bluuebunny/crossref_metadata_2025_split huggingface dataset:
Capturing the Effects of NOx and SOx Impurities on Oxy-Combustion Under Supercritical CO2 Conditions for Coal-Derived Syngas and Natural Gas Mixtures
Authors: Rahman Ramees K. , Barak Samuel , Manikantachari K. R. V. (Raghu) , Ninnemann Erik , Hosangadi Ashvin , Zambon Andrea , Vasu Subith S. 
Published: January 2021

Abstract
Direct fired supercritical carbon dioxide cycles are one of the most promising power generation method in terms of their efficiency and environmental friendliness. Two most important challenges in implementing these cycles are the high pressure (300 bar) and high CO2 dilution (&gt;80 %) in the combustor. The design and development of supercritical oxy-combustors for natural gas requires accurate reaction kinetic models to predict the combustion outcomes. The presence of small amount of impurities in natural gas and other feed streams to oxy-combustors makes these predictions even more complex. During oxy-combustion, trace amounts of nitrogen present in the oxidizer is converted to NOx and gets into the combustion chamber along with the recirculated CO2. Similarly, natural gas can contain trace amount of ammonia and sulfurous impurities which gets converted to NOx and SOx and gets back into the combustion chamber with recirculated CO2. In this work, a reaction model is developed for predicting the effect of impurities like NOx and SOx on supercritical methane combustion. The base mechanism used in this work is GRI 3.0. H2S combustion chemistry is obtained from Bongartz et al. while NOx chemistry is from Konnov et al. The reaction model is then optimized for a pressure range of 30–300 bar using high pressure shock tube data from literature. It is then validated with data obtained from literature for methane combustion, H2S oxidation and NOx effects on ignition delay. The effect of impurities on CH4 combustion up to 16 atm is validated using NOx doped methane studies obtained from literature. In order to validate the model for high pressure conditions, experiments are conducted in a high pressure (∼100 bar) shock tube facility at UCF for natural gas identical mixtures with N2O as impurity. Current results show that there is significant change in ignition delay with the presence of impurities. A comparison is made with experimental data using the developed model and predictions are found to be in good agreement. The model developed was used to study the effect of impurities on CO formation from sCO2 combustor. It was found that NOx helps in reducing CO formation while presence of H2S results in formation of more CO. The reaction mechanism developed herein can also be used as a base mechanism to develop reduced mechanism for use in CFD simulations.
Experimental Research on Dynamic Characteristics of Plasma Ignition Jet
Authors: You Binchuan , Yang Jialong , Liu Xiao , Kong Long , Yan Shilin , Zhang Zhihao 
Published: January 2021

Abstract
The performance of the ignition device has an impressive impact on the working range and reliability of gas turbines. In the extreme conditions and with low pollutant emissions, gas turbines advancing higher requirements for the better performance of the ignition device. Due to its exceptional advantages, plasma ignition technology has become a research hotspot for all the scholars around the globe. The plasma ignition device ignites by the plasma jet with high-temperature and abundant active species, which has the advantages of large ignition energy, concentrated energy and strong penetration of the plasma jet.
In the current research work, experimental research work is carried out on the plasma ignition using the plasma jet. The voltage and current features of plasma power supply are measured by a voltage probe and a current probe. The developed process of plasma jet generation is captured by a high-speed camera. The characteristics of plasma jet morphology and the law of the influence of the variable electrode gap (1.5 mm-3.5 mm) on the features of the plasma jet morphology are investigated.
The experimental results demonstrate that during plasma ignition the discharge voltage and the current have a maximum peak-to-peak value of 11.67kV and 70A. The maximum reverse voltage and the reverse current are 2000V and 15A during the discharge and breakdown. The plasma jet produced active species along with a cone-shaped high-temperature during the air breakdown. The structure of the plasma jet can be divided into two portions, central high-temperature kernel (HTK) and peripheral halo gas (PHG) by gray processing of high-speed camera pictures. Different discharge electrode gap is leading to change the size of the plasma jet high-temperature kernel and the peripheral halo gas. If the gap of the discharge electrode is increased, then the area of the high-temperature kernel is also increased.
Flow Field, Spray Distribution and Pilot Flame Stabilization in a Centrally Staged Combustor
Authors: Wang Bo , Ren Guangming , Gan Xiaohua , Lin Yuzhen 
Published: January 2021

