bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of the Centerbody Wake on the Precessing Vortex Core Dynamics of a Swirl Nozzle
Authors: Mukherjee Arnab , Muthichur Nishanth , More Chaitali , Gupta Saarthak , Hemchandra Santosh
Published: January 2021

The precessing vortex core (PVC) phenomenon in swirling jets is a helical instability in the flow driven by the coherent precession of the vortex breakdown bubble (VBB) around the flow axis, resulting in the helical rollup of the shear layer. This instabilitty is driven mainly by flow processes in the region upstream of the VBB. Centerbodies, commonly employed in combustor nozzles create a central wake recirculation zone (CWRZ) that can interfere with VBB precession and hence suppress the PVC. We study this phenomenon in a swirl nozzle with a centerbody whose end face is flush with the nozzle exit plane, using large eddy simulations (LES) and linear hydrodynamic stability analysis for flow Reynolds numbers Re = 48,767 and 82,751, based on nozzle exit diameter and bulk flow velocity. For one of the Re = 82,751 cases the centerbody end face diameter is halved resulting in the onset of coherent VBB precession. Linear stability analysis reveals a marginally unstable mode in this case. The same mode is found to be stable in the nominal cases. Structural sensitivity analysis for these two cases, shows that the VBB precession eigenmode is sensitive to changes in the time averaged flow in the VBB-CWRZ merger region. This suggests that the reduction in CWRZ length due to halving the centerbody end face diameter is the reason for the onset of VBB precession. These results suggest that in general, spatial separation between the CWRZ and VBB can result in the onset of VBB precession and the emergence of PVC oscillations in swirl flows.
Consideration of Simplified Structural Models for Turbine Vane Modal Analysis
Authors: Korpics Natalie S. , Berdanier Reid A.
Published: January 2021

Modal analysis of jet engine hardware is a necessary analytical tool utilized by engineers to understand and predict the vibrational risks to the system. Whereas blades and disks are critically analyzed due to their failure modes and effects, turbine vanes also need to be evaluated with respect to their design modal criteria to minimize potential risks to the engine. Although full hoop models of the entire system are most accurate, the time required for modeling and solution processing is typically prohibitive. Through cyclic symmetry and the use of commercial contact techniques, an analytical model may be created that provides the behavior of the entire system with a fraction of the computing time. However, methods for model simplification, including vane-only models, have not been addressed, and the potential for simplified models to accurately predict system modes is of particular interest. Accordingly, this paper studies the finite element modeling procedures for turbine vane modal analysis using multiple contact methods and cyclic symmetry applied to a turbine vane. An emphasis is placed on evaluating vane-only modeling techniques and an abbreviated turbine casing model. Additional comparisons with a traditional assembly model assess finite element model solution accuracy and efficiency. Ultimately, formal recommendations are offered for structural modeling of turbine vanes, including assessments of accuracy, reduction of frequency prediction capability, and computational efficiency gain.
Multidisciplinary Design of a Low-Noise Propeller: Part I — Multi-Fidelity Design Methodology Leveraging on Acoustic Drivers
Authors: Dumont Chloé , Baert Lieven , Lepot Ingrid
Published: January 2021

High-fidelity numerical simulations have already contributed in a significant way to the emergence of state-of-the-art turbomachinery components but are still sparingly exploited due to their cost. It is hence relevant to continue the investigations on low-fidelity tools and their combination with higher fidelity methodologies especially when breakthrough technologies are studied. Multi-fidelity approaches are key in supporting turbomachinery engineers to quickly decide on the relevance of an innovative concept, and to accelerate optimisation processes.

This paper describes a low-noise propeller design methodology developed during the IRON project (Clean Sky 2). This methodology is driven by Calypso, a platform developed by Cenaero, which integrates machine learning strategies and multifidelity aerodynamic and acoustic solvers. Two key elements of this framework are detailed and validated in this paper. The first one is a low-fidelity tool that offers a fast estimation of the steady aerodynamic performance of a propeller blade using a lifting-surface method. The second one is a far-field tonal noise prediction solver, relying on an acoustic propagation performed with Farassat’s formulation 1A of the Ffowcs-Williams and Hawkings equation. Noise source can be either obtained after a CFD computation or after a low-fidelity aerodynamic evaluation.

The low and high-fidelity aero-acoustic methodologies have been applied on 600 samples. It is shown how data mining strategies available within Calypso pave the way to astutely combine both levels of fidelity within an optimisation to quickly and efficiently explore a large design space, and to identify the key design parameters as early as possible in the design process.
A Multi-Fidelity Aero-Thermal Design Approach for Secondary Air Systems
Authors: Amirante Dario , Hills Nicholas J. , Adami Paolo
Published: January 2021

The paper presents a multi-disciplinary approach for aero-thermal and heat transfer analysis for internal flows. The versatility and potential benefit offered by the approach is described through the application to a realistic low pressure turbine assembly. The computational method is based on a run time code-coupling architecture that allows mixed models and simulations to be integrated together for the prediction of the sub-system aero-thermal performance. In this specific application the model is consisting of two rotor blades, the embedded vanes, the inter-stage cavity and the solid parts. The geometry represents a real engine situation.

