bluuebunny/crossref_metadata_2025 huggingface dataset:
Flame Response to Transverse Acoustic Forcing With Minimal Axial Coupling
Authors: Smith Travis , Emerson Benjamin , Proscia William , Lieuwen Tim
Published: August 2017

Instabilities associated with transverse acoustic modes are an important problem in gas turbines. A number of studies have reported results on the response of flames to transverse excitation, in order to understand the acoustic-velocity-heat release mechanism associated with combustion instabilities. However, all forced and self-excited transverse studies to date have strong coupling between the transverse and axial acoustic fields near the flame. This is significant, as studies suggest that the actual transverse disturbances play a negligible direct role in generating spatially integrated oscillatory heat release. Rather, they suggest that it is the induced axial disturbances that control the bulk of the heat release response. As such, there is a need to control the relative amplitudes of the axial and transverse disturbances exciting the flame, and determine their relative roles in the overall heat release response. This paper presents experimental results to address this issue. The flow field and flame edge were measured using 5kHz simultaneous sPIV and OH-PLIF, and the relative heat release fluctuations were measured through OH* chemiluminescence. The flame was forced with both strong transverse and axial oscillations, with various degrees of coupling between them, showing quite consistently that it is the axial flow disturbances that excite heat release oscillations. These observations demonstrate that the key role of the transverse motions is to set the “clock” for the frequency of the oscillations, but have negligible effect on the actual heat release disturbances exciting the instability. Rather, it is the axial disturbances, induced by inherent multi-dimensional effects that lead to the actual heat release oscillations.
Numerical Analysis of the Impact of Manufacturing Errors on the Structural Stiffness of Foil Bearings
Authors: Fatu Aurelian , Arghir Mihai
Published: August 2017

The dynamic characteristics of foil bearings operating at high rotation speeds depend very much on the mechanical characteristics of the foil structure. For this reason, the stiffness and damping of the structure of foil bearings is a problem that is the focus of many analyses. The mechanical characteristics of the foil structure (top and bump foil) are analyzed either by using a simple approach obtained for an isolated bump modeled as a beam or with more elaborate ones taking into account the three-dimensional nature of the bumps and their mutual interactions. These two kinds of models give different foil structure stiffness, with lower values for the simplified model. However, the published experimental results of the foil bearing structure tend to validate the simplified model. The present paper explains the differences between the simplified and the elaborate models by taking into account the manufacturing errors of the foil structure.

A three-dimensional model based on the non-linear theory of elasticity is developed. The model offers a unique insight into the way the bearing structure deforms when the rotor is incrementally pushed into the foil structure. Three realistic manufacturing errors, bump height, bump length and radius of the bump foil are analyzed. Bump height and length vary following a normal distribution with a given standard deviation while the radius of the bump foil is given a waviness form with an imposed peak-to-peak amplitude. Three to five cases were calculated for each kind of error. Results show that only the manufacturing errors of the bump height affect the stiffness of the foil structure by diminishing its values. Height errors of 20 μm standard deviation (4% of the average bump height and 60% of the radial clearance) may induce a 40–50% reduction of the stiffness of the foil structure, i.e. in the range of the predictions of the simplified model.
Turboelectric Distributed Propulsion System As a Future Replacement for Turbofan Engines
Authors: Łukasik Borys
Published: August 2017

The main purpose of this paper is to discuss the possibility of standard turbofan engine replacement by the turboelectric distributed propulsion system, in future commercial aviation. Paper describes how the distributed propulsion allows to reach significantly greater propulsive efficiency than state-of-the-art high bypass turbofan engines, and presents turboelectric system as the only practical method of distributed propulsion implementation. However, since extra weight of the electric components that would be added can overcome the high propulsive efficiency benefit, a detailed analysis is needed to verify the feasibility of such system. This article shows results of such analysis that was conducted for 90 PAX class regional jet. Thermodynamic cycle calculations, performed for both, turbofan engine and turboelectric distributed propulsion are presented. They prove that distributed propulsion is able to provide great reduction in fuel consumption of uninstalled propulsion system, while performed mission analysis depicts the penalty of extra mass of electric appliances, showing actual profits that are achievable. On this example, advantages and disadvantages of the turboelectric distributed propulsion system in comparison with modern turbofan engines are discuss, taking into account the potential technological development of turbofan engine and additional non-propulsive benefits that turboelectric system is able to provide. Finally, this document also presents mass estimations for different scenarios of electric appliances evolution, which highlight the technology levels that need to be achieved before the system can be introduced in commercial service.
Unsteady 360 Computational Fluid Dynamics Validation of a Turbine Stage Mainstream/Disc Cavity Interaction Using Lattice-Boltzmann Method
Authors: Mirzamoghadam A. V. , Molla-Hosseini K. , Gonzalez-Martino I. , Polidoro F.
Published: August 2017

