bluuebunny/crossref_metadata_2025 huggingface dataset:
Mistuning and Damping Experiments at Design Speed Combined With Computational Tools
Authors: D’Souza Kiran , Dunn Mike , Epureanu Bogdan I.
Published: August 2017

This paper describes a combined experimental/analytical effort which will provide measurements specifically designed to verify computational tools developed for turbomachinery applications. The hardware used for these measurements is engine-type hardware that will be operated at design speed. The specific hardware to be used is NASA Rotor 67 and the measurements will be performed in the confines of an underground spin pit facility. The experiments are aimed at identifying damping and mistuning properties of the rotor while it rotates at predetermined speed values within the facility. In addition, experiments using a modified Rotor 67 configuration containing added frictional damping elements are described. Light probe and strain gauge data will be obtained in order to compare their individual effectiveness. The response data storage is based on wide bandwidth, low noise signal conditioners used in conjunction with a high sampling-frequency data acquisition system. The rotor can be excited at specific engine-order crossings using air-jets with the number of specific active air-jets and the corresponding force transmitted by each jet estimated from computations. The experimental effort enables the identification of key parameters used in a series of computational tools that have been developed recently. The computational tools include various mistuning and (nonlinear) damping identification methods that have not yet been verified using data obtained from rotating hardware.
Investigation of a Gas Turbine Process With Reheat Combustion at Flue Gas Recirculation and Oxyfuel-Conditions
Authors: Beenken Florian , Joos Franz
Published: August 2017

In near future electrical power generation will still be supplied by fossil fuels. To reach the targets of the conference on climate change in Paris 2015 one method proposed is the CO2 sequestration and usage or alternatively storage.

Compared to coal-fired power station the amount of CO2 in the exhaust gas of gas turbine power station is much less and therefore more difficult to remove. To enhance the efficiency of the CO2-sequestration process enrichment of the CO2 in the exhaust gas could be a solution. This can be achieved by exhaust gas recirculation or by burning with pure O2 instead of air avoiding a lot of N2 in the exhaust gas, called Oxyfuel process.

The work concerns to investigations of a reheat gas turbine operating with flue gas recirculation as well as with Oxyfuel operation. The thermodynamic process has been modeled in detail considering the additional demand of cooling of the combustors and the turbines at Oxyfuel process. Additional combustion experiments have been carried out with flue gas recirculation as well as with Oxyfuel conditions burning Natural Gas with O2 in a CO2 environment to investigate the flame stability and extinction limit.

The thermophysical properties, like specific heat capacity and sound velocity, are strongly altered by the high content of CO2 and H2O in the fluid of the turbine as well as of the compressor. For example during Oxyfuel conditions the pressure ratio is expected to decrease to about 78% of air operation. The influence of flue gas recirculation and Oxyfuel process to the gas composition as well as to the heat transfer and exit conditions are discussed.
Experimental and Numerical Investigation of Transition Effects on a Low Reynolds Number Airfoil
Authors: Collison Michael J. , Harley Peter X. L. , di Cugno Domenico
Published: August 2017

Low speed, small scale turbomachinery operates at low Reynolds number with transition phenomena occurring. In small consumer product applications, high efficiency and low noise are key performance metrics. Transition behaviour will partly determine the state of the boundary layer at the trailing edge; whether it is laminar, turbulent or separated impacts aerodynamic and acoustic performance. This study aimed to evaluate a commercially available CFD transition model on a low Reynolds number Eppler E387 airfoil and identify whether it was able to correctly model the boundary layer transition, and at what expense.

CFD was carried out utilising the ANSYS Shear Stress Transport (SST) k-ω γ-Reθ transition model. The CFD progressed from 2D in Fluent v150, through to single cell thickness 3D (pseudo 2D) in CFX v172. An Eppler E387 low Reynolds number airfoil, for which experimental data was readily available from literature at Re = 200,000 was used as the validation case for the CFD, with results computed at numerous incidence angles and mesh densities.

Additionally, experimental surface oil flow visualisation was undertaken in a wind tunnel using a scaled E387 airfoil for the zero incidence case at Re = 50,000. The flow visualisation exhibited the expected key features of transition in the breakdown of the boundary layer from laminar to turbulent, and was used as a validation case for the CFD transition model.

