bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of Mayenite-Based Catalysts Effectiveness in Reducing Pollution From Biomass Gasification in Fluidized Bed Reactors
Authors: Savuto E. , Borello D. , Di Carlo A. , Natali S. , Pantaleo A. , Rispoli F.
Published: September 2016

Efficiency of catalyst materials used for tar reduction in biomass gasification plants is strongly affected by carbon deposition. For such reason, techniques for reducing catalyst poisoning are actively studied. Here the authors experimentally investigate the effectiveness of using a Mayenite support for Nickel catalyst. Mayenite was selected because it has a large number of free Oxygen anions that are able to combine with carbon producing COx and eventually prevent carbon deposition. [1] [2] [3].

Experiments are carried out with a bench scale gasifier coupled with a catalytic reactor in order to test the Nickel/Mayenite catalyst performance in the conversion of tar and methane. Ni/Mayenite catalyst is characterized by means of XRD, BET and SEM analyses before and after its use in the reactor, aiming to study carbon deposition and tar conversion efficiency.

In the tests carried out the tars present in major quantities like benzene, toluene and naphthalene reached conversions close to 100% in the first hour of test, and then stabilized to values of respectively 30%, 85% and 93%.

The catalyst was then subject to a regeneration procedure and then tested for some further hours, showing again very high conversion rates: benzene 92%, toluene 93% and naphthalene 96%.

The residual tars measured in the syngas are found to be lower than the limits imposed by the Biomass Technology Group [4] for feeding gas turbines; the syngas treated with the catalyst here developed can be thus considered suitable for the use in these energy production devices.
Sensitivity Analysis of High-Frequency Forced Response for Mistuned Bladed Discs Based on High-Fidelity Models
Authors: Tan Yuanqiu , Zang Chaoping , Zhou Biao , Duan Yongliang , Petrov E. P.
Published: September 2016

This paper proposes an effective method for sensitivity analysis of forced response of bladed discs to blade mistuning. The numerical studies of forced response of a turbine bladed disc vibrating in the frequency ranges corresponding to resonances with higher modes are also presented. The blade mistuning is modelled by specially defined mistuning matrices used for simulating experimentally measured scatter of blade natural frequencies. Based on this method, the sensitivity of forced response amplitude levels are studied for displacements and stress levels for a realistic model of a bladed disc. The effective response surface techniques are developed for explicit representation of the mistuned forced response as a function of blade mistuning elements.
Effects of Total Pressure Inlet Distortion on Transonic Fan Blade Wake Properties
Authors: Ferrar Anthony M. , Schneck William , Wicks Alfred , O’Brien Walter
Published: September 2016

This paper presents results of an experimental investigation of the impacts of total pressure distortions on the performance of a transonic turbofan. Fan rotor response to screen-produced total pressure distortions was measured by two high-frequency response probes (Kulite sensors). These probes measured the transient flow behind the fan rotor. Ensemble averaging based on a once-per-revolution encoder enabled separation of the pressure signal into its deterministic and stochastic components. The deterministic portion of the signal provided information about the effects of the distortion on the wake structure of the individual fan blades. The stochastic component of the signal gave indications of the effects of distortion on turbulence production (and losses) in the fan.

The qualitative trends provided by these high-frequency measurements show that the blade loading variations caused the wake depths and thicknesses to increase in the low pressure inlet regions. In addition, the turbulence production increased, peaking in the blade wakes. These behaviors indicate that the response of the fan was governed by a trailing edge separation that moves forward and backward on the upper blade surface in a dynamic manner.

This paper also includes discussion of the challenges associated with obtaining quantitative data with this type of probe. The results were significantly affected by probe frequency response and dynamic flow angle sensitivity. Resolving the blade wake structure and turbulence information requires probe tolerance to high-gradient flows and large flow angle fluctuations, with very high frequency response. The paper incorporates a discussion of improved probe design approaches to advance future research.
Operation of Reheat Combustors With Secondary Air Flow (SAF) Control Valves
Authors: Gao Xianfeng , Burri Daniel , Balmer Christian , Studerus Adrien
Published: September 2016

GT26 reheat gas turbines have been continuously developed and upgraded to improve the engine performance and operational flexibility. In a standard SAF flow orifices configuration typically sized for the design point, the supply pressure ratios of secondary air flow systems for base-load operation vary over ambient temperatures. The adjustable secondary air flow control valves make the active control of the cooling air supply pressure ratios possible and could provide a customized cooling air consumption and adjust engine operation conditions. This control valve concept has been comprehensively tested and validated in Alstom test power plant and operated in customer engines.

