bluuebunny/crossref_metadata_2025_split huggingface dataset:
Smoothing Techniques for Real-Time Turbine Speed Sensors
Authors: Gutierrez Louis Alberto , Pezzini Paolo , Tucker David , Banta Larry 
Published: September 2014

A data noise reduction model for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (HyPer) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior.
The system is controlled by an embedded real-time control platform provided by Woodward Industrial Control. Every sensor is monitored by the platform, and an overall strategy drives the system from start-up to shut-down. Fuel is regulated by a valve which reacts based on the speed of the turbine. There are three optical encoder sensors which are used to monitor turbine speed, and the average of these three sensors is used as feedback for a PID controller, which works to regulate fuel consumption to the combustor. The turbine speed has demonstrated fluctuation in certain conditions, which may be a result of data noise combined with a systemic instability in the flow to the turbine.
This research introduces the method of Double Exponential Smoothing as it is applied to data noise reduction in an embedded control platform. An experimental test was conducted to evaluate the performance of the fuel valve speed control when filtered by a real-time Double Exponential Smoothing Algorithm. The results demonstrate, that when compared with traditional filtering techniques, Double Exponential Smoothing offers a significant improvement in both signal volatility and data latency.
Flame Response Analysis of Syngas
Authors: Gorski Jan , Chishty Wajid Ali , Johnson Matthew 
Published: September 2014

The motivation for the work comes from the requirement to assess the feasibility of using alternative fuels in lean-premixed land-based stationary gas turbine combustion systems. Lean-premixed systems are prone to combustion instability issues and the need is to determine how the use of alternative fuels would affect such instabilities.
The paper presents the results of an acoustically-forced laminar flat flame study that was conducted to measure the influence of flow velocity oscillations on the response of syngas flames under various operating conditions and in comparison to natural gas flames.
The results indicate that syngas concentration in a methane-syngas-air mixture significantly affects the flame response. On the other hand, the ratio of hydrogen-to-carbon monoxide in the syngas was found to have a negligible effect on the flame response for a fuel blend made up of 50% methane and 50% syngas. Flame liftoff distance and flame speed were found to be important parameters that govern the flame transfer function magnitude and resonant frequency for a thermally stabilized flat flame. The paper also presents insights into flame transfer function scaling based on a refined Strouhal definition.
The Use of CO2 to Improve Stability and Emissions of an IGCC Combustor
Authors: Lewis Jonathan , Marsh Richard , Valera-Medina Agustin , Morris Steven , Baej Hesham 
Published: September 2014

The use of gas for power generation is likely to increase in the medium term. Also, the introduction of new fuels will ensure a higher generation with lower emissions under continuous operation. These scenarios lead to the conclusion that there will be a considerably more diverse range of fuel supply. However, the use of these new fuels contrasts with recent experiences of global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in their fuel characteristics. Clearly there are significant challenges for fuel flexible gas turbines, particularly emission control, combustor dynamics and flame stability.
Trials using a power derivative gas turbine combustor and a high hydrogen content fuel produced unusual flashback events, in that flashback was induced by either leaning of the fuel mixture by the increase of combustion air, or by a change in composition through the reduction of methane pilot fuel. The introduction of CO2 through the combustors pilot injector prevented flashback from occurring under these circumstances. The resulting reduction of temperature in the combustion zone, indicated by lower burner tip temperatures causes a reduction in the emissions of nitrous oxides, whilst there is minimal effect on the effective turbine inlet temperature, only a 2.3% reduction.
Investigations using a ‘generic’, radial swirl burner and stereo PIV demonstrated how the flashback depended on a combination of flow structure augmentation and changes in mixture burning rate. The injection of methane or CO2 had differing effect on these parameters of the combustion zone, but both produced combinations that facilitated stability.
Modeling and Simulation of the Dynamic Operating Behavior of a High Solar Share Gas Turbine System
Authors: Felsmann Christian , Heide Stephan , Gampe Uwe , Freimark Manfred 
Published: September 2014

