bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustically Testing Stock and Modified UAS Propellers in Both the Near and Far Field
Authors: Van Treuren Kenneth , Sanchez Ricardo , Wisniewski Charles , Leitch Paul
Published: January 2021

In an urban setting, the sound level of a drone must be acceptable. This paper compares a stock DJI Phantom 2 propeller to a stock propeller modified with a Trailing Edge (TE) notch. The purpose was to determine the extent of the near and far field noise signature of the propellers. Measurements were taken in an anechoic chamber at measurement distances of 1 ft to 24 ft. Upstream of propeller, the sound decay follows the standard decay rate (6 dB decrease for a doubling of the distance) from a location of approximately 4 ft. Downstream the sound decay does not follow standard decay rates until 22 ft. A comparison of the two propellers shows that the TE notch and stock propellers have similar Sound Pressure Level (SPL) values at all distances measured. Traverse measurements downstream of the two propellers in the wind tunnel confirms that the magnitudes of the SPL values are similar after a distance of one foot, however, there does seem to be an influence of the TE notch on the frequency spectrum, shifting frequencies slightly higher.

In addition to the single propeller tests, a DJI F550 Flame Wheel hexacopter was used to compare the stock and TE notch propellers. While the hexacopter was overall 20 dBA nosier, no discernable difference in SPL between the two propellers was measured.
Managing the Pressure to Increase the H2 Capacity Through a Natural Gas Transmission Network
Authors: Bainier Francis , Kurz Rainer , Bass Philippe
Published: January 2021

Gas Transmission System Operators (TSO1) are considering injecting hydrogen gas into their networks. Blending hydrogen into the existing natural gas pipeline network appears to be a strategy for storing and delivering renewable energy to markets [1], [2], [3].

In the paper GT2019-90348 [4], the authors have explored the efficiency of H2-blending in a natural gas pipeline network. The conclusion of the paper is: the energy transmission capacity and the efficiency decrease with the introduction of H2, nevertheless, the authors conclude that it is not an obstacle, but the way of using transmission natural gas networks should be closely studied to find an economic optimum, based both on capital and operating expenses. To establish the comparison, the paper did not take into account the limits of the equipment; all equipment was considered as compatible with any load of hydrogen blending.

In the current paper, the idea is to consider the hypothesis that the only factor which has impact on the infrastructure is the partial pressure of H2. The idea is not new, in 1802, Dalton published a law called Dalton’s Law of Partial Pressures [5]. Dalton established empirically that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual component gases. The partial pressure is the pressure that each gas would exert when it alone occupied the volume of the mixture at the same temperature.

Independent of the limits of the equipment, the authors explore the relationships between a network capacity and its associated pressures in regards to the H2 partial pressure. Within the partial pressure constraint, the goal is to find the maximum H2 flowrate. This flowrate is then compared with a flowrate which is a function of % H2.

Nevertheless, steel is subjected to hydrogen invasion while being exposed to hydrogen containing environments during mechanical loading: resulting in hydrogen embrittlement (HE). HE also depends on the textured microstructure. In the final results [6] [7], the measured fatigue data reveals that the fatigue life of steel pipeline is degraded by the added hydrogen. The H2 has an effect on the steel fatigue which is not simply due to the partial pressure.

The idea of the authors through the results of their 2 papers is to give the key points to help to find the optimum points for introducing H2 into a natural gas network, because, for them, the idea is that partial pressure is a factor in the equilibrium between H2 capacity and the remaining lifetime of the equipment.

This paper shows the interest of the pressure management. With this management, it is possible to reach a constant H2 injection flow independently of the natural gas flow in the pipeline.

