bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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

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

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

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.
Mass Mistuning Reduced Order Models for Bladed Disks With Shroud Friction Joints
Authors: Saletti Giacomo , Pourkiaee Mehrdad , Zucca Stefano
Published: August 2024

This paper introduces a new reduced order model (ROM) for nonlinear forced response analysis of mistuned bladed disks with localized contact nonlinearities. The developed technique is based on a Component Mode Synthesis (CMS) approach and introduces small frequency mistuning into the final ROM as deviations in the mass matrix. Critical to the development of CMS-based ROMs for mistuned systems, is the construction of a reduction basis that remains invariant to mistuning parameters, ensuring the ROM’s suitability for statistical analyses.

Traditionally, CMS-based reduction techniques for small mistuned systems fall into two major groups:

1. System-level approaches: in which mistuned system modeshapes are represented as a linear combination of tuned modes, typically overlooking mistuning impact on static constraint modes.

2. Component-level approaches: in which mistuning is confined to individual components (or superelements), preserving the independence of the reduction basis from mistuning patterns, typically overlooking mistuning impact on interface degrees-of-freedom (DOFs).

The proposed technique combines the strengths of both methods. It adopts a system-level approach, utilizing modeshapes of the fully stuck system within the reduction basis. Furthermore, it eliminates common assumptions on static constraint modes by incorporating mistuning effects directly into the mass matrix. As a result, the constraint modes employed in the reduction basis are precise and remain unaffected by mistuning, ensuring their invariance.

A comprehensive comparison between ROMs constructed using the new approach and the full model demonstrates the method strengths through modal and forced response analyses. The proposed approach presents a promising solution for accurate and efficient nonlinear dynamic analysis of mistuned bladed disk systems with shroud friction contacts.
Step-by-Step Evaluation of the Fuel Switch From Kerosene to Hydrogen on the Thermodynamic Cycle in Gas Turbine Engines
Authors: Görtz Alexander , Schneider Björn
Published: August 2024

Hydrogen combustion engines are one of the few possible ways forward to drastically reduce climate impact of aviation. While there is many information about the engine performance of hydrogen combustion engines it is not clear to which extend each property of the fuel switch effects the engines thermodynamic cycle and component behavior. The basic architecture is identical for both fuels but it is not known to which extend already existing and fully designed components can be used for the new application. In this work the basic differences between both fuels are presented using a thermodynamic model of simplified turbojet. The archived knowledge is applied to a reference turbo-fan for an application similar to an Airbus A320 while burning hydrogen.

Different effects occurring during the fuel switch, e.g. higher water loading after combustion and lower fuel mass flow, will be looked at separately. A retrofitted engine towards hydrogen combustion will use 1.5% less energy for the same thrust while operating at 60 K lower temperatures. The working line in the compressors will also switch towards higher mass flow rates despite the higher working fluid quality after combustion. Additionally, a new designed turbofan is presented on preliminary level for a constant fan diameter, to address the effects of different thrust requirements and has a 3.6% lower specific energy consumption.
Effects of a 3D-Printed Atomizer Component on Fuel-Spray and Flame Characteristics of a Jet-Stabilized Compact Gas Turbine Combustor Fed With Liquid Fuels
Authors: Kim Haisol , Pareja Jhon , Lammel Oliver
Published: August 2024

In this work, the effects of replacing an atomizer component of a confined jet-stabilized gas turbine combustor with a 3D-printed part have been studied. The part is called airblast, and it serves as a wall that collects and flows liquid droplets for a secondary atomization. Therefore, the liquid-surface interaction on the rough surface of the 3D-printed part was of interest.

The combustor was operated under various conditions with either a conventionally machined airblast or the 3D-printed airblast. Flames with two liquid fuels were studied for fuel flexibility, and the position of a primary fuel injection was varied to study the influence of the liquid-surface interaction length. Load flexibility was investigated with air jet velocity settings, and flame equivalence ratios of ϕ = 0.8 and 1.0 were tested.

