bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of Deterministic and Stochastic Unsteadiness of Trailing Edge Cutback Film Cooling Flows
Authors: He Xiao , Montomoli Francesco , Michelassi Vittorio , Panizza Andrea , Pulga Leonardo 
Published: August 2024

Abstract
Trailing edge cutback film cooling flows are ubiquitous in small and medium gas turbines, but they are difficult to predict accurately due to the inherent deterministic and stochastic unsteadiness that controls the effectiveness of the cooling system. To help develop accurate closure models for such flows, the characteristics of both types of unsteadiness and their effects on the mean flows are analyzed in this research. Zonal detached eddy simulation (ZDES) is performed on a trailing edge cutback flow model, and the numerical results are validated against the measured data. Then, by using spectral proper orthogonal decomposition (SPOD) reconstruction, the original dataset is segregated into deterministic and stochastic unsteadiness. The characteristics of the stress tensor and the heat flux of each type of unsteadiness are analyzed in detail, and notable differences between the two unsteadiness are identified in terms of the stress tensor anisotropy and distribution of unsteady kinetic energy and heat flux. By propagating the unsteadiness through the Reynolds-Averaged Navier-Stokes (RANS) equations, the effect of different unsteadiness on the mean flow prediction is quantified. An accurate calculation of the total stress tensor reduces the prediction error in the velocity field by 79% and cooling effectiveness by 55%. An accurate prediction of the total heat flux vector reduces the prediction error in cooling effectiveness further by 37%. These findings provide valuable knowledge for the physical understanding, turbulence modeling and aerothermal design of cutback trailing edge flows.
Design and Simulation Model of a Direct Supply Cryogenic LH2 Fuel Aircraft System for Airborne Applications
Authors: Thilker Fynn , Tramposch Andreas , Giuliani Fabrice 
Published: August 2024

Abstract
The development of efficient and sustainable aircraft engine fuel systems has become one of the primary aspects in achieving the long-term goal of net-zero CO2 emissions from aviation by 2050. This involves not only the choice of the operating fuel but also its storage and processing conditions. Previous studies suggest that using liquid hydrogen (LH2) can offer longer endurance for air vehicles and an effective engine cooling due to its high specific heat value compared to high-pressure systems. This work is part of the LIQORNE (LIQuid hydrogen for airbORNE application) project, which investigates a hydrogen aircraft fuel system with a direct cryogenic LH2 supply. In this regard, a system model has been developed, focusing on continuously feeding LH2 into the engine and recovering redundant fuel and engine heat for gasification and hydrogen expansion improvement. This approach helps to control the risk of icing and boil-off in the system components and allows for a more lightweight and compact system. By implementing continuous fuel circulation and incorporating a flow control valve near the engine injection, it is realistic to verify and achieve shorter full-throttle response times. The potential of this architecture lies in its efficiency and flexibility, as it uses LH2 not only as a combustion fuel but also utilizes the redundant fuel for cooling, tank pressure control, and heating for optimal expansion before injection. To provide initial approximations of the system’s behavior, this paper describes a simulation model created with Simscape software for a small twin-engine medium-haul aircraft. This model focuses on component dimensions, including tank, pipes, and pump in terms of their thermodynamic behavior. The fuel properties are based on the thermophysical database CoolProp, enabling accurate calculations of phase proportion, temperature, and pressure based on real gas parameters. Through validation against previous state-of-the-art studies, the model is expected to yield initial dimensions of the system volume. Consequently, a comparison of system weight between liquid and pressure-driven architectures can be conducted, along with an assessment of potential efficiency improvements. It will also verify the feasibility of boil-off regulation by the fuel system alone. Due to the parametric model design, various study cases can be applied to find the optimum operating point and adapt to different applications.
Transfer Functions for the Inverse Design of Turbomachinery for Thermal Power Storage
Authors: Folkers Steffen , Schuster Sebastian , Brillert Dieter 
Published: August 2024

Abstract
This paper is part of a priority program developing inverse design methods for thermal power storage. Turbomachinery for use in thermal power storage face specific challenges. These lay in the unconventional working fluids employed and the operating conditions of the machines. This paper discusses the inverse design of turbomachines using an approach that combines optimized aerodynamic design with its feasibility in transfer functions. The transfer functions consider the aerodynamic design by means of the Cordier diagram. It provides correlations between several basic parameters necessary for the preliminary design and can thus be used as a basis for transfer functions. To ensure the feasibility of the design the mechanical stability of the rotor and the flow stability inside the flow path are implemented as limits on the design. A set of additional design constraints are included to simplify the design process in order to enable the automated method. A selection method is applied to select the most optimal machine applicable. This way a machine can be designed for any given problem without further assumptions or other input by the designer. The machines designed by this method are analyzed through variation of the input parameters. The most important parameter has been shown to be the specific work on the working fluid. The speed of sound of the fluid was shown to possess a limited impact on the design while the volume flow through the machine showed no impact.
Experimental and Numerical Study of Thermoacoustic Instability Characteristics and Mechanisms of Swirling Flame With Outer Flame
Authors: Qi Yuanhong , Hu Bin , Shi Qiang , Ren Sanqun , Zhao Wei , Zhao Qingjun 
Published: August 2024

