bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Study on the Effect of Inter-Stage Water Injection in an Opposed-Setting-Two-Stage Centrifugal Compressor
Authors: Ni Ming , Geng Shaojuan , Wei Zuojun , Gan Xiaohua
Published: January 2021

Inter-stage water injection is currently a common method to reduce the compression work. In this paper, we evaluate the effect of this approach on an opposed-setting-two-stage centrifugal compressor which is designed for a small gas turbine numerically. The Eulerian-Lagrangian method is adopted to calculate the continuous flow field and discrete particle terms with the k-ε turbulence model. 6 water injection conditions are conducted to compare with the dry air condition. The performance curve shift to the right-up side, i.e. higher total pressure ratio, higher efficiency and larger choking mass flow. However, the larger the performance improvement gained by inter-stage injection, the worse the stability will be. Under the micro injection ratio (about 0.1%), the stall margin of the compressor is improved. Additionally, with a proper injection parameter, the loading in the diffuser can be reduced and promise a wider stall margin. Nevertheless, there still exists droplets at the outlet of the high-pressure diffuser because of the insufficient time for evaporation.
Acoustic Energy Balance During the Onset, Growth and Saturation of Thermoacoustic Instabilities
Authors: Gaudron R. , Yang D. , Morgans A. S.
Published: January 2021

Thermoacoustic instabilities can occur in a wide range of combustors and are prejudicial since they can lead to increased mechanical fatigue or even catastrophic failure. A well-established formalism to predict the onset, growth and saturation of such instabilities is based on acoustic network models. This approach has been successfully employed to predict the frequency and amplitude of limit cycle oscillations in a variety of combustors. However, it does not provide any physical insight in terms of the acoustic energy balance of the system. On the other hand, Rayleigh’s criterion may be used to quantify the losses, sources and transfers of acoustic energy within and at the boundaries of a combustor. However, this approach is cumbersome for most applications because it requires computing volume and surface integrals and averaging over an oscillation cycle. In this work, a new methodology for studying the acoustic energy balance of a combustor during the onset, growth and saturation of thermoacoustic instabilities is proposed. The two cornerstones of this new framework are the acoustic absorption coefficient Δ and the cycle-to-cycle acoustic energy ratio λ, both of which do not require computing integrals. Used along with a suitable acoustic network model, where the flame frequency response is described using the weakly nonlinear Flame Describing Function (FDF) formalism, these two dimensionless numbers are shown to characterize: 1) the variation of acoustic energy stored within the combustor between two consecutive cycles, 2) the acoustic energy transfers occurring at the combustor’s boundaries and 3) the sources and sinks of acoustic energy located within the combustor. The acoustic energy balance of the well-documented Palies burner is then analyzed during the onset, growth and saturation of thermoacoustic instabilities using this new methodology. It is demonstrated that this new approach allows a deeper understanding of the physical mechanisms at play. For instance, it is possible to determine when the flame acts as an acoustic energy source or sink, where acoustic damping is generated, and if acoustic energy is transmitted through the boundaries of the burner.
Investigation of Similarity Criteria for an Internally-Cooled Turbine Vane Based on Artificial Neural Networks: Part II — Experimental Validation
Authors: Zhao Weicheng , Wei Jingying , Chi Zhongran , Zang Shusheng
Published: January 2021

In the second part of this two-part paper, several CHT (Conjugate Heat Transfer) CFD (Computational Fluid Dynamics) simulations were conducted at low temperature and pressure conditions which a 100KW or a 400KW blower can provided, in order to investigate the reason caused the modeling deviation when the matched-Biot number criterion is used for modeling. The CFD method used in this paper is the same as the Part I. Afterwards, several experiments were carried out at a mainstream condition which the 100 KW blower can provide to validate whether the deviations predicted by CFD would appear at that target modeling conditions. The mainstream inlet temperature and pressure are 307 K and 113 kPa, respectively. The model used in this paper is the Mark II turbine as well.

The CFD and experiment results show that the main source of the modeling deviation comes from the suction side, the minimum deviation for the four modeling tests has over 0.05 (minimum wall temperature deviation has over 0.75 K). Apart from that, the reason leading to the suction side deviation is the variation of temperature boundary layer, which is caused by the unmatched aerodynamic parameters (such as mainstream Mach number and Reynolds number).
Finding the Best Architecture of an Artificial Neural Network to Model Prefilming Airblast Atomization: Not So Deep Learning
Authors: Chaussonnet G. , Gepperth S. , Holz S. , Koch R. , Bauer H.-J.
Published: January 2021