This paper is a continuation of a previous comparison dealing with URANS-based validation of the ASU-Honeywell turbine stage mainstream/disc-cavity interaction rig data. Here, the validation is with a CFD code named PowerFLOW which is based on the Lattice Boltzmann Method (or LBM). Transient LBM simulations were conducted across the previously published purge flows (Cw of 1540 to 6161), and at the higher mainstream flow condition of 2300 cfm (1.086m3/s). Sensitivity of convergence on results was investigated by increasing the number of revolutions, as well as by varying the passive scalar and temperature difference assumptions between mainstream and purge flow. Results indicate that at lower purge flow, LBM was able to significantly improve validation of sealing effectiveness measurements. For the intermediate purge flows, however, there is a departure from what the data shows. Finally, at the higher purge flow cases, LBM prediction improves at the outer radial location as compared to URANS. Moreover, on pressure validation, it has closed the gap in matching the measured steady pressures inside the lower disc cavity except at the highest purge flow. In the critical upper rim cavity, the gap between the two methods closes as purge flow increases. The outcome from this comparative tool validation study is that at the low critical purge flow case where ingestion is most critical as well as at the upper rim cavity location, sealing effectiveness predictions were significantly improved. The paper also discusses the current limitations of LBM.
Adaptation of a 60kW Commercial Natural Gas Fired Microturbine for Operation on Diesel and Diesel-Water Emulsions
Authors: Aguilar Hernandez Danilo , Sullivan-Lewis Elliot , McDonell Vincent
Published: August 2017

Injection of water into a combustor is a proven method for reducing emissions of particulate and nitrogen oxide emissions beyond what can be achieved by reducing firing temperature through fuel lean operation. However, the added complexity and cost associated with a standalone water injection circuit makes this method less desirable. A method for reducing the complexity of water injection is to premix the fuel with water as an emulsion and injecting this mixture through the existing liquid fuel circuit. In the present study, the gaseous fuel injectors of a commercial micro gas turbine generator were modified to operate on both water-in-oil emulsions and gas fuel. These injectors were installed in an otherwise unmodified engine. The original air-blast injector was modified by adding a central fuel tube and blocking the original gas fuel passages. Dual-fuel operation was achieved by injecting gaseous fuel through the annular passage surrounding the liquid fuel tube. This gas fuel passageway is used for both gas fuel delivery and for introduction of air that is used to assist in the liquid fuel atomization. The atomization behavior of these injectors has been characterized using laser diffraction and high speed video for water mass fractions of between zero and 0.5, and air-to-liquid ratios between zero and one. Additionally, pollutant emissions were measured from an engine equipped with these modified injectors and operated over the same range of water mass fraction and air-to-liquid ratio. The results confirmed viability of the modified injectors for introducing water in form of an emulsion. It was also observed that, while atomization performance was altered in a minor way, the complex interaction between evaporation and subsequent mixing resulted in non-monotonic impact on NOx emissions.
Numerical Investigation of Coolant-to-Mainstream Scaling Parameters With Film Cooling on Pressure and Suction Side of a Gas Turbine Blade
Authors: Zeng Lingyu , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2017

Most experiments of blade film cooling are conducted with density ratio lower than that of turbine conditions. In order to accurately model the performance of film cooling under a high density ratio, choosing an appropriate coolant to mainstream scaling parameter is necessary. The effect of density ratio on film cooling effectiveness on the surface of a gas turbine twisted blade is investigated from a numerical point of view. One row of film holes are arranged in the pressure side and two rows in the suction side. All the film holes are cylindrical holes with a pitch to diameter ratio P/d = 8.4. The inclined angle is 30°on the pressure side and 34° on the suction side. The steady solutions are obtained by solving Reynolds-Averaged-Navier-Stokes equations with a finite volume method. The SST turbulence model coupled with γ-θ transition model is applied for the present simulations. A film cooling experiment of a turbine vane was done to validate the turbulence model. Four different density ratios (DR) from 0.97 to 2.5 are studied. To independently vary the blowing ratio (M), momentum flux ratio (I) and velocity ratio (VR) of the coolant to the mainstream, seven conditions (M varying from 0.25 to 1.6 on the pressure side and from 0.25 to 1.4 on the suction side) are simulated for each density ratio. The results indicate that the adiabatic effectiveness increases with the increase of density ratio for a certain blowing ratio or a certain momentum flux ratio. Both on the pressure side and suction side, none of the three parameters listed above can serve as a scaling parameter independent of density ratio in the full range. The velocity ratio provides a relative better collapse of the adiabatic effectiveness than M and I for larger VRs. A new parameter describing the performance of film cooling is introduced. The new parameter is found to be scaled with VR for nearly the whole range.
Study of Constraint Issues in Elasto-Plastic Fracture Analysis Using Experimental and Finite Element Simulation
Authors: Kittur Md Ibrahim , Kodancha Krishnaraja G. , Rajashekar C. R.
Published: August 2017