The key element of the approach is the use of a fully modular coupling strategy that aims to combine (1) flexibility for design needs, (2) variable level of modelling for better accuracy and (3) in memory code coupling for preserving computational efficiency in large system and sub-system simulations.

For this particular example Reynolds Averaged Navier-Stokes (RANS) equations are solved for the fluid regions and thermal coupling is enforced with the metal (conjugate heat transfer). Fluid-fluid interfaces use mixing planes between the rotating parts while overlapping regions are exploited to link the cavity flow to the main annulus flow as well as in the cavity itself for mapping of the metal parts and leakages. Metal temperatures predicted by the simulation are compared to those retrieved from a thermal model of the engine, and the results are discussed with reference to the underlying flow physics.
Numerical Analysis of Mass Flow Leakage Through Orifices for Supercritical CO2: Two-Phase Flow Effects
Authors: Vesely Ladislav , Khadse Akshay , Curbelo Andres , Kapat Jayanta S. , Petrungaro Luca
Published: January 2021

Supercritical CO2 (sCO2) holds a great promise as a future working fluid for power generating Brayton cycles. One of the challenging research areas in sCO2 power cycles is flow leakage and the design of seals on the compressor side of the cycle. Given the compact nature of sCO2 turbomachinery, even a minimal amount of leakage can lead to a significant power efficiency loss. Hence accurate prediction of mass flow leakage rate becomes important. However, on the compressor side of the cycle, operating conditions across the seal lead to two-phase flow. This makes flow modeling very challenging because conventional one-phase flow CFD models cannot be used. This paper is an attempt to understand the behavior of two-phase sCO2 flow going through circular and annular orifices. The focus is to utilize commercially available CFD scheme for modeling phase change and two-phase flow through constrictions. Since the pressure loss across constrictions is also accompanied with reduction in temperature, the flow becomes two-phase by entering the saturation dome. CFD simulation is performed using commercially available software STAR CCM+. 2D axisymmetric geometry is considered as the computational domain. Eulerian Multi-phase Mixture model is used in conjunction with the Two-Phase Thermodynamic Equilibrium implementation. This model is intended for applications that involve two phases of the same substance that are in thermodynamic equilibrium. Fluid properties are defined over a large range of temperatures and pressures, including both the liquid and vapor phases.
Development and Testing of a 10 MWe Supercritical CO2 Turbine in a 1 MWe Flow Loop
Authors: Moore Jeffrey , Cich Stefan , Day-Towler Meera , Mortzheim Jason
Published: January 2021

sCO2 power cycles offer improved cycle efficiencies compared with traditional steam Rankine cycles. However, the turbomachinery required to support such a cycle does not exist at a commercial scale and requires development. This paper describes a new 10 MWe scale sCO2 turbine was developed and demonstrated in an sCO2 closed-loop recompression Brayton cycle. Since this turbine was developed for Concentrating Solar Power (CSP) applications, a target inlet temperature of over 700°C was chosen using funding from the US DOE SunShot initiative and industry partners. However, it can be applied to traditional heat sources such as natural gas, coal, and nuclear power. Traditional Rankine steam cycle thermal efficiencies are typically in the 35–40% range, but can be as high as 45% for advanced ultra-supercritical steam cycles. The sCO2 cycle can approach 50% thermal efficiency using externally fired heat sources. Furthermore, this cycle is also well suited for bottoming cycle waste heat recovery applications, which typically operate at lower temperatures. The high-power density and lower thermal mass of the sCO2 cycle results in compact, high-efficiency power blocks that can respond quickly to transient environmental changes and transient operation, a particular advantage for solar, waste heat, and ship-board applications. The power density of the turbine is significantly greater than traditional steam turbines and is comparable to liquid rocket engine turbo pumps. This paper describes the design and construction of the turbine and provides additional testing of the 10 MWe turbine in a 1 MWe test facility including a description of rotordynamics, thermal management, rotor aero and mechanical design, shaft-end and casing seals, bearings, and couplings. Test data for the turbine is included, as it achieves its operational goal of 715°C, 250 bara, and 27,000 rpm.
A Prognostics Approach Connecting Oxidation Damage to Mechanical Criteria
Authors: Slottner Pontus
Published: January 2021

