bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Steam Turbine Pre-Warming and Warm-Keeping Strategies Using Hot Air for Fast Turbine Start-Up
Authors: Pehle Lukas , Łuczyński Piotr , Jeon Taejun , Wirsum Manfred , Mohr Wolfgang F. D. , Helbig Klaus
Published: January 2021

Adaptability of coal-based power generating units to accommodate renewable energy sources is becoming increasingly important. In order to improve flexibility, reduce start-up time and extend the life cycle, General Electric has developed solutions to pre-warm/warm-keep steam turbines using hot air.

In this paper two main contributions to optimize the warming arrangements are presented. Firstly, the calibrated model of a 19-stage IP steam turbine is analyzed regarding time-dependent mass flow rates in a pre-warming mode. The influences on the duration time of the process and the thermally induced stress are investigated. This investigation utilizes a detailed 3D hybrid (HFEM-numerical FEM and analytical) model of the turbine including the rotor, inner casing and blading for computationally-efficient determination of transient temperature fields in individual components. The thermal boundary conditions are calculated by means of heat transfer correlations developed for this purpose. Moreover, a separate FEM model allows for the implementation of a structural mechanical analysis. As a result of this investigation, the pre-warming time can be further reduced while simultaneously lowering the thermal load in the components.

Secondly, selected pre-warming strategies are compared with the warm-keeping scenarios. This analysis is aimed at a minimum thermal energy use required for a reheating of air in a warming arrangement. Hence, the pre-warming and warm-keeping operating strategies are evaluated with regard to their energy demand before start-up. Thus, based on the duration of standstill, the most energy-efficient turbine warming strategy can be chosen to ensure hot start-up conditions.
Design of a Tip Appendage for the Control of Tip Leakage Vortices in Axial Flow Fans
Authors: Meyer Thomas O. , van der Spuy Sybrand J. , Meyer Christiaan J. , Corsini Alessandro
Published: January 2021

This paper reports on numerical investigations of passive control techniques used for the performance enhancement of a large diameter axial flow cooling fan through modification of the blade tip geometry. Using open-source software, a novel meshing strategy is developed to carry out both steady and unsteady numerical computations of a periodic section of an axial flow fan. Analysing the flow near the blade tip with a reduction in tip clearance, two predominant flow phenomena are identified. These two flow phenomena are further investigated with the aim of controlling them through implementation of a tip appendage design. Both introduced end-plate designs indicate effective control of each relevant flow phenomena. The constant thickness (CT) end-plate design is found to increase all fan performance characteristics at lower than design point (DP) flow rates while increasing the fan’s peak efficiency plateau towards the rotor stall margin. However, none of the CT end-plate designs are able to improve the fan’s performance characteristics at its DP. The introduction of a novel trailing edge (TE) end-plate design is found to increase all fan performance characteristics across the entire evaluated stable operating range, with an indicated increase of 37.3 percent in total-to-static pressure rise and a 2.9 percentage point increase in total-to-static efficiency at the fan’s DP flow rate. The aerodynamic performance results attest to the associated benefits of the investigated passive control techniques.
The Effects of Incidence and Deviation on the CFD-Based Throughflow Analysis
Authors: Li Jian , Wu Dongrun , Teng Jinfang , Zhu Mingmin , Qiang Xiaoqing
Published: January 2021

A major concern in the Computational Fluid Dynamics (CFD)-based throughflow calculation is the treatment of the incidence and deviation. This paper investigates the effects of the incidence and deviation on the CFD-based throughflow analysis by a time-marching throughflow model. The model is realized by solving complete Navier-Stokes equations with a single grid in the g-wise direction. The inviscid blade force is determined by calculating a pressure difference between the pressure and suction surfaces. The losses are introduced by imposing a blade surface skin friction factor converted from the pressure loss coefficient. And the flow discontinuity problem at the leading and trailing edges is resolved by modifying the mean blade surface to accommodate the incidence and deviation. The sensitivity of the throughflow results to the modification strategy of the mean blade surface is studied through response surface method. And the Kriging-assisted genetic algorithm (GA) is applied to determine the optimal distributions of incidence and deviation in the streamwise direction for NASA Rotor 37. Finally, four examples are provided to validate the throughflow model and to demonstrate the effects of incidence and deviation on CFD-based throughflow analysis at off-design conditions.
Accuracy Assessment of the Sellers Model in Predicting the Multi-Row Film Cooling Performance
Authors: Chen Ziyu , Li Yifei , Su Xinrong , Yuan Xin
Published: January 2021