In this investigation, the variation of J-integral considering Compact Tension (CT) specimen geometry varying a/W and σ using 2D and 3D elasto-plastic Finite Element (FE) analysis have been studied. Further, the investigation has been done to examine the relationship between the J and δ for varied a/W and σ. The plane stress and plane strain elasto-plastic FE analyses have been conducted on the CT specimen with a/W = 0.45–0.65 to extract the J and Crack-tip Opening Displacement (CTOD) values for mild steel. The comparative study of the variation of dn with a/W of mild steel with earlier results of IF steel is carried out. The study clearly infers the effect of yield stress on the variation of the magnitude of dn with reference to a/W ratio. The present analysis infers that while converting the magnitude of the CTOD to J one needs to carefully evaluate the value of dn depending on the material rather than considering it to be unity. Further, the study was extended to experimental and 3D FEA wherein J-integral and CTOD were estimated using the CT specimen. Experimental results reveal that the crack length, the specimen thickness, and the loading configuration have an effect on the fracture toughness measurements. The error analysis between the results obtained by 3D FEA and experimentation were conducted and found to be within limits.
Blade Incipient Crack Determination for Centrifugal Compressor Based on CWT-Stochastic Resonance Method
Authors: Li Hongkun , He Changbo , Zhou Qiang , Lu Fuan
Published: August 2017

Centrifugal compressor is a piece of key equipment for factories. Among the components of centrifugal compressor, impeller is a pivotal part as it is used to transform kinetic energy to pressure energy. But it usually leads to blade crack or failure as irregular aerodynamic load effect on the blade. Therefore, early crack feature extraction and pattern recognition is important to prevent it from failure. Although time series analysis for monitored signal can be used on feature extraction, incipient weak feature extraction method should be investigated. In this research, pressure pulsation sensors arranged in close vicinity to crack area are used to monitor the blade crack and feature extraction. As there are different kinds of flow interference, the pressure pulsation signal for centrifugal compressor is full of nonlinear characteristics. Therefore, how to obtain the weak information from monitored signal is investigated. Although FFT and envelope analysis have been widely used for rotating equipment, they are not suitable for the determination of incipient crack of a blade as the signal modulation and noise interference. In this research, stochastic resonance is used for the pressure pulsation signal. The results show that it is an effective tool to blade incipient crack classification on centrifugal compressor.
Installed Performance Assessment of an Array of Distributed Propulsors Ingesting Boundary Layer Flow
Authors: Goldberg Chana , Nalianda Devaiah , Pilidis Pericles
Published: August 2017

Conventional propulsion systems are typically represented as uninstalled system to suit the simple separation between airframe and engine in a podded configuration. However, boundary layer ingesting systems are inherently integrated, and require a different perspective for performance analysis. Simulations of boundary layer ingesting propulsions systems must represent the change in inlet flow characteristic which result from the local flow condition. In addition, a suitable accounting system is required to split the airframe forces from the propulsion system forces. The research assesses the performance of a conceptual vehicle which applies a boundary layer ingesting propulsion system — NASA’s N3-X blended wing body aircraft — as a case study. The performance of the aircraft’s distributed propulsor array is assessed using a performance method which accounts for installation terms resulting from the boundary layer ingesting nature of the system. A ‘thrust split’ option is considered which splits the source of thrust between the aircraft’s main turbojet engines and the distributed propulsor array. An optimum thrust split for a specific fuel consumption at cruise is found to occur for a thrust split value of 93%, for the configuration considered. In comparison, the optimum thrust split with respect to fuel consumption for the design 7500 nmi mission is found to be 91.5%. Aircraft performance estimates suggest the N3-X could achieve a maximum payload range of approximately 13650 nautical miles.
Preliminary Investigation Into the Effects of a Compressor Rim Purge Flow on OGV/Pre-Diffuser and Combustion System Aerodynamics
Authors: Walker A. D. , Koli B. , Beecroft P. A.
Published: August 2017

