bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Upstream Bend on Aerodynamic Performance of a Transonic Centrifugal Compressor
Authors: Yamada Kazutoyo , Furukawa Masato , Arai Hiromitsu , Ito Sasuga
Published: November 2019

This paper describes the influence of a bent inlet pipe installed immediately upstream of a transonic centrifugal compressor on the aerodynamic performance and the stability. In order to clarify the influence of the bent inlet pipe, the internal flow fields in the inlet pipe, the impeller, and the diffuser of the compressor have been numerically investigated by a DES (Detached Eddy Simulation). For the purpose of comparison, the simulation was also conducted for the case of uniform axial inflow using a straight pipe. In order to make clear the influence of non-uniform flow with a bent pipe as far as possible, a 90-degree bent pipe was installed immediately upstream of the compressor, that is 0.86 times the inlet inner diameter.

In the case of installing the bent pipe on the upstream of the compressor, the pressure ratio decreased on the high flow rate side in the compressor performance characteristic, whereas it increased at the low flow rate side. At the low flow rate operating point, there is a reversed flow occurring in the compressor impeller on the shroud side near the blade leading-edge. Installation of the bent pipe promotes mixing between the reversed flow and the main flow at the inlet of the compressor thanks to occurrence of a secondary flow. Since the reversed flow comes out from inside of the impeller, it has a high circumferential velocity. Therefore, the mixing of the reversed flow makes the compressor inlet flow a pre-swirl flow, and thereby the incidence decreases. As a result, leading-edge separation on the blade tip side of the impeller is suppressed, and the flow field inside the impeller is improved. In the diffuser section, when the bent pipe is installed, the circumferential velocity of the impeller exit flow increases on the hub side, whereas the radial velocity decreases. As a result, the diffuser performance is deteriorated and the diffuser stall tends to occur.
Combustion Analysis of Syngas Fuels Applied in a Micro Gas Turbine Combustor With a Rotating Casing
Authors: Ajvad Maaz , Shih Hsin-Yi
Published: November 2019

Combustion characteristics of a can combustor with a rotating casing for an innovative micro gas turbine have been modeled. The effects of syngas compositions and the rotating speed on the combustor performance were investigated. The effects of rotation on the combustion performance have been studied previously with methane as the fuel. This work extended the investigation for future application with syngas blended fuels. Two typical compositions of syngas were used namely: H2-rich (H2:CO=80:20, by volume) and equal molar (H2:CO=50:50). The analyses were performed with a computational model, which consists of three-dimension compressible k-ε realizable turbulent flow model and presumed probability density function for combustion process invoking a laminar flamelet assumption generated by detailed chemical kinetics from GRI 3.0. As syngas is substituted for methane at a constant fuel flow rate, the high temperature flame is stabilized along the wall of the combustor liner. With the casing rotating, pattern factor and exit temperature increase, but the lower heating value of syngas causes a power shortage. To make up the power, the fuel flow rate is raised to maintain the thermal load. Consequently, the high temperature flame is pushed downstream due to increased fuel injection velocity. NOx emission decreases as the rotational speed increases in both cases. Pattern factor decreases but exit temperature increases with the increase of roatation speed indicating a higher combustion efficiency. However, there is possible hotspots at exit due to higher pattern factor (PF>0.3) for H2-rich and equal molar syngas at lower speed of rotation, which needs to be resolved by improving the cooling strategy.
Flow Dynamics in a Multi-Swirler Model Combustor Based on LES and POD Analysis
Authors: Liu Weijie , Wang Huiru , Yang Qian , Xue Ranran , Ge Bing , Ji Yongbin
Published: November 2019

Swirling flow is often employed in gas turbine combustion chambers for the sake of improving flame stability. Swirling flow induces not only recirculation zones but also large coherent structures which show close relationship with flow dynamics and combustion instability. The flow dynamics including Precessing Vortex Core (PVC) in simple swirlers are extensively studied, while the flow instability characteristics in a multi-swirler combustor are not fully reported. In the present paper, Large Eddy Simulation (LES) of non-reacting turbulent swirling flow is conducted in a multi-swirler burner which comprises a pilot stage and a main stage. Flow dynamics in the multi-swirler combustor are analyzed based on phase-averaged evolution of instantaneous flowfield. Proper Orthogonal Decomposition (POD) is employed to identify the coherent structures in the multi-swirling flow. Results show that the main stage and pilot stage flow interact with each other generating highly turbulent swirling flow. PVC is successfully captured at the boundary of Main recirculation zone (MRZ) in the pilot stage with a dominant frequency of 1915 Hz. The PVC leads to periodic azimuthal flow instability. POD analyses for the velocity fields show dominant high-frequency modes (mode 1 and mode 2) in the pilot stage. However, the dominant energetic flow is damped rapidly downstream of the pilot stage that it has little effect on the main stage flow.
Mistuning Analysis of a Detuned Bladed-Disk With Geometrical Nonlinearities
Authors: Picou Anthony , Capiez-Lernout Evangéline , Soize Christian , Mbaye Moustapha
Published: November 2019

