bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic Unsteadiness of Tip Clearance Vortex in an Axial Compressor Rotor
Authors: Yang Fan , Wu Yanhui , Zhang Ziyun , Wang Zhenyang
Published: January 2021

A series of unsteady simulations, supported by experimental data, are used to characterize the periodic unsteadiness of the tip clearance vortex in an axial compressor rotor. The numerical probes detect significant periodic fluctuations in the blade tip region at near stall conditions. A reduced frequency at different condition is limited to a small range although there exist a large difference on the natural frequency. Physical explanations of the periodic fluctuations are made in terms of vortex-core identification, contour, etc. The nature of the periodic unsteadiness in the tip region is the periodic bubble-type breakdown of the tip leakage vortex induced by the broken vortex core generated by the previous breakdown. The life cycle of the broken vortex core can be summarized as three processes, generation, propagation and inducing breakdown of tip leakage vortex. The broken vortex core arrives at mid-chord of the adjacent blade, resulting in change of momentum in the tip clearance and pressure in the leading edge of the adjacent blade. The flow in this blade tip region is similarly affected by another adjacent blade. The tip leakage vortex core is bent, then the breakdown of tip clearance happens and a new broken vortex core appears accompanied by a back flow region.
Linear MPC Operating Far From Design Condition: Assessment Derived From Experiments
Authors: Rossi Iacopo , Ferrari Mario Luigi , Traverso Alberto
Published: January 2021

Model Predictive Control (MPC) is a well-known control architecture that has encountered an enormous variety of applications since the very beginning until current days. The pros and cons of such control technique are very well known and both of them rely on the embedded model, which is used to determine the control trajectory. Still, the discrepancy between embedded model and real operative conditions can affect the control response due to uncertainties in measurement chain, noise and so on. Still, it is hardly available in literature what would happen in case the plant is operating far from the design condition of the model. This is of particular interest once a linear MPC is governing a non-linear process where the linearization of the target plant must be processed to tune the MPC itself. This paper analyses experimental results from a fuel cell gas turbine hybrid system, namely SOFC/GT emulator test rig, where a linearized MPC was adopted to control stack inlet temperature. The test rig is constituted by a modified Turbec T100 micro gas turbine where a volume of 4 m3 is interposed between compressor and turbine. This emulates the impact of the SOFC on the GT. The system is connected in real-time mode to a model, which runs in parallel and reads what is going on the plant side and simulates the behavior of the associated SOFC stack. The MPC controller governs the plant according to the stack inlet temperature computed by the model in real-time mode. This MPC must be considered as a supervisor of the system, as the gas turbine was still equipped with its original control system. The plant was subject to an on-purpose strong degradation -operated via a constant venting of air from compressor to ambient. This operation strongly influenced the performance of the system, which were no longer able to operate at a level of temperature and power for which the controller was designed for. Still, a ramping down in power and back up was performed and the MPC showed performance which were in agreement with the design performance. Such surprisingly good result is explained with the complexity of the embedded model, which was derived from a completely physical model of the target system and constituted by more than 200 states.
Influence of Pre-Swirl, Rotor Speed and Blade Count on Aeroelastic Coupling Mechanisms During Stall Inception of a Transonic Compressor
Authors: Franke Daniel , Jüngst Maximilian , Möller Daniel , Schiffer Heinz-Peter , Giersch Thomas
Published: January 2021

The aeroelastic effects during stall inception in modern axial compressors have been a research focus for decades and yet are not fully understood. Experimental investigations, conducted at the 1.5-stage transonic compressor test rig at TU Darmstadt, using extensive unsteady aerodynamic and structural instrumentation, show global trends and influencing parameters on non-synchronous vibration and associated unsteady aerodynamics.

During stall inception, aerodynamic disturbances occur and vary in count, size, cell speed and trajectory. The interaction with non-synchronous blade vibration results in changing stability mechanisms, indicating influences of pre-swirl, rotor speed and blade count on the traveling aerodynamic wave as well as the coupling with the structural wave. Supplementary numerical simulations of the test setup extend the available set of aerodynamic and aeromechanical data, and support the experimental findings.