The comparison between the results from the CFD transition model and the experimental data from literature suggested varying levels of agreement based on the mesh density and CFD solver in the starting location of the laminar separation bubble, with higher disparity for the position of the reattachment point. Whether 2D or 3D, the prediction accuracy was seen to worsen at high incidence angles. Finally, the location of the laminar separation bubble between CFD and oil flow visualisation had good agreement and a set of guidelines on the mesh parameters which can be applied to low Reynolds number turbomachinery simulations was determined.
Large Eddy Simulation of Axial and Compound Angle Holes With Varying Hole Length-to-Diameter Ratio
Authors: Li Weihong , Shi Wei , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2017

The effect of hole length to diameter ratio on flat plate film cooling effectiveness and flow structures of axial and compound angle hole is investigated by large eddy simulation (LES). Film cooling simulations are performed for three blowing ratios (M) ranging from 0.4 to 1.2, three hole length-to-diameter ratios (L/D) from 0.5 to 5 and two compound angle (β: 0°, 45°). The prediction accuracy is validated by the reported hydrodynamic data and present film effectiveness data measured by pressure sensitive paint (PSP). Results indicate that discrete hole with L = 0.5 show highest film cooling effectiveness regardless of compound angle. Round hole generally shows an increasing trend as L increases from 2 to 5, while compound angle hole shows a complex trend concerning with blowing ratios and length to diameter ratios. This is associated with the fact that length-to-diameter ratio influences the in-tube flow behavior, formation of Kelvin-Helmholtz (K-H) structures, and development of single asymmetric main vortex (SAMV). Scalar field transportation features are investigated to clarify how different vortex structures affect the temperature distribution and the film cooling effectiveness. It is also demonstrated that the counter rotating vortex pair (CRVP) which is observed in the time-averaged flow field of axial hole is originated in different vortex structures with varying blowing ratios and length to diameter ratios.
Experimental and Numerical Analysis of FLOX®-Based Combustor for a 3kW Micro Gas Turbine Under Atmospheric Conditions
Authors: Seliger Hannah , Stöhr Michael , Yin Zhiyao , Huber Andreas , Aigner Manfred
Published: August 2017

This paper presents an experimental and numerical study of the flow field and heat release (HRL) zone of a six-nozzle FLOX®-based combustor at atmospheric pressure. The combustor is suitable for the use in a micro gas turbine (MGT) based combined heat and power (CHP) system with an electrical power output of 3 kW. The velocity field was measured using stereoscopic particle image velocimetry (PIV). The heat release zone was visualized by OH*-chemiluminescence (OH* CL) and the flame front by OH planar laser-induced fluorescence (OH PLIF). The results are compared with CFD simulations to evaluate the quality of the applied numerical turbulence and combustion models. The simulations were performed using Reynolds-averaged Navier-Stokes equations in combination with the k-ω-SST-turbulence model. Since the FLOX®-based combustion is dominated by chemical kinetics, a reaction mechanism with detailed chemistry, including 22 species and 104 reactions (DRM22), has been chosen. To cover the turbulence-chemistry interaction, an assumed probability density function (PDF) approach for species and temperature was used.

Except for minor discrapancies in the flow field, the results show that the applied models are suitable for the design process of the combustor. In terms of the location of the heat release zone, it is necessary to consider possible heat losses, especially at lean operating conditions with a distributed heat release zone.
A Study of s-CO2 Power Cycle for CSP Applications Using an Isothermal Compressor
Authors: Heo Jin Young , Ahn Yoonhan , Lee Jeong Ik
Published: August 2017

For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including higher cycle efficiencies, reduced component sizing, and potential for the dry cooling option, in comparison to the conventional steam Rankine cycle. Increasing number of investigations and research projects are involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems.

In this conceptual study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced compared to that of the conventional compressor under varying compressor inlet conditions.

Furthermore, the recompression Brayton cycle layout using s-CO2 as a working fluid is evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the simple recuperated Brayton cycle with an isothermal compressor performs better than the given reference recompression cycle by 6–10% points in terms of cycle thermal efficiency. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency. Adopting an isothermal compressor in the s-CO2 layout, however, can imply larger heat exchange area for the compressor which requires further detailed design for realization in the future.
Development of 1500-r/min 75-Inch Ultra-Long Last Stage Blades for Nuclear Steam Turbine
Authors: Yu Deqi , Yang Jiandao , Lu Wei , Zhou Daiwei , Cheng Kai , Yang Rui
Published: August 2017

The 1500-r/min 1905mm (75inch) ultra-long last three stage blades for half-speed large-scale nuclear steam turbines of 3rd generation nuclear power plants have been developed with the application of new design features and Computer-Aided-Engineering (CAE) technologies.

The last stage rotating blade was designed with an integral shroud, snubber and fir-tree root. During operation, the adjacent blades are continuously coupled by the centrifugal force. It is designed that the adjacent shrouds and snubbers of each blade can provide additional structural damping to minimize the dynamic stress of the blade. In order to meet the blade development requirements, the quasi-3D aerodynamic method was used to obtain the preliminary flow path design for the last three stages in LP (Low-pressure) casing and the airfoil of last stage rotating blade was optimized as well to minimize its centrifugal stress. The latest CAE technologies and approaches of Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and Fatigue Lifetime Analysis (FLA) were applied to analyze and optimize the aerodynamic performance and reliability behavior of the blade structure.

