bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation Into the Impact of Injector Geometrical Design Parameters on Hydrogen Micromix Combustion Characteristics
Authors: Sun Xiaoxiao , Agarwal Parash , Carbonara Francesco , Abbott David , Gauthier Pierre , Sethi Bobby
Published: January 2021

Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. As a part of the ENABLEH2 project, the current study focuses on the influence of design parameters on the micromix hydrogen combustion injectors. This study provides deeper insights into the design space of a hydrogen micromix injection system via numerical simulations. The key geometrical design parameters of the micromix combustion system are the sizing of the air gates and the hydrogen injector orifices together with the offset distance between air gate and hydrogen injection, the mixing distance and the injector to injector spacing.

This paper first presents results of the numerical simulation of four designs, down selected from a series of combinations of the key design parameters, including cases with low and high momentum flux ratio, weak and strong flame-flame interaction. It was discovered that the hydrogen/air mixing characteristics, and flame to flame interactions, are the main factors influencing the combustor gas temperature distributions, flame lengths and the corresponding NOx production.

The current study then focused on the effect of air gate geometry on the mixing characteristics, flame shape and temperature distribution. The momentum flux ratio was kept constant throughout this investigation by keeping the air gate area constant. Variations of the original baseline air gate design were studied, followed by a study of various novel air gate geometries, including circular, semi-circular and elliptical shapes.

It is concluded that NOx production is influenced by a number of factors including jet penetration flame interactions and air gate shape and that there is a “Sweet Spot” that results in the lowest practicable NOx production. Flatter and wider air gate shapes tend to yield the lowest temperature and consequently the lowest NOx. Reduced interaction between flames also tends to reduce NOx and by manipulating hydrogen penetration, there is the potential to further reduce the NOx production.
Pitch Control for Anticipation in the Measurement of Wind Speed for Small Wind Turbines Installed in Areas With Atypical Winds
Authors: Chavero-Navarrete Ernesto , Chavez-Luna Alfredo , Jáuregui-Correa Juan-Carlos , Trejo-Perea Mario , Carrillo-Serrano Roberto-Valentín , Rios-Moreno José-Gabriel
Published: January 2021

The production of electricity by renewable means is necessary to meet the growing energy demand and to protect the environment. Wind energy is an alternative, however, in places with a limited wind resource only the installation of small horizontal Axis wind turbines (SHAWT) is profitable. At rotor height, in this size of turbines, the wind is usually unstable with gusts and turbulence due to obstacles in its path such as buildings and trees. To reduce the effects of wind, the angle of incidence of the blade with the wind must be adaptable to guarantee the nominal rotation speed. The pitch angle is the angle of blade rotation around the longitudinal axis is commonly regulated with a Proportional-Integral-Derivative (PID) feedback controller, which works correctly when the wind is stable, but not when the wind presents drastic changes in speed, as a faster response speed is required. To correct this problem, this article presents a PID controller with automatic adjustment of the gain values and offering different response times for which a fuzzy logic controller (FLC) is used. The membership functions of the FLC are determined from the measurement of the wind speed at a calculated distance, so it is possible to anticipate the response of the actuator to the arrival of a wind gust to the rotor. The algorithm is implemented in 14 kW SHAWT where the difference of performance versus a conventional controller is quantified.
Development, Analysis, and Validation of a Simultaneous Inlet Total Pressure and Swirl Distortion Generator
Authors: Frohnapfel Dustin J. , Lowe K. Todd , O’Brien Walter F.
Published: January 2021

Over the last decade, the Turbomachinery and Propulsion Research Laboratory at Virginia Tech has researched, invented, developed, computationally analyzed, experimentally tested, and improved turbofan engine inlet distortion generators. This effort began with modernizing and improving inlet total pressure distortion screens originally conceived over half a century ago; continued with the invention of inlet swirl distortion generators (StreamVanes™) made possible only through advances in modern additive manufacturing technology; and has, thus far, culminated in a novel combined device (ScreenVanes™) capable of simulating realistic flight conditions of coupled inlet total pressure and swirl distortion in a ground-test turbofan engine research platform.

The present research focuses on the methodology development, computational analysis, and experimental validation of a novel simultaneous inlet total pressure and swirl distortion generator. A case study involving a single bend S-duct inlet distortion profile demonstrates the ability to generate a high-fidelity profile simulation, yet outlines a design process sufficiently generic for application to any arbitrary inlet geometry or distortion profile. A computational fluid dynamics simulation of the S-duct inlet provided the target profile extracted at the aerodynamic interface plane. Next, utilizing a method of inverse propagation, the planar distortion profile was propagated upstream to yield a flow field that could be manufactured by a distortion generator adequately isolated from turbomachinery effects. The total pressure distortion screen and swirl distortion StreamVane components were then designed and computationally analyzed. Upon successful computational reproduction of the S-duct inlet distortion profile, experimental hardware was fabricated and tested to validate the ScreenVane methodology and distortion generating device.