Shadowgraphy-based particle tracking analyses presented a reduced atomization performance with the 3D-printed airblast, showing large droplet size distributions. However, no significant change in the combustor performance was observed from OH* chemiluminescence images and emission data, which confirms the versatility of the combustor and assures the compatibility of 3D-printed components with the combustor of this study.
Analysis of the Flow-Field Distortions Induced by Pneumatic Pressure Probes in Test Bench Experiments on Centrifugal Compressors: Are We Testing Right?
Authors: Baroni Alberto , Romani Luca , Balduzzi Francesco , Toni Lorenzo , Grimaldi Angelo , Belardini Elisabetta , Biliotti Davide , Bianchini Alessandro , Ferrara Giovanni
Published: August 2024

Experimental testing at the test rig still plays a key role in the development of new centrifugal compressor designs for industrial applications. Although a wide set of different probes is used as per common practice, the overall impact of the probes’ dimensions on the stage performance and rangeability is often assumed to be negligible. In this study, we aimed at quantifying the intrusiveness effects of pneumatic pressure probes on the flow-field inside a vaned diffuser using a model stage of an industrial centrifugal compressor, for which different experimental setups were tested at the University of Florence test rig. Performance and rangeability were initially assessed using a conventional set of pneumatic probes inserted in the flow path. Then, comparative analyses were realized through dedicated tests by either removing all probes at the diffuser inlet or introducing only a single pressure probe in the upstream section and varying its angular position in the measuring section. Experiments revealed an impact of upstream probes much higher than expected, with a decrease in efficiency and a substantial reduction of stall margin. Moving from this experimental evidence, accurate 3D CFD simulations of the entire stage were carried out including the actual geometry of the probes for two probes configurations and three operating points. Simulations highlighted the effect probes’ wakes on downstream vanes and the induced blockage effect, which both appear in line with experimental evidence. As a handout, a recommendation on the optimal probe positioning is suggested.
Numerical Investigation of Effusion Cooling Air Influence on the CO Emissions for a Single-Sector Aero-Engine Model Combustor
Authors: Recio Balmaseda Sandra , Karpowski Tim Jeremy Patrick , Nicolai Hendrik , Koob Philipp , Greifenstein Max , Dreizler Andreas , Hasse Christian
Published: August 2024

Stricter aviation emissions regulations have led to the desire for lean-premixed-vaporized combustors over rich-quench-lean burners. While this operation mode is beneficial for reducing NOx and particulate emissions, the interaction of the flame and hot exhaust gases with the cooling flow results in increased CO emissions. Predicting CO in computational fluid dynamics (CFD) simulations remains challenging. To assess current model performance under practically relevant conditions, Large-Eddy Simulation (LES) of a lab-scale effusion cooling test rig is performed. Flamelet-based manifolds, in combination with the Artificial Thickened Flame (ATF) approach, are utilized to model the Turbulence-Chemistry Interaction (TCI) in the test-rig with detailed chemical kinetics at reduced computational costs. Heat losses are considered via exhaust gas recirculation (EGR). Local transport effects in CO emissions are included through an additional transport equation. Additionally, a Conjugate Heat Transfer (CHT) simulation is performed for good estimations of the thermal boundary conditions. Extensive validation of this comprehensive model is conducted using the available experimental dataset for the studied configuration. Subsequently, model sensitivities for predicting CO are assessed, including the progress variable definition and the formulation of the CO source term in the corresponding transport equation. To investigate the flame thickening influence in the calculated CO, an ATF-postprocessing correction is further developed. Integrating multiple sophisticated pollutant submodels and evaluating their sensitivity offers insights for future investigations into modeling CO emissions in aero-engines and stationary gas turbines.
Development of a Reactor Network Model for a Practical Gas Turbine Combustor
Authors: Gubbi Srujan , Sun Wenting , Choi Nakjeong , Park Seik , Park Jungkeuk , Lee Sanghyup , Harper Jim , Steele Robert , Noble David
Published: August 2024