A fully connected Artificial Neural Network (ANN) is used to predict the spray characteristics of prefilming airblast atomization. The model is trained from the planar prefilmer experiment from the PhD thesis of Gepperth [Experimentelle Untersuchung des Primärzerfalls an generischen luftgestützten Zerstäubern unter Hochdruckbedingungen, Vol. 75. Logos Verlag Berlin GmbH], in which shadowgraphy images of the liquid breakup at the atomizing edge capture the characteristics of the primary droplets and the ligaments. The quantities extracted from the images are the Sauter Mean Diameter, the mean droplet axial velocity, the mean ligament length and the mean ligament deformation velocity. These are the prescribed output of the ANN model. In total, the training database contains 322 different operating points at which different prefilmers, liquid types, ambient pressures, film loadings and gas velocities were investigated. Two types of model input quantities are investigated. First, nine dimensional parameters related to the geometry, the operating conditions and the properties of the liquid are used as inputs for the model. Second, nine non-dimensional groups commonly used for liquid atomization are derived from the first set of inputs. These two types of inputs are compared. The architecture providing the best fitting is determined after testing over 10000 randomly drawn ANN architectures, with up to 10 layers and up to 128 neurons per layer. The striking results is that for both types of model, the best architectures consist of a shallow net with the hidden layers in the form of a diabolo: three layers with a large number of neurons (≥ 64) in the first and the last layer, and very few neurons (≈12) in middle layer. This shape recalls the shape of an autoencoder, where the middle layer would be the feature space of reduced dimensionality. The trend highlighted by our results, to have a limited number of layers, is in contrast with recent observations in Deep Learning applied to computer vision and speech recognition. It was found that the model with dimensional input quantities always shows a lower test and validation errors than the one with non-dimensional input quantities. The best architectures for both types of inputs (dimensional and non-dimensional input) were tested versus the experiments. Both provide comparable accuracy, which is better than typical correlations of SMD and droplet velocity. As the models takes more input parameters into account compared to the correlations, they can predict the experimental data more accurately. Finally the extrapolation capability of the models was assessed by a training them on a confined domain of parameters and testing them outside this domain. It was found that the models can extrapolate at larger gas velocity. With a larger ambient pressure or a lower trailing edge thickness, the accuracy decreases drastically.
The Flow Field Characteristic Correlated With Heat Transfer Performance in a Wide Channel With Staggered Circular Pin Fins
Authors: Duan Jingtian , Zhang Ke , Xu Jin , Lei Jiang , Wu Junmei
Published: January 2021

The velocity field in a wide rectangular channel (AR = 4) with staggered circular pin fin array was measured using Particle Image Velocimetry (PIV). The cylinder pin fin has a diameter of 8 mm and height to diameter ratio (H/D) of 3. The streamwise pitch (X/D) and spanwise pitch (S/D) of pin fins are 4.5 and 2 respectively. The experiment was conducted at two Reynolds number, 10000 and 20000, based on the hydraulic diameter and bulk velocity of the channel. The mean velocity, first-order statistics of velocity fluctuation and turbulent kinetic energy components in the measured plane are given. Results show, the distribution of the cross-stream velocity fluctuation (Vrms), other than second-order statistics, has a similar pattern as that of the local Nusselt number on the end wall between pin fin rows while the flow is in developing. The Nusselt number was achieved through temperature measurement using thermochromic liquid crystal in the same geometry setup. Therefore, compared to second-order statistics, the cross-stream velocity fluctuation might be a simple but crucial flow quantity for heat transfer enhancement using pin fins in the developing region. The shedding of large vortices from circular pin fins is believed to be the primary flow structure inducing the cross-stream velocity fluctuation. Study on pin fins with various geometries is required before further conclusion drawn.
On High-Resolution Pressure Amplitude and Phase Measurements Comparing Fast-Response Pressure Transducers and Unsteady Pressure-Sensitive Paint
Authors: Bitter Martin , Stotz Stephan , Niehuis Reinhard
Published: January 2021

This paper presents the simultaneous application of fast-response pressure transducers and unsteady pressure-sensitive paint (unsteady PSP) for the precise determination of pressure amplitudes and phases up to 3,000 Hz. These experiments have been carried out on a low-pressure turbine blade cascade under engine-relevant conditions (Re, Ma, Tu) in the High-Speed Cascade Wind Tunnel. Periodic blade/vane interactions were simulated at the inlet to the cascade using a wake generator operating at a constant perturbation frequency of 500 Hz. The main goal of this paper is the detailed comparison of amplitude and phase distributions between both flow sensing techniques at least up to the second harmonic of the wake generator’s fundamental perturbation frequency (i.e. 1,000 Hz). Therefore, a careful assessment of the key drivers for relative deviations between measurement results as well as a detailed discussion of the data processing is presented for both measurement techniques. This discussion outlines the mandatory steps which were essential to achieve the quality as presented down to pressure amplitudes of several pascal even under challenging experimental conditions. Apart from the remarkable consistency of the results, this paper reveals the potential of (unsteady) PSP as a future key flow sensing technique in turbomachinery research, especially for cascade testing. The results demonstrate that PSP was able to successfully sense pressure dynamics with very low fluctuation amplitudes down to 8 Pa.
Measurement and Analysis of Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors
Authors: Jackson Richard W. , Luberti Dario , Tang Hui , Pountney Oliver J. , Scobie James A. , Sangan Carl M. , Owen J. Michael , Lock Gary D.
Published: January 2021