Comparison of the S-duct manufactured distortion and the ScreenVane manufactured distortion was used as the primary criterion for profile replication success. Results from a computational analysis of both the S-duct and ScreenVane indicated excellent agreement in distortion pattern shape, extent, and intensity with full-field total pressure recovery and swirl angle profiles matching within approximately 0.80% and 2.6°, respectively. Furthermore, experimental validation of the ScreenVane indicated nearly identical full-field total pressure recovery and swirl angle profile replication of approximately 1.10% and 2.6°, respectively, when compared to the computational results. The investigation concluded that not only was the ScreenVane device capable of accurately simulating a complex inlet distortion profile, but also produced a viable device for full-scale turbofan engine ground test.
Identification of High-Frequency Transverse Acoustic Modes in Multi-Nozzle Can Combustors
Authors: Kim J. , Gillman W. , Wu D. , Emerson B. , Acharya V. , Mckinney R. , Lieuwen T. , Isono M. , Saitoh T.
Published: January 2021

High frequency thermoacoustic instabilities are problematic for lean-premixed gas turbines. Identifying which acoustic mode is being excited is important, in that it provides insight into potential mitigation measures and mechanical stress/life. However, the frequency spacing between modes becomes quite close for high frequency instabilities in a can combustor. This makes it difficult to distinguish between the modes (e.g., the first transverse mode vs. a higher order axial/mixed mode) based upon frequency calculations alone, which inevitably have uncertainties in boundary conditions, temperature profiles, and combustion response. This paper presents a methodology to simultaneously identify the acoustic mode shapes in the axial and azimuthal directions from acoustic pressure measurements. Multiple high temperature pressure transducers, located at distinct axial and azimuthal positions, are flush mounted in the combustor wall. The measured pressure oscillations from each sensor are then used to reconstruct the pressure distributions by using a least squares method in conjunction with a solution of a three dimensional wave equation. In order to validate the methodology, finite element method (FEM) calculations with estimated post-flame temperature is used to provide the candidate frequencies and corresponding mode shapes. The results demonstrate the reconstructed mode shapes and standing/spinning character of transverse waves, as well as the associated frequencies, both of which are consistent with the FEM predictions. Nodal line location was also extracted from the experimental data during the instabilities in the pressure data.
Robust Design of a Fuel Cell-Turbocharger Hybrid System
Authors: Giugno Andrea , Mantelli Luca , Traverso Alberto
Published: January 2021

Pressurized solid oxide fuel cell systems are a particularly attractive conversion technology for their high electric efficiency, potential for cogeneration applications, low carbon emissions and high performance at part-load. In this work an innovative biofueled hybrid system is considered, where the fuel cell stack is pressurized with a turbocharger, resulting in a system with improved cost effectiveness than a microturbine-based one at small scales.

In a previous work, a detailed steady state model of the system, featuring components validated with industrial data, was developed to simulate the system and analyze its behavior in different conditions. The results obtained from this model were used to create response surfaces capable of evaluating the impact of the main operating parameters (fuel cell area, stack current density and recuperator surface) on the performance and the profitability of the plant considering system uncertainties.

In this paper, similar but extended response surfaces will be used to perform a multi-objective optimization of the system considering the capital costs of the plant and the net power produced as objectives (turbocharger is fixed in geometry). The impact of the energy market scenario on the optimal design of such a system will be investigated considering its installation in three different countries. Finally, the Pareto front produced by optimization will be used to evaluate the robustness of the top performance solutions.
Numerical Analysis of Dilution Holes Deterioration Impacting the Performance of a V2500 Combustor
Authors: Konle Marco , de Guillebon Ludovic , Schäflein Lukas
Published: January 2021

In aero engine combustors, dilution air jets are used to additionally tailor the temperature field, the emissions, and the turbine inlet profile. These jets are entering the combustion chamber at different axial and circumferential locations through dedicated holes in the combustor liners. By deterioration, the diameters of these holes can significantly change over operation time. To evaluate the impact of such deterioration in the MRO context, the authors created a numerical model of a V2500 aero engine combustor and analyzed the impact. The data of dilution holes deterioration is based on the nominal design according the engine manual and the deviation measured for three engine combustors during maintenance inspection.

The processes inside an aero engine combustor are very complex. To achieve most reliable information, a multi-physics approach was chosen for this evaluation. Validated in the past with a wide range of different academic test cases as well as industrial combustor test rigs, the evaluation allows conclusive analyses of the described deterioration. Back-to-back comparisons of individual variations reveals the most significant dilution holes row and give information about potential local shifts in combustor liner heat loads as well as in the exit profiles. Especially the distortion of the film cooling by the local interaction with the dilution jets could be observed.

