bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Characterization and Identification of Flow in a Blade Passage in Near-Stall Conditions of Axial Compressor Systems
Authors: Aung Eighdi , Schoen Marco P. , Li Jichao 
Published: November 2019

Abstract
Axial compressor systems are susceptible to unstable conditions near their optimal operating point. In particular, rotating stall and surge are conditions that need to be avoided during the operation of an axial compressor. In extreme cases these conditions may cause damage to the compressor. The onset of either condition is rather rapid, and usually does not allow for remedial control action based on the limited time available. Hence, research efforts have been focusing on the development of new detection methods that allow for more time to take corrective measures. This paper explores and compares various existing and proposed methods to identify and detect those precursors. The methods detailed in this work are tested at different operating conditions and locations. The methods investigated include the sequentially computed correlation coefficient of pressure sensor data, correlation coefficient, the Generalized Extreme Studentized Deviate Test (ESD) for outlier detection, spectral entropy, and Autoregressive (AR) models. The primary goal of evaluating these methods is based on their suitability for employment as pre-processors for dynamic system identification. By using the dynamics of the identified model rather than a static precursor, it is stipulated that the onset of stall and surge can be managed with a control concept. For this work, the extracted models are investigated for suitability to serve as precursors, and the potential as predictive models. This work may serve for future work to achieve active flow control by direct air injection at the leading edge of the blades. For this work, a one-stage compressor system with a blade geometry that allows for spike inception is utilized. Spike stall inception is a precursor to fully developed rotating stall. The subsonic compressor has 60 blades, and its operating point is controlled by a throttle and constant speed control of the rotor. The pressure data is collected with 10 Kulite™ sensors which are placed along the blade cord length on the outer casing of the compressor. The results of the tabulated performance of the various methods and resulting models indicate that an ARESD combination yields the earliest indication for spike stall inception.
The Effect of Rotor-Stator Gap on Repeating-Stage Compressor Loss
Authors: Przytarski Pawel J. , Wheeler Andrew P. S. 
Published: November 2019

Abstract
In this paper we study the effect of rotor-stator axial gap on midspan compressor loss using high fidelity Large-Eddy Simulations. For this purpose we mimic the multi-stage environment using a new numerical method which recycles wake unsteadiness from a single blade passage back into the inlet of the computational domain. As a result a type of repeating-stage simulation is obtained such as observed by an embedded blade-row. We find that freestream turbulence levels rise significantly as the size of the rotor-stator axial gap is reduced. This is because of the effect of axial gap on turbulence production, which becomes amplified at smaller axial gaps and drives increases in dissipation and loss. This effect is found to raise loss by between 7–9.5% over the range of conditions tested here. This effect significantly outweighs the beneficial effects of wake recovery on loss.
Effect of High Pressures on the Formation of Nitric Oxide in Lean, Premixed Flames
Authors: Versailles Philippe , Durocher Antoine , Bourque Gilles , Bergthorson Jeffrey M. 
Published: November 2019

Abstract
Increasingly stringent regulations are imposed on nitrogen oxides emissions due to their numerous negative impacts on human health and the environment. Accurate, experimentally validated thermochemical models are required for the development of the next generation of combustors. This paper presents a series of experiments performed in lean, premixed, laminar, jet-wall stagnation flames at pressures of 2, 4, 8, and 16 atm. To target post-flame temperatures relevant to gas turbine engines, the stoichiometry of the non-preheated methane-air mixture is adjusted to an equivalence ratio of 0.7. One-dimensional profiles of temperature and NO mole fraction are measured via laser-induced fluorescence (LIF) thermometry and NO-LIF, respectively, to complement previously published flame speed data [1]. The results reveal that, as the pressure increases, the maximum post-flame temperature stays relatively stable, and the concentration of NO produced through the flame front remains constant within uncertainty. Seven thermochemical models, selected for their widespread usage or recent date of publication, are validated against the experimental data. While all mechanisms accurately predict the post-flame temperature, thanks to consistent thermodynamic parameters, important disagreements are observed in the NO concentration profiles, which highlights the need to carefully select the models used as design tools. The lack of pressure dependence of NO formation that many models fail to capture is numerically investigated via sensitivity and reaction path analyses applied to the solution of flame simulations. The termolecular reaction H+O2 (+M) ↔ HO2 (+M) is shown to hinder the production of atomic oxygen and hydrogen radicals at higher pressures, which inhibits the formation of nitric oxide through the N2O pathway.
Field Qualification of an Improved DLE Gas Turbine Control Algorithm to Reduce Part Load Emissions
Authors: Cowell Luke , Roesch James , Camou Alejandro , Caron Tim , Ritchie Jason , Carlos Ivan 
Published: November 2019