As aero gas turbine designs strive for ever greater efficiencies the trend is for engine overall pressure ratios to rise. Although this provides greater thermal efficiency it means that cycle temperatures also increase. Traditionally turbines have been the focus of cooling schemes to enable them to survive high temperatures. However, it is envisaged that the compressor delivery air will soon reach temperatures which mean they may require similar cooling strategies to the turbine. One such concept is akin to that of a turbine “rim purge flow” which ensures that hot, mainstream flow does not get ingested into rotor cavities. However, the main gas path in compressors is generally more aerodynamically sensitive than in turbines and introduction of a purge flow may be more penalizing. It is important to understand the impact such a flow may have on the primary gas path flow of a compressor and the downstream combustion system aerodynamics. This paper presents a preliminary investigation into the effects of a purge flow which enters the main gas path immediately upstream of the high pressure compressor outlet guide vane (OGV) row. Initial, simplified, CFD predictions clearly demonstrated the potential of the purge flow to negatively affect the OGV/pre-diffuser and alter the inlet conditions to the combustion system. Consequently, an experimental assessment was carried out using an existing fully annular, isothermal test facility which incorporated a bespoke 1.5 stage axial compressor, engine relevant outlet guide vanes, pre-diffuser and downstream combustor geometry. Using CFD to guide the process the test rig was modified to allow a metered airflow to be introduced upstream of the outlet guide vanes. Importantly the flow was directed up the face of the rotor such that it picked up a representative swirl component prior to injection into the main gas path. The experimental data confirmed the CFD results and importantly demonstrated that the degradation in the combustor inlet flow resulted in an increased combustion system loss. At the proposed purge flow rate, equal to ∼1% of the mainstream flow, these effects were small with the system loss increasing by ∼4%. However, at higher purge flow rates (up to 3%) these effects became notable and the OGV/pre-diffuser flow degraded significantly with a resultant increase in the combustion system loss of ∼13%.
Investigation on the Shock Control Using Grooved Surface in a Linear Turbine Nozzle
Authors: Lei Xinguo , Qi Mingxu , Sun Harold , Hu Leon
Published: August 2017

Radial flow Variable Nozzle Turbine (VNT) enables better matching between a turbocharger and engine, and can improve the engine performance as well as decrease the engine emissions, especially when the engine works at low-end operation points. With increased nozzle loading, stronger shock wave and clearance leakage flow may be generated. The shock wave consequently introduces strong rotor-stator interaction between turbine nozzle and impeller, which is also a key concern of impeller high cycle fatigue failure. With the purpose of developing a shock wave free or low shock wave intensity turbine nozzle, the influence of grooved vane on the shock wave characteristics is investigated in present paper. A Schlieren visualization experiment was first carried out on a linear turbine nozzle with smooth surface and the behavior of the shock wave was studied. Numerical simulations were also performed on the turbine nozzle. The predicted shock wave shape, position and intensity were compared against the Schlieren images. Guided by the visualization and numerical simulation, grooves were designed on the nozzle surface where the shock wave was originated and numerical simulations were performed to investigate the influence of grooves on the shock wave characteristics. Results indicate that for a smooth nozzle configuration, the intensity of the shock wave increases as the expansion ratios increase, while the onset position is shifted downstream to the nozzle trailing edge. For a nozzle configuration with grooved vane, the position of the shock wave onset is shifted upstream compared to the one with a smooth surface configuration, and the intensity of the shock wave as well as the static pressure distortion at the nozzle vane exit plane are significantly depressed.
Double Nodal Diameter Spectrum Method and its Application in Quantification of Vibration Localization of Impellers With Splitter Blades
Authors: Liu Kaicheng , Wang Jianjun
Published: August 2017

Double nodal diameter spectrum (DNDS) method which is used to analyze nodal diameter (ND) components of the vibration modes of impellers with splitters is proposed and its application in quantification of mode localization has been studied. Firstly, ND characteristics of the typical impeller with splitter blades are analyzed by mode shapes and representative subeigenvectors. Secondly, DNDS method is proposed and DNDSs of the representative modes indicate that the tuned modes of impellers with splitter blades contain two ND components. By applying the simplified engine order (EO) excitation in the form of a travelling wave, harmonic response analysis has been carried out by which double nodal diameter vibration characteristics of the structure and the effectiveness of the DNDS method are both validated. Lastly, in terms of quantifying mode localization, the definition of mode localization factor (MLF) is improved based on DNDS. The numerical example proves that the pairing process of choosing the tuned mode corresponding to the mistuned one by utilizing both DNDS and the vibration pattern of blades when calculating the improved MLF could pick out the closest tuned mode to the mistuned one, which has a more explicit physical meaning.
Development and Experimental Validation of a Low Order Turbine Model Under Highly Pulsating Flow
Authors: Hohenberg Karl G. , Newton Peter J. , Martinez-Botas Ricardo F. , Halamek Martin , Maeda Kotaro , Bouilly Julien
Published: August 2017

The flow through radial turbines in automotive turbocharging applications is inherently highly unsteady, exhibiting high amplitude pulsations of varying frequencies. This can have a significant effect on the performance of the turbine, and therefore accurate modelling of these effects is key in good engine design, particularly in the realm of 1-D modelling. Assuming that the turbine stage acts in a quasi-steady manner can result in modelling errors. To better capture the physical effects of unsteady flow, a novel 1-D model of a radial turbine volute was developed, within the engine modelling software GT-Power. A meanline model was developed and integrated into the volute model as a means of modelling the rotor, which was assumed to be quasi steady. Experimental work was done to characterise the unsteady performance of the turbine, and the results were used to validate the model. The model showed good agreement with experimental data as well as some small improvements compared to industry standard methods of modelling.
Thermodynamic Modeling and Comparative Analysis of Supercritical Carbon Dioxide Brayton Cycle
Authors: Gkountas Apostolos A. , Stamatelos Anastassios M. , Kalfas Anestis I.
Published: August 2017