In conclusion, to optimize the H2 capacity in their current network, a proposal to the TSOs is to adjust their dispatching methodology and their Pipeline Integrity Management (PIM) [8] [9].
Coupled Mode Flutter Analysis of Turbomachinery Blades Using an Adaptation of the P-K Method
Authors: Schuff Matthias , Chenaux Virginie Anne
Published: January 2021

Current trends in turbomachinery design significantly reduce the mass ratio of structure to air, making them prone to flutter by aerodynamic coupling between mode shapes, also called coupled-mode flutter. The p-k method, which solves an aeroelastic eigenvalue problem for frequency and damping respectively excitation of the aerodynamically coupled system, was adapted for turbomachinery application using aerodynamic responses computed in the frequency domain.

A two-dimensional test case is validated against time-marching fluid-structure coupled simulations for subsonic and transonic conditions. A span of mass ratios is investigated showing that the adapted p-k method is able to predict the transition between aeroelastically stable and unstable cascades depending on the mass ratio.

Finally, the p-k method is applied to a low mass ratio fan showing that the flutter-free operating range is significantly reduced when aerodynamic coupling effects are taken into account.
Laminar Flame Characteristics of Sequential Two-Stage Combustion of Premixed Methane/Air Flames
Authors: Duva Berk Can , Wang Yen-Cheng , Chance Lauren Elizabeth , Toulson Elisa
Published: January 2021

Due to their high load flexibility and air-quality benefits, axial (sequential) stage combustion systems have become more popular among ground-based power gas turbine combustors. However, inert combustion residuals passing from the initial stage onto the secondary stage affects the reactivity and stability of the flame in the second stage of the combustor. The present study investigates laminar flame characteristics of the combustion within the second stage of a sequential combustor. The method of constant pressure for spherically expanding flames was employed to obtain laminar burning velocities (LBV) and burned gas Markstein lengths (Lb) of premixed methane/air mixtures diluted using flue gas at 3 bar and 423 K. Combustion residuals were imitated using a 19.01% H2O + 9.50% CO2 + 71.49% N2 mixture by volume, while tested dilution ratios were 0%, 5%, 10%, and 15%. Experimental results showed that the LBV was decreased by 18–23%, 36–42%, and 50–52% with additions of 5%, 10%, and 15% combustion products, respectively. As the dilution and equivalence ratios increased, the Lb values increased slightly, suggesting that the stability and stretch of the CH4/air flames increased at these conditions. Numerical results were obtained from CHEMKIN using the GRI-Mech 3.0, USC Mech II, San Diego, HP-Mech, NUI Galway, and AramcoMech 1.3 mechanisms. The GRI-Mech 3.0 and HP-Mech performed best, with an average of 2% and 3% difference between numerical and experimental LBVs, respectively. The thermal-diffusion (TD), dilution (D), and the chemical (C) effects of inert post-combustion gases on the LBV were found using numerical results. The dilution effect was primarily responsible, accounting for 79–84% of the LBV reduction.
Effects of Combustor Enclosure Flow Path on Combustor Design
Authors: Briones Alejandro M. , Thomas Nathan , Rankin Brent A.
Published: January 2021

A design optimization procedure was implemented to resize the holes of a combustor liner for practical applications. A combustor geometry evaluated without an enclosure was to be reformulated within an enclosure. The objective functions of the combustor with enclosure involved targeting the flow splits of the combustor without enclosure. Latin Hypercube Sampling (LHS) design of experiments (DOE) was utilized to obtain at least a pure quadratic response surface (RS). These were computed using Genetic Aggregate (GA). These RS were, in turn, evaluated by a multiple objective genetic algorithm (MOGA) optimizer. The focus of this study was a small-scale cavity-stabilized combustor. Steady, compressible three-dimensional simulations are performed using a multi-phase Realizable k-ε Reynolds-averaged Navier-Stokes (RANS) approach. Combustion-turbulence interaction is modeled with flamelet progress variable (FPV) and β-presumed probability density function (PDF). There are eleven input and output parameters corresponding to the combustor hole sizes and associated mass flow rates. The RS obtained with GA were principally of the Kriging kind (with constant and linear trends and damped sinusoid and Gaussian kernels). A combustor hole mass flow rate was mainly determined by its hole size but was also influenced by the other holes. The combustor flow split non-linearity shows that increasing a hole size increases its mass flow rate, but simultaneously decreases another hole flow rate. This was also verified by sensitivity analysis. Due to this non-linearity, matching flow splits between geometry without and with enclosure is challenging and may not be possible for some situations. Thus, it is concluded that optimization of the combustor geometry without the enclosure is not the best route. Rather, it would be better for the geometry to be optimized with the enclosure included in order to account for flow separation and non-linear influence of the combustor holes on the flow field.
Improvement of Turboshaft Restart Time Through an Experimental and Numerical Investigation
Authors: Ferrand Antoine , Bellenoue Marc , Bertin Yves , Marconi Patrick
Published: January 2021