This work concerns the nonlinear numerical analysis of mistuned blades for a rotating detuned bladed-disk structure with geometrical nonlinearities. The detuning phenomenon is taken into account through a deterministic approach by modifying material properties of some blades. A nonlinear reduced-order model is obtained by setting up a basis using a double projection method. The mistuning uncertainties are implemented through a nonparametric probabilistic approach for which the level of uncertainties is controlled by a hyperparameter. A numerical application is carried out on a bladed-disk structure made up of 24 blades whose finite element model has about 800,000 dofs exhibiting complex dynamic behaviors.
Unsteady Flow Interactions Between a High- and Low-Pressure Turbine: Part 2 — Rotor-Synchronic Averaging and Proper Orthogonal Decomposition of the Unsteady Flow Fields
Authors: Dellacasagrande M. , Sterzinger P. Z. , Zerobin S. , Merli F. , Wiesinger L. , Peters A. , Maini G. , Heitmeir F. , Göttlich E.
Published: November 2019

This paper, the second of two parts, presents an experimental investigation of the unsteady flow field evolving in a two-stage two-spool test turbine facility. The experimental setup, which was designed to reproduce the operating condition of modern commercial aero-engines, consists of a high-pressure turbine (HPT) stage followed by a turbine center frame (TCF) with non-turning struts, and a co-rotating low-pressure turbine (LPT) stage.

Measurements carried out with a fast-response aerodynamic pressure probe (FRAPP) were post-processed to describe the unsteady evolution of the flow downstream of the HPT rotor, through the TCF duct, and at the exit of the LPT stage. The time-resolved results presented in the first part of this paper show that deterministic fluctuations due to both rotors characterize the flow field downstream of the LPT. In order to characterize the deterministic unsteadiness induced by all the components constituting the turbine facility (HPT, TCF and LPT) and their interactions, measurements were carried out in three different planes located downstream of the HPT, at the exit of the TCF and downstream of the LPT stage. The unsteady results obtained in the plane located at the exit of the LPT are discussed in more details in this second part of this paper, providing information about the interactions between the two rotors.

A proper phase-average procedure, known as rotor synchronic averaging (RSA), which takes into account the rotorrotor interaction, was adopted to capture the unsteadiness due to both rotors. Proper Orthogonal Decomposition (POD) was also applied to provide a characterization of the major contributors in terms of energy to the deterministic unsteadiness occurring in the test turbine facility. At the exit of the LPT rotor, the perturbations induced by the HPT stage and the interactions between the two rotors were found to dominate over the unsteadiness due to the LPT only.
Effect of Squealer Rim Slot Structure on Turbine Blade Aerothermal Performance
Authors: Qian Mengcheng , Lu Shaopeng , Zhang Bo , Wang Weijie , Teng Jinfang
Published: November 2019

Recent studies have demonstrated that the turbine blade with a squealer tip has less aerodynamic loss than that with a flat tip. However, there exists an area of high heat transfer coefficient (HTC) in the frontal region of the cavity floor. The present study focuses on the effect of squealer rim slot structure on turbine blade aerothermal performance. An experiment of transient thermal measurement is carried out for a non-slot squealer tip to validate the numerical setup and the choice of turbulence model. ANSYS CFX is utilized to conduct the numerical simulations of cases with and without slot structure and they are both validated by the experimental data. Through the experimental and CFD results, it can be found that the case with a slot on the pressure side of the squealer rim has smaller area of high HTC region and the aerodynamic efficiency is raised. Moreover, the effect of different sizes of the slot is investigated numerically and it also has a great impact on the heat transfer and aerodynamics. The quantity of the flow passing through the slot can largely influence the flow field of the tip gap and the cavity. Thus, the heat transfer of these areas and the aerodynamic efficiency of the blade vary from the slot size.
CFD-Based Throughflow Analysis of Transonic Flows in Steam Turbines
Authors: Ricci Martina , Pacciani Roberto , Marconcini Michele , Macelloni Paolo , Cecchi Stefano , Bettini Claudio
Published: November 2019

A CFD-based throughflow solver is applied to the meridional analysis of low-pressure steam turbine modules. The throughflow code inherits its numerical scheme from a state-of-the-art CFD solver (TRAF code) and incorporates real gas capabilities, three-dimensional flow features and spanwise mixing models. Secondary flow effects are introduced via a concentrated vortex model. Tip gap and shroud leakage effects are modelled in terms of source vectors in the system of governing equations. The impact of part-span shrouds and snubbers are accounted for, on a local basis, through suitable body force fields.