The study reveals the convective nature of NSV, influenced by the propagation speed of aerodynamic pre-stall disturbances, depending on rotor speed and pre-swirl, as well as its interaction with blade vibration, based on specific phase synchronization conditions and rotor blade count.
Rotor Torsional Response: A Critical Parameter to Measure and Monitor for Rotating Machinery
Authors: Yuan Jing , Heyden Kenneth , Greenhill Lyn
Published: January 2021

Even though the analytical aspects of the torsional response of a rotor system are straightforward, actually measuring the torsional response has been historically very difficult and therefore somewhat neglected. It is recognized that dynamic torsional stresses can contribute significantly to the total operating stresses imposed on a rotor system in rotating machinery, as there are many reports of serious or catastrophic rotor system damage caused by high torsional stress. Thus, measuring and continuously monitoring the torsional dynamic stresses in an operating environment is fundamentally important to assure that a rotor system is operating for its intended application and to assure that impact is insignificant with any operational changes. With a brief review of torsional response analytical principles, this paper focuses on the interpretations of the torsional measurements along with the available methods for measuring and implementing the measurement results for rotating component life assessment. Also, a critique of the available methods for measuring and for monitoring rotor system torsional dynamic response in the actual operating environment is provided. In addition, the paper provides a highlight of a recently developed sensor technology. All efforts serve the purpose to re-emphasize the importance of monitoring rotor torsional response to the industry.
Process Compensated Resonance Testing for Qualifying the Metallurgical Aspects and Manufacturing Defects of Turbine Blades
Authors: Livings Richard , Smith Nick , Biedermann Eric , Scheibel John
Published: January 2021

The metallurgical aspects of turbomachinery components, both during manufacture and service intervals, are of particular interest because they dictate performance, degradation, and probability of defect formation. As certaining the microstructural state without destructive cut-ups is difficult. Nondestructive methods such as x-ray diffraction or ultrasonic testing can provide some amount of metallurgical characterization but are limited to surface measurements or point-by-point inspections. Ultrasonic Resonance methods such as Process Compensated Resonance Testing (PCRT) can greatly supplement the inspection and qualification of Industrial Gas Turbine (IGT) blades. The resonance information collected from a component forms a resonance fingerprint, which is dependent on the material, microstructure, geometry, and the presence of defects. PCRT is an established Nondestructive Testing (NDT) method that has seen extensive use in the aerospace industry for both the detection of damage/defects and undesirable microstructural deviations. This experience from aerospace applications can be leveraged for improved metallurgical inspection methodologies in the power generation industry. Here we present and discuss several PCRT case studies from the aerospace industry as well as early PCRT experiences from power generation. Ongoing and upcoming work is also briefly discussed.
Gaining Insights in Loading Events for Wind Turbine Drivetrain Prognostics
Authors: Daems Pieter-Jan , Guo Y. , Sheng S. , Peeters C. , Guillaume P. , Helsen J.
Published: January 2021

Wind energy is one of the largest sources of renewable energy in the world. To further reduce the operations and maintenance (O&M) costs of wind farms, it is essential to be able to accurately pinpoint the root causes of different failure modes of interest. An example of such a failure mode that is not yet fully understood is white etching cracks (WEC). This can cause the bearing lifetime to be reduced to 5–10% of its design value. Multiple hypotheses are available in literature concerning its cause. To be able to validate or disprove these hypotheses, it is essential to have historic high-frequency measurement data (e.g., load and vibration levels) available. In time, this will allow linking to the history of the turbine operating data with failure data. This paper discusses the dynamic loading on the turbine during certain events (e.g., emergency stops, run-ups, and during normal operating conditions). By combining the number of specific events that each turbine has seen with the severity of each event, it becomes possible to assess which turbines are most likely to show signs of damage.
Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling
Authors: Singh Samarjeet , Roy Amitesh , Reeja K. V. , Nair Asalatha , Chaudhuri Swetaprovo , Sujith R. I.
Published: January 2021

We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.
Large Eddy Simulation of the Flow Past a Circular Cylinder at Super-Critical Reynolds Numbers
Authors: Ahmadi Mohammad H. B. , Yang Zhiyin
Published: January 2021

