bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Statistical Calibration for Model Verification and Validation, Diagnosis of Model Inadequacy, and Improving Simulation Accuracy
Authors: OFlaherty Kevin , Graves Zachary , Xiong Lie , Andrews Mark
Published: August 2018

The paper presents an application of statistical calibration techniques to a bracket design fatigue model simulated in COMSOL Multiphysics®. The calibration will tune the bracket’s material properties and fatigue characteristics. For illustrative purposes, the test data used to calibrate the simulation model will be generated from the same simulation routine with the addition of an intentionally applied bias and random noise to simulate model form and physical testing errors. The accuracy and conclusions from the statistically calibrated model will be compared with the uncalibrated model as well as a model calibrated with conventional error minimization methods. Multiple metrics will be shown which can be used for model validation, including a discrepancy map which characterizes inadequacies in the simulation. The metrics used in the comparison will also include results from optimization, sensitivity analysis, and propagation of uncertainties motivated by manufacturing variations during bracket fabrication. The results will demonstrate the importance of calibrating a model before drawing design conclusions.
A Mean Stress Correction to a Ductility Exhaustion Approach for Gas Turbine Component Life Assessment
Authors: Green Richard , Douglas Jonathan , Moffat Andrew , Meyer Christopher
Published: August 2018

Components in the hot section of a gas turbine experience both load cycles and high temperature dwells as the engine is subjected to starts, changes in load, dwells and shut downs. These loading profiles can lead to damage from both fatigue and creep and can also lead to the interaction of these two damage mechanisms over the duration of the service interval. Accurate prediction of the accumulation of this damage is critical to managing the engine and avoiding unplanned down time and cost over the operational period.

Ductility Exhaustion uses the rate dependent ductility of a material to determine damage from creep and fatigue. This approach can be used to calculate damage during shakedown as a result of redistribution and relaxation due to plasticity and creep, and can be critical for accurately predicting the remaining useful life of hot section components subjected to variations in load.

This paper presents a modification to an existing approach in order to address the effects of mean stress on upper shelf ductility and improve the accuracy of the damage prediction during shakedown. The approach, based on two common superalloys, predicts how damage accumulated during the initial shakedown period can be modified to account for mean stress effects. Thereby improving the accuracy of the overall component life prediction for optimal engine management.
Mechanical Properties and Structure of Laser Beam and Wide Gap Brazed Joints Produced Using Mar M247-Amdry DF3 Powders
Authors: Gontcharov Alexandre , Tian Yuan , Lowden Paul , Brochu Mathieu
Published: August 2018

The microstructure and mechanical properties of materials produced by Wide Gap Brazing (WGB) and Laser Beam (LBW) cladding with different blends of Mar M247 and Amdry DF-3 brazing powders were studied. It was shown that LBW Mar M247 based materials comprised of 0.6 to 1 wt. % B were weldable. The weld properties were superior to WGB deposits with the same bulk chemical composition, due to the formation of a dendritic structure typical for welded joints, and the precipitation of cuboidal borides of Cr, Mo, and W in the ductile Ni-Cr based matrix. Both materials were found to have useful properties for 3D additive manufacturing (AM) and repair components manufactured from high gamma prime precipitation hardened superalloys.
Metallographic and Materials Evaluation of a Cracked Radial Steam Turbine Rotor
Authors: Gowreesan Vamadevan , Greaves Wayne
Published: August 2018

A radial steam turbine developed cracks after 220,000 hours of service. The rotor had an integral disc with eight rows of blades, and a short stub. Nine inlets on the disc channeled steam from one side to the other, and then radially outward.

Analysis of the fracture surface revealed cracks originating in some of the inlet holes, and propagating by fatigue. No material defects were found at the crack initiation sites. Hardness and microstructure (optical) across the disc were uniform, but chemical composition analysis of the alloy revealed high level of phosphorus and sulfur. In addition, the microstructure consisted of uniformly tempered martensite with manganese sulfide stringers. Although tensile properties were normal, impact testing indicated embrittlement by a shift in Fracture Appearance Transition Temperature (FATT). Metallurgical evidence of embrittlement was also found. It was concluded that service induced cyclic loading in combination with reduced crack resistance caused by embrittlement lead to cracking.
A Study on Matching Between Centrifugal Compressor Impeller and Low Solidity Diffuser and its Extension to Vaneless Diffuser
Authors: Tamaki Hideaki
Published: August 2018

A centrifugal compressor requires a wide operating range as well as a high efficiency. At high pressure ratios, the impeller discharge velocity becomes transonic and effective pressure recovery in a vaned or vaneless diffuser is necessary. At high pressure ratios, a vaned diffuser is used as it has high pressure recovery, but may have a narrow operating range. At low flow, diffuser stall may trigger surge. At high flow, choking in the throat of the vanes may limit the maximum flow rate.