The AUSM+-up upwind strategy has been adopted as a basis to construct a numerical flux scheme explicitly suited for throughflow applications. The original formulation has been adapted to handle real gas flows and to embed the treatment of body force fields in a fully consistent framework. The capability of the procedure is assessed by analysing the low-pressure modules of two large steam turbines designed and manufactured by Ansaldo Energia. These 3-stage modules include rotor tip shrouds and part-span snubbers, and feature supersonic flow and large blade twist. Throughflow predictions in terms of main performance figures and radial distributions of flow quantities are compared to experimental data and 3D steady viscous analyses. It will be shown how the proposed CFD-based throughflow model can be fruitfully used in the early stages of the design as it delivers predictions of comparable accuracy with 3D CFD analyses at a fraction of the computational time.
A Model-Based Solution for Gas Turbine Diagnostics: Simulations and Experimental Verification
Authors: Zaccaria Valentina , Stenfelt Mikael , Sjunnesson Anna , Hansson Andreas , Kyprianidis Konstantinos G.
Published: November 2019

Prompt detection of incipient faults and accurate monitoring of engine deterioration are key aspects for ensuring safe operations and planning a timely maintenance. Modern computing capabilities allow for more and more complex tools for engine monitoring and diagnostics. Nevertheless, an underlying physics-based approach is often preferable, because not only the “what” but also the “why” can be identified, providing an effective decision support tool to the service engineer.

In this work, a physics-based adaptive model is used to evaluate performance deltas and correct the data to reference conditions (gas turbine load and ambient conditions), while a data-driven correlation algorithm identifies the most likely matches within a fault signatures database. Possible faults are ordered from the highest correlation in the decision support system and the most likely fault can be selected based on the number of occurrences and the associated correlation. Gradual engine degradation can also be monitored by displaying performance deltas trends during time.

The diagnostics tool was tested on a validated performance model of a single-shaft industrial gas turbine and subsequently on experimental data. This paper presents the diagnostics system structure, the model adaptation scheme, and the results obtained from simulated and real fault data. Accurate fault isolation and severity identification were achieved in all cases, demonstrating the tool capability for decision support system.
Advanced Last Stage Blade for Nuclear Power Plant Upgrades
Authors: Siewert Christian , McCracken James R. , Thiemann Thomas
Published: November 2019

Utility steam turbines for electrical power generation are used at many places worldwide with different ambient conditions and different power plant configurations resulting in a variety of environmental and operational conditions. In some environments and operational conditions excitation mechanisms exist which may result in elevated Last Stage Blade vibrations. A particular example occurs in some steam turbine modernization projects, in which modern Last Stage Blade designs are applied in configurations with retained outer casing and diffusor designs from the original turbine design.

In this paper, operational experience with an advanced Last Stage Blade coupled by damping elements is presented. In addition, the background leading to the development of this Last Stage Blade is outlined in this paper. Vibration measurement data obtained from field measurements in certain modernized units with retained outer casings from original installation is summarized and compared to the corresponding data for a freestanding Last Stage Blade previously used in these units showing the vibrational behavior of the newly developed Last Stage Blade. Results from field inspections are also presented. The data and inspections show the Last Stage Blade with damping elements do not exhibit elevated vibrations previously indicated.
Influence of the Laminar Burning Velocity on the Transfer Functions of Premixed Methane and Propane Swirl Flames
Authors: Di Sabatino F. , Guiberti T. F. , Moeck J. P. , Roberts W. L. , Lacoste D. A.
Published: November 2019

The effects of the laminar burning velocity (SL), on the transfer functions of propane-air and methane-air swirl flames is experimentally investigated. Five equivalence ratios for each fuel are selected, to yield different values of SL. The flame transfer function (FTF), is obtained by comparing the velocity fluctuations of the incoming flow, measured with a hot wire, to the heat release rate oscillations, collecting OH* chemiluminescence with a photomultiplier tube. Phase-locked images of OH* chemiluminescence are also acquired to analyze the flame dynamics during the forcing cycle. The unforced velocity fields are measured by particle image velocimetry to assess the effects of SL on the flow fields. Changing the laminar burning velocity affects mainly the gain around 176 Hz and 336 Hz. This paper focuses on 336 Hz. The flame vortex roll-up is recognized as a key parameter controlling the gain of the FTF around 336 Hz. The analysis highlights that SL influences the gain response around 336 Hz in two competing ways: first, it enhances the flame vortex roll-up and second, it affects the stabilization distance of the flame, which influences the vortex generated by acoustic forcing.
Complex Design Method of Ceramic Blades and Metal Disk Connection
Authors: Sapronov Dmitry , Mezencev Michael , Karimbaev Telman , Reznik Sergey , Prosuntsov Pavel
Published: November 2019

This paper presents a complex approach to designing ceramic blades dovetail joints. Two ceramic materials were considered: diamond reinforced silicon carbide and hot pressed silicon nitride (only in contact testing). The model blades were made from diamond reinforced silicon carbide due to its availability and mature technology.

Part 1 describes the models of mechanical and thermal contact and contains experimental data on contact strength and thermal contact conductance.

Part 2 investigates the effect of stress concentration and scale factor on the fracture of ceramic test pieces.

Part 3 proposes a theoretical-experimental method to estimate friction coefficient in a dovetail joint. We also investigated the character of the ceramic blades fracture during the rotor spin-up.

