bluuebunny/crossref_metadata_2025_split huggingface dataset:
Burner and Flame Transfer Matrices of Jet Stabilized Flames: Influence of Jet Velocity and Fuel Properties
Authors: zur Nedden Philipp , Eck Mattias Ettore Giulio , Lückoff Finn , Paschereit Christian Oliver , Orchini Alessandro 
Published: August 2024

Abstract
To achieve the decarbonization of electrical power generation, gas turbines need to be upgraded to combust high-hydrogen content fuels reliably. One of the main challenges in this upgrade is the burner design. A promising burner concept for a high-hydrogen fuel mixture are jet burners, which are highly. flashback resistant thanks to their high bulk velocity. Due to its non-acoustically compact extension and the presence of hydrogen in the fuel mixture, new challenges arise in assessing the (thermo)acoustic response of this burner design. A burner transfer matrix (BTM) and the flame transfer function (FTF) or transfer matrix (FTM) are typically measured with the multi-microphone method (MMM) to assess the performance of new burner types in relation to thermoacoustic stability. With the switch towards hydrogen, the fuel/air mixture is significantly altered in its properties regarding the speed of sound and density, which are of fundamental importance for acoustic waves propagation and their reconstruction via the MMM, as highlighted in recent work. In this work, we extend this discussion by studying the influence of the gas composition within the burner when measuring BTMs, and its indirect effect on the assessment of FTFs. Experimentally, we achieve this by adapting the preheating temperature during the measurement of the BTM with a non-reactive mixture in order to match the speed of sound of the hydrogen-air mixture required to flow in the burner under reactive conditions. Additionally, we present an analytical model for the jet burner transfer matrix, which is validated against the experimental data. Since the BTM is fundamental for the assessment of the FTM and FTF, the propagation of the error of changing fuel mixtures in the burner is evaluated. The influence of the variation in reactant composition of the BTM on the FTM assessment is noticeable, particularly in the gain of the FTFs. Furthermore, the influence of the total mass flow and, thus, the bulk flow velocity on the FTF is analyzed.
Experimental Investigation Into the Generation Mechanisms of Additional Loss due to Incoming Wakes in Low-Pressure Turbine Cascades
Authors: Kodama Hidekazu , Funazaki Ken-ichi 
Published: August 2024

Abstract
For low-pressure (LP) turbines, there exists the loss due to incoming wakes, whose magnitude is sometimes comparable to the profile loss. For a substantial improvement in LP turbine performance, it is necessary to reduce not only the profile loss but also the additional loss. This paper aims at clarifying the generation mechanisms of additional loss so that a design guide for reducing the additional loss is introduced. A parametric set of boundary layer measurements was conducted using a low-speed linear turbine cascade test facility with a moving-bar mechanism for blades with no separation bubble on the suction surface. Four different wake-passing frequencies and three different Reynolds numbers were examined. From the boundary layer measurements, the streamwise variations of the boundary layer integral parameters were obtained along the rear part of the blade surfaces. Also, the wall-normal profile of root-mean-square of streamwise velocity fluctuation was obtained at each boundary layer measurement location. The sources of additional loss were derived by using the measured boundary layer integral parameters together with the estimated profile loss under each flow condition. It was found that the wake-boundary layer interaction loss was attributed to the breakdown of Klebanoff streaks generated in the suction surface boundary layer and the magnitude of the loss was determined by the wake-passing frequency.
Development of a Hydrogen Micro Gas Turbine Combustor: NOx Emissions and Secondary Air Injection
Authors: Tanneberger Tom , Mundstock Johannes , Rex Christoph , Rösch Sebastian , Paschereit Christian Oliver 
Published: August 2024