Solar gas turbine (GT) systems provide the opportunity to utilize solar heat at a much higher temperature than solar thermal power plants based on steam turbine cycles. Therefore gas turbine technology has the potential to improve the efficiency of future solar thermal power plants. Nevertheless, to achieve mature technology for commercial application, further development steps are required. Knowledge of the operational behavior of the solar GT system is the basis for the development of the systems control architecture and safety concept.
The paper addresses dynamic simulation of high solar share GT systems, which are characterized by primary input of solar heat to the gas turbine. To analyze the dynamic operating behavior, a model with parallel arrangement of the combustion chamber and the solar receiver was set up. By using the Heaviside step function, the system dynamics were translated into transfer functions which are used to develop controllers for the particular system configuration. Two operating conditions were simulated to test the controller performance. The first case is the slow increase and decrease of solar heat flow, as part of a regular operation. The second case is an assumed rapid change of solar heat flow, which can be caused by clouds. For all cases time plots of critical system parameters are shown and analyzed.
The simulation results show much more complex system behavior compared to conventional GT systems. This is due to the additional solar heat source, large volumes and stored thermal energy as well as the time delay of energy transportation caused by the piping system.
Numerical Aero-Thermal Analysis of a Rib-Roughened Trailing Edge Cooling Channel at Different Rotation Numbers and Channel Orientations
Authors: Pascotto Matteo , Armellini Alessandro , Casarsa Luca , Spring Sebastian 
Published: September 2014

The present work considers the aero-thermal characterization of a rib-roughened cooling channel for the trailing edge of gas turbine blades, and is based on previous findings from a smooth channel configuration. The passage is characterized by a trapezoidal cross section with high aspect-ratio, radial inlet flow, and coolant discharge at both model tip and trailing side, where seven elongated pedestals are installed. In this study, heat transfer augmentation is achieved by placing inclined squared ribs on the channel central portion.
RANS simulations with a SST turbulence model were performed using the commercial solver ANSYS CFX®v14. The numerical tool was first validated on the available experimental data and, subsequently, its capabilities were exploited in a wider range of working conditions, namely at higher rotation speed and different channel orientation. In this way it was possible to highlight the effects that ribs and working conditions have on the development of both flow and thermal fields.
The results show that rotation and channel orientation produce contrasting effects. On the rib-roughened wall, rotation/orientation generates an increase/decrease of the heat transfer; conversely, on the trailing side region rotation/orientation has a negative/positive effect on the thermal field.
An Experimental Study of the Load-Orientation Sensitivity of Three-Lobe Bearings
Authors: Khatri Rasish , Childs Dara W. 
Published: September 2014

Static and dynamic performance test results are provided for a three-lobe bearing evaluated over the following range of radial static-load orientations (taken from the leading edge of the loaded pad): 0°, 20°, 30°, 40°, 80°, 90°, and 100°. Static and dynamic test results are evaluated to determine the sensitivity of the bearing to changes in the static load direction.
The bearing has the following specifications: 100o arc angle, 0.52 preload, 70% offset, 101.74 mm minimum bore diameter, 0.116 mm radial pad clearance, and 76.3 mm axial length. The bearing is tested at 6750 rpm, 9000 rpm, 10800 rpm, and 13200 rpm, and at five different unit loads. Static measurements include hot and cold clearances, static eccentricities, and pad metal temperatures. Dynamic results include stiffness coefficients, damping coefficients, and whirl-frequency ratios (WFRs).
Dynamic tests show that the three-lobe bearing is very sensitive to load orientation at low speeds and high loads. Kxx is highest for the 80°, 90°, and 100° load orientations. Kyy is highest for the 20°, 30°, and 40° load orientations. Kxy is highest for the 80°, 90°, and 100° load orientations. The magnitude of Kyx is highest for the 0° and 20° load orientations. Cxx is largest for the 80°, 90°, and 100° load orientations, and Cyy is largest for the 0°, 20°, 30°, and 40° load orientations.
In terms of WFRs, it is generally dynamically advantageous to orient the static load vector for this bearing towards the leading edge of the pad. WFRs at 6750 rpm with loads of 1149 kPa, 1723 kPa, and 2298 kPa are equal to zero when the static load vector is pointed towards the leading edge of the pad and between 0.25 and 0.5 when the static load vector points towards the trailing edge of the pad. The bearing is not sensitive to load orientation at high speeds and light loads. At 13200 rpm, measured WFRs are between 0.2 and 0.6 at all loads and for all load orientations. Measured WFRs at the no-load condition are approximately 0.5 at all speeds.
Static data showed that the 30° and 90° load orientations yielded slightly higher measured maximum pad-metal-temperature increases at each speed relative to the other load orientations. At the highest static-load magnitudes, the pad metal temperatures are not as dependent on load orientation. The 20°, 30°, and 40° load orientations had the smallest measured eccentricity ratio, and thus the highest static stiffness.
Numerical Investigation of the Interaction Between Upstream Purge Flow and Mainstream in a Highly-Loaded Turbine
Authors: Jia Wei , Liu Huoxing 
Published: September 2014