Multi-row film cooling is widely applied in modern gas turbine cooling designs. However, there are few effective methods to predict local cooling effectiveness and the Sellers model based on the existing 1-D correlation is popular in the community but its prediction accuracy is questionable in some cases. The primary work of the current study is to analyze the prediction error of the Sellers model and to reveal the underlying flow mechanism. Considering the lateral uniformity assumption of the 1-D Sellers model, the effect of pitchwise row-to-row misalignment can hardly be included and the 2-D Sellers model is, therefore, proposed. Numerical simulations under density ratio near 1.0 are conducted on the double-row film cooling. Configurations of inline and staggered arrangements and blowing ratios from 0.5 to 2.0 are included. Cooling effectiveness can be theoretically decomposed into two parts contributed by separate rows, and this method has been validated. The footprint of coolant can, therefore, be tracked. Based on vortical interaction analysis, conclusions are obtained that pitchwise row-to-row spacing determines the overestimation or underestimation of the model-predicted result and the blowing ratio affects the absolute value of the prediction error. By comparing prediction accuracy of the two rows, the conclusion can be drawn that the prediction error is, to a greater extent, contributed by the row #2 because it is more likely to be affected by the row-to-row interaction.
Hybrid Method Based on FV Concept for Lean Blowout Limits Predictions for Aero Engine Combustors With Low Inlet Temperature
Authors: Lei Sun , Yong Huang , Xiang Feng
Published: January 2021

Lean blowout (LBO) limit is one of the most important parameters for aero engines. The LBO must be avoided during the whole flight envelope and modes. Thus the LBO limit should be predicted accurately during the research and development (R&D) process of an aero engine combustor. Some prediction models had been proposed by the previous studies. Lefebvre’s LBO model is widely used among these models due to its good accuracy and generality. Based on Lefebvre’s LBO model, the flame volume (FV) model is proposed to improve the prediction accuracy as well as keep the good generality. However, an additional equation is needed when the FV model is applied to predict the LBO limit. Based on our previous studies, the volume in the combustor liner enclosed by the iso-surface whose temperature is 900K could be chosen as the flame volume. The flame volume could be served as the additional equation and further makes the FV model available for the LBO limit prediction. This method could be named as the hybrid method based on the FV concept in this paper. On the other hand, the LBO limit at high altitude is attracting more and more attentions due to the extension of the flight envelope and modes in the recent years. Low inlet temperature is one of the most typical characteristics for the operating condition at high altitude. The temperature could reach less than −40 °C at high altitude. Compared with the normal condition, the characteristics of flow, atomization and combustion are different at the low temperature condition. In this paper, the hybrid method based on the FV concept is applied to predict the LBO limits of 11 combustors with low inlet temperature. The inlet temperature is 236.2K (corresponding to the altitude of 8km). The results show that the flame volumes obtained by the numerical simulation vary near linearly with the fuel/air ratio when the fuel/air ratio is close to the LBO limits. For all these 11 combustor configurations, the LBO limits with low inlet temperature (236.2K) obtained from the hybrid method based on the FV concept are significantly larger than those with normal inlet temperature (300K) obtained from experiments. The maximum and minimum increases are 29% and 2%, respectively. The LBO limits increases are more than 20% and 10% for 6 out of the 11 combustors and 9 out of the 11 combustors, respectively. The reasons for the increase of the LBO limits at low temperature include the decreasing of chemical reaction rate and evaporation rate, the increasing of the mean drop size.
Considerations on Axial Compressor Bleed for Sub-Idle Performance Models
Authors: Roig Tió Ferran , Ferrer-Vidal Luis E. , Azamar Aguirre Hasani , Pachidis Vassilios
Published: January 2021

The trend towards increased bypass ratio and reduced core size in civil aero-engines puts a strain on ground-start and relight capability, prompting renewed interest in sub-idle performance modelling. While a number of studies have looked at some of the broad performance modelling issues prevalent in this regime, the effects that bleed can have on sub-idle performance have not been addressed in the literature. During start-up and relight, the unknown variation in bleed flows through open handling bleed valves can have a considerable impact on the compressor’s operating line. This paper combines experimental, numerical and analytical approaches to look at the effect that sub-idle bleed flows have on predicted start-up operating lines, along with their effect on compressor characteristics. Experimental whole-engine data along with a purpose-built core-flow analysis tool are used to assess the effect of bleed model uncertainty on engine performance models. An experimental rig is used to assess the effects of reverse bleed on compressor characteristics and measurements are compared against numerical results. Several strategies for the generation of sub-idle maps including bleed effects are investigated.
Optimization Design of Turbine Blade Cooling Structure Based on Conjugate Heat Transfer
Authors: Wang Mingrui , Zhu Huiren , Xu Yang
Published: January 2021

Conjugate heat transfer (CHT) has been widely used in the analysis on flow field and heat transfer of turbine blades. In this paper, a baseline design of turbine rotor blade is selected. By improving the arrangement of film holes, turning cylindrical holes into laid back fan-shaped holes in the pressure surface (PS) and suction surface (SS), and reducing the radially inclined angle of film holes on the leading edge (LE), an optimized design (OPT) is created. Grid independence validation is conducted by comparing the pressure and temperature distributions adopting three different numbers of grids. In order to select a suitable turbulence model, experiment is performed and its values are compared with the calculation results of three different turbulence models. The distributions of static pressure, static temperature, overall cooling effectiveness and streamlines of cooling flow are compared between the OPT and baseline design by the numerical calculation results of CHT. Furthermore, the adiabatic film cooling effectiveness is calculated and the cooling performances between cylindrical holes and laid-back fan-shaped holes are compared. At last, the flow and heat transfer mechanisms are analyzed and the forming causes of low or high temperature regions on the blade are explained.