Since the deterioration of the dilution holes measured for the three combustors inspected is very small compared to the nominal design, the authors payed a lot of attention also on analyzing the model sensitivity. Increasing the spatial resolution, the plausibility of the numerical results were checked by analyzing the flow splits and the dilution jets penetration. The final step was the variation of the dilution holes individually and combined and the evaluation of resulting temperature distribution at the combustor liners and changes in the exit profile.

Due to the fact that a multi-physics solver developed in the framework of OpenFOAM could be used, the authors could do these quite intensive CFD studies highly parallelized and, thus, in an acceptable time. The scalability of the solver reported already in former publications could be shown also in this application to the real engine combustor with a high level of complexity.
Design and Aerodynamic Performance Investigations of Centrifugal Compressor for 150kW Class Supercritical Carbon Dioxide Simple Brayton Cycle
Authors: Cao Run , Li Zhigang , Deng Qinghua , Li Jun
Published: January 2021

The centrifugal compressor is the key component to improve the SCO2 cycle efficiency. In this paper, according to 150kW class supercritical carbon dioxide (SCO2) simple Brayton cycle, a centrifugal compressor with rotating speed 60000r/min is designed. For the small-scale SCO2 centrifugal compressor, the impeller tip clearance loss accounts for most of the aerodynamic loss. Therefore, the designed compressor performance is numerically studied by the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k-ε (Extended Wall Function) turbulence model. The large variations in physical properties for SCO2 near the critical make simulation be difficult to convergence. To keep the numerical stability and accuracy, 400 × 400 resolution physical properties tables are adopted by the physical properties tables verification. The designed SCO2 centrifugal compressor is with the isentropic efficiency of 73.2% and the pressure ratio of 2.207 under the design flow condition, and good off-design conditions performance are obtained. Compared to the flow condition without the impeller tip clearance, the isentropic efficiency of designed compressor decreases by 14%. For the impeller tip clearance leakage flow, the flow can be divided into three regions, the separation flow region which is along the mainstream flow direction, the back flow region which occupies the top of the impeller tip clearance and the downstream flow region which occupies the bottom of the impeller tip clearance. These flow phenomena and their causes are analyzed. The obtained results reveal that the designed centrifugal compressor meets the requirement of the aerodynamic performance for the 150kW class simple Brayton cycle. The detailed flow pattern of the designed SCO2 centrifugal compressor with consideration of the impeller tip leakage flow is also illustrated.
Geometrical Variability Modelling of Axial Compressor Blisk Aerofoils and Evaluation of Impact on the Forced Response Problem
Authors: Gambitta Marco , Kühhorn Arnold , Schrape Sven
Published: January 2021

The present work focuses on the effect of the manufacturing geometrical variability on the high-pressure compressor of a turbofan engine for civil aviation. The deviations of the geometry over the axial compressor blades are studied and modeled for the representation in the computational models. Such variability is of particular interest for the forced response problem, where small deviations of the geometry from the ideal nominal model can cause significant differences in the vibrational responses. The information regarding the geometrical mistuning is extracted from a set of manufactured components surface scans of a blade integrated disk (blisk) rotor. The optically measured geometries are parameterized, defining a set of opportune variables to describe the deviations. The dimension of the variables domain is reduced using the principal component analysis approach and a reconstruction of the modeled geometries is performed for the implementation in CFD and FEM solvers. The generated model allows a stochastic representation of the variability, providing an optimal set of variables to represent it. The aeroelastic analyses considering geometry based mistuning is carried out on a test-rig case, focusing on how such variability can affect the modal forcing generated on the blades. The force generated by the unsteady pressure field over the selected vibrational mode shapes of the rotor blades is computed through a validated CFD model. The uncertainty quantification of the geometrical variability effect on the modal forcing is performed employing Monte Carlo methods on a reduced model for the CFD solution, based on a single passage multi-blade row setup. The amplitude shift of the unsteady modal forcing is studied for different engine orders. In particular the scatter of the main engine orders forcing amplitudes for the manufactured blades can be compared with the nominal responses to predict the possible amplification due to the geometrical variability. Finally the results are compared to a full assembly computational model to assess the influence of multiple variable blades.
Lean Operation of a Pulse Detonation Combustor by Fuel Stratification
Authors: Habicht Fabian E. , Yücel Fatma C. , Hanraths Niclas , Djordjevic Neda , Paschereit Christian Oliver
Published: January 2021

Pressure gain combustion is a promising concept to substantially increase the thermal efficiency of gas turbines. One possible implementation that has been frequently investigated are pulse detonation combustors (PDCs), as they permit stable and reliable operation. At the same time, the need for part-load operation and low NOx emissions requires combustion concepts in the lean regime. However, realizing lean combustion is still very challenging in PDCs since the deflagration to detonation transition (DDT) is very sensitive to the reactant composition.