Turbulent flow past a circular cylinder at super-critical Reynolds numbers is simulated using large eddy simulation in this study. A novel combination of O- and H-grid structures is used to reduce mesh cells and, in turn, the computational cost. To investigate the influence of sub-grid scale (SGS) models on the accuracy of simulations, four different SGS models are applied to simulate the flow. In this study, the effect of mesh resolution near the wall on the accuracy of results is also evaluated by applying different y+ values at the wall. The results show that due to the complexity of the flow around the cylinder particularly at high Reynolds numbers, using very high resolution mesh near the cylinder wall, can not guarantee the accuracy of results and other parameters such as mesh resolutions at the top and bottom shear layers and the wake shortly behind the cylinder should be considered appropriately.
Thermo-Economic Assessment Under Electrical Market Uncertainties of a Combined Cycle Gas Turbine Integrated With a Flue Gas-Condensing Heat Pump
Authors: Vannoni Alberto , Giugno Andrea , Sorce Alessandro
Published: January 2021

Renewable energy penetration is growing, due to the target of greenhouse-gas-emission reduction, even though fossil fuel-based technologies are still necessary in the current energy market scenario to provide reliable back-up power to stabilize the grid. Nevertheless, currently, an investment in such a kind of power plant might not be profitable enough, since some energy policies have led to a general decrease of both the average price of electricity and its variability; moreover, in several countries negative prices are reached on some sunny or windy days. Within this context, Combined Heat and Power systems appear not just as a fuel-efficient way to fulfill local thermal demand, but also as a sustainable way to maintain installed capacity able to support electricity grid reliability. Innovative solutions to increase both the efficiency and flexibility of those power plants, as well as careful evaluations of the economic context, are essential to ensure the sustainability of the economic investment in a fast-paced changing energy field. This study aims to evaluate the economic viability and environmental impact of an integrated solution of a cogenerative combined cycle gas turbine power plant with a flue gas condensing heat pump. Considering capital expenditure, heat demand, electricity price and its fluctuations during the whole system life, the sustainability of the investment is evaluated taking into account the uncertainties of economic scenarios and benchmarked against the integration of a cogenerative combined cycle gas turbine power plant with a Heat-Only Boiler.
Introductory PZT Actuators Optimal Working Configuration Experimental Study in a Turbofan Engine Fan Rotor Blade
Authors: Botta Fabio , Rossi Andrea
Published: January 2021

Vibration suppression systems are often crucial to extend the life cycle of the structures in several engineering fields. The passive systems are the most commonly used but, in case of dynamic loads, the active systems show a greater efficiency. Since the external forces acting on a rotating blade may excite several vibrational modes simultaneously, an active multi-modal damping device could enhance the damping action. The piezoelectric (PZT) actuators seem to be the most promising but their placing on the structure plays a crucial role. In this paper, some PZT actuators have been mounted on the surface of an actual rotor blade from the second fan stage of a turbofan engine and their working configuration has been optimized on the basis of a previously developed model. Thereby, the actuators are able to efficiently damp the most detrimental resonant mode or a resonant modes coupling. The experimental results show that the proposed system well suits the application and may be considered as an alternative method to deal with vibration issues in turbomachinery blades.
A Comprehensive Modeling of Centrifugal Compressor Vibrations for Early Fault Detection
Authors: Libeyre François , Bainier Francis , Alas Pascal
Published: January 2021

In the last decade, the development of machine connectivity has made possible early fault detection with remote analysis of operating data. Solutions aiming to reduce maintenance costs and production losses due to unplanned downtimes were brought to market. These solutions provide with a model of the equipment in healthy conditions using machine learning techniques applied on historical data. During operation a warning is issued when expected and actual measurements do not match.

Although these solutions have proven their value to detect abnormal behaviors, they generate a large number of alarms that require resource to be analyzed. Moreover, these solutions rely on a large number of sensors that need to work correctly both for the learning and the monitoring phase. This generates additional maintenance even though these sensors are often not essential to operate the machine. Lastly the solutions are expensive: their application is usually limited to critical machines with risks of production loss. Indeed, they are not economic for a Transmission System Operator that has ensured the availability of its network with redundancy.

