bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection
Authors: Reichel Thoralf G. , Terhaar Steffen , Paschereit Oliver 
Published: September 2014

Since lean premixed combustion allows for fuel-efficiency and low emissions, it is nowadays state of the art in stationary gas turbines. In the long term, it is also a promising approach for aero engines, when safety issues like lean blowout (LBO) and flame flashback in the premixer can be overcome. While for the use of hydrogen the LBO limits are extended, the flashback propensity is increased. Thus, axial air injection is applied in order to eliminate flashback in a swirl-stabilized combustor burning premixed hydrogen. Axial injection constitutes a non-swirling jet on the central axis of the radial swirl generator which influences the vortex breakdown position. In the present work changes in the flow field and their impact on flashback limits of a model combustor are evaluated. First, a parametric study is conducted under isothermal test conditions in a water tunnel employing particle image velocimetry (PIV). The varied parameters are the amount of axially injected air and swirl number. Subsequently, flashback safety is evaluated in the presence of axial air injection in an atmospheric combustor test rig and a stability map is recorded. The flame structure is measured using high-speed OH* chemiluminescence imaging. Simultaneous high-speed PIV measurements of the reacting flow provide insight in the time-resolved reacting flow field and indicate the flame location by evaluating the Mie scattering of the raw PIV images by the means of the Qualitative Light Sheet (QLS) technique.
The isothermal tests identify the potential of axial air injection to overcome the axial velocity deficits at the nozzle outlet, which is considered crucial in order to provide flashback safety. This effect of axial air injection is shown to prevail in the presence of a flame. Generally, flashback safety is shown to benefit from an elevated amount of axial air injection and a lower swirl number. Note, that the latter also leads to increased NOx emissions, while axial air injection does not. Additionally, fuel momentum is indicated to positively influence flashback resistance, although based on a different mechanism, an explanation of which is suggested. In summary, flashback-proof operation of the burner with a high amount of axial air injection is achieved on the whole operating range of the test rig at inlet temperatures of 620 K and up to stoichiometric conditions while maintaining single digit NOx emissions below a flame temperature of 2000 K.
Bayesian Belief Network for Robust Engine Design and Architecture Selection
Authors: Kestner Brian K. , Perullo Christopher A. , Sands Jonathan S. , Mavris Dimitri N. 
Published: September 2014

Designing propulsion system architectures to meet next generation requirements requires many tradeoffs be made. These trades are often between performance, risk, and cost. For example, the core of an engine is the most expensive and highest risk area of a propulsion system design. However, a new core design provides the greatest flexibility in meeting future performance requirements. The decision to upgrade or redesign the core must be justified by comparison with other lower risk options. Furthermore, for turboshaft applications, the choice of compressor, whether axial or centrifugal, is a major decision and trade with the choice being heavily driven by both current and projected weight and performance requirements. This problem is confounded by uncertainty in potential benefits of technologies or future performance of components. To address these issues this research proposes the use of a Bayesian belief network (BBN) to extend the more traditional robust engine design process. This is done by leveraging forward and backward inference to identify engine upgrade paths that are robust to uncertainty in requirements performance. Prior beliefs on the different scenarios and technology uncertainty can be used to quantify risk. Forward inference can be used to compare different scenarios.
The problem will be demonstrated using a two-spool turboshaft architecture modeled using the Numerical Propulsion System Simulation (NPSS) program. Upgrade options will include off the shelf, derivative engine (fixed core) with no technologies, derivative engine with new technologies, a new engine with no technologies, and a new engine with new technologies. The robust design process with a BBN will be used to identify which engine cycle and upgrade scenario is needed to meet performance requirements while minimizing cost and risk. To demonstrate how the choice of upgrade and cycle change with changes in requirements, studies are performed at different horsepower, ESFC, and power density requirements.
Experimental and Numerical Investigation of Non-Impregnated Aramid Fibers and Winding for Combined Fan Case
Authors: Krundaeva Anastasia N. , Shmotin Yury N. , Didenko Roman A. , Karelin Dmitry V. 
Published: September 2014

