bluuebunny/crossref_metadata_2025 huggingface dataset:
Steam Turbine Casing Analyses to Determine Pressure and Temperature Limits – Crossover Piping and Pipe Flanges
Authors: Smith Paul T. , Schirato Jason , Neil Adam R. , Griffin Daniel J.
Published: September 2023

To ensure safe and reliable operation, steam turbine casings and piping must have acceptable stresses and maintain sealing when subjected to internal pressures and temperatures. Analysts conduct structural evaluations using finite element analysis (FEA) techniques to show acceptance. This paper outlines the analytical methods used to perform these types of analyses, provides analysis examples, and summarizes the process to create pressure and temperature limit maps.

Finite element models determine pipe loads and stresses from static structural analyses for normal operation and hydro test conditions, and transient analyses for heat-up and cool-down conditions. As part of the turbine model, the piping is evaluated for stress acceptability when subjected to internal steam pressure and temperature. The pipe flanges are reviewed for sealing capabilities and consider the effects of bolt stress relaxation at elevated temperatures, joint contact surface separation, and penetration of the internal pressure into the sealing surface.

A series of analyses on the pipe and pipe flange models we re used to create pressure and temperature limit maps. These maps allow an engineer to determine the acceptability of the piping for a particular application.
Investigating the Mixture Quality in Multi-Injector Burner Systems, Part II: Model Application
Authors: Marquez Macias Fabian , Hirsch Christoph , Sattelmayer Thomas , Huth Michael , Meisl Jürgen
Published: September 2023

Multi-injector burner systems offer a high spatial-temporal mixture homogeneity due to their small size and thus have a high NOx emission reduction potential at increasing flame temperatures. This potential is reduced due to the sensitivity of the mixing quality to inflow distortions caused by the flow path in the burner head. A deep understanding of the link between the inflow conditions and the mixture quality helps to optimize the flow field upstream of the injectors within the spatial and pressure loss constraints of gas turbine combustors to obtain minimal NOx emissions. This paper presents a new model approach for determining the mixture quality in multi-injector burners with output-based Proper Orthogonal Decomposition (O-POD). The sensitivity to the inflow distortion is considered with the so-called observable vector, which describes the injector inflow conditions and is given as model input. The target quantity is the Probability Mass Function (PMF) of the equivalence ratio at the injector outlet. This model allows a fast estimation of the mixing PMF for arbitrary inflow conditions, which is otherwise only accessible with complex time-resolved experimental or numerical approaches. The performance of the model was demonstrated with 21 reference datasets, for which a good agreement between the experimental results and the model output was obtained.
Numerical Investigation of the Flow Structure of Cryogenic Hydrogen in Corrugated Metal Flexhoses Due to Fluid Structure Interactions
Authors: Tran Patrick K. , Congiardo Jared F. , Fortier Craig R. , Fernandez Erik , Kapat Jayanta S.
Published: September 2023

In this paper, details of flow field characteristics and pressure drop of cryogenic hydrogen in corrugated metal flexhoses will be numerically evaluated using multiphase flow physics coupled with fluid structure interactions. Multiphase flow regime is often influenced by concentration ratio, shape factor, and orientation of the piping. Corrugated metal flexhoses are commonly used as part of cryogenic commodity transportation for their ability to operate in a large range of temperatures and pressures with a high degree of geometric flexibility. These sharp changes in the geometry of the flexhose convolutions are one of the leading factors of liquid and gas phase entrainment which can significantly reduce the efficiency of piping systems and fuel delivery systems to the engine components. The entrained gas phase hydrogen can eventually propagate in successive convolutes leading into the permanent entrapment of the gas phase hydrogen in the corrugations. The volume fraction up to 5% gas phase with various convolute heights and pitch will be evaluated, with a hose length to diameter ratio (L/D) range between 20 to 60 and a Reynolds number range between 5,000 to 350,000 based on the hose hydraulic diameter. The findings of the study contribute to a better understanding of multiphase flow physics of hydrogen in corrugated metal flexhoses.
A Comparison of Flow Path Designs for Axial Turbines Operating with Pure CO2 and CO2 Mixtures
Authors: Salah Salma I. , White Martin T. , Sayma Abdulnaser I.
Published: September 2023

