bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and functional responses in sun spurge (Euphorbia helioscopia L.) against post‐emergence herbicides in wheat (Triticum aestivum L.)
Authors: Iftikhar Mishal , Ahmad Iftikhar , Hameed Mansoor , Fatima Sana , Ahmad Farooq , Ashraf Muhammad , Nazish Zoya , Ahmad Muhammad Sajid Aqeel , Muneeb Ahmad
Published: January 2021

We investigated changes in plant morphology, anatomy and physiology in a commonly occurring weed, Euphorbia helioscopia L. due to exposure to post‐emergence herbicides. Weed plants were sprayed with one of the following herbicides: pyrimidinyl sulphonylharnstoffe (PS), tribenuron‐methyl (TM), fluroxypyr‐methyl tribenuron‐methyl (FMTM) and bromoxynil (Br). The PS treatment significantly decreased plant height, promoted initiation of side branches and induced a prostrate habit. A specific response of root anatomy to PS and Br treatments was the high proportion of storage parenchyma. The Br‐treated plants showed thickest roots with a significantly large storage parenchyma, not only in the central portion of roots, but also in the cortical parenchyma outside the vascular tissue. A high proportion of xylem in the central portion of roots in the TM or FMTM‐treated plants provides a strong survival response in E. helioscopia. Disintegration of stem cortical parenchyma is the most prominent response of E. helioscopia when treated with a herbicide like PS or FMTM. Survival against these herbicides relates to a complete ring of vascular bundles and intact cortical parenchyma outside the vascular tissue. Increased leaf thickness was recorded in most of the cases except in the FMTM‐treated plants. The PS‐treated plants showed midrib thickness with two distinct vascular bundles. The cortical region, however, was found to be damaged by tissue collapse forming a large lysigenous aerenchyma. Euphorbia helioscopia had altered morphology, anatomy and physiology in response to herbicide application, which changed its growth in the field. To achieve control of this weed species, alternative strategies or higher doses of herbicide should be applied. Further research is required to determine the interaction of surviving weed plants with the crop.
Merkstenen
Authors: Bouckaert Jos
Published: January 2021

In de universitaire wereld staat kennis centraal. Die wordt doorgegeven, maar ook in vraag gesteld. Dankzij creatief wetenschappelijk onderzoek verleggen kennisgrenzen zich voortdurend. De impact van de academische wereld op maatschappelijke domeinen zoals de technologie, de industrie, de economie en de medische sector kan niet overschat worden. Om deze belangrijke maatschappelijke functie te blijven vervullen, heeft de moderne universiteit zich ontpopt tot een dynamische en ondernemende instelling. Vertrekkend vanuit zijn persoonlijke ervaring en kennis van het innovatielandschap in België heeft Jos Bouckaert de ontwikkeling van de ondernemende onderzoeksuniversiteit beschreven. Elke fase is opgevat als merksteen, een cruciale stap in een groter verhaal. In dit lijvige werk schetst Bouckaert hoe in de tweede helft van de 20e eeuw een unieke constellatie van politici, rectoren, ondernemers, filantropen en vooral wetenschappers de basis legde van de huidige kenniseconomie in België. Met de postume uitgave van dit levenswerk brengen collega’s en vrienden hulde aan Jos Bouckaert.
Evolving as a Digital Scholar
Authors: Van Petegem Wim , Bosman JP , De Klerk Miné , Strydom Sonja
Published: January 2021

What does it take to become a digitally agile scholar? This manual explains how academics can comfortably navigate the digital world of today and tomorrow. It foregrounds three key domains of digital agility: getting involved in research, education and (community) service, mobilising (digital) skills on various levels, and acting in multiple roles, both individually and interlinked with others. After an introduction that outlines the foundations of the three-dimensional framework, the chapters focus on different roles and skills associated with evolving as a digital scholar. There is the author, who writes highly specialised texts for expert peers; the storyteller, who crafts accessible narratives to a broader audience in the form of blogs or podcasts; the creator, who uses graphics, audio, and video to motivate audiences to delve deeper into the material; the integrator, who develops and curates multimedia artefacts, disseminating them through channels such as websites, webinars, and open source repositories; and finally the networker, who actively triggers interaction via social media applications and online learning communities. Additionally, the final chapters offer a blueprint for the future digital scholar as a professional learner and as a “change agent” who is open to and actively pursues innovation. Informed by the authors’ broad and diverse personal experience, Evolving as a digital scholar offers insight, inspiration, and practical advice. It equips a broad readership with the skills and the mindset to harness new digital developments and navigate the ever-evolving digital age. It will inspire academic teachers and researchers with different backgrounds and levels of knowledge that wish to enhance their digital academic profile.
Heat Transfer Due to Thermoelastic Wave Propagation in a Porous Rod
Authors: Singh Baljeet
Published: January 2021