Inflight shutdown of one engine for twin-engine helicopters have proven beneficial for fuel consumption. A new flight mode is then considered, in which one engine is put into sleep mode (the gas generator is kept at a stabilized, sub-idle speed by means of an electric motor, with no combustion), while the second engine runs almost at nominal load. The ability to restart the engine in sleep mode is then critical for safety reasons. Indeed, the certification of this flight mode involves ensuring a close-to-zero failure rate for in-flight restarts as well as a fast restart capability of the shutdown engine. In this paper, the focus is made on improving the restart time of the shutdown turboshaft engine. Fast restart capability is necessary for flight management reasons. Indeed, in case of a failure of the engine operating close to nominal load while the other one is in sleep mode, there is no more power available and the helicopter can lose up to 15–20 meters per second during autorotation. The restart time becomes a critical parameter to limit the loss of altitude. In the configuration studied, the fast restart is achieved thanks to the electric motor designed to deliver a high torque to the gas generator shaft. This electric motor is powered by an additional battery, more powerful than the conventional one dedicated for standard restarts.

The aim of the paper is to assess the potential restart time saving using an approach combining test rig data analysis and numerical results generated by a thermodynamic model able to simulate at very low rotational speed.

A gas turbine engine starting process is composed of two main phases: the light-up phase and the acceleration phase. It is important to understand the detailed phenomenology of these two phases as well as the various sub-systems involved, first to highlight the influencing parameters of both phases and then to establish an exhaustive listing of the possible time optimizations.

From the test rig campaign, conducted at Safran Helicopter Engines on a high power free turbine turboshaft engine, we are able to accurately break down the phases of the start-up sequence, which helps us to identify what steps of the sequence worth shortening. With the engine performance thermodynamic model, we can then use the information gathered from the test rig analysis to further predict how to save time and to give guidelines for developing new control strategies.

The results of this study show that a fast restart going from sleep mode to max power speed can be up to 60% faster than a conventional restart going from sleep mode to idle speed. This is significantly faster, especially if one takes into account the higher final speed targeted by the fast restart.
Effect of Partial Admission and Swirl Brakes on Destabilization Force of Labyrinth Gas Seal
Authors: Iwasaki Makoto , Kawashita Rimpei , Omura Naoto , Matsumoto Kazuyuki , Murata Kenichi , Hombo Ryokichi
Published: January 2021

Destabilization forces in labyrinth seals can cause subsynchronous vibration and many researchers have investigated the destabilization force under full admission (FA). It is known that partial admission (PA) can increase rotor instability, but there is little knowledge about seal fluid force under PA.

In this study the experiment was conducted in order to confirm the effect of PA and swirl brakes (SB) on swirl velocity and destabilization force. For the experiment, a 500mm diameter rotor was used so that size of the labyrinth seal can be close to the large-scale steam turbine. According to the experimental results, it was found that (1) average swirl velocity and destabilization force under PA became larger than FA, (2) relationship between average swirl velocity and destabilization force under PA was almost same with that of FA, (3) seal fluid force under PA had anisotropy by the instant rotor position, (4) SB reduced 70% of swirl velocity and destabilization force under both FA and PA.