Supercritical CO2 (sCO2) mixtures have been found to be promising for enhancing the performance of power cycles for concentrated solar power (CSP) applications, with up to a 6% enhancement in cycle efficiency compared to a simple recuperated CO2 cycle depending upon the mixture and cycle configuration chosen. Given that turbine efficiency significantly affects the overall plant performance, it is important to confirm whether turbines operating with CO2 mixtures can achieve the same efficiencies compared to pure CO2, whilst exploring whether the use of mixtures introduces any differences in the turbine design. This study aims to investigate the differences in turbine flow path designs produced for pure CO2 compared to CO2 mixtures, whilst taking into account aerodynamic, rotordynamic and mechanical design aspects, as assessed during the mean-line design process. The aim of this study extends to evaluating the effect of key turbine design variables, such as the loading coefficient, flow coefficient and degree of reaction, on the flow path design and overall aerodynamic performance. Multiple flow path designs have been produced for axial turbines operating with pure CO2 and mixtures of CO2 with titanium tetrachloride (TiCL4), hexafluorobenzene (C6F6) and sulphur dioxide (SO2) for installation in a 100 MWe CSP plant. It is found that turbines operating with either pure CO2 or CO2 mixtures result in overall total-to-total efficiencies in excess of 92.5%; where the highest turbine efficiency is achieved for the turbine operating with pure CO2, whilst this reduces by a maximum of 1.1 percentage points for the CO2/TiCL4 mixture. This reduction in efficiency is because the CO2/TiCL4 turbine is limited to a maximum of six design stages in order to meet the imposed mechanical design criteria, whilst the pure CO2 turbine can accommodate thirteen stages leading to higher aerodynamic efficiency. The difference between the two cases is the result of a higher mass-flow rate for the CO2/TiCL4 mixture (66% greater than for pure CO2), which results in high rotor bending stresses and limits the number of stages to comply with the design criteria. It is also found that designing the turbine at loading and flow coefficients of 0.8 and 0.6 respectively, whilst fixing the degree of reaction and pitch-to-chord ratio to values of 0.5 and 0.85 respectively, resulted in an efficiency enhancement of 0.2% with respect to a baseline design produced at loading and flow coefficients of 1.0 and 0.5. This increase is due to being able to increase the number of stages from eleven to fifteen. This indicates that there is not much benefit in modifying key design parameters to improve the turbine efficiency as the 0.2% efficiency enhancement is considered within the margin of accuracy of mean-line flow path design.
Effect of Heat Treatment on the Morphology of γ′ Precipitates in LW 4275 and LW 4280
Authors: Jena Ashutosh , Gontcharov Alexandre , Lowden Paul , Brochu Mathieu
Published: September 2023

This study investigates the microstructural evolution of the γ′ precipitates in precipitation hardened Ni-based superalloys LW 4275 and LW 4280 comprising 5.2–5.5 wt. % Al, fabricated by laser powder bed fusion. The as-built microstructure established the presence of discrete carbides, while no signs of γ′ precipitates were present in either LW 4275 or LW 4280 specimens due to a high cooling rate of ∼1e+6 °C/sec. Both specimens were heat treated under a sub-solvus temperature of 1080 °C and super-solvus temperature of 1150 °C, which was established by Thermo-Calc modeling, followed by aging at 705 °C for 24h. Scanning electron microscope (SEM) examinations of samples subjected to sub-solvus heat treatment revealed that the size and volume fraction of the primary γ′ increased while the size and volume fraction of the secondary γ′ decreased as the solutionization period increased from 4 to 24h. Studies of the samples subjected to the super-solvus heat treatment revealed that the volume fraction and size of the γ′ precipitates increased with the increasing solutionization time from 4 h to 24h for both alloys. Finally, a detailed investigation of the morphological evolution of γ′ precipitate after both types of heat treatments was addressed.
Oxidation Performance of Fe-Ni-Co-Cr-Mn High Entropy Alloy and its Al-Containing Variants in Supercritical CO2
Authors: Ilinich Margarita , Huang Xiao , Zanganeh Kourosh
Published: September 2023

In this study, a new material type, known as high entropy alloy (HEA), is being evaluated for use in supercritical CO2 (sCO2) Brayton power cycle. This cycle is a promising power generation technology that offers an increased efficiency and smaller footprint compared to the conventional Rankine steam cycle. However, the construction of components that operate in the high temperature and pressure regions of the cycle requires the use of expensive high-performance alloys such as Inconel 740H and Incoloy 800HT. As an alternative to these alloys, three compositions of HEAs are evaluated, namely, FeNiCoCrMn (HEA-1), FeNi1.5CoCrMnAl0.5 (HEA-2), FeNi1.5CoCrAl0.5 (HEA-3). The alloy samples were exposed to sCO2 at 700 °C, 20 MPa for 600 hours. They were then evaluated through weight measurements and characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). The results showed that HEA-3 outperformed the two other compositions. It experienced an impressively low mass gain of 0.04 mg/cm2, compared to 0.65mg/cm2 and 0.25 mg/cm2 for HEA-1 and HEA-2, respectively. The lack of Mn enabled HEA-3 to form protective Cr2O3 oxides, whereas the other two compositions formed porous oxides containing MnO and Mn3O4. Furthermore, the results showed that HEA-3 has the potential to outperform many conventional superalloys being evaluated for sCO2 applications. Additional test campaign has been planned to study the effects of prolonged exposure of HEA-3 to high temperature and pressure sCO2 environment to further assess its performance and to do initial benchmarking with respect to other Ni-based alloys.
Design of Aerodynamically Balanced Transonic Compressor Rotors
Authors: Lefas Demetrios , Miller Robert J.
Published: September 2023