A low solidity diffuser allows a good pressure recovery because it has vanes to guide the flow and a wide operating range as there is no geometrical throat to limit the maximum flow. In experimental studies at a pressure ratio around 4:1, the author has replaced vaned diffusers with a range of low solidity diffusers to try to broaden the operating range. The test results showed that the low solidity diffuser also chokes. In this paper, a virtual throat is defined and its existence is confirmed by flow visualization and pressure measurements. A method to select low solidity diffusers is proposed based on test data and the fundamental nature of the flow.

The extension of the proposed method to the selection of a vaneless diffuser is examined and a design approach for a vaneless diffuser system to minimize surge flow rate without limiting the attainable maximum flow rate is proposed.
Simulation of the Primary Jet Breakup of Non-Newtonian Fuels: Basic Research for Simulation-Assisted Design of Low-Grade Fuel Burner
Authors: Müller Thomas , Kadel Kathrin , Habisreuther Peter , Trimis Dimosthenis , Zarzalis Nikolaos , Sänger Alexander , Jakobs Tobias , Kolb Thomas
Published: August 2018

The research work of the present study is focused on the numerical simulation of primary breakup of high-viscosity non-Newtonian fluids. For the experimental investigation of fluid properties such as viscosity, surface tension and flow behaviour on the jet breakup an external mixing twin-fluid nozzle is used, as investigated in a previous study [Müller et al., ASME Turbo Expo 2016, GT2016-56371]. To describe the disintegration process of the fluids, characteristic features like liquid jet morphology, breakup length, breakup frequency and spray angle are evaluated. Furthermore, the primary breakup of slurries is simulated without discretizing the particles as a third phase, which heavily reduced the computational effort. Instead, the physical properties (density, viscosity) of the liquid phase take the influence of the particles into account.

The primary breakup was investigated using the open source CFD software OpenFOAM. To gather the morphology of the primary breakup and the flow field characteristics compressible large eddy simulations (LES) were performed and the movement of the gas-liquid interface was captured by means of the Volume of Fluid-Method (VOF).

The conducted simulations showed good agreement with experimental results with respect to the characteristic features (e.g. breakup length) and the significant influence of viscosity and surface tension on the primary breakup. It is reasonably justified that the used OpenFOAM code and VOF is sufficient to simulate the primary breakup of particle laden liquids without discretizing particles as a third phase. Moreover, those findings contribute to a better understanding of the physics responsible of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.
Investigating Discrepancies in Vibration Bending Fatigue Behavior of Additively Manufactured Titanium 6Al-4V
Authors: Scott-Emuakpor Onome , Holycross Casey , George Tommy , Sheridan Luke , Carper Emily , Beck Joseph
Published: August 2018

The vibration bending fatigue life uncertainty of additively manufactured Titanium (Ti) 6Al-4V specimens is studied. In this investigation, an analysis of microscopic discrepancies between 10 fatigued specimens paired by stress amplitude is correlated to the bending fatigue life scatter. Through scanning electron microscope (SEM) analysis of fracture surfaces and grain structures, anomalies and distinctions such as voids and grain geometries are identified in each specimen. This data along with previously published results are used to support assessments regarding bending fatigue uncertainty. Corrections on stress and scatter based on microscopic features are implemented to the stress versus fatigue life comparisons. The results of this investigation show that the bending fatigue life uncertainty can be bounded by cold-rolled Ti 6Al-4V data when correcting the tested stress amplitude values with stress concentration effects and variation due to microstructure geometries. The understanding gained from this study is important for future development of a predictive vibration bending fatigue life model that will include the probability of geometry, density, and location of voids as an artifact of LPBF build parameters.
Scale-Resolving Simulations of Low-Pressure Turbine Cascades With Wall Roughness Using a Spectral-Element Method
Authors: Garai Anirban , Diosady Laslo T. , Murman Scott M. , Madavan Nateri K.
Published: August 2018

The accurate prediction of wall–roughness effects in turbomachinery is becoming critical as turbine designers address airfoil surface quality and degradation concerns arising from the shift to advanced ceramic matrix composite (CMC) or additively–manufactured airfoils operating in higher temperature environments. In this paper, a recently developed computational capability for accurate and efficient scale–resolving simulations of turbomachinery is extended to analyze the boundary–layer separation and transition characteristics in a rough–wall low–pressure turbine (LPT) cascade. The computational capability is based on an entropy–stable discontinuous–Galerkin spectral–element approach that extends to arbitrarily high orders of spatial and temporal accuracy, and is implemented in an efficient manner on a modern high–performance computer architecture. Results from the scale–resolving simulations of both smooth and rough airfoil cascades are presented and compared to previous experiments and numerical simulations. The results show that the suction–surface boundary layer undergoes laminar separation, transition, and turbulent reattachment for the smooth airfoil cascade, while in the presence of roughness the separation and transition behavior of the suction–surface boundary layer is substantially modified. The differences between the smooth and rough airfoil cascades are then highlighted by a detailed analysis of their respective turbulent flow fields.
Research on Optimal Matching Method of Variable Stator Vanes for Multi-Stage Compressor Based on Genetic Algorithm
Authors: Wang Zhitao , Fan Kuo , Ma Wenqi , Li Tielei , Li Shuying
Published: August 2018