The objective of the authors was to focus on the monitoring of radial vibrations of centrifugal compressors. Experience proves this is one of the most critical data for early fault detection. The goal was to develop a smart modelling based on historical data using essential parameters influencing rotor-dynamics. As a result, a clear correlation was found between the operating point and the vibration level. That can be easily shown on a centrifugal compressor map.

A second-degree polynomial equation was successfully tested. The model equation relies only on two compressor physics parameters: flow coefficient and speed. We discuss in the paper the impact of other essential parameters. The method has been applied on different type of centrifugal compressors, with different bearing technology (magnetic...) or shaft driving equipment (gas turbine, electric motor drive).

A fault detection case study using this method is described, eg: vibration variation due to abnormal opening of an anti-surge control valve.

In conclusion this method is a simple alternative to usual condition monitoring solutions. Similarly to what was described in the GT2014-25242 for a Predictive Emission Monitoring System [1], equations based on physical parameters prove to be an efficient modelling technique. Moreover, it helps monitoring teams to better understand the underlying relation between parameters. Indeed, to achieve a complete monitoring of a centrifugal compressor health, this method can be combined with first-principle performance models that use the same physical parameters.
Influence of Coating Technologies on Frictional Properties of Foil Bearings During Start/Stop Conditions
Authors: Dadouche Azzedine , Yang Qi , Kim Daejong
Published: January 2021

The main objective of this paper is to study and compare the performance characteristics of foil bearings for a typical turboblower during start/stop conditions. The test bearings feature three-segment bump foils and a full smooth top foil with a nominal diameter of 70 mm and an aspect ratio of 1. All foils are made out of Inconel 718 and have a thickness of 0.2 mm (0.008”). Three coatings, applied to the top foil, have been evaluated during the test campaign: PTFE, Molybdenum-Titanium Nitride (MoTiN) and Molybdenum-Aluminum-Titanium Nitride (MoAlTiN). MoTiN and MoAlTiN were applied using physical vapor deposition (PVD) technology. Each bearing was instrumented with sixteen thermocouples located within the bearing sleeve 1 mm away from its inner diameter. Thermocouples allow the measurement of the bearing temperature in the axial and circumferential directions. Bearing displacement was measured using eight proximity probes located at each side of the bearing (four per side). Overall vibrations of the bearing under test were measured via two accelerometers located on top of the bearing housing in the vertical and horizontal directions. In addition, a torque arm mechanism was used to measure the bearing shear force; hence deduce the friction coefficient, friction torque and total power loss. The paper discusses friction and wear results obtained after one hundred start-stop tests for each bearing. A tribological and microstructural analysis is also presented and discussed.
Analysis of the Convergence Rate of Turbulence Model Uncertainties for Transonic Axial Compressor Simulation
Authors: Perez Ethan , Kelly Ryan T. , Matsui Kotaro , Tani Naoki , Jemcov Aleksandar
Published: January 2021

Numerical experiments were performed to assess the effect of numerical discretization error on the convergence rate of polynomial chaos (PC) approximations for a transonic axial compressor stage. A random variable with a uniform distribution and expected value of one was introduced into the expression for turbulent viscosity of the k-ω SST turbulence model. Model uncertainty was quantified from the expected value and standard deviation estimates obtained via univariate non-intrusive polynomial chaos. Spectral projection and point collocation were both used and their results were compared. The effect of discretization error on convergence of the PC approximation was investigated using a grid refinement study with four grids. The PC expansion was computed for each grid while maintaining the same boundary conditions, basis functions, model evaluations, random variable distribution, and polynomial order. The quantities of interest (QOIs) were total–to–total pressure ratio, total–to–total temperature, and adiabatic efficiency. The grid resolution was found to have an influence on resulting surrogate models and the estimates of expected value and standard deviation for all QOIs. However, the estimates converged towards final values as the mesh was refined. Point collocation provided different estimates from spectral projection and the difference was also found to depend on the mesh size.
Performance and Emission Assessment of Thermo-Electric Power Plant for Rotorcraft Propulsion
Authors: Roumeliotis Ioannis , Arena Francesco , Liu Yize , Vouros Stavros , Pachidis Vassilios , Broca Olivier , Toure Djiby , Unlu Deniz
Published: January 2021

This paper assesses a gas turbine based parallel rotorcraft hybrid electric propulsion system in terms of overall performance and emissions. Three different electric power train technology levels and three different power management strategies are considered for identifying the potential benefits of hybridization in relation to technology advancements and quantifying the effect of PMS. For this analysis, a Passenger Air Transport of a twin-engine medium helicopter is used.