This paper describes a simple and efficient physics-based method for designing optimal transonic multistage compressor rotors. The key to this novel method is that the spanwise variation of the parameter which controls the three-dimensional shock structure, the area ratio between the throat and the inlet, ‘Athroat /Ainlet’, is extracted directly from the 3D CFD. The spanwise distribution of the area ratio is then adjusted iteratively to balance the shock structure across the blade span. Because of this, the blade design will be called ‘aerodynamically balanced’. The new design method converges in a few iterations and is physically intuitive because it accounts for the real changes in the 3D area ratio that directly controls the shock structure. Specifically, changes in both the spanwise 3D flow and in the rotor’s operating condition; thus aiding designer understanding. To demonstrate this, two example design cases are shown in the paper. A transonic rotor within a multistage civil compressor with variable upstream stator vanes, and an embedded rotor within a multistage military fan. The method is shown to: (1) improve both the operating range and the design efficiency while retaining the compressor’s overall matching, and (2) allow a balanced design to be simultaneously achieved at multiple shaft speeds. The result is a method which simplifies the multistage transonic compressor rotor design process and therefore has great practical utility.
Influence of Rotor Blades on Convergent-Divergent Nozzle Aerodynamics and Overall Supersonic Turbine
Authors: Moroz Leonid , Burlaka Maksym , Yudin Aleksandr
Published: September 2023

Single-stage axial pressure compound and two-row velocity compound supersonic turbines have a very high specific work, which allows for high power levels at high-pressure ratios and small flow rates in a very compact dimensional envelope. However, despite their mechanical simplicity, the supersonic aerodynamic effects in these turbines are very complex. There are many design and analysis methodologies for these turbines, which are currently used in the industry. Nevertheless, several important parameters are still insufficiently investigated. In an earlier paper (GT2022-83387), the authors considered the influence of convergent-divergent nozzle arrangement parameters on aerodynamic losses and overall supersonic turbine performance, which partially closed the knowledge gap. However, the flow at the nozzle ring’s exit is influenced by the rotor blades, especially by the geometry of the blades leading edge; axial clearance between the nozzle and rotor cascades; and a combination of other nozzle arrangement parameters at different Mach numbers. This is not well studied and needs to be further investigated, which will be the focus of this paper.

This paper examines the qualitative and quantitative influence on aerodynamic losses of the rotor blade, such as the leading edge geometry; axial clearance; and meridional flow angle at the exit of convergent-divergent conical nozzles. The methods utilized to determine the influence of these parameters are provided and the results are discussed. An approach to incorporate the quantitative corrections of the nozzle loss models is presented and a comparison with experimental data is performed. The incorporated models allow for designing and analyzing the supersonic turbines considering more parameters enabling the opportunity to fine-tune the design to specific requirements with higher confidence and accuracy.
Choking Handling in a 1D Compressor Modelling Fully Integrated in Engine Performance Simulations
Authors: Ruiz Domingo Javier
Published: September 2023

For engine performance modeling, industry standard is using turbomachinery 0D maps. With this approach, compressors are modeled as a “black box” providing the output parameters as a function of the input parameters regardless of the number of stages.

These 0D maps are only valid at the reference conditions used to obtain the maps, which include : the variable geometry settings (IGV/VSV), clearances, blade untwist, Reynolds number, specific heat ratio, intermediate bleeds, etc. When the 0D map is used at off reference conditions, it has to be used with correction factors that take into account the change between the reference conditions of the map and the actual ones.

These correction factors are applied as a development of the compressor 0D map in Taylor series, where only the first perturbation term is kept. Therefore, there is no cross terms between effects, even if a compressor with several stages is likely to have cross terms of higher orders.

An alternative approach is to implement 1D compressor models in the engine performance cycle. However, the handling of choking conditions has precluded using this type of modeling. This paper provides an innovative approach for choking handling for multi row compressors without hampering the convergence of the engine performance cycle.

A mathematical set-up was developed; it allows dealing with choked rows while keeping the number of unknown variables to a minimum.

This mathematical scheme was tested with a research two stage compressor. Although more than one row could be choked at the same time, there was no convergence issues, and the 1D model was able to replicate the overall map.
On the Flow Physics During the Transition of a Variable Pitch Fan From Nominal Operation to Reverse Thrust Mode
Authors: Vitlaris Dimitrios , Rajendran David John , Pachidis Vassilios , Tunstall Richard , Whurr John
Published: September 2023

The flow field during the transition of a VPF from nominal operation to reverse thrust mode at typical ‘Approach Idle’ engine power setting and aircraft touchdown speed of 140 knots is described in this work. An integrated airframe-engine-VPF research model that features a future 40000lbf geared high bypass ratio engine installed on a twin-engine airframe in landing configuration is used to explore the flow field in a fully transient URANS simulation with imposed wall motion. A novel methodology that implements an adaptation of a mesh displacement equation to mimic the fan blade aerofoil rotation is developed. The implementation of this method with gradual, small step deformation along with an automated mesh update routine enables a high quality, near ‘real-time’ simulation of the complete transition.

