bluuebunny/crossref_metadata_2025_split huggingface dataset:
Leading Edge Contamination of a C-D Compressor Blade Using Large Eddy Simulation
Authors: Katiyar S. , Sarkar S. 
Published: January 2021

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
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

Abstract
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.