Also it was found that CFD analysis could predict the effect of PA and SB on swirl velocity and seal fluid force. For predicting the effect of SB under FA, new steady state CFD analysis method applying frozen rotor interface at SB region was proposed.
Investigation of the Loss Generation in a Turning Vane Frame at Different Inlet Turbulence Conditions
Authors: Riebl Sebastian F. , Wakelam Christian , Niehuis Reinhard
Published: January 2021

The integrated concept of a turning vane frame (TVF) located between the high pressure turbine (HPT) and the low pressure turbine (LPT) can consist of structural vanes and aerodynamically assisting splitters, thus offering insight into the behavior of mixed blade cascades. In order to judge the sensitivity of the flow through a TVF to different turbulence conditions, the presented investigation focuses on the effects of different turbulence intensities and integral turbulent length scales. It is based on steady state RANS simulations validated against results from steady five hole probe measurements and static profile pressure distributions. The flow and loss behavior of the TVF under varying incoming turbulence conditions is investigated using a second law analysis of the loss generation, combined with a secondary flow field analysis relying on the established Q-criterion and the recently presented vortex visualization parameter (VVP)-method. The secondary flows were identified as key loss drivers at all turbulence conditions and changes in secondary flow patterns, as well as loss generation effects for the different passages were identified and discussed. The vortex structures in the upper half of the passage were found to be most sensitive to an increase in turbulence level. Increases in loss generation per passage were found to be most pronounced for the pressure side splitter to vane passage and the suction side splitter to pressure side splitter passage. Changes in profile boundary layer thickness and entropy production rate were found to contribute to alterations in loss generation only on a minor level.
CFD Modeling of Pulverized Coal Combustion Using Relax to Chemical Equilibrium Model With Turbulence-Chemistry Interaction
Authors: Thakre Piyush , Goldin Graham
Published: January 2021

A comprehensive numerical investigation of 2.4 MW IFRF swirl-stabilized coal furnace is conducted. A novel Relax to Chemical Equilibrium (RTCE) model with turbulence-chemistry interaction is used for the gas-phase combustion and the results are compared with the standard Eddy Break-Up (EBU) model. In the RTCE model, the species compositions are relaxed towards the local chemical equilibrium at a characteristic time scale determined by the local flow and turbulence. The turbulence-chemistry interaction is treated using the Eddy Dissipation Concept (EDC) model. The simulation uses a Lagrangian-Eulerian framework to treat the particle transport and the fluid-particle interactions. In all, fifteen species have been included in the RTCE model. For coal particles, a one-step devolatilization, first-order char oxidation, particle porosity, and particle radiation models are employed. The NOx emissions model includes both thermal and fuel NOx pathways. It was found that RTCE model performs well in predicting the overall temperature distribution in the IFRF coal furnace. The predicted temperature, NOx and CO at the outlet match very well with the experimental data, showing marked improvement over the EBU model. The overall NOx profile is also predicted better by the RTCE model.
DGEN Aeropropulsion Research Turbofan Core/Combustor-Noise Measurements: Experiment and Modal Structure at Core-Nozzle Exit
Authors: Boyle Devin K. , Henderson Brenda S. , Hultgren Lennart S.
Published: January 2021

Data from a recent core/combustor-noise source-diagnostic test utilizing a small turbofan engine are analyzed. The campaign continued the exploration begun in a baseline test, but with more extensive acoustic instrumentation. Both tests were aimed at developing a better understanding of propulsion-noise sources and their impact on the farfield noise signature, in order to enable improved turbofan noise-prediction methods and noise-mitigation techniques. Simultaneous high-data-rate acoustic measurements (93 channels in total) were obtained using a circumferential sensor array at the core-nozzle exit in conjunction with sideline and farfield microphone arrays for several relevant engine operational points. Measurements were repeated for different circumferential and sideline array configurations, as well as for redundancy. The unsteady pressure field at the core-nozzle exit is documented in detail. Previous work suggested that the ±1 azimuthal duct mode could be cut-on at this location, which would have implications for combustor-noise modeling and prediction. The modal decomposition of the combustor noise at the core-nozzle exit verifies this observation. Select farfield sound-pressure-level spectra are also presented.
Blade Surface Pressure Measurements on a Low Pressure Rise Axial Flow Fan
Authors: Rohwer Johannes , van der Spuy Sybrand J. , von Backström Theodor W. , Louw Francois G.
Published: January 2021