This paper investigates the propagation of thermoelastic waves in a homogeneous, linear, and isotropic porous solid. For physical and mathematical simplicity, one-dimensional wave propagation in a porous solid rod is considered to explain the concept of heat transfer caused by motion. The solutions of governing equations show that the transfer of heat in a porous rod is not only due to the conduction but also produced by the local particle displacement phenomenon. It is observed that the time-averaged transfer of heat depends on the circular frequency, porosity, thermal conductivity, thermal relaxation, specific heat, and other material coefficients.
Modeling of Residual Stresses After Shot Peening and the Effect of Accounting Their Influence on the Stress State of Turbine Blade Fir Tree Roots
Authors: Vasilyev Boris , Zhukov Nikita , Kiselev Igor , Selivanov Alexander
Published: January 2021

Numerical modeling approaches have been developed for simulating shot peening processes and consideration of compressive residual stresses when performing strength calculations of turbine wheel joints.

A three-stage method is presented to combine strength analyses of turbine blade with the output of LS-DYNA simulations (RS diagrams) of multiple impacts. Predictions of RS distributions obtained using the suggested approach are compared with experimental data and good correlation was achieved. The effect of the RS diagrams obtained using various SP parameters on the stress-strain state of the turbine blade root and the values of its cyclic durability are estimated.
Blade Damping Mechanisms and Some Recent Failures
Authors: Gowreesan Vamadevan , Guzman Armando , Greaves Wayne
Published: January 2021

The rotating blades of a steam turbine perform the important task of converting the thermal energy of the steam into rotating mechanical work or torque. Hence, these blades have to be very robust and they need to be installed properly in the discs of the turbine. Damping mechanisms are used to improve the stiffness of the blades and to minimize the vibrations of the blades. Different types of blade damping mechanisms are used in steam turbines. Shroud bands, lashing or damping wires, pins, tie-bolts and lashing stubs/ snubbers are the most common types of damping mechanisms used in steam turbines. Several factors such as stress distribution, additional centrifugal stresses due to the added weight of the damping mechanisms, aerodynamic effects, resulting harmful mode shapes and critical vibration frequencies etc., need to be considered in the selection and the design of the damping mechanisms.

Due to the various types of operating conditions and stresses, the damping mechanisms can experience failure in service. Metallurgical evaluations of some of the recent failures of damping mechanisms are discussed here. Failures of shroud bands, blade tenons, tie-bolts and damping wires are the particular examples presented. SCC (stress corrosion cracking), fatigue and overload were found to be the main modes of failures in these examples. The purpose of discussing these examples is to make the designers, the manufacturers and the users aware of these potential issues so that corrective actions can be taken.
On the Probabilistic Endurance Prediction Approach for Turbomachinery Blades and Vanes
Authors: Kulkarni Davendu Y. , Peng Caetano
Published: January 2021

The design and aeromechanical assessment of turbomachinery blades and vanes comprises a wide range of complex processes that tend to be based on conventional deterministic methods. These processes often provide a ‘snapshot’ evaluation of the new component designs at the nominal operating conditions. While the deterministic methods can predict the high cycle fatigue (HCF) endurance with reasonable accuracy; they assume that the conservative safety factors applied to cover for the parametric variations, uncertainties and unknowns will not change during the product life cycle. This approach is intended to be conservative and in some cases may overlook the lack of robustness.

The present paper proposes a robust design analysis approach based on probabilistic methodology for the aeromechanical assessment of rotor blades and stator vanes of turbomachinery. The robust design approach can account explicitly for the effects of design and manufacturing variability. This methodology can reduce the levels of conservatism in the deterministic approach and can provide a more thorough risk assessment.

This paper offers a generalised aeromechanical analysis formulation based on probabilistic methods to evaluate the HCF capability of turbomachinery components. Herein, this methodology is demonstrated by using a typical stator vane of an aero engine compressor and it is based on Monte-Carlo and DOE simulations. The methodology consists of parametric sensitivity studies and identification of the most influential parameters that control the HCF endurance. Future ideas and roadmap of the aeromechanical probabilistic analysis capability development are also discussed.
New Numerical Analysis Method for Creep Lifetime of Gas Turbine Materials by Using the Discrete Cosine Transform
Authors: Hiraguchi Hideo
Published: January 2021

Recently the Discrete Cosine Transform[1], [2], [3] which is a modified Fourier Transform has begun to be used to express coefficients of creep equations using the power law or the exponential law such as Bailey-Norton law[4], [5] and θ Projection[6], [7], [8], [9], [10]. In addition, the Discrete Cosine Transform has begun to be used to express a creep equation itself. We have already found that the Discrete Cosine Transform can express the temperature and stress dependence property of the coefficients of the creep equations at the same time by the two-dimensional Discrete Cosine Transform using 8 × 8 discrete signals[11]. Furthermore, we have already found that the Discrete Cosine Transform can fit measured creep strain values very well from the primary creep region to the tertiary creep region using 8 discrete signals and it can estimate creep strain values between the measured points by interpolation very well[12]. However it has not been known if the Discrete Cosine Transform can predict the long term creep curve by using the short term creep data yet. Therefore, as a next stage, we tried to estimate the long term creep curve from the short term creep data of gas turbine materials by extrapolation using the Discrete Cosine Transform. As a result, we were able to obtain a useful numerical analysis method by utilizing the Discrete Cosine Transform Coefficients and others as a new extrapolation method. It is found that this new numerical method would be able to predict the configuration of 150,000-hour creep curve by using 500-hour to 13,000-hour short term creep data.
Heat Transfer of Impinging Jet-Row Onto Trapezoidal Channel With Different Effusion and Discharge Conditions
Authors: Chang Shyy Woei , Chiang Pei-An , Cai Wei Ling
Published: January 2021

