bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Adaptive GPA to an Industrial Gas Turbine Using Field Data
Authors: Ramadhan Ericcson , Li Yi-Guang , Maherdianta Deplian
Published: November 2019

The gas turbine inspection activities provided by the manufacturers and user maintenance scheme may be different from each other. To accommodate the difference, performing engine diagnostic as a condition-based monitoring technique is necessary to support Asset Performance Management (APM) adopted by the gas turbine users to improve the scheme.

This paper provides an application of a novel Adaptive Gas Path Analysis (Adaptive GPA) to diagnose performance and health condition of a GE industrial gas turbine MS5001PA operated by PT Pupuk Kaltim (PKT). In the application, an engine thermodynamic model is constructed, adapted, and validated on the actual engine performance based on its gas path measurements. To estimate the health condition from the degraded engine data, two steps are applied in the Adaptive GPA diagnostic process. The first step is the estimation of degraded engine performance status and the second step is the prediction of engine health status at the gas turbine component level. Adaptive GPA results show that satisfactory predictions of the engine degradation have been achieved. In other words, the compressor has been predicted 5.56% degradation in flow capacity and 4.26% degradation in efficiency respectively, which is an indication of compressor fouling. Combining the diagnostic results, manufacturer’s recommendations, and user maintenance strategy, it is relatively safe and allowable to increase the maintenance inspection interval from 12,000 to 16,000 hours. Therefore, the adaptive GPA is proven to be beneficial to support condition-based maintenance decisions.
Transient Regime Simulation From Idle to Maximum Take-Off Flight Conditions of Cooled Cooling Air Heat Exchanger for an Aero Gas Turbine Heat Management
Authors: Mucci Alberto , Kholi Foster Kwame , Ha Man Yeong , Min June Kee , Beecroft Peter A. , Yoon Sang Youl , Yun Won Geun , Sibilli Thierry
Published: November 2019

The quest for improving the thermal efficiency of gas turbines has raised the turbine entry temperatures (TET) and hence the operating pressure ratios (OPR). However, the combination of high TET and high cooling flow temperature makes the cooling of the hot sections more challenging. A cooled cooling air heat exchanger (CCAHX) can be used to cool the high-temperature compressor offtake, showing improved steady aerothermal performance in terms of pressure and temperature. Presented here is the experimental testing of the CCAHX and the process used to generate a highly representative transient simulation of its dynamic performance between idle and Maximum Take-Off (MTO) flight conditions. Said simulation is primarily used to predict the performance during further experiments. Due to the harsh experimental conditions, the simulation guarantees safe operations of the test facility while advising on the right procedures to use during real scale tests. Due to the complex internal structure of the heat exchanger, a one-dimensional computational fluid dynamics (CFD) commercial software was employed to validate the models using results from steady-state data for a single CCAHX unit. Derived procedures from the 1D analysis are used to guide the transient testing at real scale flight conditions, where the core and fan flows are thermally-linked to two CCAHXs in a back-to-back configuration. Results show that the approach considered here can correctly predict the performance of a complex heat exchanger system in transient, fast-changing operations, as calculations in real flight conditions showed good agreement with experimental results of a real scale test.
Identification of Metal Temperature Distribution in Steam Turbine During Start-Up Operation Using Particle Filter and Model Order Reduction
Authors: Ito Hiroshi
Published: November 2019

In steam turbines (STs), evaluation technology of thermal deformations during transient operations is increasingly important, because of a demand for improvement of operability such as shortening startup time. However, it is still difficult to predict temperatures of metal parts with sufficient accuracy due to complexity of heat transfer phenomena.

The present study puts its focus on developing a method to identify metal temperatures of STs during start-up operations using particle filter (PF), a kind of sequential Bayesian filter utilizing ensemble approximation, and model order reduction (MOR) technique.

In this method, a self-organizing state-space model is used to calculate time evaluations of metal temperatures, and heat transfer coefficient (HTC) parameters and steam bulk temperature parameters. And an optimal estimate of these is obtained through iterations of a short-time prediction and a correction of variables using measured temperatures. In this state-space model, state variables including HTC and bulk temperature parameters are treated as random variables, and the time evolution of each variable is modeled as follows;

(1) Metal temperature is modeled using a reduced order model (ROM) in order to reduce computational time of PF. The ROM is constructed from a finite element model for unsteady heat transfer analysis using MOR technique.

(2) HTC is modeled as a random walk model where its changes during one time step is randomly determined using Gaussian noise. Here, the magnitude of this noise is adjusted automatically.

(3) Bulk temperature is modeled using prediction formulas with Gaussian noise added.

