bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Liquid and Gaseous Fuel on Lifted Flames at Elevated Pressure Stabilized by Outer Recirculation
Authors: Sedlmaier Julia , Habisreuther Peter , Zarzalis Nikolaos , Jansohn Peter 
Published: September 2014

Lifting a flame from the flow generating nozzle to some distance apart has a wide variety of effects on the properties of the resulting combustion phenomenon. The reason of this influence is the generation of a non-reacting flow domain where mixing takes place prior to the combustion reaction. It is obvious that the quality of premixing that can be achieved strongly depends on the time that is given to flow and the intensity of the turbulence that is mixing fuel and air. The most important parameter that is characterizing this time is the size of the premixing zone quantified by the so called lift-off height (LOH). Additionally, when employing liquid fuel the lift-off of a flame provides time to achieve better pre-evaporation of the fuel. As a consequence, better mixing of fuel and air helps to avoid high temperature regions that may be a result from an inhomogeneous equivalence ratio distribution. From safety considerations a major advantage of this method compared to the application of a premixing duct is that the risk of hardware destruction by flame flash back can be eliminated.
The current work extents the knowledge on lifted flames by the investigation of flames that are generated with an airblast atomizing nozzle that was designed to resemble systems close to application. Lifting of the flame is achieved applying a combination of swirling and non-swirling inflow ducts.
A wide range of operating conditions as well as gaseous and liquid fuels are used to investigate their influence on the lift-off height. The lift-off height and location of the reaction zone was determined by means of chemiluminescence of OH* and it is shown, that the impact of pressure drop and preheating temperature on the LOH is different for gaseous and liquid fuels.
A CFD Methodology for Assessment and Improvement of Aerodynamic Stability of a Premixed Swirler Burner
Authors: Geng Weiqun , Magni Fulvio , Ruck Thomas 
Published: September 2014

A methodology is presented in this paper how to assess and to improve burner aerodynamic stability of a premixed swirl burner by means of CFD. Steady-state RANS has been widely used for complex industrial applications for decades because of its good reproducibility of mean flow and acceptable turn-around time. With affordability of high performance cluster it becomes feasible to extend steady-state RANS to unsteady-state LES for industrial applications. It is especially beneficial for swirl burners to assess burner stability directly because swirling flow is in fact an unsteady-state phenomenon, which RANS cannot fully capture. This paper shows an industrial practice for how to improve burner design using both RANS and LES. The former helps find potential problems in the flow field, e.g. flow separation. The latter quantifies their impact on flow stability/turbulent fluctuations, e.g. helical modes generated by coupling of flow disturbances and swirling flow. Improvement measures were worked out to supress such flow fluctuations and to enhance stability of burner aerodynamics.
Another critical issue for burner design, reverse flow within the burner, was also discussed because it is a potential risk. When a flame instantaneously enters the burner backwards it can be stabilized in the recirculation zone and damage hardware. The risky region was eliminated by enhancing axial momentum of the air inflow.
The strong turbulent fluctuations within the burners interfere with burner stability significantly and lead to a bad flashback resistance in macroscopic view [1]. In the second part of the paper, atmospheric tests verify the improvement of burner stability via improved flashback resistance and show an upgrading of aerodynamic behaviour via reduced burner pressure drop.
Time-Linearized Forced Response Analysis of a Counter Rotating Fan: Part II — Analysis of the DLR CRISP2 Model
Authors: Gómez Fernández Io Eunice , Blocher Michael 
Published: September 2014