The blade was well tuned to avoid any possible excitation and resonant vibration. The blades and test rotor have been manufactured and the rotating vibration test with the vibration monitoring had been carried out in the verification tests.
Engine Fleet-Management: The Use of Digital Twins From a MRO Perspective
Authors: Kraft Joern , Kuntzagk Stefan
Published: August 2017

Engine operating cost is a major contributor to the direct operating cost of aircraft. Therefore, the minimization of engine operating cost per flight-hour is a key aspect for airlines to operate successfully under challenging market conditions.

The interaction between maintenance cost, operating cost, asset value, lease and replacement cost describes the area of conflict in which engine fleets can be optimized.

State-of-the-art fleet management is based on advanced diagnostic and prognostic methods on engine and component level to provide optimized long-term removal and work-scoping forecasts on fleet level based on the individual operation. The key element of these methods is a digital twin of the active engines consisting of multilevel models of the engine and its components. This digital twin can be used to support deterioration and failure analysis, predict life consumption of critical parts and relate the specific operation of a customer to the real and expected condition of the engines on-wing and at induction to the shop. The fleet management data is constantly updated based on operational data sent from the engines as well as line maintenance and shop data.

The approach is illustrated along the real application on the CFM56-5C, a mature commercial two-spool high bypass engine installed on the Airbus A340-300. It can be shown, that the new methodology results in major improvements on the considered fleets.
Strong Azimuthal Combustion Instabilities in a Spray Annular Chamber With Intermittent Partial Blow-Off
Authors: Prieur Kevin , Durox Daniel , Schuller Thierry , Candel Sébastien
Published: August 2017

The present article reports original experiments carried out in the MICCA-Spray combustor developed at EM2C, CNRS and CentraleSupélec. This system comprises 16 swirl spray injectors. Liquid n-heptane is injected by hollow cone simplex atomizers. The combustion chamber is formed by two cylindrical quartz tubes allowing full optical access to the flame region and it is equipped with eight pressure sensors recording signals in the plenum and chamber. A high speed camera provides images of the flames and photomultipliers record the light intensity from different flames. For certain operating conditions, the system exhibits well defined instabilities coupled by the first azimuthal mode of the chamber at a frequency of about 750 Hz. These instabilities occur in the form of bursts with a moderate level of growth. Examination of the pressure and the light intensity signals gives access to the acoustic energy source term. Analysis of the phase between the two signals during the instability bursts (growth, limit cycle, decay) is carried out using cross-spectral analysis. At limit cycle, large amplitude of pressure oscillations are reached with peak values around 5000 Pa (or 5% of the mean pressure in the chamber), and these levels persist over a finite period of time. Detailed analysis of the signals using the spin ratio indicates that the standing mode is predominant. The chamber can exhibit a spinning mode but with a lower amplitude of acoustic fluctuation. Analysis of the flame dynamics at the pressure anti-nodal line reveals a strong longitudinal pulsation with heat release rate oscillations in phase and increasing linearly with the acoustic pressure even at the highest oscillation levels. At the pressure nodal line, the flames are subjected to large transverse velocity fluctuations leading to a transverse motion of the flames and partial blow-off. Scenarios and modeling elements are developed to interpret these features. To the best of our knowledge, this is the first time that azimuthal instabilities are characterized in a well-controlled annular combustor with swirled spray flames.
Time-Resolved Measurements of Intermediate Concentrations in Fuel-Rich n-Heptane Oxidation Behind Reflected Shock Waves
Authors: Loparo Zachary E. , Lopez Joseph G. , Neupane Sneha , Vasu Subith S. , Partridge William P. , Vodopyanov Konstantin
Published: August 2017

The chemical kinetics of the oxidation of n-heptane (C7H16) — an important reference compound for real fuels — are well studied at stoichiometric and lean conditions. However, there is only limited information on the chemical kinetics of fuel-rich combustion. In order to improve the accuracy of chemical kinetic models at these conditions, the oxidation of rich n-heptane mixtures has been investigated. Combustion of n-C7H16/O2/Ar mixtures at equivalence ratios, ϕ, of 2.0 behind reflected shock waves has been studied at temperatures ranging from 1075 to 1418K and at pressures ranging from 1.6 to 1.9atm. Reaction progress was monitored by recording ethylene (C2H4) concentration time-histories and initial n-heptane decay rates at a location 2cm from the endwall of a 13.4m long, 14cm inner diameter shock tube. Ethylene and n-heptane concentration time-histories were measured using absorption spectroscopy at 10.532μm from a tunable CO2 laser and at around 3.4μm from a continuous wave distributed feedback interband cascade laser (ICL), respectively. The measured concentration time-histories were compared with modeled predictions from the Lawrence Livermore National Lab (LLNL) detailed n-heptane reaction mechanism. To the best of our knowledge, the current data are the first time-resolved n-heptane and ethylene concentration measurements conducted in a shock tube at these conditions.
Influence of Backward and Forward Facing Steps on the Flow Through a Turning Mid Turbine Frame
Authors: Bauinger Sabine , Malzacher Franz , Goettlich Emil , Heitmeir Franz
Published: August 2017