As a validation problem, a cold start-up operation of a ST unit of a gas turbine combined cycle (GTCC) is considered. The proposed method is applied to the problem, and boundary conditions (BCs) are identified using measured temperatures at 68 measurement points. Then, the heat transfer analysis based on finite element analysis (FEA) is performed using the identified BCs. As a result of this FEA, it is confirmed that the calculated metal temperature tends to agree better with measurements compared with that of initial FEA, and that the errors of the calculated temperature at measurement points reduce by 41% on average compared with initial FEA. From this result, it is concluded that this proposed method is effective for metal temperature identification during start-up operations.
Investigation of Combustor-Turbine-Interaction in a Rotating Cooled Transonic High-Pressure Turbine Test Rig: Part 1 — Experimental Results
Authors: Krumme Alexander , Buske Clemens , Bachner Johannes R. , Dähnert Jerrit , Tegeler Marc , Ferraro Federica , Gövert Simon , Kocian Frank , di Mare Francesca , Pahs Andreas
Published: November 2019

Within the scope of European Commission FP7 project FACTOR, dedicated to combustor-turbine-interaction research, a clean-sheet design of a rotating turbine test rig featuring a non-reacting combustor simulator was created and built among the partners. German Aerospace Center DLR provided the operational facility NG-Turb to which the rig was adapted and was responsible for global rig integration and operation, also including aerodynamic probe measurements of the flow field.

The rig and experimental set-up is described and post-processed results from probe traverses in several measurement planes are presented and discussed. Special attention is paid to the comparison and influence of two combustor-NGV clocking positions on the periodic turbine flow field, made possible by rig adaptation during the campaign. The strongly distorted and nonuniform turbine inlet flow created by the combustor simulator proved challenging for the probe measurements, but at the same time set a realistic boundary condition enabling the analysis of ‘CTI’ by flow structures migrating through the blade rows.
Advances in High-Speed Linear Design Technology: Novel Approach to Sidewall Geometry Design for Erosion Tests
Authors: Sokolov Maksim , Lorenz Max , Rostamian Mirco , Koch Christian , Weissschuh Matthias , Staudacher Stephan
Published: November 2019

Test rigs for compressor cascade testing reported in literature are characterized by a high level of complexity. This is especially the case if a variable incidence should be allowed for or the flow conditions reach transonic or supersonic flow regimes. Incidence alteration capability is preferable for obtaining a more comprehensive picture of cascade properties. However, it necessitates a complex kinematic set-up in order to rotate the blades and to adjust the sidewall setting such that flow periodicity across the passages is ensured. Additionally, a complex sealing system is usually required to guarantee minimum flow disturbance. Often, a suction system is also introduced for boundary layer control and regulation of flow conditions. In the case of erosion testing the situation is exacerbated as the application of such conventional adjustment devices is ruled out due to the presence of solid particles in the flow. In this work an investigation of a new cascade design for erosion testing with variable incidence was conducted. A fixed sidewall geometry is proposed which ensures periodic flow conditions in the speed range of M = 0.5 up to M = 0.78 while allowing incidence adjustments in the range of i = ±10° as assessed by means of CFD. The novel design paradigm enables such flexibility by virtue of a self-regulating flow induced by flow separation from the fixed sidewall geometry. The latter has the benefit of not requiring a specialized mechanical setup and sealing due to the absence of movable parts in the flow. The calculated results show acceptable periodicity of various flow parameters within the passage at 50 percent blade height for all incidence settings considered. The conducted investigation has demonstrated that specially designed fixed sidewalls may enable sufficiently accurate transonic erosion testing under various incidence angles while making cascade erosion testing more economical and time efficient.
Experimental Investigations of Turbulent Flow in a Rotating Ribbed Channel in Terms of the Effect of Coriolis Force
Authors: You Haoliang , Li Haiwang , You Ruquan , Tao Zhi , Shi Jincheng
Published: November 2019

In the current work, the effect of Coriolis force is considered in a rotating rectangular rib-roughened channel. Time-resolved PIV (Particle Image Velocimetry) was used to measure the flow field. The Reynolds number is fixed at 10000, and the rotation numbers range from 0 to 0.52. The ribs obstruct the channel by 10%. The mean velocity fields and Reynolds shear stress fields are obtained. Due to the effect of Coriolis force, the flow fields are different between leading and trailing side. Furthermore, the vortex and the reattachment are also investigated. Based on the results, it can be inferred that Coriolis force plays a significant effect on the vortices. Coriolis force enlarges the vortex near the leading side, but suppresses the vortex near the trailing side. An interesting phenomenon has been found. Because of the Coriolis force pointing to the trailing side, the main stream is supposed to be pushed to the trailing side. But the results show that a velocity deficit appears near the trailing side. This phenomenon indicates that the Coriolis force is not the only force affecting the flow, but the secondary flow is also an important factor that cannot be ignored in a rotating ribbed channel.
Investigation of a Combined Inverted Brayton and Rankine Cycle
Authors: Kennedy Ian , Duda Tomasz , Liu Zheng , Ceen Bob , Jones Andy , Copeland Colin D.
Published: November 2019

Waste heat recovery is a vitally important technology to address increasingly stringent emissions legislation and environmental concerns over CO2. One such means of recovering thermal energy is the inverted Brayton cycle (IBC). This paper presents an experimental study of a novel combination of the IBC with a Rankine cycle for the first time. The IBC requires cooling of the exhaust gases after expansion. If the gases contain water vapour, as is the case for hydrocarbon combustion, and cold enough coolant is available, the water can be condensed, pressurized and re-boiled for expansion in a Rankine cycle.