Abstract
On the way to defossilization, green hydrogen is a promising way to substitute natural gas and oil in the gas turbine industry.
In the scope of the H2mGT project, a micro gas turbine (mGT) burner with 100 % hydrogen firing is developed and validated. The project is funded by the German BMWK and it is a collaboration between TUB and the manufacturer Euro-K GmbH. It consists of three phases: 1. Atmospheric pressure tests with a fused silica combustion chamber; 2. Atmospheric pressure tests with counterflow-cooled steel flame tube and secondary air injection; 3. Validation of the burner in the mGT at elevated pressure levels. The current study will present the results of Phase 2.
The hydrogen burner used in the project is based on a swirl-stabilized burner of TUB and was scaled to 36 kW thermal power at atmospheric conditions. The burner design features a variable swirl intensity, additional axial momentum of air in the mixing tube, a movable central fuel lance and pilot nozzles at the front plate. Furthermore, the burners steel flame tube is exchangeable, which allows the evaluation of different dilution hole patterns and, thus, the variation of the ratio of primary and secondary air. The study presents temperature, pressure, and emission measurements. It is found that the flame can be operated over a large range of equivalence ratios and preheating temperatures up to 500 °C. As expected, the NOx emissions are mainly influenced by the local equivalence ratio, which can be controlled by the fuel mass flow or the dilution hole pattern in the flame tube. Furthermore, the results show a decrease of NOx when the power density is increased at constant equivalence ratios, and a rise of NOx during the fuel transition from natural gas to hydrogen. The results indicate certain differences to the findings of Phase 1.
Micro-Mixing Combustion: Experimental Assessment of the Impact of Fuel Preheating on Combustion Stability
Authors: Bellavance X. , Landry-Blais A. , Plante J.-S. , Picard M. 
Published: August 2024

Abstract
Micro-mixing combustion is a promising technology in the field of gas turbine combustion because of its safeness against autoignition and flashback while having NOx emissions near premixed levels. This technology is especially well suited for the combustion of hydrogen because of its high reactivity. Because of the potential safety and low NOx emissions of micro-mixing combustion, there is the desire to use this technology with a larger fuel spectrum. However, using micro-mixing technologies, stable combustion is limited to reactive fuels such as hydrogen or high hydrogen fuel blends. Our previous work demonstrated excellent combustion stability with high inlet temperatures up to 1000K with hydrogen, propane, natural gas or Jet fuel A1 as fuels. However, using propane as fuel, stable combustion was limited to inlet temperatures higher than 600K. In this paper, the impact of preheating the fuel prior to its injection on the combustion stability is assessed using propane as fuel because of its stability limitation. For micro-mixing injector configuration discussed in this publication, preheating fuel prior its injection allowed to decrease dynamic instability magnitude under 3 dB for most of the unstable data points (Sound pressure level variation at instability dominant frequency). Those stability gains were obtained while achieving similar levels of NOx emissions. Thermoacoustic instabilities were then linked to observed flame positions.
Validation of Transition Prediction of Baseline and High-Lift Airfoils in a Low Speed Cascade
Authors: Jennerjohn Christianer Mary K. , Nguyen Bao Q. , Rogers Daniel , Giebert Dietmar , Aksoy Hakan , Marks Christopher R. , Fletcher Nathan J. , Clark John P. 
Published: August 2024

Abstract
Due to the high cost of fuel, mitigation methods to reduce the engine weight while improving efficiency are necessary. One method for reducing engine weight includes a reduction in airfoil count. However, this approach can have the potential for added risk due to increased losses at off-design conditions. For the low-pressure turbine, the low Reynolds number off-design conditions become particularly of concern for increased loss generation. This current paper focuses on the validation of transition predictions for two low-pressure turbine airfoils using linear turbine cascade data. The baseline airfoil had a Zweifel loading coefficient of 1.1, and this airfoil was re-designed at a higher pitch spacing to increase the loading to 1.3. The experimental data includes pressure loadings at various Reynolds numbers ranging from 20K to 200K as well as loss measurements to quantify the Reynolds lapse rate at two levels of incoming turbulence. Additional tests for the high lift airfoil included simultaneously acquired suction surface hot film and midspan PIV data at two low Reynolds numbers and three different turbulence intensities. Comparisons between the Reynolds lapse rate of the baseline and increased lift airfoil show it is possible to increase the lift on the airfoil while only marginally increasing the loss for two turbulence conditions. Suction-side reattachment locations are indicated by three different methods: airfoil loading using Cp, suction surface hot film data, and midspan particle image velocimetry (PIV). These are in turn compared to results of flowfield simulations using a commercial solver where the Langtry-Menter Transition model was employed. Overall, the flowfield simulations for both airfoils compared favorably with experimental data for the Reynolds lapse rate as well as boundary layer separation and reattachment points on the suction surface at low Reynolds numbers.
Correlation and Repeatability Improvement Between Tie Bolt Stretch and Vibration Levels Using Automated Stretch Tool and Regression Analysis
Authors: Horvath Lajos H. , Savela Gregory M. , Mathuria Parag H. , Seyler Joshua R. 
Published: August 2024