This paper focuses mainly on combustor cooling improvement with this secondary air flow control valves. G26 reheat combustors with the adjustable secondary air flow control valves have improved significantly sequential combustor cooling and combustor performance. The supply pressure ratios of secondary air flow system over wide part load range which are originally lower and critical with a standard orifice configuration have been raised and results in more cooling air flows to the combustor cooling system than original standard orifice configuration. This increased cooling air flow improves SEV combustor liner and SEV burner cooling over large range of part load operation. The metal temperatures of the SEV liners and SEV burners are reduced significantly over part load, while the highest metal temperatures are recorded over part load operation with previously installed standard orifices configuration. In addition, the supply pressure ratios in secondary air flow systems with fixed throttling element are lower during oil operation than the corresponding ratios for fuel gas operation. The cooling supply pressure ratios in cooling systems with SAF control valves are optimized to supply the required combustor cooling air flow for oil operation. The optimized cooling can also be achieved through adjustment of SAF control valves for high-fogging (HF) engines between dry operation and wet operation. In addition, pulsation reduction at oil operation can be achieved by fully opening of MBH30 control valve.
Advanced and Transformational Hydrogen Turbines for Integrated Gasification Combined Cycles
Authors: Shelton Walter W. , Ames Robin W. , Dennis Richard A. , White Charles W. , Plunkett John E. , Fisher James C. , Dalton Richard P.
Published: September 2016

The U.S. Department of Energy’s (DOE) provides a worldwide leadership role in the development of advanced fossil fuel-based energy conversion technologies, with a focus on electric power generation with carbon capture and storage (CCS). As part of DOE’s Office of Fossil Energy, the National Energy Technology Laboratory (NETL) implements research, development, and demonstration (RD&D) programs that address the challenges of reducing greenhouse gas emissions. To meet these challenges, NETL evaluates advanced power cycles that will maximize system efficiency and performance, while minimizing CO2 emissions and the costs of CCS. NETL’s Hydrogen Turbine Program has sponsored numerous R&D projects in support of Advanced Hydrogen Turbines (AHT). Turbine systems and components targeted for development include combustor technology, materials research, enhanced cooling technology, coatings development, and more. The R&D builds on existing gas turbine technologies and is intended to develop and test the component technologies and subsystems needed to validate the ability to meet the Turbine Program goals. These technologies are key components of AHTs, which enable overall plant efficiency and cost of electricity (COE) improvements relative to an F-frame turbine-based Integrated Gasification Combined Cycle (IGCC) reference plant equipped with carbon capture (today’s state-of-the-art). This work has also provided the basis for estimating future IGCC plant performance based on a Transformational Hydrogen Turbine (THT) with a higher turbine inlet temperature, enhanced material capabilities, reduced air cooling and leakage, and higher pressure ratios than the AHT.

IGCC cases from using system-level AHT and THT gas turbine models were developed for comparisons with an F-frame turbine-based IGCC reference case and for an IGCC pathway study. The IGCC pathway is presented in which the reference case (i.e. includes F-frame turbine) is sequentially-modified through the incorporation of advanced technologies. Advanced technologies are considered to be either 2nd Generation or Transformational, if they are anticipated to be ready for demonstration by 2025 and 2030, respectively. The current results included the THT, additional potential transformational technologies related to IGCC plant sections (e.g. air separation, gasification, gas cleanup, carbon capture, NOx reduction) are being considered by NETL and are topics for inclusion in future reports.
Experimental Investigation of a SOFC/MGT Hybrid Power Plant Test Rig: Impact and Characterization of a Fuel Cell Emulator
Authors: Hohloch Martina , Huber Andreas , Aigner Manfred
Published: September 2016

The main topic of the paper is the experimental investigation of a solid oxide fuel cell (SOFC) / micro gas turbine (MGT) hybrid power plant test rig. This comprises the proof of concept, the characterization of the operational range and the influence of the coupling on the MGT. The operational concept of the hybrid power plant is designed to reach a maximum flexibility in electrical power output. Therefore the power plant is operated at different MGT shaft speeds and electrical power outputs of the SOFC, thus leading to different SOFC temperatures.

Instead of a real fuel cell an emulator was developed and built to emulate the fluid dynamic and thermodynamic behavior of a real SOFC. The test rig is based on a Turbec T100PH micro gas turbine. A specially designed interface connects the facility to the tubing system and the SOFC emulator. For the present investigation the SOFC emulator has been equipped with a gas preheater. It emulates the varying heat output of the fuel cell. The gas preheater is composed of a natural gas combustor based on the FLOX® technology, with a swirl-stabilized pilot stage and allows a wide range of emulating different SOFC outlet temperatures. In addition installations have been integrated into a pressure vessel, representing the SOFC cathode volume, to analyze the increase in residence time and pressure loss.