With a major drive for carbon-neutral energy sources, the viability of alternative fuels such as hydrogen and ammonia are being actively investigated. One idea currently being explored is to retrofit existing natural gas power generation technologies for use with these alternative fuels. Computational models that can replicate the behavior of these types of systems can be useful in optimizing operating conditions for this type of retrofit as well as providing guidance for updated designs. In this work, a reactor network model is developed for a practical gas turbine combustion system to simulate emissions data observed in detailed laboratory experiments with highly reduced computation time. Such work can enhance both the analytical models as well as assist in validating measurements in experiments. The design methodology of such a reactor network model for a gas turbine combustor is explored, as well as the effect of key parameters in simulations on the results. This includes the complexity of the model and the sensitivity of the results to any added details in modeling. Results show that possible air leakage and radiative effects can lead to discrepancy between simulation and measured values for turbine inlet temperature. NOx values and its ability to explain differences in simulation and experiments is discussed. The implemented chemical reactor network also shows areas for improvement such as more accurate geometric calculations and implementation of “recycling” to simulate recirculating gas. The sensitivity of the results to different chemical kinetics mechanisms is also shown, indicating room for possible improvements to chemical kinetics. The conversion of NO to NO2 and the usefulness of simulating this effect is also discussed.
Simultaneous Design Optimization of Binary CO2-Mixture-Based Power Cycles for Concentrated Solar Power Applications
Authors: Mutlu Balkan , Patchigolla Kumar , Thanganadar Dhinesh
Published: August 2024

This paper introduces a novel approach for optimizing binary CO2-mixture-based both condensing and non-condensing power cycles for high-temperature CSP applications, featuring a simple recuperative layout. It synchronously optimizes cycle design parameters, dopant selection, and working fluid composition. Scenarios investigated include two maximum cycle temperatures: 550°C for conventional solar power towers and 700°C for advanced systems, across three design dry bulb temperatures: 30°C, 35°C, and 40°C. Investigated dopants include SO2, C6F6, TiCl4, a non-organic dopant (NOD), and C2H3N. The multi-objective optimization focuses on thermal efficiency and specific work, while the suggested methodology allows for the expansion of the dopant list, to include any interesting dopant as long as their thermophysical properties are captured in 3D look-up tables using accurate Equation of State (EoS) and binary interaction parameters (BIP). Results show that including specific work as an optimization objective enhances cost effectiveness by minimizing power block costs, and helps to select optimized designs while retaining high efficiencies. Additionally, considering ΔT as an objective could further reduce potential thermal energy storage (TES) costs, increasing the cost competitiveness of CO2-mixture-based cycles to increase their chances in market entry.
Leakage Loss Reduction by Shroud Cavity Shape Improvement in Reaction Turbine
Authors: Sato Masahiro , Ndong Kazunobu , Taniguchi Hiroaki
Published: August 2024

In a steam turbine blade row, leakage flows through the radial clearance between the shroud at the tip of the blade and the sealing fins resulting in a reduction in efficiency, known as leakage loss.

During turbine operation, radial clearances are affected by various factors such as thermal deformation resulting in elongation difference between the rotor and casing, deflection due to the rotor’s weight, and changes in the state of the bearing oil film.

The design strategy commonly adopted to reduce the amount of leakage flow includes: reducing seal fin tip clearance, increasing the number of seal fins, etc...

All these countermeasures are implemented while satisfying the clearance under operating conditions.

Besides the leakage flow, another source of losses to be reduced is the difference in circumferential velocity component between the main flow leaving the moving blade passage, and the flow coming out of the shroud cavity of these same blades.

The focus in recent years has been on reducing this flow discrepancy, also called mixing loss. It should however be noted that the situation is different for reaction and impulse turbines. Generally, as the shroud cavity circumferential velocity after a stationary blade passage is slower than that after a nozzle passage, reducing the problematic velocity component coming out of the shroud cavity in a reaction turbine will not be as effective as it would be for an impulse turbine.

A final point to consider is manufacturability. Structures installed to correct the shroud cavity outflow in the axial direction often require non-axis-symmetrical geometries, hardly machined by just the use of a vertical lathe.