The heat transfer performances of the trapezoidal channel with the impinging row jets normal to the channel apex wall with no effusion and three effusion conditions from one, two and three rows of bleeding holes along the channel apex, or, and, channel sidewalls were studied. At each effusion condition, the airflow extraction from the channel tip were regulated as full open conditions, and 0% (full close), 5%, 10% of the total airflow rate fed into the trapezoidal channel via the impinging row jets. For each effusion and discharge condition, the full-field heat transfer data over the channel apex and sidewalls were measured at channel Reynolds numbers of 5000, 7500, 10000, 12500 and 15000 using the steady-state infrared thermography method. The corresponding axial distributions of the jet mass flow rate at each effusion and discharge condition were measured at all the Reynolds numbers tested. While the crossflow and channel flow confinement significantly affected the axial distribution of the jet flow rate for the channel without effusion, the impact of effusion and discharge conditions on the distribution of the airflow rate through the row jet was negligible for the effusion channels. Without effusion, the strong crossflow effects acted with the weakened jet momentums near the sealed channel hub to substantially reduce the regional heat transfer rates. With effusion, the flow confinement formulated by the cavity-like channel hub and the crossflow developed along the test channel were significantly suppressed, leading to the even distribution of jet flow and the recovered impinging-jet heat transfer properties over the channel hub region. The preferential heat transfer performances among the present test channels with and without effusion gave rise to the channel with three rows of effusion holes. Relative to the heat transfer impacts caused by varying the row number of the effusion holes, the impacts of tip extraction were less evident; but the overall heat transfer performance was improved by reducing tip discharge. With leading-edge cooling applications to a gas turbine blade, three sets of heat transfer correlations that evaluated the regionally averaged Nusselt numbers over the channel apex and side walls with and without effusions at various tip extractions were devised.
LM9000 Passive Clearance Control (PCC)
Authors: Marchetti Simone , Nappini Duccio , De Prosperis Roberto , Di Sisto Paolo
Published: January 2021

This paper describes the design of the Free Power Turbine (FPT) of the LM9000, in particularly the design of its Passive Clearance Control (PCC) system.

The LM9000 is the aero-derivative version of the GE90-115B jet engine. Its core engine has many common parts with the GE90; what differs is the booster (low pressure compressor) and the lower pressure turbine (LPT).

The booster of the LM9000 is without fan because the engine is not used to provide thrust but torque only, subsequently it has a new flow path [5].

The LPT has instead been replaced by an intermediate pressure turbine (IPT) and by the FPT. The IPT drives the booster, while the FPT is a free low-pressure turbine designed for both power generation and mechanical drive industrial applications, including LNG production plants.

Due to its different application, the LM9000 FPT flow path differs sensibly from the GE90 LPT, however as the GE90 it is provided of a clearance control system that cools the casing in order to reduce its radial deflection.

It is not the first time that a clearance control system has been used in industrial applications; in GE aero-derivative power turbines is already present in the LM6000 and LMS100.

Design constraints, system complexity, high environment variability because the PCC is located outside the GT, harsh environments and long periods of usage still make the design of this component challenging.

The design of the PCC has been supported by extensive heat transfer and mechanical simulations. Each PCC component has been addressed with a dedicated life calculation and all the blade and seal clearances have been estimated for all the operating conditions of the engine. Simulations have been validated by an extensive test campaign performed on the first engine.
Effects of Inlet Guide Vanes on the Performance and Stability of an Aeronautical Centrifugal Compressor
Authors: Poujol Nicolas , Trébinjac Isabelle , Duquesne Pierre
Published: January 2021

A research centrifugal compressor stage designed and built by Safran Helicopter Engines is tested at 3 IGV (Inlet Guide Vanes) stagger angles. The compressor stage includes 4 blade rows: axial inlet guide vanes, a backswept splittered impeller, a splittered vaned radial diffuser and axial outlet guide vanes. The methodology for calculating the performance is detailed, including the consideration of humidity in order to minimize errors related in particular to operating atmospheric conditions.

The shift of the surge line towards lower mass flow rate as the IGV stagger angle increases highly depends on the rotation speed. The surge line shift is very small at low rotation speeds whereas it significantly increases at high rotation speeds. A firstorder stability analysis of the impeller and diffuser subcomponents shows that the diffuser (resp. impeller) is the first unstable component at low (resp. high) rotation speeds. This situation is unaltered by increasing the IGV stagger angle.