In modern high pressure turbine, a certain amount of cooling air is bled off from compressor and then directly injected into the inter-stage gap between the stationary and rotating components. This paper presents a computational study of the interaction between mainstream flow and purge flow, with the objectives of evaluating the impacts of purge flow on turbine aerodynamic design parameters, tracing the loss sources involved with the injection of purge flow and describing the secondary flows near the hub region. The purge flow through the rim seal has been varied between 0–2% of the main flow and the axial position of rim seal has been also changed. Steady-state simulation using a 3D RANS solver is presented with particular emphasis on the mechanisms of loss production.
It is found that purge flow has a primary effect on the spanwise distribution of turbine aerodynamic design parameters, especially near the hub region. The losses brought about by the injection of purge flow can be divided into four parts: reaction redistribution between vane and blade in one stage, a shear layer between purge flow and mainstream flow due to different circumferential momentum, hub passage vortex interaction and decrease of output work near the end wall. However these four loss sources are not independent of each other. Shear induced vortex (SIV) and slot leakage vortex (SLV) appear near the hub region after purge flow is introduced. The shear induced vortex is formed due to the shear interaction between mainstream flow and purge flow which develop into hub passage vortex. The slot leakage vortex is formed due to the relative motion of the cavity disks and its strength is relatively weak compared with the shear induce vortex. The results gained from this paper may give some useful guidelines for turbine aerodynamic design and end wall profile optimization.
Sensitivity Analysis of Autoignition Simulation at Gas Turbine Operating Conditions
Authors: Prause Juliane , Noll Berthold , Aigner Manfred , Syed Khawar 
Published: September 2014

The demand to reduce CO2 emissions favors the use of alternative hydrogen-rich fuels, which can stem from pre-combustion carbon capture or power-to-gas technologies. These fuels are characterized by a higher reactivity and reduced ignition delay time compared to natural gas. Therefore, current combustor designs need to be adapted to the new requirements. Numerical modeling greatly assists the further development of such systems. The present study aims to determine how far a sophisticated combustion CFD method is able to predict autoignition at real engine conditions.
Scale-resolving computations of autoignition were performed at elevated pressure (15 bar) and intermediate temperatures (> 1000 K). The conditions are similar to those occurring in premixing ducts of reheat combustors. A nitrogen-diluted hydrogen jet is injected perpendicularly into a stream of hot vitiated air. The scale-adaptive simulation method (SAS) as proposed by Menter and co-workers has been applied. The chemistry is captured by direct inclusion of detailed kinetics. Subgrid fluctuations of temperature and species are considered by an assumed probability density function (PDF) approach. The results are compared with appropriate experimental reference data. The focus of the present work is set on the identification of the major sources of uncertainty in the simulation of autoignition. Despite the very challenging operating conditions, satisfactory agreements could be obtained within experimental uncertainties.
Numerical Investigation of Inlet Distortion on the Stall Inception of a Radial Compressor
Authors: Vagnoli S. , Verstraete T. 
Published: September 2014