Abstract
Many large commercial aircraft utilize an auxiliary power unit (APU) to provide ground and in-flight power and start assist. The gas turbine APU can have a radial flow rotor system made up of a compressor and turbine section which are joined mechanically for ease of assembly and later maintenance activity. In a typical application, these two modules are assembled using a tie-bolt, an adaptor and a curvic coupling. The tie-bolt stretch along with all the internal rotor geometric interfaces is known to greatly influence rotor generated vibration. The tie-bolt is loaded or stretched to achieve the required contact stiffness between the impeller and turbine. This contact stiffness must be maintained throughout the APU ground-flight cycle to ensure that the operational loads do not degrade the rotor condition throughout the design service life. The rotor system is mounted using two bearings, typically a ball bearing for thrust and a roller bearing. These bearings in-turn transit vibration to the APU components, housing, and surrounding aircraft hardware. In some applications, the APU also provides the bleed air to the main engine start. This model of APU is generally inclusive of an additional impeller, called a load compressor. In that case, the turbomachinery consists of the three rotors, whereas assembly features of those three rotors exist two curvic couplings, adapter and tie bolt as required.
It will be shown here how the tie-bolt stretch as a manufacturing assembly operation can be related to rotor generated vibration. Further, through regression analysis an approach to optimizing this stretch a priori for a given set of hardware to minimize vibration for a production unit subject to production style detail part and assembly tolerances is presented. The investigation focuses on optimizing any specific stretched state to best position a rotor assembly in the zone between elastic and plastic limits so to actively minimize vibration to best approach analytical prediction. As a result of knowledge gained here, this approach can be used as a predictive tool for optimizing and projecting operational characteristics of a complex jet engine rotor assembly system with curvic couplings involving dis-similar homogeneous metals. Included in this investigation is the impact of straightness of a rotor assembly with multiple curvics and its impact on vibration, where minimizing or eliminating the undesired post assembly trim balance process (a.k.a. in situ balancing) or other reworking of the assemblies at final engine test was the objective.
Investigation of Endwall Secondary Flows in a Low Aspect Ratio Transonic Turbine, Part I: Passage Normal Shock
Authors: Jennerjohn Christianer Mary K. , McQuilling Mark , McKeever Craig 
Published: August 2024

Abstract
A significant source of loss in turbines includes the generation of endwall secondary flows and subsequent mixing losses downstream of a blade row. In the case of reduced aspect ratios, these secondary flows assume a greater spanwise penetration attributing to increased loss generation. In the first part of this two part series, the endwall secondary flow of a low aspect ratio turbine with AR = 0.66 (airfoil span to axial chord length) and Zweifel loading coefficient (Zw = 1.0) is characterized at an exit isentropic Mach number of 0.95. Both experimental and numerical findings are compared. Numerical predictions are validated by airfoil static pressures and downstream survey measurements in the SLU linear turbine cascade polysonic wind tunnel facility. Numerical analysis is completed using Cadence Fine/Turbo employing RANS with the SST k-omega turbulence closure model. This paper discusses the development of the endwall secondary flows throughout the airfoil passage including the development of the main secondary flow vortices (passage, counter and corner vortices) in conjunction with trailing edge shock impingement. Further, the subsequent mixing losses of the endwall secondary flows are shown with contours of pressure loss coefficient for five downstream survey planes ranging from 0.2Cx to 2.0Cx downstream of the trailing edge. Results show the effect of shock impingement and resulting shock boundary layer interaction on the suction surface resulting in an impact on the endwall secondary flow vortex development unique to a low aspect ratio turbine. The combination of endwall secondary flows and suction surface shock result in shock vortex and shock boundary layer interactions which affect the downstream mixing losses. Finally, the resulting work presents a new schematic detailing the endwall secondary flow development for low aspect ratio turbines in the transonic regime.
Improved Stall Recovery in “Electrified” Gas Turbine Engines
Authors: Jing Zhenhao , Neumeier Yedidia , Prasad J. V. R. , James Darrell K. 
Published: August 2024