Over the last 3 years, several Institutes of the German Aerospace Center (DLR) investigated the possible gains of a counter rotating fan arrangement manufactured from CFRP designed with an automated optimization tool chain. While counter rotating fans promise aerodynamic efficiency improvements, they might suffer from aerodynamic exitation phenomena as well. The wakes, potential fields and shocks on the blade suction sides might cause blade vibrations leading to high cycle fatigue. Therefore, numerical investigations into aerodynamic excitation are necessary to estimate the amplitude of induced vibrations. At the Institute of Aeroelasticity, a time-linearized loosely coupled approach was used to determine the aerodynamic forcing of the blade rows of this counter rotating fan arrangement.
A finite element model consisting of shell elements was created for the blades in order to be able to model the CFRP material properties. Subsequently, nonlinear finite element load calculations (inertia and blade surface pressure) with a modal analysis in the last step were performed to generate a Campbell diagram of the rotor blades. Critical operating points were identified from the Campbell diagram. Nonlinear steady CFD simulations of these operating points were performed. Based on these calculations, time-linearized unsteady simulations at the crititcal inter-blade phase angle were performed with forced blade motion to determine the aerodynamic damping. Similarly, time-linearized unsteady simulations were performed with gust boundary conditions to determine the aerodynamic forcing. The results of aerodynamic damping and aerodynamic forcing simulations were combined to yield the predicted forced response amplitude of the eigenmode shape that is going to be excited at the respective critical operating point.
As a last step, a nonlinear finite element displacement simulation is conducted to determine the static and dynamic stresses and strains during a forced response vibration. These static and dynamic stresses and strains are then compared to the material properties of the CFRP material to determine if the blades will keep their structural integrity over time. The results of these calculations are presented and discussed.
Thermal Modeling and Mechanical Integrity Based Design of a Heat Shield on a High Pressure Module Solar Steam Turbine Inner Casing With Focus on Lifetime
Authors: Stein Peter , Marinescu Gabriel , Born Dominik , Lerch Michael 
Published: September 2014

As part of the renewable energies and because of their low environmental impact, solar thermal power plants enjoy a wide acceptance in the public. In the past years, several projects have been launched to install plants even with a total power output level beyond 200 MW, which require large size steam turbines. Steam turbines of solar power plants face much more start-ups and shutdowns, compared to typical fossil type baseload machines. In order to provide the required lifetime of steam turbine components, i.e. in high- and intermediate-pressure modules, accurate calculation methods of temperatures and heat transfer coefficients are essential for natural cooling and start-up assessment. Beside rotors, also turbine inner casings face high thermal stresses, especially close to the inlet spiral. At these conditions high thermal stress occurs, which prevents the part to meet the technical requirements.
The paper below gives a solution how to avoid this high stress and a calculation method for inner casings. A heat-shield introduced around the inlet spiral separates the active cooling domain of the turbine cavity relative to a narrow domain around the inlet spiral, where the fluid velocity is negligible. A method on how to simplify heat transfer calculations below the heat shield region is investigated and discussed. The results are verified vs. a CFD based sensitivity analysis. Finally a reduction of the peak stress on the configuration with heat-shield is demonstrated relative to the peak stress calculated without heat-shield.
Numerical Study on Increased Energy Density for the DLN Micromix Hydrogen Combustion Principle
Authors: Haj Ayed A. , Kusterer K. , Funke H. H.-W. , Keinz J. , Kazari M. , Kitajima J. , Horikawa A. , Okada K. , Bohn D. 
Published: September 2014

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for Dry Low NOx (DLN) hydrogen combustion. Thus, the development of DLN hydrogen combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines.
The DLN Micromix combustion principle for hydrogen fuel is being developed since years to significantly reduce NOx-emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flashback and the low NOx-emissions due to a very short residence time of reactants in the flame region of the micro-flames.
For the low NOx Micromix hydrogen application the paper presents a numerical study showing the further potential to reduce the number of hydrogen injectors by increasing the hydrogen injector diameter significantly by more than 350% resulting in an enlarged diffusion-type flame size. Experimental data is compared to numerical results for one configuration with increased hydrogen injector size and two different aerodynamic flame stabilization design laws.
The applied design law for aerodynamic stabilization of the miniaturized flamelets is scaled according to the hydrogen injector size while maintaining equal thermal energy output and significantly low NOx emissions. Based on this parameter variation study the impact of different geometric parameters on flow field, flame structure and NOx formation is investigated by the numerical study.
The numerical results show that the low NOx emission characteristics and the Micromix flame structure are maintained at larger hydrogen injector size and reveal even further potential for energy density increase and a reduction of combustor complexity and production costs.
Effects of Air Jets Through Combustor Liner Holes on Emissions of Lean Staged Combustor
Authors: Yamamoto Takeshi , Shimodaira Kazuo , Kurosawa Yoji , Nakamura Naoki 
Published: September 2014