In this paper unsteady CFD computations are used to study the stability and the rotating stall inception of a transonic radial compressor, considering two different configurations influencing the inlet flow. The prediction of the surge and stall limit for a centrifugal compressor is a key parameter for operating such machines, and hence requires attention already in the early design phase. Moreover, the operating margin can be dramatically influenced by non-uniform inlet conditions due to for example bended pipes mounted close to the inlet, as found more often today due to space limitation and optimization. In this case, it is not trivial to understand how the performance of the machine will be affected.
The influence on the stability limit of an elbow installed in front of the compressor inlet is analyzed in this paper by means of unsteady RANS simulations: results for two different configurations, with elbow and with straight inlet placed in front of the compressor, are compared. All simulations are done modeling the whole annulus of the radial machine, using high performance computing, in order to accurately take into account the non-periodic phenomena leading to stall inception. Moreover, mechanisms leading to flow separation for unstable solutions are studied, pointing out how they are influenced by the unsteady interactions of the tip leakage vortices with the main flow and by the distorted flow from the inlet elbow.
Unsteady Effects of a Generic Non-Axisymmetric Rotor Endwall Contour on a 1½ Stage Turbine Test Rig at Off Design Conditions
Authors: Dunn Dwain , Snedden Glen , von Backström Theodor 
Published: September 2014

With the current drive to improve fuel efficiency and reduce emissions, in gas turbine engines various methods have been investigated. Previously it has been shown that a generic rotor endwall contour could improve the efficiency of a 1½ stage test turbine at design conditions. The current investigation looked at the increased and decreased loading conditions to determine if the contour introduces detrimental effects at off design conditions.
A previous unsteady analysis of the design condition found that the contoured rotor does have an effect on the flow field, reducing the magnitude of the hub endwall secondary flow region as well as reducing fluctuations in the velocity.
Experimental results showed that the increased load case presented with an increase in hub endwall secondary flow structure when compared to the design case. This increase was to be expected due to the increased turning of the flow due to the increased loading operating condition. The contoured rotor had a weaker hub endwall secondary flow system, with the high momentum flow distributed more in the span wise direction. The variation in the velocity was also found to be smaller for the contoured rotor.
The decreased loading case showed similar improvements, but the extent of the change was less due to the lower turning of the flow (due to a faster rotor).
The numerical results show that the hub endwall secondary flow vortex of the contoured rotor was not as tightly wrapped as that of the annular rotor. The rotor outlet flow was thus more uniform due to the more dispersed vortex system. As seen with the experimental results, the extent of the change due to the contoured rotor changes with loading. The differences present in the decreased loading case being relatively insignificant.
It was concluded that the generic contour does not introduce any unsteady effects at off design conditions that were not observed in the design case.
Hydrogen Enriched Combustion Testing of SIEMENS Industrial SGT-400 at Atmospheric Conditions
Authors: Lam Kam-Kei , Geipel Philipp , Larfeldt Jenny 
Published: September 2014

In order to further extend the turbine fuel flex capability, a test under atmospheric conditions of a full-scale SGT-400 burner was performed to study the combustion behavior when operating on hydrogen enriched natural gas.
A high speed camera was installed in the rig to investigate the flame dynamics on different operation conditions. NOx emissions were measured for all presented conditions. The combustion system was instrumented with thermocouples on all the key locations to allow flame position monitoring and to avoid flame attachment on the hardware. Further measurements included static pressure probes to monitor combustor pressure drop.
The test was conducted in a systematic matrix format to include the most important combustion parameters in order to identify their individual effects on the combustion behaviors. The quantity of hydrogen in natural gas, fuel split, air preheat temperature, air reference velocity and flame temperature were the combustion related variables studied in the presented test campaign. The volumetric hydrogen quantity could be increased to 30% maintaining stable operation for all measured conditions. Higher hydrogen contents up to 80 vol-% were reached without flash back tendency. A glowing spark igniter prevented testing at even higher hydrogen contents. Hydrogen enriched gas showed higher NOx emissions and improved blowout limit. Hydrogen blending in the fuel also reduced the combustor pressure drop, lowered the prechamber temperature and raised the pilot tip temperature.
Developing a Reduced-Order Model of Non-Synchronous Vibration in Turbomachinery Using Proper Orthogonal Decomposition Methods
Authors: Clark Stephen T. , Besem Fanny M. , Kielb Robert E. , Thomas Jeffrey P. 
Published: September 2014