Oxidation of gas turbine parts is one of the damage mechanisms limiting firing rate and outage interval, thereby reducing potential efficiency and increasing operational cost. While oxidation isn’t an immediate integrity threat in itself, it has indirect impact by reducing load carrying cross sections, changing weight and stiffness distribution, causing cooling air leakages, changing material properties, changing parts aerodynamics characteristics et cetera. This in turn potentially results in shorter creep life, drifting eigenfrequencies, overheating of other parts, increased brittleness and performance loss. Since it is very complicated to analyze all these possible situations in detail, parts are often rejected because of their appearance rather than because of actually approaching a level of damage where it will have consequences on the operability of the turbine. Further, the rules tend to be general rather than customer specific, being set for the entire allowed operation envelope of the part rather than based upon the particular conditions of the unit where the part is in service. This paper presents a simple, first-step prognostics model that connects oxidation damage to local one-dimensional stress and stiffness and local cross-sectional force. An example is given where simple oxidation models are used to predict a detailed oxidation state with regard to multiple aspects. Herein, this oxidation state includes different aspects with regard to the type of oxidation and includes additional characteristics to be considered in the following. By connecting the model to measured characteristics instead of pure oxidation criteria it will be easier to: firstly, apply more relevant criteria that can be evaluated on a site-by-site basis. This will allow high-precision oxidation prognostics with criteria relevant for the operational safety of the equipment. Secondly, more accurately compare predictions to experiences, allowing more detailed operation experience evaluation as well as more relevant input to root cause investigations. This will allow more accurate root cause determination and will result in fewer data points needed to draw statistically sound conclusions from field experiences. Providing such possibility has a significant impact on corresponding applications, as it includes larger operation. Simultaneously, risks can be controlled and quantified better than today providing an important benefit for an application like gas turbines depending strongly on the reliability of the components utilized. The model is general in its nature and is formulated to allow application with any oxidation rule that can be formulated as a mathematical algorithm that is suitable for time integration. The main limitations are its restriction to one space dimension and the assumption of a constant temperature field. If the model is found useful, natural next steps are to extend the model to three space dimensions and a more complex temperature model. The model should also be tested with more accurate oxidation models.
Introduction of a Smartphone Application in an Aeroengine Technology Course
Authors: Aslanidou Ioanna , Gaitanis Aggelos , Kalfas Anestis I.
Published: January 2021

The main goal of an engineering course is for the students to achieve the defined educational goals, enhance their problem-solving capabilities and develop the essential engineering mindset. The continuous improvement of a course is essential to maintain its challenging nature while improving the course quality. Adapting the teaching methods used to new types of students can provide a significant improvement in student learning.

In that context, a digital tool is employed in an advanced course in Aeroengine Technology. A smartphone application that calculates gas turbine performance is introduced in the course to help students understand some of the key concepts. The purpose of the application is to provide the students with an interactive tool to understand the gas turbine thermodynamic cycle. An exercise regarding this application is assigned to note the performance of different engine technologies used in aircraft propulsion through the years. The assignment with the application is combined with a larger assignment on gas turbine performance. The application is also employed in the final exams of the course.

The purpose of this paper is to present the use of the application in the course and to address any challenges that arise in the implementation of the app in the learning process. The employed teaching methods received positive feedback from the students who indicated that the app assignment helped them understand some of the key concepts in the course. After all, the main aim of the use of novel teaching methods should be to make learning more interesting, so that students get more involved in a course.
Thermodynamic Analysis of a Novel Ammonia-Water Cogeneration System for Maritime Diesel Engines
Authors: Cheng Ziyang , Wang Yaxiong , Sun Qingxuan , Wang Jiangfeng , Zhao Pan , Dai Yiping
Published: January 2021

This paper proposes a novel cogeneration system based on Kalina cycle and absorption refrigeration system to meet the design requirements of China State Shipbuilding Corporation, which is efficiently satisfy the power and cooling demands of a maritime ship at the same time. Unlike most of the combined systems, this cogeneration system is highly coupled and realizes cogeneration without increasing the system complexity too much. The basic ammonia mass fraction of this novel system is increased, so that the ammonia concentration of ammonia-water steam from the separator can be higher, which contributes to lower refrigerating temperature and thus less heat loss in the distillation process. In addition, higher ammonia concentration solution makes overheating easier, which improves the thermal efficiency. Moreover, the system has two recuperators to make further improvement of the thermal efficiency. Thermodynamic models are developed to investigate the system performance and parametric analysis is conducted to figure out the effects of including working fluid temperature at the outlet of the evaporator, working fluid temperature at superheater outlet, mass fraction of ammonia in basic solution, turbine inlet pressure, temperature of cooling water at the inlet of condensers and the refrigeration evaporation temperature on the system performance. Furthermore, the cogeneration system is optimized with genetic algorithm to obtain the best performance, which achieves 333.00kW of net power output, 28.83 kW of cooling capacity and 21.81% of thermal efficiency. Finally, the performance of the proposed system is compared with an optimized recuperative organic Rankine cycle (ORC) system and an optimized Kalina cycle system 34 (KCS34) using the same heat source. The results show that the thermal efficiency and power output of the novel cogeneration system is 3.89% and 1.05% higher than that of the recuperative ORC system and KCS34 system respectively.
Study on Film Cooling Performance Improvement of NGV Leading Edge Subject to Distortion Profiles of Low NOx Combustor
Authors: Zhang Wenhao , Wang Zhihao , Wang Zhiduo , Feng Zhenping
Published: January 2021