Fan performance characteristic tests of axial flow fans provide information on the global flow field, based on stable inlet flow field distribution. More information is often required on the local flow distribution existing in the vicinity of the fan blades under installed conditions. A 1.542 m diameter scale model of an axial flow fan, termed the M-Fan is tested in an ISO 5801, type A, test facility. The M-fan was specifically designed for low-pressure, high flow rate application in air-cooled or hybrid condensers. The scaled version of the M-fan was designed to have a fan static pressure rise of 116.7 Pa at a flow rate of 14.2 m3/s.

Two specially constructed M-Fan blades are manufactured to conduct blade surface pressure measurements on the blades. The fan blades are equipped with 2 mm diameter tubes that run down the length of the fan blades in order to convey the measured pressure. Piezo-resistive pressure transducers, located on the hub of the fan, measure the static pressure distribution on the blades and the data is transferred to a stationary computer using a wireless telemetry setup. The blade pressure measurement setup is re-commissioned from a previous research project and its performance is qualified by testing and comparing to experimental results obtained on the B2a-fan. Excellent correlation to previous results is obtained.

The experimental M-fan results are compared against results from a periodic numerical CFD model of a fan blade modelled in an ISO 5801, Type A test facility configuration. The experimental tests and numerical model correlate well with each other. The experimental blade surface pressure measurements have a minimum Pearson correlation to the numerically determined values of 0.932 (maximum 0.971).
Thermo-Structural Analysis of Steam Turbine Start-Up With and Without Integrated Pre-Warming System Using Hot Air
Authors: Łuczyński Piotr , Pehle Lukas , Wirsum Manfred , Mohr Wolfgang F. D. , Vogt Jan , Helbig Klaus
Published: January 2021

Motivated by the urgent need for flexibility and start-up capability improvements of conventional power plants in addition to extending their life cycle, General Electric provides its customers with a product to pre-warm steam turbines using hot air.

In this paper, the transient thermal and structural analyses of a 19-stage IP steam turbine in various start-up operating modes are discussed in detail. The presented research is based on previous investigations and utilises a hybrid (HFEM - numerical FEM and analytical) approach to efficiently determine the time-dependent temperature distribution in the components of the steam turbine. The simulation strategy of the HFEM model applies various analytical correlations to describe heat transfer in the turbine channel. These are developed by means of extensive unsteady multistage conjugate heat transfer simulations for both start-up turbine operation with steam and pre-warming operation with hot air. Moreover, the complex numerical setup of the HFEM model also considers the thermal contact resistance (TCR) on the surfaces between vane and casing as well as blades and rotor. Prior to the analysis of other turbine start-up operating modes, the typical start-up turbine process is calculated and validated against an experimental data as a benchmark for subsequent analysis. In addition to heat transfer correlations, the simulation of a turbine start-up from cold state uses an innovative analytic pressure model to allow for a consideration of condensation effects during first phase of start-up procedure.
Optimization of Vaneless Volute and Mixed Flow Impeller for Pulsating Flow
Authors: Liu Zheng , Copeland Colin , Tuechler Stefan
Published: January 2021

Vaneless turbocharger turbines are commonly used for automotive engines due to their low cost and better off-design performance. It consists of a vaneless volute and a radial or mixed flow rotor, where both components are important to the overall device performance. With the pulsating nature of the exhaust flows, most energy is contained at the peak of the pulse. Therefore, during one engine cycle, optimizing the turbine performance for the peak pulse region is more straightforward to improve the cycle-averaged shaft power generation.