Abstract
Centrally staged lean premixed prevaporized low emission combustor has achieved great commercial success in the past decade. Pilot flame characteristics is with key importance to centrally staged combustor, which is considered not entirely up to the design of pilot stage, but also influenced by the flow field and fuel distribution of the combustor. The flow field and fuel distribution behaviors in centrally staged combustor are not very clear since the role of LRZ is unknown, as well as the pilot flame stabilization mechanism. The goal of this paper is to study the flow field, spray distribution and pilot flame stabilization in centrally staged combustor. This paper designs a comparison scheme of the dome lip for study. Particle image velocimetry, Planar Mie scattering measurements and high-speed camera experiments are conducted to get an in depth understanding on the flow field, spray distribution characteristics and pilot flame stabilization in a centrally staged combustor. The flow field with a 3.0 mm lip incline is quite different. Two PRZs forms, one connected with the LRZ and the other at the outlet of pilot stage. Pilot flow no longer joins to the main flow but flows alone in the center. It seems like it is the decoupling pilot stage air cutting PRZ into two PRZs. The pilot spray has a conical boundary and it is probably formed by the high velocity main air flow. A considerable number of fuel droplets are involved in LRZ with the lip incline. Two shapes of pilot flame are observed, the V-shaped flame and double root flame. High-speed camera has captured the flame stabilization process close to LBO. As for the V-shaped pilot flame, the central flame root performs an extinction/relight cycle close to LBO. The cycle duration time is much longer than the critical time of swirl cup methane flame previously reported. As for the double root pilot flame, the central flame root is lighted before the lip flame root and it is the central flame that plays the leading role in stabilizing the whole flame. The lip flame root can weaken the quench effect of main air and broaden the flame stability boundary. A relatively large lip height is recommended for the consideration of the LBO performance.
Dynamics of Shock Waves Interacting With Laminar Separated Transonic Turbine Flow Investigated by High-Speed Schlieren and Surface Hot-Film Sensors
Authors: Börner Marcel , Niehuis Reinhard 
Published: January 2021

Abstract
The results presented in this paper are based on experimental investigations on a generic transonic low pressure turbine profile at high subsonic exit Mach numbers. Here, the flow on the suction side reaches a maximum isentropic Mach number of approximately 1.2 and features a large separation bubble in a transonic flow regime characterized by Surface Hot-Film measurements. The measurements are supplemented by Schlieren images recorded with a high-speed camera at 19.2 kHz. A highly unsteady normal shock wave on the suction side is observable upstream of the trailing edge. It is interacting with laminar separated flow which is rarely documented in literature. The interaction of the normal shock with the boundary layer flow seems to amplifies the ongoing transition process over the separation bubble and the flow reattaches shortly downstream. A statistical analysis of the Schlieren images reveals characteristic low frequencies of the shock wave motions and a pulsation of the separation bubble. Additionally, the statistical information of the time-dependent signal from the Surface Hot-Film sensors demonstrate the instabilities influencing the boundary layer linked to the unsteadiness in the main flow.
Experimental and Numerical Study on the Effects of the Relative Position of Film Hole and Orientation Ribs on the Film Cooling With Ribbed Cross-Flow Coolant Channel
Authors: Li Bingran , Liu Cunliang , Ye Lin , Zhu Huiren , Zhang Fan 
Published: January 2021

Abstract
To investigate the application of ribbed cross-flow coolant channels with film hole effusion and the effects of the internal cooling configuration on film cooling, experimental and numerical studies are conducted on the effect of the relative position of the film holes and different orientation ribs on the film cooling performance. Three cases of the relative position of the film holes and different orientation ribs (post-rib, centered, and pre-rib) in two ribbed cross-flow channels (135° and 45° orientation ribs) are investigated. The film cooling performances are measured under three blowing ratios by the transient liquid crystal measurement technique. A RANS simulation with the realizable k-ε turbulence model and enhanced wall treatment is performed. The results show that the cooling effectiveness and the downstream heat transfer coefficient for the 135° rib are basically the same in the three position cases, and the differences between the local effectiveness average values for the three are no more than 0.04. The differences between the heat transfer coefficients are no more than 0.1. The “pre-rib” and “centered” cases are studied for the 45° rib, and the position of the structures has little effect on the film cooling performance. In the different position cases, the outlet velocity distribution of the film holes, the jet pattern and the discharge coefficient are consistent with the variation in the cross flow.
The related research previously published by the authors showed that the inclination of the ribs with respect to the holes affects the film cooling performance. This study reveals that the relative positions of the ribs and holes have little effect on the film cooling performance. This paper expands and improves the study of the effect of the internal cooling configuration on film cooling and makes a significant contribution to the design and industrial application of the internal cooling channel of a turbine blade.
Aerodynamic Damping Analysis for Radial Turbine Featuring a Multi-Channel Casing Design
Authors: Hassan Ahmed Farid , Müller Tobias , Schatz Markus , Vogt Damian M. 
Published: January 2021