The layer of non-impregnated aramid fibers is widely used in the containment systems of aircraft gas turbine engines. Such systems are found to be especially cost-effective and light weight for mitigating engine debris during a fan blade-out event. This is mostly because non-impregnated aramid fibers have a high strength per unit weight. Moreover, it is inexpensive to manufacture such a containment system compared to traditional metallic systems. To properly utilize this advantage, it is necessary to have a finite element (FE) analysis modeling methodology for daily design tasks. Non-impregnated aramid fibers winding for fan case modeling for engine containment systems is a difficult task.
This research implied both experimental and modeling techniques, and data characterizing the behavior of fabric materials for engine containment systems. This research was aimed at addressing engine containment modeling issues. Thus this work has resulted in the following major accomplishments:
• Experimental Characterization of Non-impregnated Aramid Fibers: the fabric material model originally was created during this phase. The independent laboratory tests conducted at NPO Saturn form the basis of this model. These material models are general enough to be used as the constitutive model for both static and dynamic/explicit FE analyses.
• Static Ring Tests: Static tests of containment wraps subjected to loads through a blunt nose impactor were performed at NPO Saturn. Ballistic tests of containment wraps subjected to a high-velocity projectile were performed at NPO Saturn. These tests provided the test cases (the benchmark results) to validate the developed FE methodology.
• FE Material Model Development: The material models were used by the research team in the FE simulation of static and ballistic tests. The static test results have been validated by NPO Saturn using the ANSYS FE program. The ballistic test results were validated by NPO Saturn using the LS-DYNA FE program.
• Engine Fan Blade-Out (FBO) Simulation: The knowledge gained from previous tasks was used by NPO Saturn for the the numerical simulation of real engine FBO events involving the existing production engine models and compared to the test results (employing thelayer of non-impregnated aramid fibers containment).
• Combined Fan and Metal Case Comparison: The relative comparison between the non-impregnated aramid fibers and the metal materials in engine FBO containment systems has been carried out in order to ascertain that the non-impregnated aramid fibers case is more advantageous.
Experimental and Numerical Investigation of Fuel-Air Mixing in a Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustor
Authors: Agbonzikilo Festus Eghe , Stewart Jill , Sadasivuni Suresh Kumar , Owen Ieuan , Riley Mike , Sanderson Victoria 
Published: September 2014

This paper presents the results of an investigation in which the fuel/air mixing process in a single slot within the radial swirler of a dry low emission (DLE) combustion system is explored using air/air mixing. Experimental studies have been carried out on an atmospheric test facility in which the test domain is a large-scale representation of a swirler slot from a Siemens DLE SGT-400 combustion system. Hot air with a temperature of 300°C is supplied to the slot, while the injected fuel gas is represented using air jets with temperatures of about 25°C. Temperature has been used as a scalar to measure the mixing of the jets with the cross-flow. The mixture temperatures were measured using thermocouples while Pitot probes were used to obtain local velocity measurements. The experimental data have been used to validate a computational fluid dynamics (CFD) mixing model.
Numerical simulations were carried out using CFD software ANSYS-CFX. Due to the complex three-dimensional flow structure inside the swirler slot, different RANS turbulence models were tested. The shear stress transport (SST) turbulence model was observed to give best agreement with the experimental data. The momentum flux ratio between the main air flow and the injected fuel jet, and the aerodynamics inside the slot, were both identified by this study as major factors in determining the mixing characteristics. It has been shown that mixing in the swirler can be significantly improved by exploiting the aerodynamic characteristics of the flow inside the slot. The validated CFD model provides a tool which will be used in future studies to explore fuel/air mixing at engine conditions.
Part Load Performance and Operating Strategies of a Natural Gas–Biomass Dual Fuelled Microturbine for CHP Generation
Authors: Camporeale Sergio Mario , Fortunato Bernardo , Torresi Marco , Turi Flavia , Pantaleo Antonio Marco , Pellerano Achille 
Published: September 2014