The steam produced from the cycle can be utilized in a number of ways. In this study, steam is injected through a series of de Laval nozzles directed into the main turbine to produce additional shaft power in a compact arrangement. To minimize the size of the system, additive manufacturing was used for the heat exchangers, giving high performance per unit volume. The study demonstrates the feasibility of the cycle in producing power from waste heat using humid gas that already is present in most applications.

The experimental results show that the system is able to generate power at very low exhaust temperatures where the standard IBC would cease to operate. With an IBC inlet temperature of 370 °C, approximately 5 kJ/kg of specific shaft work was produced with 5 g/s of steam flow rate. At higher exhaust temperatures, the IBC and the Rankine cycle started to work together to increase the shaft power resulting in much higher specific work. At 620 °C, a specific shaft work of 41 kJ/kg was generated at a steam flow of 9 g/s. For the present turbomachinery sizes, this corresponded to 1933 W of power at 47 g/s of main exhaust flow.

A model of the thermodynamic system was created in order to study the sensitivity of the system to parameters such as the steam expander pressure ratio and efficiency. Higher steam pressure and higher steam expander efficiency both led to greater power generated for the same operating point, particularly at high IBC turbine inlet temperatures. The peak specific work for the range of parameters explored in the paper was 68 kJ/kg with a steam expander efficiency of 70% and exhaust conditions of 600 °C and 50 g/s. The plots produced in this study can be used as a guide for others considering this system to understand the expected power generated under a range of conditions.
Advanced S-CO2 Brayton Power Cycles in Nuclear and Fusion Energy
Authors: Syblik Jan , Vesely Ladislav , Entler Slavomir , Dostal Vaclav , Stepanek Jan
Published: November 2019

Cooling system is one of the most important part of the power plants and cooling systems based on S-CO2 (Supercritical Carbon Dioxide) coolant seems nowadays perspective alternative to Helium and Rankine steam power cycles. Due to many advantages of S-CO2, these cooling systems are researched on many institutions and the results confirm that it should be successful for the future cooling systems design. One of the main objectives is comparison of the possible cooling mediums of DEMO2 (Demonstration power plant 2) with focusing on different power cycles with S-CO2. The First part of this article targets on comparison of three main coolants: steam, helium and S-CO2. The second part of this article focuses on the new software called CCOCS (Cooling Cycles Optimization Computational Software) which was developed on CTU in Prague. This software works on deeper optimization of the power cycles with various coolants and initial conditions. The third part describes advanced S-CO2 power cycles and enlarges past research, which was based on optimization of S-CO2 Brayton Simple power cycle and S-CO2 Re-compression power cycle both with recuperation and their usage in fusion and Fission energy engineering. It is possible to heighten thermodynamic efficiency of power cycle by changing the layout of the power cycle and the main objective of this paper is to compare four advanced layouts, describe the results of the optimization of these cycles and outline advantages and disadvantages of chosen optimized layouts.
Numerical Investigation of Rotation Effects on the Flow and Heat Transfer on the Turbine Blade Tip Underside With Bleed Hole at Different Locations
Authors: Zhao Zhiqi , Luo Lei , Kan Xiaoxu , Qiu Dandan , Zhou Xun
Published: November 2019

High thermal load on the turbine blade tip surface leads to high temperature corrosion and severe structural damage. One common way is to deliver a part of coolant through bleed holes onto the tip portion for cooling purpose. In this study, numerical simulations are performed to investigate the effects of rotation on the internal tip heat transfer in a simplified rotating two-pass channel with a bleed hole, which is applicable to the internal cooling passage of typical gas turbine blade. The bleed hole is placed on the tip wall of a two-pass channel at different locations, i.e. the ratio of distance from the outlet-side wall to width of the tip wall is 0.07, 0.21, 0.5, 0.78, 0.93, respectively. A smooth channel without bleed hole is used as Baseline. The Reynolds number is fixed at 10,000. The Ro numbers are varied from 0 to 0.4. Results show that a three-dimensional vortex, which is induced by the Coriolis force, is found at the bend region. It transports the fluid from the trailing side to leading side, which is beneficial to enhance tip heat transfer. The middle-mounted hole shows a better heat transfer augmentation compared to other hole arrangement. The rotation have a notable effect on the heat transfer and flow structures. Compared to the smooth channel, the heat transfer augmentation is about 34%.
Unsteady Flow Interactions Between a High- and Low-Pressure Turbine: Part 1 — Time-Resolved Flow
Authors: Sterzinger P. Z. , Zerobin S. , Merli F. , Wiesinger L. , Dellacasagrande M. , Peters A. , Maini G. , Heitmeir F. , Göttlich E.
Published: November 2019

