bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow Through a Steam Turbine Cascade With a Single Damaged Blade: Effect of Blade Height on Loss and Outflow Angle Distribution
Authors: Schmalacker Michael , Cakievski Leon , aus der Wiesche Stefan , Schatz Markus 
Published: October 2022

Abstract
Flow measurements were made in a steam turbine cascade with a single blade of reduced height modeling a blade damage. In the experiments, the height of the single blade varied from full span (i.e., no tip clearance) up to totally removing the blade. The experimental investigation was supported by computational fluid dynamics (CFD) simulations which enabled further insight into local flow phenomena and mechanisms. It was found that the additional loss due to a gap increased strongly for the usual clearance level of a few percent of the blade chord but reached a relatively stable high loss plateau for higher clearances or rudimentary blades in the cascade flow channel. The tip-leakage vortex remained to be the dominant downstream flow feature and contains a high amount of loss, but for rudimentary blades, it transforms to the vortex pattern also observed for finite wings. Regarding the impact on the outflow angle distribution, the local downstream flow field can be interpreted by using the relations for cascades with high and low solidity.
Pollutant Emissions Reporting and Performance Considerations for Hydrogen-Hydrocarbon Fuels in Gas Turbines
Authors: Douglas Christopher M. , Shaw Stephanie L. , Martz Thomas D. , Steele Robert C. , Noble David R. , Emerson Benjamin L. , Lieuwen Timothy C. 
Published: October 2022

Abstract
Hydrogen (H2) fuel for gas turbines is a promising approach for long duration storage and dispatchable utilization of intermittent renewable power. A major global discussion point, however, is the potential air quality impact of hydrogen combustion associated with nitrogen oxide (NOx) emissions. Indeed, several studies in the combustion literature have reported elevated NOx concentrations in terms of dry ppmv NOx at 15% oxygen (O2) as a fuel’s H2 fraction is increased. Yet, as emphasized in this work, this practice of directly comparing emissions on the basis of dry ppmv at a reference O2 concentration (ppmvdr) is inappropriate across hydrogen and hydrocarbon fuel blends due to differing concentration changes induced by drying and referencing the corresponding exhaust gasses. This paper addresses three distinct approaches for comparing emissions consistently across fuel blends. Furthermore, it presents examples that quantify the differences in the apparent pollutant emissions between each approach and the usual ppmvdr reporting practice across the full range of hydrogen-methane mixture ratios. In the first approach, ppmvdr emissions values are related to their actual volume concentration. Here, our calculations demonstrate that hydrogen and methane flames producing the same true pollutant concentration exhibit a 40% relative difference in ppmvdr values, resulting in a significant potential exaggeration of NOx emissions for high %H2 fuels. However, this concentration-based approach does not account for changes in the volumetric flow rate of exhaust gasses or the slightly different amounts of heat release required to achieve the same flame temperature across fuels. These effects are captured naturally in the second approach, where the emissions are quantified in terms of the emitted mass per unit of heat release. With this cycle-independent approach, our comparative calculations at equal mass-per-heat emission rates reveal 36% higher ppmvdr values for hydrogen flames than methane flames. Finally, the third approach accounts not only for the thermodynamic properties of the mixture, but also for the system’s overall cycle efficiency, which is shown to depend weakly upon the fuel composition. This method quantifies emissions in terms of the emitted mass per unit of useful shaft work output, a metric also used by environmental regulators. Illustrative results within a simulated F-class gas turbine cycle are presented, indicating 39% higher ppmvdr values for hydrogen flames at equal mass-per-work emission rates. Hence, in all of the considered approaches, ppmvdr emissions values are inflated for H2 fuel blends relative to hydrocarbon fuels, making them unsuitable for direct comparisons of emissions among conventional and alternative fuels.
Numerical Investigation of a Turbine Vane Frame for Co- and Counter-Rotating Configuration
Authors: Krajnc Nicolas , Merli Filippo , Hafizovic Asim , Peters Andreas , Göttlich Emil 
Published: October 2022