The focus of this paper is on the part load performance of a small scale (100 kWe) combined heat and power (CHP) plant fired by natural gas and solid biomass to serve a residential energy demand. The plant is based on a modified regenerative micro gas turbine (MGT), where compressed air exiting from recuperator is externally heated by the hot gases produced in a biomass furnace; then the air is conveyed to combustion chamber where a conventional internal combustion with natural gas takes place, reaching the maximum cycle temperature allowed by the turbine blades. The hot gas expands in the turbine and then feeds the recuperator, while the biomass combustion flue gases are used for pre-heating the combustion air that feeds the furnace. The part load efficiency is examined considering a single shaft layout of the gas turbine and variable speed regulation. In this layout, the turbine shaft is connected to a high speed electric generator and a frequency converter is used to adjust the frequency of the produced electric power. The results show that the variable rotational speed operation allows high the part load efficiency, mainly due to maximum cycle temperature that can be kept about constant.
Different biomass/natural gas energy input ratios are also modelled, in order to assess the trade-offs between: (i) lower energy conversion efficiency and higher investment cost when increasing the biomass input rate; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid. The strategies of baseload (BL), heat driven (HD) and electricity driven (ED) plant operation are compared, for an aggregate of residential end-users in cold, average and mild climate conditions.
Application of a Fuzzy Logic Controller for Speed Control on a Small-Scale Turbojet Engine
Authors: Üşenmez Serdar , Ekinci Sinan , Uzol Oğuz , Yavrucuk İlkay 
Published: September 2014

Having a small-scale turbojet engine operate at a desired speed with minimum steady state error, while maintaining good transient response is crucial in many applications, such as UAVs, and requires precise control of the fuel flow.
In this paper, first the mathematical model of a Small-Scale Turbojet Engine (SSTE) is obtained using system identification tests, and then based on this model, a classical PI controller is designed. Afterwards, to improve on the transient response and steady state performance of this classical controller, a Fuzzy Logic Controller (FLC) is designed. The design process for the FLC employs logical deduction based on knowledge of the engine behavior and iterative tuning in the light of software- and hardware-in-the-loop simulations.
The classical and fuzzy logic controllers are both implemented on an in-house, embedded Electronic Control Unit (ECU) running in real time. This ECU is an integrated device carrying a microcontroller based board, a fuel pump, fuel line valves, speed sensor and exhaust gas temperature sensor inputs, and starter motor and glow plug driver outputs. It mainly functions by receiving a speed reference value via its serial communication interface. Based on this reference, a voltage is calculated and applied to the fuel pump in order to regulate the fuel flow into the engine, thereby bringing the engine speed to the desired value. Pre-defined procedures for starting and stopping the engine are also automatically performed by the ECU. Further, it connects to a computer running an in-house comprehensive Graphical User Interface (GUI) software for operating, monitoring, configuration and diagnostics purposes.
The designed controllers are used to drive a generic SSTE. Reference inputs consisting of step, ramp and chirp profiles are applied to the controllers. The engine response using both controllers are recorded and inspected. The results show that the FLC exhibits a comparable performance to the classical controller, with possible opportunities to improve this performance.
Study on Mistuning Identification of Vehicle Turbocharger Turbine BLISK
Authors: Hattori Hiroaki 
Published: September 2014