Abstract
This study investigates the potential for stall control and recovery of “electrified” gas turbine engines that incorporate advanced electric generator/motor system capable of adding or reducing torque from the engine shaft. In parallel to the conventional stall recovery action, such as reducing fuel flow, electric motors are utilized to drive the engine shaft to accelerate, thus enhancing the stall recovery process. This idea is assessed using simulations of compressor flow during engine transients using a recently developed model capable of capturing the propagation of compression and expansion waves as well as shock waves in the compressor. A lumped-parameter combustor-turbine model is coupled with the aforementioned compressor flow model to simulate flow transients. This study considers a single-shaft gas turbine engine equipped with an electric motor that encounters stall at 75% speed during a cold acceleration. It is found that, compared to the traditional engine that plunges to surge, the “electrified” engine recovers from stall and accomplish the engine acceleration after receiving assistance from an electric motor providing mechanical power equivalent to 3% of the maximum dry thrust fuel combustion power. Such an electric power corresponds to the power required to drive the engine shaft to continue accelerating while the control logic reduces the TIT to recover stall.
A Static/Dynamic Coupled Harmonic Balance Method for Dry Friction Systems Containing Rigid Body Modes
Authors: Liu Jiale , Fan Yu , Wu Jian , Wu Yaguang , Shen Qingyang , Zhang Dayi 
Published: August 2024

Abstract
A harmonic balance method for under-constrained dry friction systems containing rigid body modes (HBM-RBM) is proposed. This method aims to overcome the encountered obstacle when applying the harmonic balance method to turbine blades damped by underplatform dampers. The inspiration for HBM-RBM comes from the free interface modal synthesis method. The key innovation involves deriving the elastic inversion of the singular stiffness matrix through the elimination of rigid body modes. In this way, the general HBM framework can be adopted, and the frequency response of under-constrained dry friction systems can be solved in a static/dynamic coupled manner. The accuracy and efficiency are both verified on a lumped parameter model and a finite element model of turbines with UPDs from a real gas turbine. A comparative study between the HBM-RBM and the commonly adopted way of imposing artificial grounding springs (HBM-AGS) is conducted. Results demonstrate that the HBM-RBM holds a significant advantage over HBM-AGS, as it eliminates the need for artificial grounding springs (AGS) and avoids the necessity for numerous trial cases to determine AGS stiffness.
Off-Design Performance Analysis of Centrifugal Compressor of a Small Gas Turbine Engine
Authors: Dhinne Giridhar Kumar 
Published: August 2024