The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 1013. This phenomenon creates a conjugate problem: the Nusselt numbers depend on the radial temperature distribution of the discs, and the disc temperatures depend on the Nusselt numbers. Furthermore, Coriolis forces in the rotating fluid generate cyclonic and anti-cyclonic circulations inside the cavity. Such flows are three-dimensional, unsteady and unstable, and it is a challenge to compute and measure the heat transfer from the discs to the axial throughflow in the compressor. In this paper, Nusselt numbers are experimentally determined from measurements of steady-state temperatures on the surfaces of both discs in a rotating cavity of the Bath Compressor-Cavity Rig. The data are collected over a range of engine-representative parameters and are the first results from a new experimental facility specifically designed to investigate buoyancy-induced flow. The radial distributions of disc temperature were collected under carefully-controlled thermal boundary conditions appropriate for analysis using a Bayesian model combined with the equations for a circular fin. The Owen-Tang buoyancy model has been used to compare predicted radial distributions of disc temperatures and Nusselt numbers with some of the experimentally determined values, taking account of radiation between the interior surfaces of the cavity.

The experiments show that the average Nusselt numbers on the disc increase as the buoyancy forces increase. At high rotational speeds the temperature rise in the core, created by compressibility effects in the air, attenuates the heat transfer and there is a critical rotational Reynolds number for which the Nusselt number is a maximum. In the cavity, there is an inner region dominated by forced convection and an outer region dominated by buoyancy-induced flow. The inner region is a mixing region, in which entrained cold throughflow encounters hot flow from the Ekman layers on the discs. Consequently, the Nusselt numbers on the downstream disc in the inner region tend to be higher than those on the upstream disc.
A Robust Model Reference Adaptive Control Framework for Integrated Flight Propulsion System
Authors: Wang Haonan , Wang Xi
Published: January 2021

In this paper, a robust model reference adaptive control framework for the integrated flight propulsion system has been proposed. It could serve as a general controller structure for the integrated flight propulsion system. The linear state feedback controller using LQR method is firstly designed under deterministic uncertainty-free conditions, serving as the reference model. Robust adaptive controller is thereafter introduced to make the system state trajectories converge to the reference model under parametric uncertainties. It is worth noting that, such an arrangement makes the whole control framework easy to be implemented as a modification to existing well designed linear controllers. Besides, high order complexities of the system can be resolved by decomposing it using singular perturbation method based on time scale. A formal stability proof will be provided.

The whole control framework has been implemented on a trim point of an F-16 model. Only actuator anomalies have been concerned as uncertainties to verify the effectiveness of the control framework. However, this structure can be easily extended to accommodate other parametric uncertainties. The simulation results of the controller implemented on the nonlinear system near an equilibrium point will be provided. Superior performance regarding stability and robustness can be observed from the simulation results with robust adaptive augmentation controller used.
Experimental Investigation of a Radial Wave Engine Utilizing a Rotary Valved Pressure Gain Combustor
Authors: Akbari Pejman , Brady Grant M. , Sell Brian C. , Polanka Marc D.
Published: January 2021

In this paper a deflagrative pressure gain combustor employing rotary valves is introduced that can reduce combustor length by allowing the combustion process to take place in the radial direction rather than in the axial direction with sufficient resident time. The engine is described in some detail with respect to geometry, components, and potential benefits. A demonstrator rig was designed, built, and tested for concept verification. A series of initial tests sweeping equivalence ratio from 0.4 to 0.8 using ethylene as fuel and mass flows from 75 g/s to 150 g/s is presented. The turbine rotor was driven to above 200 RPM with just four of the combustor passages operating. The initial results indicate the feasibility of the rotary valve radial engine concept and identified key challenges associated with the concept. Further studies are needed address existing challenges and to promote the engine development.
Comparison of Viscoplastic Modeling of an Equiaxed and Directionally Solidified Ni-Base Superalloy
Authors: O’Nora Nathan , Torkaman Alex , Gordon Ali P.
Published: January 2021