Calculation results show that compared with the baseline design, the area average temperature drops by 2.6% on the PS and by 3.7% on the SS. The area average overall cooling effectiveness increases by 9.3% on the PS and by 14.1% on the SS. The cooling performances are promoted greatly on the PS and SS but change little on the LE and TE. Obviously, the improvements are successful.
Experimental Investigation of Film Cooling Performance on Blade Endwall With Diffusion Slot Holes and Stator-Rotor Purge Flow
Authors: Yu Zhiqiang , Liu Jianjun , Li Chen , An Baitao , Xu Guangyao
Published: January 2021

This paper focuses on the influences of the discrete hole shape and layout on the blade endwall film cooling effectiveness. The effect of upstream purge slot injection on the film cooling performance of the discrete hole was also investigated. The diffusion slot hole was first applied to the blade endwall. As a comparison, the cooling performance of the fan-shaped hole was also measured. Totally, six discrete-hole cooling configurations (2 hole shapes × 3 layouts) were investigated. Experiments were performed in a seven-blade linear cascade with the exit Reynolds number of 2.64 × 105. The average blowing ratios (BR) of the discrete holes changed from 0.5 to 2.5, and the coolant mass flow ratio of the purge slot (MFR) was fixed at MFR = 1.5%. The distributions of the cooling effectiveness on the blade endwall were measured by the pressure sensitive paint technique. Results indicate that the diffusion slot hole significantly increases the film cooling effectiveness on the blade endwall compared to the fan-shaped hole, especially at high blowing ratio. The maximum relative increment of the cooling effectiveness is over 40%. The layout with the discrete holes arranged lining up with the tangent direction of the blade profile offset curves exhibits a comparable film cooling effectiveness with the layout with the discrete holes arranged according to the cross-flow direction. The film cooling effectiveness on the pressure surface corner is remarkably enhanced by deflecting the hole orientation angle towards the pressure surface. The combination of purge slot and diffusion slot holes supplies a full coverage film cooling for the entire blade endwall at MFR = 1.5% and BR = 2.5. In addition, the slot injection leads to a non-negligible influence on the cooling performance of the discrete holes near the separation line.
Durable Abrasive Tip Design for Single Crystal Turbine Blades
Authors: Nagy Douglas , Tollett Robert
Published: January 2021

In order to create and maintain peak efficiency in turbine stages, it is useful to minimize hot air leakage over blade tips. For unshrouded blades, this means creating minimal clearance over the airfoil tip with rub-tolerate zero-gap materials systems. In this study, a refractory abrasive tip material was developed and applied to a plain turbine blade tip to work in conjunction with an abradable coating on the tip-shoe. Process development efforts resulted in abrasive material that could be as much as 2mm thick. Further, the abrasive media included imbedded grits that would remain in back-up until such time as they were exposed and were pressed into service. Application methods of both furnace brazing and induction brazing were explored as were pre and post consolidation net shaping. Evaluation testing included compatibility for the application process onto single-crystal blades. Performance testing included rub-rig testing and long-term oxidation testing. Service testing included commercial engine operation for 14,000 hours followed by metallurgical re-evaluation. Service performance was mechanically successful, although some material transfer from the tip-shoe was observed which decreased the abrasive nature of the tip. Metallurgically, some intergranular oxidation was observed, but the grits themselves were well retained and were sufficiently refractory to avoid microstructural or oxidation degradation. A production implementation of the coating by an induction heating process is shown.
Impact of the Stabilized Finite Element Method on Acoustic and Vortical Perturbations in Thermoacoustic Systems
Authors: Hofmeister Thomas , Hummel Tobias , Sattelmayer Thomas
Published: January 2021