For this work, reality effects, more precisely backward and forward facing steps, and their influence on the flow through a two-stage two-spool turbine rig under engine-relevant conditions were experimentally investigated. The test rig consists of a HP and a LP stage, with the two rotors rotating in opposite direction with two different rotational speeds. An S-shaped transition duct, which is equipped with turning struts (so-called turning mid turbine frame or TMTF) and making therefore a LP stator redundant, connects both stages and leads the flow from a smaller to a larger diameter.

This test setup allows the investigation of a TMTF deformation, which occurs in a real aero-engine due to non-uniform warming of the duct during operation — especially during run up — and causes backward and forward facing steps in the flow path. This happens for non-segmented ducts, which are predominantly part of smaller engines. In the case of the test rig, steps were not generated by varying temperature but by shifting the TMTF in horizontal direction while the rotor and its casing were kept in the same position. In this way, both backward and forward facing steps between duct endwalls and rotor casing could be created. In order to avoid steps further downstream of the interface between HP rotor and TMTF, the complete aft rig was moved laterally too. In this case, the aft rig incorporates amongst others the LP rotor, the LP rotor casing and the deswirler downstream of the LP stage.

In order to catch the influence of the steps on the whole flow field, 360 deg rake traverses were performed downstream of the HP rotor, downstream of the duct and downstream of the LP rotor with newly designed, laser-sintered Combi-Rakes for the measurement of total pressure and total temperature. Only the compact design of the rakes, which can be easily realised by additive manufacturing, makes the aforementioned 360 deg traverses in this test rig possible and allows a number of radial measurements positions, which is comparable to those of a five hole probe. To get a more detailed information about the flow, also five hole probe measurements were carried out in three measurement planes and compared to the results of the Combi-Rakes.
Numerical Investigation of Effect of Inlet Distortion on Compressor Flow Field and Stability
Authors: Zhang HaoGuang , An Kang , Tan Feng , Wu YanHui , Chu WuLi
Published: August 2017

The compressor aerodynamic design is conducted under the condition of clean inlet in general, but a compressor often operates under the condition of inlet distortion in the practical application. It has been proven by a lot of experimental and numerical investigations that inlet distortion can decrease the performance and stability of compressors. The circumferential or radial distorted inlet in mostly numerical investigations is made by changing the total pressure and total temperature in the inlet ring surface of the compressors. In most of inlet distortion experiments, distorted inlets are usually created by using wire net, flashboards, barriers or the generator of rotating distortion. The fashion of generating distorted inlet for experiment is different from that for numerical simulation. Consequently, the flow mechanism of affecting the flow field and stability of a compressor with distorted inlet for experiment is partly different than that for numerical simulation.

In the numerical work reported here, the inlet distortion is generated by setting some barriers in the inlet ring surface of an axial subsonic compressor rotor. Two kinds of distorted inlet are investigated to exploring the effect of distorted range on the flow field and stability of the compressor with ten-passage unsteady numerical method. The numerical results show that the inlet distortions not only degrade the total pressure and efficiency of the compressor rotor, but also decrease the stability of the rotor. The larger the range of distorted inlet is, the stronger the adverse effect is. The comprehensive stall margin for the inlet distortion of 24 degrees and 48 degrees of ten-passages is reduced about 3.35% and 5.88% respectively. The detailed analysis of the flow field in the compressor indicates that the blockage resulted from tip clearance leakage vortex (TLV) and the flow separation near the suction surfaces of some blades tip for distorted inlet is more serious than that resulted from TLV for clean inlet. Moreover, the larger the range of distorted inlet is, the larger the range of the blockage is. The analysis of unsteady flow shows that during this process, which is that one rotor blade passes through the region affected by the distorted inlet, the range of the blockage in the rotor passage increases first, then reduces, and increases last.
Numerical Investigation of an Asymmetric Double Suction Centrifugal Compressor With Different Backswept Angle Matching for a Wide Operating Range
Authors: Zhang Hanzhi , Lao Dazhong , Wei Longyu , Yang Ce , Qi Mingxu
Published: August 2017