The flow field during transition is characterised by the evolution from full typical forward flow through the engine to the development of massive recirculation regions at the feather pitch setting and finally to development of a reverse flow from the bypass nozzle to the fan passages. In the paper, the transient development of the various flow features through different stations of the engine flow path apropos the fan blade aerofoil rotation to reverse thrust mode are discussed in detail in the paper. Also, the temporal development of the mass flow ingested through the engine, airframe decelerating force and distorted flow at the core engine inlet are described. A hitherto unresolved fan power peaking during the middle of the transition and higher power requirement at reverse thrust mode is captured. The effect of fan rotational speed in terms of engine power setting and the aircraft touch down velocity on the transition flow physics is explored. A comparison of this fully transient approach with discrete steady state runs for different stagger angle settings is presented. The flow physics during transition to reverse thrust mode as described in this study is critical in understanding the feasibility of using VPF for reverse thrust in future aircraft. The new capability to study the transition in a fully transient simulation can be used as a design development aid to define design and control characteristics of the reverse thrust VPF.
Two-Phase Cryogenic Expander for Nitrogen Rejection and Cooling Process in Natural Gas Applications
Authors: Karakas Enver S. , Stasenko David
Published: September 2023

A typical refinery process of natural gas requires cyclic cooling (liquefaction) and vaporization of the fluid in stages to separate and remove certain impurities, primarily nitrogen, from the ‘raw’ gas.

Natural gas from underground sources often has nitrogen contamination due either to its natural occurrence or from previous nitrogen injection to enhance recovery of the natural gas. Nitrogen content must be limited or reduced by a nitrogen rejection process in order to meet the heating value requirement for the natural gas. This process is fundamentally a refrigeration cycle, within which the process pressure must be reduced; traditionally via a throttling process with a Joule-Thomson valve. Replacing the Joule-Thomson valve with a two-phase flashing expander can improve the overall efficiency of this refrigeration process with enhanced cooling, and electrical power co-generation.

This paper considers prior art, and reviews the current design considerations and technical challenges for a two-phase expander to be used in the Nitrogen Rejection process. Hydraulic and aerodynamic components of such two phase expanders are reviewed, and their operational characteristics are studied in this paper. Thermodynamic analyses of cooling and liquefaction processes are conducted to quantify the benefits of two phase expanders in terms of cooling, energy recovery and production rate. Site operational data and performance characteristics of an actual two-phase expander are reviewed to better understand two phase expansion within the expander.
Assessing Transfer Matrix Models and Measurements Using Acoustic Energy Conservation Principles
Authors: Latour Véranika , Rajendram Soundararajan Preethi , Durox Daniel , Renaud Antoine , Candel Sébastien
Published: September 2023

Acoustic transfer matrices are now widely used in the analysis of combustion dynamics of gas turbines. The reliability of the analysis depends on the quality of the determination of the transfer matrices of the individual acoustic elements composing the overall acoustic network of the system. These matrices are, in some simple cases, deduced analytically, using one-dimensional acoustic modeling. However, for more complex elements, such as swirlers, perforated plates or injector units, the transfer matrix has to be obtained experimentally using an impedance tube. A few models that attempt to account for the dynamics of some key elements like the injector unit are also available in the literature. There are, however, uncertainties in the experimental determination of the transfer matrix coefficients and questions raised by the modeling so that it is worth examining experimental results and assessing transfer matrix models using acoustic energy conservation principles. The general idea is to consider the acoustic power flow in the element represented by the transfer matrix T, and compare the power input to the power output. This is best accomplished by obtaining a representation in terms of a scattering matrix S, which may be deduced from the transfer matrix T. It is first shown that standard models like those corresponding to a constant area duct or to an area change comply with acoustic energy conservation. This analysis is then employed to assess the L-ζ model that has been widely used to describe injection unit dynamics. It is shown that acoustic power is dissipated in the injection element only if a certain condition is met by the modeled transfer matrix coefficient T12. The expression that is commonly used for this coefficient fulfills this condition. The power dissipation in the injector is evaluated and shown to be linked to the head loss and typical Mach number in this unit. Finally, acoustic conservation principles are used to assess transfer matrices of a family of injectors determined experimentally and check that the data is compatible with these principles.
Performance Evaluation of an Axial Compressor With Modified Blades Using Leading Edge Tubercles
Authors: Sidhu Satpreet S. , Asghar Asad , Allan William D. E.
Published: September 2023