Engine components are subjected to both high temperatures and cyclic loads resulting in fatigue and creep effects. Directionally-solidified (DS) Ni-base superalloys were developed in order to produce favorable creep properties in the primary stress axis of turbine blades by casting the grains longer along this axis. Doing so causes the material to exhibit anisotropic behavior, which allows for improved fatigue and creep strength but also adds complexity to modeling the material. To predict the life of components accurately, it is necessary to use a high-fidelity constitutive model to relate the loading and the deformation of the material. The dual-phase microstructure of these DS superalloys evolves with time, rendering the yield surface of the material a challenge to track. Furthermore, components made from these materials are subjected to complex loading conditions, often seeing cycling temperature in addition to loads, known as thermomechanical fatigue (TMF), and cyclic loads with dwells, known as creep-fatigue (CF). Viscoplasticity models are able to capture the complex behaviors of these materials under complex loading conditions, including the hysteresis effects, rate-dependence, and stress relaxation, etc., making them attractive models to use with critically heated and loaded parts. These models, originally designed for equiaxed materials, have been adapted for use with anisotropic materials, such as DS superalloys. An isothermal anisotropic viscoplasticity model and parameter identification framework has been calibrated within a dedicated parameter identification framework. Principally, the constitutive model is based on the Chaboche viscoplasticity model featuring Armstrong-Frederick kinematic hardening. The performance of a preliminary model is presented for both an equiaxed (i.e., conventionally cast, CC) and DS materials within the same strength class, though more data is needed for validation. With regard to the stress relation associated with creep-fatigue, a fitting-technique for the static recovery model that has shown promise in isotropic materials is expanded to capture the behavior of the DS alloy. Previously developed methods for finding kinematic hardening constants for isotropic material based on Ramberg-Osgood constants at various orientations are expanded to an anisotropic case. These techniques allow for the capturing of more complex loading conditions with a limited number of tests, allowing for cost savings when developing the constitutive model. The model is implemented with three non-linear kinematic hardening terms with static recovery, allowing for the capture of rate and hold time effects, and non-linear isotropic hardening, allowing for the capture of cyclic hardening. The ability to capture the low cycle fatigue (LCF) behavior of both the equiaxed and DS alloys are examined through comparisons with test data.
A Model of Inlet Circumferential Fluctuation in Compressor Cascades
Authors: Yue Zixuan , Li Zefeng , Jin Donghai , Gui Xingmin
Published: January 2021

Through-flow methods are widely used in turbomachinery design and performance prediction due to its fast calculation. In the past, circumferentially-averaging through-flow methods tended to ignore circumferential fluctuation source term (CFST) in the governing equations, leading to an inaccurate result when blades showed a strong three-dimensional feature. To solve this problem, CFST needs to be properly modeled. In this paper, three-dimensional numerical simulation is conducted to find the area where CFST dominates. The influence of inlet Mach number, incidence, camber angles and sweep angle on the CFST in this area is analyzed. A model for CFST is constructed. Three-dimensional verification of this model suggests that within the common scope of use of aerospace compressor designing, this model shows a good accuracy.
Thermo-Structural Analysis of a Micro Gas Turbine Jet- and Recirculation- Stabilized Combustion Chamber
Authors: Cirigliano Daniele , Grimm Felix , Kutne Peter , Aigner Manfred
Published: January 2021

Modern Micro Gas Turbines must be capable to operate at different load points, in order to fulfill the demand of Combined Heat and Power for which they are designed. The combustion chamber structures are therefore subjected to regularly variable thermal loads, yet remaining physically constrained at the rest of the structure. Hence, they experience variable metal temperatures, temperature gradients and thermal stresses which can lead to thermal failure. Typical failure mechanisms in combustion chambers are fatigue and creep. Oxidation can also play an important role.

In the present study, Computational Fluid Dynamics methods are used for validation of flow prediction, combustion and heat transfer of an atmospheric combustion chamber. Convective and radiative heat losses towards the ambient are specifically taken into account, leading to better agreement with experimental data from preceding studies. The comparison is presented in this paper. The real-scale machine-operated combustion chamber is then tested at its nominal high-pressure conditions. In this respect, the hereby validated numerical models are employed to simulate the high-pressure operation. A fully coupled Thermo-Structural analysis is performed in order to account for heat fluxes within the solid materials. By so doing, wall temperature distributions can be obtained.

The results from Fluid Dynamics simulations serve as input for a Finite Elements Analysis, which provides equivalent stress, strain and deformation distributions by using a linear elastic mechanical model. Such distributions highlight the most critical areas, allowing a first estimate of the components’ life according to thermo-mechanical fatigue. The additional influence of Creep and Oxidation is currently under development at DLR Stuttgart and will be presented in subsequent works.
Scalable Heat Transfer Characterization on Film Cooled Geometries Based on Discrete Green’s Functions
Authors: Saavedra Jorge , Athmanathan Venkat , Paniagua Guillermo , Meyer Terrence , Straub Doug , Black James , Ramesh Sridharan
Published: January 2021

The aerothermal characterization of film cooled geometries is traditionally performed at reduced temperature conditions, which then requires a debatable procedure to scale the convective heat transfer performance to engine conditions. This paper describes an alternative engine-scalable approach, based on Discrete Green’s Functions (DGF) to evaluate the convective heat flux along film cooled geometries. The DGF method relies on the determination of a sensitivity matrix that accounts for the convective heat transfer propagation across the different elements in the domain. To characterize a given test article, the surface is discretized in multiple elements that are independently exposed to perturbations in heat flux to retrieve the sensitivity of adjacent elements, exploiting the linearized superposition. The local heat transfer augmentation on each segment of the domain is normalized by the exposed thermal conditions and the given heat input. The resulting DGF matrix becomes independent from the thermal boundary conditions, and the heat flux measurements can be scaled to any conditions given that Reynolds number, Mach number, and temperature ratios are maintained.