This two-part paper presents the unsteady flow interactions between an engine-representative high-pressure turbine (HPT) and low-pressure turbine (LPT) stage, connected by a turbine center frame (TCF) duct with non-turning struts. The setup was tested at the high-speed two-spool test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology and includes relevant purge and turbine rotor tip leakage flows. Due to the complexity of such a test, the unsteady component interactions in an HPT-TCF-LPT module have not received much attention in the past and require additional analysis to determine new approaches for further performance improvements on the system level. The flow downstream of an HPT is highly unsteady and dominated by statorrotor interactions, which affect the flow behavior through the downstream TCF and LPT. To capture the unsteady flow structures, time-resolved aerodynamic measurements were carried out with a fast-response aerodynamic pressure probe (FRAPP) at three different measurement planes. In this first part of the paper, the time-resolved and phase-averaged flow fields with respect to the HPT and LPT trigger are studied. Since the two rotors are uncorrelated, the applied method allows the identification of the flow structures induced by either of them. Upstream of the LPT stage, the HPT flow structures evolving through the TCF duct dominate the flow fields. Downstream of the LPT stage, the flow is affected by both the HPT and the LPT secondary flow structures. The interactions between the various stator rows and the two rotors are detected by means of time-space plots and modal decomposition. To describe the fluctuations induced by both rotors, particularly the rotor-rotor interaction, the Rotor Synchronic Averaging (RSA) is used to analyze the flow field downstream of the LPT. The second part of the paper decomposes the flow fields to gain additional insight into the rotor-rotor interactions using the Proper Orthogonal Decomposition (POD) and RSA methods. The paper highlights the need to account for the HPT-induced unsteady mechanisms in addition to the LPT flow structures and the interaction of both to arrive at improved LPT designs.
Sequential Combustion in Gas Turbines: The Key Technology for Burning High Hydrogen Contents With Low Emissions
Authors: Bothien Mirko R. , Ciani Andrea , Wood John P. , Fruechtel Gerhard
Published: November 2019

Excess energy generation from renewables can be conveniently stored as hydrogen for later use as a gas turbine fuel. Also, the strategy to sequestrate CO2 from natural gas will require gas turbines to run with hydrogen-based fuels. In such scenarios, high temperature low emission combustion of hydrogen is a key requirement for the future gas turbine market. Ansaldo Energia’s gas turbines featuring sequential combustion have an intrinsic advantage when it comes to fuel flexibility and in particular hydrogen-based fuels. The sequential combustion system is composed of two complementary combustion stages in series: one premix stage followed by an auto-ignited second stage overcoming the limits of traditional premix combustion systems through a highly effective extra tuning parameter, i.e. the temperature between the first and the second stage. The standard Constant Pressure Sequential Combustion (CPSC) system as applied in the GT36 engine is tested, at high pressure, demonstrating that a modified operation concept allows stable combustion with no changes in combustor hardware for the whole range of natural gas and hydrogen blends. It is shown that in the range from 0% to 70% (vol.) hydrogen, stable combustion is achieved at full nominal exit temperature, i.e. without any derating and thus clearly outperforming other available conventional premixed combustors. Operation between 70% and 100% is possible as well and only requires a mild reduction of the combustor exit temperature. By proving the transferability of the single-can high pressure results to the engine, this paper demonstrates the practicality of operating the Ansaldo Energia GT36 H-Class gas turbine on fuels containing unprecedented concentrations of hydrogen while maintaining excellent performance and low emissions both in terms of NOx and CO2.
Kinetics Modeling on NOx Emissions of a Syngas Turbine Combustor Using RQL Combustion Method
Authors: Liu Haoyang , Qian Wenkai , Zhu Min , Li Suhui
Published: November 2019

To avoid flashback issues of the high-H2 syngas fuel, current syngas turbines usually use non-premixed combustors, which have high NOx emissions. A promising solution to this dilemma is RQL (rich-burn, quick-mix, lean-burn) combustion, which not only reduces NOx emissions, but also mitigates flashback. This paper presents a kinetics modeling study on NOx emissions of a syngas-fueled gas turbine combustor using RQL architecture. The combustor was simulated with a chemical reactor network model in CHEMKIN-PRO software. The combustion and NOx formation reactions were modeled using a detailed kinetics mechanism that was developed for syngas. Impacts of combustor design/operating parameters on NOx emissions were systematically investigated, including combustor outlet temperature, rich/lean air flow split and residence time split. The mixing effects in both the rich-burn zone and the quick-mix zone were also investigated. Results show that for an RQL combustor, the NOx emissions initially decrease and then increase with combustor outlet temperature. The leading parameters for NOx control are temperature-dependent. At typical modern gas turbine combustor operating temperatures (e.g., < 1890 K), the air flow split is the most effective parameter for NOx control, followed by the mixing at the rich-burn zone. However, as the combustor outlet temperature increases, the impacts of air flow split and mixing in the rich-burn zone on NOx reduction become less pronounced, whereas both the residence time split and the mixing in the quick-mix zone become important.
Comparison of Electron-Beam Physical Vapor Deposition and Plasma-Spray Physical Vapor Deposition Thermal Barrier Coating Properties Using Synchrotron X-Ray Diffraction
Authors: Northam Matthew , Rossmann Lin , Sarley Brooke , Harder Bryan , Park Jun-Sang , Kenesei Peter , Almer Jonathan , Viswanathan Vaishak , Raghavan Seetha
Published: November 2019

