bluuebunny/crossref_metadata_2025_split huggingface dataset:
Smart Passive Control of Thermoacoustic Instability in a Bluff-Body Stabilized Combustor: A Lagrangian Analysis of Critical Structures
Authors: Premchand C. P. , Raghunathan Manikandan , Raghunath Midhun , Reeja K. V. , Sujith R. I. , Nair Vineeth 
Published: January 2021

Abstract
The tonal sound production during thermoacoustic instability is detrimental to the components of gas turbine and rocket engines. Identifying the root cause and controlling this oscillatory instability would enable manufacturers to save in costs of power outages and maintenance. An optimal method is to identify the structures in the flow-field that are critical to tonal sound production and perform control measures to disrupt those “critical structures”. Passive control experiments were performed by injecting a secondary micro-jet of air onto the identified regions with critical structures in the flow-field of a bluff-body stabilized, dump, turbulent combustor. Simultaneous measurements such as unsteady pressure, velocity, local and global heat release rate fluctuations are acquired in the regime of thermoacoustic instability before and after control action. The tonal sound production in this combustor is accompanied by a periodic flapping of the shear layer present in the region between the dump plane (backward-facing step) and the leading edge of the bluff-body. We obtain the trajectory of Lagrangian saddle points that dictate the flow and flame dynamics in the shear layer during thermoacoustic instability accurately by computing Lagrangian Coherent Structures. Upon injecting a secondary micro-jet with a mass flow rate of only 4% of the primary flow, nearly 90% suppression in the amplitude of pressure fluctuations are observed. The suppression thus results in sound pressure levels comparable to those obtained during stable operation of the combustor. Using Morlet wavelet transform, we see that the coherence in the dominant frequency of pressure and heat release rate oscillations during thermoacoustic instability is affected by secondary injection. The disruption of saddle point trajectories breaks the positive feedback loop between pressure and heat release rate fluctuations resulting in the observed break of coherence. Wavelet transform of global heat release rate shows a redistribution of energy content from the dominant instability frequency (acoustic time scale) to other time scales.
Numerical Studies of Novel Aero Engine Secondary Combustors for Low-NOx Emissions
Authors: Rolt Andrew , Martínez Bueno Victor , Romanelli Mirko , Sun Xiaoxiao , Gauthier Pierre , Sethi Vishal , Celis Cesar 
Published: January 2021

Abstract
Gas turbine thermal efficiency and fuel burn are very dependent on turbine entry temperature and overall pressure ratio (OPR). Unfortunately, increases in these two parameters compromise other key aspects of engine operation and tend to increase emissions of nitrogen oxides (NOx). The European Horizon 2020 ULTIMATE project researched advanced-cycle aero engines with synergistic combinations of novel technologies to increase thermal efficiency without increasing emissions. One candidate technology was the addition of secondary combustion to increase the mean temperature of heat addition to improve thermal efficiency while limiting the primary combustor flame temperatures and NOx formation. However, an overall reduction in NOx also requires the secondary combustor to be a low-NOx design. This paper describes numerical studies carried out on novel aero engine secondary combustor concepts developed in two MSc-thesis research projects. The studies have explored the potential of oxy-poor-flame combustion concepts. These annular combustor designs featured two distinct regions: (i) the vortex zone, which promotes recirculation of combustion products, a prerequisite for low-oxygen combustion, and (ii) a through-flow region where part of the incoming flow bypasses the vortex before the flows mix again. These studies have demonstrated the advantages and some limitations of the proposed designs and emissions assessments in comparison with previous secondary combustor studies. They suggest very low NOx is achievable with oxy-poor combustion, but will be more difficult if the incoming oxygen levels are above 10%. More-accurate assessments will require LES modelling and inclusion of the primary combustor in the simulations. However, if the low overall NOx emissions would include relatively higher levels of nitrous oxide (N2O) then this might raise concerns with respect to global warming.
Numerical Investigation Into the Impact of Injector Geometrical Design Parameters on Hydrogen Micromix Combustion Characteristics
Authors: Sun Xiaoxiao , Agarwal Parash , Carbonara Francesco , Abbott David , Gauthier Pierre , Sethi Bobby 
Published: January 2021