The work presented here investigates the characteristics of the different impeller backswept angle matchings for a wide stable operating range in an asymmetric double suction centrifugal compressor. The numerical simulation was employed to investigate the influence of different backswept angle matchings on the stable operating range. The aim is to propose a proper change of the backswept angle matching between two impeller sides to improve the impeller power capability and mass flow distribution, furthermore, to delay the operating mode transition and widen the stable operating range of the compressor. Firstly, the method to determine the optimum backswept angle matching obtained by the theory calculation. Then, three matching models were proposed and analyzed in detail. In three matching models, the backswept angle differences between the front and rear impeller side are 0°, 10° and 20°, respectively. The analysis mainly focused on the influence of the different backswept angle matchings on the compressor flow field characteristics and the mass flow distribution characteristics. The results show that the change of the impeller backswept angle matching can improve the mass flow distribution characteristics for two impeller sides and further reduce the stall mass flow rate of the double suction compressor. The model that the backswept angle difference is 10° can delay the operating mode transition and reduce the stall mass flow of the double suction compressor. The model that the backswept angle difference is 20° can also reduce the stall mass flow and finally enable the front impeller into the stall condition. Therefore, the proper change of the backswept angle matching can achieve the purpose of reducing the stall mass flow and widening the operating range for the double suction centrifugal compressor.
Effects of Nozzle Helmholtz Number on Indirect Combustion Noise by Compositional Perturbations
Authors: Magri Luca , O’Brien Jeffrey , Ihme Matthias
Published: August 2017

By modeling a multi-component gas, a new source of indirect combustion noise is identified, which is named compositional indirect noise. The advection of mixture inhomogeneities exiting the gas-turbine combustion chamber through subsonic and supersonic nozzles is shown to be an acoustic dipole source of sound. The level of mixture inhomogeneity is described by a difference in composition with the mixture fraction. An n-dodecane mixture, which is a kerosene fuel relevant to aeronautics, is used to evaluate the level of compositional noise. By relaxing the compact-nozzle assumption, the indirect noise is numerically calculated for Helmholtz numbers up to 2 in nozzles with linear velocity profile. The compact-nozzle limit is discussed. Only in this limit, it is possible to derive analytical transfer functions for (i) the noise emitted by the nozzle and (ii) the acoustics travelling back to the combustion chamber generated by accelerated compositional inhomogeneities. The former contributes to noise pollution, whereas the latter has the potential to induce thermoacoustic oscillations. It is shown that the compositional indirect noise can be at least as large as the direct noise and entropy noise in chocked nozzles and lean mixtures. As the frequency with which the compositional inhomogeneities enter the nozzle increases, or as the nozzle spatial length increases, the level of compositional noise decreases, with a similar, but not equal, trend to the entropy noise. The noisiest configuration is found to be a compact supersonic nozzle.
Experimental and Numerical Investigation of Vibration Transmission Between Two Parallel Plate Partially Immersed in a Fluid
Authors: Vasudevan Sumathi , Jalaldeen S. , Sajish S. D. , Selvaraj P. , Murugan S.
Published: August 2017

The dynamic characteristics of a structure are modified considerably when it is immersed in a dense fluid. Dynamic interaction between fluid and structure includes the phenomenon of Fluid Structure Interaction (FSI). In the present study, transmission of vibration between two parallel plates partially immersed in a fluid is investigated considering FSI. It is assumed that the plates are clamped along their edges and the fluid is bounded between the two parallel plates to form a rigid rectangular container. Excitation of one plate by an impact load results in the response of the opposite plate. An experiment was conducted and the results were compared with the three-dimensional Finite Element Method (FEM) analysis using CAST3M. Wet dynamic displacement, the frequency of vibration of the two parallel plates with variation in the fluid level are the parameters considered in the present study. Effect of liquid free surface and viscous damping are considered. A benchmark validation from literature has been presented for the free vibration of immersed cantilever plate using CAST3M. It is observed that the damping ratio decreases with an increase in the fluid level and the displacement of the response plate increases. This study especially has been carried out towards the investigation of vibration transmission between structures partially immersed in the liquid sodium in Fast reactors. The objective of the present work is the numerical verification and experimental validation of the FEM model which would make it convenient while analyzing the vibration of immersed structures with FSI.
Effects of Oscillations in the Mainstream on Film Cooling at Various Blowing Ratios
Authors: Baek Seung Il , Yavuzkurt Savas
Published: August 2017