Under the effect of inlet distortion profiles (including hot-streaks, total pressure profiles, and swirling flow angle patterns), the film cooling performance on the leading edge (LE) region of GE-E3 nozzle guide vanes (NGVs) has been numerically investigated in this paper. Firstly, the complicated inlet distortion profiles of a low NOx combustor chamber has been decoupled to single factors to explore the individual and the coupling effects on the film cooling performance of the NGV LE region (Case 1 to Case 4). Then the original and three modified film-hole configurations are compared and discussed under the quasi-real environment (Case 5 to Case 8). The results indicate that total pressure profile tends to draw more coolant toward the midspan and the residual swirl promotes turnover of the cooling film to the other side of NGVs near the enwalls of LE region. Under the combined effects of different distortion profiles, the cooling film is redistributed on the LE region with some area near the stagnation lines with poor coverage. The upwash or downwash of boundary layer fluid caused by the complicated vortex in passages draws the cooling film on NGV surfaces. And this effect will be strengthened or weakened by the injection angles of holes. Finally, the filmhole configuration in Case 8 with counter-inclined film-hole rows arranged along the stagnation lines shows the best film cooling performance, which has positive effects on the decrease of high temperature region induced by hot streak (HS), and results in more uniform temperature distribution.
Numerical Investigation on the Aerodynamic Performance of a Low-Pressure Steam Turbine Exhaust Hood Using DOE Analysis
Authors: Diurno Tommaso , Fondelli Tommaso , Nettis Leonardo , Maceli Nicola , Arcangeli Lorenzo , Andreini Antonio , Facchini Bruno
Published: January 2021

Nowadays, the rising interest in using renewable energy for thermal power generation has led to radical changes in steam turbine design practice and operability. Modern steam turbines are required to operate with greater flexibility due to rapid load changes, fast start-up, and frequent shutdowns. This has given rise to great challenges to the exhaust hood system design, which has a great influence on the overall turbine performance converting the kinetic energy leaving the last stage of LP turbine into static pressure.

The radial hoods are characterized by a complex aerodynamic behavior since the flow turns by 90° in a very short distance and this generates a highly rotational flow structure within the diffuser and exhaust hood outer casing, moreover, the adverse pressure gradient can promote the flow separation drastically reducing the hood recovery performance. For these reasons it is fundamental to design the exhaust system in order to ensure a good pressure recovery under all the machine operating conditions.

This paper presents a Design of Experiment analysis on a low-pressure steam turbine exhaust hood through CFD simulations. A parametric model of an axial-radial exhaust hood was developed and a sensitivity of exhaust hood performance as a function of key geometrical parameters was carried out, with the aim of optimizing the pressure recovery coefficient and minimizing the overall dimensions of the exhaust casing. Since hood performance strongly depends on a proper coupling with the turbine rear stage, such a stage was modeled using the so-called mixing-plane approach to couple both stator-rotor and rotor-diffuser interfaces. A detailed analysis of the flow field in the exhaust hood in the different configurations was performed, detecting the swirling structures responsible for the energy dissipation in each simulation, as well as correlating the flow field with the pressure recovery coefficient.
Towards a Detailed Liquid Fuel Injection Model for Gas Turbine Combustor CFD
Authors: Wang L. , Ozogul H. , Kaushik T. , Bhat A. , Rida S.
Published: January 2021

Fuel injection modeling plays an important role in Computational Fluid Dynamics (CFD) based combustor design and performance analysis. The specification of initial fuel spray size, velocity, and location strongly affects the subsequent fuel air mixing and combustion processes. Current common practice of introducing fuel spray in combustor CFD relies on either experimental correlations built from spray data measured at locations further away from injector exit or simplified theoretical models that have limited applications. This often leads to large uncertainties in spray initial conditions and inconsistencies in combustor model performance. Although much progress has been made in multiphase simulation of primary atomization, involving a two-phase flow solver in combustor CFD to resolve liquid fuel injection processes is still not feasible in the foreseeable future. Standalone fuel injection simulations, however, can provide valuable information on initial spray distributions required for accurate fuel injection modeling in combustor CFD. In this paper the approach of using a standalone or separate detailed fuel injection simulation to provide initial spray boundary condition for combustor CFD is demonstrated in a Liquid Jet In Cross Flow (LJICF) configuration. The primary atomization (PA) of the LJICF is simulated using a Volume of Fluid (VOF) solver on a fine mesh, and the blobs and ligaments from the PA simulation are collected and transferred to another separate simulation of spray using a Lagrangian particle tracking solver on a coarser mesh. The results from the Lagrangian simulation are compared with experimental data as well as the results from a conventional fuel injection model. The differences from the comparisons are discussed to reveal the challenges and new modeling needs associated with this detailed fuel injection model. These include the effect of mesh resolution on the spray boundary condition, the need for blockage modeling, and the need for ligament breakup modeling.
Scavenge Performance of an Optimized Shallow Sump at Various Flow Conditions
Authors: Chandra Budi , Johnson Kathy
Published: January 2021

