bluuebunny/crossref_metadata_2025_split huggingface dataset:
Understanding the Effect of Three-Dimensional Design in Tandem Blade
Authors: Kumar Amit , Kumar Akshay , Chhugani Hitesh , More Shubhali , Pradeep A. M. 
Published: September 2023

Abstract
In order to maximize the pressure ratio and efficiency, compressor designers have tried several unconventional design approaches. Tandem blading is one such unconventional design that promises a higher-pressure ratio per stage through a higher diffusion factor. The nozzle shape created between the forward and aft blades of a tandem configuration acts as a passive boundary layer control mechanism. The boundary layer growth over the aft rotor is therefore effectively controlled with the help of this gap-nozzle flow. The flow complexity is likely to increase in the case of a tandem rotor due to the twin leakage vortices, twin wake regions, and their interaction with the hub and casing boundary layers. Modern compressor blades are often designed with three-dimensional blade techniques such as sweep, lean, dihedral, end bent, etc., to reduce the various losses and achieve optimum performance. However, to the best of the author’s knowledge, the effect of 3D blade designs on the performance of tandem rotors has not been fully explored so far. A comprehensive numerical investigation is undertaken to understand the effect of 3D designs on the performance of tandem blades. Axial sweep and dihedral failed to improve the performance of the tandem rotor. Significant improvement in the stall margin is observed for the forward chordwise-swept and negative lean tandem rotors and is largely attributed to lower tip incidence. The performance penalty of the forward-swept and negatively leaned cases can be reduced by integrating compound or variable lean and sweep into the design.
Investigations of the Unsteady Shock-Boundary Layer Interaction in a Transonic Compressor Cascade
Authors: Munoz Lopez Edwin J. , Hergt Alexander , Klinner Joachim , Grund Sebastian , Karboujian Jirair , Flamm Jasmin , Gümmer Volker 
Published: September 2023

Abstract
The performance of compressor blades in transonic flow conditions is heavily hampered by unsteady flow effects caused by the Shock-Boundary Layer Interaction (SBLI). Even though these effects have been subject to research for a long period of time, very little is still known about the physical mechanisms driving the unsteadiness. In order to help elucidate the nature of these interactions in turbomachines, the recently designed Transonic Cascade TEAMAero was tested at the DLR’s Transonic Cascade Wind Tunnel facility in Cologne. The cascade flow was measured with a unique high-speed Schlieren configuration capturing three adjacent passages simultaneously, along with unsteady total pressure measurements at the outlet, and unsteady acceleration measurements on the tunnel sidewalls. The results indicate that the main oscillation of the shocks is broadband at relatively low frequencies around 550 Hz for the aerodynamic design point, and 180 Hz for the off-design point. A further high-frequency tone is observed around 1140 Hz throughout. These frequencies were also observed with the different measurement devices employed. Cross-correlations between the signals indicate that there are different mechanisms at play between the passages that cause both upstream and downstream transmission of information. Because of this, the shock oscillations were not always in-phase between adjacent passages. The results help characterize the SBLI behavior of the cascade in the wind tunnel, aiding future numerical and experimental efforts aiming to decipher the inherent mechanisms causing it.
Integrally Bladed Rotor Modal Identification Under Traveling Wave Excitation With High Density Measurement Points
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L. 
Published: September 2023

Abstract
Vibration testing of an Integrally Bladed Rotor (IBR) is often completed through Traveling Wave Excitation (TWE) bench tests composed of multiple, simultaneously excited inputs. Often, each blade has many output locations. For IBRs with many blades, as often found in the high pressure compressor, the total number of outputs can be several orders of magnitude. Formulation of a full output spectral density matrix from all measurements will then contain an exponential number of values at each frequency bin that can be detrimental to computational resources during the spectral density matrix formulation as well as down-stream system identification algorithms. An online algorithm is proposed for collecting and analyzing TWE data to reduce the large, computationally burdensome data sets into a manageable number of subsets for subsequent system identification. Furthermore, a frequency domain decomposition technique is also proposed for system identification that also attempts to reduce the data size through singular value decomposition. Identified system poles can be averaged from each subset, but mode shapes require stitching each subset together to identify the full mode shape at all output locations. The developed approaches are tested on synthetic TWE data and compared to baseline system identification results obtained using the full spectral density matrix. Results indicate the data subsets accurately compare to the baseline without much loss in accuracy.
Predictions of the Wake of a Three-Bladed Wind Turbine Using Dynamic Mode Decomposition
Authors: Morales-Ramirez Carlos Mario , Benavides-Moran Aldo G. 
Published: September 2023