Abstract
Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. As a part of the ENABLEH2 project, the current study focuses on the influence of design parameters on the micromix hydrogen combustion injectors. This study provides deeper insights into the design space of a hydrogen micromix injection system via numerical simulations. The key geometrical design parameters of the micromix combustion system are the sizing of the air gates and the hydrogen injector orifices together with the offset distance between air gate and hydrogen injection, the mixing distance and the injector to injector spacing.
This paper first presents results of the numerical simulation of four designs, down selected from a series of combinations of the key design parameters, including cases with low and high momentum flux ratio, weak and strong flame-flame interaction. It was discovered that the hydrogen/air mixing characteristics, and flame to flame interactions, are the main factors influencing the combustor gas temperature distributions, flame lengths and the corresponding NOx production.
The current study then focused on the effect of air gate geometry on the mixing characteristics, flame shape and temperature distribution. The momentum flux ratio was kept constant throughout this investigation by keeping the air gate area constant. Variations of the original baseline air gate design were studied, followed by a study of various novel air gate geometries, including circular, semi-circular and elliptical shapes.
It is concluded that NOx production is influenced by a number of factors including jet penetration flame interactions and air gate shape and that there is a “Sweet Spot” that results in the lowest practicable NOx production. Flatter and wider air gate shapes tend to yield the lowest temperature and consequently the lowest NOx. Reduced interaction between flames also tends to reduce NOx and by manipulating hydrogen penetration, there is the potential to further reduce the NOx production.
Pitch Control for Anticipation in the Measurement of Wind Speed for Small Wind Turbines Installed in Areas With Atypical Winds
Authors: Chavero-Navarrete Ernesto , Chavez-Luna Alfredo , Jáuregui-Correa Juan-Carlos , Trejo-Perea Mario , Carrillo-Serrano Roberto-Valentín , Rios-Moreno José-Gabriel 
Published: January 2021

Abstract
The production of electricity by renewable means is necessary to meet the growing energy demand and to protect the environment. Wind energy is an alternative, however, in places with a limited wind resource only the installation of small horizontal Axis wind turbines (SHAWT) is profitable. At rotor height, in this size of turbines, the wind is usually unstable with gusts and turbulence due to obstacles in its path such as buildings and trees. To reduce the effects of wind, the angle of incidence of the blade with the wind must be adaptable to guarantee the nominal rotation speed. The pitch angle is the angle of blade rotation around the longitudinal axis is commonly regulated with a Proportional-Integral-Derivative (PID) feedback controller, which works correctly when the wind is stable, but not when the wind presents drastic changes in speed, as a faster response speed is required. To correct this problem, this article presents a PID controller with automatic adjustment of the gain values and offering different response times for which a fuzzy logic controller (FLC) is used. The membership functions of the FLC are determined from the measurement of the wind speed at a calculated distance, so it is possible to anticipate the response of the actuator to the arrival of a wind gust to the rotor. The algorithm is implemented in 14 kW SHAWT where the difference of performance versus a conventional controller is quantified.
Development, Analysis, and Validation of a Simultaneous Inlet Total Pressure and Swirl Distortion Generator
Authors: Frohnapfel Dustin J. , Lowe K. Todd , O’Brien Walter F. 
Published: January 2021