Initially three different configurations of the test rig, no SOFC emulator – tube only, SOFC emulator with pressure vessels and fully equipped SOFC emulator (pressure vessels, installations and gas preheater) are compared regarding the influence of the different volumes, residence times and pressure losses. The operating range of the test rig equipped with gas preheater in cold (no fuel) as well as in hot conditions is investigated. As the velocity at the entrance of the gas turbine combustor increases with increased fuel cell outlet temperature the surge margin is strongly influenced. The operating range was determined for different shaft speeds and preheating (SOFC outlet) temperatures. Finally the transient behavior of the gas preheater and its impact on the MGT is analyzed. The results provide the required basis to implement a cyber physical system, in which the SOFC emulator is controlled by a SOFC model, as well as the basis for the real coupling of MGT and SOFC.
About the Distribution of the Mach Number and Losses Under Consideration of the Diffusion Factor: Profile Distribution and Losses for Low Pressure Turbine Profiles With High Diffusion Factors Under Steady Flow Conditions
Authors: Brachmanski Roland , Niehuis Reinhard
Published: September 2016

The results of this investigation consist of two linear cascades at high diffusion factors. The present measurements for each low pressure turbine profile were conducted at midspan under a range of Reynolds- and exit Mach numbers. The exit Mach number was varied in a range covering low subsonic up to values where a transonic flow regime on the suction side of the blade could be expected. The variation of the exit Mach number was also used to create different locations of the maximum Mach number and to evaluate the resulting total pressure losses.

This work focuses on two profiles with a diffusion factor in a range of 0.18 ≤ DF ≤ 0.22, which is considered as a comparable level for the two cascades. The profile A is a front-loaded design and has shown no obvious flow separation on the suction side of the blade. Compared to the profile A the design B is a more aft-loaded profile which indicates flow separation on the suction side for all investigated Reynolds numbers.

The integral total pressure losses were evaluated by wake traverses downstream of the profile. To determine the isentropic Mach numbers and the character of the boundary layer along the suction side of the profile, static pressure tappings and measurements with a flattened Pitot probe were carried out. Numerical studies were also conducted to investigate further the influence of a reduced turbulence intensity on the boundary layer of the suction side of design B.

The results show that the optimum of the integral total pressure losses are significantly dependent on the Reynolds number. Therefore a correlation between the maximum Mach number on the suction side and the integral total pressure losses has been successfully established. A significant change of the turbulence intensity at the inlet of the cascade leads to shift of the location of the maximum Mach number. It also results in an equivalent change of the total pressure losses, which has been predicted by the trend line. However, the trend lines, which are based on the data of the integral total pressure losses of an attached boundary layer, are not able to predict the integral total pressure loss or the location of the maximum Mach number on the suction side of the blade since an open separation bubble occurs.
Acoustic Mode Analysis: Numerical and Experimental Results of a Turning Mid Turbine Frame
Authors: Zerobin S. , Bader P. , Faustmann C. , Marn A. , Göttlich E. , Heitmeir F.
Published: September 2016

In the present paper, a comparison of the numeric and experimental results obtained from the acoustic mode analysis for a turning mid turbine frame (TMTF) is presented. The investigated turning mid turbine frame is part of the two-stage two-spool test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics of Graz University of Technology. In this specific test turbine a transonic turbine stage (HP) is followed by a low pressure turbine stage (LP) consisting of a TMTF with 16 highly 3D-shaped turning struts and a counter-rotating low pressure rotor.

The experimental dataset is obtained by a measurement section downstream of the low pressure rotor which is instrumented with acoustic sensors. This microphone array is wall flush mounted in the outer casing which is traversable over 360 degrees in circumferential direction. The numerical setup consists of the whole test turbine including the experimental measurement section downstream of the low pressure rotor. Since the periodicity of the test setup equals 90 degrees the CFD calculations were performed accordingly using the unsteady inhouse Navier-Stokes code LINARS.

For both, numerical and experimental datasets the same post-processing tools are used in order to perform the acoustic mode analysis of the unsteady data. At first a comparison in terms of noise generation and propagation of the results is done by the frequency spectra, the emitted sound pressure and sound power level of both rotors independently. Since the emitted sound pressure level rises to a maximum at the first blade passing frequency of the HP rotor as well as the LP rotor the further analysis focuses on these two specific frequencies only. Therefore the acoustic field at those frequencies is characterized by azimuthal and radial modes. For a correct comparison between the numerical and experimental results numeric data taken from the same geometric locations as the microphones’ positions (thus the measurement locations) is processed.

Hence, this paper provides a deep insight into the capability of using unsteady CFD calculation in combination with the acoustic mode analysis in order to obtain the noise generation and propagation in turbines.
Influence of Nanoparticles on Spray Performance of Alternative Jet Fuels
Authors: Kannaiyan Kumaran , Sadr Reza
Published: September 2016

Recently, several studies have demonstrated that the addition of nanoscale high-energetic metal particles to liquid fuels as fuel additives has a positive effect not only on the combustion performance but also in reducing the pollutant formation. However, most of those studies were performed for conventional fuels with high volume concentrations of nanoparticles, which will have a considerable effect on the hydrodynamic and thermophysical properties of the fuel. Such a change in fuel properties can in turn affect the atomization, mixing and evaporation characteristics of the liquid fuels. This study investigates the spray performance of an alternative gas-to-liquid (GTL) jet fuel with the addition of alumina nanoparticles at atmospheric condition and compared with that of the pure fuel. Macroscopic and microscopic measurement of the spray characteristics are performed using optical diagnostic techniques. Results show that the addition of nanoparticles tends to reduce the liquid sheet breakup length when compared to that of the pure fuel case. Furthermore, the droplet size and droplet velocities are observed to be slightly different between the pure fuel and nanofuel cases.
Parametric Geometry and CFD Process for Turbofan Nacelles
Authors: Heidebrecht Alexander , Stańkowski Tomasz , MacManus David
Published: September 2016