Oil scavenge flow in aero-engine bearing chamber remains largely a challenging problem for many engine designers. Research campaign on scavenge flow has been conducted by G2TRC – Gas Turbine and Transmissions Research Centre (previously Rolls Royce University Technology Centre in Gas Turbine Transmission Systems) at the University of Nottingham. It was recognized that a deep sump performs better than shallower one due to its ability to “shield” the collected oil in the sump from the shaft windage thus reducing the amount of oil being picked up by the bulk air rotation. However, such a deep sump design cannot be employed in some engines and especially at certain locations where space is limited.

A parametric study combined with phenomenological approach on shallow sump geometry has been conducted and presented in the previous publication where a certain optimized shallow sump variant was proposed depending on whether the flow in the chamber is wall film dominated or airborne droplets dominated. The parametric phenomenological approach was employed since it can be done relatively quicker than typical data gathering through an experiment. However the approach relies on qualitative interpretation of the flow features, and its application in bearing chamber flow research has never been validated before. This paper presents the results of quantitative measurements of residence volumes of an optimized shallow sump variant identified in the parametric phenomenological study. Comparison was then made with the residence volumes of some existing engine sumps.

It was found that the optimized shallow sump for wall film dominated flow has lower residence volumes compared to some existing engine sumps. In some cases, the residence volume can be reduced by up to 75%. An optimized shallow sump variant for airborne droplets dominated was also identified in the previous parametric phenomenological study, although the residence volume measurement is yet to be conducted. The optimized shallow sump for wall film dominated flow was also identified as a good sump regardless of the flow regime. However when it was tested in airborne droplets dominated flow, its residence volumes are higher than some of the existing engine sumps. This highlights the importance of considering the flow regime in the bearing chamber in any attempt to optimize a sump geometry.
Numerical Investigations on the Heat Transfer Performance of Transonic Squealer Tip With Different Film Cooling Layouts
Authors: Jiang Shijie , Li Zhigang , Li Jun , Song Liming
Published: January 2021

Tip leakage flow in high speed turbine induce significant thermal loads and give rise to intense thermal stresses on blade tip, while increasing inlet pressure tends to accelerate leakage velocity beyond transonic regime. The present research quantifies heat transfer and film cooling effect on a squealer tip with three film cooling layouts, three coolant mass flow rates and a relative casing movement. The results indicate that area-averaged HTC of PS layout is higher than that of CAM layout by 6.9% and that of SS layout by 5.7% when coolant flow rate equals to 0.6% mainstream flow rate. By comparison, it is clearly observed that area of the high heat transfer coefficient regions are significantly enlarged when the flow rate of coolant is increased. With relative casing movement, a significant high HTC stripe parallel to pressure side rim is formed. In case of the PS layout, heat transfer coefficient is reduced by 7.3% with casing movement. While in case of CAM layout and SS layout, heat transfer coefficient increased by 4.8% and 2.3% with casing movement, respectively. Detailed flow patterns with three film cooling layouts are also illustrated.
Split Training Method to Generate Data Driven Model for Gas Turbine Engine Anomaly Detection
Authors: Takiguchi Yu , Shiono Satoshi
Published: January 2021

This paper presents a new method named Split Training Method (STM) for generating a data driven model of gas turbine engines to be used for anomaly detection and prognosis. The data driven model in this study simulates the relationship among engine parameters, such as sensor outputs and control inputs from pilots. More accurate trend monitoring of the relationship among engine parameters enables earlier anomaly detection with high accuracy.

Machine learning techniques such as clustering, nonlinear regression, classification and optimization are used in STM. The input data for generating a simulation model is extracted from the training data by applying clustering algorithm to split into some clusters and outliers. This is why our method is named “Split” Training. Outliers are excluded from training data and each cluster of training data generates a simulation model with nonlinear regression. Data points in the test data are classified to each cluster and used for evaluation of the corresponding model accuracy. In order to generate the simulation model with the highest accuracy, training data extraction is optimized by changing clustering shapes. The shapes of the optimized clusters are unique to individual engines and simulation target parameters.