In JAXA, combustion technologies have been developed with a target that is an 80% NOx reduction of the CAEP/4 standard. A lean staged fuel nozzle with a pilot mixer and a main one in a coaxial arrangement has been developed by single-sector combustor tests under LTO cycle conditions of the target engine with a total pressure ratio of 25.8.
In this study, effects of air jets through combustion liner holes on combustion characteristics was investigated. Combustion tests were conducted by using four single-sector combustor liners with different air holes, no air holes, six air holes with short distance from the fuel nozzle, six air holes with long distance from the fuel nozzle, and one air flow path with three swirlers. From these results, air jets affect NOx emissions and combustion efficiency. Numerical analyses are also conducted by using a commercial large eddy simulation code, Front Flow Red. Quench of high temperature of pilot burned gas and NOx generation by air jets are captured by numerical simulations.
Optical Methods for Studies of Self-Excited Oscillations and the Effect of Dampers in a High Pressure Single Sector Combustor
Authors: Meier U. , Lange L. , Heinze J. , Hassa C. , Sadig S. , Luff D. 
Published: September 2014

Self-excited periodic instabilities in a staged lean burn injector could be forced by operating the combustor at off-design conditions. These pressure oscillations were studied in a high pressure single sector combustor with optical access. Two damper configurations were installed and tested with respect to their damping efficiency in relation to the configuration without dampers.
For a variety of test conditions, derived from a part load case, time traces of pressure in the combustor were measured, and amplitudes were derived from their Fourier transformation. These measurements were performed for several combinations of the operating parameters, i.e., injector pressure drop, air/fuel ratio, pilot/main fuel split and preheat temperature. These tests “ranked” the respective damper configurations and their individual efficiency with respect to the configuration without dampers. Although a general trend could be observed, the ranking was not strictly consistent for all operating conditions.
For several test cases, preferably with pronounced self-excited pressure oscillations, phase-resolved planar optical measurement techniques were applied to investigate the change of spatial structures of fuel, reaction zones and temperature distributions over a period of an oscillation. A pulsating motion was detected for both pilot and main flame, driven by a pulsating transport of the liquid fuel. This pulsation, in turn, is caused by a fluctuating air velocity, in connection with a prefilming airblast type atomizer. A phase shift between pilot and main injector heat release was observed, corresponding to a shift of fuel penetration.
Local Rayleigh indices were calculated qualitatively, based on phase-resolved OH chemiluminescence used as marker for heat release, and corresponding pressure values. This identified regions, where a local amplification of pressure oscillations occurred. These regions were largely identical to the reaction regions of pilot and main injector, whereas the recirculation zone between the injector flows was found to exhibit a damping effect.
Development of a Conjugate Heat Transfer Simulation Methodology for Prediction of Steam Turbine Cool-Down Phenomena and Shell Deflection
Authors: Mukhopadhyay Debabrata , Brilliant Howard M. , Zheng Xiaoqing 
Published: September 2014

Shell deflection during shutdown, cool-down process is a phenomenon well known to the steam turbine community. The main reason for this phenomenon is slower cooling of the top half shell and a relative faster cooling of the bottom half shell. There are multiple reasons for such thermal behavior of the two half casings, including natural heat convection from the bottom half to the top half, asymmetrical distribution of mass, dissimilar behavior of thermal insulation over the top and the bottom halves, etc. Shell deflection poses considerable challenge to the clearance engineer in terms of configuring operating clearance which ensures rub free operations. Understanding the cool-down process for the rotor is also equally important as the allowable steam inlet temperature during the hot or warm restart will depend on prevailing local temperature of the rotor.
This paper describes an exemplary physics-based cool-down prediction methodology capable of accurately capturing the rotor cool-down process. The methodology involves development of a full 3D rotor casing thermal model, integrated conjugate heat transfer FE model and validated with measured field data.
A Low Order Model for Predicting Turbocharger Turbine Unsteady Performance
Authors: Cao Teng , Xu Liping 
Published: September 2014

In this paper, a low order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three dimensional CFD method with multiple one-dimensional meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential non-uniformity. It also still maintains the desirable properties of being easy to set up and fast to run.
The model has been validated against a experimentally validated full three-dimensional URANS solver. The loss model in the meanline model is calibrated by the full 3D RANS solver under the steady flow states. The unsteady turbine performance under different inlet pulsating flow conditions predicted by the model was compared with the results of the full 3D URANS solver. Good agreement between the two was obtained with a speed up ratio of about four orders of magnitude (∼104) for the low order model.
The low order model was then used to investigate the effect of different pulse wave amplitudes and frequencies on the turbine cycle averaged performance. For the cases tested, it was found that compared with quasi-steady performance, the unsteady effect of the pulsating flow has a relatively small impact on the cycle averaged turbine power output and the cycle averaged mass flow capacity while it has a large influence on the cycle averaged ideal power output and cycle averaged efficiency. This is related to the wave dynamics inside the volute and the detailed mechanisms responsible are discussed in this paper.
Acoustic Design and Validation of Radial Inflow Turbine
Authors: Nordwall G. , Demeulenaere A. , Ferrante P. 
Published: September 2014