A parametric geometry definition for a generic turbofan nacelle was developed for use in preliminary design, based on Class-Shape Transformation curves. This takes as input a set of six intuitive variables which describe the main dimensions of a nacelle. This set is the same set of inputs as required by a preliminary nacelle design method to which the aerodynamic properties of resulting shapes were compared. An automated computational fluid simulation process was developed and implemented which generates meshes and quickly conducts an analysis of the resulting nacelle shapes using a commercial code. Several geometries were generated and analysed using this process to show whether the aerodynamic properties of the generated shapes are in line with the expected performance of a fan cowl of equal dimensions. It was found that the aerodynamic performance of the parametric fan cowls significantly exceeds predictions from an established preliminary fan cowl design method and is very close in performance to existing designs. The drag of an equivalent parametric fan cowl can therefore be used as a predictor of nacelle performance with greater accuracy than established preliminary design methods. It is therefore suited as a tool to develop improved preliminary design methods, and for studies of the design space for preliminary nacelle design.
Effect of Ice and Blade Interaction Models on Compressor Stability
Authors: Saxena Swati , Woo George T. K. , Singh Rajkeshar , Breeze-Stringfellow Andrew , Nakano Tsuguji , Szucs Peter
Published: September 2016

Incidents of partial or total thrust loss at cruise due to engine icing (mainly ice crystals and super-cooled water droplets at altitudes greater than 10,000 feet) have been recorded over the past several years. As air traffic continues to increase in subtropical areas where high moisture laden air is present at subfreezing conditions, engine icing probability increases. There is a need to better understand compressor dynamics under icing conditions which will help designers to develop more accurate and fast ice detection systems and anti-icing mechanisms. Stage re-matching occurs due to heat exchange between air and ice which dictates the stall inception stage in the compressor. It has been shown that compressor stages re-match under icing conditions — front stages are choked while rear stages throttle due to ice melting and evaporation. Such an analysis uses various empirical models to represent ice-breakup and water-splash processes as ice/water particles interact with rotors/stators. The following paper presents a compressor stall sensitivity analysis around different splash models. The effect of droplet splash at both rotor and stator blades, blade solidity effect and trailing edge shed effect are modeled. A representative 10 stage high speed compressor section operating near design point (100% Nc) is used for the study. Results show that T3 drop and overall compressor operability is a function of evaporating stages and droplet-blade interaction models influence them. A comprehensive compressor stability envelope has been evaluated for different models. It is observed that droplet-blade interaction behavior influences overall compressor stability and stall-margin predictions can vary by as much as 25% with different models. Therefore, there is a need for better calibration and continual improvement of empirical models to capture compressor inter-stage dynamics and stage re-matching accurately under ice/water ingestion.
Coupled CFD and Heat Transfer Analysis for a Small Scale Gas Turbine Combustor
Authors: Pişkin Altuğ , Topal Ahmet
Published: September 2016

Gas turbine combustor design process has significant number of design parameters because of contained complex phenomena. One of the most complicated of these is the heat transfer process of combustor liners. Heat transfer studies are performed in preliminary design phase by the help of one-dimensional tools and combustor geometry is shaped to satisfy design requirements. However; in the detail design phase, a fine tuning can be required to optimize it by using 3D CFD analysis. Conjugate heat transfer is a powerful tool to simulate interaction between reacting flow and combustor liners in detail design phase. But it is difficult to use computationally expensive conjugate heat transfer analysis in design iterations for calculating liner metal temperatures because of the high computation times. Its application will be mainly limited to optimized final geometries and steady simulations. On the other hand, when the 3D liner temperatures are required for structural evaluation during the preliminary design phase; coupled analysis of Finite Element Analysis (FEA)/ Computational Fluid Dynamics (CFD) can provide quick alternative solution. Coupled analysis requires lower mesh size and less calculation time comparing to the conjugate analysis. During a coupled analysis, an iterative boundary information exchange is conducted until the desired convergence criterion is reached.

In this study, a series of numerical analyses are evaluated and the relevant rig test thermal paint results are presented. Numerical analyses consist of coupled analyses with various boundary condition cases. Some of these cases have the complete set of boundary conditions and they assumed as comparable to the test condition. In the coupling process, FEM use the near wall gas temperature data that comes from CFD solution and CFD uses wall temperature data that comes from the FEM solution. Heat transfer coefficients are not coupled and they are obtained from empirical heat transfer correlations.