Considering the background above, the research presented in this paper focused on investigating the shroud cavity shape suitable for leakage flow reduction.

An improved shroud cavity shape was developed and the mechanism used by this new design to reduce leakage flow by using the generated counter vortex is discussed.
Topological Shape and Performance Optimisation of Microchannel Diffusion-Bonded Heat Exchangers Used in sCO2 Brayton Cycle
Authors: Vishwakarma Shubham Kumar , Srivastava Adhip , Kumar Pramod , Dutta Pradip , Somanath Nagendra
Published: August 2024

In recent years, Micro-Channel Heat Exchangers (MCHEs) have received significant interest in the context of energy systems and devices for supercritical carbon dioxide (sCO2) compact power blocks. The unprecedented ability of MCHEs to sustain extremities of both temperature and pressure makes them an ideal choice as recuperators/gas-cooler in a sCO2 Brayton cycle. The proposed approach uses a cylindrical-shaped heat exchanger with circular/non-circular channel holes that are topologically optimised. The channels are laser drilled into thin discs instead of electrochemically etched. The length is achieved by stacking and joining prepared discs with diffusion bonding. The MCHEs propose channels with different cross-sectional shapes and configurations defined in a cylindrical geometry as a novel alternative for conventional heat exchangers. The analysis focuses on enhancing heat transfer by arriving at suitable optimised forms and numbers of hot and cold channels based on the specified operating, manufacturing, and design constraints.

The numerical analysis uses a three-dimensional computational fluid dynamics (CFD) model, which accommodates the nonaxisymmetric behavior that arises in a global meshing system. The Navier Stokes (N-S) and energy equations are solved in cylindrical coordinates. The steady-state energy and momentum transport equations are discretised in a Finite Volume (FV) framework utilising a collocated grid. The approach provides flexibility to vary radial distribution of channels and the number of holes based on specified operating, manufacturing, and design constraints. The full-scale CFD model, which is an accurate method for performing property evolution studies, is computationally expensive. Hence, a parallel computing approach is adopted for a real, efficient, and versatile numerical model for evaluating the analyses and then performing optimization.

Enhancement in heat exchanger performance is achieved using an Elite Genetic Algorithm (EGA), resulting in an optimised heat exchanger geometry. The geometric parameters used to guide the EGA in generating multiple improved heat exchanger geometries, allow for design trade-offs along the Pareto front between heat exchanger efficiency and geometric location of channels. The current approach offers a promising method for optimising heat exchanger performance, resulting in nonintuitive designs that were previously unattainable. The process is demonstrated with an optimized design. The results predicted are validated using a commercial CFD solver. Test cases have shown a close agreement in temperature and velocity distributions.
The Unsteady Shock-Boundary Layer Interaction in a Compressor Cascade – Part 1: Measurements With Time-Resolved PIV
Authors: Klinner Joachim , Munoz Lopez Edwin J. , Hergt Alexander , Willert Chris
Published: August 2024

In the first part of this 3-paper-series time-resolved PIV is performed in the transonic cascade to elucidate the shock-boundary layer interaction process and to provide comparative data for numerical studies and analysis in part 2 and 3. The application of modern high-speed camera technology combined with a dual-pulse high-speed laser system enabled TR-PIV in the cascade for image areas covering ∼ 30% of the chord and ∼ 6% of the blade pitch, at fs = 20 kHz or 0.18tc for the acquisition of multiple time sequences with duration of ∼ 2000 tc. The sampling rate is sufficient to capture fluctuations of the separating region and accompanying movements of the shock system. To enable correlations of density variations of the shock system and velocity data, shadowgraphs are acquired synchronously with TR-PIV recordings at the same sampling rate. The TR-PIV and shadowgraph measurement setups, the image processing and the resulting spatial resolutions are described in this part. A analysis of power spectral densities along near-wall rows in PIV data reveals the chord-wise spatial distribution of specific peaks and bands, which are also visible in the shock buffet spectrum. A SPOD of TR-PIV data is conducted to enable inspection of spatio-temporal modes of velocity fluctuations at specific broad peaks and tones in the buffet frequency range. Results indicate, that upstream of the main shock oblique shock waves occur at higher order harmonics of the fundamental buffet frequency and at specific high-frequency tones. To locate possible sources of distinct tones at the entrance of the center passage, a SPOD of high-speed schlieren recordings is performed, capturing the shock systems in three passages. The results show that with these high-frequency tones opposing vibrations of bow and lip shocks occur for neighboring blades.
Development of a Virtual Chemistry Reaction Mechanism for H2/CH4 Turbulent Combustion Modelling
Authors: Castellani Simone , Andreini Antonio , Meloni Roberto
Published: August 2024