The novelty of STM is that the training data is selected in accordance with the characteristics of the data itself and not selected on the condition determined in advance.

The result of comparison between STM and the conventional method shows significant accuracy enhancement.
Techno-Economic Optimization of a Combined Cycle Combined Heat and Power Plant With Integrated Heat Pump and Low-Temperature Thermal Energy Storage
Authors: Garcia Jose , Smet Vincent , Guedez Rafael , Sorce Alessandro
Published: January 2021

The present study presents a techno-economic analysis of a novel power plant layout developed to increase the dispatch flexibility of a Combined Cycle Gas Turbine (CCGT) coupled to a District Heating Network (DHN). The layout includes the incorporation of high temperature heat pumps (HP) and thermal energy storage (TES). A model for optimizing the short-term dispatch strategy of such system has been developed to maximize its operational profit. The constraints and boundary conditions considered in the study include hourly demand and price of electricity and heat, ambient conditions and CO2 emission allowances. To assess the techno-economic benefit of the new layout, a year of operation was simulated for a power plant in Turin, Italy. Furthermore, different layout configurations and critical size-related parameters were considered. Finally, a sensitivity analysis was made to assess the performance under different market scenarios.

The results show that it is indeed beneficial, under the assumed market conditions, to integrate a HP in a CCGT plant coupled to a DHN, and that it remains profitable to do so under a variety of market scenarios. The best results for the assumed market conditions were found when integrating a 15 MWth capacity HP in the 400 MWel CCGT-CHP. For this case study, the investment in the HP would yield a net present value (NPV) of 1.22 M€ and an internal rate of return (IRR) of 3.04% for a lifetime of 20 years. An increase was shown also in operational flexibility with 0.14% of the electricity production shifted while meeting the same heating demand. Additionally, it was found that the TES makes the system even more flexible, but does not make up for the extra investment.
Effect of Reynolds Number on Five-Hole Probe Performance: Experimental Study of the Open-Access Oxford Probe
Authors: Passmann Maximilian , aus der Wiesche Stefan , Povey Thomas , Bergmann Detlef
Published: January 2021

There is relatively little literature concerning the effect of Reynolds number on multi-hole aerodynamic probe performance. In particular, there is almost no discussion in the literature of the underlying mechanisms of Reynolds number (Re) sensitivity for such probes. In order to close this gap, detailed investigations of the effect of Re on a five-hole probe have been performed using both PIV techniques and oil flow visualizations. Wind- and water-tunnels were used to cover a wide range of Re. The open-access Oxford Probe was used for these studies because of the readily available data-sets and processing routines, and to allow future comparisons by other authors. Complex flow dynamics including flow separation and re-attachment were identified, which cause Re-sensitivity of the calibration map at low Re even for low yaw or pitch angles.

By comparing calibration maps across a wide range of Re, we demonstrate that the Oxford Probe can be employed without much loss of accuracy at lower Re levels than initially (conservatively) suggested, and quantify the errors in the extreme low-Re regime.

Overall we demonstrate the robustness of the Oxford Probe concept across a wide range of Re conditions, we more clearly defined the low-Re limit for the probe design and quantify errors below this limit, and we illustrate the fundamental mechanisms for Re-sensitivity of multi-hole probes.
Enhanced Early Warning Diagnostic Rules for Gas Turbines Leveraging on Bayesian Networks
Authors: Escobedo Ernesto , Arguello Liliana , Sepe Marzia , Parrella Ilaria , Cioncolini Stefano , Allegorico Carmine
Published: January 2021

The monitoring and diagnostics of Industrial systems is increasing in complexity with larger volume of data collected and with many methods and analytics able to correlate data and events.

The setup and training of these methods and analytics are one of the impacting factors in the selection of the most appropriate solution to provide an efficient and effective service, that requires the selection of the most suitable data set for training of models with consequent need of time and knowledge.

The study and the related experiences proposed in this paper describe a methodology for tracking features, detecting outliers and derive, in a probabilistic way, diagnostic thresholds to be applied by means of hierarchical models that simplify or remove the selection of the proper training dataset by a subject matter expert at any deployment.

This method applies to Industrial systems employing a large number of similar machines connected to a remote data center, with the purpose to alert one or more operators when a feature exceeds the healthy distribution.

Some relevant use cases are presented for an aeroderivative gas turbine covering also its auxiliary equipment, with deep dive on the hydraulic starting system.

The results, in terms of early anomaly detection and reduced model training effort, are compared with traditional monitoring approaches like fixed threshold.