The procedure is applied to two different geometries, a cantilever flat plate and a film cooled flat plate with a 30 degree 0.125” cylindrical injection orifice with length-to-diameter ratio of 6. First, a numerical procedure is applied based on conjugate 3D Unsteady Reynolds Averaged Navier Stokes simulations to assess the applicability and accuracy of this approach. Finally, experiments performed on a flat plate geometry are described to validate the method and its applicability. Wall-mounted thermocouples are used to monitor the surface temperature evolution, while a 10 kHz burst-mode laser is used to generate heat flux addition on each of the discretized elements of the DGF sensitivity matrix.
Design Method and Numerical Simulation Analysis of Special-Shaped Centrifugal Impeller: Part I — Design Method
Authors: Lei Jian , Qin GuoLiang
Published: January 2021

This paper presents the design method of the special-shaped centrifugal impeller based on the streamline curvature method. Some conclusions described in this article will be thoroughly analyzed and demonstrated in the second part. The second part mainly involves case analysis and numerical simulation of performance parameters. The design of a centrifugal impeller must yield blades that are aerodynamically efficient, easy to manufacture, mechanically sound, especially low noise during running. The blade shape is generated by specifying surface velocity distributions and consists of straight-line elements that connect points at hub and shroud. The new impeller changed the channel structure from the classic radial outflow to axial outflow and removed the U-shaped diffuser flow passage. At the same time, the anti-noise technology is applied to optimize the flow channel design. The theoretical comparison between the classic centrifugal impeller and the new impeller shows that, in the aspect of energy saving, the flow field distribution of the new impeller is more uniform, gas flow loss is significantly reduced and the compressor efficiency is obviously improved. In addition, due to the noise elimination characteristics of the distributed flow passage, the noise of the new impeller is obvious lower than the traditional centrifugal impeller. But due to the complexity of the flow channel form, the flow resistance of the flow channel will increase, however this resistance increase can be controlled by the flow channel design.
Novel Feature Based Approach for Turbomachinery Design and Analysis
Authors: Kannan Ashwin , Dubasi Krishna Kishor , Nasti Adele , Keskin Akin , Clough Joshua
Published: January 2021

Current turbomachinery design and analysis is a time consuming process, involving multiple teams and multi-disciplinary physics to be considered during the design stages. The geometry definition is a key enabler requiring better, clean and flexible designs at desired level of fidelity for all analyses. In order to achieve this, a fully parametric approach has been developed using a feature library (user defined features – UDFs) in a CAD package together with multiple tools to prepare the geometry for analysis.

The paper will describe the approach towards feature library creation for a whole aero engine application, the relevant steps to prepare the geometry for analysis, and the limitations. The feature library has been used to enable a new aero engine conceptual design from the whole engine aerodynamic gas path definition all the way to the structural design, providing the additional flexibility to perform trade-off studies through design of experiments (DOE). Results will be shown on variation of critical design parameters such as casing thicknesses, flange positions, and number of struts.

The selected example will clearly demonstrate the time-saving and better-quality product achieved compared to the traditional process, and the ability of the engineer to explore the design space better with inter-linked analysis tools through a master geometry definition.
Extensive Validation of HAWT Unsteady Modelling Using BEM and CFD
Authors: Peraro Raffaele , Menegozzo Luca , Dal Monte Andrea , Benini Ernesto
Published: January 2021

The present work aims to present two different approaches to model the unsteady aerodynamics of horizontal-axis wind turbines (HAWTs). A complete and extensive comparison has been established between the results obtained using a low-fidelity calculation tool, as the Blade Element Momentum (BEM), and a high-fidelity technique, as the Computational Fluid Dynamics (CFD). Regarding the first calculation strategy, an accurate revision in polar diagrams calculation and the implementation of yaw and dynamic stall routines have endowed the BEM code to predict the machine performance under unsteady flow conditions. In order to achieve an accurate validation, the proposed BEM solver has been tested on AOC 15/50 and NREL Phase VI wind turbines. Referring to CFD techniques, a three-dimensional unsteady model has been improved to study the aerodynamic behaviour of the machine in case of yawed incoming wind.
30 Years of Dry Low NOx Micromix Combustor Research for Hydrogen-Rich Fuels: An Overview of Past and Present Activities
Authors: Funke Harald H.-W. , Beckman Nils , Keinz Jan , Horikawa Atsushi
Published: January 2021