The present work investigates an approach to realize lean combustion in PDC by applying fuel stratification experimentally. The scope is to find the necessary increase of fuel concentration inside the pre-detonation chamber to provide reliable DDT with respect to the overall equivalence ratio. Emission measurements in the exhaust of the PDC allow for a quantification of the NOx emissions as a function of the injected fuel profile.

A valveless PDC test rig is used, which contains a shock focusing geometry for detonation initiation and is ignited by a spark plug close to the upstream end wall. The subsequent expansion of the burned gas and interaction of the flame front with turbulence leads to the formation of a leading shock inside the pre-detonation chamber, which is then focused inside a converging-diverging geometry. The successful initiation of a detonation wave by shock focusing is very sensitive to the pressure ratio across the leading shock, which can be influenced by initial pressure, reactant composition and flow velocity.

Results reveal that fuel stratification allows for reliable detonation initiation at a global equivalence ratio of ϕglob = 0.65, whereas repeatable successful operation with non-stratified fuel injection is limited to ϕglob ≥ 0.85.
Wall Temperature Measurements in a Full Scale Gas Turbine Combustor Test Rig With Fiber Coupled Phosphor Thermometry
Authors: Nau Patrick , Görs Simon , Arndt Christoph , Witzel Benjamin , Endres Torsten
Published: January 2021

Wall temperature measurements with fiber coupled online phosphor thermometry were, for the first time, successfully performed in a full scale H-class Siemens gas turbine combustor. Online wall temperatures were obtained during high-pressure combustion tests up to 8 bar at the Siemens CEC test facility. Since optical access to the combustion chamber with fibers being able to provide high laser energies is extremely challenging, we developed a custom-built measurement system, consisting of a water-cooled fiber optic probe and a mobile measurement container. A suitable combination of chemical binder and thermographic phosphor was identified for temperatures up to 1800 K on combustor walls coated with a thermal barrier coating (TBC). To our knowledge these are the first measurements reported with fiber coupled online phosphor thermometry in a full scale high-pressure gas turbine combustor. Details of the setup and the measurement procedures will be presented. The measured signals were influenced by strong background emissions, probably from CO2* chemiluminescence. Strategies for correcting background-emissions and data evaluation procedures are discussed. The presented measurement technique enables detailed study of combustor wall temperatures and using this information an optimization of the gas turbine cooling design.
Influence of Inlet Distortions on the Forced Vibration of a High Pressure Compressor Rig
Authors: Franz Falco , Kühhorn Arnold , Giersch Thomas , Figaschewsky Felix , Schrape Sven
Published: January 2021

This paper aims at getting a better understanding of the simulative prediction of low engine order excitations in axial compressors. The focus is on the influence of inlet distortions on the forced response of a 4.5-stage research compressor rig. The papers starts with a brief description of the rig. After that the numerical setups required to conduct aerodynamic damping and forced response analyses are presented. Experimental data obtained during a rig test campaign show a significant response of a fundamental mode of the rotor 2 blisk to a low engine order 4. This resonance is studied throughout the paper. A superposition effect of different low engine order 4 sources was observed when changing the clocking of the inlet distortion. The vibrational amplitudes are computed using a subset of nominal system modes model incorporating a measured mistuning distribution. Measured amplitude versus blade patterns are compared with those computed by the aeromechanical models. The observed superposition effect is a key finding and is leveraged to establish comparability of the results.
Exploring Applicability of Acoustic Heat Transfer Enhancement Across Various Perturbation Elements
Authors: Agarwal Tapish , Stratmann Maximilian , Julius Simon , Cukurel Beni
Published: January 2021

The requirements of improved heat transfer performance on turbine surfaces and internal cooling passages drive the research into exploring new methods for efficiency enhancements. Addition of ribbed structures inside the cooling ducts has proven to be most practical, which increases heat transfer from surfaces to fluid flow at the cost of some pressure loss. Many active and passive methods have been proposed for enhancing the heat transfer, where acoustic excitation has been recently shown to be an effective option. Moreover, the existing pressure fluctuations due to rotor-stator interactions can also be utilized as a source of excitation. However, the sensitivity of the phenomenon to various flow and geometric parameters has not been fully characterized.