As one of the anti-surge technique, the adjusting scheme of VSV under off-design conditions has a significant impact on the performance of gas turbine. With the limitation of time and cost, it is difficult to study the adjusting scheme of VSV by experimental method under a wide operating range. With the development of the gas turbine simulation, integrated simulation technology is used to study the simulation of whole or part of gas turbine from different views and levels. It has become an effective way to optimize the performance of gas turbine. Based on the existing one-dimensional HARIKA algorithm and the zero dimensional gas turbine simulation model, a new compressor characteristic module and a scaling interface module are built up for studying the characteristics of the variable geometry compressor. The compressor one-dimensional characteristic calculation program is embedded into the zero dimensional gas turbine general model to replace the original compressor characteristic module. Taking the surge margin of LC and the efficiency of gas turbine as the optimization objectives, the optimal VSV matching angle of multi-stage compressor is obviously benefit from using the optimization algorithm based on genetic algorithm. In addition, this paper also analyzes the steady-state performance of the gas turbine. After optimization, the efficiency of the three-shaft gas turbine under different operating conditions was improved by 1.912% on average and the surge margin was increased by 2.78% meanwhile, the fuel consumption was reduced. Thus, the optimization of this paper has proved to be of great significance to improve the performance of gas turbine.
Impact of Nonuniform Stagger Angle Distribution on High-Pressure Compressor Rotor Performance
Authors: Zheng Siyu , Teng Jinfang , Wu Yu , Guo Fushui , Lu Shaopeng , Qiang Xiaoqing
Published: August 2018

The focus of the present study is to find a solution to the manufacturing tolerances of rotor stagger angle in the high pressure compressor. The manufacturing processes of compressor blades may lead the stagger angle to be out of tolerance, which would reduce the performance of the high-pressure compressor. Meanwhile, the assembly may cause the nonuniform distribution of the variable blades. To investigate the influence of stagger angle variability and its nonuniform distribution in multiple passages, amount of 3D numerical simulations of a high pressure compressor rear-stage rotor were conducted in the present paper. The Gaussian Probabilistic Density Function was used to obtain the sampled blades with variable stagger angles, and then the blades were randomly allocated in a single passage to a half period, respectively. Numerical results show that with the increase of passage number, the total performance varies more stably. In order to get an appropriate tolerance range of the stagger angle to control the deterioration of the total performance, different ranges were tried, and [−1.5°, +1.5°] was determined as the final range to do further analyses. The different stagger angle distribution along the circumferential direction of a specific group of several sampled blades led to the different performance variations. When the stagger angle distribution approximately satisfied the sinusoidal function during assembly, the rotor performance was better than other distributions. Hence, the sinusoidal function during assembly is an effective solution to the manufacturing tolerances of rotor stagger angle.
Multi-Objective Optimization of Inclined Discrete Cavities in a Centrifugal Compressor Using Hybrid Optimization Techniques
Authors: Ma Sang-Bum , Kim Kwang-Yong
Published: August 2018

In order to extend the operating range of a centrifugal compressor, inclined discrete cavities located upstream of the impeller leading edge were optimized in this work. Aerodynamic performance analysis was performed using three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. A parametric study on aerodynamic performances of the centrifugal compressor with the inclined discrete cavities was conducted with six geometrical parameters. Through the parametric study, three geometric parameters were selected as design variables for optimization. Peak adiabatic efficiency and stall margin were selected as objective functions. The Latin hypercube sampling method was used to select the design points, and the radial basis neural network was used to construct surrogate models of the objective functions. A hybrid method combining the particle swarm optimization showed better overall performance in finding global optimum than the genetic algorithm. Pareto-optimal solutions provided the designs which enhance considerably both the performance parameters compared to the reference design.
A Comparison of the Transfer Functions and Flow Fields of Flames With Increasing Swirl Number
Authors: Gatti M. , Gaudron R. , Mirat C. , Zimmer L. , Schuller T.
Published: August 2018