The paper presents an overview of the past and present of low-emission combustor research with hydrogen-rich fuels at Aachen University of Applied Sciences. In 1990, AcUAS started developing the Dry-Low-NOx Micromix combustion technology. Micromix reduces NOx emissions using jet-in-crossflow mixing of multiple miniaturized fuel jets and combustor air with an inherent safety against flashback. At first, pure hydrogen as fuel was investigated with lab-scale applications. Later, Micromix prototypes were developed for the use in an industrial gas turbine Honeywell/Garrett GTCP-36-300, proving low NOx characteristics during real gas turbine operation, accompanied by the successful definition of safety laws and control system modifications. Further, the Micromix was optimized for the use in annular and can combustors as well as for fuel-flexibility with hydrogen-methane-mixtures and hydrogen-rich syngas qualities by means of extensive experimental and numerical simulations. In 2020, the latest Micromix application will be demonstrated in a commercial 2 MW-class gas turbine can-combustor with full-scale engine operation. The paper discusses the advances in Micromix research over the last three decades.
Operation of SGT-600 (24 MW) DLE Gas Turbine With Over 60 % H2 in Natural Gas
Authors: Magnusson Rikard , Andersson Mats
Published: January 2021

Hydrogen is one of the leading options for storing energy from renewables and surplus electricity. Hydrogen is also a major constituent in various streams in the chemical industry and cannot always be used for better purposes than flaring or heat and power generation.

Siemens has identified the 24MWe SGT-600 3rd generation DLE gas turbine as a candidate for having a high hydrogen capability. The burners for using hydrogen in the SGT-600 have been developed for and by Additive Manufacturing technology. The advantages of this technology have been integrated into the presented design and therefore allowing:

• Rapid prototyping with possibilities for fast turnaround of tests and screening of various concepts

• Manufacturing of complex geometries with smart gas passages, very innovative cooling and mixing concepts

• Small series and minimum waste with reduced cost

• Good repeatability and stability of product quality

Burner development was carried out according to “the standard method within the industry”, meaning CFD-analysis, atmospheric single burner combustion testing followed by pressurized single burner combustion testing and finally a full-scale machine test at the SIEMENS Industrial Turbomachinery AB (SIT) test rig facility in Sweden. The rig is used for full scale testing of gas turbines in the power output range from 15MW to 62MW. It allows testing not only with standard natural gas but also gas mixtures with e.g. hydrogen or nitrogen can be run. The test facility has liquid fuel capability.

During the burner development process, a project including two SGT-600 running on up to 60 volume % hydrogen was awarded to Siemens. This meant that a very definite target for the development was set and the results of these efforts are presented in this paper.

An adapted 3rd gen. DLE burner design proved to be capable of using 100% hydrogen at SGT-600 full load conditions at the single burner high pressure tests giving only 35 ppm NOx@15%O2. This was a major step in the development of a hydrogen burner for the SGT-600.

The following full engine test with the same burner type showed the possibility to run with 60 vol-% H2 at 0–100% load while keeping stable combustion and achieving emissions below 25 ppm NOx@15%O2 in the standard operating range of the SGT-600. At lower loads higher hydrogen contents were tested (95 vol-%) but the flow capacity of the fuel system limited the full exploration of hydrogen capability of the SGT-600 3rd gen. DLE gas turbine.

The 3rd gen. DLE burner is also used in the 33MWe SGT-700 and the 62MWe SGT-800, which will also benefit from the development of the increased SGT-600 hydrogen capability. The results open the possibility of using H2 rich gas more widely in all gas turbine configurations using 3rd gen. DLE burner.
Lessons Learned From Freespans at Pipeline Watercourse Crossings
Authors: Ferris Gerry
Published: January 2021

Over the past 10 years inspections (site visits, boat based surveys or diver surveys) have been completed at nearly 20,000 pipeline watercourse crossings for 20 different pipeline owners. During the last 10 years there have been 721 unique locations where an exposed pipeline was found and at 213 of these locations a freespan was encountered. Only one of the freespans resulted in the failure (loss of product) of the pipeline. This record illustrates what is now become widely accepted, that pipeline exposure does not necessarily lead to pipeline failure. The record adds to this, pipeline freespan does not necessarily lead to failure. This highlights that the relevant question for “water loading caused pipeline failure” is: Does the combination of freespan length and water velocity exceed a combination that would lead to vortex induced vibration or the exceedance of the static load limit of the pipe?
Probabilistic Digital Twins for Transmission Pipelines
Authors: Ayello Francois , Liu Guanlan , Yang Yonghe , Cui Ning
Published: January 2021

Digitalization in the oil and gas industry has led to the formation of digital twins. Digital twins bring closer the physical and virtual world as data is transmitted seamlessly between real time sensors, databases and models. The strength of the digital twin concept is the interconnectivity of data and models. Any model can use any combination of inputs (e.g. operator owned data sets and sensors, third-party databases such as soil composition or weather data, results from other models such as flow assurance, threat modelling or risk modelling). Consequently, the result of one model may become the input of another. This strength is also a weakness, as uncertain (or missing data) will lead to a great source of uncertainty and may lead to wrong results. Worst case scenarios have been used to solve this issue without success. This paper presents a new concept: probabilistic digital twins for pipelines. Probabilistic digital twins do not lose uncertainty as results pass from one model to another, thus providing greater confidence in the final results. This publication reviews the probabilistic digital twin concept and demonstrates how it can be implemented using gas pipeline data from West Pipeline Company, CNPC.
Negligible Crack Growth Thresholds
Authors: Lamborn Lyndon , Nelson Greg , Harter James
Published: January 2021

This paper initiates use of fracture mechanics best practice growth models and tools for pipeline steels with full tri-region da/dN characterization. The utilities associated with establishing negligible crack growth thresholds are demonstrated.