This paper seeks to advance linear stability analyses of thermoacoustic systems conducted with the stabilized Finite Element Method (sFEM). Specifically, this work analyzes and quantifies the impact of the Streamline-Upwind-Petrov-Galerkin (SUPG) artificial diffusion scheme on (eigen)mode shapes and damping rates of the isentropic Linearized Euler Equations (LEE) in frequency space. The LEE (eigen)mode shapes are separated into acoustic and vortical perturbation components via a Helmholtz decomposition and their sensitivity on the employed stabilization scheme is investigated separately. The regions where numerical stabilization mainly acts on the perturbation types are identified and explanations for the observations are provided. A methodology is established, which allows the quantification of the impact of artificial diffusion on the acoustic field in terms of a damping rate. This non-physical damping rate is used to determine the physically meaningful, acoustic LEE damping rate, which is corrected by the contribution of artificial diffusion. Hence, the presented method eliminates a main shortcoming of LEE eigen-frequency analyses with the sFEM and, as a result, provides more accurate information on the stability of thermoacoustic systems.
Experimental Two-Phase Flow Analysis Inside a Laboratory Scale Jet-Engine Combustion Chamber Using PIV
Authors: von Langenthal Thomas , Zarzalis Nikolaos , Loukou Alexandra
Published: January 2021

The characterization of the two-phase kerosene/air flow near the nozzle of an aero engine combustor is important in order to understand the combustion characteristics of the burner. Typically, Particle Image Velocimetry (PIV) or Laser Doppler Velocimetry (LDV) is used to measure velocities inside aero engine combustors. However, these measurement techniques rely on tracer particles to visualize the flow field and are usually only able to measure the velocity field of one phase at a time. In the case of PIV measurements both the flow tracers and the kerosene droplets scatter the laser light and thus, appear on the PIV recordings. Depending on droplet size and flow velocity, these kerosene droplets do not necessarily follow the airflow leading to errors in the derived velocity field. This work presents a method on how to separate kerosene droplets from flow tracers depending on their optical characteristics in the PIV recording. This phase separation enables the independent measurement of the flow fields of both the gaseous and liquid phase at the same time using a standard PIV setup. The method is demonstrated on a laboratory scale aero engine combustor operated at atmospheric conditions. The test rig features liquid kerosene combustion with realistic inlet temperatures and pressure drop as well as good access for optical measurement techniques. The phases are separated by filtering the images with noise reduction filters for suppressing the signal of the flow tracers, and edge detection filters to detect the kerosene droplets. The detected kerosene droplets are removed from the PIV pictures and the pictures are evaluated using standard PIV cross-correlation. Afterwards the liquid phase images are evaluated using Particle Tracking Velocimetry (PTV). This phase separation can lead to errors in the derived velocity fields because of incorrect and incomplete particle detection or due to errors in the cross correlation at the edges of detected particles. These errors in the phase separation are quantified by evaluating artificial two-phase flow PIV pictures with similar optical properties to the actual two-phase PIV pictures, and comparing the derived velocity fields to the results calculated using the original, unaltered pictures. The obtained results show, that in the setup under investigation, gaseous and liquid phase can have significantly different flow fields with kerosene droplets moving in the opposite direction of the recirculating airflow. The influence of essential parameters like seeding and spray density are discussed and at positions with a sufficient data rate, the instantaneous slip velocity between droplets and gaseous flow is calculated. Generally, the presented method appears to be suitable for studying combustion with liquid kerosene injection.
Application of Spectral Method for Vibration-Induced High-Cycle Fatigue Evaluation of an HP Turbine Blade
Authors: Ubulom Iroizan
Published: January 2021

A method of fluid-structure interaction coupling is implemented for a forced-response, vibration-induced fatigue life estimation of a high-pressure turbine blade. Two simulations approaches; a two-way (fully-coupled) and one-way (uncoupled) methods are implemented to investigate the influence of fluidsolid coupling on a turbine blade structural response. The fatigue analysis is performed using the frequency domain spectral moments estimated from the response power spectral density of the two simulation cases. The method is demonstrated in light of the time-domain method of the rainflow cycle counting method with mean stress correction. Correspondingly, the mean stress and multiaxiality effects are also accounted for in the frequency domain spectral approach. In the mean stress case, a multiplication coefficient is derived based on the Morrow equation, while the case of multiaxiality is based on a criterion which reduces the triaxial stress state to an equivalent uniaxial stress using the critical plane assumption. The analyses show that while the vibration-induced stress histories of both simulation approaches are stationary, they violate the assumption of normality of the frequency domain approaches. The stress history profile of both processes can be described as platykurtic with the distributions having less mass near its mean and in the tail region, as compared to a Gaussian distribution with an equal standard deviation. The fully-coupled method is right leaning with positive skewness while the uncoupled approach is left leaning with negative skewness. The directional orientation of the principal axes was also analyzed based on the Euler angle estimation. Although noticeable differences were found in the peak distribution of the normal stresses for both methods, the predicted Euler angle orientations were consistent in both cases, depicting a similar orientation of the critical plane during a crack initiation process. It is shown that the fatigue life estimation was conservative in the fully-coupled solution approach.
Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180-Degree Tip Turn With Different Turning Vane Configurations
Authors: Alsaleem Sulaiman M. , Wright Lesley M. , Han Je-Chin
Published: January 2021