At low rotation speeds below a given mass flow rate, rotating instabilities at the impeller inlet are detected at zero IGV stagger angle. Their occurrence is conditioned by the relative flow angle at the tip of the leading edge of the impeller. As the IGV stagger angle increases, the mass flow decreases to maintain a given inlet flow angle. Therefore, the onset of the rotating instabilities is delayed towards lower mass flow rates.

At high rotation speeds, the absolute flow angle at the diffuser inlet near surge decreases as the IGV stagger angle increases. As a result, the flow is highly alternate over two adjacent channels of the radial diffuser beyond the surge line at IGV stagger angle of 0°.
On the Leakage and Dynamic Force Coefficients of a Novel Stepped Shaft Pocket Damper Seal: Experimental and Numerical Verification
Authors: Yang Jing , San Andrés Luis , Lu Xueliang
Published: January 2021

High performance turbomachinery favors annular seals with a large damping coefficient to ensure rotor system stability. Pocket damper seals (PDSs), a variation of labyrinth seals with axial blades (ribs) and adding circumferential partition walls (ridges), produce a favorable damping performance. To further enhance the damping characteristic and reduce leakage, a novel stepped shaft PDS is hereby introduced. The invention has a unique arrangement of steps on the rotor surface, each facing an upstream rib in a pocket row. Thus, the step and a blade tip form a tight clearance (c1), while the rotor surface and the downstream blade tip make a larger clearance (c2). The convergence-divergence variation of cross-section areas along the flow direction increases the PDS damping coefficient. To validate the performance of the novel design, a stepped shaft PDS (c1/c2 = 0.5) with four axial ribs and eight circumferential pockets is built and tested. A comprehensive investigation, experimental and computational, produces the seal leakage and dynamic force coefficients for the stepped shaft PDS, as well as similar performance characteristics for an identical PDS with a smooth rotor surface (c1/c2 = 1, i.e., a uniform clearance PDS). The stepped shaft PDS operates with air at supply pressure (PS) ranging from 1.1 bar to 3.2 bar. The measured leakage for the stepped shaft PDS is 50% of that for the uniform clearance PDS. Computational fluid dynamics (CFD) and bulk flow model (BFM) predictions of leakage agree well with the test data. For PS = 2.3 bar, the test damping coefficient (C) for the stepped shaft PDS is ∼ 1.5 times greater than the one for the uniform clearance PDS. With an increase in PS to 3.2 bar, the stepped shaft PDS shows a two and one half increase in damping coefficient. In comparison to the test data, a CFD model over estimates C by 29% for operation at PS = 3.2 bar, though capturing the variation trend versus whirl frequency. The BFM largely under predicts C for the stepped shaft PDS and is abandoned for future work. Both the test data and CFD predictions demonstrate the superior damping performance of the stepped shaft PDS, thus providing a novel alternative seal configuration for turbomachinery usage.
High Pressure Optical Measurements of Temperature at Turbine Rotor Inlet Conditions
Authors: Egbert Scott C. , Zeltner Darrel , Rezasoltani Mohsen , Tree Dale R.
Published: January 2021

The measurement of combustion product gas temperature is valuable for the development and control of many combustion systems. In gas turbine engines, measurement of the rotor inlet temperature remains particularly challenging because of harsh operating conditions and limited access. The Integrated Spectral Band Ratio (ISBR) method is a non-intrusive optical emission gas temperature measurement technique suitable for this application. Optical fibers made of sapphire were used to transmit the radiative signal from the post combustion zone to a Fourier Transform Infrared (FTIR) spectrometer without the need for probe cooling. The ratio of spectral bands of H2O, nominally 100 cm−1 wide between 4600 and 6200 cm−1 were used to infer temperature. ISBR and thermocouple measurements were obtained during two temperature sweeps; one at high load and one at low load (pressures of 1.2 and 0.7MPa, respectively). The average of three thermocouples 76 mm downstream of the ISBR measurements were consistently on the order of 200 K lower, consistent with a radiative correction and the heat loss between the two measurements. The change in ISBR temperature (95 K) during the sweep was similar to the change in average thermocouple temperature (89 K). Repeatability of the optical measurement at a given operating condition was on the order of ± 15 K and the absolute uncertainty of a single ISBR temperature measurement was estimated to be ± 61 K. A linear correlation with an R-squared value of 0.97 was also found between raw optical signal and thermocouple measurements suggesting that once a calibrated measurement is obtained, changes in gas temperature can be determined using a correlation of the raw signal to produce the temperature.
Experimental Investigation of the Performance of H-Darrieus Wind Turbines With Tubercle Leading Edge Blades
Authors: Du Longhuan , Dominy Robert G. , Ingram Grant
Published: January 2021