Part 4 deals with automating the design process of the ceramic blades dovetail joints using experimental data.
Numerical Investigation of Combustion Instabilities in a Single Element Lean Direct Inject (LDI) Combustor Using Flamelet Based Approaches
Authors: Patwardhan Saurabh , Nakod Pravin , Orsino Stefano , Arguinzoni Carlo
Published: November 2019

In this paper, high-fidelity large eddy simulations (LES) along with flamelet based combustion models are assessed to predict combustion dynamics in low-emissions gas turbine combustor. A model configuration of a single element lean-direct-injection (LDI) combustor from Purdue University [1] is used for the validation of simulation results. Two combustion models based on the flamelet concept, i.e., steady diffusion flamelet (SDF) model and flamelet generated manifold (FGM) model are employed to predict combustion instabilities. Simulations are carried out for two equivalence ratios of φ = 0.6, and 0.4 and the results in the form of mode shapes, peak to peak pressure amplitude and power spectrum density (PSD) are compared with the experimental data of Huang et al. [1]. The effect of variation in the time step size for transient simulations is also studied. The time step sizes corresponding to Acoustic Courant numbers of 4, 8 and 16 are tested. Further, two numerical solver options, i.e., pressure based segregated solver and pressure based coupled solver are used in understanding their effect on the solution convergence regarding the number of time steps required to reach the limit cycle of the pressure oscillations. An additional test for reducing the overall simulation time is explored using a truncated (half) calculation domain and applying an appropriate acoustic impedance boundary condition at the truncated location. The simulation results from this test for the equivalence ratio of φ = 0.6 are compared with the simulation results from the corresponding full domain test. Overall, the simulation results compare well with the experimental data and trends are captured accurately. A clear dominant acoustic mode of 4L is observed for the equivalence ratio of 0.6 that compares well with the experimental data. For the equivalence ratio of 0.4, simulation results show that there is no dominant frequency and the energy is distributed among the first five modes. It is consistent with the observations in the experiments. Both combustion models (SDF and FGM) used in this study capture the combustion instabilities accurately. It builds confidence in flamelet based combustion models for the use in combustion instability modeling which is traditionally done using finite rate chemistry models based on reduced kinetics.
Prediction of Geometrically Induced Localization Effects Using a Subset of Nominal System Modes
Authors: Maywald Thomas , Heinrich Christoph R. , Kühhorn Arnold , Schrape Sven , Backhaus Thomas
Published: November 2019

It is widely known that the vibration characteristics of blade integrated discs can dramatically change in the presence of manufacturing tolerances and wear. In this context, an increasing number of publications discuss the influence of the geometrical variability of blades on phenomena like frequency splitting and mode localization. This contribution is investigating the validity of a stiffness modified reduced order model for predicting the modal parameters of a geometrically mistuned compressor stage. In detail, the natural frequencies and mode shapes, as well as the corresponding mistuning patterns, are experimentally determined for an exemplary rotor. Furthermore, a blue light fringe projector is used to identify the geometrical differences between the actual rotor and the nominal blisk design. With the help of these digitization results, a realistic finite element model of the whole compressor stage is generated. Beyond that, a reduced order model is implemented based on the nominal design intention. Finally, the numerical predictions of the geometrically updated finite element model and the stiffness modified reduced order model are compared to the vibration measurement results. The investigation is completed by pointing out the benefits and limitations of the SNM-approach in the context of geometrically induced mistuning effects.
Aeroelastic and Aerodynamic Investigation of a Low Pressure Turbine Under the Influence of a Circumferential Inlet Distortion
Authors: Simonassi L. , Zenz M. , Bruckner P. , Heitmeir F. , Marn A.
Published: November 2019

Modern low pressure turbine (LPT) architectures of aero engines are designed in order to optimize weight, decrease the fuel consumption and noise emissions. This can be achieved with the use of lighter materials or by reducing the size of the engine. In particular, decreasing the axial distances between the blade rows and shortening the turbine centre frame. As a consequence, it becomes more and more important to investigate the influence of inflow circumferential distortions of total pressure and temperature that can be originated by struts, flow injections and measurement instrumentation.

This work presents the results of an experimental investigation on the influence of total pressure inflow inhomogeneity on the aerodynamics and on the vibrations of a low pressure turbine stage. The measurements were carried out in a one and a half stage subsonic test turbine facility at nominal engine relevant operating conditions and during speed transient operation, including a resonance crossing. Steady and unsteady aerodynamic measurements were performed with a five-hole-probe (5HP) and a fast response aerodynamic pressure probe (FRAPP) respectively, while the LPT rotor vibration data were acquired using strain gauges applied on different blades, in combination with a telemetry system. Analysis in the frequency domain as well as a curve fitting method were applied to estimate the blades forced response and the critical damping. It will be shown that the distortion creates steady and unsteady aerodynamic alterations, causing direct effects on the rotor vibration characteristics.
Development of a CFD Methodology to Reproduce the Effects of Macro Turbulence on Wind Turbines and its Application to the Particular Case of a VAWT
Authors: Balduzzi Francesco , Zini Marco , Ferrara Giovanni , Bianchini Alessandro
Published: November 2019