Serpentine, varying aspect ratio cooling passages, are typically used in cooling advanced gas turbine blades. These passages are usually connected by sharp, 180-deg bends. In the open literature, most of the internal cooling studies use a fixed cross-sectional area for multi-pass channels. Studies that use varying aspect ratio channels, along with a guide (turn) vane to direct the flow with turning, are scarce. In general, studies show that the incorporation of turning vanes in the bend region of a multi-pass channel keeps the heat transfer rate high while reducing pressure loss. Therefore, the current study investigates the effect of using different guide (turn) vane designs on both the detailed heat transfer distribution and pressure loss in a multi-pass channel with an aspect ratio of (4:1) in the entry passage and (2:1) in the second passage downstream of the vane (s). The first vane configuration is one solid-vane with a semi-circular cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circular cross-section; two broken vanes are located downstream in the first passage (entering the turn), and one broken vane is upstream in the second passage (exiting the turn). For a Reynolds number range 15,000 to 45,000, detailed heat transfer distributions were obtained on all surfaces within the flow passages by using a transient liquid crystal method. The results show that the turning vane configurations have large effects on the heat transfer, in the turning bend and second passage, and the overall pressure drop. Results show that including the semi-circular vane in the turning region of a multi-pass channel enhanced the overall heat transfer by around 29% with a reduction in pressure loss by around 20%. Moreover, results show that the quarter-circular vane design provides higher overall averaged heat transfer enhancement than the semi-circular vane design by around 9% with penalty of higher pressure drop by 6%, which yields higher thermal performance by 7%, over the Reynolds number range.
Industrial Wastewater As an Enabler of Green Ammonia to Power via Gas Turbine Technology
Authors: Hewlett S. G. , Pugh D. G. , Valera-Medina A. , Giles A. , Runyon J. , Goktepe B. , Bowen P. J.
Published: January 2021

This experimental study follows on from detailed Chemkin-Pro numerical analyses assessing the viability of by-product ammonia (NH3) utilization for power generation in gas turbines (GTs). This study looks specifically at NH3 in the industrial wastewaters of steelworks, resulting from the cleansing of coke oven gas (COG). The by-product NH3 is present in an aqueous blend of 60–70%vol water and is normally destroyed.

An experimental campaign was conducted using a premixed swirl burner in a model GT combustor, previously employed in the successful combustion of NH3/hydrogen blends, with favorable NOx and unburned fuel emissions. This study experimentally investigates the combustion performance of combining anhydrous and aqueous by-product NH3 in an approximate 50:50%vol blend, comparing the performance with that of each ammonia source unblended. Green anhydrous NH3, a rapidly growing research topic, is a carbon-free energy vector for renewable hydrogen. Some potential benefits of combining the two sources are suggested.

Ammonia combustion presents two major challenges, poor reactivity and a potential for excessive NOx emissions. Prior numerical analyses predicted that 15%vol addition of steelworks COG, at an inlet temperature of 550 K, may provide sufficient support for raising the reactivity of the NH3-based fuels, whilst limiting undesirable emissions. Therefore, addition of 10, 15 and 20%vol COG to each NH3-based fuel was investigated experimentally at 25 kW power with inlet temperatures > 500 K, at atmospheric pressure.

As nitric oxide (NO) emissions decrease significantly with increasing fuel-to-air ratio, experiments were conducted at equivalence ratios (Φ) between 1.0 and 1.3, the precise range of Φ for each blend being optimized according to the modeling predictions for emissions. Leading blends, anhydrous NH3 with 15%vol COG and the 50:50%vol blend with 15%vol COG, achieved < 100 ppm and < 200 ppm NO respectively.

Modest-sized steel plants produce ∼10 metric tons of by-product NH3/day. Aspen Plus was used to model a Brayton-Rankine cycle with integrated recuperation. Adopting typical losses (48% cycle efficiency) and ∼1.2 MPa combustor inlet pressure, the net electrical power generation of 15%vol COG blended with 10 tonnes/day of aqueous industrial NH3 and 25 tonnes/day of anhydrous NH3 (i.e. achieving a 50:50%vol blend) was ∼4.7 MW, ∼47% more power than for the same amount of anhydrous NH3 with 15%vol COG. This significant increase, indicates how industrial NH3 could enable green NH3 to power.
Investigation of Similarity Criteria for an Internally-Cooled Turbine Vane Based on Artificial Neural Networks: Part I — Comparison of Similarity Criteria
Authors: Zhao Weicheng , Chi Zhongran , Zang Shusheng
Published: January 2021

This study explores the suitable criterion for the temperature and pressure modeling to measure the overall cooling effectiveness and the reason leading to modeling deviation at relatively low temperature and pressure test condition (Part II), taking the internally-cooled Mark II vane as an example. The method used in this study includes Artificial Neural Network (ANN), Conjugate Heat Transfer (CHT) Computational Fluid Dynamics (CFD) and experiments (Part II).