The performance of a Rolls-Royce A250 gas turbine axial compressor was evaluated for four different compressor configurations employing a flow control device called leading-edge tubercles. The tubercle shape was selected based on optimization performed in a 2-D compressor cascade for the design conditions of a first stage compressor rotor blade. The A250 compressor was tested without flow control to establish its compressor map for baseline performance. Tubercle shape was manufactured onto the leading edge of each compressor blade using a technique called Sinker EDM. An operational axial compressor with tubercle-modified rotor and stator blades was tested. For the final configuration, a compressor with modified rotor blades only was tested. The fully modified compressor showed slight improvements in the pressure rise along with increased mass flow rate, with a slightly open bleed valve at the fifth stage. At high speeds, the modified compressor configurations were unable to improve performance over the baseline. However, subsequent analysis revealed encouraging affects on stability. High frequency pressure transducer results showed that in the baseline compressor, stall precursors appeared first at the first stage that then propagated downstream in the compressor. The modified compressor completely eliminated the presence of stall cell in the first stages. With flow control, the stall developed at the last stage before propagating upstream. The challenging blade modification method precluded careful finishing of tubercle edges. Degraded modified compressor performance is attributed to this. Leading-edge tubercles showed potential for their application on compressors, demonstrating slight performance improvement in some ranges of operation and the elimination of stall cells known to lead to complete compressor stall in the baseline compressor.
The Hybrid Pathway to Flexible Power Turbines: Part A, Novel Autoencoder Methods for the Automated Optimization of Thermal Probes and Fast Sparse Data Reconstruction, Enabling Real-Time Thermal Analysis
Authors: Baker Mark , Rosic Budimir
Published: September 2023

The global drive towards renewable energy is imposing challenging operating requirements on power turbines. Flexible load-leveling applications must accept more frequent and demanding start-stop cycles. Full transient analyses are too computationally expensive for real-time simulation across all operating regimes so monitoring relies on sparse physical measurements. Alone, these sparse data lack the fidelity for real-time prediction of a complex thermal field.

A new hybrid methodology is proposed, coupling data across a range of fidelities to bridge the limitations in the individual analyses. Combining several fidelity methods in parallel: low-order models, corrected by real-time physical measurements, are calibrated with high-fidelity simulations. The multi-faceted hybrid approach enables the real-time speed of low-order analysis at high resolution. This paper series develops the critical enabling features of the hybrid method.

Real-time cross-fidelity data transition is fundamental to the hybrid methodology. A novel neural network autoencoder method is presented, facilitating complex thermal profile reconstruction. Uncovering a compressed latent space, autoencoders leverage underlying data features for fast simulation. Coupled with a dynamic mask and top-k selection, thermal probe placement can be automatically optimized. The autoencoder method is demonstrated on a turbine casing, reconstructing over 500 hours of transient operation in real-time, whilst reducing the required number of measurements by half.
Numerical Study of the Effect of Fuel Heating Value Change on Combustion for Siemens Energy Dry Low Emission Combustor
Authors: McManus Liam , Sadasivuni Suresh , Liu Kexin , Munktell Erik
Published: September 2023

Reacting flow simulation with lower or medium calorific value fuels is a challenge with the existing combustion models and chemical mechanisms. This paper attempts for numerical validation on the effect of fuel heating value or Wobbe Index (WI) of fuel on combustion performance for an industrial gas turbine Dry Low Emissions (DLE) combustor which is an SGT-300 twin shaft system. The engine produces up to 9 MWe power which was rig tested in Lincoln at High Pressure Air Facility (HPAF) with single combustor consisting of main burner, pilot burner, combustor can and transition duct. In this paper, the Simcenter STAR-CCM+® solver is used to perform numerical simulations of the DLE combustor in the HPAF rig configuration. Large Eddy Simulations with a Flamelet Generated Manifold (FGM) combustion model and kinetic rate closure are used. The GRI-MECH 3.0 chemical mechanism is used to generate flamelet manifolds for each configuration of varied calorific value. Change in fuel heating value was achieved through diluting natural gas with CO2 and CO2 volume concentration varied from 22.7% to 32.1% which resulted in WI from 30 MJ/m3 to 25 MJ/m3. Flame structure and combustion dynamics signatures were investigated in detail at ISO full load engine condition for these fuels and compared with UK natural gas. Results from numerical study were compared with those from HPAF test.
An Optimal CFD Strategy for Intake in Crosswind Conditions
Authors: Chennuru Venkata Y. T. , Zhao Fanzhou , Vahdati Mehdi
Published: September 2023

Crosswind can reduce the operability of an aeroengine significantly at static or near static operating conditions. CFD predictions of the flow at crosswind conditions will play an important part in future designs, however, accurate numerical predictions of the flow within the intake remain challenging even for simulations of cases with intake only. The main objective of this paper is to demonstrate the importance of numerical setup and to determine an optimal computational model for crosswind investigations that can be used by other researchers. By considering the flow to be inherently unsteady, the influence of inlet and exit boundary conditions, and grid sensitivity is studied by using URANS simulations. Numerical predictions of the time-averaged intake pressure recovery (IPR) and the motion of the vortex on the ground are compared against the existing experimental data. The results show that for an intake under crosswind, the ground vortex that forms under the intake and the in-duct separation, when present, exhibit unsteady behaviour that become stronger as the crosswind velocity is increased. The steady-state simulation is only representative at lower crosswinds. The intake flow separation and ground vortex predictions are influenced by the inlet boundary layer profiles. Moreover, acoustic reflection was observed at the intake exit boundary which propagates upstream, creating artificial unsteady frequencies in IPR. The reflection is generated from the use of uniform boundary conditions at the intake exit and is not dissipated in the grid due to the long wavelength; this can be mitigated by using a choked nozzle at the intake exit. Acoustic reflection was also observed at the far-field exit boundary. These reflections are caused from interaction of trailing vortex and far-field boundary.
Modeling, Analysis, and Control of the Power and Temperature Dynamics of a Heavy-Duty Gas Turbine
Authors: Müller Eric Andre
Published: September 2023