The frequency response of premixed swirled flames is investigated by comparing their Transfer Function (FTF) between velocity and heat release rate fluctuations. The equivalence ratio and flow velocity are kept constant and four different swirling injectors are tested with increasing swirl numbers. The first injector features a vanishing low swirl number S = 0.20 and produces a flame anchored by the recirculating flow in the wake of a central bluff body. The three other swirling injectors produce highly swirled flows (S > 0.6) leading to a much larger internal recirculation region, which size increases with the swirl level. When operating the burner at S = 0.20, the FTF gain curve smoothly increases to reach a maximum and then smoothly decreases towards zero. For the highly swirled flames (S > 0.6), the FTF gain curve shows a succession of valleys and peaks attributed to interferences between axial and azimuthal velocity fluctuations at the injector outlet. The FTF phase-lag curves from the vanishing low and highly swirled flames are the same at low frequencies despite their large differences in flame length and flame aspect ratio. Deviations between the FTF phase lag curves of the different swirled flames start above the frequency corresponding to the first valley in the FTF gain of the highly swirled flames. Phase averaged images of the axial flow fields and of the flame chemiluminescence are used to interpret these features. At forcing frequencies corresponding to peak FTF gain values, the cold flow response of all flames investigated is dominated by large coherent vortical structures shed from the injector lip. At forcing frequencies corresponding to a valley in the FTF gain curve of the highly swirled flames, the formation of large coherent structures is strongly hindered in the cold flow response. These observations contrast with previous interpretations of the mechanisms associated to the low FTF response of swirled flames. It is finally found that for flames stabilized with a large swirl number, heat release rate fluctuations result both from large flame luminosity oscillations and large flame volume oscillations. For conditions leading to a small FTF gain value, both the flame luminosity and flame volume fluctuations are suppressed confirming the absence of strong perturbations within the flow at these frequencies. The experiments made in this work reveal a purely hydrodynamic mechanism at the origin of the low response of swirling flames at certain specific frequencies.
Effect of Aft Rotor on Forward Rotor Blade Wakes in Open Rotor Propulsion Systems
Authors: DeLorenzo Charles , Deleon Jared , Slaboch Paul E.
Published: August 2018

NASA’s Environmentally Responsible Aviation (ERA) project supported the collection of a large stereoscopic Particle Image Velocimetry (PIV) dataset of the Open Rotor Propulsion Rig (ORPR) in the 9 × 15 Low Speed Wind Tunnel at the NASA Glenn Research Center (GRC). The data collection effort acquired a volume of three component velocity measurements composed of 30 planes from near the hub radially outward towards the tip. The PIV cameras and laser were mounted to a traverse that allowed the entire data acquisition system to move from plane to plane. The PIV data acquisition was triggered on the front rotor such that the front rotor was always in the same position for each acquisition event. The aft rotor position was not recorded and varied randomly during the acquisition.

Because the position of the aft rotor was not synchronized to either the forward rotor or the camera it was necessary to separate individual PIV images based off of the phase of the aft rotor before they could be processed. The phase of the aft rotor was determined by locating the outline of the rotor in the PIV images and determining its position relative to a known point. This process was conducted by an image processing algorithm. Previous algorithms were able to make a relatively accurate 3D model of the wake between the forward and aft rotors, however some small inaccuracies were present. Improvements to this algorithm allowed for more accurate phase averaging, which yielded an improved PIV dataset. Both rotors were set to the same nominal rotational speed, however variations in motor control and other physical mechanisms allowed for some differences in the true RPM of the two rotors.

The effects of the aft rotor on the front rotor blade wakes within the inter-rotor flow field of the ORPR were examined. The aft rotor potential field was shown to have significant upstream impact on the front rotor wakes, altering their topology approaching the aft rotor. The wake strength was quantified through determination of the minimum velocities that occurred within a wake while a defined velocity deficit from the free stream velocity was used to determine the width of the wake. This work has potential applications to the radiated acoustics and efficiency of open rotor propulsion systems.
Experimental Investigation on Heat Up and Cool Down Procedure of a Steam Turbine Valve Casing
Authors: Xu Sihua , Hu Zhiqiang , He Jin , Xiao Lei , Li YueYue
Published: August 2018

Specification about flexible operation for steam turbine is now put forward by the new power plant client and discussed by regular users more frequently in China. This calls for more accurate design works than past to evaluate the influence to life time of the steam turbine components. As widely known, the transient temperature field analysis is most important boundary to life prediction. It is especially a challenge for complex structure component. Experimental investigation is a necessary and good measure for this task.

In this paper, an experimental investigation on heat up and cool down procedure of a steam turbine inlet valve casing is presented. The valve body with more than 70 temperature sensors is heat-up to 470°C, and then been cool-down to room temperature. The heat transfer behavior is investigated. The results are used to explain the thermal behavior during startup and the closing down of the steam turbine.
Novel Test Facility for Investigation of the Impact of Thermally Induced Stress Gradients on Fatigue Life of Cooled Gas Turbine Components
Authors: Thiele Marcus , Gampe Uwe , Fischer Kathrin A.
Published: August 2018

A novel test facility has been designed and set up for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients with respect to the damage evolution of cooled gas turbine components. Thermally induced stress gradients differ from geometrically induced stress gradients. From the point of view of stress mechanics, they are independent from external loads. From the perspective of material mechanics, their impact on service life is influenced by locally different material properties and strength. However, the impact of thermally induced stress gradients on the cyclic life of high loaded, cooled components is not precisely known. In order to increase knowledge surrounding these mechanisms, a research project was launched. To achieve high temperature gradients and extended mechanical stress gradients, large heat fluxes are required. The authors developed a test bench with a unique radiant heating to achieve very high heat fluxes of q̇ ≥ 1.6MW/m2 on cylindrical specimen. Special emphasis has been placed on homogenous temperature and loading conditions in order to achieve valid test results comparable to standard low cycle or thermo-mechanical fatigue tests. Different test concepts of the literature were reviewed and the superior performance of the new test rig concept was demonstrated.