The identification of the combustion model is always guided by the compromise between accuracy and computational cost. While species transport models offer accuracy, their computational cost requirement can become prohibitive, especially when dealing with higher-order hydrocarbon fuels. To mitigate this, the virtual mechanism definition aims to optimise the predictivity minimizing the amount of information to be transported. Thereby the virtual mechanism leverages fictitious species and a few step reactions whose parameters calibration is performed with a genetic algorithm. This work outlines the procedure for the derivation of a virtual reaction mechanism for the study of lean H2/CH4 fuel mixtures with 60% of H2 content (by vol.). These conditions require an adequate characterization of the virtual species differential diffusion oriented to reconstruct the flame sensitivity towards the aerodynamic stretch. After the mechanism derivation, its predictivity has been validated on a swirl-stabilized perfectly premixed turbulent test case. The artificially thickened flame model has been adopted to allow the flame front discretization on an LES grid and to model the turbulence chemistry interaction. The numerical results show a very good agreement with the experimental optical measurements confirming the effectiveness of this approach for predicting the H2/CH4 blend.
Uncertainty Quantification Analysis on the Cooling Flow Rate of the Cooled Turbine in a Novel H2/O2 Cycle
Authors: Ma Bangyan , Shi Lei , Zhu Xiaocheng , Du Zhaohui
Published: August 2024

Using renewable energy, such as wind and solar, is one of the important ways to reduce carbon emissions. However, wind and solar energy have significant instability and uncontrollability. Hydrogen is a clean energy source and has great potential for development. In the future, hydrogen-fueled cycle will play an important role and is one of the main ways to achieve carbon neutrality. However, components in the cycle are affected by uncertainties. Therefore, the stochastic analysis is paramount in the design stage. In this work, a PCE method is employed to evaluate the variabilities in the coolant consumption and the isentropic efficiency of cooled turbines employed in a novel hydrogen-fueled cycle, considering the influence of the uncertainties in Stanton number empirical relationships and manufacturing errors. Sobol indices are utilized to denote the contribution of each input and to find the key parameter. The results showed that heat transfer at outer blade wall is the key factor which contributes about 85% to the total uncertainty in coolant consumption and isentropic efficiency. It was also discovered that the uncertainties in the coolant consumption and isentropic efficiency are higher for lower pressure cooled turbines.
Research on Effect of Endwall Contouring of Vane Diffuser on Stable Operating Range of Centrifugal Compressor
Authors: Cui Qin , Qin Guoliang , Lei Jian , Wang Yi , Jia Cheng
Published: August 2024