The present study investigates various aspects of convective heat transfer enhancement and turbulent flow modulation caused by acoustic forcing on separating and reattaching flow over isolated rib obstacles. A parametric study is conducted; rib obstacles of various sizes and shapes (including rectangular, squared, triangular, semi-cylindrical, etc.) are installed in a low-speed, fully turbulent wind tunnel and measurements are taken at different velocities and excitation frequencies. Static pressure and spatially resolved surface temperature measurements are performed to quantify the ramifications of acoustic excitation on the wetted wall. Within the favorable Strouhal number range of 0.1–0.25, an optimum value of 0.16 is observed. It is shown that triangular ribs are more prone to acoustic heat transfer enhancement than rectangular or cylindrical perturbations. A linear correlation between static pressure recovery rate and acoustic heat transfer enhancement is observed, which is invariant to change in size/shape of the rib as well as flow and excitation parameters.
Experimental and Numerical Characterization of a Novel Natural Gas Low NOx Burner in Gas Turbine Realistic Environment
Authors: Cerutti Matteo , Nassini Pier Carlo , Pampaloni Daniele , Andreini Antonio
Published: January 2021

A fundamental milestone in the development of a low NOx burner technology is the demonstration of its capabilities in realistic environment. This is especially true for the novel burner subject of this paper, which has been extensively characterized throughout single burner scale experiments. An exhaustive description of the early development phases of the novel burner has been provided by authors in recently published works.

The most promising geometry was selected for the assessment in real combustor arrangement, consisting of a full-scale annular combustor test rig. This paper reports the main results of such an assessment. Pollutant emissions and pressure pulsations have been measured at gas turbine relevant operating conditions. Moreover, dedicated blow-out tests have been performed to obtain the extinction equivalence ratio at both ambient and pressurized conditions, as done during the past single burner rig campaign. Basically, an adequate set of data has been gathered, allowing a direct comparison between full-annular and reduced-scale tests.

A general alignment of behaviour has been observed, as both low NOx capability and blow-out characteristics of full-annular arrangement turned out to be substantially unchanged with respect to single burner. Nevertheless, some discrepancies in magnitude have been highlighted and discussed. Details have been given involving deeper numerical analysis by means of a dedicated model developed by the authors in previous works. Indeed, improvement to the model has been introduced in the context of this paper to overcome some limitations arisen in predicting emissions. Finally, a preliminary stability analysis has been carried out, with the aim to describe the onset of thermoacoustic instability tendency as observed in the full-annular tests.
A Methodology to Characterize Modal Damping in Vibrating Systems: Application to the Case of Gas Turbine Combustion Chambers
Authors: Amedei Andrea , Meli Enrico , Rindi Andrea , Pucci Egidio
Published: January 2021

The present paper proposes a methodology to characterize the modal damping ratio as a function of frequency in vibrating systems, with a focus on gas turbine combustion chambers. Proposed methodology correlates the modal damping ratio to the system modal eigenfrequencies, accurately considering the damping physical effects on the system dynamics and goes beyond the standard proportional damping hypothesis and similar techniques present in the literature.

The methodology has been compared under free-free conditions with standard damping ratio laws that can be found in the literature and which may lead sometimes to an overestimation of the real damping ratio values. Experimental data obtained through dedicated ping tests performed on two components of an industrial gas turbine annular combustion chamber have been used for the methodology validation: comparison between simulated and experimental results seems to be encouraging and the proposed methodology for modal damping ratio characterization turns out to be better, with respect to the standard ones, in reproducing not only the experimentally estimated damping law (as a function of the frequency), but also the typical Force Response Functions (FRFs) of the considered vibrating systems.

Finally, since the adopted procedure is numerically efficient and based only on low cost experimental techniques, it can be used for describing modal damping in vibrating systems since the early phases of the design, by increasing the design accuracy and reducing times and costs.
Prompt Atomization Mechanism of the Tangentially Injected Prefilming (TIP) LDI Injector
Authors: Wang Yuwei , Han Xiao , Lin Yuzhen
Published: January 2021

Lean direct injection (LDI) combustion is one of the promising low pollution combustion technologies. One challenge of implementing LDI combustion is to achieve quick fuel-atomizing and mixing with air. In this paper, the spray characteristics and the prompt atomization process of the tangentially injected prefilming (TIP) LDI injector are investigated by experiments; the energy transmission model suitable for the prompt atomization process and the semi-empirical estimation model of SMD for the conical liquid film are derived. All experiments were carried out under 20°C and atmospheric pressure by using kerosene as the fuel. Firstly, effects of We and ALR on the spray distribution and SMD were studied by Mie scattering and Malvern spraytec laser diffraction system respectively, which were carried out at the operating conditions of We varying from 664 to 2656 and ALR varying from 16.3 to 24.5. Results show that large We is beneficial to disperse the spray in primary zone downstream the swirler. Then, breakup regimes of liquid film and droplets evolution were characterized by a high-speed camera with a long-distance microscope (LDM). Breakup regimes show that the film is torn up by the fierce outer airstream immediately. The primary breakup process does not rely on the surface waves anymore, which conforms to the prompt atomization mechanism. Finally, the energy transmission of the conical liquid film during the whole atomization process was analyzed, from which the semi-empirical estimation model of SMD was derived. The calculated and the measured SMD have good consistency, which demonstrates the applicability of the prompt atomization energy transmission model on a conical liquid film.
The Multi-Phase Flow Test Facility “EMMA” to Investigate Local Heat Transfer Coefficients and Liquid Water Films at Wet Steam Conditions
Authors: Lapp Florian Felix , Hecker Simon , Schuster Sebastian , Brillert Dieter
Published: January 2021