The austenitic stainless steel 316L was chosen as the model material for commissioning and validation of the test facility. The investigation of thermally induced stress gradients and, based on this analysis, low-cycle fatigue tests with superimposed temperature gradients were conducted.

Linear elastic finite element studies were performed to calculate the local stress-strain field and the service life of the test specimens. The test results show a considerable influence of the temperature gradient on the low-cycle fatigue life of the investigated material. Both the temperature variation over the specimen wall and thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results increase the understanding of fatigue damage mechanisms under local unsteady conditions and can serve as a basis for improved lifetime calculation methods.
The Heron Fan: Concept Description and Preliminary Aerothermodynamic Analysis
Authors: Schöning Finn , Kozulovic Dragan
Published: August 2018

The Heron Fan is a new concept of a fuel powered jet engine that does not utilize a conventional core engine. The fan, a single axial compressor of high diameter, creates thrust, similar to a turbofan. Its blades are hollow with inner channels to transport the core air from the hub to the tip, inducing radial compression. The combustion chamber is located in the casing region, either integrated in the blades or in an external ring. After burning, the core air is returned to the blades and is blown out through an expansion device with a large component in circumferential direction. This propels the fan in the opposite direction. The expansion device may be realized by nozzles integrated in the blade trailing edge or by turbine stages integrated in the blade tip region. Subsequently, the core air mixes with the bypass air, which passes the fan axially, and ejects through the main nozzle, producing thrust. To achieve higher compression ratios, it is possible to install core air compressor stages ahead of the fan.

The main purpose of this concept is to reduce weight and complexity of the engine, leading to lower production and operating costs. This is achieved by simplifying the engine architecture, integrating the functions and shortening some of the components. In particular, the core engine has been rearranged, thus eliminating the second and in some cases the third shaft. Further, the complete expansion and parts of the compression have been integrated in the fan blade. To assess the aero-thermodynamic parameters, a preliminary cycle analysis has been done, where the most influential parameters were varied. The results show, that the above listed benefits can be achieved while maintaining an efficiency comparable to conventional turbofans. Further, a feasibility study in terms of geometry, internal flow, component implementation and installation has been done, in order to qualify the concept and to identify the most critical aspects. To incorporate the corresponding thoughts and results, as well as to find and eliminate conceptual conflicts and opposing trends, a CAD model has been generated. Overall, the results are sound and encouraging, hence justifying future investigations. However, the Heron Fan concept also brings structural, thermal and aerodynamic challenges which are illustrated and briefly discussed, but still need detailed investigation.
A 3D Conjugate Approach for Analysing a Double-Walled Effusion-Cooled Turbine Blade
Authors: Ngetich Gladys C. , Ireland Peter T. , Murray Alexander V. , Romero Eduardo
Published: August 2018

A double-wall cooling scheme combined with effusion cooling offers a practical approximation to transpiration cooling which in turn presents the potential for very high cooling effectiveness. The use of the conventional conjugate CFD for the double-wall blade can be computationally expensive and this approach is therefore less than ideal in cases where only the preliminary results are required.

This paper presents a computationally efficient numerical approach for analysing a double-wall effusion cooled gas turbine blade. An existing correlation from the literature was modified and used to represent the two-dimensional distribution of film cooling effectiveness. The internal heat transfer coefficient was calculated from a validated conjugate analysis of a wall element representing an element of the aerofoil wall and the conduction through the blade solved using a finite element code in ANSYS*.

The numerical procedure developed has permitted a rapid evaluation of the critical parameters including; film cooling effectiveness, blade temperature distribution (and hence metal effectiveness) as well as coolant mass flow consumption. Good agreement was found between the results from this study and that from literature. This paper shows that a straightforward numerical approach that combines an existing correlation for film cooling from the literature with a conjugate analysis of a small wall element can be used to quickly predict the blade temperature distribution and other crucial blade performance parameters.
Aerodynamic Similarity Principles and Scaling Laws for Windmilling Fans
Authors: Prasad Dilip
Published: August 2018