Abstract
Radial turbine featuring a Multi-channel Casing (MC) is a new design under investigation for enhancing the turbine controllability. The idea behind this new design is to replace the traditional spiral casing with a MC, which allows controlling the mass flow by means of opening and closing control valves in each channel. The arrangement of the closed and opened channel is called the admission configuration, while the ratio between the counts of the open channels to the total number of channels is called the admission percentage.
Among several aspects, when applying different admission configurations, the aerodynamic damping during resonant excitation is considered during the design of the turbine. The present study aims at investigating the effect of different MC admission configurations on the aerodynamic damping as an extension to an aerodynamic forcing study, which already assessed the different forcing patterns associated with these different admission configurations.
Due to the asymmetry of the flow in circumferential direction resulting from the different partial admission configurations, the computational model is solved as full 3D time-marching, unsteady flow using ANSYS CFX in a one-way fluid-structure analysis. Two different modeling approaches have been considered in this study to investigate their capability of predicting the damping ratio for different MC admission configurations: a) the conventional isolated rotor approach and b) a full model consisting of the rotor and its casing. The results show that the casing affects the aerodynamic damping behavior, which can only be captured by the full model. Furthermore, the damping ratios for all different admission configurations have been calculated using the full stage model.
Experimental and Numerical Study on the Flow Field Around a Parallel-Foil Turbine
Authors: Wang Yulu , Zhang Di , Xie Yonghui 
Published: January 2021

Abstract
An experiment facility of parallel-foil turbine is proposed in this study. The flow field around foils at different reduced frequency, pitching amplitude and plunging amplitude is measured by 2D Particle Image Velocimetry (PIV) system. And the energy extraction performance at different motion parameters is analyzed numerically. The comparison between experimental and numerical flow field is conducted at different reduced frequency. The evolution of flow field and the aerodynamic force with different pitching amplitude and plunging amplitude are discussed. The effect of pitching amplitude and plunging amplitude on energy extraction performance is obtained. Results indicate that the pitching amplitude can increase the range and the strength of acceleration area by varying the pitching velocity and the effective angle of attack. The optimal extraction performance appears at 70°. Due to the increase in plunging amplitude, the energy extraction performance and efficiency increase gradually. The optimal plunging amplitude is 1.0. The pitching amplitude and the plunging amplitude influence the power output by affecting the vortex shedding and the flow reattachment in oscillation process.
Aerothermal Effect of Cavity Welding Beads on a Transonic Squealer Tip
Authors: Vieira Joao , Coull John , Ireland Peter , Romero Eduardo 
Published: January 2021

Abstract
High pressure turbine blade tips are critical for gas turbine performance and are sensitive to small geometric variations. For this reason, it is increasingly important for experiments and simulations to consider real geometry features. One commonly absent detail is the presence of welding beads on the cavity of the blade tip, which are an inherent by-product of the blade manufacturing process. This paper therefore investigates how such welds affect the Nusselt number, film cooling effectiveness and aerodynamic performance.
Measurements are performed on a linear cascade of high pressure turbine blades at engine realistic Mach and Reynolds numbers. Two cooled blade tip geometries were tested: a baseline squealer geometry without welding beads, and a case with representative welding beads added to the tip cavity. Combinations of two tip gaps and several coolant mass flow rates were analysed. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness on the tip, which is supplemented by heat transfer coefficient measurements obtained via infrared thermography. Drawing from all of this data, it is shown that the weld beads have a generally detrimental impact on thermal performance, but with local variations. Aerodynamic loss measured downstream of the cascade is shown to be largely insensitive to the weld beads.
Numerical and Experimental Study on Rotating Stall in Industrial Centrifugal Compressor
Authors: Miura Toshimasa , Yamashita Hideaki , Takeuchi Ryota , Sakai Naoto 
Published: January 2021

Abstract
Centrifugal compressors employed in the oil and gas industry are operated at high gas pressure conditions and are used in a wide operation range. Accurate prediction of the rotating stall and the destabilizing aerodynamic force is one of the key technologies for these compressors, because rotating stall can sometimes cause severe problems with subsynchronous shaft vibration and limit its operation range. Thus, the aim of this study is to establish a method of accurately predicting the inception of rotating stall and its effect on shaft vibration. To achieve this, numerical investigations are carried out by unsteady Reynolds-averaged Navier-Stokes (RANS) simulation with a full annulus model of the compressor stage. Also, to assess the accuracy of the simulation qualitatively and quantitatively, a high-pressure compressor test rig that contains a shrouded impeller and a vaneless diffuser is built. To investigate the effect of the rotating stall on the shaft vibration, an experiment is carried out at relatively high gas pressure with the inlet pressure level exceeding 30 barA.
In the first part of the study, the accuracy of compressor performance prediction is studied by steady computational fluid dynamics (CFD) simulation. It is found that by taking the wall roughness effect into account, the predicted performance shows good agreement with the experimental result. Thus, a subsequent study of the rotating stall is also carried out by considering its effect.
In the second part of the study, the accuracy of predicting the rotating stall is studied. In the experiment, two types of rotating stall are measured. One is a multiple-cell stall induced in the vaneless diffuser, for which the speed of rotation is relatively low and the other is a one-cell stall induced in the impeller region. The properties of the multiple-cell stall agree with the previous experimental and numerical studies, and the rotating stall has the limited effect on shaft vibration. Conversely, the one-cell stall shows severe subsynchronous vibration. In this study, both types of stall prediction are examined by CFD simulation. It is found that the simulation can predict the inception of the rotating stall with relatively high accuracy as the predicted results show good agreement with the experimental results in terms of cell count, rotation speed, pressure fluctuation level and the effect on shaft vibration. Through this study, the effectiveness of unsteady CFD simulation is confirmed for these types of stall and vibration prediction.
Numerical Investigation of Effect of Blade Surface Slot on the Performance and Flow Field of a Low Speed Centrifugal Fan
Authors: Zhang HaoGuang , Dong FeiYang , Zhang XuDong , Chu WuLi 
Published: January 2021