The objective of this study is to understand the effects of flow oscillations in the mainstream and film cooling jets on film cooling at various blowing ratios (0.5, 0.78, 1.0 and 1.5). These oscillations could be caused by the combustion instabilities. They are approximated in sinusoidal form for the current study. The effects of different frequencies (0, 2, 16, 32 Hz) on film cooling are investigated. Simulations are performed using URANS Realizable k-epsilon and LES Smagorinsky-Lilly turbulence models. The results indicate that if the frequencies of the mainstream and the jet flow are increased at a low average blowing ratio of M = 0.5, the adiabatic film cooling effectiveness is decreased and the heat transfer coefficient is increased due to increased disturbance in jet and main flow interaction with increasing frequency. It was observed that when the frequency of the mainstream and the cooling jet flow is increased at M = 0.5, the amplitude of the pressure difference between the mainstream and the plenum is increased resulting in increased amplitude of coolant flow rate oscillations leading to more jet lift off and more disturbance in the main flow and coolant interaction. Consequently, adiabatic film cooling effectiveness is decreased and heat transfer coefficient is increased. If the frequency of the mainstream is increased from 0 Hz to 2, 16, or 32 Hz at M = 0.5, the centerline effectiveness is decreased about 10%, 12%, or 47% and the spanwise-averaged Stanton number ratio is increased about 4%, 5%, or 9% respectively. If the frequencies of the main flow and the jet flow are increased at higher blowing ratios of M = 1.0 and 1.5, adiabatic effectiveness is increased and the spanwise-averaged heat transfer coefficient are decreased. Under steady flow conditions jet lift off is generated for these high blowing ratios. If the frequency of the mainstream and the jet flow is increased, the amplitude of coolant jet flow rate oscillation is increased for the same reason as mentioned above for M = 0.5. This leads to less jet lift off during the cycle resulting in more frequent coolant contact with the wall and consequently increased centerline effectiveness as frequency increases. In addition, the entrainment of hot gases underneath the jet doesn’t lead to higher mixing between the hot mainstream and the coolant and this results in decreased heat transfer coefficient. This is also indicated by the turbulent kinetic energy levels. Some representative results are: when the frequency of the main flow is increased from 0 Hz to 2, 16, or 32 Hz at M = 1.0, the centerline effectiveness is increased about 8%, 19%, or 320%. Also, if the oscillation frequency is increased from 2 Hz to 16, or 32 Hz at M = 1.0, the spanwise-averaged Stanton number ratio is decreased around 2%, to 5% respectively. It seems like the cut off point for low and high blowing ratio behavior of cooling jets is around M = 0.78.
Numerical Studies on the Intrusive Influence of a Five-Hole Pressure Probe in a High-Speed Axial Compressor
Authors: Sanders Christoph , Terstegen Marius , Hölle Magnus , Jeschke Peter , Schönenborn Harald , Fröbel Tobias
Published: August 2017

In this investigation, CFD calculations are conducted to evaluate the differences between five-hole pressure probe-determined flow quantities and the unaffected flow quantities without the probe’s intrusive influence. The blockage effect of the probe is described and evaluated. Furthermore, the influence of this effect is used to estimate the error when using measured stator outflows as forcing functions for the following rotor blades.

To compare the flow field, both with and without the probe’s influence, a five-hole pressure probe is traversed numerically at midspan behind each stator row of a 2.5-stage axial compressor. For reproducing the blockage of the probe accurately, the full annulus of the respective stator row has to be modeled. In order to minimize the calculation time, a study to reduce the number of stator passages was successfully performed. To evaluate the flow quantities using the probe, a calibration polynomial is set up numerically. CFD simulations of the probe geometry within a uniform flow field for each pitch and yaw angle, as well as Mach number combination, are performed for this purpose. Moreover, the pressure probe data for the numerical traverses are corrected to account for velocity gradients in the wake region. The comparison of Mach number, with and without the probe’s influence, shows differences both in the width and the depth of the wake. The results of the Fourier-transformed wake profile for both cases are compared and changes in the first harmonic of Mach number of up to −13% identified. Finally, the first harmonic of the flow quantities is used to perform linearized CFD calculations and to evaluate the influence of disturbed forcing functions on the aerodynamic work of the following rotor blade. The average difference in aerodynamic excitation is about −12% with a maximum deviation of more than −30%.

The results presented aim to draw attention to intrusive probe influences and their consequences for validating numerical results against experiments. Special attention is given to the discrepancies of forced response calculations with varying gust boundary conditions.
On the Impact of Simulation Approaches on the Predicted Aerodynamic Damping of a Low Pressure Steam Turbine Rotor
Authors: Fuhrer Christopher , Vogt Damian M.
Published: August 2017

The determination of the aerodynamic damping is a major task in predicting flutter stability and therefore safety margins for turbine operation. Throughout the current work the energy method is employed to predict the aerodynamic damping for a last stage rotor blade numerically. The focus is put on the prediction of the aerodynamic damping with different traveling wave mode representations and on the influence of the blade fixation at the root. The Fourier transformation-method, the influence-coefficients-method and a direct traveling wave mode calculation are employed.