Electron-beam physical vapor deposition (EB-PVD) is widely used for the application of thermal barrier coatings (TBCs) to turbine blades in jet engines. An emerging method, plasma-spray physical vapor deposition (PS-PVD), is a hybrid technique whereby coatings can be applied via the liquid phase to form lamellar microstructures or via the vapor to form columnar microstructures similar to that of EB-PVD. In this study, PS-PVD and conventional EB-PVD coated samples of a columnar configuration were prepared and thermally cycled to 300 and 600 cycles. These samples were subsequently characterized in-situ, under thermal load using synchrotron x-rays. From the high-resolution x-ray diffraction (XRD) patterns, the residual and in-situ strain in the TGO layer was obtained during a thermal cycle. At high temperature, the TGO layer for both deposition methods displayed a constant near zero-strain for all samples as anticipated. In the samples with 300 thermal cycles, both deposition methods showed similar strain profiles in the TGO layer. For samples with 600 cycles, PS-PVD samples showed a more significant strain relief in the TGO at room temperature compared to similarly cycled EB-PVD samples. This could explain the coating lifetime performance between the two deposition methods. The findings support ongoing efforts to tune the manufacturing of PS-PVD coatings towards the goal of meeting or exceeding the performance of currently used coatings on jet engines. This will pave the way for more affordable high temperature coating alternatives that meet durability needs.
Research on the Effects of Dimples and Protrusions on Flow and Heat Transfer in Matrix Cooling Channels in Turbine Blades
Authors: Luan Yigang , Yang Lianfeng , Yin Yue , Zunino Pietro
Published: November 2019

Nowadays, gas turbine engines play an indispensable role in modern industry, which have been widely used especially in the aviation, marine and energy fields. The turbine inlet temperature is one of the most important factors that influences the performance of the turbine engine. It’s acknowledged that the higher turbine inlet temperature contributes to the overall gas turbine engine efficiency. Therefore, the internal cooling technology of turbine blades is of vital importance. This paper mainly studies the effects of dimples and protrusions on flow and heat transfer in matrix cooling channels and optimize the performance of the matrix cooling structure by numerical simulation and experiment methods. Thirteen cases have been calculated under Re = 10,000∼80,000 by the commercial code ANSYS Fluent. Structures with different layouts of dimples and protrusions were considered, such as the number, distance and the depth ratio. The original model has been strengthened due to the dimple and protrusion structure, which improves heat transfer performance as well as the thermal performance factor (TPF) on condition that the pressure loss increases slightly. Meanwhile, the optimized structures have been made and tested by the transient liquid crystal technique (TLC). A comparison between the CFD results and the experimental data is made. Note that the heat transfer performance is much better when the ratio of the dimple depth and the dimple diameter is equal to 0.3, compared with the ratio of 0.1 and 0.2. In terms of the cases with two sides dimples, the heat transfer can be enhanced by increasing the number of the dimples. In addition, the heat transfer performance is the best when both of dimples and protrusions are applied. Nu/Nu0 and TPF increase by up to approximately 7% and 5% respectively.
Solution of Thermoacoustic Eigenvalue Problems With a Non-Iterative Method
Authors: Buschmann Philip E. , Mensah Georg A. , Nicoud Franck , Moeck Jonas P.
Published: November 2019

Gas turbine combustors are prone to undesirable combustion dynamics in the form of thermoacoustic oscillations. Analysis of the stability of thermoacoustic systems in the frequency domain leads to nonlinear eigenvalue problems; here, ‘nonlinear’ refers to the fact that the eigenvalue, the complex oscillation frequency, appears in a nonlinear fashion. In this paper, we employ a non-iterative strategy based on contour integration in the complex eigenvalue plane, which returns all eigenvalues inside the contour. An introduction to the technique is given, and is complemented with guidelines for the specific application to thermoacoustic problems. Two prototypical nonlinear eigenvalue problems are considered: a network model of the classical Rijke tube with an analytic flame response model and a finite element discretization of an annular model combustor with an experimental flame transfer function. Computation of all eigenvalues in a domain of interest is vital to assess stability of these systems. We demonstrate that this is generally challenging for iterative strategies. An eigenvalue solver based on contour integration, in contrast, provides a reliable, non-iterative method to achieve this goal.
Large Eddy Simulation of Lean Blow-Off in a Premixed Swirl Stabilized Flame
Authors: Nassini Pier Carlo , Pampaloni Daniele , Andreini Antonio , Meloni Roberto
Published: November 2019