The most significant challenge associated with employing small-scale H-Darrieus wind turbines is to ensure that they self-start without compromising their efficiency at the design operating condition. One of the key and straightforward methods to improve the turbine performance is to choose an optimized blade profile. It has been shown that by creating rounded protuberances (tubercles) around the blade leading edge, not only do the blades demonstrate a more gradual stall characteristic but also that the tubercles significantly increase the blade lift performance in the post-stall regime at the expense of slightly degraded lift performance in the pre-stall regime. This effect might be beneficial for the H-Darrieus turbine application where the blades experience extreme incidence range during the turbine start-up period. Therefore, in this study the performance of standard NACA0021 blades is compared experimentally to a modified set of blades which have a sinusoidal tubercle configuration along the original NACA0021 blade leading edge (0 ≤ x ≤ 0.3c). Time-accurate, self-starting data were recorded from wind tunnel tests under different flow conditions and the power coefficient (Cp) versus tip speed ratio (λ) curve was calculated. It is demonstrated conclusively that blades with an appropriate configuration of tubercle leading edges can considerably improve turbine self-starting capability. To the best of the authors’ knowledge, this study provides the first experimental data of H-Darrieus wind turbine performance with tubercle leading edge blades and the data are valuable for future designs and for the validation of simulation models.
Wall-Resolved Large-Eddy Simulation of the LS89 Cascade Using an Explicit Local Time-Stepping Method
Authors: Martin Benjamin , Duchaine Florent , Gicquel Laurent , Odier Nicolas , Dombard Jérôme
Published: January 2021

In most turbomachinery CFD simulations, a large heterogenity of mesh refinement exists because specific flow regions are known to require small cell sizes for proper prediction. This leads to large cell volume ratios between the smallest and largest cells. In the context of explicit solvers where the timestep is imposed by stability constraints and smallest cell size, large difference in cell sizes may directly lead to a waste of CPU time since this timestep is much smaller than required in the majority of cells. The introduction of a Local Time-Stepping (LTS) is a potential solution to such an observation. The computational domain is divided in multiple sub-domains and each sub-domain will meet its local stability constraints, relaxing the limit of maximal allowed timesteps. In the following, this technique is applied to a wall-resolved Large-Eddy Simulation (LES) of the LS89 turbine vane cascade dividing the domain in two parts: one part containing the near-wall region of the blade (with prism layers at the blade surface leading to a small timestep) and a second part composed of the remaining volume. To evaluate the strategy, a standard wall-resolved simulation and its LTS counterpart are compared to experimental data. Overall, for the LS89 configuration that is known as challenging, there is an excellent agreement between simulations and experiment. More importantly, a 31% speedup is achieved on this configuration while giving identical results when comparing the single domain and the LTS cases despite the significant simulation cost reduction for the latter.
Leading Edge Contamination of a C-D Compressor Blade Using Large Eddy Simulation
Authors: Katiyar S. , Sarkar S.
Published: January 2021

A large-eddy simulation (LES) is employed here to predict the flow field over the suction surface of a controlled-diffusion (C-D) compressor stator blade following the experiment of Hobson et al. [1]. When compared with the experiment, LES depicts a separation bubble (SB) in the mid-chord region of the suction surface, although discrepancies exist in Cp. Further, the LES resolves the growth of boundary layer over the mid-chord and levels of turbulence intensity with an acceptable limit. What is noteworthy that LES also resolves a tiny SB near the leading-edge at the designed inflow angle of 38.3°. The objective of the present study is to assess how this leading-edge bubble influences the transition and development of boundary layer on the suction surface before the mid-chord. It appears that the separation at leading-edge suddenly enhances the perturbation levels exciting development of boundary layer downstream. The boundary layer becomes pre-transitional followed by a decay of fluctuations up to 30% of chord attributing to the local flow acceleration. Further, the boundary layer appears like laminar after being relaxed from the leading edge excitation near the mid-chord. It separates again because of the adverse pressure gradient, depicting augmentation of turbulence followed by the breakdown at about 70% of chord.
The Use of Integrated Mild/Partial Gasification Combined (IMPGC) Cycle Technology As a Potential Retrofit Option for Pulverized Coal Plants
Authors: Long Henry A. , Wang Ting
Published: January 2021