Based on existing reports and databases, most of the installations in highly turbulent sites in fact fail to reach the expected energy yield, resulting in still or underperforming turbines that also give bad press for the technology. A better understanding of the real performance of wind turbines under highly turbulent conditions is then pivotal to ensure the economic viability of new installations. To this end, the possible use of Computational Fluid Dynamics (CFD) techniques could provide notable benefits, reducing the time-to-market and the cost with respect to experiments. On the other hand, it is intrinsically not easy to reproduce properly intense and large-scale turbulence with the techniques of common use for research and industry (e.g. CFD unsteady RANS), while the only methods that are granted to do so (e.g. DNS or LES) are often not computationally affordable. Moving from this background, this study presents the development a numerical strategy to exploit at their maximum level the capabilities of an unsteady Reynolds-Averaged Navier-Stokes (RANS) approach in order to reproduce fields of macro turbulence of use for wind energy applications. The study is made of two main parts. In the first part, the numerical methodology is discussed and assessed based on real wind tunnel data. The benefits and drawbacks are presented also in comparison to other existing methods. In the second part, it has been used to simulate the behavior under turbulence of a H-Darrieus vertical-axis wind turbine, for which unique wind tunnel data were available. The simulations, even if preliminary, showed good matching with experiments (e.g. confirming the increase of power), showing then the potential of the method.
Adaptive Control of Micro Gas Turbine for Engine Degradation Compensation
Authors: Zaccaria Valentina , Ferrari Mario L. , Kyprianidis Konstantinos
Published: November 2019

Micro gas turbine engines in the range of 1–100 kW are playing a key role in distributed generation applications, due to the high reliability and quick load following that favor their integration with intermittent renewable sources. Micro-CHP systems based on gas turbine technology are obtaining a higher share in the market and are aiming at reducing the costs and increasing energy conversion efficiency. An effective control of system operating parameters during the whole engine lifetime is essential to maintain desired performance and at the same time guarantee safe operations. Because of the necessity to reduce the costs, fewer sensors are usually available than in standard industrial gas turbines, limiting the choice of control parameters. This aspect is aggravated by engine aging and deterioration phenomena that change operating performance from the expected one. In this situation, a control architecture designed for healthy operations may not be adequate anymore, because the relationship between measured parameters and unmeasured variables (e.g. turbine inlet temperature or efficiency) varies depending on the level of engine deterioration. In this work, an adaptive control scheme is proposed to compensate the effects of engine degradation over the lifetime. Component degradation level is monitored by a diagnostic tool that estimates performance variations from available measurements; then, the information on the gas turbine health condition is used by an observer-based model predictive controller to maintain the machine in a safe range of operation and limit the reduction in system efficiency.
Multi-Physics Simulation Based Approach for Life Prediction of a Gas Turbine Combustor Liner
Authors: Shrivastava Sourabh , Andrade Prem , Carpenter Vinay , Masal Ravindra , Nakod Pravin , Orsino Stefano
Published: November 2019

Better life assessment of hot-components of an aero-engine can help improve its reliability and service life, while, reducing associated maintenance cost. Accurate prediction of Thermo-Mechanical Fatigue (TMF) is one of the crucial aspects of life prediction. Therefore, fully resolved simulation methodologies have gained attention as an ingredient for solving TMF problems owing to their potential for providing comprehensive insights into a system having hot components undergoing transient loading during operation.

The present work focuses on a multi-physics simulation-based approach for the life-prediction of a representative gas-turbine combustor liner with an objective of providing a complete framework for TMF analysis of an actual aero-engine combustor liner. The presented methodology consists of a coupling between Computational Fluid Dynamics (CFD) and Finite Element Method (FEM). Thermal loads on the representative aero-engine combustor are predicted using Conjugate Heat Transfer (CHT) modeling in the CFD analyses for different operating conditions suitable for a flight cycle. A load cycle is then constructed using these thermal loads and is transferred to the structural analysis to evaluate the stresses in the liner. Results are obtained regarding spatially varying thermal expansion resulting in inelastic strains as governed by temperature and rate dependent material behavior. Stress and plastic strain history information from the structural analysis are processed to predict the life of different regions of the combustor liner. Different simulation methods for conjugate heat-transfer, load-cycle, material property extraction, thermal-stresses, and fatigue are evaluated, and an overall methodology involving accuracy and reasonable computational cost is proposed. The proposed methodology is numerically verified, and the verification results are presented in this work.
Effect of Natural Gas Composition on Low NOx Burners Operation in Heavy Duty Gas Turbine
Authors: Romano Serena , Cerutti Matteo , Riccio Giovanni , Andreini Antonio , Romano Christian
Published: November 2019

Development of lean-premixed combustion technology with low emissions and stable operation in an increasingly wide range of operating conditions requires a deep understanding of the mechanisms that affect the combustion performance or even the operability of the entire gas turbine.

Due to the relative wide range of natural gas composition supplies and the increased demand from Oil&Gas customers to burn unprocessed gas as well as LNG with notable higher hydrocarbons (C2+) content; the impact on gas turbine operability and combustion related aspects has been matter of several studies.