Abstract
The importance of expanded operating flexibility with reduced emissions on dry low emissions (DLE) gas turbines to lower loads has grown in importance for operators in many applications including natural gas transmission. Solar Turbines has developed an improved emissions control algorithm for Solar’s SoloNOx DLE gas turbines being offered as Enhanced Emissions Control. The new algorithm reduces carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions from idle to 50% load. The corresponding startup and shut down emissions are reduced so that operators can obtain permits for operation over longer periods outside of low emissions mode. The algorithm has been evaluated in field trials at two different compressor stations using different gas turbine engine models. Solar’s Taurus™ 60 was tested at a field site in West Virginia and a Mars® 100 was tested near Houston, Texas in the United States. The new control scheme reduces emissions from part load down to idle. The new controls extend the bleed valve or variable guide vanes’ operating range where they modulate to control combustor temperature from idle to full load. The pilot fuel schedule is also changed to work more directly with the combustor temperature control.
Two field trials were completed to measure emissions continuously for more than 10 months at each site to validate the effectiveness of the new algorithm. Operation of the test units was largely at loads over 50% and the continuous data served to validate that the new algorithm with the modifications to pilot control did not change the emissions signature in the ‘low emissions mode.” In addition, multiple site visits were completed to map emissions from idle to 50% load over a range of engine settings. This mapping fully documented the complete emissions performance of the test units from idle to 100% load over a range of ambient temperatures from below freezing to 38°C.
The field trials validate that the improved controls reduce CO and UHC emissions from idle to 50% load when compared to the current production algorithm. The testing also validated that the emissions above 50% load were unchanged compared to the current control algorithm. Specifically, CO and UHC emissions were reduced by 35 to 99% over the idle to 50% load operating range. By optimizing the pilot fuel controls the NOx emissions were also reduced 20 to 75% from idle to 50% load. The algorithm makes it possible to offer 15 ppm NOx warranties for the subject engine models in gas transmission applications down to 40% load that have been restricted to 50% load and higher. Over the wide ambient temperature range experienced during the field trial periods, emissions were consistent and no clear trends were documented with ambient temperature or engine speed (load).
Numerical Study on the Flow and Heat Transfer Characteristics With Different Rib Structures Placed on the Impingement Plate
Authors: Ding Yong-feng , Zhu Hui-ren , Gao Qiang 
Published: November 2019

Abstract
Jet impingement cooling is an important way to cool turbine blades. Ribbed channels are widely used in the chord region of turbine blades and are an important internal cooling structure. In the design process of the internal cooling structure of the conventional turbine blade, it is the primary consideration of the designer to improve the heat transfer coefficient at the surface of the inner cooling passage. With the development of the design of the inner cooling structure of the turbine blade, the pressure loss caused by the inner cooling passage has been paid more and more attention. Therefore, many studies have begun to comprehensively consider the potential of various rib structures in enhancing heat transfer and reducing flow resistance. In the design process of the internal cooling structure of the conventional turbine blade, the rib is placed on the blade, which increases the blade burden. In this paper, the classic rib structure is changed, and the rib is placed on the impingement plate to research its heat transfer characteristics. In this study, the effects of ribs of different structures on heat transfer were tested. Calculate the working conditions of Reynolds number Re = 15000, 20000, 25000, 30000. The numerical calculation of the SST k-w model is used to evaluate the average Nusselt number of the target plate and the flow coefficient of the channel, and the heat transfer distribution and flow field are analyzed. This study is expected to achieve better coordination between improved heat transfer and reduced flow resistance.
Overall Cooling Effectiveness on a Gas Turbine Vane With Swirl-Film Cooling
Authors: Du Haifen , Xie Danmei , Chen Wei , Mei Ziyue , Zhang Jing 
Published: November 2019

Abstract
Numerical calculation of conjugate heat transfer is carried out to study the effect of combined film and swirl cooling at the leading edge of a gas turbine vane with a a cooling chamber inside, in which 3-D steady RANS approach with the k-ω SST turbulence model is used. Two different kinds of coolant chamber configuration (C1 and C2) are selected. In C2, the cooling chamber is composed of a front cavity and a back cavity, and the two cavities are connected by a passage which is divided into 16 segments. The comparative investigations between C1 and C2 cases have been carried out to study the effect of different cooling chambers at M = 0.25, 0.5, 1 and 2. For two cases, overall cooling effectiveness increases with M increasing. In C1 case, with increasing M, differences of mass flow through film holes rows will decrease. The variation of mass flow from holes changes by less than 26.7% at M = 2. However, in C2 case, mass flow through S1 and S2 is significantly larger than that through other film holes rows. Area-averaged overall effectiveness in C2 is larger by 2.5% at M = 0.25 compared to C1 case.
Experimental Rotordynamic Force Coefficients for a Diffusion Bonded Compliant Hybrid Journal Gas Bearing Utilizing Fluid-Filled Hermetic Dampers
Authors: Gary Keith , Ertas Bugra 
Published: November 2019

