bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Dynamic Design Process of NovaLT™ Annular Combustors
Authors: Lal Bihari , Dabiru Venkata Rambabu , Provenzale Michele , Funghi Federico , Pucci Egidio , Allegorico Maddalena , Del Puglia Eugenio 
Published: January 2021

Abstract
NovaLT™ family gas turbines are new addition to Baker Hughes product portfolio covering 0–35MW power segment, setting a new standard in their class. These Gas Turbines are designed for high efficiency, maximized availability, longer maintenance intervals with modular replacement approach and equipped with low emission annular combustors.
Combustors are typically subjected to several failure mode mechanisms such as Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF), creep, buckling, oxidation, wear out and their interactions. The design of combustor for High Cycle Fatigue (HCF) is key challenge due to many unknown/uncertain parameters in operation such as constraints of hardware, damping capability, nature and magnitude of dynamic loads.
This paper is focused on structural dynamic design process of NovaLT™ annular combustors. While operating in inherent vibratory environment, caused by either combustion process or stationary/rotating structure, can result in HCF cracking of hardware due to resonance conditions coupled with unavailability of adequate damping in system.
Thus, a robust yet proportionately conservative structural dynamic design, successfully operating in various engine conditions, allowing flexible combustion operability limits, is needed.
Main purpose of this paper is to discuss about product design cycle, challenges and key observations through Annular Combustor design case studies, including experimental measurement of vibratory loads and dynamic response in real operating conditions, as well as a data matched structural dynamic prediction.
High-Fidelity Calculation of Floating Offshore Wind Turbines Under Pitching Motion
Authors: Ortolani Andrea , Persico Giacomo , Drofelnik Jernej , Jackson Adrian , Campobasso M. Sergio 
Published: January 2021

Abstract
The unsteady aerodynamics of floating offshore wind turbine (FOWT) rotors is more complex than that of fixed–bottom turbine rotors, and the uncertainty of low-fidelity aerodynamic predictions, such as those of the blade element momentum theory (BEMT) codes, is higher for the former rotors. Navier-Stokes CFD can improve the understanding of FOWT rotor and wake aerodynamics, and help improve lower-fidelity models. To highlight this potential, blade–resolved analyses of the in-house compressible CFD COSA code and the commercial incompressible CFD code FLUENT were used to investigate the unsteady flow of the NREL 5 MW rotor subjected to prescribed harmonic pitching past the tower base. CFD results were compared to the predictions of the FAST wind turbine code, using BEMT for rotor aerodynamics. Improved tuning of the COSA numerical set-up enabled close matching of the FAST rotor power and loads in fixed–tower mode, and high resolution of the near field wake dynamics; similar agreement levels were obtained with the FLUENT simulations. A novel user-defined function approach, enforcing an additional rigid body motion of the rotor grid conformal to the tower motion, enabled the FLUENT FOWT rotor simulations of this study, and provided new general-purpose FLUENT functionalities for FOWT analyses. All predicted periodic patterns of rotor power and thrust were found to be qualitatively similar, but the power peaks of both CFD predictions were significantly higher than those of FAST. Inspection of the CFD profiles of blade static pressure highlighted and quantified significant compressible flow effects on FOWT rotor power and loads. The blade–resolved analyses of the rotor downstream flow field revealed wake features unique to pitching turbine rotors, primarily the space- and time–dependence of the wake generation, highlighted by the intermittency of the tip vortex shedding.
Effects of Jet Impingement on Convective Heat Transfer in Effusion Holes
Authors: Huelsmann Nathan C. , Thole Karen A. 
Published: January 2021

Abstract
A common design for cooling the combustor liner of gas turbines is a double-wall composed of impingement jets that feed effusion cooling holes. An important cooling mechanism associated with the effusion hole is the convective cooling provided to the liner wall, which is in contact with the hot main gas flowing through the combustor. While the combination of impingement jets and effusion holes have been studied before, mostly in terms of cooling effectiveness, investigators have not fully evaluated the effect the impingement jet has on the local internal convection within the effusion hole. This study evaluates the detailed effects of the impingement geometry on the local convective heat transfer coefficients within the effusion hole, which provides insights as to the design decisions for cooling combustor liners. Using a scaled-up, 3D-printed effusion hole with a constant heat flux boundary condition, local convective heat transfer coefficients were measured for a range of impingement geometries and positions relative to the effusion holes. Results showed a strong influence on the convective heat transfer resulting from the placement of the impingement hole relative to the effusion hole. In particular, the results showed a strong sensitivity to circumferential and radial placement of the impingement jet with little sensitivity to the jet-to-effusion distance.
Nozzle Passage Endwall Effectiveness Values With Various Combustor Coolant Flow Rates: Part 2 — Endwall and Vicinity Surface Effectiveness Measurements
Authors: Nawathe Kedar P. , Zhu Rui , Lin Enci , Kim Yong W. , Simon Terrence W. 
Published: January 2021