Around 50% of the world’s electrical power supply comes from the Rankine cycle, and the majority of existing Rankine cycle plants are driven by coal. The problem is that coal power plants are environmentally unfriendly; particularly, older plants have low thermal efficiency and poor emissions. In addition, the conventional and common practices for retrofitting those older plants can only provide incremental improvements for plant performance and emissions. This paper introduces the concept of the Integrated Mild/Partial Gasification Combined (IMPGC) Cycle as one promising new technology that has the potential to significantly increase the thermal efficiency of these older plants as well as reduce their emissions. In contrast to the conventional Integrated Gasification Combined Cycle (IGCC), IMPGC makes use of warm gas cleanup as well as mild and partial gasification to conveniently and seamlessly convert a simple Rankine cycle to a combined cycle, greatly improving the efficiency of the plant without altering the base plant’s design. Three different scenarios in total were simulated in addition to a simple subcritical Rankine cycle plant as a baseline for comparison: (1) a case using the same fuel input as the original baseline, (2) a case with the same total maximum power output as the baseline, and (3) a case where the turbine with the highest steam pressure (HPST) has the same mass flow rate through it as the equivalent turbine from the baseline case. The results show that IMPGC can improve the efficiency of Rankine cycles by up to nine (9) points (or ∼23%) and has the potential to augment total net power output by up to 2.5 times. This paper will analyze the specific challenges associated with retrofitting these plants and examine how the retrofit affects the plant performance and emissions.
Analysis of the Unsteady Flow Field Inside a Fan-Shaped Cooling Hole Predicted by Large-Eddy Simulation
Authors: Agarwal Shubham , Gicquel Laurent , Duchaine Florent , Odier Nicolas , Dombard Jérôme
Published: January 2021

Film cooling is a common technique to manage turbine vane and blade thermal environment. Optimizing its cooling efficiency is furthermore an active research topic which goes in hand with a strong knowledge of the flow associated with a cooling hole. The following paper aims at developing deeper understanding of the flow physics associated with a standard cooling hole and helping guide future cooling optimization strategies. For this purpose, Large Eddy Simulations (LES) of the 7-7-7 fan-shaped cooling hole [1] is performed and the flow inside the cooling hole is studied and discussed. Use of mathematical techniques such as the Fast Fourier Transforms (FFT) and Dynamic Mode Decomposition (DMD) is done to quantitatively access the flow modal structure inside the hole based on the LES unsteady predictions. Using these techniques, distinct vortex features inside the cooling hole are captured. These features mainly coincide with the roll-up of the internal shear layer formed at the interface of the separation region at the hole inlet. The topology of these vortex features is discussed in detail and it is also shown how the expansion of the cross-section in case of shaped holes aids in breaking down these vortices. Indeed upon escaping, these large scale features are known to not be always beneficial to film cooling effectiveness.
Modelling Conjugate Heat Transfer Within a Gas Turbine Secondary Air System Using Thermo-Fluid System Simulation
Authors: Hunt David , Yuan Youming
Published: January 2021

This paper presents a novel approach that couples system modelling of both the thermo-fluid system and the thermal solid system by modelling conjugate heat transfer within a single 1D system analysis solver and applies it to the Secondary Air System of a Gas Turbine.

The Secondary Air System design has to balance minimizing engine bleed whilst ensuring sufficient cooling. To achieve this, designers model both the secondary air flow and the temperature distribution in solid components.

System CFD tools like Simcenter Flomaster may be used to solve flow, pressure and temperature distributions and a 3D thermal solver used to perform the thermal analysis of the blade and disc solids. The thermal interaction between the secondary flow system and the solid components is a key part of the model and is known as conjugate heat transfer analysis (CHT).

This approach is problematic early in the design cycle when detailed or stable geometry information may not be available for the 3D thermal tool.

An approach that couples the modelling of both the thermo-fluid system and the thermal solid system within a single 1D/system analysis tool offers the advantage of faster modelling and consistent model accuracy of both fluid and solid components, especially in the early concept design stage.

This 1D-CHT approach has been implemented within Simcenter Flomaster and validated using an idealized analytical solution. It is shown that the model can be applied to the analysis of gas turbine secondary air systems including cavity flows and thermal analysis of the rotor and stator discs that form the thermal boundary of these cavities using Simcenter Flomaster alone.
Strip-Yield Modeling of Load-Time-Temperature Effects on Crack Growth in Engine Materials
Authors: Newman James C. , Sullivan Rani
Published: January 2021

Plastic and creep deformations around a crack front and in the wake of a moving crack under cyclic loading are implemented into the life-prediction code, FASTRAN (a strip-yield model). Creep deformations are modeled by stress relaxation around the crack-tip location, since the crack-front material is under displacement control due to the surrounding elastic material. Sinusoidal and trapezoidal loading are considered. A modified linear superposition model was used to compute the cyclic- and time-dependent damage, which was based on the stress-intensity-factor concept for creep-brittle materials. Application of the modified strip-yield model was made on two sets of test data on Inconel-718 alloy. The environments were laboratory air or helium gas. From the literature, the “environment” had been shown to be a major contributor to damage magnitudes. Thus, the time-dependent crack-growth constants were selected to match the test data. In addition, the effects of a small overload on time-dependent damage, and the effects of stress relaxation and varying temperatures on crack-opening stresses and cyclic crack-tip-opening displacements, were studied.
Experiment-Based Preliminary Design Guidelines for Consideration of Profile Vortex Shedding From Low-Speed Axial Fan Blades
Authors: Daku Gábor , Vad János
Published: January 2021