Conventional power plants are obliged to compensate for the fluctuations in power generation, due to the rising amount of renewable energies, to ensure grid stability. Consequently, steam turbines are more frequently facing load variation and startup/shut-down cycles leading to an increase of thermal stress induced by phase change phenomena. The review of existing test facilities providing measurement data of heat transfer coefficients influenced by multiphase phenomena, such as surface wettability and dry-out, revealed the necessity for a new measurement application. This paper presents the design of the Experimental Multi-phase Measurement Application “EMMA” to generate the required conditions in combination with an academic turbine housing geometry. The performed investigations are focused on the local distribution of heat transfer coefficients (HTC) and the surface wettability affected by phase change phenomena. Two main film formation mechanisms can be observed, depending on the thermal gradient between the fluid and the wall. These are a) saturated/superheated steam in contact with a sub-cooled wall leading to film-wise/drop-wise condensation and b) primary condensed wet steam droplets depositing on a superheated wall, leading to evaporation. Both, the liquid film and the local heat transfer are measured simultaneously. An overview of applicable thickness measurement methods for transparent liquid films is given and the applied optical measurement system is further described. Moreover the HTC measurement methods are presented considering the occurring case of phase change.
Hybrid Numerical-Experimental Model Update Based on Correlation Approach for Turbine Components
Authors: Saeed Zeeshan , Firrone Christian Maria , Berruti Teresa Maria
Published: January 2021

Bladed-disks in turbo-machines experience high cycle fatigue failures due to high vibration amplitudes. Therefore, it is important to accurately predict their dynamic characteristics including the mechanical joints at blade-disk (root joint) or blade-blade (shroud) interfaces. These joints help in dampening the vibration amplitudes. Before the experimental identification of these joints, it is of paramount importance to accurately measure the interface degrees-of-freedom (DoF). However, they are largely inaccessible for the measurements. For this reason, expansion techniques are used in order to update the single components before their coupling. But the expansion can be affected adversely if the measurements are not properly correlated with the updated model or if they have significant errors.

Therefore, a frequency domain expansion method called System Equivalent Model Mixing (SEMM) is used to expand a limited set of measurements to a larger set of numerical DoF. Different measured models — termed the overlay models — are taken from an impact testing campaign of a blade and a disk and coupled to the numerical model according to the SEMM. The expanded models — termed the hybrid models — are then correlated with the validation channels in a round-robin way by means of Frequency Response Assurance Criteria (FRAC). The global correlations depict whether or not a measurement and the respective expansion is properly correlated. By this approach, the least correlated channels can be done away with from the measurements to have a better updated hybrid model.

The method is tested on both the structures (the blade and the disk) and it is successfully shown that removing the uncorrelated channels does improve the quality of the hybrid models.
A Combined Experimental and Numerical Characterization of the Flowfield and Heat Transfer Around a Multiperforated Plate With Compound Angle Injection
Authors: Laroche Emmanuel , Donjat David , Reulet Philippe
Published: January 2021

The aerodynamic and thermal behaviour of multiperforated zones in combustors is essential to the development of future combustion chambers. Detailed databases are therefore essential for the validation of RANS/LES solvers, but also regarding the derivation of heat transfer correlations used in 0D/1D in-house codes developed by engine manufacturers. In the framework of FP7 EU SOPRANO Program, the test-rig used in a previous study is modified to be compatible with anisothermal conditions. The plate studied is a 12:1 model with a 90° compound angle injection. A heating system is used to generate a moderate temperature gradient of about 20 K between the secondary hot flow and the main cold flow. The aerodynamic field is acquired by a PIV 2D-3C (Particle Image Velocimetry) system. The surface heat transfer coefficient is derived based on surface temperature distribution acquisitions. Several heating power levels are tested, which allows to evaluate the convective heat transfer coefficient and reference temperature through a linear regression. Measurements are conducted on both sides of the plate, which also gives access to those quantities on the injection/suction sides. From a numerical point of view, the configuration is studied using the unstructured ONERA in-house CEDRE solver. A systematic comparison is presented between the experimental and numerical database.
Effect of Geometric Uncertainty on a One Stage Transonic Compressor of an Industrial Gas Turbine
Authors: Venkatesh S. , Suzuki K. , Vahdati M. , Salles L. , Rendu Q.
Published: January 2021

The geometrical uncertainties can result in flow asymmetry around the annulus of compressor which in turn can detrimentally affect on the compressor stability and performance. Typically these uncertainties arise as a consequence of in-service degradation and/or manufacturing tolerance, both of which have been dealt with in this paper. The paper deals with effects of leading edge damage and tip gap on rotor blades. It was found that the chord-wise damage is more critical than radial damage.