The propulsion systems mission simulation and emissions calculation are performed in Simcenter Amesim. The assessment framework integrates a thermal power-plant model, an electric power plant model for the hybrid electric cases, a helicopter simulation model and suitable pollutant emissions calculation correlations.

For establishing NOx emission correlations that can be used for turboshaft engine calculations, a systematic evaluation of different correlations available in the literature is performed. The correlations are compared for different operating points against a calibrated stirred reactor model. The suitable correlations are utilized in the framework. The propulsion system is sized according to the technology levels and power management strategy considered, updating the helicopter Take-Off Weight for each case.

The results indicate that there is potential for efficiency betterment and CO2 emissions reduction. The benefits strongly depend on the power management strategy and energy and power density of the electric power train. For current technology level and for the cases examined herein no benefits in terms of overall performance and emissions accrue. If future technology level is considered, hybridization may offer benefits in terms of performance to the expense of NOx emissions for the case that the power train is used for boosting and the gas turbine is scaled down. Power splitting may offer block fuel, turbine life and NOx benefits to the expense of overall energy performance.
Effects of Trailing Edge Thickness and Blade Loading Distribution on the Aerodynamic Performance of Simulated CMC Turbine Blades
Authors: Giel Paul W. , Shyam Vikram , Juangphanich Paht , Clark John P.
Published: January 2021

The aerodynamic performance of three blade sets that represent the geometric manufacturing constraints of Ceramic Matrix Composite (CMC) blades was measured experimentally in a large-scale transonic turbine blade cascade. The trailing edge thicknesses of CMC blades are anticipated to be significantly larger than those of current state-of-the-art metallic blades. The blades tested in the current study had trailing edge thicknesses of 5%, 7%, and 9% relative to the blade axial chord. The three blade sets were designed with matching throat dimensions, so the blade loading distributions were varied to retain similar overall loading levels. Data were acquired at four Reynolds numbers, covering a factor of six range. All data were acquired at the design isentropic exit Mach number of 0.74. Measurements include blade loading and five-hole probe surveys at two downstream stations. The effects of inlet turbulence intensity were also quantified. Total pressure loss data were integrated to determine overall loss levels for each of the three measured blade passages. Excellent periodicity was noted. For low inlet turbulence levels, losses were surprisingly lower for the thickest trailing edge at low Reynolds numbers, but were highest at the maximum Reynolds number. In general, losses were found to scale well with Reynolds number, although front loading was found to significantly reduce the sensitivity of loss to Reynolds number. For high inlet turbulence intensity, losses were found to scale with trailing edge thickness as expected, and the Reynolds number sensitivity was reduced for all three blade sets. Loss levels at the highest Reynolds number were comparable at low and high inlet turbulence intensity levels.
A Fully Non-Adiabatic Flamelet Generated Manifold Model for High Fidelity Modeling of Turbulent Combustion in Gas Turbine Like Conditions
Authors: Yadav Rakesh , Verma Ishan , Modak Abhijit , Li Shaoping
Published: January 2021