An atmospheric combustor test rig was used to apply thermal paint and thermocouple measurements were taken from the combustor outer liner. Numerical and experimental values of the liner temperatures are also compared and analyzed.
An Automated Approach to Nacelle Parameterization Using Intuitive Class Shape Transformation Curves
Authors: Christie Robert , Heidebrecht Alexander , MacManus David
Published: September 2016

A tool to create parametric aerodynamic shapes using intuitive design variables based on class shape transformation curves is presented. To enable this, a system has been developed which accepts arbitrary constraints and automatically derives the analytical expressions which describe the corresponding class shape transformation curves. Parametric geometry definitions for fan cowl and intake aero-lines were developed using the generalized method. CFD analysis of the fan cowl shows that despite the simple geometry definition its performance characteristics are close to what would be expected of a finished design. The intake geometry was generated in a similar way and met the typical performance metrics for conventional intakes. This demonstrates the usefulness of the tool to quickly and robustly produce parametric aero-lines with good aerodynamic properties, using relatively simple intuitive design variables.
Thermodynamic Multi-Criteria Optimization of the Unified Engine Core for the Line of Turbofan Engines
Authors: Rybakov Viktor N. , Kuz'michev Venedikt S. , Tkachenko Andrey Y. , Krupenich Ilia N.
Published: September 2016

Although development of the line of gas turbine engines on the basis of a unified engine core is a widely used practice, the method of selection of the most efficient values of engine core parameters has virtually never been published.

The paper describes the method of optimization of values of engine core parameters jointly with optimization of values of every engine forming the line of engines developed on the basis of this core. Both stages of optimization are multi-objective and fulfilled using the results of simulation of engine as a subsystem of the airframe.
Multicriteria Optimization of Axial Low Pressure Compressor of Gas Turbine Power Plant
Authors: Popov Grigorii , Goriachkin Evgenii , Kolmakova Daria , Novikova Yulia
Published: September 2016

The paper shows a method of the gas-dynamic refining of three-stage axial compressor based on the joint usage of mathematical optimization software IOSO and CFD complex NUMECA. The optimizer is used for automatic change of the compressor geometry in order to find the optimal design. The aim was to preserve the original design, for this reason only the geometrical parameters of rotor blades and guide vanes were varied without changing the contours of the meridional flow part and blade roots.

The optimization task was multiobjective. It was necessary to find a compromise between the efficiency increase and improvement of the gas-dynamic stall margins of the compressor at the primary operational mode and to prevent the deterioration of parameters at other modes. Compressor parameters were calculated at three engine modes, corresponding to the temperature of the air at the engine inlet — −15 °C, +15 °C, and +45 °C, at each step of the optimization. Parameters of the compressor were calculated in operational and stall points of its characteristics at the modes corresponding to −15 °C and +15 °C. Parameters of compressor were calculated in choking point at the mode corresponding to −+45 °C. The optimization problem was solved in two formulations with different degree of parameters variation at the modes of operation corresponding to the −15 °C and +45 °C.

Finite volume model of the compressor that is used in the optimization was created in the meshing software NUMECA AutoGrid. Configuring and solution of the task were carried out in the solver NUMECA FINE/Turbo. Comparison of calculated characteristics of the base compressor with the experimental data was performed before optimization.

Analysis of the impact of optimized compressor on the engine operation was performed. The position of the working line of base and optimized compressor variants was indicated. It was shown that optimized compressor has efficiency increase by 1.1% compare to the base while operating as the engine component.
Spanwise Spectra, Reynolds Stresses and Correlations From DNS of Turbine Like APG Boundary Layers
Authors: Simens Mark P. , Gungor Ayse G.
Published: September 2016

It is becoming more apparent that to be able to fully understand the adverse pressure gradient boundary flow in general or downstream of reattachment it is needed to understand the relation between the upstream flow structures and the downstream flow structures. In this work the results for three different direct numerical simulations (DNS) of adverse pressure gradient (APG) flows are presented. The three cases have the same overall characteristics with respect to the imposed APG and the Reynolds number Reδ099 at the inlet. However, the first case has no additional perturbations imposed, in the second case the flow is tripped by a trip wire and in the third case a periodic wake is superimposed on the flow. The main points that are discussed are the spanwise spectra, two-dimensional correlations, and Reynolds stress budgets for the three different flow cases. Attention is in particular directed to a comparison between the three different cases.