Abstract
Over the last decade, the Turbomachinery and Propulsion Research Laboratory at Virginia Tech has researched, invented, developed, computationally analyzed, experimentally tested, and improved turbofan engine inlet distortion generators. This effort began with modernizing and improving inlet total pressure distortion screens originally conceived over half a century ago; continued with the invention of inlet swirl distortion generators (StreamVanes™) made possible only through advances in modern additive manufacturing technology; and has, thus far, culminated in a novel combined device (ScreenVanes™) capable of simulating realistic flight conditions of coupled inlet total pressure and swirl distortion in a ground-test turbofan engine research platform.
The present research focuses on the methodology development, computational analysis, and experimental validation of a novel simultaneous inlet total pressure and swirl distortion generator. A case study involving a single bend S-duct inlet distortion profile demonstrates the ability to generate a high-fidelity profile simulation, yet outlines a design process sufficiently generic for application to any arbitrary inlet geometry or distortion profile. A computational fluid dynamics simulation of the S-duct inlet provided the target profile extracted at the aerodynamic interface plane. Next, utilizing a method of inverse propagation, the planar distortion profile was propagated upstream to yield a flow field that could be manufactured by a distortion generator adequately isolated from turbomachinery effects. The total pressure distortion screen and swirl distortion StreamVane components were then designed and computationally analyzed. Upon successful computational reproduction of the S-duct inlet distortion profile, experimental hardware was fabricated and tested to validate the ScreenVane methodology and distortion generating device.
Comparison of the S-duct manufactured distortion and the ScreenVane manufactured distortion was used as the primary criterion for profile replication success. Results from a computational analysis of both the S-duct and ScreenVane indicated excellent agreement in distortion pattern shape, extent, and intensity with full-field total pressure recovery and swirl angle profiles matching within approximately 0.80% and 2.6°, respectively. Furthermore, experimental validation of the ScreenVane indicated nearly identical full-field total pressure recovery and swirl angle profile replication of approximately 1.10% and 2.6°, respectively, when compared to the computational results. The investigation concluded that not only was the ScreenVane device capable of accurately simulating a complex inlet distortion profile, but also produced a viable device for full-scale turbofan engine ground test.
Identification of High-Frequency Transverse Acoustic Modes in Multi-Nozzle Can Combustors
Authors: Kim J. , Gillman W. , Wu D. , Emerson B. , Acharya V. , Mckinney R. , Lieuwen T. , Isono M. , Saitoh T. 
Published: January 2021

Abstract
High frequency thermoacoustic instabilities are problematic for lean-premixed gas turbines. Identifying which acoustic mode is being excited is important, in that it provides insight into potential mitigation measures and mechanical stress/life. However, the frequency spacing between modes becomes quite close for high frequency instabilities in a can combustor. This makes it difficult to distinguish between the modes (e.g., the first transverse mode vs. a higher order axial/mixed mode) based upon frequency calculations alone, which inevitably have uncertainties in boundary conditions, temperature profiles, and combustion response. This paper presents a methodology to simultaneously identify the acoustic mode shapes in the axial and azimuthal directions from acoustic pressure measurements. Multiple high temperature pressure transducers, located at distinct axial and azimuthal positions, are flush mounted in the combustor wall. The measured pressure oscillations from each sensor are then used to reconstruct the pressure distributions by using a least squares method in conjunction with a solution of a three dimensional wave equation. In order to validate the methodology, finite element method (FEM) calculations with estimated post-flame temperature is used to provide the candidate frequencies and corresponding mode shapes. The results demonstrate the reconstructed mode shapes and standing/spinning character of transverse waves, as well as the associated frequencies, both of which are consistent with the FEM predictions. Nodal line location was also extracted from the experimental data during the instabilities in the pressure data.
Robust Design of a Fuel Cell-Turbocharger Hybrid System
Authors: Giugno Andrea , Mantelli Luca , Traverso Alberto 
Published: January 2021