Pipeline operators are often presented with decisions that could be supported with scientifically vetted and situationally accurate stress thresholds for negligible crack growth. The threshold stress-intensity factor, ΔKth, is the value for ΔK where the crack growth rate, da/dN, approaches the minimum threshold crack growth rate. Stress-intensity factors at or below this threshold value result in crack growth small enough for operators to practically ignore it in pipeline integrity assessments. Previously, a ΔKth value of 2.0 MPa*m0.5 had been suggested for general use in API 579[1]. The API 579 value appears conservative when compared to industry experience and established ΔKth for similar steel alloys across all stress ratios.

By establishing an on-shore pipeline specific ΔKth which considers a pipeline-specific da/dN threshold and stress ratio effects, operators are afforded the opportunity to:

• exclude certain pipelines or portions of pipelines from crack growth susceptibility,

• identify features with no life limit,

• adjust load / boundary conditions to preclude growth,

• improve computational efficiency by discarding load cycles below threshold, and,

• more accurately simulate crack growth scenarios

Pipeline crack growth testing has been researched to derive reasonable and prudent negligible ΔKth values through a closer examination of loading scenarios and environments which affect ΔKth. A da/dN threshold for when diminishingly small crack growth rates can be neglected for typical pipeline assets was determined based on observed pressure fluctuation frequencies. Applications and value derived from deployment of ΔKth are illustrated for North American pipeline assets. Environmental and blunting effects on ΔKth for near-neutral pH stress corrosion cracking previously developed are shown for comparison and utility.

Fully established negligible growth thresholds pave the way toward adoption of next-level fracture mechanics best practice models and tools such as AFGROW and NASGRO, and facilitates crack growth simulations and root-cause analysis.
Near Neutral pH Stress Corrosion Crack Growth Model Evaluation: PipeOnline™
Authors: Lamborn Lyndon , Nelson Greg , Stilwell Genevieve
Published: January 2021

The pipeline industry has long sought a unified near-neutral pH stress corrosion cracking (NNpHSCC) growth model, which fully describes salient growth elements. In response to this gap, the Pipeline Research Council International (PRCI) has funded a multi-year research project, partnering with the University of Alberta (Project SCC-2-12). With the project nearing completion, application of the proposed near-neutral pH stress corrosion cracking growth model to two operating pipelines with known populations of stress corrosion crack features is presented.

The remaining life of each crack feature detected by crack in-line inspection tools, under known loading, is calculated for two segments of operating pipelines in North America. The PRCI developed model, referred to as PipeOnline™, is compared to the legacy Enbridge linear growth and Paris Law models.

A calibration technique for correcting the length and depth of the ILI feature calls provided by the in-line inspection vendor is reviewed, which takes into account tool tolerance and corrects length and depth to more closely match field findings. Efficiency improvements gleaned from this calibration technique are illustrated. While this calibration methodology is unique to the pipeline operator, the method is reviewed to allow other operators to readily implement the technique if it is found to be warranted.

The PipeOnline model is tested for the post-calibration dimensions and compared to the legacy growth model. Each of the required inputs is defined, and methods of quantification are shown. Negligible growth thresholds are reviewed, and the truncation of stress cycles below the growth threshold is discussed. The strategy of deployment is shown, along with the proportion of features that are predicted to remain in dormancy.

Methods to account for mean stresses and load application frequency are presented. The resulting PipeOnline re-inspection interval is compared to that predicted by typical existing growth models and then contrasted with excavation results on the asset. Calibration of the governing equation coefficients with rationale for each term is proposed for the pipeline segments examined in the study, and recommendations made for potential implementation for other operators, along with follow-on research.
Slope Movement Inspection Using Axial Strain Data Across Multiple Lines and Repeat Inspections
Authors: ElSeify Mohamed , Cornu Sylvain , Karé Raymond , Fathi Ali , Richmond John
Published: January 2021

Axial strain inspection using the AXISS™ is an established tool in the pipeline operator’s toolbox to assess pipeline geotechnical threats and other strain related events. Consequently, there is a large database of axial strain data for several different pipelines operating in different environments and from multiple inspections at the same geographical locations.