Abstract
Dynamic force coefficients are presented from experimental results of a radial gas bearing with hermetically sealed squeeze film dampers (HSFD) in the bearing support. HSFDs are a relatively new technology aimed to increase damping levels in gas bearings while sustaining an oil-free bearing sump. Past HSFD designs proved bulky and contained many components making it difficult to employ in size limited environments such as jet engines, while the diffusion bonded bearing discussed in the present paper provides a compact integral design. Test results for a three-inch diameter bearing using a test rig providing static loads up to 80 lbs, controlled-dynamic orbital motion, and speeds up to 27 krpm are shown. Results include frequency and speed dependent direct and cross-coupled rotordynamic force coefficients. Dynamic testing showed little dependence on rotor speed or static load and exhibited frequency dependency at lower excitation frequencies. Cross-coupled terms are generally an order of magnitude lower than direct terms. Results show the direct stiffness coefficients increasing with frequency while direct damping decays radically with frequency. Comparison of the overall gas bearing coefficients with a companion paper [1], showing bearing support coefficients, reveals a drastic reduction in damping when engaging the gas film. The results also indicate the bearing can withstand vibration levels representative of a large rotor system critical speed at lower excitation frequencies.
Working Fluid Selection for a Waste Heat Recovery Organic Rankine Cycle (ORC) Applied to a Petroleum Distillation Process
Authors: Peralta Sergio , Celis Cesar 
Published: November 2019

Abstract
This work describes a working fluid selection process for an ORC based power plant that uses as heat source waste heat from a petroleum distillation furnace. Sixteen (16) organic fluids previously considered for similar applications are analyzed based on environmental, safety and physical properties. Two different power plants layouts, a basic one and another featuring an internal heat exchanger (IHE), are analyzed. The combinations between working fluids and plant layouts seek to maximize the ORC-based power plant thermal efficiency. ORC exergy destruction and exergy efficiency are also accounted for. In this work, the close interrelation between working fluids thermo-physical properties and expander dimensionless characteristics is also assessed. The main results indicate that R245ca and R245fa are the working fluid leading to both the highest thermal (∼16%) and exergy efficiencies (∼23%), and the lowest exergy destructions (∼703 kW). Based on required properties of the selected working fluid, an axial turbine design seems to be the most appropriate ORC expander technology for the particular application discussed in this paper. The outcomes from this work will be used as the basis for the detailed design of the components of an ORC-based power plant focused on increasing the overall efficiency of petroleum distillation processes.
Numerical Study of Heat Transfer in Novel Wavy Trailing Edge Design for Gas Turbine Airfoils
Authors: Parbat Sarwesh , Yang Li , Chyu Minking , Siw Sin Chien , Lee Ching-Pang 
Published: November 2019

Abstract
The strive to achieve increasingly higher efficiencies in gas turbine power generation has led to a continued rise in the turbine inlet temperature. As a result, novel cooling approaches for gas turbine blades are necessary to maintain them within the material’s thermal mechanical performance envelope. Various internal and external cooling technologies are used in different parts of the blade airfoil to provide the desired levels of cooling. Among the different regions of the blade profile, the trailing edge (TE) presents additional cooling challenges due to the thin cross section and high thermal loads. In this study, a new wavy geometry for the TE has been proposed and analyzed using steady state numerical simulations. The wavy TE structure resembled a sinusoidal wave running along the span of the blade. The troughs on both pressure side and suction side contained the coolant exit slots. As a result, consecutive coolant exit slots provided an alternating discharge between the suction side and the pressure side of the blade. Steady state conjugate heat transfer simulations were carried out using CFX solver for four coolant to mainstream mass flow ratios of 0.45%, 1%, 1.5% and 3%. The temperature distribution and film cooling effectiveness in the TE region were compared to two conventional geometries, pressure side cutback and centerline ejection which are widely used in vanes and blades for both land-based and aviation gas turbine engines. Unstructured mesh was generated for both fluid and solid domains and interfaces were defined between the two domains. For turbulence closer, SST-kω model was used. The wall y+ was maintained < 1 by using inflation layers at all the solid fluid interfaces. The numerical results depicted that the alternating discharge from the wavy TE was able to form protective film coverage on both the pressure and suction side of the blade. As a result, significant reduction in the TE metal was observed which was up to 14% lower in volume averaged temperature in the TE region when compared to the two baseline conventional configurations.
Condition Monitoring of Wind Turbine Planetary Gearboxes Under Different Operating Conditions
Authors: Mauricio Alexandre , Sheng Shuangwen , Gryllias Konstantinos 
Published: November 2019