Supercritical CO2 cycles is a promising technology for the next generation power conversion cycles. Supercritical CO2 Brayton cycles offer equivalent or higher cycle efficiency when compared with steam cycles at similar temperatures. This paper presents an investigation of the sCO2 recompression cycle, where recompressing a fraction of the flow without heat rejection, results in an increase in thermal efficiency. A thermodynamic analysis of a 600 MWth power cycle has been carried out, in order to study the effect of the most significant design parameters on the components performance and cycle efficiency, using two different simulation tools to model the recompression system. An iterative model using basic thermodynamic equations describing the system’s components was employed in this direction. The system was also modeled by means of commercial process modeling software for comparison. Hence, useful results regarding the operating pressures and temperatures of the cycle and how they affect the recuperators, the compressor and the turbine performance have been derived. Finally, a comparative analysis of the results of the two simulation tools and those of a reference cycle from the bibliography is carried out, showing deviations in the range of 2.8 to 4%.
Flow and Heat Transfer Analysis in a Single Row Narrow Impingement Channel: Comparison of PIV, LES, and RANS to Identify RANS Limitations
Authors: Hossain Jahed , Fernandez Erik , Garrett Christian , Kapat Jay
Published: August 2017

The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall cooling schemes have become more practical. In this study, the Reynolds number based on jet diameter was ≃15,000, with the jet plate having fixed jet hole diameters and hole spacing. The height of the channel is 3 times the impingement jet diameter. The channel width is 4 times the jet diameter of the impingement hole. The channel configuration was chosen such that the crossflow air is drawn out in the streamwise direction (maximum crossflow configuration). The impinging jets and the wall jets play a substantial role in removing heat in this kind of configuration. Hence, it is important to understand the evolution of flow and heat transfer in a channel of this configuration. The dynamics of flow and heat transfer in a single row narrow impingement channel are experimentally and numerically investigated. Particle Image Velocimetry (PIV) was used to reveal the detailed information of flow phenomena. The detailed PIV experiment was performed on this kind of impingement channel to satisfy the need for experimental data for this kind of impingement configuration, in order to validate turbulence models. PIV measurements were taken at a plane normal to the target wall along the jet centerline. The mean velocity field and turbulent statistics generated from the mean flow field were analyzed. The experimental data from the PIV reveals that flow is highly anisotropic in a narrow impingement channel. To support experimental data, wall-modeled Large Eddy Simulation (LES), and Reynolds Averaged Navier-Stokes (RANS) simulations (SST k-ω, v2–f, and Reynolds Stress Model (RSM)) were performed in the same channel geometry. The Wall-Adapting Local Eddy-viscosity SGS mdoel (WALE) [1] is used for the LES calculation. Mean velocities calculated from the RANS and LES were compared with the PIV data. Turbulent kinetic energy budgets were calculated from the experiment, and were compared with the LES and RSM model, highlighting the major shortcomings of RANS models to predict correct heat transfer behavior for the impingement problem. Temperature Sensitive Paint (TSP) was also used to experimentally obtain a local heat transfer distribution at the target and the side walls. An attempt was made to connect the complex aerodynamic flow behavior with results obtained from heat transfer, indicating heat transfer is a manifestation of flow phenomena. The accuracy of LES in predicting the mean flow field, turbulent statistics, and heat transfer is shown in the current work as it is validated against the experimental data through PIV and TSP.
Pulsation-Amplitude-Dependent Flame Dynamics of High-Frequency Thermoacoustic Oscillations in Lean-Premixed Gas Turbine Combustors
Authors: Berger Frederik M. , Hummel Tobias , Schuermans Bruno , Sattelmayer Thomas
Published: August 2017

This paper presents the experimental investigation of pulsation-amplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different levels of pulsation amplitudes is assessed and interpreted. Spatial dynamics of the flame are measured by imaging the OH* chemiluminescence signal synchronously to the dynamic pressure at the combustor’s face plate. First, linear thermoacoustic stability states, modal dynamics, as well as flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character in the direction of the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all levels of the oscillation amplitude. Second, distributed flame dynamics are investigated by means of visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of the respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a non-compact flame-describing function. While results show a nonlinear contribution for the individual growth rates, the superposition of flame deformation and displacements balances out to a constant flame driving. This latter observation contradicts the state-of-the-art perception of root-causes for limit-cycle oscillations in thermoacoustic gas turbine systems, for which the heat release saturates with increasing amplitudes. Consequently, the systematic observations and analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.
Dry Air Cooling and the sCO2 Brayton Cycle
Authors: Sienicki James J. , Moisseytsev Anton , Lv Qiuping
Published: August 2017