Abstract
Effective coolant schemes are required for providing cooling to the first stage stator vanes of gas turbines. To correctly predict coolant performance on the endwall and vane surfaces, these coolant schemes should also consider the effects of coolant streams introduced upstream in the combustor section of a gas turbine engine. This two-part paper presents measurements taken on a first-stage nozzle guide vane cascade that includes combustor coolant injection. The first part of this paper explains how coolant transport and coolant-mainstream interaction in the vane passage is affected by changing the combustor coolant and endwall film coolant flow rates. This paper explains how those flows affect the coolant effectiveness on the endwall. Part one showed that a significant amount of coolant injected upstream of the endwall is present along the pressure surface of the vanes as well as over the endwall. Part two shows effectiveness measurement results taken in this study on the endwall and pressure and suction surfaces of the vanes. Sustained endwall coolant effectiveness is observed along the whole passage for all cases. It is uniform in the pitch-wise direction. Combustor coolant flow significantly affects cooling performance even near the trailing edge. The modified flow field results in the pressure surface being cooled more effectively than the suction surface. While the effectiveness distribution on the pressure surface varies with combustor and film coolant flow rates, the suction surface remains largely unchanged.
Analysis of the Heat Transfer Within Combustor Liners Using a Combined Monte Carlo and Two-Flux Method
Authors: Johnson Andressa L. , Zhao Xinyu 
Published: January 2021

Abstract
One of the consequences of increasing the efficiency of gas turbine combustors is the higher combustion temperatures within the chamber. Advances on managing larger heat loads have been made to protect the combustor wall and turbines. Among those are thermal barrier coatings (TBCs) deposited on metal walls and forced air cooling such as through effusion holes. Historically, both the flame and TBCs have received a simplified gray treatment using effective absorptivities and emissivities. However, studies have shown that the gray analysis can considerably under-predict the cold metal side temperature resulting in misguided combustor life estimates. In this study, non-gray radiation is compared to gray and black radiation by combining three-dimensional Monte Carlo Ray Tracing (MCRT) solution of non-gray flames in a model gas turbine combustor to one-dimensional energy balance within combustor liners. A recent large eddy simulation (LES) of a gas turbine combustor is analyzed, where both gray and non-gray models are exercised. A two-band spectral model is employed for the TBC, where a translucent band and an opaque band are identified. A line-by-line treatment for gas-phase radiation is adopted, and the incident radiative energy on the combustor wall is collected using the MCRT solver, where the fraction of radiative energy within the translucent band is collected and compared with those obtained from the blackbody assumption. The temperature distributions along the multi-layered combustor wall are computed and parametric comparison is conducted. The effects of the nongray flame radiation are more prominent at elevated pressures than at atmospheric pressure, leading to a difference of approximately 150 K in the prediction of peak temperature on the hot side of the TBC. The gray model is found to over-predict the TBC temperature at downstream locations, but under-predict the TBC temperature near the flame locations. The present study proposes a methodology to estimate the wall temperatures when radiation within the TBC is considered. Future work includes application of the methodology to more realistic combustors where both radiative fluxes and convective fluxes can be accurately captured.
Experimental Study on Flutter Stability of Transonic Cooled Turbine Blade Stage With 3-Dimensional Mode Shape Excitation
Authors: Kang Jeongseek , Perez Ethan , Vorobiev Alex , Morris Scott , Cameron Joshua , Kim Daehyun , Im Hongsik , Montgomery Matthew 
Published: January 2021

Abstract
It is well known that mode shape plays very important role in stability of turbine blade since the aerodynamic work per cycle and aerodynamic damping depend on mode shape. With the advancements of theoretical formulation with influence coefficient method, experimental studies with rigid body blade motion have significantly improved understanding of turbine flutter mechanisms and design parameters. However rigid body motion cannot accurately match the complex mode shapes of modern turbine blade, so there are limitations of accuracy on experimental evaluation of flutter stability with rigid body blade motion.
This study utilized 3-dimensional mode shapes for evaluating aerodynamic work per cycle and stability of turbine blade through experimental method. A transonic annulus turbine cascade rig was built at Notre Dame Turbomachinery Laboratory. Three center blades with modern cooled 3-dimensional aero design were instrumented with 144 EA of ultraminiature fast-response pressure transducers on the blade surface at 50%, 75%, and 95% of blade spans. Center blade and adjacent blades were designed to have the same blade mode shape as a reference turbine blade and the center blade was actuated with an electromagnetic shaker at natural frequencies of 1st bending and 1st torsional modes to simulate the same level of reduced frequencies under engine operating condition. Mode shape scanning of test blade through laser doppler vibrometer confirmed the design intent of blade bending and torsional mode shapes and their frequencies. All the dynamic pressure measurements on the three center blades were synchronized with blade position measurement and influence coefficient method was applied to calculate aerodynamic work per cycle and damping parameter. It was found that pressure side generally stabilizes the blade and that there was strong stable zone from leading edge to about 20% in arcwise coordinate torward suction side. After this zone, a destabilizing zone follows and this can be strong enough to destabilize the blade in some range of nodal diameter.
Proof of Concept for a Novel Interstage Injection Design in Axial Compressors
Authors: Doerr T. , Braun S. , Schuster S. , Brillert D. 
Published: January 2021