Windmilling requirements for aircraft engines often define propulsion and airframe design parameters. The present study is focused is on two key quantities of interest during windmill operation: fan rotational speed and stage losses. A model for the rotor exit flow is developed, that serves to bring out a similarity parameter for the fan rotational speed. Furthermore, the model shows that the spanwise flow profiles are independent of the throughflow, being determined solely by the configuration geometry. Interrogation of previous numerical simulations verifies the self-similar nature of the flow. The analysis also demonstrates that the vane inlet dynamic pressure is the appropriate scale for the stagnation pressure loss across the rotor and splitter. Examination of the simulation results for the stator reveals that the flow blockage resulting from the severely negative incidence that occurs at windmill remains constant across a wide range of mass flow rates. For a given throughflow rate, the velocity scale is then shown to be that associated with the unblocked vane exit area, leading naturally to the definition of a dynamic pressure scale for the stator stagnation pressure loss. The proposed scaling procedures for the component losses are applied to the flow configuration of Prasad and Lord (2010). Comparison of simulation results for the rotor-splitter and stator losses determined using these procedures indicates very good agreement. Analogous to the loss scaling, a procedure based on the fan speed similarity parameter is developed to determine the windmill rotational speed and is also found to be in good agreement with engine data. Thus, despite their simplicity, the methods developed here possess sufficient fidelity to be employed in design prediction models for aircraft propulsion systems.
Numerical Study of a Micro Gas Turbine Integrated With a Supercritical CO2 Brayton Cycle Turbine
Authors: Reale Fabrizio , Iannotta Vincenzo , Tuccillo Raffaele
Published: August 2018

The primary need of reducing pollutant and greenhouse gas emissions has led to new energy scenarios. The interest of research community is mainly focused on the development of energy systems based on renewable resources and energy storage systems and smart energy grids. In the latter case small scale energy systems can become of interest as nodes of distributed energy systems. In this context micro gas turbines (MGT) can play a key role thanks to their flexibility and a strategy to increase their overall efficiency is to integrate gas turbines with a bottoming cycle.

In this paper the authors analyze the possibility to integrate a MGT with a super critical CO2 Brayton cycle turbine (sCO2 GT) as a bottoming cycle (BC). A 0D thermodynamic analysis is used to highlight opportunities and critical aspects also by a comparison with another integrated energy system in which the waste heat recovery (WHR) is obtained by the adoption of an organic Rankine cycle (ORC).

While ORC is widely used in case of middle and low temperature of the heat source, s-CO2 BC is a new method in this field of application. One of the aim of the analysis is to verify if this choice can be comparable with ORC for this operative range, with a medium-low value of exhaust gases and very small power values. The studied MGT is a Turbec T100P.
Numerical and Experimental Investigation on an Effusion-Cooled Lean Burn Aeronautical Combustor: Aerothermal Field and Emissions
Authors: Mazzei L. , Puggelli S. , Bertini D. , Andreini A. , Facchini B. , Vitale I. , Santoriello A.
Published: August 2018

Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NOx and soot in particular). Its implementation however involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. Also the conditions at the combustor exit are a concern, as high turbulence, residual swirl and the impossibility to adjust the temperature profile with dilution holes determine a harsher environment for nozzle guide vanes.

This work describes the final stages of the design of an aeronautical effusion-cooled lean burn combustor. Full annular tests were carried out to measure temperature profiles and emissions (CO and NOx) at the combustor exit. Different operating conditions of the ICAO cycle were tested, considering Idle, Cruise, Approach and Take-Off. Scale-adaptive simulations with the Flamelet Generated Manifold combustion model were performed to extend the validation of the employed CFD methodology and to reproduce the experimental data in terms of RTDF/OTDF profiles as well as emission indexes. The satisfactory agreement paved the way to an exploitation of the methodology to provide a deeper understanding of the flow physics within the combustion chamber, highlighting the impact of the different operating conditions on flame, spray evolution and pollutant formation.
Characterization of a Supersonic Turbine Downstream of a Rotating Detonation Combustor
Authors: Liu Zhe , Braun James , Paniagua Guillermo
Published: August 2018

Rotating detonation combustors offer theoretically a significant total pressure increase, which may result in enhanced cycle efficiency. The fluctuating exhaust of rotating detonation combustors, however, induces low supersonic flow and large flow angle fluctuations at several kHz which affects the performance of the downstream turbine. For such flows, power extraction can be achieved by either integrating a diffuser with a conventional subsonic turbine or a nozzle with a supersonic turbine. In this paper, a numerical methodology is proposed to characterize a supersonic turbine exposed to fluctuations from rotating detonation combustors without any dilution. The inlet conditions of the turbine were extracted from a three dimensional unsteady Reynolds-Averaged Navier-Stokes simulation of a nozzle attached to a rotating detonation combustor, optimized for minimum flow fluctuations and a mass-flow averaged Mach number of 2 at the nozzle outlet. In a first step, a supersonic turbine able to handle steady Mach 2 inflow was designed based on a method of characteristics solver and total pressure loss was assessed. Afterwards unsteady simulations of eight stator passages exposed to periodic oblique shocks were performed. Total pressure loss was evaluated for several oblique shock frequencies and amplitudes. The unsteady stator outlet profile was extracted and used as inlet condition for the unsteady rotor simulations. Finally, a full stage unsteady simulation was performed to characterize the flow field across the entire turbine stage. Power extraction, airfoil base pressure, and total pressure losses were were assessed, which enabled the estimation of the loss mechanisms in supersonic turbine exposed to large unsteady inlet conditions. Frequency analysis of the pressure field across the turbine rows was used to evaluate the damping of the oblique shock waves.
Sensitivity of Reduced Kinetic Models: The CFD Simulation of SCO2 Oxy-Combustion
Authors: Liu Zefang , Gao Xiang , Karimi Miad , Ochs Bradley , Acharya Vishal , Sun Wenting , Delimont Jacob , Andrews Nathan
Published: August 2018