It was found that a zigzag pattern of arranging the damaged rotor blades (i.e. most damaged blades between two least damaged blades) would give the best possible performance and stability when performing maintenance and overhauling while a sinusoidal pattern of arrangement had the worst performance and stability. This behaviour of zigzag arrangement of random damaged blades is consonant with the behaviour of zigzag arrangement in random tip gaps. It is also shown in this work that the level of damage has a bigger impact on the compressor performance and stability than the number of damaged blades.
Platform Centered Reduction: A Process Capturing the Essentials for Blade-Damper Coupled Optimization
Authors: Gastaldi Chiara , Gola Muzio M.
Published: January 2021

The purpose of this document is to continue along the line of research of the authors in the direction of developing an attractive tool for designers in the initial design phase of the damping of the turbomachinery blades. In particular, in order to guide their initial choice of a dry friction underplatform damper in the most appropriate way. The paper shows how, to this purpose, certain reasonable simplifications are introduced in the procedure and in the model, leaving the customary full high fidelity computations to the final design verification analysis. The key simplifications here considered are:

– the blade neck is modelled with Euler beam finite elements so to speed up the updating of its dimensions during the optimisation process;

– the contact forces exerted by the dampers on the two sides of the blade platform are represented by the resultant forces and moments applied to a reference point on the platform, associated to its displacements and rotations;

– as an improvement to the model proposed in the paper presented at Turbo Expo 2019, the airfoil is now obtained from a full 3D FE model after a component mode synthesis reduction; this choice is justified by the facts that the airfoil is by large the item with most complex shape and that during the coupled optimization of the damper the airfoil is considered to be of fixed shape.

It is shown that the process captures the essentials of the nonlinear dynamics of the blade-damper problem without sacrificing in any way the accuracy of the results.

This hybrid model is then employed in the process where the domains of optimal matching between the damper and the blade is searched for by exploring the influence of blade neck thickness (flexibility) and damper mass. Such a purposely simplified process allows a clear identification of relationships between relevant blade features and response with a focus on fatigue life. At the same time, it allows an assessment of the interplay between blade parameters and damper parameters in determining the modal features and the damping capabilities. It is shown how different matching solutions may be identified depending on the expected forcing level on the blade.
Sizing and Operation of a Hybrid Energy Plant Composed of Industrial Gas Turbines, Renewable Energy Systems and Energy Storage Technologies
Authors: Bahlawan Hilal , Gambarotta Agostino , Losi Enzo , Manservigi Lucrezia , Morini MIrko , Spina Pier Ruggero , Venturini Mauro
Published: January 2021

Hybrid energy plants, which include both fossil fuel technologies and renewable energy systems, can provide an important step towards a sustainable energy supply. In fact, the hybridization of renewable energy systems with gas turbines which are fed by fossil fuels allows an acceptable compromise, so that high fossil fuel efficiency and high share of renewables can be potentially achieved. Moreover, electrical and thermal energy storage systems increase the flexibility of the energy plant and effectively manage the variability of energy production and demand.

This paper investigates the optimal sizing of a hybrid energy plant which combines an industrial gas turbine, renewable energy systems and energy storage technologies. The considered renewable energy system is a photovoltaic system, while the energy storage technologies are electrical energy storage and thermal energy storage. Moreover, a compression chiller and a gas boiler are also considered. For this purpose, the load profiles of electricity, heating and cooling during a whole year are taken into account for the case study of the Campus of the University of Parma (Italy). The sizing optimization problem of the different technologies composing the hybrid energy plant is solved by using a genetic algorithm, with the goal of minimizing primary energy consumption. Moreover, different operation strategies are analyzed and compared so that plant operation is also optimized.

The results demonstrate that the optimal sizing of the hybrid energy plant, coupled with the optimized operation strategy, allows high average cogeneration efficiency (up to 84%), thus minimizing primary energy consumption.
Dynamic Stress Analysis of Exposed Pipes Subjected to Moving In-Line Inspection Tool
Authors: Mostaghimi Hamid , Hassani Mohsen , Yu Deli , Hugo Ron , Park Simon
Published: January 2021