The most important conclusion is that the flow downstream of reattachment is strongly correlated with the flow structures at transition for almost the whole numerical domain.
Numerical Simulation of Particulates in Multi-Stage Axial Compressors
Authors: Saxena Swati , Jothiprasad Giridhar , Bourassa Corey , Pritchard Byron
Published: September 2016

Aircraft engines ingest airborne particulate matter, such as sand, dirt, and volcanic ash, into their core. The ingested particulate is transported by the secondary flow circuits via compressor bleeds to the high pressure turbine and may deposit resulting in turbine fouling and loss of cooling effectiveness. Prior publications focused on particulate deposition and sand erosion patterns in a single stage of a compressor or turbine. The current work addresses the migration of ingested particulate through the high pressure compressor and bleed systems. This paper describes a 3D CFD methodology for tracking particles along a multi-stage axial compressor and presents particulate ingestion analysis for a high pressure compressor section. The commercial CFD multi-phase solver ANSYS CFX R has been used for flow and particulate simulations. Particle diameters of 20, 40, and 60 microns are analyzed. Particle trajectories and radial particulate profiles are compared for these particle diameters. The analysis demonstrates how the compressor centrifuges the particles radially towards the compressor case as they travel through the compressor; the larger diameter particles being more significantly affected. Non-spherical particles experience more drag as compared to spherical particles and hence a qualitative comparison between spherical and non-spherical particles is shown.
Radial Stages With Non-Uniform Pressures at Diffuser Inlet
Authors: Japikse David , Krivitzky Eric M.
Published: September 2016

The design of centrifugal stages with an impeller and a downstream diffuser has generally been based on the assumption of axisymmetric flow at the impeller discharge. Flow entering the diffuser has customarily been assumed to also be axisymmetric, at least on a time-averaged basis, while laying out the diffuser vanes, establishing the preferred incidence, and sizing the throat areas. Recent stage studies have shown that the flow is often not fully axisymmetric, that not all diffuser passages perform the same way even at the design or best efficiency points, and that the actual time-averaged diffuser inlet flow conditions (distortion) may be changing from one operating point to another.

In this study, comprehensive time-averaged (steady) results from one test rig with a large array of impeller exit pressure taps is examined. Supporting results from five other test rigs are reviewed to broaden the picture of possible flow states. Hypotheses, suitable for future evaluation, are given to begin the explanation of the actual flow states and to guide further research. The current status of CFD to understand these phenomena is discussed.
An Investigation Into the Variation of Centrifugal Compressor Sensitivity to Inlet Swirl With Initial Form Parameter Selection
Authors: Krivitzky Eric M.
Published: September 2016

Fixed-geometry centrifugal compressors have inherent limitations in the off-design operating range and performance that can be delivered. Variable inlet swirl, typically introduced with variable inlet guide vanes, has been a frequent tool implemented across many industries to extend the stable operating range and off-design efficiency. However, a review of available data in the literature reveals a large disparity in the effectiveness of variable inlet swirl for useful map movement. An ideal configuration responds to preswirl with a significant reduction in the mass flow at instability along with increased efficiency. Unfortunately, some cases reveal no movement in the surge line, with increases in inlet swirl only serving to reduce the stage efficiency.

This study investigates underlying causes for the variation in sensitivity to inlet swirl amongst various compressor designs, represented by form parameters. An analytical model is established and then verified using CFD and selected test data to explore fundamental causes for decreased sensitivity to inlet swirl. Analytical and computational results suggest a new understanding of the governing parameters for inlet swirl sensitivity, and thus provide insight into the scenarios when inlet swirl is an effective tool for manipulation of performance characteristics. Synthesizing the underlying trends, guidelines are developed for design selections and operational situations when inlet swirl can be effectively implemented as a means to extend the stable operating range and off-design efficiency.
Study of the Wall Thermal Condition Effect in a Lean-Premixed Downscaled Can Combustor Using Large-Eddy Simulation
Authors: Mira D. , Vázquez M. , Houzeaux G. , Gövert S. , Kok J. W. B. , Mahiques E. I. , Panek L.
Published: September 2016

The primary purpose of this study is to evaluate the ability of LES, with a turbulent combustion model based on steady flamelets, to predict the flame stabilization mechanisms in an industrial can combustor at full load conditions. The test case corresponds to the downscaled Siemens can combustor tested in the high pressure rig at the DLR. The effects of the wall temperature on the prediction capabilities of the codes is investigated by imposing several heat transfer conditions at the pilot and chamber walls. The codes used for this work are Alya and OpenFOAM, which are well established CFD codes in the fluid mechanics community. Prior to the simulation, results for 1-D laminar flames at the operating conditions of the combustor are compared with the detailed solutions. Subsequently, results from both codes at the mid-plane are compared against the experimental data available. Acceptable results are obtained for the axial velocity, while discrepancies are more evident for the mixture fraction and the temperature, particularly with Alya. However, both codes showed that the heat losses influence the size and length of the pilot and main flame.
On the Influence of a Hubside Exducer Cavity and Bleed Air in a Close-Coupled Centrifugal Compressor Stage
Authors: Kaluza Peter , Landgraf Christian , Schwarz Philipp , Jeschke Peter , Smythe Caitlin
Published: September 2016