The present investigation seeks to comprehensively analyze the impact of diverse endwall contouring strategies on the operational stability of a singular high-pressure ratio centrifugal compressor stage. Employing numerical simulation techniques, this study systematically examines the implications of contoured wall positions, specifically convex profiles at the pressure side and/or concave profiles at the suction side, as well as asymmetric endwall contouring, on both performance metrics and internal flow dynamics within the centrifugal compressor stage. And the stability enhancement mechanism of endwall contouring is clarified. The results demonstrate that employing full circular contoured vaned diffusers on the hub-side wall can achieve a maximum improvement in stall margin of 15.10%. Additionally, the diffuser featuring solely convex profiles at the pressure side on the hub-side wall exhibits an augmented stall margin by 8.39%, coupled with a reduction in performance loss at low flow rate conditions. The application of an asymmetric endwall contouring scheme improves stall margin by 8.39%, and mitigates the performance loss across the entire operating range. At the near-stall point, the contoured endwalls redirect fluid towards the suction side, thereby mitigating the incidence at the vane leading edge and attenuating the interaction between the impeller trailing edge vortex and the diffuser leading edge vortex. Moreover, concave profiles at the suction side serve to accelerate the fluid on the suction side along the flow direction, thereby suppressing the corner separation to weaken the passage blockages. Simultaneously, contoured endwall increases the negative static pressure rise within the flow channel away from the volute tongue. The advantages of endwall contouring in vane diffusers extend to the improvement in the circumferential nonuniformity of flow fields and the enhancement in diffuser stability. Consequently, this research lays the foundation for optimizing the flow control method of endwall contouring on the centrifugal compressor.
On a New Cyclic Symmetry Formulation Accounting for Boundaries Undergoing Nonlinear Forces
Authors: Quaegebeur Samuel , Thouverez Fabrice
Published: August 2024

Although cyclic symmetry theory was initially developed for linear structures, the introduction of nonlinear forces on internal nodes of the fundamental sector does not affect the methodology. Nevertheless, the method is ill-suited when nonlinear forces are applied at the cyclic boundary. The purpose of this paper is to provide a complement to this theory and to propose a cyclic symmetry formulation for structures undergoing nonlinear forces at their cyclic boundary. A complete nonlinear cyclic formulation for such systems is derived in this work. The advantages of such an approach lies in the reduction of computational costs using the cyclic symmetry properties.

The methodology is employed to characterize the dynamics of several mechanical systems. First, it is validated on simplified models of a cyclic system. Two nonlinearities are considered: a one-dimensional friction contact interface and a cubic nonlinearity. Both cases exhibit very different dynamics behaviors, yet, the results obtained with the new strategy are shown to be very accurate. Once the approach is validated, it is employed on a industrial finite element model of turbine bladed disk featuring contact interfaces between the blades’ shrouds. The capability of the method to handle large systems is thus demonstrated. For all cases, periodic excitation are applied following either a traveling or standing wave shape for different engines orders.
Spectral Heat Transfer Coefficient for Thermal Design Analysis - Part 1: Augmenting Law of Cooling for Non-Isothermal Wall
Authors: He Li
Published: August 2024

There are two major issues of interest in relation to Newton’s law of cooling. The first is its applicability for flow bounded by a non-isothermal wall where the surface temperature is non-uniform. The second is the restriction by the basic linear assumption. In terms of the first question, a general Green’s function-based framework exists but its implementation as a working method for practical applications has been lacking, attributable to the inherent locality of Green’s function. Instead of setting up and solving the local-local influence and response, a new Spectral Heat Transfer Coefficients (SHTC) method takes a different avenue. It sets up and solves global-to-local temperature-heat flux influences for a small number of low order spectral modes of wall temperature disturbances in a range of physically relevant and numerically resolvable length scales. The present work is aimed at applying the SHTC methodology to turbine blade aerothermal analysis. Two aerothermal regimes are considered respectively. In the first part (Part 1 of the two-part article), the SHTC approach is described and case-studied for a linear regime where the flow energy equation behaves linearly and the corresponding temperature field is passively dictated by the velocity field. In the companion paper (Part 2), the methodology will be extended to a nonlinear aerothermal regime, where the temperature field will be actively interacting with (rather than passively influenced by) the velocity field.
Flame Characteristics of a Piloted Single-Nozzle Hydrogen Lean Direct Injection (LDI) Burner
Authors: Dere Rojhat , Ezenwajiaku Chinonso , Balachandran Ramanarayanan , Talibi Midhat
Published: August 2024

In line with the global drive to decarbonise energy systems, there is an urgent need to develop new dry low-NOx (DLN type) combustion concepts to enable efficient utilisation of alternative fuels, such as hydrogen. New combustor configurations require a detailed study of flame behaviour, including stabilisation, structure and dynamics, as well as other performance parameters such as combustor emissions.