The paper presents hot wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds-number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt-trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for consideration of profile VS in preliminary design of axial fans in moderation of VS-induced blade vibration and noise emission.
A Novel Approach to the Stabilization of Auto-Igniting Flames Within a Gas Turbine Sequential Combustor, Through the Control of Static Temperature Variation Along the Premixing and Flame Zones
Authors: Syed K. J. , Benim A. C. , Pasqualotto E. , Payne R. C.
Published: January 2021

The present work proposes a novel concept for a sequential burner and combustor that can be located downstream of a first stage combustor or downstream of a turbine stage in the case of a reheat gas turbine. The novel aspect is the method of flame anchoring, which, instead of relying on dump expansion as in the present state-of-the-art, relies on setting up a static temperature gradient through the premixing and flame zones. The advantage of this is that anchoring of the auto-igniting flame is not dependent on fluid mechanic phenomena, and reaction can proceed at rates governed by the chemical kinetics. Under these circumstances, CO can reach its equilibrium in ≪ 1ms, which allows for compactness and the potential of single digit NOx emissions at hot gas temperatures in excess of 2100K.

Pressure loss is a critical aspect, as the concept requires flows to be accelerated to high velocities (M∼0.7). However, it is shown that pressure losses can be limited to 4–5%.

The concept is evaluated through analytical and 1D approaches, while the feasibility of achieving a design that meets the desired turbulence characteristics at an acceptable pressure loss is demonstrated by way of 3D CFD.
The Effects of Inlet Boundary Layer Condition and Periodically Incoming Wakes on Secondary Flow in a Low Pressure Turbine Cascade
Authors: Schubert Tobias , Chemnitz Silvio , Niehuis Reinhard
Published: January 2021

A particular turbine cascade design is presented with the goal of providing a basis for high quality investigations of endwall flow at high-speed flow conditions and unsteady inflow. The key feature of the design is an integrated two-part flat plate serving as a cascade endwall at part-span, which enables a variation of the inlet endwall boundary layer conditions. The new design is applied to the T106A low pressure turbine cascade for endwall flow investigations in the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at the Bundeswehr University Munich. Measurements are conducted at realistic flow conditions (M2th = 0.59, Re2th = 2·105) in three cases of different endwall boundary layer conditions with and without periodically incoming wakes. The endwall boundary layer is characterized by 1D-CTA measurements upstream of the blade passage. Secondary flow is evaluated by Five-hole-probe measurements in the turbine exit flow. A strong similarity is found between the time-averaged effects of unsteady inflow conditions and the effects of changing inlet endwall boundary layer conditions regarding the attenuation of secondary flow. Furthermore, the experimental investigations show, that all design goals for the improved T106A cascade are met.
A Life Prediction Model for Single-Crystal Nickel-Base Alloys Under Low-Cycle Fatigue
Authors: Irmak Firat , Wijeyeratne Navindra , Yun Taejun , Gordon Ali
Published: January 2021

In the development and assessment of critical gas turbine components, simulations have a crucial role. An accurate life prediction approach is needed to estimate lifespan of these components. Nickel base superalloys remain the material of choice for gas turbine blades in the energy industry. These blades are required to withstand both fatigue and creep at extreme temperatures during their usage time. Nickel-base superalloys present an excellent heat resistance at high temperatures. Presence of chromium in the chemical composition makes these alloys highly resistant to corrosion, which is critical for turbine blades. This study presents a flexible approach to combine creep and fatigue damages for a single crystal Nickel-base superalloy. Stress and strain states are used to compute life calculations, which makes this approach applicable for component level. The cumulative damage approach is utilized in this study, where dominant damage modes are capturing primary microstructural mechanism associated with failure. The total damage is divided into two distinctive modules: fatigue and creep. Flexibility is imparted to the model through its ability to emphasize the dominant damage mechanism which may vary among alloys. Fatigue module is governed by a modified version of Coffin-Manson and Basquin model, which captures the orientation dependence of the candidate material. Additionally, Robinson’s creep rupture model is applied to predict creep damage in this study. A novel crystal visco-plasticity (CVP) model is used to simulate deformation of the alloy under several different types of loading. This model has capability to illustrate the temperature-, rate-, orientation-, and history-dependence of the material. A user defined material (usermat) is created to be used in ANSYS APDL 19.0, where the CVP model is applied by User Programmable Feature (UPF). This deformation model is constructed of a flow rule and internal state variables, where the kinematic hardening phenomena is captured by back stress. Octahedral, cubic and cross slip systems are included to perform simulations in different orientations. An implicit integration process that uses Newton-Raphson iteration scheme is utilized to calculate the desired solutions. Several tensile, low-cycle fatigue (LCF) and creep experiments were conducted to inform modeling parameters for the life prediction and the CVP models.
Numerical Investigation of Rotor and Journal Bearing Parameters on Nonlinear Vibration of a Highly Flexible Rotor Considering Journal Angular Motion With Experimental Verification
Authors: Koondilogpiboon Nuntaphong , Inoue Tsuyoshi
Published: January 2021