Moreover, this study explains the advantages of this probabilistic approach in a business application like the fleet monitoring and diagnostic advanced services.
Parameter Estimation and Performance Seeking of a Marine Gas Turbine Based on Extended Kalman Filter
Authors: Wang Zhitao , Zhang Junxin , Qi Wanling , Li Shuying
Published: January 2021

Marine gas turbines have been widely used and developed in the field of marine power. It is important to make them operated safely and efficiently. In this paper, a marine triaxial gas turbine is taken as an example to study the method of estimating the health state of the gas path using extended Kalman filter (EKF). To verify the accuracy of EKF, a comparison was made between linearized Kalman filtering (LKF) and EKF. In addition, the sequential quadratic programming (SQP) algorithm is used to seek the performance in case of gas path abnormal. The combination of parameter estimation and performance seeking forms a comprehensive method for diagnosis and optimization of marine gas turbines.

The results show that the EKF method is an effective method for combining nonlinear systems with traditional Kalman filter. EKF has a good estimation effect on the gas path health state under different operating conditions. Also, the marine triaxial gas turbine achieved the target performance under the constraints of the SQP algorithm. Performance seeking restores the output power of the marine gas turbine and reduces the inlet and outlet temperatures of turbines. It can effectively prevent the problem of excessive combustion and ensure the safe and stable operation of the marine gas turbine.
Soot Emission Optimization of a Helicopter Engine: From Injector Design to Engine Tests Validation
Authors: Duchaine Patrick , Bouyssou Quentin , Pascaud Stéphane , Exilard Gorka , Viguier Christophe
Published: January 2021

Even though no regulation currently exists on helicopter gas turbines, soot production in aeronautic engines is of paramount importance to comply with future rules, as well as to offer environmental-friendly products on the market. Thus, design modifications of the combustion liner and fuel injectors are one way to explore in order to reduce soot emission levels of existing combustors. These design changes are driven both by fundamental knowledge of soot production mechanisms and by advanced combustion and pollutants modelling. The major difficulty is to reduce soot emissions while not deteriorating other combustion performances: NOx and CO emissions, lean blow-off limits and service lifetime.

The objective of the present study is to optimize fuel injectors of a recent Safran Helicopter Engines research combustor. The injector design modifications are driven by one main guideline: reducing soot emissions can be achieved by lowering the equivalence ratio downstream of the injector. Detailed designs are achieved thanks to advanced RANS injector and LES combustion computations.

Then, in order to mitigate main identified risks — management of soot emissions and lean blow-off limits — engine tests were performed very early in the demonstration process. A combustor is successively equipped with one standard and two modified geometries of fuel injectors on an engine test bench. Experimental results show that the two modified injector geometries reduce smoke numbers by a factor of respectively 2 and 9 and slightly deteriorates lean blow-off limits. These measurements are also compared to CFD computations. Leung et al. model (Combust Flame 1991), relying on phenomenological descriptions of soot formation combined with a LES computation of the combustor, well predicts a significant decrease in smoke level, even if it does not perfectly match engine data. Concerning lean blow-off limits, LES modelling predict a decrease in lean blow-off limits, which do not agree qualitatively with engine test results.

As a conclusion, this study identifies a design driving factor for soot reduction, with possibly acceptable impacts on other combustion performances like lean blow-off limits.
Experimental and Numerical Investigation of Ultra-Wet Methane Combustion Technique for Power Generation
Authors: Zhang Kai , Dybe Simeon , Shen Yazhou , Schimek Sebastian , Paschereit Christian Oliver , Duwig Christophe
Published: January 2021

Using steam as a heat carrier and working media has merits to increase electric efficiency up to 60% and decrease NOx emission to single-digit compared to dry gas turbine cycles. These attribute primarily to the physical properties of steam as having high heat capacity to reduce local flame temperature, and hence reduce emissions by inhibiting the thermal NOx forward reaction rate. In this work, ultra-high steam content with a steam-to-air mass ratio of up to 40% is premixed with methane-air mixture before entering into a swirl-stabilized HP-burner for combustion. A significant change of flame from V-shape (attached) to M shape (detached) is observed through a transparent combustion chamber whilst changing steam content. The measurement of chemiluminescence OH* is conducted with an intensified CCD-camera band-pass filtered at 320nm. Following these measurements, large eddy simulation is used to capture reacting flow features. Reasonably well agreements between experimental data and numerical results are obtained for both attached and detached flames in terms of the OH* distribution. Slight inconsistency of OH* intensity is mainly due to uncollected wall temperature which leads to either over- or under-prediction of chemical reaction rate depending on the experimental flame positions. Distributed flame front is clearly identified with LES for wet methane combustion associated with 35% steam-to-air ratio corresponding to a high Karlovitz number flame. Slightly unstable combustion is observed when the steam-to-air ratio exceeds 40% featuring an onset of flame blow-off. In addition, interaction between precessing vortex core and the flame is presented for different level of steam dilution, and conclusions are drawn regarding the flame stabilization. The in-depth understanding of the ultra-wet combustion is an important step towards the use of sustainable, steam-diluted biosyngas for electricity production.
Very Large Eddy Simulation of Flow and Heat Transfer in a Pulsating Impinging Jet
Authors: Liu Fangyuan , Mao Junkui , Han Xingsi , Xia Zhaoyang
Published: January 2021