Abstract
Previous research has identified that a stable outer flame existing in swirling flame can enhance the flameout characteristics of swirl combustion. However, it may exhibit thermoacoustic instability under low equivalence ratio conditions. In this study, the combustion instability characteristics of swirling flame with outer flame under different operating conditions were investigated. The sound pressure was captured by microphone, and the OH* chemiluminescence was acquired at 10 kHz simultaneously. The results indicate that the amplitude of pressure pulsation induced by combustion instability undergoes a process of formation, development, weakening and disappearance starting from higher equivalence ratio until flameout. The instability frequency increases linearly from 560 Hz to 720 Hz as the airflow rate increases, and then gradually converges until the flow rate is sufficiently high. Subsequently, Reynolds stress model (RSM) and Flamelet Generated Manifold (FGM) combustion model were employed to conduct unsteady RANS simulation for an unstable condition. The flame pattern captured by simulation is generally consistent with OH-PLIF observations. By examining the flow field structure, it was observed that the air separated when it left the inner and outer swirl nozzles — a phenomenon not previously reported in other studies — suggesting its potential as a novel approach for studying swirling combustion dynamics. Furthermore, pressure spectrum characteristics obtained from simulation results exhibit similarities to experimental findings. The physical field of a single pressure pulsation period was investigated. It is founded that the pressure pulsation in the combustion chamber causes the fuel passage periodically releases fuel pellets into the combustion chamber, which resulting in variations in heat release. Dual spiral vortex and PVC in the inner swirl nozzle were captured. The fuel pellet reacts violently in the downstream of the flame under the enrolling action of large-scale coherent structure and the transport effect of jet air. This feature is highly consistent with the spectral proper orthogonal decomposition (SPOD) mode derived from the chemiluminescence data.
SGT5-4000F Hydrogen Capability – High Pressure Combustion Rig Tests Part II
Authors: Blätte Lutz , Goeb Dominik , Gruhlke Pascal , Prade Bernd , Schildmacher Kai-Uwe , Streb Holger , Vogtmann Daniel 
Published: August 2024

Abstract
Gas turbines are expected to play a crucial role in stabilizing the grid as renewable energy sources continue to grow but remain volatile. The Siemens Energy SGT5-4000F heavy-duty gas turbine fleet, with over 360 units in operation and more than 23 million accumulated operating hours, is one of the largest in the world. Efforts are now focused on minimizing the carbon dioxide (CO2) footprint of both the existing fleet and new units with the goal of a carbon-neutral future. The transition from pure natural gas to mixtures of hydrogen and natural gas to reduce CO2 emissions is an initial step in this direction. High-pressure combustion rig tests were conducted at the Siemens Energy Clean Energy center to assess the feasibility of higher hydrogen content in the SGT5-4000F gas turbine. Forced flashback tests were performed to establish robust hydrogen combustion limits for real-world engine applications. A flashback stability map was derived based on the test data. Theoretical considerations led to the definition of potential operation regimes with different risks of flashback for the SGT5-4000F. Complementary ignition tests showed that reliable ignition at high H2 content is feasible if ignition conditions are carefully chosen to avoid flame stabilization in the pilot burner.
This paper summarizes the rig test results and defines the theoretical maximum hydrogen limitations of the SGT5-4000F combustion system. With the ability to operate at elevated H2 content, the SGT5-4000F can play a significant role in reducing the CO2 footprint of the energy sector.
Hydrogen Fueling and GT Demand Changes Impact Insights Through Modeling
Authors: Harper James , Pezzini Paolo , Hubel Moritz 
Published: August 2024

