumentation for Developing an Anomaly Detection Method Using Vibration- and Acoustic Measurement Data
Authors: Linnemann Nick , Dolle Bastian , Brillert Dieter
Published: August 2024

In various industrial applications, acoustic measurement data is used for condition-based monitoring and predictive maintenance. These concepts enable the early detection of faulty machine behavior as well as the efficient planning of maintenance. Time-resolved measurements offer a promising approach for fault identification since every industrial process has a unique spectral fingerprint that allows for the differentiation between operating points as well as normal and faulty machine behavior. For this purpose, the acoustic reference state of the machine is determined and compared with measurement data obtained during operation to quantify the changes in the acoustic signal. In the field of turbomachinery, however, this method is not yet widely used due to the complexity of the process and the high overall noise level.

In this paper, a single-stage centrifugal compressor is equipped with high-frequency accelerometers and free-field microphones in addition to conventional process data instruments for anomaly detection. Time-resolved spectral evaluation methods and their advantages for gaining information about sequence of effects and distinguishing time-dependent phenomena are presented. Moreover, an approach for specifying a confidence interval to determine the degree of amplitude fluctuation in frequency domain between measurements is shown. In order to further verify the repeatability of the measurement result, the impact of material warming and compressor reassembly on the measurement data is examined statistically. Furthermore, a method for synchronizing time-resolved measurements in frequency domain is elaborated. Sensor positioning for optimal measurement results is discussed and the reference state with which future measurements will be compared with is determined using the above-mentioned techniques.
Assessment of Fatigue Interaction in Coated Superalloys
Authors: Moffat Andrew , Finley James M. , Alieninov Philipp , Meyer Christopher
Published: August 2024

Coatings are commonly used in industrial gas turbines to protect materials from oxidation when operating at high temperatures. However, coatings can be ignored when assessing the lives of critical components.

This study explores the influence of coatings on the fatigue lives of CMSX-4 single-crystal superalloy material via experiments and analysis. Experimental results show that coatings significantly reduce the fatigue life of the superalloy base material. Scanning electron microscopy of the failed specimens indicates that cracks initiate in the coating and propagate into the superalloy base material, leading to premature fracture.

Analysis results show that coating stresses are maximized at high temperatures and under compressive loading due to the dissimilar thermal expansion of the coating and the superalloy base material. Therefore, operation under these conditions leads to a higher likelihood of coating cracks. Analysis indicates notable stress concentrations occur in the base material in the region of coating cracks.

The Langer fatigue model is modified to consider the influence of coating cracks on fatigue life. The modified Langer model shows a general improvement in accuracy when predicting the fatigue lives of coated CMSX-4 material. These findings indicate that the influence of coatings should be considered when lifing critical gas turbine industrial components.
Influence of Dilution and Effusion Flows in Generating Variable Inlet Profiles for a High-Pressure Turbine
Authors: Schaeffer Chad B. , Barringer Michael D. , Lynch Stephen P. , Thole Karen A.
Published: August 2024

The elevated flow temperatures and pressures exiting gas turbine combustors affect the efficiency and durability of the high-pressure turbine stage. Understanding the effects that result from the upstream dilution and effusion flow interaction in creating the combustor exit profiles are important to advancing gas turbines. Understanding how common combustor features, such as dilution jets and effusion cooling, interact based on computational predictions guided the design of a non-reacting profile simulator capable of producing a wide range of non-uniform temperature profiles representative of those entering high-pressure turbines. The mechanical design of a new simulator device, which will be experimentally tested in the future, is presented in this paper along with computational predictions of flow and thermal fields. The simulator was designed for modular installation into the Steady Thermal Aero Research Turbine (START), which is a continuous-duration, steady-state turbine facility that houses a single-stage test turbine. Features of the simulator included interchangeable liner panels with multiple rows of dilution jets and wall effusion cooling to study various hole diameters and patterns. The dilution jets generate elevated turbulence intensities and tailor the temperature profiles in the radial and circumferential directions. The air mass flow distribution and source flow temperatures are independently controlled. To aid in the simulator design, computational fluid dynamics (CFD) simulations using Reynolds-averaged Navier Stokes modeling were conducted with a two-level Design of Experiments (DOE) approach to determine a number of engine-representative target profiles with temperature shapes that are mid-radius peaked, outer-diameter peaked, inner-diameter peaked, and uniform. A sensitivity analysis of the CFD DOE results determined which factors significantly affected the profile shape so that the target profiles could be produced. The analysis indicated the main contributor to the temperature profile shape at near-wall vane radial span locations of 0–15% and 85–100% was the injection temperature of the effusion flow. The main contributor at radial span locations of 15–40% and 60–85% was the injection temperature of the third-row dilution jets, and at the mid-radius location of 40–60% vane radial span, the main contributor was the diameter of the first-row dilution holes.
Teaching Aero-Engine Performance: From Analytics to Hands-on Exercises Using Gas Turbine Performance Software
Authors: Jeschke Peter , Koschel Wolfgang , Klumpp Christian , Weintraub Daniel
Published: August 2024

In this paper, we present an approach for teaching turbojet engine performance that combines mathematical analysis with the use of gas turbine performance software to provide students with a comprehensive and in-depth understanding of engine performance and how it is affected by design parameter choices.