Commercially available and cost effective finned tube air coolers are an enabling technology that makes practical dry air cooling for the supercritical carbon dioxide (sCO2) Brayton cycle by which heat is directly rejected from CO2 to the air atmospheric heat sink. With dry air cooling, sCO2 Brayton cycle conditions need to be re-optimized to increase the main compressor inlet temperature and pressure (e.g., 35 °C and 8.2 MPa) relative to water cooling to limit the air cooler size to a practical value, and to increase the compressor outlet pressure (e.g., 25 MPa) to maintain a high efficiency. With reoptimization, the plant efficiency for the AFR-100 Sodium-Cooled Fast Reactor Nuclear Power Plant (NPP) is similar to that with once-through water cooling, while the NPP capital cost per unit output electrical power ($/kWe) is roughly estimated to be only 2 % greater. For the AFR-100 application, no unique benefit is identified for the sCO2 Brayton cycle relative to the superheated steam cycle with respect to the capability to use dry air cooling.
A Physically Based Model for High Temperature Deformation of Inconel 718Plus™
Authors: Ozturk Utkudeniz , Cabrera Jose Maria , Calvo Jessica
Published: August 2017

The microstructural evolution of Inconel 718Plus during hot forming operations is modeled through a physically based model which includes the effects of precipitating particles.

Inconel 718Plus has been a successful alloy since its introduction in 2003 owing to its moderate cost, good formability and weldability, and its higher maximum service temperature compared to its ancestor, Inconel 718.

It is well known that the service performance and hot-flow characteristics of this alloy are strongly dependent on the microstructure, particularly the grain size. Thus, comprehension of the microstructural evolution and its modeling is an important task.

In precipitation hardening superalloys and microalloyed steels, it is particularly more challenging to model the microstructural evolution in the processing windows where material softening and precipitation processes take place concurrently. The model presented in this work is based on dislocation density evolution which is considered as a result of the competition between dislocation generation and dynamic recovery at the early stages of deformation.

In the hardening region, recovery through climb is described by the diffusion of vacancies and glide is assumed to be proportional to the strain rate in accordance with the models proposed by Bergstrom. Since the deformation is assumed to be controlled by glide and climb, the peak stress is modeled based on a modified hyperbolic-sine model which takes into account the temperature dependence of self-diffusion of Nickel and elastic modulus.

It is known that under high temperature deformation conditions Inconel 718Plus may undergo dynamic precipitation. Second-phase particles in the material may impede the grain boundary motion and contribute to an increase in flow-stress due to Orowan looping. To account for the dynamic precipitation, the present model combines previously obtained experimental results and precipitation models to predict volume fraction and particle radius. For the peak stress modeling, the effect of precipitation is expressed as an extra stress term.

The flow stress is calculated for the deformed and the recrystallized material separately and the total flow stress for the material is calculated using a law of mixtures considering the fraction of recrystallized material, while recrystallization is described as a nucleation-growth process via Avrami formalism.

Cylindrical compression tests were employed to observe the hot flow behavior and validate the model. The predictions are compared with the experimental findings and good agreement is observed.
Health Estimation of Gas Turbine: A Symbolic Linearization Model Approach
Authors: Yang Qingcai , Cao Yunpeng , Yu Fang , Du Jianwei , Li Shuying
Published: August 2017

This paper is mainly concerned with the health estimation of a gas turbine using a symbolic linearization model approach. Health parameters will change with the degradation of gas turbine performance. Monitoring and evaluating these health parameters can assist in the development of predictive control techniques and maintenance schedules. Currently, various health parameter estimation methods have been studied extensively, but there have been less related studies on how to obtain statespace models. In this paper, a symbolic linearization model method is presented to overcome the shortcoming of high time consumption suffered by existing methods. In this method, each component model of the dynamic nonlinear gas turbine model is decomposed into several sub-modules, each of which contains a simple nonlinear equation. By means of symbolic computation, a linear model of the components is derived by linearizing these sub-modules, and then the generalized linear state-space model of the gas turbine is derived from the relationship among the components. In the generalized linear state-space model, the Jacobian matrices are functions of the parameters under a steady-state operating condition. Therefore, it is easy to obtain a linear model that represents the dynamics of the gas turbine under a given operating condition. To estimate the health parameters of a gas turbine, a piecewise linear model is developed using the proposed approach, and this model is verified in a simulation environment. The results show that the developed piecewise linear model can capture the behavior of a gas turbine quite closely. Then, a linearized Kalman filter is designed for estimating the health parameters under steady-state and transient conditions. The results show that the generalized linear model established using the presented method can be used to accurately estimate the health parameters of a gas turbine.
Effect of Pilot Flame on Flame Macrostructure and Combustion Instability
Authors: Li Jihang , Peluso Stephen , Quay Bryan , Santavicca Domenic , Blust James , Srinivasan Ram
Published: August 2017