Abstract
This paper presents the numerical comparison of a turbine vane frame (TVF) for future high-bypass turbofan engines for architectures with a co-rotating setup between the high-pressure turbine (HPT) and the low-pressure turbine (LPT) and with a counter-rotating setup. The flow field in the TVF is impacted by the decision of a co- or counter-rotating architecture which is driven not only by aerodynamics but also by the dynamic and mechanical design constraints in an engine.
As boundary conditions for the steady RANS simulation, measurements are used which were carried out in the engine-representative two-spool rig at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology. The test vehicle in this rig consists of an HPT with nearly axial exit flow and a counter-rotating LPT connected via the TVF with aft-loaded struts and splitters. To reproduce a realistic HPT flow field, purge air is provided by a secondary air system (SAS). The inlet and outlet boundary conditions are defined based on the five-hole probe (5HP) measurement set up- and downstream of the TVF, acquired for three different purge conditions (0%, 100% = nominal, and 200%).
To simulate a co-rotating configuration, the measured inlet flow field has been mirrored. The focus of this paper is to gain additional insights into the general flow behavior of a TVF in a co- and counter-rotating configuration, respectively. A special focus is placed on the differences between the development of strut secondary flows on their way through the TVF depending on the inlet flow field. Additionally, a duct loss comparison of the two configurations and its sensitivity to different purge flow levels is presented.
An Investigation of Non-Linear Surge Characteristic in a High-Speed Centrifugal Compressor
Authors: Hayashi Yoshihiro , Cao Teng 
Published: October 2022

Abstract
In centrifugal compressors, it is common to observe a rapid reduction in surge margin towards high rotational speed, which shows a non-linear surge characteristic against the change of rotational speed. This paper presents a comprehensive experimental and numerical study to understand the flow mechanisms leading to the non-linear surge behavior in a highspeed centrifugal compressor. It shows that for the studied compressor there are two critical flow coefficients (ϕ = 0.255 and 0.136) where the stability of the compressor stage is significantly weakened. At a higher speed, the impeller rotating stall happens at the first critical point where the diffuser instability is also enhanced. This is caused by the increase of the flow non-uniformity at impeller exit as well as increased diffuser inflow angle due to the impeller compressibility effect. Therefore, both the impeller and diffuser’s instability are matched and trigger the surge at a high flow coefficient. In contrast, at a lower speed, the diffuser instability is not enhanced by impeller rotating stall, this mismatch of the two component’s instability allows the compressor to pass through the first critical point and extend the surge limit to the second critical point where the diffuser reaches the stability limit and causes the rotating stall spontaneously. By these different behaviors in each speed, the non-linearity of surge characteristic is established.
A New Approach to Estimate Particulate Matter Emissions From Ground Certification Data: The nvPM Mission Emissions Estimation Methodology (MEEM)
Authors: Ahrens Denise , Méry Yoann , Guénard Adrien , Miake-Lye Richard C. 
Published: October 2022

Abstract
Estimating non-volatile Particulate Matter (nvPM) — or black carbon — emissions during an aircraft mission is extremely challenging because of the lack of reliable data in flight. For this reason, a detailed study has been undertaken to estimate in-flight emissions from data measured on the ground during engine certification. Aircraft engine emissions certification is based on the “Landing and Take-Off” (LTO) cycle developed by the Committee on Aviation Environmental Protection (CAEP) of the International Civil Aviation Organization (ICAO). It represents operations below 3000ft. The aim of this regulation is to control and reduce pollutant emissions in the vicinity of the airport. Carbon monoxide (CO), unburnt hydrocarbon (UHC), and Nitrogen oxides (NOx) have been regulated using the LTO cycle by different international standards for four decades. New certification standards on nvPM have been introduced recently. The first one, put in place in CAEP10, regulates the peak nvPM mass concentration. It has been in effect since 2020. The second set established in CAEP11 regulates the nvPM mass and number emissions on the LTO cycle and it becomes effective in 2023. With these regulations, manufacturers are now reporting nvPM emissions data publicly. All emissions data of in-production engines, and some legacy engines, are available in the engine emissions data bank (EEDB), downloadable from the European Union Aviation Safety Agency (EASA) website [1]. Methodologies have been proposed to estimate emissions at altitude and calculate total mission emissions for NOx, i.e. the “Boeing Fuel Flow Method” [2] or the “DLR Döpelheuer and Lecht” [3–5] methodology, which are only relying on these publicly available data from the EEDB. In the following, a new methodology for estimating nvPM emissions at altitude is proposed. The methodology was developed and validated in the framework of the CAEP technical working groups. It comprises four dedicated steps. In the present article, the different steps are explained and validation data is provided as applicable. Examples of in-production engines are analyzed, discussed, and compared against the full methodology using proprietary engine performance and emissions certification data. Following the proposed methodology, total nvPM mass and number mission emissions can be estimated and used for emissions inventories and evaluation of climate impacts.
Investigation of the Impact of Realistic Inlet Distortions on a 1.5-Stage Transonic Compressor
Authors: Werner Jan , Karl Maximilian , Mütschard Silas , Schiffer Heinz-Peter , Biela Christoph , Robens Sebastian 
Published: October 2022