Modern gas turbines usually adopt very lean premixed flames to meet the current strict law restrictions on nitric oxides emissions. In such devices, strong combustion instabilities and blow-off susceptibility often prevent from achieving a stable flame in leaner conditions. Numerical models to predict the lean blow-off in turbulent flames are essential to prevent such instabilities, but the simulation of blow-off still represents a challenge, requiring the appropriate modelling for the turbulence-chemistry interactions and the highly transient behaviour of the flame near the extinction limit.

The present work explores the capabilities of the widely-used Flamelet Generated Manifold model in predicting the lean blow-off of a turbulent swirl-stabilized premixed flame within LES framework. An atmospheric premixed methane-air flame, experimentally studied at the University of Cambridge, is firstly analyzed in three operating conditions approaching blow-off to validate the numerical setup. An extended Turbulent Flame Closure (TFC) model, implemented within the FGM framework in Fluent to introduce the effect of stretch and heat loss on the flame, reproduces the evolution of the key flame characteristics. Then, the chosen setup is used to study the blow-off inception and the dynamics in two conditions with different flow rate. An accelerated numerical procedure with progressive step reductions of equivalence ratio is used to trigger the blow-off. The extinction equivalence ratio is predicted quite accurately, showing that the Extended TFC is suitable for the study of the blow-off, without an increase in computational cost. The validity of the model could be extended, allowing the study of lean blow-off in realistic conditions and complex flames of gas turbine combustors.
Impact of Exit Duct Dynamic Response on Compressor Stability
Authors: Zhang Wenqiang , Vahdati Mehdi , Zhao Fanzhou
Published: November 2019

Abrupt distortions can appear as a result of transient crosswind or during rapid aircraft maneuvers. Such distortions are known to reduce the aerodynamic stability of engines and therefore present a major concern to all aero-engine manufacturers. To assess the aerodynamic stability of fan blades due to distortions, rig tests are usually carried out to establish the loss in stall margin. In such test campaigns, an exit duct (which is followed by a nozzle) is placed downstream of the fan blade and the operating condition of the fan is controlled by this nozzle. It is shown in this paper that in such rig tests the length of duct downstream of a fan has a significant impact on fan stall margin. The key contributor for such interaction is the dynamic response of the exit duct and the aerodynamic stability of the fan is affected by the acoustic reflection from the exit nozzle. To study the underlying physics, transient response in the exit duct downstream of a transonic fan stage was studied numerically using a simplified model. Simulation results, along with calculations based on analytical theories, confirmed the generation, propagation and reflection of waves induced by the inlet distortion. A quantitative relationship concerning the lengths of the compression system is introduced which determines whether a duct setup would have beneficial or detrimental influences on compressor aerodynamic stability. The findings of this research have great implications for the stability assessment of fans as the stability margin can be affected by the waves generated in bypass ducts.
Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers
Authors: Ertas Bugra
Published: November 2019

The following paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the initial concepts using modular hermetic squeeze film dampers presented in past research, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design developed to reduce space envelope, cost, and improved overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Non-rotating bearing support test results show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid-structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase; ultimately effecting dynamic cavity pressures and force coefficients.
An Investigation of Combustion Properties of a Gasoline Primary Reference Fuel Surrogate Blended With Butanol
Authors: Richter Sandra , Braun-Unkhoff Marina , Herzler Jürgen , Methling Torsten , Naumann Clemens , Riedel Uwe
Published: November 2019

Currently, many research studies are exploring opportunities for the use of novel fuels and of their blends with conventional, i.e. petroleum-based fuels. To pave the way for their acceptance and implementation in the existing energy market, a comprehensive knowledge about their combustion properties is inevitable, among others. Within this context, alcohols, with butanol in particular, are considered as attractive candidates for the needed de-fossilization of the energy sector.

In this work, we report on the oxidation of mixtures of n-heptane/i-octane (PRF90, primary reference fuel, a gasoline surrogate) and addition of n-butanol, 20% and 40%, respectively, in a combined experimental and modeling effort. The focus was set on two fundamental combustion properties: (i) Ignition delay times measured in a shock tube, at ambient and elevated pressures, for stoichiometric mixtures, and (ii) Laminar burning velocities, at ambient and elevated pressures. Moreover, two detailed chemical kinetic reaction mechanisms, with an in-house model among them, have been used for investigating and analyzing the combustion of these mixtures.