In this paper, results of experimental test campaign of an annular combustor for heavy-duty gas turbine are presented with focus on the effect of fuel composition on both emissions and flame stability.

Test campaign involved two different facilities, a full annular combustor rig and a full-scale prototype engine fed with different fuel mixtures of natural gas with small to moderate C2H6 content. Emissions trends and blowout for several operating conditions and burner configurations have been analyzed.

Modifications to the burner geometry and fuel injection optimization have shown to be able to reach a good trade-off while keeping low NOx emissions in stable operating conditions for varying fuel composition.
High Pressure Compressor Aerodynamic Performance at Uncertain Boundary Conditions
Authors: Magin Philip , Danner Florian , Voigt Matthias , Mailach Ronald
Published: November 2019

The intended operating point of turbomachinery is subject to numerous kinds of uncertainty. These range from varying ambient conditions, across geometric deviations in a component, to system related loading variability resulting in engine-to-engine variation in component matching. In order to guarantee safe operation at all conditions, it is essential to consider the above uncertainties when designing turbomachinery.

In the present work, a probabilistic assessment is performed of the influence of possible operational uncertainties on the aerodynamic performance metrics of an aero-engine multistage high pressure compressor (HPC). To propagate uncertainties, Monte Carlo simulations (MCS) with Latin Hypercube Sampling (LHS) were performed, with both correlated and uncorrelated inputs. Each sample consisted of a steady state computational fluid dynamics (CFD) evaluation of the compressor. The statistical input for the boundary conditions was acquired from a MCS of the engine cycle performance at cruise, accounting for flight-to-flight variations in ambient conditions and engine-to-engine variations in component properties.

With the chosen approach, it is possible to quantify the variability in aerodynamic performance of an HPC that is subject to uncertain operating conditions and thus shows the importance of input correlations. Results highlight that deterministically determined performance metrics can differ considerably from the statistical mean, revealing the benefits of a probabilistic assessment. In contrast to performing MCS on the cycle only, a CFD based assessment can also be used to draw conclusions on the aerodynamic mechanisms responsible for changes in efficiency or surge margin.
Effect of CO2 Dilution on the Laminar Burning Velocities of Premixed Methane/Air Flames at Elevated Temperature
Authors: Duva B. C. , Chance L. E. , Toulson E.
Published: November 2019

With increased interest in reducing emissions, the staged combustion concept for gas turbine combustors is gaining in popularity. For this work, the effect of CO2 dilution on laminar burning velocities of premixed methane/air flames was investigated at elevated temperature through both experiments and numerical simulations. Validation of the experimental setup and methodology was completed through experimental testing of methane/air mixtures at 1 bar and 298 K. Following validation, high temperature experiments were conducted in an optically accessible constant volume combustion chamber at 1 bar and 473 K. Laminar burning velocities of premixed methane/air flames with 0%, 5%, 10% and 15% CO2 dilution were determined using the constant pressure method enabled via schlieren visualization of the spherically propagating flame front. Results show that laminar burning velocities of methane/air mixtures at 1 bar increase by 106–145% with initial temperature increases from 298 K to 473 K. Additions of 5%, 10% and 15% CO2 dilution at 1 bar and 473 K cause a 30–35%, 51–54% and 66–68% decrease in the laminar burning velocity, respectively. Numerical results were obtained with CHEMKIN [1] using the GRI-Mech 3.0 [2] and the San Diego [3] mechanisms. Excellent agreement was observed between the GRI-Mech 3.0 [2] and experimental data at ϕ ≤ 1.2 for methane/air mixtures at 1 bar and 298 K. However, for mixtures at ϕ < 1.3, 1 bar and 473 K, mixtures at ϕ < 1.2 for 5% and 10% dilutions, and for mixtures at ϕ < 0.9 for 15% dilution, laminar burning velocities predicted by the GRI-Mech 3.0 mechanism [2] were slightly higher than experimental results. The San Diego mechanism [3] showed good agreement with experimental data at ϕ ≤ 0.9 for methane/air mixtures at 1 bar and 298 K. However, for mixtures at ϕ > 0.9, 1 bar and 298 K, mixtures at ϕ > 1.2, 1 bar and 473 K, and mixtures at ϕ > 1.1 with 5%, 10% and 15% dilution, the San Diego mechanism [3] predicted slower laminar flame speeds than the experimental results. On the other hand, the laminar burning velocities predicted by the San Diego mechanism [3] were slightly faster than the experimental results for leaner mixtures. Additionally, the dilution, thermal-diffusion, and chemical effects of CO2 on the laminar burning velocities of methane/air mixtures were investigated numerically by diluting the mixtures with both chemically active and inactive CO2 following the determination of the most important elementary reactions on the burning rate through sensitivity analysis. Lastly, it was shown that CO2 dilution suppresses the flame instabilities during combustion, which is attributable to the increase in the burned gas Markstein length (Lb) with the addition of diluent.
Analysis of Vortex Ingestion Impact on the Dynamic Response of the Fan in Resonance Condition
Authors: Berthelon Thomas , Dugeai Alain , Langridge Jonathan , Thouverez Fabrice
Published: November 2019