Abstract
Gas Turbine fleet operation is likely to see significant change over the coming years. An increase fluctuating load demand due the increase in Variable Renewable Energy (VRE) and an increase in low carbon fuels usage such as hydrogen is possible for much of the fleet. A simulation study has been initiated based on the energy source and demand changes to which gas turbines will be subject. The impact of these changes is a function of policy, technology, capacity, and regulations. To evaluate these changes a gas turbine model which simulates the gas turbine major components, and the fuel delivery system is utilized. The fidelity of the model was determined based on a compromise between the need to model the thermodynamic and system design details which accurately simulate transient effects of supply and demand variations for the study purposes and minimizing computational demands of the model to enable fast simulation of multiple cases for evaluation. The model boundary conditions are varied to evaluate the impact of multiple scenarios in varying fuel supply and power demand to assess the system response, identify potential issues, and evaluate potential solutions to those issues. The model is used to predict the demand on and demands of the gas turbine and subsequently how those demands will result changes to the operation of the power plant. Issues that are tracked in the model include potential transients in combustion temperature, hydrogen blend, and load demand. Traditional control methods for meeting fuel supply, temperature, and power requirements are then compared to a model predictive control methodology. These results serve as a first step in analyzing the new operation that existing gas turbines may be subject, what issues may arise with nominal system control, and some potential solutions to those issues with system control updates.
New Fiber-Optic Measurement Method for Analysis of Unsteady and Wavy Liquid Film Thickness Under High-Speed Gas Flow
Authors: Iioka Daiki , Mizumi Shunsuke , Tabata Soichiro , Sanada Toshiyuki , Mizushima Yuki 
Published: August 2024

Abstract
The experimental analysis of liquid film flow driven by highspeed gas flow is a challenging task. It is difficult to measure due to its thin thickness of less than 500 microns and the presence of a complex wavy interface, including roll waves and 3D waves. Thickness information obtained through conventional methods has been measured and analyzed as average values. However, more than their temporal/spatial resolutions are needed to reveal the unsteady wave characteristics that require our attention. To address this limitation, we introduce a fiber-optic method, the Optical-fiber-based Reflective Probe (ORP), which excels at measuring these thin and temporally fluctuating thicknesses due to its impressively high sampling frequency, exceeding 1 MHz.
In this study, we first ensure the accuracy of ORP measurements for wavy film flows. We systematically evaluate the measurement precision of ORP across various curved interfaces through experimental and numerical methods.
Then, we provide a practical demonstration of the ORP. In this experiment, high-speed airflow is introduced into a rectangular test rig to create a liquid film flow by injecting tap water onto a channel plate. The liquid film is measured using high-speed cameras in conjunction with the ORP. According to this experiment, we will delve into a discussion of the time-series thickness of the liquid film, interfacial wave velocity, frequency properties in the flow.
Comparison of Ash Deposition Models in Gas Turbine Blade Rows for Alternative Solid Fuels With Low Ash Melting Temperatures
Authors: Wunder Luis , Bernhardt Daniel , Beckmann Michael 
Published: August 2024

Abstract
For a sustainable future, it is essential to prepare gas turbines for the use with biogenic residual and waste materials. One problem that needs to be solved when using these fuels is the problem of deposits, mainly due to their ash composition with low melting temperature. For this reason, the deposition behavior caused by the ashes of biogenic residual and waste materials must first be understood before suitable countermeasures are taken in the second step. At first, an exemplary fuel composition was created in this work. In the next step, a thermodynamic calculation typical for the utilization of these materials was carried out with this composition. As part of this work, physical processes that mainly lead to the deposition of fly ash particles were also discussed. Finally, typical adhesion models were listed in the literature and applied to the calculated particle composition. A viscosity and energy model was used to carry out the calculations. The results show a high influence of phosphor on the deposits. Overall, the calculated ash showed a uniform proportion of oxides, phosphates, sulphides, slag and salts. It could also be shown that salt condensation can have a significant influence.
Physics Guided Graph Neural Networks (PG-GNNs): Numerical Investigation of High-Pressure Turbine Flow
Authors: Li Zhihui , Montomoli Francesco 
Published: August 2024

Abstract
This work presents the first attempt to use Graph Neural Networks (GNNs) for high-pressure turbine vane flow, while enforcing physics conservation, which we called Physics Guided Graph Neural Networks (PG-GNNs). Compared to conventional neural networks, GNNs are more effective in handling irregular graphical data, such as in turbomachinery, where flow fields are often presented as data points on a mesh (graphical data). While GNNs are shown effective in many engineering areas, in turbomachinery there is a need for enhanced accuracy, and this requires additional physical constraints. For these reasons PG-GNNs are proposed, by enforcing Euler governing equations into the training process. The performance of PG-GNNs is then evaluated by solving both forward and inverse problems. In the forward problem, the PG-GNNs can accurately capture the turbine flow field based on some labelled data randomly distributed inside the turbine passage. As for the inverse problem where the boundary conditions are incomplete, PG-GNNs show obvious advantages over the traditional computational fluid dynamics (CFD) approaches in reconstructing the whole flow field by only utilizing partial flow information from either the velocity components or the near-wall pressure. The proposed approach provides a promising solution for prediction and analysis in advanced turbomachinery design and optimization.
LES Investigation of Film Cooling in Rotating Detonation Combustors
Authors: Ramanagar Sridhara Shreyas , Andreini Antonio , Polanka Marc D. , Bohon Myles D. 
Published: August 2024