Operational flexibility of a gas turbine power plant crucially depends on an accurate feedforward control of the prime mover. Since the power & temperature dynamics of a gas turbine are characterized by a non-minimum phase transmission zero, the associated feedforward control problem cannot be solved through system inversion, as the resulting controller would be unstable. In this article, a model-based feedforward controller that overcomes the problem of the non-minimum phase transmission zero is derived based on a validated model of Ansaldo Energia’s GT36 gas turbine. The controller is designed to follow a reference model trajectory on the power output and to enable a configurable but consistent trade-off between temperature control performance and increasingly harsh actuator commands. In a simulation case study, the functionality of the controller is verified, and the specific benefits of its design are discussed. Finally, the strong dynamic capabilities of the GT36 are demonstrated by comparing the ideal response of the linear system with measured engine data in a rapid de-loading/loading transient.
Experimental Investigation of the Effect of Bleed on the Aerodynamics of a Low-Pressure Compressor Stage in a Turbofan Engine
Authors: Spanelis Apostolos , Denman Paul A. , Mariah Ian , Walker A. Duncan
Published: September 2023

The compression system in modern turbofan engines is split into several stages linked by s-shaped transition ducts. Downstream of the low-pressure system, a handling bleed is often required for off-design performance and/or to extract ice/water and foreign debris prior to the air entering the high-pressure compression stages. The inclusion of this bleed and various structural vanes can introduce unwanted component interactions and compromise the aerodynamic performance of the upstream low-pressure compressor stage and downstream transition duct. This paper presents an experimental investigation of the aerodynamic performance of a compressor transition duct and bleed for a very high bypass ratio turbofan. A fully annular, low-speed test facility incorporating a 1½ stage axial compressor was used to examine the mean and unsteady flow in the last stage of a low-pressure compressor and the downstream transition duct. The transition duct incorporated load bearing struts, including a so-called King strut with twice the thickness of the regular struts. The bleed utilized a 360° annular slot located on the casing immediately downstream of the low-pressure rotor and upstream of the outlet guide vane. The results showed that the King strut, caused a similar flow distortion and redistribution in the OGV like the Regular struts, and had otherwise imposed a negligible effect on overall performance over a range of rotor flow coefficients. The addition of bleed had a more notable effect, generating an increasing outboard bias in the rotor efflux, as the flow migrated towards the offtake. At the design flow operating point, the OGV were relatively insensitive to this until the highest bleed rate (18%) where evidence of stall was observed. At a lower operating point, the change of rotor swirl and additional OGV incidence caused earlier onset of stall and a full OGV stall was observed above 10% bleed. Increasing bleed was observed to cause a gradual increase in duct loss up to the point of OGV stall when losses increased more rapidly.
Development of 5MW Hydrogen Gas Turbine Suitable for Eco-Friendly Power Plant Energy Grid
Authors: Shin Youngjun , Cho Eun-Seong , Hwang Jeongjae , Kim Minkuk
Published: September 2023

Doosan, the Heavy-duty gas turbine OEM manufacturer, have been successfully achieving the progress of developing hydrogen gas turbine combustor. Considering the low hydrogen production rate, the safety of hydrogen flame, and above all, the connection with green hydrogen production through eco-friendly energy generation, we started to develop a 5MW small sized gas turbine for 100% hydrogen, and we plan to gradually expand it to medium and large sizes combustors.

This paper presents the results of testing four different types of good performance nozzles, selected from among the designed hydrogen concept nozzles with the idea for anti-flashback. The nozzles were verified and updated through commercial CFD analysis, and in this study, they were tested in an actual hydrogen atmospheric pressure test. The nozzle characteristics were compared and analyzed, and the results show that all nozzles performed well under base load conditions, with low NOx emissions and no flashback. Extreme conditions were also tested to check flame stability, such as the Lean blow out and the Flashback. The study concludes that the designed nozzles show promise for use in actual Full CAN combustors, and updates will be made to improve their shortcomings.
Experimental Investigation of Additional Loss Associated With Incoming Wakes in Low-Pressure Turbine Cascades
Authors: Kodama Hidekazu , Funazaki Ken-ichi
Published: September 2023