In aero-engine applications, centrifugal compressors are often close-coupled with their respective diffusers to increase efficiency at the expense of a reduced operating range. The aim of this paper is to show that state-of-the art steady state CFD simulations can model a hubside cavity between an impeller and a close-coupled diffuser and to enhance the understanding of how the cavity affects performance. The investigated cavity is located at the impeller trailing edge and bleed air is extracted through it. Due to geometrical limitations the mixing plane is located in the cavity region. Therefore, previous analyses used only a cut (“simple”) model of the cavity. With the new, “full” cavity model, the region inside the cavity right after the impeller trailing edge is not neglected anymore. The numerical setup is validated using experimental data gathered on a state-of-the art centrifugal compressor test-rig. For the total pressure field in front of the diffuser throat a clear improvement is achieved. The results presented reveal a drop in stage efficiency by 0.5%-points caused by a new loss mechanism at the impeller trailing edge. On the hubside, the fundamentally different interaction of the cavity with the coreflow increases the losses in the downstream components resulting in the mentioned stage efficiency drop. Finally, varying bleed air extraction is investigated with both cavity models. Only the full cavity model captures the changes measured in the experiment.
Pressure Distortion Effects on Rim Seal Performance in a Linear Cascade
Authors: Gibson Jeffrey , Thole Karen , Christophel Jesse , Memory Curtis , Praisner Thomas
Published: September 2016

Rim seals are used to prevent the ingress of hot gas into the cavities beneath turbine platforms. As these cavities are not actively cooled, high-pressure air, known as purge flow, is taken from the compressor and introduced beneath the platform to prevent hot gas from penetrating through the gaps between stationary and rotating hardware. Improving the rim-seal geometry however, is made difficult by a lack of understanding of the salient fluid mechanics associated with this region. This study investigates both the impact of a vane-induced static pressure distortion as well as the influence of the pressure distortion of a downstream blade row on an engine-relevant rim seal in a stationary, linear cascade. Vane alterations resulted in minimal change to rim seal performance; however, adding the pressure distortion of a downstream blade row was found to disturb the trench flow resulting in poorer performance of the seal.
Large Eddy Simulation of a Multiple-Injection Dry Low NOx Combustor for Hydrogen-Rich Syngas Fuel at High Pressure
Authors: Yunoki Keita , Murota Tomoya , Asai Tomohiro , Okazaki Teruyuki
Published: September 2016

The successful development of coal-based integrated gasification combined cycle (IGCC) technology requires gas turbines capable of achieving the dry low-nitrogen oxides (NOx) combustion of hydrogen-rich syngas for low emissions and high plant efficiency. Therefore we have been developing a multiple-injection burner for hydrogen-rich syngas fuel in order to achieve high efficiency and low environmental load. This burner consists of a perforated plate with multiple air holes and fuel nozzles. The multiple air holes and the fuel nozzles are arranged coaxially. The burner is based on the concept of premixed combustion configured by mixing fuel and air in the each air hole rapidly and dispersing fuel with multiple fuel-air jet. This rapid mixing can reduce NOx emissions by getting homogeneous lean premixed combustion, and preventing flashback despite the high flame speed for hydrogen-rich syngas fuels. The unsteady phenomena that occur in the combustion field should be understood in detail in order to confirm this burner concept. However, their measurement under high pressure is difficult. Meanwhile computational fluid dynamics (CFD) is able to investigate the detailed distributions of various emissions and temperature even though under combustion fields of high pressure and high temperature. The purpose of this paper is to validate this concept of the multiple-injection burner by using CFD. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing, so the combustion field coexisting with premixed combustion and non-premixed combustion is complicated. Therefore, we have developed a hybrid turbulent combustion (HTC) model applicable to both non-premixed and premixed flames. The HTC model is hybridized with the flamelet progress variable (FPV) model and a flame propagation model. The FPV model is based on the laminar flamelet concept. The flame propagation model considers the flame stretch effect, diffusion enhancement effect, and increasing rate of flame surface area. The turbulent flow model adopts large eddy simulation (LES) with a dynamic sub-grid scale (SGS) based on the local inter-scale equilibrium assumption (LISEA4). Both the turbulent combustion model and turbulent flow model were programmed into a simulation tool based on the OpenFOAM library. We validated the concept of this burner for hydrogen-rich syngas fuel by using the simulation tool. The simulation results showed the rapid mixing of fuel and air in the air holes, and by using HTC model we confirmed that premixed combustion is the combustion configuration of this multiple-injection burner. In addition, the multiple-injection burner has high flame stability. There is no zone of high temperature in the air hole and high temperature is maintained near the burner. The multiple-injection burner can thus maintain flame stability without any flashback.
Investigation on the Effect of Streamwise Grooves on Controlling Corner Flow Separation
Authors: Yi Weilin , Li Jiabin , Yu Jia , Ji Lucheng
Published: September 2016

Flow separations often take place in the junction of blades and endwalls and limit seriously the aerodynamic loading increase of turbomachinery, which are caused mainly by mixing of the boundary layers on blades and endwall surfaces and the transverse secondary flow generated by the pressure difference between the pressure and suction side.