Abstract
In this study the aerodynamic impacts of inlet distortions caused by a gas turbine inlet manifold are analyzed experimentally. The investigation is performed at the new transonic compressor test rig at Technical University of Darmstadt, that features high modularity and extensive instrumentation. The existing axial air inlet system of the test rig is replaced by a scaled inlet manifold. Analog to the design of a real gas turbine intake, bearing support struts are integrated in the experimental setup to investigate their interaction with the inlet distortions.
For the detailed analysis of compressor performance, the measurement systems were extended to resolve the flow over the whole circumference at three different axial positions. At the stage inlet a traversable rake with radially distributed five hole probes allows the quantification of the inflow conditions. To determine global compressor characteristics and analyze the propagation of inlet distortions through the compressor, a fully traversable instrumentation at the stage exit is installed. Additionally, a 360°-traversable rotor casing ring, instrumented with unsteady measurement systems, enables the analysis of the effects of non-uniform inflow conditions on the unsteady flow field of the rotor.
Study on the Non-Reacting Flowfield Characteristics of Lean Premixed Injector Modules With the Convergent Outlet
Authors: Sun Fujun , Suo Jianqin , Guo Luhua 
Published: October 2022

Abstract
To form lifting flame and prevent auto-ignition and flashback, this paper proposed an original lean premixed injector with a convergent outlet. The influence of key structures (swirler-vanes angles, swirler-vanes profiles and premixing section lengths) on flowfield characteristics of lean premixed injector was investigated by the combination of laser diagnostic experiments and numerical simulations. The results show that there is a stable and sizeable detached central recirculation zone (CTRZ) downstream of the all six injectors and the detached distance from the convergent outlet decreases with the increase of the swirl number (SN) of the injector. With the increase of the swirler-vanes angle or the premixing section length, the SN of the injector increases, resulting in the CTRZ closer to the convergent outlet. Compared with the straight swirler-vanes, the SN of the curved swirler-vanes with the same angle is smaller, and the size of the its CTRZ is smaller and more backward. In addition, The peak value of the reflux ratio, which is also an important parameter to measure the flowfield characteristics, increases with the increase of the SN of the injectors.
Assessment of Two Harmonic Balance Method-Based Numerical Strategies for Blade-Tip/Casing Interactions: Application to NASA Rotor67
Authors: Vadcard Thibaut , Colaïtis Yann , Batailly Alain , Thouverez Fabrice 
Published: October 2022

Abstract
The study presented in this paper focuses on the analysis of rubbing interactions — including unilateral contact and dry friction — between a rotating fan blade and a rigid casing by frequency domain methods. Two previously published Harmonic Balance Method-based methodologies are assessed: 1) an approach relying on augmented lagrangians and 2) a second method using a regularized penalty law combined with a Lanczos σ-approximation filter. Asa reference point for this comparison, a time-domain numerical strategy relying on a Lagrange multiplier-based contact treatment is considered. All computations are run with the NASA rotor 67 fan blade, an open industrial blade geometry. As it undergoes structural contacts, this blade features an intricate dynamics response, thus making it a challenging case study for nonlinear iterative solvers. The contact scenario is chosen to be an ovalization of the casing with no external forcing. This scenario induces highly nonlinear reponses of the blade and complex phenomena such as isolated frequency response curves. The results presented underline a very good agreement of the different strategies with the reference time marching approach. An in-depth comparison is made with an emphasis on nonlinear frequency response curves and time signals. In order to investigate further onto the frequency domain strategies, a comparative analysis is carried out on isolated nonlinear frequency response curves, referred to as isolas. Finally, a physical analysis of these isolas is presented through an in-depth investigation of the main modal contributions for each computed solution. In the end, this paper provides new qualitative elements allowing for a better understanding of rubbing interactions that may not be efficiently obtained with time marching procedures.
Symmetry Breaking in an Experimental Annular Combustor Model With Deterministic Electroacoustic Feedback and Stochastic Forcing
Authors: Humbert Sylvain C. , Orchini Alessandro , Paschereit Christian Oliver , Noiray Nicolas 
Published: October 2022

Abstract
In this study, we use an annular combustor experimental model with electroacoustic feedback to investigate systematically the effect of stochastic forcing and of non-uniform flame response distribution on azimuthal thermoacoustic modes. We break the symmetry of a nominally degenerate mode of azimuthal order m by imposing a non-zero 2m Fourier component of the flame gain, b2m, and of the time-delay, ε2m. Various orientations between the gain and the time-delay staging patterns are considered. In addition, stochastic forcing is introduced. First, all experiments are performed without noise, as well as at the maximum noise intensity. We observe that the mode nature that dominates in the presence of an intense noise may be far from the one observed in noise-free conditions. To better understand the effect of noise in the presence of asymmetries, we repeat some of the experiments at various noise intensities. Although our results confirm that for the axisymmetric configuration and for some asymmetric configurations pure spinning modes are never reached, we also observe some radically different behaviors. For a noise-free experiment leading to a purely standing mode, the introduction of a sufficient amount of noise can lead to beating. We also observe that, for a mode that is nearly standing in the absence of noise, an increase in the noise intensity leads to the predominance of mixed modes with a clearly favored spinning direction. We explain our experimental results with the aid of low order models.
Acoustic Localisation of High-Pressure Burst in a Confined Space
Authors: Bacci David , Ireland Peter , Hussain Zahid 
Published: October 2022