Blade vibration is one of the most critical items to be solved in turbocharger design. Turbocharger has much broader operating range than other turbo machinery and some unavoidable resonance may remain in operating range. In such a critical situation, predicting resonant vibration level is desirable for evaluating criticality. Additionally, knowing what amount of margin should be taken for the predicted nominal vibratory stress (known as “Magnification Factor”) is also important for the structural design. Blade to blade vibration response have significant scatter in real rotor. This kind of phenomena is called as “mistuned bladed disk effect” and discussed by many researchers in aero-engine field. Some research studies have appeared also in the automotive turbocharger field but its feature is not well understood especially on the item of mistuning identification and the cause of mistuning. Considering above situation, studies on mistuned vibration were performed for turbine BLISK of automotive turbocharger. Three type of mistuning (frequency mistuning, geometric mistuning, and mistuning of macroscopic property of directionally solidified material) were assumed and these effect on above items (mistuning identification and the cause of mistuning) were investigated.
This paper consists of three parts. At first, frequency mistune model and geometry mistune models were prepared. To build a frequency mistuning model, FMMID proposed by Feiner and Griffin [6] is applied. After the basic function test by virtual BLISK model with known mistuning, FMMID was applied to the actual BLISK. Natural frequency mistuning of each blade was identified by FMMID based on the modal measurement result. Obtained frequency mistuning is reflected to the (geometry tuned) FE model by changing the Young’s modulus of each blade in corresponding rate. The 3D measurement was also performed to the same BLISK and dimensional information from this measurement was reflected to the geometrically mistuned (material property tuned) FE model.
In the next step, vibration analysis (eigenvalue and frequency response) was performed and these results were compared to the measurement result. Vibration measurement in operating condition was performed at the resonant point of mode3 and nozzle count excitation frequency by utilizing the NSMS (Non-intrusive stress measurement system). Analytical result of the frequency mistuning model shows a good agreement with the experimental, while the analytical results of the geometrically mistuned model did not match to the experimental result.
At the last part, cause of discrepancy between the analytical result of the geometry mistuning model and the measured result was investigated from the view point of the effect of the anisotropy of elastic constants on the vibration characteristics of the DS (Directionally Solidified) blades.
Nonlinear Dynamic Study on Effects of Rub-Impact Caused by Oil-Rupture in a Multi-Shafts Turbine With a Squeeze Film Damper
Authors: Shiau T. N. , Wang C. R. , Liu D. S. , Hsu W. C. , Young T. H. 
Published: September 2014

An investigation is carried out the analysis of nonlinear dynamic behavior on effects of rub-impact caused by oil-rupture in a multi-shafts turbine system with a squeeze film damper. Main components of a multi-shafts turbine system includes an outer shaft, an inner shaft, an impeller shaft, ball bearings and a squeeze film damper. In the squeeze film damper, oil forces can be derived from the short bearing approximation and cavitated film assumption. The system equations of motion are formulated by the global assumed mode method (GAMM) and Lagrange’s approach. The nonlinear behavior of a multi-shafts turbine system which includes the trajectories in time domain, frequency spectra, Poincaré maps, and bifurcation diagrams are investigated.
Numerical results show that large vibration amplitude is observed in steady state at rotating speed ratio adjacent to the first natural frequency when there is no squeeze film damper. The nonlinear dynamic behavior of a multi-shafts turbine system goes in its way into aperiodic motion due to oil-rupture and it is unlike the usual way (1T = >2T = >4T = >8T etc) as compared to one shaft rotor system. The typical routes of bifurcation to aperiodic motion are observed in a multi-shafts turbine rotor system and they suddenly turn into aperiodic motion from the periodic motion without any transition. Consequently, the increasing of geometric or oil parameters such as clearance or lubricant viscosity will improve the performance of SFD bearing.
Film Cooling Hole Shape Optimization Using Proper Orthogonal Decomposition
Authors: Nita Kozo , Okita Yoji , Nakamata Chiyuki , Kubo Seiji , Yonekura Kazuo , Watanabe Osamu 
Published: September 2014