In this study, the nonlinear vibration (bifurcation type) of a highly flexible rotor supported by a journal bearing (JB) and self-aligning rolling element bearing (REB) under various configurations of rotor large disk mass/position, bearing length-to-diameter (L/D) ratio, and preload was investigated using two different bearing models: the model that considers both lateral and angular motion (Model A) and the model that considers just lateral motion (Model B). The rotor was modelled by 1-D finite elements (FE), and its degrees-of-freedom (DOF) was reduced to the DOF of the JB’s node by real mode component mode synthesis (CMS). Then, the shooting method and arclength continuation were applied to the reduced rotor model to obtain nonlinear limit cycles. Also, parallel computing was applied to the shooting method to shorten the calculation time. The stability of the obtained limit cycles was then determined by Floquet multiplier analysis. The experiment on the test rig with the same rotor and bearing parameters utilized in the calculation was carried out to verify the bearing models in each configuration. The calculation and experimental results showed that the bifurcation type calculated by Model A agreed with experimental results in all configurations. In addition, if the L/D ratio was short or the large disk position was near the rotor midspan, the bifurcation type obtained from both Model A and B agreed with the experimental results. The discrepancy in bifurcation type obtained from both bearing models only occurred in the cases that the L/D ratio was long and the large disk position was near the JB. Lastly, decreasing the L/D ratio, increasing preload, and moving the large disk position closer to the JB tended to change the bifurcation type from subcritical to supercritical.
Effects of Clearance on the Performance of a Labyrinth Seal Under Wet-Gas Conditions
Authors: Zhang Min , Childs Dara W. , Tran Dung L. , Shrestha Hari
Published: January 2021

The labyrinth seal is one of the most popular non-contact annular seals used in centrifugal compressors to improve machine efficiency by reducing the secondary flow leakage. Reducing the radial clearance Cr can effectively decrease the seal’s leakage and therefore increase the machine efficiency. However, reducing Cr can also introduce undesired effects on the machine’s vibration behaviors. This paper experimentally studies the impact of reducing Cr on the leakage and rotordynamic coefficients of a 16-tooth see-through labyrinth seal under wet-gas conditions. The test seal’s inner diameter is 89.256 mm. Two rotors with different diameters are used to obtain two radial clearances (0.102 mm and 0.178 mm). Tests are carried out at a supply pressure of 62 bars, three speeds from 10krpm to 20 krpm, three pressure ratios from 0.21 to 0.46, and six inlet liquid volume fractions (LVFs) from zero to 15%. The test fluid is a mixture comprised of air and silicon oil. Test results show that, for all pure-air and mainly-air conditions, decreasing Cr decreases (as expected) the test seal’s leakage mass flow rate. For all test cases, direct dynamic stiffness KΩ is negative, producing a negative centering force on the associated rotor. For inlet LVF ≤ 8%, the effects of decreasing Cr on KΩ are negligible. When inlet LVF = 12% and 15%, decreasing Cr increases KΩ (decreases the magnitude). In other words, when inlet LVF = 12% and 15%, decreasing Cr reduces the test seal’s negative centering force on the rotor, and would increase the critical speeds of the rotor. The value of the effective damping Ceff near 0.5ω represents the seal’s capability to suppress the rotor’s potential whirling motion at about 0.5ω. For all pure-air and mainly-air conditions, decreasing Cr generally increases the Ceff value near 0.5ω; i.e., decreasing Cr improves the test seal’s stabilizing capability against the rotor’s potential whirling motion at about 0.5ω.
A Steady Transonic Linear Cascade for True Scale Cooling Measurements
Authors: Zuccarello Jeremy , Saltzman David , Lynch Stephen , Haydt Shane , Whitfield Christopher
Published: January 2021

The design and benchmarking measurements for a steady, transonic linear cascade for film cooled airfoils are presented. The facility holds up to 11 true scale turbine airfoils with high span to chord ratio for two-dimensional flow at the airfoil midspan. Mainstream air is continuously supplied by a compressor, while desiccant dried air is used as the cooling flow to match coolant-to-mainstream density ratios. The cooling system supplies three airfoils, each with independent circuits, to enable parametric studies of cooling with periodicity for central airfoils. Independent Mach and Reynolds number control at steady conditions is achieved by using control valves and a bypass loop. Incidence angle studies can be performed by using a turntable and modular guide wall system. Optical windows include a zinc selenide window for spatially resolved surface temperature measurements using infrared thermography, as well as glass windows for flowfield measurements using laser-based diagnostics. The infrared camera setup enables a 360 degree view around the surface of the central airfoil. For laser-based diagnostics, laser sheets can be delivered to the central airfoil through glass inserts in the guidewalls. Current benchmarking results include static pressures on the blade surface and endwall, inlet boundary layer, and freestream turbulence measurements at various Mach numbers, Reynolds numbers, and incidence angles. Results indicate excellent periodicity over a wide range of conditions. Near term work in the facility will investigate film cooling at transonic conditions for a representative modern blade geometry.