This study sought to optimize both the volute and rotor simultaneously for the peak point of the pressure pulse (2.4 bar). Thirteen design parameters in total are considered during the optimization process. Six volute design parameters were used to control the aspect ratio, intake area, exit area, and the circumferential distribution of the cross-sectional area. Seven rotor parameters were utilized to modify the cone angle, blade axial location, and the camber-line angle distribution. The optimization was conducted by a novel optimization algorithm based on Kriging surrogate model, and compared with the conventional genetic algorithm. Commercial turbulent viscous CFD solver ANSYS-CFX was used to predict the turbine performance. Full-stage turbine, including ten blade passages, is explicitly modeled for better accuracy. In order to ensure the matching between turbocharger and engine maintained the same as the original turbine, special attention was paid to constraint the swallowing capacity characteristic of the optimized turbine to be similar to the baseline turbine, with a maximum 2.5% difference at the design point. Compared with the baseline turbine, the turbine efficiency was improved by 3 percentage points with the using the genetic algorithm, and an improvement of 3.65 percentage points was achieved by using the Kriging surrogate model based optimization algorithm. Although the optimized turbine has a lower peak efficiency, the optimal velocity ratio of optimized design shifted from the baseline value of 0.71 to 0.61, implying a better performance will be achieved under high loading conditions. The improvement of the turbine performance is attributed to a better blade loading that is achieved in the 0.2–0.4 stream-wise location. The elementary effectiveness has been studied, and the camber-line distribution of the rotor is found to be the most influential factor on the turbine performance.
A Large Design Space Multidisciplinary Optimization of a Mixed Flow Micro Gas Turbine Compressor Stage
Authors: Ochabski Thomas , van der Spuy Johan , Hildebrandt Thomas
Published: January 2021

A parametrization method for the simultaneous optimization of the impeller and diffuser of a mixed flow compressor stage across a wide geometrical diversity is presented. The optimization focused on determining the optimal mixed flow (meridional) angle for a predefined set of constraints. The number of parameters required to achieve the large geometric diversity associated with a variable mixed flow angle was greatly reduced by coupling the endwall and camber Bézier control points with user-defined functions. The influence of geometric features on design performance was assessed using a Pearson correlation coefficient map. It was observed that stage total-to-static pressure ratio, and efficiency, were strongly influenced by diffuser outlet passage height and diffuser vane wrap angle. This was due to these parameters’ control of flow separation magnitude at the diffuser hub in the radial-to-axial bend. The method improved design point efficiency by 4.24 percentage points (to 86.24%) and increased the operating range by 6.7% at the cost of a decreased design point pressure rise, when compared to the baseline design.
Numerical Investigation of Active Flow Control Using Tip Synthetic Jet on the Performance of a High-Speed Axial Compressor Rotor
Authors: Wang Guang , Chu Wuli
Published: January 2021