The effect of a pilot flame on the dynamic stability characteristics of a single-nozzle lean-premixed swirl combustor operating on natural gas fuel is investigated. Experiments are performed at a fixed inlet temperature and inlet velocity over a broad range of overall fuel-lean equivalence ratios with varied amounts of pilot fuel. The stability results are presented in the form of a dynamic stability map which is a three-dimensional graph of the normalized rms pressure fluctuation versus the overall equivalence ratio and percent pilot. The dynamic stability map identifies boundaries between stable and unstable combustion and results are presented characterizing the transition across one of these boundaries. Time-averaged two-dimensional chemiluminescence images of the stable flame and phase-averaged two-dimensional chemiluminescence images of the unstable flame are used to gain an understanding of the effect of the pilot on dynamic stability through changes in flame structure.
Design of Fault Detection System for a Heavy Duty Gas Turbine With State Observer and Tracking Filter
Authors: Liu Yongwen
Published: August 2017

There exist many approaches for gas turbine engine condition monitoring and fault diagnosis. Among them, gas path analysis depends on the relations between deviations of performance parameters and deviations of measurements, such as pressure, temperature, at some positions in the flow path. A dynamic tracking filter combined with a nonlinear gas turbine model can be used to implement a fault detection system. The dynamic tracking filter is composed with multiple feedback loops in which the residuals between model output and measurement are driven to zero by adjusting the performance parameters. In many cases, the number of measurement parameters is less than that of performance parameters, which impose a limit on the application of tracking filter in practical situations. In the present study, the tracking filter is retrofitted to be driven by the error between state of the model and the estimated state reconstructed from the engine measurement. For the time being, only linear time-invariant (LTI) state observer is considered. A nonlinear simulation model of the heavy-duty gas turbine under study is used to derive the linear system model needed for the design of LTI state observer. Input vector and output vector are chosen according to the practical situations. The linear system model obtained around the nominal operating point is observable, so a state observer can be designed. With 6 state variables observable from the engine, 6 performance parameters can be tracked with the proper design of tracking filter. The structure of the tracking filter consists of a static decoupling matrix DM and in series with 6 PI controllers.

Deviations of performance parameters are implanted into the gas turbine model by scaling the performance maps used; and then simulation results are taken as measurements needed for the tracking filter to run. Tracking results of performance parameters in different cases are given to show the tracking capability for isolated performance deviations and concurrent performance deviations.
High-Loaded Compressor Blisk-Type Impeller Multidisciplinary Optimization
Authors: Buyukli Tatiana , Salnikov Anton , Fedorchenko Yury
Published: August 2017

The current work concerns the approach to the problem of the optimal design of experimental HPC blisk-type impellers. This approach is based on the use of modern optimization methods and a unified parameterized multidisciplinary 3D model, which was specially developed for the problem-solving method, which was formulated. The model included the HPC air-gas channel and the finite-element model of the HPC first stage impeller sector with one blade.

At each optimization iteration a consecutive call to different parts of the unified model takes place and as a result the impeller sector and air-gas channel sector solid models, and the 3D strength and aerodynamic analysis computational grids are modified, and then the necessary characteristics are performed.

This approach allows us to solve the problem of the agreement between the different requirements and the different impeller characteristics (aerodynamic, strength, weight, etc.), because these characteristics are carried out within unified computational space at each optimization iteration. During the process, according to the optimization problem statement, the characteristics of aerodynamics, strength, and weight are taken into account either as criterions or as restrictions.

As an additional restriction, the design and technological requirements are used. The improvement in the structure characteristics is carried out by searching the optimal combination of dimensions using the optimizer IOSO.

The approach described is applied for the improvement of HPC blisk-type first stage impeller characteristics. As an optimization criterion mass minimizing is used, as a restriction — the requirements are the static strength of the blade and disk, the condition of the blade in terms of dangerous resonance detuning, and the requirements for the conservation of stage and HPC pressure ratio, efficiency and flow rate.

As a result of the optimization, when the first four natural resonance frequency detuning of the blade is carried out, the total impeller mass is reduced by approximately 10% and the aerodynamic characteristics remain unchanged. In addition, the disk weight is reduced by about 12%.

At the same time, all the formulated restrictions on aerodynamic and strength characteristics are not broken.