The average overall cooling effectiveness of the vane was selected as the target modeling parameter. After comparing the modeling error, the results show that matched-Biot number criterion has the best performance at both constant coolant temperature and temperature ratio conditions. The maximum modeling error is 6.4% and 1.2% for those two conditions, respectively.

Furthermore, the performance of these similarity criteria based on empirical correlations without the ANN model were also investigated, which is more feasible in engineering use. The accuracy of matched-Biot number criterion has an obvious decrease in this condition, but it is still the best selection at constant coolant temperature conditions. While the mass flow ratio criterion becomes the most accurate one at constant temperature ratio conditions.
A High-Speed Disk Rotor Rig Design for Tip Aerothermal Research
Authors: Lu S. , Zhang Q. , He L.
Published: January 2021

The relative casing motion can greatly vary the Over-Tip-Leakage (OTL) flow structure and thermal performance. The existing tip experimental research facilities include stationary linear cascade, cascade rigs with low speed moving belt, or high-speed rotor rigs are either not capable of reproducing the high relative casing Mach number, or extremely expensive and still difficult for optical measurement. This paper presents a highspeed disk rotor design which can simulate the high casing relative speed. The unique feature of this rig design concept is that it enables full optical access of the tip surface under the engine-representative OTL flow condition. In this paper, the feasibility of the design concept is demonstrated and assessed by RANS CFD simulation, both in component level and whole rig system level. The design idea demonstrated in this paper can be useful for a wide range of tip leakage flow studies.
Modeling Complex Contact Conditions and Their Effect on Blade Dynamics
Authors: Gastaldi Chiara , Gross Johann , Scheel Maren , Berruti Teresa M. , Krack Malte
Published: January 2021

Dry friction devices such as underplatform dampers are commonly included in turbine bladed disks designs to mitigate structural vibrations and avoid high cycle fatigue failures. The design of frictionally damped bladed disks requires adequate models to represent the friction contact. A widely used approach connects contact node pairs with normal and tangential springs and a Coulomb friction law. This simple model architecture is effective in capturing the softening behavior typically observed on frictionally damped structures subjected to increasing forcing levels.

An unexpected hardening behavior was observed on the frequency response functions of two-blades-plus-damper system tested by the authors in a controlled laboratory environment. The reason behind this unexpected behavior will be carefully analyzed and linked to the damper kinematics and to the dependence of contact elasticity on the contact pressure. The inadequacy of contact models with constant spring values will be discussed and alternatives will be proposed. The importance of being able to represent complex contact conditions in order to effectively predict the system dynamics is shown here using a laboratory demonstrator, however its implications are relevant to any other case where large contact pressure variations are to be expected. The nonlinear steady state simulations of the blades-plus-damper system will be carried out using an in-house code exploiting the Multi-Harmonic Balance Method (MHBM) in combination with the Alternating Frequency Time (AFT) Method.
Gas Turbine Performance Digital Twin for Real-Time Embedded Systems
Authors: Panov V. , Cruz-Manzo S.
Published: January 2021

This contribution reports on the development of Performance Digital Twin for industrial Small Gas Turbines. The objective of this study was the development of automation systems with control and monitoring functionalities, capable of addressing the requirements of future gas turbine plants for increased availability and reliability by use of Digital Twin technology.

The project explored development of Performance Digital Twin based on Real-Time Embedded computing, which can be leveraged with Internet-of-Things (IOT) Cloud Platforms. The proposed solution was provided in a form of modular software for a range of hardware platforms, with corresponding functionalities to support advanced control, monitoring, tracking and diagnostics strategies.

The developed Digital Twin was designed to be used in offline mode to assist the software commissioning process and in on-line mode to enable early detection of degradation and fault modes typical for gas path components. The Performance Digital Twin is based on a dynamic gas turbine model which was augmented with a Kalman tuner to enable performance tracking of physical assets.

To support heterogeneity of gas turbine Distributed Control Systems (DCS), this project explored deployment of Digital Twin on multiple platforms. In the paper, we discuss model-based design techniques and tools specific for continuous, discrete and hybrid systems.

The hybrid solution was deployed on PC-based platform and integrated with engine Distributed Control System in the field. Monitoring of gas turbine Performance Digital Twin functionalities has been established via Remote Monitoring System (STA-RMS). Assessment of deployed solution has been carried out and we present results from the field trial in this paper.