The investigated rotor geometry was taken from the open literature, a root was designed and an iterative process was installed to determine the cold blade geometry. It became apparent, that the influence-coefficients-method is capable of predicting the overall stability curve computationally efficient, whereas the Fourier-transformation-method showed advantages in the identification of the least stable point for a finer mesh. Nevertheless, all methods predicted a potential flutter risk for the current operating point. The influence of the additional blade root with a completely fixed support on the aerodynamic damping is minor.
A Comparative Study of Contrasting Machine Learning Frameworks Applied to RANS Modeling of Jets in Crossflow
Authors: Weatheritt Jack , Sandberg Richard D. , Ling Julia , Saez Gonzalo , Bodart Julien
Published: August 2017

Classical RANS turbulence models have known deficiencies when applied to jets in crossflow. Identifying the linear Boussinesq stress-strain hypothesis as a major contribution to erroneous prediction, we consider and contrast two machine learning frameworks for turbulence model development. Gene Expression Programming, an evolutionary algorithm that employs a survival of the fittest analogy, and a Deep Neural Network, based on neurological processing, add non-linear terms to the stress-strain relationship. The results are Explicit Algebraic Stress Model-like closures. High fidelity data from an inline jet in crossflow study is used to regress new closures. These models are then tested on a skewed jet to ascertain their predictive efficacy. For both methodologies, a vast improvement over the linear relationship is observed.
Measurements of the Leakage Through a High Pressure Steam Turbine Power Plant Gland Seal
Authors: Stein Peter , Born Dominik , König Martin
Published: August 2017

Today’s power market asks for highly efficient turbines which can operate at a maximum flexibility, achieving a high lifetime and all of this on competitive product investments. In line with the demands for reduction of CO2, the machine efficiencies are continuously increased. To further increase efficiencies, deeper insight into the single components is required to better understand the individual contributions to the overall performance. This work focuses on the measurement of leakages through High Pressure Steam Turbine gland sealing. Gland sealing technologies are frequently in focus of research and development activities. Various concepts were and are still developed and proven to work in test rigs. Typically such test rigs form an idealized environment with ideal manufacturing and low tolerances compared to real plant components. For this work real gland sealing components from a power plant were taken, a test rig developed around them and the different leakage path massflow rates determined. The advantage of using real plant components is i.e. in the real life relevance of the gained results by considering real design manufacturing tolerances, surface qualities etc.. By testing numerous gland segments from manufacturing and installing them in different orders, even statistical relevant information may be gained with respect to the influence of manufacturing on the seal tightness. This work presents the development of a test rig around a real plant gland seal and the tested leakages through the various paths of the tested component. The here gained information enables further development and optimization of advanced sealing technologies.
Optimization of Statistical Methodologies for Anomaly Detection in Gas Turbine Dynamic Time Series
Authors: Ceschini Giuseppe Fabio , Gatta Nicolò , Venturini Mauro , Hubauer Thomas , Murarasu Alin
Published: August 2017

Statistical parametric methodologies are widely employed in the analysis of time series of gas turbine sensor readings. These methodologies identify outliers as a consequence of excessive deviation from a statistically-based model, derived from available observations. Among parametric techniques, the k-σ methodology demonstrates its effectiveness in the analysis of stationary time series. Furthermore, the simplicity and the clarity of this approach justify its direct application to industry. On the other hand, the k-σ methodology usually proves to be unable to adapt to dynamic time series, since it identifies observations in a transient as outliers.

As this limitation is caused by the nature of the methodology itself, two improved approaches are considered in this paper in addition to the standard k-σ methodology. The two proposed methodologies maintain the same rejection rule of the standard k-σ methodology, but differ in the portions of the time series from which statistical parameters (mean and standard deviation) are inferred. The first approach performs statistical inference by considering all observations prior to the current one, which are assumed reliable, plus a forward window containing a specified number of future observations. The second approach proposed in this paper is based on a moving window scheme.

Simulated data are used to tune the parameters of the proposed improved methodologies and to prove their effectiveness in adapting to dynamic time series. The moving window approach is found to be the best on simulated data in terms of True Positive Rate (TPR), False Negative Rate (FNR) and False Positive Rate (FPR). Therefore, the performance of the moving window approach is further assessed towards both different simulated scenarios and field data taken on a gas turbine.
SGT-750 Fuel Flexibility: Engine and Rig Tests
Authors: Lindman Olle , Andersson Mats , Bonaldo Alessio , Larsson Anders , Janczewski Jacek , Persson Magnus
Published: August 2017

This paper provides a description of the fuel flexibility tests performed in:

• a gas turbine

• a high pressure combustion rig

• an atmospheric combustion rig

with the combustion system used in Siemens recently developed gas turbine SGT-750.

The gas turbine test campaign was run with natural gas blends with up to 50vol% nitrogen or 40vol% carbon dioxide. Ignition and engine starts with inert gas blends were also tested.