Abstract
Current turbofan systems are designed to be robust to high-pressure pipe rupture, inside their structure. Such failure event is typically detected through slow-response thermocouples Nevertheless, this approach has several limitations and typically requires sensing equipment to be placed close to harsh environmental areas.
An alternative route is represented by the introduction of an acoustic sensor, capable to detect the associated blast generated by the sudden breach of air through the fissure.
The aim of the study is to explore the feasibility of the concept of locating a sudden pressure rise (representing pressurised pipe rupture) in a closed environment, representative of the typical volume between the engine core and nacelle. A new system to locate the position of a burst, based on the analysis of an acoustic footprint, is presented and its performance is analysed.
Acoustic Flame Transfer Function Measurements in a Liquid Fueled High Pressure Aero-Engine Combustor
Authors: Venkatesan Krishna , Cross Arin , Han Fei 
Published: October 2022

Abstract
This paper describes an experimental approach and study of thermo-acoustic flame transfer functions in a high-pressure liquid-fueled rich burn combustor. The presence of high background flame luminosity in high-pressure sooty flame combustors precludes the application of any direct optical flame transfer function method. Instead, an acoustic method based on multiple microphones was employed to characterize the combustor acoustic pressure and velocity responses to acoustic forcing. A high-pressure siren device was employed to acoustically excite the combustor air flow over a broad range of frequencies from 150–1000Hz and modulate the combustor inlet dynamic pressure amplitudes. The acoustic pressures measured from the microphones located upstream and downstream of the flame were processed to obtain swirler impedances and flame transfer functions. Nonlinear behavior of the liquid fuel flame transfer function was studied by systematically varying the siren excitation pressure amplitudes. A parametric study of varying inlet air pressure, inlet air temperature, and thermal power was performed to study the impact of operating conditions on the measured liquid flame transfer function.
Development of an Acoustic Excitation Test Bench to Support the Validation of Bladed Disks
Authors: Ligot Jérôme , Denis Sophie , Hoffait Sébastien , de Cazenove Jean , Golinval Jean-Claude 
Published: October 2022

Abstract
This paper proposes a mixed hardware and software solution to impose different controlled dynamic load patterns to a bladed disk using non-intrusive acoustic excitation. The test bench is coupled to an autonomous measurement system consisting of an infrared Laser Doppler Vibrometer (LDV) placed on a robotic arm.
The development of the test bench is described from the definition of the requirements up to the calibration of the different components (acoustic excitation devices, power amplifiers, LDV positioning, etc.). The relation between the supplied voltage and the resulting pressure acting on the blade is also assessed.
The main application of the developed test bench consists in the imposition of Standing or Traveling Waves Excitation in order to appropriate a given nodal diameter content and experimentally study the response to typical excitation pattern encountered when integrated on motor.
Another application consists in the experimental mistuning measurement through modal analysis and the use of the Inverse Component Mode Mistuning method.
Experimental Investigation on the Accuracy of Blade Tip Timing Spectral Analysis Methods
Authors: Xiao Zhicheng , Meng Yiming , Ouyang Hua 
Published: October 2022

Abstract
The amplitude of spectral analysis of the tip timing data from individual blade observations is significant to turbomachinery health monitoring and aeroelastic researches. The accuracy of non-uniform discrete Fourier transform (NUDFT), extended discrete Fourier transform (EDFT), and compressed sensing (CS) is studied systematically. The benchmark data is obtained on a novel test bench where blade tip displacement can be acquired by laser displacement sensor directly. In the experiment, all three methods can successfully recognize the dominant 1F vibration but fail to discover the underlying 1T component. The accuracy of NUDFT to estimate the transient amplitude is approximately 69%. For EDFT and CS, the values are 30% and 84%, respectively. The number of cycles included in an analysis batch is found to influence the results. The robustness of the methods is discussed. The three methods are applied to a single-rotor rig and NSV is discovered in a field test. All of them could capture the frequency feature. It is determined that the blade is vibrating in the first flex mode. The difference between the measured frequency and the simulation is only 2.7%. Regarding the amplitude, CS yields the most convincing estimations.