The discrete solution was deployed on a range of Programable Logical Controller (PLC) platforms and has been tested by integrating Digital Twin in virtual engine Distributed Control System network. The Performance Digital Twin was embedded in Single Master PLC and Master-Slave PLC configurations, and we present results from the system testing using virtual gas turbine assets. The IoT Platform MindSphere was integrated within virtual engine network, and in this contribution, we explore expansion of the developed system with Cloud based applications and services.
A Numerical Study on Conjugate Heat Transfer for Supercritical CO2 Turbine Blade With Cooling Channels
Authors: Khadse Akshay , Curbelo Andres , Vesely Ladislav , Kapat Jayanta S.
Published: January 2021

The first stage of turbine in a Brayton cycle faces the maximum temperature in the cycle. This maximum temperature may exceed creep temperature limit or even melting temperature of the blade material. Therefore, it becomes an absolute necessity to implement blade cooling to prevent them from structural damage. Turbine inlet temperatures for oxy-combustion supercritical CO2 (sCO2) are promised to reach blade material limit in near future foreseeing need of turbine blade cooling. Properties of sCO2 and the cycle parameters can make Reynolds number external to blade and external heat transfer coefficient to be significantly higher than those typically experience in regular gas turbines. This necessitates evaluation and rethinking of the internal cooling techniques to be adopted.

The purpose of this paper is to investigate conjugate heat transfer effects within a first stage vane cascade of a sCO2 turbine. This study can help understand cooling requirements which include mass flow rate of leakage coolant sCO2 and geometry of cooling channels. Estimations can also be made if the cooling channels alone are enough for blade cooling or there is need for more cooling techniques such as film cooling, impingement cooling and trailing edge cooling. The conjugate heat transfer and aerodynamic analysis of a turbine cascade is carried out using STAR CCM+. The turbine inlet temperature of 1350K and 1775 K is considered for the study considering future potential needs. Thermo-physical properties of this mixture are given as input to the code in form of tables using REFPROP database. The blade material considered is Inconel 718.
Reliability Analysis on Fatigue Life of Turbine Disk Regarding for the Correlation Between Divided Zones
Authors: Chen Gaoxiang , Fan Jiang
Published: January 2021

Failure of a turbine disk may occur in multiple parts of the disk. It should be taken into consideration that during the process of failure, the failure risk of other relevant parts tend to increase due to the change of stress state of the disk. Therefore, the failure risks of different parts are related. This paper puts forward a reliability analysis method considering the failure correlation between different zones of the disk. Firstly, the dependence between the low cycle fatigue (LCF) of the whole turbine disk and the LCF of each zone is considered in building a multivariate reliability model based on Copula function theory. With utilizing the sample points obtained by finite element method (FEA), the multidimensional maximum likelihood theory is used to estimate the parameters in the marginal distribution of turbine disk life and the correlation coefficients in the Copula model, and to quantify the failure correlation between each zone of the turbine disk. With regard to the lifetime output of different zones, fourth-order polynomial high-precision surrogate models are established, which greatly improves the efficiency of Monte Carlo simulation. Eventually, the LCF life reliability analysis of GH720Li turbine disk is performed.
An Investigation of Fundamental Combustion Properties of the Oxygenated Fuels DME and OME1
Authors: Ngugi John M. , Richter Sandra , Braun-Unkhoff Marina , Naumann Clemens , Riedel Uwe
Published: January 2021

Demands of energy will increase worldwide. The use of alternative and renewable energy resources is an attractive option to counteract climate change connected with the burning of fossil fuels. Moreover, improvements in fuel flexibility are a pre-requisite to meet the challenge of a sustainable production of energy in the near future. Within this context, oxygenated molecules, in particular ethers are of high interest because they can be produced renewably. In addition, ethers are promising considerably reduced emissions of particles and soot. In future, ethers might play a role as an alternative fuel (blend) for power generation in gas turbines and in the transport sector.

Dimethylether (DME: CH3OCH3) and oxymethylenether (OMEn: CH3O(CH2O)nCH3) are regarded as some of the most promising alternatives to fossil fuels, in particular in compression ignition engines.

In this work, we report on a combined experimental and modeling study: The oxidation of mixtures of dimethylether as well as of the simplest oxymethylenether (OME1) was investigated. The focus was put on two fundamental combustion properties: (i) ignition delay times measured in a shock tube device, at ambient and elevated pressures up to 16 bar, for stoichiometric mixtures, and (ii) laminar flame speed data, at ambient and elevated pressures up to 6 bar, determined for OME1. The experimental data base was used for the validation of several detailed chemical-kinetic reaction mechanisms taken from literature. Sensitivity analysis was performed for the two selected targets to allow a better insight into the oxidation network within the envisaged wide parameter range.