In the first part, we present the derivation of a universally valid analytical model for turbojet engine cycle design, which is the basis of the aircraft propulsion courses at RWTH Aachen University. The analytical model allows for the calculation of specific thrust as well as thermal and propulsive efficiencies as a function of pressure ratios and burner exit temperature. These are all expressed as differentiable functions. Their mathematical extremes form a basis for examining the intricate relationships in turbojet engine design.

In the second part, we move from theory to practice. We utilize the GasTurb software for gas turbine performance analysis, computing turbojet engine cycles for a wide range of cycle design parameters, including pressure ratios and burner exit temperatures. The analytically derived trends are validated and errors introduced by simplifications are assessed. Differences between the analytical approach and software-based performance simulations of real engines, like temperature-dependent gas properties and secondary air systems, are emphasized and discussed, thus providing a bridge to real-world applications.

In summary, this paper describes a two-step approach to teaching turbojet engine design using analytics and gas turbine performance software. Each approach alone can be used to enrich and extend existing engine performance courses. Combining the approaches has significant benefits, improving understanding and inspiring students to pursue further research in the field of jet engines.
Temperature Field Measurements in Swirl Spray Flames Using Two-Line Planar Laser Induced Fluorescence Thermometry
Authors: Tao Chao , Zhang Chi , An Qiang , Xue Xin
Published: August 2024

This paper investigates the temperature fields in a centrally staged swirl spray combustor using two-line OH planar laser induced fluorescence (PLIF) thermometry at elevated inlet pressures and temperatures up to 0.62 MPa and 650 K. The pilot and main stages of the combustor were supplied with RP-3 kerosene. OH radicals were excited using the Q1(5) and Q1(14) transitions within the A2Σ←X2Π (1, 0) band. Two laser excitation systems were operated simultaneously, where the two beams were spatially combined and separated by a small interval in time. The PLIF signals excited at the two wavelengths were captured by two identical sets of imaging system. The calibration coefficient needed for quantitative conversion from fluorescence ratio to temperature was determined based on results from independent coherent anti-Stokes Raman scattering (CARS) measurements. To enhance the quality of instantaneous temperature fields, a joint threshold mask was developed to remove the noise and weak signals in the raw PLIF images. The high temperature zones in the temperature field were then obtained. In both instantaneous and mean temperature fields, the pilot and main stage flames were identified. In addition, the radial position of the pilot flame showed marked variations at a nominally fixed condition. By extracting the radial profiles, a consistency between the peaks of PLIF intensity and temperature was found, suggesting that PLIF images could be a qualitative substitute for the high temperature zones in the temperature fields of these complex swirl spray flames. This study demonstrates the feasibility of temperature field measurements using two-line OH PLIF in aero-engine model combustors.
Numerical Analysis of Jet Impingement Heat Transfer for Gas Turbine Rotor Blades
Authors: Pagnoni Filippo , Archambaud Damien , Gonzalez-Martino Ignacio , Bonnal Benoît
Published: August 2024

Jet impingement is widely adopted for turbine blade cooling due to the higher heat transfer rate compared to conventional forced convection solutions. Although RANS turbulence modeling is suitable for industrial scale applications, it lacks of accuracy when dealing with jet impingement heat transfer. The present study aims at comparing the aerodynamics and heat transfer of a leading edge cooling cavity for rotating turbine blade applications. The cooling cavity consists of a single array of jets impinging on a leading edge channel provided with three arrays of cooling holes. Different CFD approaches are proposed: RANS/URANS simulations and high-fidelity VLES simulations based on Lattice Boltzmann Methods (LBM). In all cases, commercial CFD solvers are used: ANSYS Fluent and SIMULIA PowerFLOW®, respectively. Despite similar averaged simulation results, substantial local differences emerge when comparing the different models against each other. With the LBM approach, the normalized Nusselt evolution is flattened with respect to RANS simulations. The latter provides higher amplitude fluctuations in both the radial and span-wise directions. The results indicate that unsteady approach is more reliable in capturing jet flow behavior within the cavity and heat transfer performance at the leading edge wall, under the effects of rotation.
Emissions Comparison of 100% SAF With Bio-Aromatics and Conventional (Fossil) Jet Fuel
Authors: Jarin Jean-Baptiste , Champion-Réaud Jean-Louis , Sallinen Reetu , Steenwinkel Edgar
Published: August 2024

It is recognized that Sustainable Aviation Fuels (SAF) will play a significant role in the decarbonization of air mobility and various pathways and feedstocks are considered for their production. This may lead to differences in chemical and physical properties when compared to conventional, fossil, aviation fuel (CAF). SAF available today are blended with CAF and after blending they are compliant with the Jet Fuel norm (ASTM1655). But the goal of achieving 100% SAF could be problematic, as the absence of aromatics, one of the characteristics of SAF produced today, could lead to leaks in the seal. Adding renewable aromatics (Synthesized Aromatic Kerosene, or SAK) to the SAF is therefore seen as an opportunity to reach 100% SAF without impacting the aircraft and airport’s fuel infrastructures, potentially enabling a faster decarbonization of the sector. In this study, we have compared the emissions of a 100% SAF which contains 9% of SAK issued from the biomass (SAF-SPK/A) with a CAF.