Abstract
The objective of this study is to develop a reduced order model (ROM) that accurately predicts the key features of the wake generated by a wind turbine, based on the results of a computational fluid dynamics (CFD) simulation with the actuator line model (ALM). The simulation of a three-bladed up-wind wind turbine was performed using Reynolds-averaged Navier-Stokes (RANS) equations and the finite volume method. The two-equation turbulence model K-ωSST was used to approximate the Reynolds stresses and the Actuator Line Method (ALM) was used to simulate the effect of the wind turbine rotor on the flow field, representing the rotor blades as a distribution of forces acting on the fluid. Data from the RANS simulation was collected to be used by the Dynamic Mode Decomposition (DMD) algorithm. Velocity field was defined as the object of study for the construction of the reduced order model (ROM). From the implementation of the DMD algorithm, the eigenvalues and energy content were obtained for the field of interest. From these results, the main modes and their spectrum were calculated. The velocity field reconstruction was performed using the DMD algorithm, and the RMSE was computed relative to the simulation and experimental data, yielding a good approximation. Due to the turbulence model used, very stable results were obtained in the reduced order model, showing great capability to predict the fields of interest in time.
Understanding the Role of Attractive Forces in Additively Manufactured Parts With Internal Particle Dampers
Authors: Kiracofe Daniel , Diaz Daniel , Postell Matthew , Celli Dino , Hollkamp John , Napper Lorean , Scott-Emuakpor Onome , George Tommy 
Published: September 2023

Abstract
Captured powder damping, creating a particle damper inside an additively manufactured part by leaving behind a pocket of unfused powder, is a technology that allows significant vibration reduction with no additional cost or weight. This is attractive for aerospace applications where weight is at a premium and high cycle fatigue issues are common. Previous work in this area has mostly been experimental, with some modeling, but the modeling has been primarily limited to a fixed excitation amplitude. Recent experimental work suggests the damping is strongly dependent on the excitation amplitude, with an order of magnitude change in quality factor possible as excitation is varied. Previous models of additively manufactured components with embedded internal particle dampers were unable to accurately capture this variation. This work advances beyond those models by incorporating attractive (van der Waals) forces. Upon introducing attractive forces into the model, the match with experiment is significantly improved. This is demonstrated on a real-world part (a wind tunnel rake) over three orders of magnitude of base excitation. This proves for the first time that particle dampers using fine powder can exhibit different behaviors than dampers using macro-sized particles (for which van der Waals forces are negligible). The improved model can be used to help optimize particle damper design for specific applications.
Modelling Ammonia-Hydrogen-Air Combustion and Emission Characteristics of a Generic Swirl Burner
Authors: Mazzotta Luca , D’Alessio Francesco , Meloni Roberto , Morris Steve , Goktepe Burak , Lamioni Rachele , Cerutti Matteo , Romano Christian , Galletti Chiara , Creta Francesco , Borello Domenico , Valera-Medina Agustin 
Published: September 2023

Abstract
Ammonia (NH3) is considered a valued alternative carbon-free fuel able to reduce greenhouse gas (GHG) emissions with respect to conventional fuel, therefore it has attracted the interest of gas turbine manufacturers over the last years. However, the use of ammonia in existing gas turbine combustors entails not yet resolved challenges: based on currently available studies, the simultaneous coexistence of high NOx emissions and poor flame stability is expected when typical lean premixed technologies are used. NOx containment strategies may lead to significant combustion architectural changes. The use of NH3/H2 blends is a valued way to improve the flame stability, even though in some cases it is obtained to the detriment of the emission performances. However, there is still a lack of knowledge and experimental data on the use of ammonia and hydrogen-ammonia blends under typical operating conditions of gas turbines. The combustion process of both pure NH3 and a NH3/H2 fuel blends is here analysed using two kinetics processors, i.e. CHEMKIN-PRO and CANTERA: detailed reaction mechanisms have been tested and compared in terms of laminar flame speed, ignition delay times and extinction strain rate with the aim to identifying the most suitable ones for the evaluation of NOx emissions. The generic swirl burner being used in Cardiff University’s Gas Turbine Research Centre has been considered as validation test case. Evaluations have been carried out by means of 2D axisymmetric RANS simulations leading to a significant reduction of the computational time. Different pressures and mass flow rates are evaluated to understand the correlation in the formation of NOx emissions for pollutants reduction purpose. A direct comparison between experimental and numerical results is carried out in terms of flow field, flame shape and NOx emissions. Results show that NOx emissions decrease significantly with increase in pressure, also indicating guidelines for using a simplified RANS analysis, which leads to improved computational efficiency, allowing wide sensitivity and optimisation analyses to support the design development of an industrial combustion system.
Asymptotic Evaluation of Nonlinear Friction Effects in Realistic LPT Rotors
Authors: Rodríguez-Blanco Salvador , González-Monge Javier , Martel Carlos 
Published: September 2023