The present paper aims at experimentally investigating the influence of wake-passing frequency, Reynolds number and suction surface diffusion rate on the additional loss due to incoming wakes to the profile loss in low-pressure turbine (LPT) cascades and discussing a design guide for reducing the additional loss. Using a moving-bar mechanism, the unsteady effects of incoming wakes were measured in a low-speed linear turbine cascade facility. The wake-passing frequency was varied by adjusting the moving-bar speed. The different airfoils with different surface velocity distributions were tested to examine the effect of suction surface diffusion rate. For each test case in an unsteady flow condition, the additional loss due to incoming wakes was derived by subtracting the profile loss from the measured total pressure loss across the cascade. Here the profile loss was estimated by using the friction drag force, which was calculated by the measured surface velocity distribution, and the pressure drag force, which was calculated by the measured surface pressure distribution and the predicted base pressure. The resultant additional loss includes all kinds of losses associated with incoming wakes, such as mixing loss of incoming wakes enhanced in the blade passage and unsteady interaction loss between incoming wakes and surface boundary layers. It was demonstrated that, in an unsteady flow condition, a substantial performance improvement was obtained in the entire Reynolds number range by applying the surface velocity distribution with no laminar separation to a low solidity blade row.
Partially Premixed Hydrogen-Methane Flame Simulations at Relevant Gas Turbine Conditions With a Thickened Flame Model Enhancement
Authors: Meloni Roberto , Orsino Stefano , Ansari Naseem , Yadav Rakesh , Bessette Didier , Castellani Simone , Nassini Pier Carlo , Andreini Antonio , Boxx Isaac
Published: September 2023

The prediction of the behavior of stratified flames involving the hydrogen will represent a crucial task for the improvement of the Gas Turbine (GT) combustors performance in the next years. The Computational Fluid Dynamic (CFD) models usually employed to help the design definition need major revisions and improvements to provide reliable insights in this context.

In this paper, an enhancement of the standard Thickened Flame Model (TFM) will be introduced trying to adapt the transport equation source term of each species to the combustion regime, the latter identified by the local flame index value. Being the TFM mainly devoted to describing a perfectly premixed flame, its mathematical formulation needs be redefined when also the diffusive regime has to be accounted for. The proposed approach will be validated against detailed measurements executed on a Jet in Cross Flow (JICF) fed with two moderate volumetric contents of H2 in blend with CH4. The selected operating conditions are relevant for the transfer of the methodology to real GT applications in terms of both temperature and pressure of the oxidizer.

In particular, the ability of the model to predict the anchoring of the flame close to the fuel injection location only in the case of high H2 content (as highlighted by the experiments) will be investigated. Analogously, the correlation between the strain rate and the thermal field leading to a different flame anchoring mechanism of the jet when a low H2 mixture is considered will be addressed as well. The numerical findings in terms of flame position and morphology will be compared with the PLIF acquisition while the flow field will be characterized through the PIV measurements.
The Prediction of Condensation Characteristics of Supercritical Carbon Dioxide in the Laval Nozzle During Supersonic Flow
Authors: Huang Zhe , Shen Xin , Chen Laijie , Ouyang Hua , Du Zhaohui
Published: September 2023

The non-equilibrium condensation and nucleation process contribute to enormous challenges to accurately predict the condensation behaviors in rotating machines. Considering the similarity of flow, the analysis of the condensation characteristics in the Laval nozzle is the basis for the study in the compressor. In this paper, an Eulerian-Eulerian Source term (EES) numerical model is developed to investigate non-equilibrium condensation features in supersonic compressible flow in nozzle. High precision real gas property table is introduced to calculate the thermophysical properties of CO2 in nozzle. The difference of droplet distribution and liquid fraction between EES model and homogeneous equilibrium (HEM) model is discussed. The relationships between inlet parameters, condensation site and nucleation rates are also analyzed. The numerical analysis result shows that although the prediction deviation of EES model and HEM model at outlet temperature and pressure is less than 3%, the liquid mass fraction at the outlet of HEM model is 12% larger than that of EES model. Shock wave of supersonic flow causes the forward movement of condensation site in HEM model, indicating that HEM model might overestimate condensation characteristics and aerodynamic effects in the nozzle. Decreasing the inlet pressure and increasing the inlet temperature delay the occurrence of condensation and reduce the liquid mass fraction, but could also bring about the increase of the droplet average radius at the outlet. These results provide valuable suggestions in the analysis of non-equilibrium condensation characteristics of supersonic flow and the design of compressor inlet conditions.
Time-Frequency Analysis of the Synchronous Response of Rotor Components: A Guideline for the Parameters’ Choice
Authors: Carassale Luigi
Published: September 2023

The measured synchronous response of rotor components may be analyzed with two objectives. On the one hand, the estimation of the response amplitude is necessary for structural calculations such as the assessment of the low-cycle fatigue safety margin. On the other hand, it is used for system identification purpose with particular interest for damping. Both these tasks can be carried out efficiently and accurately using the time-frequency analysis based on the continuous wavelet transform. A major issue that limits a wide use of this tool is the lack of criteria to guide the analysist to a proper choice of the parameters involved in the wavelet transform. This paper discusses this problem from a theoretical and practical point of view and provides a criterion valid for the analysis of the response during resonance crossings.
Squeeze Film Dampers Design and Application in High-Speed Radial Outflow Turbines for Small Size Organic Rankine Cycles
Authors: Gheller Edoardo , Chatterton Steven , Bassi Federico , Scala Michele , Dassi Ludovico , Pennacchi Paolo
Published: September 2023