Abstract
A common technique to increase the thermal efficiency and the power output of gas turbines is to inject water upstream of the compressor section. Through the evaporation of the water throughout the compressor, an isothermal process is approached. A recently-developed technology for this enhanced process is Interstage Injection in which water is injected directly between the stages. One advantage of this over wet compression is the avoidance of icing, since the local temperatures at the injection positions are already above melting point. Moreover, stage characteristics and load distribution can be rearranged within the compressor by individually adjusting the injection amount in different stages. However, there is little practical understanding of this process, and suitable injection methods have still to be found.
This paper therefore demonstrates the implementation of a novel technology of Interstage Injection in an axial compressor test rig whereby twin jet nozzles are integrated directly into the trailing edge of the first stator row to deliver a homogenous spray over the entire radial span. Due to the resultant blade complexity, blades are manufactured by selective laser melting and subsequently installed in an enhanced four-stage axial compressor. The installed control and measurement principles of the test rig are presented and results demonstrate the functionality of the innovative design.
Mass Spring Interlocked Bladed Disk Model
Authors: Córdoba Oscar 
Published: January 2021

Abstract
A simplified bladed disk model with cantilever and interlock conditions is described. Blade is composed of three masses, two for the lower and higher part of the shroud, and one for the main core of the blade. A similar scheme is employed in the disk. The different masses in the model are linked with springs introducing the stiffness between them. Additional disk restrictions reduce the model capabilities but account the effect of common boundary conditions. The model simplicity allows an analytical solution with polynomials to understand the fundamentals of vibration. The extended stiffness and mass matrix with Lagrange multipliers are used. The modal frequencies and modes as function of the nodal diameter are studied. The interlock solution is compared to cantilever and different sorts of frequency curves have been identified and classified. Some basic conclusions related to the model parameters are achieved.
Aero-Thermal Aspects of Film Cooled Nozzle Guide Vane Endwalls: Part 1 — Aerodynamics
Authors: Alqefl Mahmood H. , Nawathe Kedar P. , Chen Pingting , Zhu Rui , Kim Yong W. , Simon Terrence W. 
Published: January 2021

Abstract
The first stage turbine of a modern gas turbine is subjected to high thermal loads which lead to a need for aggressive cooling schemes to protect its components from melting. Endwalls are particularly challenging to cool due to the complex system of secondary flows near them that wash the protective film coolants into the mainstream. This paper shows that without including combustor cooling, the complex secondary flow physics are not representative of modern engines. Aggressive injection of all cooling flows upstream of the passage is expected to interact and change passage aerodynamics and, subsequently, mixing and transport of coolants. This study describes, experimentally, the aero-thermal interaction of cooling flows near the endwall of a first stage nozzle guide vane passage. The test section involves an engine-representative combustor-turbine interface geometry, combustor coolant flow and endwall film cooling flow injected upstream of a linear cascade. The approach flow conditions represent flow exiting a cooled, low-NOx combustor. This first part of this two-part study aims to understand the complex aerodynamics near the endwall through detailed measurements of passage three-dimensional velocity fields with and without endwall film cooling. The aerodynamic measurements reveal a dominant vortex in the passage, named here as the Impingement Vortex, that opposes the passage vortex formed at the airfoil leading edge plane. This Impingement Vortex completely changes our description of flow over a modern film cooled endwall.
Numerical Investigation of the Effect of Flutter Instability of the Blade on the Unsteady Flow in a Modern Low-Pressure Turbine
Authors: Naung Shine Win , Rahmati Mohammad , Farokhi Hamed 
Published: January 2021