Abstract
Digitally enhanced services for wind power could reduce Operations and Maintenance (O&M) costs as well as the Levelised Cost Of Energy (LCOE). Therefore, there is a continuous need for advanced monitoring techniques which can exploit the opportunities of Internet of Things (IoT) and Big Data Analytics, revolutionizing the future of the energy sector. The heart of wind turbines is a rather complex epicyclic gearbox. Among others, extremely critical gearbox components which are often responsible for machinery stops are the rolling element bearings. The vibration signatures of bearings are rather weak compared to other components, such as gears, and as a result an extended number of signal processing techniques and tools have been proposed during the last decades, focusing towards accurate, early, and on time bearing fault detection with limited false alarms and missed detections. Envelope Analysis is one of the most important methodologies, where an envelope of the vibration signal is estimated usually after filtering around a frequency band excited by impacts due to the bearing faults. Different tools, such as Kurtogram, have been proposed in order to accurately select the optimum filter parameters (center frequency and bandwidth). Cyclic Spectral Correlation and Cyclic Spectral Coherence, based on Cyclostationary Analysis, have been proved as very powerful tools for condition monitoring. The monitoring techniques seem to have reached a mature level in case a machinery operates under steady speed and load. On the other hand, in case the operating conditions change, it is still unclear whether the change of the monitoring indicators is due to the change of the health of the machinery or due to the change of the operating parameters. Recently, the authors have proposed a new tool called IESFOgram, which is based on Cyclic Spectral Coherence and can automatically select the filtering band. Furthermore, the Cyclic Spectral Coherence is integrated along the selected frequency band leading to an Improved Envelope Spectrum. In this paper, the performance of the tool is evaluated and further extended on cases operating under different speeds and different loads. The effectiveness of the methodology is tested and validated on the National Renewable Energy Laboratory (NREL) wind turbine gearbox vibration condition monitoring benchmarking data set which includes various faults with different levels of diagnostic complexity as well as various speed and load operating conditions.
Assessment of Long Term Creep Using Strain Rate Matching From the Stepped Isostress Method
Authors: Mach Robert , Pellicotte Jacob , Haynes Amanda , Stewart Calvin 
Published: November 2019

Abstract
Creep testing is an ongoing need, particularly with the development of new candidate alloy systems for advanced energy systems. The conventional creep test (CT) is regarded as a proven method to gather creep data however, the test is impractical due to being real-time: lasting up to 105 hours to characterize the service of long-lived turbomachinery components. Accelerated methods to gather the long-term creep properties of materials are needed to reduce the time to qualification of new materials. The time-temperature-stress-superposition principle (TTSSP) and the derivative time-temperature superposition principle (TTSP), time-stress superposition principle (TSSP), stepped isothermal method (SIM), and stepped isostress method (SSM) are accelerated creep tests (ACT) commonly used to predict the long-term creep behaviors of polymers and composites. The TTSP and TSSP tests require multiple specimen tested at various temperatures/stresses whereas the SIM and SSM tests employ a single specimen where temperature/stress are periodically step increased until rupture. The stepped creep deformation curve can then be time and strain shifted to produce a master creep curve. While these ACTs are useful tools to predict long-term creep, the drawback is the lack of mathematical laws to determine the virtual start time and time shift factors, especially for different materials.
In this paper, a new self-calibration approach is developed and compared to existing SSM data for Kevlar 49. This new approach focuses on matching the creep strain rates between stress steps and fitting the data to a master curve using a modified theta projection model. This is performed using a MATLAB code consisting of five subroutines. The first subroutine takes the stress, time, and creep strain from SSM/SIM tests, and segregates the data intro arrays corresponding to each stress level. The second subroutine finds the constants for the modified theta projection model for each stress level. The third subroutine performs a time shift adjustment using creep strain rate matching. The fourth subroutine calculates the accelerated time of rupture. The last subroutine generates accelerated creep versus time plots. Kevlar 49 SSM data is gathered from literature and run through the MATLAB code. The master curves generated from the MATLAB are compared to the conventional creep curve of Kevlar 49 as well as the master curve gathered from literature in order to validate the feasibility of this new approach. The goal of this project is to vet if the self-calibration approach can produce results similar to the reference calibration approach.