Abstract
The study of the dynamical response of a bladed-disk usually requires finite element models with a very large number of degrees of freedom. In the case of the vibration produced by an external forcing, the dissipation associated with the nonlinear friction at the contact interfaces compensates the energy pumped into the structure and limits the growth of the vibration, producing a limit cycle oscillation. The small effect of nonlinear friction, which typically involves a very small subset of nodes, is therefore crucial for the calculation of the final response of the system. Friction laws are strongly nonlinear and can even show discontinuities, as a consequence, the equations of motion are numerically very stiff. On top of that, large integration times over many elastic cycles are typically needed to reach convergence. In the study of the forced response of a bladed-disk, this means that a quite significant computational effort goes into computing a single point of the resonance curve. Despite all these numerical difficulties, the resulting response is in most cases very similar to the one produced by a one dimensional nonlinear oscillator. In this work, we investigate the forced response of a realistic LPT rotor with 144 blades, and derive an asymptotically simplified model to directly capture this low dimensional dynamics. This asymptotic model is obtained using a multiple scales perturbation method, where the elastic time scale is filtered from the system, and only the evolution on the long time scale associated with the nonlinear friction is described. The resulting model consists of a single complex differential equation, and the computation of the resonance curve is reduced to just the evaluation of an analytical expression. The results of the asymptotic description show very good agreement with high fidelity time domain simulations of the full bladed-disk, and the computation times are reduced by several orders of magnitude.
Harmonic Response of Damped Fan Blades With Viscoelastic Patches Under Centrifugal Pre-Stress
Authors: Couet Matteo , Deü Jean-François , Rouleau Lucie , Thouverez Fabrice , Gruin Marion 
Published: September 2023

Abstract
Turboshaft engine fan blades are subject to high dynamic loads, particularly on new engine architectures such as Open Rotor. These loads can induce aeroelastic phenomena such as flutter or forced vibrations, which can lead to fatigue damage and potentially compromise the integrity of the engine. To reduce the fatigue stress experienced by these structures, external structural damping can be added to the blade with active or passive treatments. Constrained viscoelastic patches have been shown to be an effective passive damping treatment, relying on the energy dissipation capabilities of these materials while undergoing shear stresses.
In this paper, an in-house numerical model based on previous studies is developed to predict the dynamic behavior of a slender fan blade with a constrained viscoelastic patch. This numerical model is validated through a confrontation with experimental test data. A particular interest is given to the elastomer and its material non-linear behavior, which had not been previously studied. This allows a better quantification of the efficiency of the damping treatment under various operating conditions, such as rotation speed and temperature to permit future patch optimization.
Analysis of High-Frequency Dynamics of a Reacting Jet in Crossflow Based on Large Eddy Simulation
Authors: Bonnaire Philip , Polifke Wolfgang 
Published: September 2023

Abstract
Distributed combustion systems have shown the potential to reduce emissions as well as increase load and fuel flexibility. A characteristic feature of such systems is a reacting jet in cross-flow, which exhibits complex vortical structures. In this paper, a generic combustion chamber with elliptic reacting jets in cross-flow is examined, operating under lean-premixed conditions at elevated pressure and exhibiting high-frequency transverse mode shapes. It can be seen that depending on the orientation of the elliptical shape of the jet to the crossflow, thermoacoustic modes can be suppressed. A multidimensional Fast Fourier Transform shows that low aspect ratios (major axis of the jet aligned with the crossflow) result in the mixed 1L1T mode of first longitudinal and first transverse structure, while this mode disappears at high aspect ratios. To get a more detailed insight into the different vortex systems of the various aspect ratios, Dynamic Mode Decomposition is applied. This modal decomposition technique reveals for low aspect ratios a shear layer mode that oscillates at a frequency close to the acoustic mixed mode. For this configuration, a mode representing a flapping motion is also identified. For high aspect ratios, the shear layer vortex increases its frequency and a higher-frequent mode appears in the acoustic spectrum.
Study of the Variation in Component Level Characteristics of a Centrifugal Compressor Across the Compressor Map Using CFD and Experiments With Detailed Instrumentation on a Gas Stand
Authors: Thiyagarajan Janakiraman , Fredriksson Carl , Anton Nicholas , Fridh Jens , Genrup Magnus 
Published: September 2023