The paper develops a reduced-order model of non-synchronous vibration (NSV) using proper orthogonal decomposition (POD) methods. The approach was successfully developed and implemented, requiring between two and six POD modes to accurately predict CFD solutions that are experiencing non-synchronous vibration. This POD method was first developed and demonstrated for a transversely-moving, two-dimensional cylinder in cross-flow. Later, the method was used for the prediction of CFD solutions for a two-dimensional compressor blade.
This research is the first to offer a proper orthogonal decomposition approach to the reduced-order modeling of non-synchronous vibration in turbomachinery. Modeling non-synchronous vibration is especially challenging because NSV is caused by complicated, unsteady flow dynamics; this initial study helps researchers understand the causes of NSV, and aids in the future development of predictive tools for aeromechanical design engineers.
Rotordynamic Performance of a Negative-Swirl Brake for a Tooth-on-Stator Labyrinth Seal
Authors: Childs Dara W. , Mclean James E. , Zhang Min , Arthur Stephen P. 
Published: September 2014

In the late 1970’s, Benckert and Wachter (Technical University Stuttgart) tested labyrinth seals using air as the test media and measured direct and cross-coupled stiffness coefficients. They reported the following results: (1) Fluid pre-swirl in the direction of shaft rotation creates destabilizing cross-coupled stiffness coefficients, and (2) Effective swirl brakes at the inlet to the seal can markedly reduce the cross-coupled stiffness coefficients, in many cases reducing them to zero. In recent years, “negative-swirl” swirl brakes have been employed that attempt to reverse the circumferential direction of inlet flow, changing the sign of the cross-coupled stiffness coefficients and creating stabilizing stiffness forces. This study presents test results for a 16-tooth labyrinth seal with positive inlet preswirl (in the direction of shaft rotation) for the following inlet conditions: (1) No swirl brakes, (2) Straight, conventional swirl brakes, and (3) Negative-swirl swirl brakes. The negative-swirl swirl-brake designs were developed based on CFD predictions. Tests were conducted at 10.2, 15.35, and 20.2 krpm with 70 bars of inlet pressure for pressure ratios of 0.3, 0.4, 0.5.
Test results include leakage and rotordynamic coefficients. In terms of leakage, the negative-swirl brake configuration leaked the least, followed by the conventional brake, followed by the no-brake design. Normalized to the negative-swirl brake configuration, the conventional-brake and no-brake configurations mass flow rate were greater, respectively, by factors of 1.04 and 1.09.
The direct stiffness coefficients are negative but small, consistent with past experience. The conventional swirl brake drops the destabilizing cross-coupled stiffness coefficients k by a factor of about 0.8 as compared to the no-brake results. The negative-swirl brake produces a change in sign of k with an appreciable magnitude; hence, the stability of forwardly-precessing modes would be enhanced.
In descending order, the direct damping coefficients C are: no-swirl, negative-swirl, conventional-swirl. Normalized in terms of the no-swirl case, C for the negative and conventional brake designs are, respectively, 0.7 and 0.6 smaller.
The effective damping Ceff combines the effect of k and C. Ceff is large and positive for the negative-swirl configuration and near zero for the no-brake and conventional-brake designs.
The present results for a negative-brake design are very encouraging for both eye-packing seals (where conventional swirl brakes have been previously employed) and division-wall and balance-piston seals where negative shunt injection has been employed.