Abstract
Pressurized solid oxide fuel cell systems are a particularly attractive conversion technology for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. In this work an innovative biofueled hybrid system is considered, where the fuel cell stack is pressurized with a turbocharger, resulting in a system with improved cost effectiveness than a microturbine-based one at small scales.
In a previous work, a detailed steady state model of the system, featuring components validated with industrial data, was developed to simulate the system and analyze its behavior in different conditions. The results obtained from this model were used to create response surfaces capable of evaluating the impact of the main operating parameters (fuel cell area, stack current density and recuperator surface) on the performance and the profitability of the plant considering system uncertainties.
In this paper, similar but extended response surfaces will be used to perform a multi-objective optimization of the system considering the capital costs of the plant and the net power produced as objectives (turbocharger is fixed in geometry). The impact of the energy market scenario on the optimal design of such a system will be investigated considering its installation in three different countries. Finally, the Pareto front produced by optimization will be used to evaluate the robustness of the top performance solutions.
Numerical Analysis of Dilution Holes Deterioration Impacting the Performance of a V2500 Combustor
Authors: Konle Marco , de Guillebon Ludovic , Schäflein Lukas 
Published: January 2021

Abstract
In aero engine combustors, dilution air jets are used to additionally tailor the temperature field, the emissions, and the turbine inlet profile. These jets are entering the combustion chamber at different axial and circumferential locations through dedicated holes in the combustor liners. By deterioration, the diameters of these holes can significantly change over operation time. To evaluate the impact of such deterioration in the MRO context, the authors created a numerical model of a V2500 aero engine combustor and analyzed the impact. The data of dilution holes deterioration is based on the nominal design according the engine manual and the deviation measured for three engine combustors during maintenance inspection.
The processes inside an aero engine combustor are very complex. To achieve most reliable information, a multi-physics approach was chosen for this evaluation. Validated in the past with a wide range of different academic test cases as well as industrial combustor test rigs, the evaluation allows conclusive analyses of the described deterioration. Back-to-back comparisons of individual variations reveals the most significant dilution holes row and give information about potential local shifts in combustor liner heat loads as well as in the exit profiles. Especially the distortion of the film cooling by the local interaction with the dilution jets could be observed.
Since the deterioration of the dilution holes measured for the three combustors inspected is very small compared to the nominal design, the authors payed a lot of attention also on analyzing the model sensitivity. Increasing the spatial resolution, the plausibility of the numerical results were checked by analyzing the flow splits and the dilution jets penetration. The final step was the variation of the dilution holes individually and combined and the evaluation of resulting temperature distribution at the combustor liners and changes in the exit profile.
Due to the fact that a multi-physics solver developed in the framework of OpenFOAM could be used, the authors could do these quite intensive CFD studies highly parallelized and, thus, in an acceptable time. The scalability of the solver reported already in former publications could be shown also in this application to the real engine combustor with a high level of complexity.
Design and Aerodynamic Performance Investigations of Centrifugal Compressor for 150kW Class Supercritical Carbon Dioxide Simple Brayton Cycle
Authors: Cao Run , Li Zhigang , Deng Qinghua , Li Jun 
Published: January 2021

Abstract
The centrifugal compressor is the key component to improve the SCO2 cycle efficiency. In this paper, according to 150kW class supercritical carbon dioxide (SCO2) simple Brayton cycle, a centrifugal compressor with rotating speed 60000r/min is designed. For the small-scale SCO2 centrifugal compressor, the impeller tip clearance loss accounts for most of the aerodynamic loss. Therefore, the designed compressor performance is numerically studied by the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k-ε (Extended Wall Function) turbulence model. The large variations in physical properties for SCO2 near the critical make simulation be difficult to convergence. To keep the numerical stability and accuracy, 400 × 400 resolution physical properties tables are adopted by the physical properties tables verification. The designed SCO2 centrifugal compressor is with the isentropic efficiency of 73.2% and the pressure ratio of 2.207 under the design flow condition, and good off-design conditions performance are obtained. Compared to the flow condition without the impeller tip clearance, the isentropic efficiency of designed compressor decreases by 14%. For the impeller tip clearance leakage flow, the flow can be divided into three regions, the separation flow region which is along the mainstream flow direction, the back flow region which occupies the top of the impeller tip clearance and the downstream flow region which occupies the bottom of the impeller tip clearance. These flow phenomena and their causes are analyzed. The obtained results reveal that the designed centrifugal compressor meets the requirement of the aerodynamic performance for the 150kW class simple Brayton cycle. The detailed flow pattern of the designed SCO2 centrifugal compressor with consideration of the impeller tip leakage flow is also illustrated.
Geometrical Variability Modelling of Axial Compressor Blisk Aerofoils and Evaluation of Impact on the Forced Response Problem
Authors: Gambitta Marco , Kühhorn Arnold , Schrape Sven 
Published: January 2021