Abstract
A compressor map with variations in component level characteristics is introduced. This novel approach to plot component level characteristics identify and give context to the critical design parameters such as flow angles, pressure coefficients, and loss coefficients across the entire compressor map along with the conventional performance parameters. Compressor design involves a significant amount of CFD at a stage level, but the decisive importance of component performance, design and analysis are many times overshadowed by 3D CFD, both steady RANS and unsteady RANS/LES/DES. Although the authors support the development of high-fidelity computational tools, validating these computational results with experimental measurements is essential. A detailed analysis of the Scania’s in-house designed compressor stage tested in the Scania Gas stand shows that in order to create an optimal design, component level performance assessment is necessary for the impeller, diffuser and volute. The variation of performance parameters along a speed line and across varied tip speeds are shown along with indications for the onset of instabilities at a component level. This is a crucial input for the design of a compressor stage. In addition to detailed analysis of experimental results, this work includes predictions from two different CFD solvers and discussion of deviations between them. Both the CFD solvers can be used to predict performance parameters at a stage level for most parts of the map. For operating conditions close to surge and higher tip speeds (565 m/s), there are major deviations in the CFD solvers’ predictions. The impeller pressure rise and efficiency could be predicted well with the CFD solvers for most of the tip speeds. However, deviations between measurements and predictions increase with increasing tip speeds. The diffuser performance is predicted well by one of the solvers. The other solver underpredicts the diffuser and overpredicts the volute performance. These are also important inputs for 1D design and also for positioning of the best characteristics on the compressor map for the optimal operation of the machine. The goal of this work is to quantify performance predictions on a component level accurately, so that stage level optimization is worth executing. Further, such validated models could aid reliable design predictions and an optimization of the entire compressor stage.
Laminar Burning Speed Measurements of Hydrogen/Natural Gas Mixtures
Authors: Yovino Louis , Kim Gihun , Rahman Ramees Khaleel , Vasu Subith S. 
Published: September 2023

Abstract
To address the shortage of fossil fuels and the environmental impact of exhaust emissions, research efforts in combustion seek to identify candidates for sustainable fuels. Hydrogen is an example, from which water is produced as the main combustion product. However, when used as neat hydrogen, it is very difficult to control hydrogen combustion due to its high flame speed, pre-ignition propensity, and flashback characteristics. One method to control hydrogen combustion is to blend it with a well-established fuel. Natural gas is a common fuel for use in engines or gas turbines. Natural gas is characterized by slow flame speeds and poor lean-burn ability; thus, engine power is decreased in the lean-burn region. Consequently, natural gas engines are typically operated at stoichiometric conditions to maximize output. Blending hydrogen to natural gas has several advantages: (i) Control of hydrogen’s ignition characteristics, (ii) extension of Natural gas’s lower flammability limit — making it easier to ignite, and (iii) reduced greenhouse gas emissions. In this study, the laminar burning speed (LBS) for neat natural gas and natural gas/hydrogen mixtures at 5 atm and 296 K were measured. Schlieren optical imaging was utilized to validate laminar flame conditions and further investigate the structure of natural gas/hydrogen flames. Results indicate that replacing 50% of natural gas with hydrogen increases the peak laminar burning velocity by a factor of ∼1.6 times. LBS simulations were conducted with NUI 1.1 and UCF NG/H2 mechanisms; Predictions by both mechanisms were found to be satisfactory for neat NG mixtures. However, for 50% NG/ 50% H2 mixture, the true LBS for fuel-lean conditions was under-predicted by both models, while predictions for fuel-rich conditions were satisfactory. Additionally, a literature review and similar experimental analysis will be performed for methane, ammonia, and hydrogen fuel blends to better understand the combustion phenomena of natural gas fuels.
Characterization of Spray Field for Water-Emulsified Diesel Using a Pressure Swirl Atomizer Under a Non-Reacting Environment
Authors: Suleiman Baha , Selim Hatem , Dawood Alaaeldin , Song Jinkwan , Lee Jong Guen , Khalidi Abdurrahman , Al-Ahmadi Kamal , Al-Ghamdi Ibrahim , Badr Eid , Al-Gahatani Mohammed 
Published: September 2023

Abstract
Employing a mixture or an emulsion of water and diesel fuel is considered a way to reduce gas emissions such as NOx and soot in a gas turbine. This study presents detailed experimental results on the spray characteristics of a water-diesel emulsion injected by a pressure swirl atomizer with a 90-degree spray angle and a flow number of 0.58 under a non-reacting environment at high pressure and temperature conditions. Acquiring this data is a key step when configuring a combustor that will employ emulsified fuels. In addition, this study seeks to confirm that the emulsion stays intact when it gets sprayed into the combustor. Furthermore, this study attempts to understand if a water-diesel emulsion prepared by a sonicator improves fuel atomization as compared to a water-diesel mixture prepared by a static mixer, i.e., not a proper emulsion.
Tests are conducted in a high pressure and temperature testing facility at two ambient pressure and three ambient temperature conditions and the mass-based water to diesel ratio (W/D) is varied from 11% to 100%. Phase Doppler Particle Anemometry (PDPA) is employed to measure the spray characteristics. Through a backlit high-speed photography, overall spray patterns over different test conditions are visualized. Mie-scattering and planar laser-induced fluorescence imaging are utilized to visualize the mixture field.
In general, the results indicate that emulsion stays intact as it gets sprayed into the combustor; and emulsion is a better solution to reduce emissions than a statically mixed mixture.