In general, the experimental data agree well with the model predictions of the in-house reaction model, for the temperatures, pressures, and fuel-air ratios studied. Room for improvements is seen for PRF90. The results achieved were also compared to those of n-butanol reported recently; the findings demonstrated clearly the effect of the n-butanol sub model on binary fuel-air mixtures consisting of PRF and n-butanol. From the present work it can be concluded that the addition of n-butanol to gasoline appears to be an attractive alternative fuel for most types of heat engines.
Effects of Velocity Ratio on Trends in Film-Cooling Adiabatic Effectiveness and Turbulence
Authors: Stratton Zachary T. , Shih Tom I.-P.
Published: November 2019

For film-cooling of a flat plate with cooling jets issuing from round holes, turbulent mixing has been shown to scale with the velocity ratio (VR). In this paper, large-eddy simulations (LES) were performed to investigate the effect of varying blowing ratio (BR = 0.5 – 1.3), density ratio (DR = 1.1 – 2.1), and momentum-flux ratio (MR = 0.2–0.8) on adiabatic effectiveness and turbulence, while keeping the VR fixed at 0.46 and 0.63. Simulations based on Reynolds-Averaged Navier-Stokes (RANS) equations with the realizable k-ϵ and shear-stress transport k-ω models were also performed. The LES results show that separation and spreading of the film-cooling jet increase as BR, DR, and MR increase while VR remains constant. For a given VR, the LES predicts an absolute difference between the minimum adiabatic effectiveness of the lowest and highest MRs to be 2 to 5 times greater than those predicted by RANS. This is because RANS with either model cannot respond appropriately to changes in MR. However, RANS can correctly predict that adiabatic effectiveness decreases as VR increases. The LES results show the turbulent kinetic energy and Reynolds stresses near the film-cooling hole to change considerably with MRs at a constant VR, while turbulent heat flux changes negligibly. This suggests that while improved turbulence models for heat flux can improve RANS prediction of spreading, capturing trends, however, requires improved modeling of the Reynolds stresses.
An Assessment of the Implicit Non-Iterative PISO Solution Procedure for the Prediction of Combustor Performance
Authors: Karalus Megan , Krishnamoorthy Niveditha , Reynolds Bob , Mallouppas George
Published: November 2019

Large Eddy Simulation (LES) of gas turbine combustors has gained traction as a key tool in the design process. Accurate prediction of the multiphysics of reacting flows — evaporating fuel spray, turbulent mixing, turbulent chemistry interaction, radiation, and conjugate heat transfer to name a few — is key to the accurate prediction of combustor performance. The overall solution time for a standard LES simulation on an industrial system can be burdensome because of the small time and length scales required to capture the aforementioned multiphysics to an acceptable level. Any performance improvements are therefore welcomed. In this paper, we compare the implicit non-iterative PISO solution procedure with the implicit iterative SIMPLE method for the Large Eddy Simulation of a Honeywell combustor using the commercial software, Simcenter STAR-CCM+ v13.04. Time averaged simulation results are validated against rig data. Results show that the PISO solution method provides results which are similar to those found using the SIMPLE method, and accurate when compared to rig data, but at up to a 3.4X speed-up for this liquid fueled gas turbine combustor.
Flow Induced Dynamics of Plate Seals
Authors: Trivedi Deepak , Kerr Bernardo
Published: November 2019

Plate seals can provide low leakage at rotor-stator interfaces with large pressure drops in turbomachinery within a limited axial span. When designed with a self-correcting hydrostatic feedback mechanism, non-contact operation could be achieved even in the presence of large rotor transients. Flow induced dynamical instability is one of the key design challenges in plate seals for rotor-stator sealing in turbomachinery. The instabilities are caused by potentially multiple flow induced vibration mechanisms operating during different flow regimes. This paper investigates mechanisms of vortex induced flutter in compliant plate seals, which happens when the vortex shedding frequency of the plates comes close to one of the natural frequencies of vibration of the structure. An experimental methodology based on optical flow analysis of high speed videography is proposed to characterize vibrations of the ensemble of plates (“leafpack”.) Experiments show that the compliant plates vibrate in the flow field with amplitude dependent on the pressure drop. Additionally, the vibrations of individual plates are highly coupled to each other, leading to phase-locking or phase-drifting depending on boundary conditions. The leafpack has a characteristic frequency and exhibits traveling wave phenomena under certain conditions of pressurization. Using experimental insights, plate seals are modeled as a ring of a large (∼103) number of locally coupled oscillators, with nonlinear stiffness arising from hydrostatic forces. A two-way coupling exists between the structural and fluid wake dynamics. Using center manifold reduction, the coupled fourth order dynamics of the system is reduced to second order and transform the equations into the normal form for investigating the possibility of mitigating flow induced vibrations through the phenomenon of amplitude death. Conditions under which successful induction of amplitude death could eliminate plate vibration in the mode under consideration is discussed.
Development of Production Eddy Current Inspection Process for Additively Manufactured Industrial Gas Turbine Engine Components
Authors: Kemerling Brandon , Ryan Daniel
Published: November 2019