In this work, a piloted single-nozzle lean direct injection (LDI) burner was investigated where hydrogen was injected into the main air stream in a jet-in-crossflow configuration. Hydrogen was injected relatively close to the combustor inlet to create a partially premixed mixture in order to avoid flashback. The main flame was surrounded by 12 circumferential premixed hydrogen-air pilot flames. The flame stabilisation and the dynamics of the main flame were studied in the presence of the pilot flames, taking into account the complex interactions between them. The bulk air velocity of the main flame was varied from 30 m/s to 90 m/s, while the equivalence ratio was varied from 0.2 to 0.6. Two pilot schemes were employed; P1 - the pilot flow rate was kept proportional to the air flow rate of the main flame, and P2 - the pilot flow rate was kept constant irrespective of main air flow rate conditions. The equivalence ratio of the pilot was kept stoichiometric for both schemes. Flame structure and dynamics were evaluated from OH* chemiluminescence measurements utilising both, a photomultiplier tube and a high-speed intensified imaging system.

The lean blow off limit was observed to increase from 0.1 to 0.13 as the bulk air velocity was increased from 30 m/s to 90 m/s. At all bulk air velocities tested, the amplitude of the acoustic pressure oscillations was the highest at ϕg = 0.4 and decreased on either side (for richer or leaner mixtures). The results also showed that for a fixed main bulk air velocity, the flame stabilisation was characterised by extinction and auto-ignition events at low equivalence ratios (around 0.2 to 0.3), while for higher equivalence ratios, lifted flames were observed. The flame root and flame tip positions, estimated from OH* chemiluminescence images, increased as the global equivalence ratio was changed from 0.15 to 0.4, beyond which the flame root position decreased slightly while the flame tip position remained more or less at the same value. The results from this work will help develop a detailed understanding of the flame behaviour in lean hydrogen flames and hence inform design efforts towards the development of new architectures for stable, low-emission 100% hydrogen combustors.
Aerodynamic Optimization of an Axial Turbine Blade and Diffuser
Authors: Dasadhikari Kingshuk , Kimura Yasunori , Kuwamura Yoshihiro , Isoda Hokuto , Hiratani Fumito
Published: August 2024

This paper presents a multi-component optimization approach for improving overall performance of the axial turbine blade and axial-radial diffuser of a marine turbocharger. Blade throat-to-pitch distribution and diffuser passage shape are concurrently optimized, exploiting coupling between blade exit flow and diffuser pressure recovery to boost overall efficiency.

Algorithmic approaches are used for shape generation of both blade and diffuser. For the blade, a spanwise twisting and re-staggering approach fixing turbine mass-flow is adopted. For the diffuser, a NURBS-based process allowing for non-axisymmetric passages is developed by visual programming. Steady RANS CFD is used for aerodynamic evaluation and optimization is performed by a parallelized hill climbing method for both axisymmetric and non-axisymmetric passages.

The best design from concurrent optimization with axisymmetric passage achieves overall efficiency improvement of +0.49% (abs) compared to the base case. This performance is 40% higher than the combination of best blade and diffuser optimized individually. The best concurrently optimized design consists of a blade with triple-peak, W-profile throat-to-pitch distribution with more uniform mid-span flow and accelerated tip-side flow and swirl combined with a diffuser with 14% higher passage area ratio and 9% higher pressure recovery without sacrificing separation margin. Over 70% of efficiency gain is due to the blade, far exceeding the effect of passage shape. This design also retains its performance improvement under overloaded operation, showing viability for actual use. Best design with non-axisymmetric passage achieves +0.04% (abs) further improvement but shows little difference in terms of flow mechanisms.

This result shows the utility of this approach in exploiting coupled mechanisms between turbomachinery components. In future, this approach could support existing part-by-part design methods with greater understanding of the influence of interdependencies between components on overall performance.