Current research on supercritical carbon dioxide (SCO2) oxy-combustion is lacking studies on the performance of kinetic models. An optimized 13 species kinetic model is proposed in the present work for CH4/O2/CO2 oxy-combustion. This 13 species kinetic model is developed based on the detailed USC Mech II mechanism with the Global Pathway Selection algorithm, and then optimized with a genetic algorithm covering conditions of pressure from 150 atm to 300 atm, temperature from 900 K to 1800 K and equivalence ratio from 0.7 to 1.3. The autoignition of 13 species kinetic model presents less than 12% error relative to that of the USC Mech II. The performance of the proposed kinetic model is evaluated using a generic jet in crossflow combustor. Simulations at identical conditions are conducted in ANSYS Fluent for both the 13 species model and a global 5 species model. Results were then compared to evaluate the sensitivity of these two kinetic models to the CFD simulations. The results show a better mixing between the fuel and the oxygen, a longer autoignition delay and a more reasonable temperature distribution using the 13 species kinetic model. It is indicating the importance of choice on kinetic models in numerical simulation.
Mistuning Evaluation Comparison via As-Manufactured Models, Traveling Wave Excitation, and Compressor Rigs
Authors: Gillaugh Daniel L. , Kaszynski Alexander A. , Brown Jeffrey M. , Beck Joseph A. , Slater Joseph C.
Published: August 2018

As-manufactured rotors behave quite differently than nominal, as-designed rotors due to small geometric and material property deviations in the rotor, referred to as mistuning. The mistuning of a 20 bladed, integrally bladed rotor (IBR) will be evaluated via analytical methods, bench-top testing, and using a rotating compressor research facility. Analytical methods consist of the development of an as-manufactured model based on geometry measurements from a high fidelity optical scanning system. Benchtop testing of the IBR is done using a traveling wave excitation (TWE) system that simulates engine order excitation in stationary bladed disks for the purpose of determining potentially high responding blades due to mistuning. The compressor research facility utilizes blade tip timing (BTT) to measure the blade vibration of the IBR. The resonant response of the IBR at various modes and harmonic excitations is investigated. A comprehensive mistuning and force amplification comparison between the as-manufactured model, TWE, and the compressor rig is performed. Mistuning of each method is evaluated using three different methods. First, the tuned absorber factor (TAF), which is a metric to determine potential high responding blades, is determined for each system. Next, mistuning is analyzed by isolating individual blades both experimentally on the bench and analytically to determine the mistuning patterns. Lastly, the mistuning determined by each system will be evaluated using a reduced-order model, namely the Fundamental Mistuning Model Identification (FMM ID). It will be shown that TAF shows variability between each method providing indications TAF may not be the best approach of force amplification predictions. Basic mistuning agreements exist when isolating blades both experimentally and analytically exhibiting as-manufactured models are capable of representing full experiments. System ID methods provide a basic agreement between both the mistuning pattern and the mistuning amplification for all three methods analyzed. This ultimately shows the importance and the ability to use as-manufactured models to help increase detailed understanding of IBR’s.
Numerical and Experimental Investigation As Applied to Effects of Labyrinth-Type Casing Treatments on Performance of High-Loaded Compressor First Stage
Authors: Mileshin V. I. , Zhdanov V. V. , Petrovitchev A. M.
Published: August 2018

In connection with the development of a new family of high-pressure HPC with ultra-high pressure ratio and the number of stages 10–11, a special attention should be paid to the development of the first high-load stage, because compressor performance directly depends on its excellence. Despite the fact that the stage at nominal rotational speeds can have optimal performance, stall margins at intermediate rotational speeds can decrease because of a sizable IGV closure. One of the ways to increase stall margins is the use of labyrinth-type casing treatments.

The Stage “A-1” studied in this work is a full-scale first stage in a six-stage high-pressure compressor (HPC) for a core demonstrator.