Abstract
Modern aeronautical Low-Pressure Turbines (LPTs) are prone to aeroelastic instability problems such as flutter. The aerodynamic performance of a modern LPT is often influenced by the interaction between the transient flow and the dynamic behaviour of the blade. Therefore, the investigation and understanding of the physics behind the interaction between the unsteady flow and the flutter phenomenon of the blade in an LPT, which is normally left out by existing studies, is an important aspect of the research to improve the aerodynamic performance of the turbine as well as to ensure the blade mechanical integrity. In this paper, a novel analysis is conducted to explore the flutter instability in a modern LPT, T106A turbine, using two inter blade phase angles (IBPAs), and their effects on the unsteady flow field are investigated. The zero degree and 180 degrees IBPAs are considered in this paper. A high-fidelity direct numerical simulation method is used for the flow simulations. Another distinctive feature of this paper is the use of the 3D model to analyse the effects associated with the 3D blade structure and the 3D vibration mode. The investigation and identification of adequate working ranges of the harmonic balance method, which has been widely used for the aeromechanical analysis of turbomachines, are also presented in this work. This paper will bridge a key gap in the knowledge of aeroelasticity modelling and analysis of modern LPTs.
On Predicting Weld Specimen Fatigue Life Based on Defect Data
Authors: Roychowdhury Sushovan , Månsson Tomas 
Published: January 2021

Abstract
Prediction of fatigue life based on internal defect data is an important research topic for components built through both traditional welds and modern additive manufacturing. In this work, a systematic approach is taken to investigate application of fracture mechanics principle for this purpose. To this end, fatigue test samples are prepared from TIG-welded titanium alloy sheets and also representative weld repairs of cast plates. Metro-tomography is employed to obtain information about internal defects in the specimens before fatigue testing. After fatigue testing, fractography is used to identify the defect that led to failure and to gather information on its location and size. The information from metro-tomography and fractography are then directly compared to assess the accuracy of the tomography data. Simple fracture mechanics methods are employed to estimate the fatigue life for each specimen, considering separately tomography and fractography data. Such estimates are then compared with fatigue life from tests. Through such quantitative comparisons, the work highlights the advantages and the challenges of the fracture mechanics approach to assess the fatigue life of test specimens with internal defects. A key observation is that life estimates employing a fracture mechanics approach are reasonable when the defect leading to failure is known, but the challenge may lie in a-priori identification of the defect that would eventually lead to failure.
Quick Start of an Industrial Gas Turbine Engine Through the Development of “Silent Start” VGV Schedule
Authors: Krishnababu Senthil , Panov Vili , Jackson Simon , Dawson Andrew 
Published: January 2021

Abstract
In this paper, research that was carried out to optimise an initial variable guide vane schedule of a high-pressure ratio, multistage axial compressor is reported. The research was carried out on an extensively instrumented scaled compressor rig. The compressor rig tests carried out employing the initial schedule identified regions in the low speed area of the compressor map that developed rotating stall. Rotating stall regions that caused undesirable non-synchronous vibration of rotor blades were identified. The variable guide vane schedule optimisation carried out balancing the aerodynamic, aero-mechanical and blade dynamic characteristics gave the ‘Silent Start’ variable guide vane schedule, that prevented the development of rotating stall in the start regime and removed the non-synchronous vibration. Aerodynamic performance and aero-mechanical characteristics of the compressor when operated with the initial schedule and the optimised ‘Silent Start’ schedule are compared. The compressor with the ‘Silent Start’ variable guide vane schedule when used on a twin shaft engine reduced the start time to minimum load by a factor of four and significantly improved the operability of the engine compared to when the initial schedule was used.
The Effect of Wall Thermal Boundary Condition on Natural Convective Shutdown Cooling in a Gas Turbine
Authors: Fahy Daniel D. , Ireland Peter 
Published: January 2021

Abstract
As a civil gas turbine cools down, asymmetric natural convective heat transfer causes the bottom sector of the rotor to cool faster than the top; this circumferential thermal gradient can potentially cause the shaft to deflect — a phenomenon called thermal or rotor bow. Rotor bow is tremendously difficult to predict due to its dependence on a number of engine design parameters, in addition to the complex nature of natural convective flows.
A novel experimental facility has been developed to gain further understanding into shutdown cooling of a gas turbine. The scope of this paper is to quantify the effect of basic design features on natural convective cooling in an engine annulus during shut-down; specifically the influence of the thermal boundary wall conditions and the annular diameter ratio. In addition to this, a low-cost, robust thermocouple probe has been developed and validated, which allows for accurate temperature measurements in a natural convective boundary layer.
An extensive experimental campaign has been completed. The key finding is that the local radial wall temperature difference was found to be the most influential parameter on the local heat transfer. Non-isothermal walls did not alter the overall distribution of the inner wall equivalent conductivity. This was true for both cylindrical and conical sections. An appropriate characteristic length for use in the Rayleigh number definition for both the concentric cylinder and conical sections have been validated. The conical inner section (5° hade angle) did not affect the overall heat transfer in the range of conditions tested. Therefore, the mean surface heat transfer for non-isothermal inner and outer profiles, within the range −0.4 &lt; ΔRa/RaLc &lt; 0.4, where the thermal gradient is negative in the clockwise from top-dead-centre, can be predicted using isothermal correlations for RaLc &lt; 5.0 × 105 and Dr &lt;= 1.5.