Firstly, focusing on a linear diffusion cascade with 42 degrees turning angle, it can be found that the transverse secondary flow can be reduced by inviscid hub and the flow separation is eliminated further through the numerical comparison between the viscous and inviscid hub cases. So the transverse secondary flow is the dominate factor for the flow separation in this cascade. We should try to control the transverse secondary flow to reduce the flow separation.

Secondly, based above analysis, the flow separation can be controlled effectively if we can cut off the secondary flow. So nine kinds of streamwise groove schemes are designed and analyzed. It can be seen that the streamwise grooves at the end wall inhibit obviously the transverse secondary flow but the flow structure change is different at different span. There is an optimum combination of width and height of groove, and the height is more important than width.

Thirdly, the detailed flow analysis of best scheme with smaller width, moderate height are carried out. It can decrease the separation zone scope at the corner zone, reduce the energy loss coefficient and also reduce the flow loss.
The Effect of FSTI to the Combined Separation Control Strategy of Surface Roughness With Upstream Wakes
Authors: Shuang Sun , Zhi-jun Lei , Xin-gen Lu , Yan-feng Zhang , Jun-qiang Zhu
Published: September 2016

Boundary layer separation can lead to partial loss of lift and higher aerodynamic losses on low-pressure turbine airfoils at low Reynolds number in high bypass ratio engines. The combined effects of upstream wakes and surface roughness on boundary layer development have been investigated experimentally to improve the performance of ultra-high-lift low-pressure turbine (LPT) blades. The measurement was performed on a linear cascade with an ultra-high-lift aft-loaded LP turbine profile named IET-LPTA with Zweifel loading coefficient of about 1.37. The wakes were simulated by the moving cylindrical bars upstream of the cascade. The time-mean aerodynamic performance and the boundary layer behavior on suction surface had been measured with two 3-hole probes and a hot-wire probe. Three roughness heights ranging from 8.8–20.9μm combined with three roughness deposit positions ranging from 5.2%–39.5% suction surface length formed a large measurement matrix. The roughness with height of 8.8μm (1.05×10−4 chord length) covering 5.2% suction surface reduced the profile loss across the whole Reynolds number range. Under the effect of roughness associated with upstream wakes, the freestream turbulence intensity (FSTI) is responsible in part for the development of the wake-induced transition region, calmed region and natural transition region of the boundary layer. The transition length and the transition onset of the boundary layer were also affected by the FSTI.
Stall Warning Approach With Application to Stall Precursor-Suppressed Casing Treatment
Authors: Fanyu Li , Jun Li , Xu Dong , Dakun Sun , Xiaofeng Sun
Published: September 2016

The present work develops a stall warning approach with application to a stall enhancement system. This technique is proposed on the basis of the periodicity of pressure signals sampled by the dynamic pressure sensor which is located on the casing wall at the rotor leading edge. A parameter called Rc, defined to evaluate this periodicity, is calculated by pressure signals within 1 blade pitches in the current one and previous one shaft period. Statistical estimates are implemented on Rc within statistical windows which move with sampling. The probabilities of Rc less than a threshold Rcth are calculated and used as a criterion for stall warning. Experiments are carried out on a low speed compressor with a stall precursor-suppressed (SPS) casing treatment, an efficient stall enhancement system. Results show that the probability increases significantly when the stall boundary is approached. At the same work point, the value of probability will decrease when the SPS casing treatment is turned on. This approach successfully generates a stall warning signal and then triggers the SPS casing treatment when the stall margin needs to be extended.
Investigation of Ducted Inverse Nonpremixed Flame Using Dynamic Systems Approach
Authors: Sen Uddalok , Gangopadhyay Tryambak , Bhattacharya Chandrachur , Misra Arpan , Karmakar Suman , Sengupta Preetam , Mukhopadhyay Achintya , Sen Swarnendu
Published: September 2016

Gas turbine combustion has a number of practical applications, including aviation engines, ocean vessels, and tanks. The various advantages of normal diffusion flames, such as increased flame stability and reduced susceptibility to dynamic instabilities, has made it the de facto industrial standard. However, high NOx emission and sooting from such flames is a major problem, particularly for heavier hydrocarbons fuels. In that regard, the inverse diffusion flame offers a feasible alternative; but the dynamic response of such a flame, particularly in ducted conditions — where the unsteady heat release interacts with the duct acoustics — is relatively less researched. In the present work, an experimental investigation of a laboratory-scale inverse diffusion flame has been carried out. The inverse diffusion flame is found in applications like rocket motors, gas turbine combustors, and furnaces. In the present study, inverse diffusion flame from a coaxial burner inside a quartz tube was studied. The position of the duct with respect to the flame was kept fixed, while the global equivalence ratio was varied by keeping the air flow rate constant and changing the fuel flow rate. Various tools of nonlinear dynamics such as phase space reconstruction and recurrence quantification have also been used for dynamic characterization of such flames. The results show that the dynamics of the flame strongly depends on the global equivalence ratio.