The design of high-performance small-scale Organic Rankine Cycle (ORC) systems is heavily dependent on optimizing major power plant components. In Radial Outflow Turbines (ROT) greater efficiency is achieved by increasing the rotation speed and decreasing sealing losses by reducing the clearance of labyrinth seals. These solutions, together with the use of high molecular weight organic fluids, might lead to potential rotor dynamics issues related to super-critical rotor design and seal induced instability. To overcome this problem, a Squeeze Film Damper (SFD) is introduced to an overhung rotor configuration with angular contact ball bearings. Its effectiveness in reducing the amplification factor due to unbalance and seal instability is discussed and demonstrated by finite element (FE) simulations. A sensitivity analysis is performed on key SFD parameters of clearance, length, and groove size and an optimal design is selected.
Experimental Validation of a Seal Flutter Model
Authors: Corral Roque , Greco Michele
Published: September 2023

In this paper, the predictions of an analytical model for seal flutter have been compared with the experimental data of a rotating multi-cavity labyrinth seal test rig. The experiments were conducted to assess the flutter inception in a large set of operating conditions by varying the rotational speed and the total pressure ratio across the seal. The analytical model derived by Corral et al. (2022, “ Effective Clearance and Differential Gapping Impact on Seal Flutter Modelling and Validation,” ASME J. Turbomach, 144 (7), pp. 071010) has been previously validated by using a frequency domain linearized Navier-Stokes solver retaining the effect of the effective gaps and the kinetic energy carried over to the downstream fin. A set of 3D steady RANS simulations has been carried out to reduce the uncertainty in the steady characteristics of the seal that are used to inform the flutter model. The simulations consider the static deformation due to the pressure and the centrifugal force through a set of numerical models with geometrical gap differences. The stability has been investigated in a large range of operating conditions. It is concluded that the analytical model can be used to quickly predict the modes susceptible to flutter, provided that the steady flow field and the effective running clearances of the seal are well predicted.
A Methodology to Quantify Product Competitiveness and Innovation Requirements for Micro Gas Turbine Systems in Hydrogen Backup Applications
Authors: Tilocca Giuseppe , Sánchez David , Torres-García Miguel , Escamilla-Perejón Antonio , Minett Simon
Published: September 2023

Micro gas turbines are an on-site power and heat generation technology with a small footprint, low gaseous (NOx) and acoustic emissions, low maintenance and high-grade heat. They entered the market at the dawn of the twentieth century; nevertheless, they achieved minimal success and a marginal role in the microgeneration market. Reciprocating internal combustion engines raised considerable barriers hindering their market deployment, and Fuel Cells are also set to compete in this segment.

In this scenario, this work presents an analysis of competitiveness grounded in the Theory of Constraints. To this end, a specific Key Performance Indicator has been produced, which combines technical, economic, and operational factors according to the end-user requirement. This indicator is a function of several penalty factors representing technology and market barriers, which aims to yield a unique insight into the most competitive technology for a given application, accounting for the uncertainty deriving from technical and economic elements.

This novel methodology is applied to a new potential niche market: Power-to-Hydrogen-to-Power for remote applications. The methodology is applied to an independent rural community in South Wales, for which a backup power system is assessed. Four technologies are considered in the analysis: reciprocating engines, fuel cells and two different microturbines layouts.

Finally, this work provides an overview of the possible R&D&I paths necessary to increase the competitiveness of micro gas turbines in certain markets.
Emissions and Flame Structure Assessment of Aeroengine Micromixing Injectors for Lean Direct Injection of Hydrogen and Hydrogen/Natural Gas Blends
Authors: Tran Britney , Gomez Escudero Iker , McDonell Vincent
Published: September 2023

The present study focuses on whether adapting low emissions liquid fuel injection concepts can be applied to gaseous mixtures. The goal is to develop an injector with specific geometric characteristics that will achieve the lowest emissions. This is conducted by evaluating emissions and flame diagnostics on a set of test hardware that has been developed for combustion of pure hydrogen and hydrogen/methane mixtures. The current test hardware adapts lean direct injection concepts from aeroengine injectors to a ground-based engine based on target flows associated with a Solar Turbines Industrial Engine gas turbine. A statistical test plan was developed to assess these geometric characteristics using a three level Box Behnken design. The test plan investigates the effect of injector flow splits, air swirl, fuel swirl, pressure drop, preheat temperature, fuel composition, and the adiabatic flame temperature on the flame structure and emissions performance. A total of 16 injectors were considered for a total of 688 test points for emission and imaging data. Emissions data were reported on a mass basis in ng/J and chemical reactor network analysis were conducted to further interpret emissions behavior. Images were also captured to analyze the flame structure features of interest including reaction volume, flame length, flame spread, and flame width. With these results, a predictive model for emissions was made to conclude the most optimal injector configuration is to have the highest level of air split (more volume of air through the injector plate versus the injector) and air swirl angle for both methane and hydrogen gas mixtures. The predictive emissions level for all of these cases were below 10 ng/J.