Performance and behavior: The tests did not identify any performance differences between the two fuels, including turbine reactivity and equipment degradation. This was later confirmed by Bell Helicopter during an experimental test flight campaign. Emissions: the lower CO2 impact is mainly due to the life cycle analysis of the SAF, but the test also showed reduced CO2 emissions during the combustion. While NO and NOx were found equivalent, significant reduction in CO and soot (Smoke Number, SN) were measured: −20 to −50% depending on the mass fuel flow. These improvements could be explained by the lower content of aromatics as well as the nature of these aromatics and this will be further investigated in future studies.
IndRNN-Based Data-Driven Modeling Integrated With Physical Knowledge for Engine Performance Monitoring
Authors: Xiao Dasheng , Xiao Hong , Wang Zhanxue
Published: August 2024

Monitoring the whole performance status of aircraft engines is of paramount importance for ensuring flight safety, control system and prognostic health management. This work introduced an aircraft engine deep learning model that integrated with engine physical knowledge. Firstly, component networks were established for each engine component (e.g., fan, turbine, nozzle) using the independently recurrent neural network (IndRNN), self-attention mechanism, and residual network. Subsequently, based on the physical spatial alignment of engine components, the data transfer between component networks was determined to establish the whole engine model. Case studies were conducted on exhaust gas temperature (EGT) prediction for two civil aircraft engines and thrust prediction for another two turbofan engines. When processing the actual engine running data, the data augmentation method was invested to address the issue of non-uniform distribution of engine working states in the training data. Compared with three pure data-driven models based on IndRNN, recurrent neural network and long short-term memory, the model introduced in this work demonstrated superior precision in both steady states and transient states. Specifically, the achieved mean absolute relative error (MARE) was 0.54% for EGT prediction and 0.41% for thrust prediction. When adjusting the time steps, the introduced model showed steadier predictions with minimal MARE fluctuation compared to the three pure data-driven models, enhancing overall predictive stability.
Numerical-Experimental Comparison of the Performance of a Mixed-Flow Fan Designed for Electric Vehicles
Authors: Aldi Nicola , Pinelli Michele , Piovan Mattia , Suman Alessio , Zanini Nicola , Mollica Enrico , Menichini Filippo
Published: August 2024

Due to the ecological-green transition, Battery Electric Vehicles (BEV) will replace the Internal Combustion Engine (ICE) ones, since they are less pollutant in terms of carbon and noise emissions. Inside a BEV one of the major sources of noise, especially during battery charging, is related to the cooling system, which is composed of one or two axial fans and the heat exchangers. This work aims to investigate the possibility of reducing the noise emission, and increasing the efficiency of the cooling system, using a mixed-flow fan rather than an axial-flow one. In fact, it can supply comparable performances when compared to an axial fan but with quite lower rotational speed, i.e. with lower noise and reduced friction losses. In the first phase of the present work, the mixed-flow fan has been designed with a design procedure based on the available literature, starting from the inputs received from the customer, i.e. geometrical constraints, pressure rise, and power consumption. After this preliminary design process, detailed CFD simulations have been performed in order to validate the assumptions made. Thereafter the initial fan geometry has been modified to take into account the manufacturability constraints, related to the plastic injection molding process, and the fan geometry has been optimized and finalized. Different numerical approaches have been investigated to evaluate the influence of the numerical setup on the results. Finally, the optimized geometry has been prototyped and tested in a standard airflow test bench in order to assess the real performance of the mixed-flow fan and to identify the most suitable numerical approach that should be used to simulate this kind of turbomachine.
Flutter Parameter Study on a Complex Inlet Swirl Distortion Generator
Authors: Hefner Cole , Guillot Stephen , Gillespie John , Hayden Andrew , Lowe Todd , Untaroiu Alexandrina
Published: August 2024

StreamVane devices consist of a custom designed complex vane pack that is used to produce inlet swirl distortion for fan tests, compressor tests, and ground testing of jet engines. Due to being placed upstream of these expensive test rigs, their structural integrity is very important. Since very little research has been conducted on flutter of complex vane packs like StreamVanes, this work focused on examining flutter of one of these models in more detail as well as studying the effects of various parameters on the critical flutter speed and frequency of these devices. For this study, a quad swirl StreamVane that was previously experimentally found to flutter was further analyzed using unsteady CFD with periodic mesh deformation based off the mode shape. This showed the flow in the passage between the fluttering vanes switching between a choked state and a subsonic state as the vanes moved together and apart from each other. This initial quad swirl model was then used as the basis for a series of small-scale flutter tests. These tests examined multiple parameters including chord length, vane thickness, blockage effects, and turning angle variation. To further analyze any potential causes of the excitation, oil flow visualization was conducted and found to show some leading-edge separation and minor corner separation but no pattern to indicate these flow features are responsible for the unsteady loading driving flutter. The results in this paper provide insight into the flutter behavior of these complex vane packs.