While metal additive manufacturing (AM) promises substantial efficiency gains to the gas turbine manufacturing sector, uncertainty about the quality of parts produced via AM has been a significant hindrance to widespread implementation. Although high fidelity inspection techniques involving computed tomography (CT) and destructive testing have been effective for low volume development activities, new quality assurance solutions are needed that enable rapid, low-cost inspection of serial production AM components. Solar Turbines Incorporated is actively engaged in the development of inspection processes for high production volume AM part acceptance capability of combustion and turbine hot section components. Eddy current inspection (ECI) was identified as a potential non-destructive evaluation (NDE) solution. Based on the principles of electromagnetism, ECI has been successful on conventional materials for surface and near-surface crack detection. However, limited industry data is available regarding the effectiveness of ECI on AM material. The nature of AM-induced discontinuities, specifically for metal laser powder bed fusion (L-PBF) processing, demands high measurement resolution to detect fine features such as bulk porosity, lack of fusion and interlayer discontinuities. Development activities were thus executed to determine the suitability of ECI for detection of AM discontinuities. NDE training sets were printed with intentional variations in key L-PBF processing parameters to simulate the conditions which produce relevant AM material discontinuities. The training sets were then evaluated with a custom ECI system to determine the inspection capability and sensitivity. Inspections were conducted as a function of multiple input frequencies to determine the optimal tradeoff between measurement resolution and depth of penetration. Additional characterization of the training sets was conducted via metallographic analysis to establish correlations between the ECI results and AM material quality. An optimized multi-frequency inspection setting was identified to provide suitable measurement resolution for near surface AM material inspection. Correlations developed between ECI scan data and materials characterization results have enabled the ability to rapidly discriminate between varying discontinuity levels in AM components. Based on these efforts, ECI is considered a suitable inspection technique for materials produced via the L-PBF AM process.
Supercritical CO2 Tests for Hydrostatic Film Stiffness in Film-Riding Seals
Authors: Trivedi Deepak , Bidkar Rahul A. , Wolfe Christopher E. , Mortzheim Jason
Published: November 2019

Fluid film stiffness is a key design parameter for film-riding seals — a large positive film stiffness ensures stable seal operation with the seal faithfully tracking the rotor in the presence of varying inertial and friction loads. A hydrostatic supercritical CO2 (sCO2) film-riding seal relies on feed ports pressurized with sCO2 to generate film stiffness needed for reliable seal operation. The high-pressure supercritical CO2 expands to lower pressures through the seal bearing face, and during this expansion, undergoes large temperature changes along with a phase change to gaseous state and possibly liquid state. These large temperature changes and phase changes are important design considerations specific to sCO2 as the working fluid. From this perspective, film-stiffness test data with sCO2 as the working fluid is valuable for both understanding the physics as well as for validating the predictions of computational fluid dynamics (CFD) models of sCO2 expansion across a seal bearing face. In prior work, we described a non-rotating stiffness test rig for characterizing fluid film stiffness and presented air-based test data with the rig. In this paper, we present sCO2-based data obtained by connecting this previously described stiffness rig to a newly commissioned sCO2 flow loop (flow rate about 0.1 kg/s, pressures up to 16.5 MPa, temperatures up to 464 K). The test data presented in this paper include seal bearing pressures and fluid/metal temperatures for varying film thickness, seal bearing face tilt and inlet/supply pressures. The test data show significant temperature reduction as the supercritical flow expands across the seal bearing face. The measured bearing pressure was compared with the predictions of a 3D CFD model with real gas CO2 properties, with about 4% error between the measurements and the predictions. The sCO2-based test data in this work and the air-based test data from prior work are used to calculate fluid film stiffness over a range of film thicknesses. It is seen that the sCO2-based data and air-based data tend to collapse on a normalized stiffness curve, which is characteristic of the bearing geometry. Moreover, it is seen that the hydrostatic seal film stiffness generally scales with the supply pressure and can be adjusted to high stiffness values typically expected in hydrodynamic film-riding seals.
Investigation of Mixed Micro-Compressor Casing Treatment Using Non-Matching Mesh Interface
Authors: Patel Purvic , Zha Gecheng
Published: November 2019

In this paper, a non conservative interpolation boundary condition, for the non-matching mesh blocks, was developed and validated for the micro compressor casing treatment. The conservative variables were interpolated in the halo layers of non-matching mesh interface using Finite Element Method (FEM) type linear interpolation shape functions, instead of using overset grids. Using this new boundary condition, the effect of casing treatment on stall margin and compressor performance is investigated for a mixed flow type micro-compressor. The computed compressor performance map for the casing treatment case is compared with the experimental results and shows good agreement except in the region close to stall. With the application of the casing treatment, improvement in the stall margin is observed without the loss of efficiency over the operating range.