In-line inspection is a non-destructive assessment method commonly used for defect assessment and monitoring of pipelines. The passage of an ILI tool through an excavated or exposed section of a pipe during an integrity assessment can excite vibrations and exert substantial forces, stress, and deflections on the pipe due to the weight and speed of the ILI tool. When the excitation frequency due to the ILI tool movement is close to the natural frequency of the overall structure, the dynamic stress generated within the pipe can be large enough to the extent that it imposes integrity concern on the line. This research aims to study effects of the ILI tool passage through floating and partially supported pipes under a variety of boundary and loading conditions. A finite element method is used to model the pipe with moving ILI tool. The model is developed based on Timoshenko beam theory with planar degrees-of-freedom and the differential equations of motion are solved numerically to predict displacement, strain, stress, and frequency responses of the pipe. The model is further validated using a lab-scale experimental setup. The comparison of the simulation to experimental results show how the proposed model is capable of predicting pipe dynamics, effectively.
Dynamic Thrust Loads on Piping From Blowdown Stacks to Silencers at a Remote Distance Away
Authors: Botros Kamal K. , Martens Michael
Published: January 2021

Current trends in greenfield natural gas compression facilities and high-pressure gas transmission pipelines are designs for high pressure operation, e.g. PN150. At such high pressures, sound pressure level (SPL) of the noise generated during a planned blowdown can be as high as 165–175 dBA at 1 m distance away from the blowdown stack tip. Even double hearing protection would not be sufficient for an operator opening the blowdown valve at the blowdown assembly even for a short period of time. Blowdown silencers mounted on top of the blowdown stack are limited to the degree of noise suppression they offer (typically of the order of 30 to 40 dB), let alone the requirement for extensive support structures to hold the massive weight on the stack top. One innovation to alleviate this issue, is to place a silencer on a skid on a ground-level pad/support system, at a sufficient distance away from the blowdown stack. In this way, the blowdown valve operator would be exposed to a much lower SPL, as well as the silencer can be as large as desired being skid mounded on the ground. The main issue to be addressed is the dynamic thrust loads That would otherwise be afflicted on the various pipe segments of the piping connecting the blowdown stack top to the location of the blowdown silencer located distance away. Clearly this piping will include several above ground pipe segments, bends, tees and fittings that need to be adequately supported to withstand the dynamic loads as the blowdown valve opens. This paper presents a model approach based on solving the temporal-spatial governing equations in the form of 1-D hyperbolic differential equations, with boundary conditions accounting for the blowdown valve size and type, trim characteristics and opening time, upstream gas pressure and temperature, and downstream restriction equivalent orifice size at the inlet to the blowdown silencer. Results are presented for a case study of a single and dual blowdown assemblies equipped with reduced-bore ball valves (8″ × 6″), with lead piping of NPS 8 joining into NPS 12 header and finally splitting into two ground mounted silencers some 30 meters away. Thrust loads at each segment of these connecting piping were found to depend on whether one or dual blowdown valves are open simultaneously, upstream pressure, and more importantly the location of the choke point (Mach = 1) whether at the blowdown valve itself or at the silencer inlet diffuser orifice. The later was found to be the most critical parameter. The most important objective when designing such a system is to ensure that the choke point is at the silencer inlet orifice to minimize thrust loading on the blowdown valve(s) as well as along the entire lead piping.
Sand Dune Migration Monitoring for Pipeline Hazard Risk Mitigation: The Peru LNG Coastal Section Case
Authors: Ravet Fabien , Silva Christian , Gil Rodolfo , Maguire Simon , Rochat Etienne
Published: January 2021

Pipelines often cross challenging terrains where natural hazards are the main risk for their integrity. Environmental conditions can also worsen over the infrastructure lifetime. To reduce the risk of disasters, integrity programs are developed implementing tools for early detection of threats that can lead to a failure with dramatic social, environmental and economic consequences. Fiber optic (FO) monitoring solutions have been widely used and implemented as one of the most efficient prevention tools of these programs. These solutions include geotechnical monitoring, third party intrusion detection and eventually small or pinhole like leak detection.

FO based geotechnical monitoring has been successfully operated along the Sierra section of the Peru LNG pipeline since 2010, detecting minor landslides and erosion events. It has also been implemented along other hydrocarbon transport systems to allow the early detection of such events. However, these natural hazards are not the only ones threatening the pipeline. In fact, the coastal section experiences other phenomenon such as sand dune migration and eolian erosion that put the pipeline at risk. Recently, the FO monitoring was extended to the coastal region using the existing communication fiber optic cable to sense temperature changes. Very localized events are thermally detected, their spatial and temporal signature analyzed. The comparison of this data with thermal models identified sections that are close to be exposed or whose soil cover is less than 50cm over a spatial extension that does not exceed a couple of meters. Depth of cover of 10 to 30cm is estimated from such analysis. These results are confirmed by past and ongoing site inspections. Such positive results again illustrate the potential value of fiber optic sensing to mitigate geohazard risks. It not only enhances the efficiency of the integrity program detecting and localizing threats, it also improves and rationalizes the maintenance activities as focused surveys can be conducted.