The total optimization process is automated and takes place without user participation.
Aerodynamic Design and Analysis of a Two-Stage High-Load Low-Reaction Transonic Aspirated Counter-Rotating Compressor
Authors: Sun Shijun , Wang Songtao , Chen Shaowen
Published: August 2017

The design and numerical analysis of a two-stage, highly-loaded aspirated counter-rotating compressor is presented in the current paper. Compared with the conventional counter-rotating compressor (CRC), the CRC designed in this study included the stator downstream of each rotor. The stator in the counter-rotating compressor was used for enabling static pressure rise and turning the flow towards the axial direction which would decrease inlet relative velocity and inlet flow angle respectively in the following stage. With the low-reaction design concept in combination with boundary layer suction, the two-stage counter-rotating compressor produced a total pressure ratio of 5.99 at an adiabatic efficiency of 88.15%(η1), 85.35%(η2) by aspiration only implemented on the stators. The primary intent of this unconventional design was to mitigate the complexity of the bleed system design, eliminate the adverse effects of aspiration on the blade strength in the rotating parts and finally improve the structural stability of the compressor under the premise of achieving a high-load design. The tip speed of the two rotors was 370m/s and 377.5m/s, respectively at the design rotational speeds. The design aspiration requirement for the configuration reached 22.25% of the inlet mass flow. Detail design parameters, flow characteristics and aerodynamic performance were presented and discussed. The results show that the low-reaction design methodology based on an increase in rotor exit axial velocity was feasible and the integration between low-reaction design method, aspiration and counter-rotating technology could substantially improve the stage loading coefficient meanwhile a high efficiency could be achieved.
Investigation on the Effect of Surface Wettability on a Two-Phase Flow in a Compressor Cascade
Authors: Neupert Niklas , Harbeck Janneck Christoph , Joos Franz
Published: August 2017

In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Despite the positive thermodynamic effect on the cycle droplets entering the compressor increase the risk of water droplet erosion. Further deposited water leads to a higher sensitivity towards fouling due to an increased stickiness of the blades. Therefore erosion resistant hydrophobic coatings are applied to the first stages of compressors. Although some patents claim the use of such coatings the aerodynamic impact of a different wettability is not regarded so far. This issue was addressed in the field of aerodynamic efficiency of wings in heavy rain showing higher penalty for hydrophobic coatings.

In this study the issue of a different blade surface wettability in a linear transonic compressor cascade is addressed. Different coatings are applied resulting in contact angles of 51–95°. The inflow Mach number was fixed at design inflow Mach number and the inflow angle was varied over a broad range. The effect on the water film pattern is analyzed in terms of position of film breakup, rivulet width and totally wetted surface.

The performance of the cascade under two-phase flow was analyzed using LDA/PDA measurement technique in terms of loss coefficient based on wake momentum thickness and flow turning. It is shown that the wettability of the surface has significant effects on the film structure leading to a lower fraction of wetted surface with increasing contact angle. The influence on performance is limited to effects in the proximity of the surface and is dependent on operation point. While in design conditions hydrophilic coating show lower losses the trend is vice-versa for off-design conditions.

The data represent first experimental work on the influence of surface wettability in a droplet-laden flow supporting positive features for hydrophobic coatings in gas turbine compressors.
On the Importance of Engine-Representative Models for Fan Flutter Predictions
Authors: Stapelfeldt Sina , Vahdati Mehdi
Published: August 2017

This paper examines the factors which can result in discrepancies between rig tests and numerical predictions of the flutter boundary for fan blades. Differences are usually attributed to the deficiency of CFD models for resolving the flow at off-design conditions. This work was initiated as a result of inconsistencies between the flutter prediction of two rig fan blades, called here Fan F1 and Fan F2. The numerical results agreed well with the test data in terms of flutter speed and nodal diameter for both fans. However, they predicted a significantly higher flutter margin for F2 than for Fan F1, while rig tests showed that the two blades had similar flutter margins. A new set of flutter computations for both blades using the whole LP domain (intake, fan, OGV and ESS) was therefore performed. The new set of computations considered the effects of the acoustic liner and mistuning for both blades. The results of this work indicate that the previous discrepancies between CFD and tests were due to:

1. Differences in the effectiveness of the acoustic liner in attenuating the pressure wave created by the blade vibration as a result of differences in flutter frequencies between the two fan blades.

2. Differences in the level of unintentional mistuning of the two fan blades due to manufacturing tolerances.

In the second part of this research, the effects of blade misstaggering and inlet temperature on aerodynamic damping were investigated.

The data presented in this paper clearly show that manufacturing and environmental uncertainties can play an important role in the flutter stability of a fan blade. They demonstrate that aeroelastic similarity is not necessarily achieved if only aerodynamic properties and the traditional aeroelastic parameters, reduced frequency and mass ratio, are maintained. This emphasises the importance of engine-representative models, in addition to an accurate and validated CFD code, for the reliable prediction of the flutter boundary.