In order to weaken the negative effect of tip leakage flow and improve the tip flow condition, this paper introduces synthetic jet into the flow control field of axial compressor, and proposes a method of active flow control by arranging synthetic jet at the tip. A high-speed axial compressor rotor of the author’s research group is taken as the numerical simulation object. On the basis of keeping geometric parameters of the synthetic jet actuator unchanged, this paper studies the influence of applying tip synthetic jet on aerodynamic performance of the compressor rotor at three axial positions of −10%Ca, 0%Ca and 21.35%Ca respectively. The results show that when tip synthetic jet is in the above three positions, comprehensive stability margin of the compressor rotor increases by 2.62%, 3.77% and 12.46% respectively, and efficiency near stall point increases by 0.22%, 0.25 and 0.47% respectively. This shows that when tip synthetic jet is far away from blade, the aerodynamic performance improvement of the compressor rotor is limited, and when tip synthetic jet is just above the leading edge, the effect of expanding stability is the best and the efficiency is the most improved. The mechanism of tip synthetic jet can increase the stability of the compressor rotor is that when the actuator is in the blowing stage, it can blow the low-speed air flow of blade top to downstream, and when the actuator is in the suction stage, it can suck the low-speed air flow of blade top into slot, so as to alleviate the top blockage and realize the stability expansion. The mechanism of tip synthetic jet can improve the efficiency of compressor rotor is that the blowing and suction of actuator weaken the intensity of tip leakage flow, reduce the size of vortex core and also reduce the flow loss of the compressor rotor correspondingly.
Investigation of the Flow Field and the Pressure Recovery in a Gas Turbine Exhaust Diffuser at Design, Part-Load and Over-Load Condition
Authors: Bauer Maximilian , Hummel Simon , Schatz Markus , Kegalj Martin , Vogt Damian M.
Published: January 2021

The performance of axial diffusers installed downstream of heavy duty gas turbines is mainly affected by the turbine load. Thereby the outflow varies in Mach number, total pressure distribution, swirl and its tip leakage flow in particular.

To investigate the performance of a diffuser at different load conditions, a generic diffuser geometry has been designed at ITSM which is representative for current heavy duty gas turbine diffusers. Results are presented for three different operating conditions, each with and without tip flow respectively. Part-load, design-load and over-load operating conditions are defined and varied at the diffuser inlet in terms of Mach number, total pressure distribution and swirl. Each operating point is investigated experimentally and numerically and assessed based on its flow field as well as the pressure recovery.

The diffuser performance shows a strong dependency on the inlet swirl and total pressure profile. A superimposed tip flow only influences the flow field significantly when the casing flow is weakened due to casing separation. In those cases pressure recovery increases with additional tip flow.

There is a reliable prediction of the CFD simulations at design-load. At part-load, CFD overpredicts the strut separation, resulting in an underpredicted overall pressure recovery. At over-load, CFD underpredicts the separation extension in the annular diffuser but overpredicts the hub wake. This leads to a better flow control in CFD with the result of an overpredicted overall pressure recovery.
Study on the Influence of Self-Circulating and Slot Combined Casing Treatment on the Stability of Transonic Compressor
Authors: Yan Song , Chu WuLi , Shen Zhengjing
Published: January 2021

Casing treatment (CT) has proven to be an effective way to enhance stability, and has a very important role in enhancing the stability of the compressor. Researchers have made great achievements and progress in the study of single-type CT structure, but less research on combined-type CT structure. In this paper, the isolated rotor of a high-load axial-flow compressor is taken as the research object, and the numerical simulation method is used to study the enhancing stability mechanism of the combined-type casing treatment (ASCT) by combining the axial slot casing treatment (ASC) and the self-circulating casing treatment (SCT). The study found that the reasonable choice of the ASCT scheme can make the enhancing stability effect of the ASCT higher than that of the single-type CT structure scheme. Through detailed quantitative analysis of the rotor’s internal flow field, it was found that ASC and SCT can suction the airflow downstream of the rotor passage, and then spray it into the main flow from the upstream of the rotor passage, and the blade tip blockage is reduced, the flow capacity of the blade tip passage is improved, and the rotor stability is enhanced by suppressing tip clearance leakage flow. The ASCT has both the spraying effect of the ASC and the SCT, and has the best improvement effect on the flow blockage zone in the rotor passage, and the obtained enhancing stability effect is also best. In addition, the circulation and re-injection of the airflow after CT has aggravated the flow blending loss in the blade tip zone, which has reduced the rotor efficiency. The ASCT has both the characteristics of the effect of the ASC and the SCT on the rotor efficiency, resulting in a large reduction in the rotor efficiency after using the ASCT.
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

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 (>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

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

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

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

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

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

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

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.