Abstract
High-power density combustors like Rotating Detonation Combustors (RDC) offer significant benefits. However, they must overcome many challenges to be integrated into a gas turbine. Cooling the RDC is one of the most significant, due to the high heat loads generated by the combustion process. Preliminary analysis of the required cooling system has shown that cold-side convective cooling is insufficient to cool combustor walls unless a protective barrier is applied to the hot side surface. Therefore, this work explores the feasibility of film cooling a RDC. A high-fidelity LES investigation was employed due to the uniqueness of this problem. Namely, it was expected that the detonation wave and the downstream oblique shock wave would have a significant impact on the flow exiting cooling holes for this type of combustor.
This investigation represents the first attempt to integrate a full coverage film cooling scheme in a RDC. The reference RDC geometry is provided by TU Berlin. Three different coolant plenum pressures were simulated generating three different coolant mass flows in the post-detonation region. The results showed there is a period when each hole is effectively ‘blocked’, and coolant does not flow out of the hole. As the detonation wave passes, the film is able to recover and reform along the outer wall of the RDC. This process occurs at the detonation frequency of 7.5 kHz creating an unsteady, periodic flow behavior. Overall, the average gas temperature near the wall shows a significant reduction with the use of film cooling. These early results suggest that film cooling can be applied in an RDC flowfield.
Cavitation Measurements and Flow Visualization on a Hydrofoil With Different Tip Gaps
Authors: Deniz Sabri 
Published: August 2024

Abstract
Many types of hydraulic turbomachinery must often operate in the cavitating regime. Cavitation on the hydraulic turbomachinery can lead to unwanted effects such as noise, vibrations, turbomachine efficiency drop, and erosion on surfaces. As far as turbomachinery performance is concerned, the main research interest is focused on the flow over the runner blades, which can be evaluated as hydrofoils for an analysis. In spite of considerable research, there are still many features of the cavitation problem that have not been explored or understood, if especially the effects of the tip gap are considered.
This paper investigates the behavior of cavitation on a hydrofoil. A NACA0012 profile hydrofoil is investigated at incidence angles ranging from 0° through 8° and with varying cavitation numbers, σ, between 0.2 and 2.5. The Reynolds number defined with the chord length is 106. Flow visualization is carried out using a high-speed camera with recordings around the hydrofoil from the top and from one side. With flow visualization, the dynamics and spatial structures of the cavities are explored. The cavitation behavior around the hydrofoil is especially investigated for different tip gaps in order to determine the effect of the tip gap variation on the cavitation. With the pressure measurements for different tip gaps, the influence of the tip gap size change on the hydrofoil cavitation characteristics are determined for different cavitation numbers and angle of incidences. Using the flow visualization, the development of the tip leakage and tip separation vortices are also explored.
Design of a Centrifugal Compressor Family for High Temperature Heat Pump Applications Using Water (R-718) As Refrigerant
Authors: Parisi Simone , Weel Mogens , Haglind Fredrik , Elmegaard Brian 
Published: August 2024

Abstract
Development of high-temperature heat pumps to provide heat between 100 °C and 200 °C is considered a promising avenue for the decarbonization of industry, with water identified as one of the most promising refrigerant due to high performance, safety, and environmental compatibility. In this work a family of high-speed compressors for water vapor was developed, with the aim of providing a modular system covering the temperature range between 60 °C and 180 °C using five independent stages, each driven by a high-speed electric motor.
An elevated degree of part commonality was reached by constraining the design, using the same high speed electric motor, impeller diameter, and impeller back face shape for all the stages. This resulted in a range of flow coefficients between 0.010 and 0.187 at peripheral speeds up to 583 m/s.
In addition to traditional configurations employing a vaneless diffuser and volute, for the lowest flow coefficient stage a “diffuserless” configuration was tested.
After a preliminary design with mean line tools, an iterative design was performed using finite element modeling to evaluate the mechanical design, ensuring target stress, deformation, and first resonance mode frequency. The acceptable designs were then iteratively evaluated with computational fluid dynamics simulations, with the aim to maximize isentropic efficiency.
Despite the constraints due to part commonality requirements and high peripheral speed, isentropic efficiencies up to 80 % and in line with common practice are achieved for all but the highest flow coefficient stage. The diffuserless configuration shows a promising 3.6 % pt. increase in isentropic efficiency when compared to the traditional design with vaneless diffuser.