Film cooling is a very effective cooling method for protecting the turbine blades exposed to hot gas from the heat. Since its cooling effectiveness is highly dependent on the shape of the hole, a wide variety of concepts and design parameters regarding hole shapes have been researched. However, there are no well-defined ways to determine the optimum shape of a film cooling hole.
The CFD is a powerful tool for film cooling hole optimization. But with the number of parameters that define the film cooling hole shapes being so numerous, analytical optimization with CFD often requires computational resources that are unrealistic for the average design environment. Accordingly, for CFD to be effective in the optimization process, it is necessary to reduce the number of computations or shorten the calculation time per computation.
In order to solve this problem, this paper presents a novel approach of applying 3D-POD (3D-Proper Orthogonal Decomposition) to the optimization of film cooling holes. POD is one of the most important component analysis methods and has the potential to reduce the number of parameters.
From the computation results, a solution group was made by the RSM (Response Surface Method) and assessment functions, i.e., film cooling effectiveness, heat transfer coefficient, mixing loss, concentration of stress and robustness were considered first. In the end, however, considering the sensitivity of each objective function, the optimal hole shapes were obtained with only the film effectiveness being evaluated.
In the following sections, this method and its results are described in detail.
Laminar Flamelet Based NOx Predictions for Gas Turbine Combustors
Authors: Sripathi Mohan , Krishnaswami Sundar , Danis Allen M. , Hsieh Shih-Yang 
Published: September 2014

Stringent emissions regulations have led engine manufacturers to focus on fuel-efficient low emission technologies. Basic understanding and modeling of fundamental mechanisms governing formation and destruction of NOx, CO and UHC is essential to reduce pollutant emissions. Recent advances in turbulent combustion modeling have enabled designers to use CFD as a design tool for evaluating low emission concepts at the conceptual design phase.
Prediction of pollutant NOx for gas turbine combustors has proven successful for design validation applications. The challenge is to provide quick and accurate estimates of NOx for application to gas turbine combustor preliminary design phase, which can be characterized by multiple design changes, varying operating conditions and a variety of fuel staging concepts. NOx formation processes are typically slow compared to the fast hydrocarbon oxidation reactions. As a result, NOx predictions are typically performed as a post-processing step on thermal field obtained from reacting flow simulations. This work builds on prior work on flamelet approach [1,3] by suitably blending it with FLUENT®’s species transport. NOx production within gas turbine combustors has contributions from two major sources: flame front & post-flame thermal NO. The flame front contributions are obtained from flamelet based computations involving detailed chemistry whereas the slow evolution of post-flame NOx is tracked by explicitly solving for NO species transport. The closure of turbulence-chemistry-interactions is derived from Girimaji’s [2] assumed PDF closure using temperature-composition correlations. A Gaussian PDF shape is used with mean and variance of temperatures accounting for the first and second moments, required for PDF weighting computations. The formulation has been validated against SANDIA D flame, and then extended to GE Aviation’s fielded combustors over a wide range of operating conditions, with errors within 11% at Take-Off condition. The model has also been used for pre-test predictions on a number of combustors under development.
IDDES Study of the Shock Induced Flow Separation in a Transonic Compressor Rotor at Near Stall Condition
Authors: Shi Ke , Fu Song , Morris Scott C. 
Published: September 2014

The IDDES (Improved Delayed Detached Eddy Simulation) method was applied to simulate the highly unsteady flow in a transonic compressor at near-stall operating condition. Shock induced separated flow on the casing wall in front of the blade leading edge and the flow separation induced by the shock impinging on the blade suction surface were investigated in detail with the help of IDDES.
The 3D separation in the corner of blade suction side surface and the casing wall in the front portion of the blade was shown to be a vortex-like separation spiraling out from the blade suction surface, connecting to the blade suction wall and the casing wall. Blade tip leakage flow also contributed to the formation of the separation vortex. At near stall condition, shock wave was pushed forward out of the blade passage. The upstream propagation of the separation vortex and the related high entropy region were considered to be a characteristic phenomenon of the flow at near stall condition in this transonic compressor rotor.
The results of the present study explain the origin and the formation of the high entropy region in a transonic compressor rotor near the blade leading edge, which can be closely related to the spike type stall inception observed by other researchers in the transonic case.