The fuel flexibility tests were continued in a single burner high pressure combustion rig. Both inert and reactive gas blends were tested. High concentrations of inert gases were tested at simulated cold ambient conditions (down to −60°C) at high and low loads. Reactive gases, such as ethane, propane, butane and hydrogen, were tested at high load operation. Also syngas blends were tested.

To simulate ignition at extreme arctic conditions an atmospheric rig test was performed with cold air supplied from evaporated liquid air.

The different gas fuel blends were run with low NOx emissions, often below 10 ppm, without water injection.

This paper includes description of the test setups and evaluation of the emissions and combustion stability for the tested gas blends.
Quantitative CO PLIF Measurements in Aeroengine Gas Turbine Combustion Chambers Under Realistic Conditions
Authors: Voigt Lena , Heinze Johannes , Aumeier Thomas , Behrendt Thomas , di Mare Francesca
Published: August 2017

Wall cooling in aero engine gas turbine combustors is one of the main issues in the development of advanced combustion concepts, especially for lean combustion technology. Here fuel is burned in a mixture with a lean equivalence ratio and the CO oxidation is prone to quenching effects caused by mixing processes between cooling film and reacting burner flow. The information about the distribution of CO concentrations is of great interest in such a configuration in order to increase the understanding of the impact of large scale mixing processes. Up to now planar laser measurements of the CO emissions within the flame region have not been realized under realistic operation conditions such as elevated pressure. A new planar and quantitative CO LIF measurement technique has been developed for measurements especially at elevated pressures and first results are presented in this contribution. Numerical simulations have been performed to support the measurements.
High-Speed Shadowgraphy Measurements of an Erosive Particle-Laden Jet Under High-Pressure Compressor Conditions
Authors: Hufnagel M. , Koch C. , Staudacher S. , Werner-Spatz C.
Published: August 2017

Erosive damage done to jet engine compressor blading by solid particles has a negative influence on the compressor aerodynamic properties and hence decreases performance. The erosive change of shape has been investigated in a multitude of experiments ranging from eroding flat plates to eroding full engines. The basic challenge to transfer the results from very simple tests to real life erosion remains. Up to date measurement techniques today allow closing this gap. The necessary experimental and analytical steps are shown. The erosion resistance of Ti-6Al-4V at realistic flow conditions with fluid velocities ranging from 200 to 400 m/s is used. The erodent used was quartz sand with a size distribution corresponding to standardized Arizona Test Dust A3 (1 to 120 μm). Flat plates out of Ti-6Al-4V were eroded at different impingement angles. The particle velocities and sizes were investigated using a high speed laser shadowgraphy technique. A dimensional analysis was carried out to obtain nondimensional parameters suitable for describing erosion. Different averaging methods of the particle velocity were examined in order to identify a representative particle velocity. Compared to the fluid velocity and the mean particle velocity, the energy averaged particle velocity is found to be the best representation of the erosiveness of a particle stream. The correlations derived from the dimensional analysis are capable of precisely predicting erosion rates for different rig operating points. The results can be applied to the methodology published in [1].
Overall Cooling Effectiveness Measurements on Pressure Side Surface of the Nozzle Guide Vane With Optimized Film Cooling Hole Arrangements
Authors: Rhee Dong-Ho , Kang Young Seok , Cha Bong Jun , Lee Sanga
Published: August 2017

Most of the optimization researches on film cooling have dealt with adiabatic film cooling effectiveness on the surface. However, the information on the overall cooling effectiveness is required to estimate exact performance of the optimization configuration since hot components such as nozzle guide vane have not only film cooling but also internal cooling features such as rib turbulators, jet impingement and pin-fins on the inner surface. Our previous studies [1,2] conducted the hole arrangement optimization to improve adiabatic film cooling effectiveness values and uniformity on the pressure side surface of the nozzle guide vane. In this study, the overall cooling effectiveness values were obtained at various cooling mass flow rates experimentally for the baseline and the optimized hole arrangements proposed by the previous study [1] and compared with the adiabatic film cooling effectiveness results. The tests were conducted at mainstream exit Reynolds number based on the chord of 2.2 × 106 and the coolant mass flow rate from 5 to 10% of the mainstream. For the experimental measurements, a set of tests were conducted using an annular sector transonic turbine cascade test facility in Korea Aerospace Research Institute. To obtain the overall cooling effectiveness values on the pressure side surface, the additive manufactured nozzle guide vane made of polymer material and Inconel 718 were installed and the surface temperature was measured using a FLIR infrared camera system. Since the optimization was based on the adiabatic film cooling effectiveness, the regions with rib turbulators and film cooling holes show locally higher overall cooling effectiveness due to internal convection and conduction, which can cause non-uniform temperature distributions. Therefore, the optimization of film cooling configuration should consider the effect of the internal cooling to avoid undesirable non-uniform cooling.