The primary design task for the labyrinth-type casing treatment (CT) is to keep performance at design rotational speeds (n = 100%) or improve them, if possible, and increase stall margins at intermediate speeds (n = 70% and n = 80%). The labyrinth-type CT consisting of 3 circumferential grooves located above the middle of the blade chord projection is specially designed and manufactured for this stage. Our computations show that the use of the labyrinth-type CT leads to a shift of performance towards higher airflow and efficiency that is a good agreement with experimental data. An increase in stall margins without changes in efficiency is found by calculations, whereas the test, on the contrary, shows no influence on stall margins and an increase in efficiency by ∼1.5% (the same as at rated speeds). Both investigated turbulence models (SST and k-ε) do not provide good agreement with the experimental data. The SST model captures CT influence, but decreases stall margin. The k-ε model show agreement with the test in stall margin, but cannot capture CT influence. In addition, both models show lower efficiency compared with the experimental data.

To verify the NUMECA Fine Turbo (version 11.1) mathematical model and numerical method, calculated and experimental characteristics of the Stage A-1 with a smooth flow passage and a labyrinth-type CT are compared. The NUMECA Autogrid 5 grid generator is used to build the grid.
Acceptability of Defects Under Combined Cycle Fatigue for a Precipitation Hardened Steel
Authors: Patriarca Luca , Foletti Stefano , Beretta Stefano , Riva Andrea , Parodi Simona
Published: August 2018

Compressor blades can be subjected to Combined Cycle Fatigue (CCF) conditions considering the superposition of the service cycles characterized by a low cycle fatigue cycle controlled by the centrifugal, pressure and thermal load and the blade vibrations. Simple assessment concepts are available in the literature based on the mean minus three sigma concept for life and strength, but these do not generally deliver acceptance maps for defects, in particular for CCF conditions.

The present work is devoted to use an analytical approach for crack growth rate for life and strength in CCF conditions aimed to determine acceptance maps for defects focusing on the differences with simple deterministic assessments. The experimental results have demonstrated that, for the specific precipitation hardening steel studied, the small cracks under CCF are able to propagate at growth rates comparable to the absence of crack closure. By using these results, in this paper the crack growth rate variability was used to determine maps for the acceptability of surface damage on components subjected to CCF.
A Reduced Order Constitutive Modeling Approach for a Material Subjected to Combined Cycle Fatigue
Authors: Gordon Ali P. , Bouchenot Thomas
Published: August 2018

Material selection for key components is a critical step in the design process where high temperature and large loads are involved. Service conditions, however, may be more aggressive than those to which many materials have been exposed to in laboratory conditions. For example, key combustion equipment will experience super-imposed thermal, mechanical, and vibratory loading. Despite the more recent efforts to characterize materials under these so-called combined extreme environments (CEEs), the temperature- and rate-dependent cyclic hardening/softening responses are still relatively under-characterized. A method to develop first approximations of constitutive model/parameters for materials under extreme service conditions is presented. The method is exercised on IN617 a Ni-base alloy often employed for high temperature applications. The approach shows that a minimal collection of tensile, creep, and LCF data are needed to develop predictions of materials under thermomechanical fatigue with vibratory loading.
Numerical and Experimental Estimation of the Turbine Blade Damper Efficiency
Authors: Shorr Boris , Serebriakov Nikolay , Mel'nikova Galina , Shadrin Dmitri , Vasilyev Boris , Stadnikov Alexander
Published: August 2018

Prevention of high cycle fatigue failures of blades caused by increased level of vibrational stresses is important problem in engine design and development. Different types of dampers are usually installed under the blade platforms in the region between the shanks of adjacent blades are usually used to reduce the vibrational stresses in the turbine blades. The action of these dampers is based on the vibrational energy dissipation by the dry friction forces arising due to the relative displacement of the contacting surfaces of the damper and the blade. Adoption of a reliable choice of damper design mass and stiffness at the design stage of the aircraft engines requires an experimentally validated estimation of its damping efficiency and its influence on the blade frequency characteristics. The dampers need to be tested under conditions that are maximally close to the operational conditions.

This paper presents an analysis of the stress gauging results of a turbine wheel with box-type dampers of various mass. The tests were carried out on a dynamic bench where resonance oscillations of a stage for a given mode were excited by one of the harmonics to a given rotational speed under the corresponding forces pressing the dampers onto the blade platform. An estimation of the damper efficiency in a wider range of pressing forces was also obtained by conducting the laboratory tests using on a specially designed vibration unit that simulates the dampers effect on a set of three blades.

Numerical analysis of the damper mass and stiffness influence on the frequency and damping characteristics of a real turbine wheel was performed. Obtained experimental data and the GAP model of contact interaction of the insert with blades were used in the MSC. Nastran software package. Analysis showed a satisfactory correlation between the calculated and experimental estimates of the decrease in resonant stresses and resonance frequency changes when the dampers are inserted.

The results presented here confirm the possibility of increasing the reliability of the choice of mass and stiffness of turbine blade dampers at the design stage.