Abstract
This paper describes the work carried out to evaluate the off-design performance of a centrifugal compressor which consists of an impeller, a vaneless diffuser, a radial vaned diffuser, a radial-to-axial 90° bend and an axial diffuser (also called as de-swirl vanes), used for small gas turbine engine applications. As the flow through the centrifugal impeller is three dimensional, inviscid, and highly complex in nature, an effort is made to predict the performance as accurate as possible by exploring various flow and loss models from the literature. Impeller flow is analyzed using Jet-Wake theory (or Two-zone modeling). Losses due to mixing at impeller exit, clearance and leakage, and losses due to friction are included. Vaneless diffuser is analyzed by solving momentum integral equation in radial and tangential directions. Performance of the vaned diffuser is estimated based on the Runstadler’s data plots. Radial-to-axial bend and De-swirl vanes are analyzed based on fluid dynamics relations and necessary empirical correlations. A computer program is developed, to calculate aero-thermodynamic properties of each component and the overall stage performance characteristics at different speeds ranging from 60 percent to 100 percent of design speed. A performance map is generated which consists of adiabatic efficiency and total-total pressure ratio values with respect to mass flow function. Predicted results are validated with performance characteristics of a 3.5 pressure ratio centrifugal compressor used for aero-engine applications. The results are very encouraging when compared with the experimental values. Choking flow is well predicted and the estimation of surge flow is not included in this method and is to be developed as a continuation of this research work.
Numerical Investigations on the Aerodynamic Performance of Supercritical Carbon Dioxide Centrifugal Compressor
Authors: Cao Run , Yang Rui , Deng Qinghua , Li Jun , Song Liming , Gao Tieyu 
Published: August 2024

Abstract
Study on steady and unsteady aerodynamic performance of supercritical carbon dioxide (SCO2) has great significant on improving SCO2 centrifugal compressor performance. In this paper, the SCO2 centrifugal compressor volute has been designed under the assumption of equal density. The effects of the asymmetric volute structure on the upstream flow and flow characteristics in the volute are studied. The unsteady flow structures of pressure and radial velocity at the impeller-diffuser interface are captured. The results show that under the steady calculation the total-static isentropic efficiency of the SCO2 centrifugal compressor is 71.0%, and the total-static pressure ratio is 2.190 at the design condition; The uneven pressure distribution caused by the volute tongue will affect the pressure distribution at the diffuser outlet. While at the diffuser inlet, the periodic distribution of pressure is basically unaffected by the volute; Under the unsteady calculation, the time-average total-static isentropic efficiency is 71.7% and time-average total-static pressure ratio is 2.227 at the design condition; The different relative positions between the impeller blades and diffuser blades are the main causes for the unsteady flow structures of the impeller-diffuser interface. When the impeller blade and diffuser blade are at the same position, under the effects of the impeller blade wake and flow acceleration near the diffuser blade leading edge, the pressure is the lowest and the back flow at the impeller tip clearance is the most obvious; The overprediction of the blade tip clearance back flow causes the efficiency under the steady calculation lower than the time-average total-static efficiency under the unsteady calculation. This paper can provide reference for the aerodynamic performance analysis for SCO2 centrifugal compressor.
Understanding the Potential and the Challenges of a NGCC Integrated With Hydrogen-Assisted EGR and CO2 Capture
Authors: Vantaggiato Elettra , Riboldi Luca , Anantharaman Rahul , Carcasci Carlo , Andreini Antonio , Roussanaly Simon , Ditaranto Mario 
Published: August 2024

Abstract
CO2 capture plays an important role in the energy transition. As the integration of CO2 capture on a gas turbine energy system induces an efficiency penalty, there has been growing interest in the development of combustion systems integrated with CO2 capture with improved efficiency and operability. This study investigates the potential and the challenges of a NGCC integrated with H2-assisted EGR and CO2 capture. A fit-for-purpose model of a GT, along with an in-house tool to model the CO2 capture process, were employed to capture the key effects of EGR. The results show that the CO2 capture energy requirement and equipment sizes consistently decrease at increasing EGR rates, with the conclusion that the EGR level should be as high as possible. On the other hand, a higher EGR rate determines a decrease of the O2 concentration to the combustor, with problems with combustion stability. The addition of H2 piloting to stabilize the flame allows achieving otherwise unfeasible EGR rates with an overall positive impact on the system energy efficiency. The main energy consumption of the integrated system is associated with the CO2 capture, underscoring the importance of EGR in reducing it. The additional energy penalties of the overall system are minor. As the energy consumption and efficiency are proxies for operating costs, and the equipment sizes are proxies for capital costs, this study represents a basis for further economic evaluations.