Abstract
The main objective of this study is to understand the mechanisms of affecting the performance and flow field of a low speed centrifugal fan with blade surface slots. In the investigation, a spanwise slot, which is placed within the range of about 60% to 100% of the blade span, is applied to each blade surface of the impeller, and the partial blade pressure and suction surfaces for each blade are connected via the blade surface slot. The full-passage unsteady numerical results indicate that the performance of fan including the volute is improved among the overall mass flow rate by applying the blade surface slot, and the blade surface slots generate about an enhancement of 3.6% for the total pressure improvement, an improvement of 2.6% for the efficiency respectively at the design mass flow rate.
The flow field analyses show that the injecting flows discharging from the blade surface slots can encourage the low energy flows near the blade suction surface in some blade passages. Hence, the boundary layer separations of the blade suction surface are restrained by the injecting flows, and the flow condition in the passag is considerately improved. Moreover, the adverse effect caused by the low energy flows is very serious in the partial blade passages near the shroud, while the flows in the blade surface slots have few positive effect on the low energy flows. So, the improvement by the slots on the flow fields is very small near the shroud region. Because the boundary layer separations on the blade suction surface are absent in most of the blade passages at about 60% of the blade span, the flows emerging from the slots have passive effects on the passage mainstreams. Further, in the case of blade surface slots, there is an obvious vortex near the blade trailing edge at about 60% of the blade span, and the vortex is close to the blade suction surface at some instants. As a result, the wake flow losses in the passage become large with the application of the slots. Briefly, within the slotted span range, the improvement of the flow field in the blade passages becomes large and then gets small, as the blade span decreases. Furthermore, the flow condition in the volute is improved thanks to the amelioration of the flows in some blade passages, and the degree of the second flows in the volute is weakened with the application of blade surface slots. Consequently, the flow losses in the volute are reduced effectively.
Experimental and Numerical Study on Pressure Losses and Flow Fluctuations in a High-Pressure Valve Assembly of Steam Turbine Governing System
Authors: Slama Vaclav , Mrozek Lukas , Rudas Bartolomej , Simurda David , Hala Jindrich , Luxa Martin 
Published: January 2021

Abstract
Aerodynamic measurements and numerical simulations carried out on a model of a high-pressure valve assembly used for nozzle governing of a turbine with 135MW output are described in this paper. Aim of the study is to investigate effects of control valve’s strainers on pressure losses and unsteadiness in the flow field. It is an important task since undesirable flow fluctuations can lead to operational reliability issues. Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) where an aerodynamic tunnel is installed. Numerical simulations were carried out in the Doosan Skoda Power (DSP) Company using ANSYS software tools. The experimental model consists of one of two identical parts of the real valve assembly. It means it consists of an inlet pipeline, a stop valve, a valve chamber with two independent control valves, its diffusers and outlet pipelines. The numerical model consists of both assembly parts and includes also an A-wheel control stage in order to simulate the real turbine operating points. The different lifts of the main cone in each control valve for its useful combinations were investigated. Results were evaluated on the model with control valve’s strainers, which were historically used in order to stabilize the flow, and without them. The results of the experimental measurement were compared with the numerical results in the form of pressure losses prediction. From measured pressure fluctuations, it was found out where and for which conditions a danger of flow instabilities occurs. It can be concluded that there is a border, in terms of operating conditions, where the flow field starts to be unstable and this border is different dependent of the fact whether the control valve’s strainers are used or not. Therefore, the areas of safe and danger operational reliability can be predicted. The influence of the control valve’s strainers on the maximal amplitude of periodic fluctuations appears only for the cases when valves are highly overloaded. For normal operating conditions, there is no difference. As a result, the control valve’s strainers do not have to be used in standard applications of valve assemblies. Furthermore, a loss model for valve pressure loss estimation could be updated. Therefore, a pressure loss should be predicted with a sufficient accuracy for each new turbine bid with similar valve assemblies.