Ultra high by-pass ratio (UHBR) turbofan configurations are promising concepts to address the issue of aircraft fuel burn reduction. The large fan diameter and the small ground clearance of these configurations can lead to ingestion of ground vortex during take-off phases. This vortex can be responsible of high level of vibrations and possible failure due to high cycle fatigue. The objective of the work described in this paper is to investigate the forced response due to ground vortex ingestion of a large civil fan in resonance condition. This paper is separated in three sections. The first one consists of characterizing the flow distortion induced by a ground vortex. The second part consists of evaluating the blade vibrations induced by this vortex with decoupled aeromechanical method. The numerical predictions are then compared to experimental results. And finally, the last part consists of proposing a low fidelity model based on swirl distortion in order to estimate modal aerodynamic forces in ground vortex ingestion case.
Assessing Manufacturing Repeatability of Inherently Damped Nickel Alloy Components via Forced-Response Testing
Authors: Scott-Emuakpor Onome , George Tommy , Runyon Brian , Sheridan Luke , Holycross Casey , O’Hara Ryan
Published: November 2019

The ability to repeat an additive manufacturing (AM) process that fabricates a unique specimen with inherent damping capability is explored. Using the Laser Powder Bed Fusion (LPBF) AM process, four Inconel 718 components with the same internal and external geometries are manufactured. The damping performance of the four specimens are determined to make comparisons against each other, previously studied inherently damped specimens, and fully-fused components of the same material and external geometry. Results of the study demonstrate similarities in the damping performance of each beam despite the specimens being made with three different fabrication parameters, two different LPBF scan strategies, and two different build sequences. Moreover, the measured inherent damping in the four beams is significantly higher (9–16 times) compared to the damping of a fully-fused beam. The results of the inherently damped beams in this study is also compared to previous specimens of different geometries using a shear-displacement criterion that determines the effectiveness of damping. The results show an 85% correlation between damping performance and calculated shear-displacement value. Therefore, despite three sets of fabrication parameters, two scan strategies, and two build sequences for the same geometry/dimensioned specimen, the results firmly demonstrate inherent damping repeatability is strongly driven by the unique geometry of the component, which ensures repeatability with minimal sensitivity in the manufacturing process.
Laser Additive Manufacturing of Titanium Aluminides for Turbomachinery Applications
Authors: Vogelpoth Andreas , Schleifenbaum Johannes Henrich , Rittinghaus Silja
Published: November 2019

The defect-free processing of TiAl alloy TNM™-B1 by means of Laser Powder Bed Fusion (LPBF) is demonstrated by manufacturing of an automobile turbocharger wheel. Similar precision cast material was used as reference. TNM™-B1 was manufactured crack free with a density > 99.5% using elevated process temperatures above the brittle-to-ductile transient temperature (BDTT). The preheating temperature was provided by an induction preheating system. To minimize oxygen pick up during the LPBF process, the process atmosphere was actively cleaned using a gas-purification system.

Produced test samples were analyzed in as-built and heat-treated condition regarding density, micro structure and phases by means of a Light Optical Microscope (LOM) and Scanning Electron Microscopy (SEM). Micro hardness was measured according to Vickers. Oxidation measurements were performed by means of carrier-gas hot extraction. Mechanical properties were determined using room temperature tensile tests. The final automobile turbocharger wheel was analyzed for defects using a Micro-Computer Tomography scanner (MCT).

Besides bulk test samples, thin-walled specimens can be manufactured with sufficient density. Depending on the process parameters, an oxygen content < 1000 ppm could be reached. The as-built microstructure consists of lamellar (α2+γ) colonies and nearly globular γ as well as β/β0 at the grain boundaries. High cooling rates in the magnitude of 105 to 106 K/s provide small grain sizes of 1–7 μm. Hardness measurements reveal an increased hardness (515-560HV0.3) compared to cast material (390HV0.3). Samples for tensile tests show tensile strength around 840 MPa and a total elongation of 1.1% for LPBF-manufactured and hot isostatic pressed (HIP) samples. The CT analysis of the turbocharger wheel confirms that complex geometries made of TiAl can be additively manufactured free of cracks.
Additive Manufacture of Prototype Turbine Blades for Hot-Fired Engine Performance Validation Trials
Authors: Adair David , Kirka Michael , Ryan Daniel
Published: November 2019

Additive manufacturing (AM), also known as 3D printing, is a rapidly developing technology with tremendous potential in both developmental and production applications. Solar Turbines Incorporated is committed to AM technology for gas turbine applications. The ability to metal 3D print novel designs of turbine blades capable of actual turbine engine operation would effectively reduce design validation cycle time, and allow acquisition of key performance data early in a design campaign. In support of Solar’s advanced manufacturing development and ongoing engine efficiency improvement goals, Solar initiated a project to print a full set of Mercury™ 50 stage 2 turbine blades to be run in a development engine.