Abstract
The present work focuses on the effect of the manufacturing geometrical variability on the high-pressure compressor of a turbofan engine for civil aviation. The deviations of the geometry over the axial compressor blades are studied and modeled for the representation in the computational models. Such variability is of particular interest for the forced response problem, where small deviations of the geometry from the ideal nominal model can cause significant differences in the vibrational responses. The information regarding the geometrical mistuning is extracted from a set of manufactured components surface scans of a blade integrated disk (blisk) rotor. The optically measured geometries are parameterized, defining a set of opportune variables to describe the deviations. The dimension of the variables domain is reduced using the principal component analysis approach and a reconstruction of the modeled geometries is performed for the implementation in CFD and FEM solvers. The generated model allows a stochastic representation of the variability, providing an optimal set of variables to represent it. The aeroelastic analyses considering geometry based mistuning is carried out on a test-rig case, focusing on how such variability can affect the modal forcing generated on the blades. The force generated by the unsteady pressure field over the selected vibrational mode shapes of the rotor blades is computed through a validated CFD model. The uncertainty quantification of the geometrical variability effect on the modal forcing is performed employing Monte Carlo methods on a reduced model for the CFD solution, based on a single passage multi-blade row setup. The amplitude shift of the unsteady modal forcing is studied for different engine orders. In particular the scatter of the main engine orders forcing amplitudes for the manufactured blades can be compared with the nominal responses to predict the possible amplification due to the geometrical variability. Finally the results are compared to a full assembly computational model to assess the influence of multiple variable blades.
Lean Operation of a Pulse Detonation Combustor by Fuel Stratification
Authors: Habicht Fabian E. , Yücel Fatma C. , Hanraths Niclas , Djordjevic Neda , Paschereit Christian Oliver 
Published: January 2021

Abstract
Pressure gain combustion is a promising concept to substantially increase the thermal efficiency of gas turbines. One possible implementation that has been frequently investigated are pulse detonation combustors (PDCs), as they permit stable and reliable operation. At the same time, the need for part-load operation and low NOx emissions requires combustion concepts in the lean regime. However, realizing lean combustion is still very challenging in PDCs since the deflagration to detonation transition (DDT) is very sensitive to the reactant composition.
The present work investigates an approach to realize lean combustion in PDC by applying fuel stratification experimentally. The scope is to find the necessary increase of fuel concentration inside the pre-detonation chamber to provide reliable DDT with respect to the overall equivalence ratio. Emission measurements in the exhaust of the PDC allow for a quantification of the NOx emissions as a function of the injected fuel profile.
A valveless PDC test rig is used, which contains a shock focusing geometry for detonation initiation and is ignited by a spark plug close to the upstream end wall. The subsequent expansion of the burned gas and interaction of the flame front with turbulence leads to the formation of a leading shock inside the pre-detonation chamber, which is then focused inside a converging-diverging geometry. The successful initiation of a detonation wave by shock focusing is very sensitive to the pressure ratio across the leading shock, which can be influenced by initial pressure, reactant composition and flow velocity.
Results reveal that fuel stratification allows for reliable detonation initiation at a global equivalence ratio of ϕglob = 0.65, whereas repeatable successful operation with non-stratified fuel injection is limited to ϕglob ≥ 0.85.