The Cheecham slope, located south east of Fort McMurray, Alberta, is a known geohazard site crossed by six individual pipelines. The lines were constructed between 1999 and 2013 and have a size range of 10” to 36”. Five out of the six lines, 12” to 36”, have been inspected using the axial strain tool. The pipelines inspected cover a range of characteristics including, different vintages, pipe diameters and positions in the ROW. These differences, and the ILI runs provide an insight into the effect of a landslide event on the strain response of these pipelines.

Axial strain measurement of the multiple pipelines in the Cheecham slope’s ROW allows: i) a direct comparison between lines ii) evaluation of the strain profile across the slope iii) assessment of the magnitude of the axial strain in terms of pipe characteristics e.g. pipe vintage and mechanical properties. More importantly, the axial strain data may provide an additional tool to assess the effectiveness of strain mitigation steps carried out over the years.

An increase in the frequency of axial strain ILI runs resulted in additional data being available and more importantly data from run to run inspections spread over months or sometime years. A single run captures the strain at the time of inspection but run to run inspections provide an additional comparative tool to evaluate and monitor pipeline movement. Two out of the five lines inspected have run to run axial strain data. This paper takes the Cheecham slope as a case study to discuss the benefits of run comparison of ILI axial strain data either by comparing strain values of repeated runs for a single line or by the cross comparison of strain responses of different lines in the same ROW. The paper aims to demonstrate how run to run analysis of ILI axial strain data can be implemented as part of geohazard risk management program to asses strain risk profiles of these locations and to assess the effectiveness of strain mitigation programs previously undertaken by operators.
A Feature-Specific Probabilistic Assessment of Pipeline Defect Size From ILI MFL Signal Using Convolutional Neural Network
Authors: Chen Jenny Jing , Westwood Stephen , Heaney David
Published: January 2021

When estimating pipeline burst pressure, one of the prevalent sources of uncertainty that needs to be factored into the calculation is the model error in the estimation of feature depth and length from the in-line inspection tool. Due to modeling technique limitation, as of today many ILI vendors have feature specific error bounds depending on the morphologies of the corrosion, this error can only be reported to operators as an overall error known as the ILI tool tolerance which is usually obtained from samples of excavation data or pull test data. At the most, the error is reported by classes based on corrosion morphologies specified by Pipeline Operators Forum. For example, a commonly reported corrosion depth sizing specification is ±10% of pipe wall thickness at 80% confidence for the General type of corrosion. This can be interpreted as that the error of each reported depth estimations is assumed to fall in a normal distribution with a mean equal to 0 and standard deviation equal to 7.8% of wall thickness. The shape of the distribution, the mean and standard deviation will then be used as constants to factor in the burst pressure calculation.

However, these factors are never constant for a sample of defects in reality. In fact, they ought to be variables on an individual feature basis. An example of such an approach would be a feature specific error tolerance, this could be that the estimated depth of a feature is 36%wt in an interval of [30%, 48%] of wall thickness with 80% confidence. This is believed to greatly reduce the level of uncertainty when it comes to failure pressure estimation or other type of pipeline risk assessment. The advancement in Machine Learning today, deep learning with deep neural networks, allows feature-specific error tolerance to be obtained after analyzing visual imagery of MFL signal. In this paper we will describe a novel approach to predict the size of metal loss defects and more importantly the distribution associated with each prediction. We will then discuss the benefits of this approach has with respect to risk assessment such as failure pressure estimation.
Pipeline Leak Detection Using a Moderate Gain Nonlinear Observer
Authors: Cunha Sérgio B. , Baptista Renan M.
Published: January 2021

Most pipeline control systems use some sort of autonomous leak detection system as a safety feature. Among the pipeline leak detection techniques, state observers stand out as the most sophisticated and promising technique. But its use has been inhibited as the dynamic models employed so far are large and estimating the states of nonlinear systems is not trivial.

Pipeline pressure and flow dynamics have been modelled in the literature by means of different numerical solutions to a pair of first order partial differential equations that express mass and linear momentum conservation. The numerical solution requires discretizing the pipeline length in a finite number of segments, resulting in a system of equations with size of twice the number of segments. Although there is nothing wrong with this approach, a smaller system is more convenient if one is concerned exclusively with pressure and flow at the pipeline entrance and exit sections. In this paper, energetic modelling principles are employed to obtain a pair of first order ordinary differential equations representing the dynamics of long liquid pipelines.

A recently introduced nonlinear observer enables straightforward use of linear, constant-gain observers with Lipschitz nonlinear dynamics. This observer gives the designer freedom to choose the observer eigenvalues and enables mathematically proven asymptotic stability with low gains. In this paper this observer, using a second-order model to represent the pipeline dynamics, is used as a pipeline leak detection algorithm.

Initially the observer was employed directly as a leak detection algorithm, the leak being indicated by a non-transient difference between the measured and the estimated flows. Afterwards the leak was modeled as a disturbance flow and a disturbance observer was designed. Both algorithms were verified by means of computer simulations. It was found that the two methodologies are capable of detecting and estimating very small leaks, but the disturbance observer seems capable of indicating small holes further way from the measuring points.