Solar leveraged years of experience with design and serial production of AM components in support of this project. A significant challenge faced when printing turbine blades is producing metal with mechanical properties sufficient to withstand the rigors of engine operation. As a rotating component within the hot section of the engine, turbine blades experience high centrifugal and pressure loads at elevated temperatures. After investigation of possible alloys capable of meeting the requirements of the Mercury™ 50 design envelope, the gamma prime (γ’) strengthened nickel superalloy Inconel™ 738LC was selected to provide the best opportunity for successful development engine testing.

Solar partnered with Oak Ridge National Laboratory (ORNL) to produce the Inconel™ 738LC blades with Electron Beam Melting (EBM) powder bed fusion process. Once a rough blade shape was printed, the fir-tree attachment, blade tip shroud, and air flow path surfaces were finished using both conventional and non-conventional machining processes. In-process monitoring, metallurgical evaluations, mechanical testing, and non-destructive inspection techniques were used to validate the printed blade material integrity and conformance to geometric design intent. Planned future activities include assembly of the AM blades onto a disk for spin pit testing to validate the mechanical integrity and design margin of the blades. The final phase of the project will be to install the bladed disk assembly into a Mercury™ 50 engine at Solar Turbines to conduct a series of hot-fired engine performance tests.
Pressure Profile Measurements Within the Gas Film of Journal Foil Bearings Using an Instrumented Rotor With Telemetry
Authors: Shalash K. , Schiffmann J.
Published: November 2019

Foil bearings are strong candidates to support oil-free turbomachinery. Although foil bearings are a widely used technology, models describing their behavior are not validated using the film pressure, which is the fundamental variable of any fluid film bearing. This paper presents pressure profiles measured within the gas film of a journal foil bearing. The pressure is measured using an instrumented rotor with embedded pressure probes and wireless telemetry. The measurements yield the simultaneous circumferential pressure profiles at two axial positions inside the bearing. Proximity probes on the bearing allowed the measurement of the corresponding rotor orbits. The bearing under investigation is a bump type compliant journal bearing, with a nominal diameter of 40mm, an L/D = 1, and was tested up to 37.5 krpm. Load-displacement and break-away tests were performed on the test bearing in order to identify bearing parameters necessary for reproducibility. The pressure profiles are compared to a frequency domain foil bearing model. This paper is a step towards further fundamental understanding of the foil bearing behavior, and the validation of the rich modelling literature.
An Assessment of Machine Learning Techniques for Predicting Turbine Airfoil Component Temperatures, Using FEA Simulations for Training Data
Authors: Tallman James A. , Osusky Michal , Magina Nick , Sewall Evan
Published: November 2019

This paper provides an assessment of three different machine learning techniques for accurately reproducing a distributed temperature prediction of a high-pressure turbine airfoil. A three-dimensional Finite Element Analysis thermal model of a cooled turbine airfoil was solved repeatedly (200 instances) for various operating point settings of the corresponding gas turbine engine. The response surface created by the repeated solutions was fed into three machine learning algorithms and surrogate model representations of the FEA model’s response were generated. The machine learning algorithms investigated were a Gaussian Process, a Boosted Decision Tree, and an Artificial Neural Network. Additionally, a simple Linear Regression surrogate model was created for comparative purposes. The Artificial Neural Network model proved to be the most successful at reproducing the FEA model over the range of operating points. The mean and standard deviation differences between the FEA and the Neural Network models were 15% and 14% of a desired accuracy threshold, respectively. The Digital Thread for Design (DT4D) was used to expedite all model execution and machine learning training. A description of DT4D is also provided.
Transient Performance of Separated Flows: Experimental Characterization of Flow Detachment Dynamics
Authors: Saavedra J. , Paniagua G.
Published: November 2019

The operation of compact power units at low Reynolds environments is constrained by the boundary layer detachment in the low pressure turbines stages. Flow separation is prompt by the lack of momentum on the near wall region when exposed to adverse pressure gradients. Transient flow conditions or periodic flow perturbations induced to the near wall flow may delay or prevent the flow detachment. The present investigation experimentally analyzes the behavior of separated flows based on ad-hoc wall mounted hump. The test article mimics the performance of the aft portion of the suction side of a low pressure turbine where flow separation occurs at low Reynolds and fully attached flow takes place at high Reynolds. The inception of separated flow under sudden flow release was investigated in a linear wind tunnel. The extension of the separated region and its transient development was monitored through surface pressure and temperature measurements and hotwire traverses. The inlet flow conditions to the test article were interrogated with total pressure, total temperature and hotwire traverses. A fast opening valve upstream of the settling chamber was sequentially actuated at low frequency to study the behavior of the recirculation bubble under sudden flow acceleration. Due to the sudden flow release, the near wall region overcomes the adverse pressure gradient. As the flow acceleration dilutes the boundary layer detaches and the separated flow region grows in the stream-wise direction. The comparison of the experimental results with 2D and 3D transient Computational Fluid Dynamic simulations demonstrates the ability of Unsteady Reynolds Average Navier-Stokes models to predict the dynamics of this phenomenon. However, CFD over-predicts the extension of the recirculated flow region. The integration of this research towards future control strategies will enable efficient operation of turbine-hybrid systems operating at high power.