A radial inflow turbine installed in a large extraction facility in Canada has shown to be a significant contributor to the noise generated in that facility. These high sound pressure levels have led to the expenditure of millions of dollars in sound abatement measures over the last 20 years, and pose a health danger to employees.
Based on shop testing and field data, it was believed that a new rotor design could dramatically reduce the noise generated. It was further believed that Computational Fluid Dynamics with Aeroacoustic analyses was capable of predicting this improvement. Such a process can allow parts to be designed and installed quickly, when time and budget does not allow for detailed factory testing.
This paper describes this turbine redesign procedure and the details of the analyses performed throughout the process.
This new rotor has now been installed on-site, and measurements have been made before and after the replacement. This offers a unique opportunity to validate the numerical work performed through this redesign, which is also presented in the paper.
Alternative Method to Simulate a Sub-Idle Engine Operation in Order to Synthesize Its Control System
Authors: Sukhovii Sergii I. , Sirenko Feliks F. , Yepifanov Sergiy V. , Loboda Igor 
Published: September 2014

The steady-state and transient engine performances of gas turbine control system development are usually evaluated by applying full thermodynamic engine models. Most models only address the operating range between the idle and maximum power points, but more recently, they also address a sub-idle operating range.
The lack of information about the component maps at the sub-idle modes creates major challenges for the starting system and control system designers. A common method to cope with the problem extrapolates the performances of the engine components to the sub-idle operation range. Precise extrapolation is a challenge to be studied by many scientists. As a rule, many scientists are only concerned about particular aspects of the problem such as the lighting combustion chamber or the turbine operation under the turned-off conditions of the combustion chamber. However, there are no known reports about a model that considers all of these mentioned aspects and simulates the engine starting.
To synthesize a thermodynamic model of starting, most known methods require the performance of the components in the sub-idle range. The proposed paper addresses a new method that simulates the engine starting. The method substitutes the non-linear thermodynamic model with a linear dynamic model, which is supplemented with a simplified static model. The latter model is the set of direct relations between parameters that are used in the control algorithms instead of commonly used component performances. Specifically, the static model consists of simplified relations between the gas path parameters and the corrected rotational speed.
The paper also describes an algorithm for model synthesis and its practical application to real data.
Validation Results for a Diverse Set of Turbomachinery Cases Using a Density Based OpenFOAM® Solver
Authors: Anderson Mark R. , Bonhaus Daryl L. 
Published: September 2014

A validation study of a variety of compressible flow turbomachinery cases is presented with comparisons to test data using OpenFOAM. OpenFOAM is open-source code consisting of various solvers and computational libraries focused on CFD. The study used a particular solver version with a density based approach that was derived from the “extended” branch of OpenFOAM. The example cases all consisted of single blade row designs at steady state and were run fully viscous (unless noted otherwise) with various turbulence models.
The results showed a definite superiority of the density based solver over other OpenFOAM solvers in a test suite of simplified cases as well as in more complex examples in actual turbomachinery designs. A typical Laval nozzle case and transonic bump case are presented demonstrating the basic ability of the solver to capture shocks and to handle transonic flow in general. Actual turbomachinery applications consisted of a two-dimensional transonic compressor cascade, a moderately supersonic two-dimensional turbine cascade, two radial compressor cases, and a radial inflow turbine.
The results showed the solver to be very capable of capturing pressure distributions and, most importantly, aerodynamic loss through the machines. The ability of the solver to accurately model performance in a wide range of different designs and across the entire performance map was demonstrated. Detailed comparisons to highly regarded test data are shown.
Special examination was made of the computational costs of the solver which were quite high with run times coming in at about 10 times longer than other commercial compressible flow solvers. Several acceleration methods are discussed which significantly improved run time performance.