The findings of the present work will contribute to a better understanding of the combustion of these specific ethers, and to the design and optimization of burners and engines as well.
Modeling the Transport of Fuel Mixture Perturbations and Entropy Waves in the Linearized Framework
Authors: Kaiser Thomas Ludwig , Oberleithner Kilian
Published: January 2021

In this paper a new method is introduced to model the transport of entropy waves and equivalence ratio fluctuations in turbulent flows. The model is based on the Navier-Stokes equations and includes a transport equation for a passive scalar, which may stand for entropy or equivalence ratio fluctuations. The equations are linearized around the mean turbulent fields, which serve as the input to the model in addition to a turbulent eddy viscosity, which accounts for turbulent diffusion of the perturbations. Based on these inputs, the framework is able to predict the linear response of the flow velocity and passive scalar to harmonic perturbations that are imposed at the boundaries of the computational domain. These in this study are fluctuations in the passive scalar and/or velocities at the inlet of a channel flow. The code is first validated against analytic results, showing very good agreement. Then the method is applied to predict the convection, mean flow dispersion and turbulent mixing of passive scalar fluctuations in a turbulent channel flow, which has been studied in previous work with Direct Numerical Simulations (DNS). Results show that our code reproduces the dynamics of coherent passive scalar transport in the DNS with very high accuracy and low numerical costs, when the DNS mean flow and Reynolds stresses are provided. Furthermore, we demonstrate that turbulent mixing has a significant effect on the transport of the passive scalar fluctuations. Finally, we apply the method to explain experimental observations of transport of equivalence ratio fluctuations in the mixing duct of a model burner.
Rapid Characterization of Fatigue Performance With Application to Additive Manufactured Components
Authors: Celli Dino A. , Shen M.-H. Herman , Scott-Emuakpor Onome E. , George Tommy J.
Published: January 2021

The aim of this paper is to provide a fatigue life prediction method which can concurrently approximate both SN behavior as well as the inherent variability of fatigue efficiently with a limited number of experimental tests. The purpose of such a tool is for the quality assessment and verification of components using Additive Manufacturing (AM) processes and other materials with a limited knowledgebase. Interest in AM technology is continually growing in many industries, such as aerospace, automotive, or biomedical. But components often result in highly variable fatigue performance. The determination of optimal process parameters for the build process can be an extensive and costly endeavor due to either a limited knowledgebase or proprietary restrictions. Quantifying the significant variability of fatigue performance in AM components is a challenging task as there are many causes including machine to machine differences, recycles of powder, and process parameter selection. Therefore, a life prediction method which can rapidly determine the fatigue performance of a material with little or no prior information of the material and a limited number of experimental tests is developed as an aid in process parameter selection and fatigue performance qualification. This is performed by using a previously developed and simplistic energy based fatigue life prediction method, or Two Point method, to predict the inherent variability associated with fatigue performance. The proposed approach is verified by using predicted distributions of stress and cycles to failure and comparing with experimental data at 104 and 106 cycles to failure. SN life prediction is modeled via a modified Random Fatigue Limit (RFL) model where the two RFL model parameters are evaluated using Bayesian statistical inference and stochastic sampling techniques for distribution estimation. This is performed in a dynamic way such that the life prediction model is continually updated with the generation of experimental data.
Influence of Splitter Blades on the Performance of a Single-Stage Centrifugal Compressor With Pressure Ratio 12.0
Authors: Zhang Wenchao , Sun Zhenzhong , Wang Baotong , Zheng Xinqian
Published: January 2021

High performance centrifugal compressors with high pressure ratio are highly applied in turboshaft engines in order to obtain higher power-to-weight ratio and lower fuel consumption. The optimization of the aerodynamic configuration design of splitter blades is one of the effective ways to achieve higher efficiency. An in-house designed single-stage centrifugal compressor with a pressure ratio up to 12.0 is studied in this paper. By using a three-dimensional CFD (computational fluid dynamic) method, this paper investigates influences of the number of splitter blades and their leading edge position on the flow field characteristics and aerodynamic performance of the centrifugal compressor with ultra-high pressure ratio. Results show that three critical flow characteristics lead to severe losses in centrifugal compressor impeller when only full blades are applied. Those flow characteristics include the strong shock wave, the severe tip clearance flow at the inlet region and the severe flow separation at the rear region. Therefore, the inlet blade number should be reduced to decrease the loss caused by strong shock waves and tip clearance flow, while the outlet blade number should be sufficient enough to suppress flow separation. By optimizing the number and the leading edge position of splitters, the performance can be improved under the reduction of combined losses caused by shock waves, tip clearance flow and flow separation. When an aerodynamic configuration with single-splitters is used, numerical results indicate that the leading edge position of splitter blades should be located at 60% of the main blade chord length, and the centrifugal impeller isentropic efficiency with ultra-high pressure ratio can be increased from 82.4% (the aerodynamic configuration with only full blades) to 89.5%; when an aerodynamic configuration with double-splitters is used, the leading edge positions of middle and short splitter blades should be respectively located at 40% and 60% of the main blade chord length, and the impeller isentropic efficiency can be further improved to 90.9%.