The steady impinging jets applied in turbomachine have been comprehensively studied but the pulsating jets still need to be further researched. The flow field and heat transfer characteristics of pulsating impinging jet impinging on a flat plate have been simulated using the improved very large eddy simulation established with SST k–ω model. Two time-mean Reynolds numbers (6,000 and 23,000) in the conditions of frequency = 10Hz and steady state at the constant jet–to–surface distance (6D) were considered. The velocity, vortices, and Nusselt number distributions on the plate surface were investigated to emphasize on the vortex structures in the flow and its relation to the heat transfer. The investigation has revealed the advantage of the improved very large eddy simulation for predicting the dynamical generating process of flow structures in pulsating jets. Calculated results showed pairs of vortices were organized and induced from the jet exit, and propagated along with the jet region periodically. The vortices grew with the entrainment towards the ambient fluid and resulted in accelerated interaction in the wall jet region. Meanwhile, the vortices had strong interaction with the core region and weakened velocity in the core region. Results showed that the time–mean local Nusselt number of pulsating jet was lower in the stagnation region at both investigated Re numbers but not reduced in the wall jet region.
Numerical Simulation Model of Electrothermal De-Icing Process on Composite Substrate
Authors: Guo Xiaofeng , Guo Zhiqiang , Yang Qian , Dong Wei
Published: January 2021

A numerical simulation model of electrothermal de-icing process on carbon fiber reinforced polymer (CFRP) composite is conducted to study the effect of thermal properties of the substrate on the ice melting process. A novel melting model which is based on the enthalpy-porosity method is applied to study the transient ice melting process and heat transfer of the de-icing sys-tem. Multi-layered electrothermal de-icing systems including composites with different fiber orientation are used to analyze the effects of orthotropic heat conductivity of the CFRP composite on the ice melting process and heat transfer. Movement of the ice-water interface, the melted zone thickness and the melted zone area on CFRP composite are investigated on the three-dimensional electrothermal de-icing unit. The effects of thermal properties of substrate on the temperature distribution of the ice-airfoil interface are analyzed. The computational results show that the thermal properties of substrates affect the temperature on the ice-airfoil interface, the temperature distribution in the substrate, ice melting area, ice melting rate and ice melting volume significantly. The time that ice starts to melt on the CFRP composite substrate is earlier than that on the metal substrate. However, it takes more time for the ice to melt completely on the ice-CFRP interface than that on the ice-metal inter-face. The orthotropic heat conductivity of CFRP composite results in strong directivity of the melting area on the ice-CFRP in-terface. A ratio parameter is defined to represent the matching degree of substrate materials and geometry model of de-icing system. The simulation model can be applied to study electrothermal de-icing system of nacelle inlet and airfoil made of composite. The results in present work is also helpful to predict the change of temperature during de-icing process and provide guidelines for the optimizing the electrothermal de-icing system to reduce power consumption according to the fiber structure of composite.
An Optimized Correlation for Turbulent Flame Speed for C1-C3 Fuels at Engines-Relevant Conditions
Authors: Burke Eoin M. , Yousefian Sajjad , Güthe Felix , Monaghan Rory F. D.
Published: January 2021

The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Four correlations based on previous works by Zimont, Kobayashi, Ronney and Muppala have been selected for the present study. Using a Matlab-based Nelder-Mead simplex direct search method, each correlation’s adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.
Boundary Conditions for Compressor Cascade Ice Crystal Icing Testing
Authors: Nagorski Matthias , Koch Christian , Staudacher Stephan
Published: January 2021

At the Altitude Test Facility (ATF) of the University of Stuttgart a linear compressor cascade test rig serves the investigation of ice crystal icing (ICI) under engine realistic conditions. A numerical model of the first stage of NASA Stage 67 is validated with experimental data taken from literature and used to investigate the respective ice crystal icing conditions for prospective cascade experiments. Eleven operating points simulating climb conditions with constant non-dimensional power setting through ascending parcels of moist air are selected for analysis. Only the melting-dominated regime is considered. The 3D flow field is obtained using a RANS approach in combination with a Spalart-Allmaras one-equation turbulence model. The droplet and ice crystal trajectories are calculated based on an Eulerian framework. The computation of the surface energy balance is adapted from the Messinger model taking into account unsteady phenomena. Four of eleven selected operating points indicate the onset of substantial ice accretion. A static wet bulb temperature of freezing constitutes in general the lower icing limit for rig experiments. The upper icing limit depends on the ice water content impinging and sticking to the target surface.