Flamelet Generated Manifold (FGM) has proven to be an efficient approach to model turbulent combustion across different regimes of combustion. The manifolds are generally created by solving laminar premixed or opposed flow configurations. Gas turbine combustors often involve many strong non-adiabatic events such as multiple temperature boundaries, quenching from cooling and effusion holes, conjugate heat transfer, soot radiation interaction, phase change from spray and the modulation of inlet conditions. The adiabatic assumption of the underlying flamelet generation in the FGM is, therefore, prone to errors in the prediction of flame speed, liner temperatures, and pollutant formation. In this work, a novel approach to generate fully non-adiabatic manifold is proposed and validated. The FGM manifold is created using a series of non-adiabatic flamelets, each flamelet is solved in one-dimensional physical space. The non-adiabatic flamelets are generated with an optimal combination of freely propagating and burner stabilized flames. This hybrid method of the flamelet configuration allows modeling large heat gain and loss without encountering any unrealistic temperature in the flamelet solution. Such fully non-adiabatic flamelets are then convoluted to generate a five-dimensional Non-adiabatic Flamelet Generated Manifold (NFGM) Probability Density Function (PDF.). The average properties such as temperature, mixture density, species concentration, rate of reaction, etc. from PDF are then coupled with the CFD solution. The non-adiabatic flamelets and corresponding NFGM is implemented into ANSYS Fluent software version 2020R1. This approach is validated first for canonical cases, followed by gas turbine like conditions of swirl stabilized methane fueled turbulent flame, developed at DLR Stuttgart as the PRECCINSTA combustor. The experimental data for this combustor is available for multiple operating conditions. A stable operating point (φ = 0.83, P = 30 kW) is chosen. The proposed nonadiabatic NFGM is used with Stress blended eddy simulation (SBES). The current NFGM-SBES results are compared with experimental data as well as the previously published works. The impact of modeling heat release in flamelet is used to analyze the M-shape versus V-shape flame transition and the peaks of the carbon monoxide in mixing shear layers. The findings from the current work, in terms of accuracy, validity and best practices while modeling NFGM-SBES are discussed and summarized. The improved results of NFGM compared to adiabatic FGM are encouraging and provides a potential high-fidelity tool for accurate, yet efficient modeling of turbulent combustion inside gas turbines.
A Novel SOFC Thermal Management Strategy of SOFC-GT Hybrid System With Anode and Cathode Control Loops
Authors: Chen Jinwei , Li Yuanfu , Zhang Huisheng , Lu Zhenhua
Published: January 2021

The SOFC performance and lifetime highly depend on the operation condition, especially the SOFC operation temperature. The temperature fluctuation causes thermal stress in electrodes and electrolyte ceramics. On the other hand, it also needs to maintain a sufficiently high temperature to enable the efficient transport of oxygen ions across the electrolyte. Therefore, it is necessary to design an effective SOFC temperature management system to guarantee safe and efficient operation. In this paper, a two-side temperature control method is proposed to avoid the temperature difference between anode and cathode. Therefore, the SOFC thermal management system includes two control loops. The anode inlet temperature and cathode inlet temperature are controlled by blowers adjusting the recirculated flow rate. In addition, the control performance of the proposed SOFC thermal management system is compared with one-side temperature control systems. The results show that both anode control loop and cathode control loop are essential to get a better control performance. The SOFC would operate with less efficiency with only anode temperature control. On the other hand, the safety problem would occur with only cathode temperature control. The temperature gradient would be more than the upper limit at a part load condition. Therefore, the SOFC thermal management strategy with anode and cathode temperature control loops is feasible for the SOFC-GT system.
Effect of Ribs on Heat Transfer and Pressure Drop in a U-Bend Channel With Double-Layer, Dome-Shaped Turning Vanes
Authors: Wu Bin , Yang Xing , Liu Zhao , Feng Zhenping
Published: January 2021

In this paper, the combined effects of ribs and double-layer, dome-shaped turning vanes on heat transfer and pressure drop are investigated in an idealized U-bend channel. Five kinds of ribs including transverse ribs, 45° ribs, 135° ribs, V-shaped ribs, and reverse V-shaped ribs combined with one kind of double-layer, dome-shaped turning vanes are applied. Baseline results are compared with the above composite cooling structures. Numerical simulations are performed by solving 3D, steady Reynolds-averaged Navier-Stokes (RANS) equations with k-ω turbulence model. The channel aspect ratio is 1:2 and its hydraulic diameter is 93.13 mm, respectively. Based on the cooling air inlet velocity and the channel inlet hydraulic diameter, the inlet Reynolds numbers are ranging from 100,000 to 440,000. The detailed three-dimensional fluid flow, pressure and heat transfer distributions are presented. Moreover, the thermal performances of the U-bend channel are also evaluated and compared with different cases.

The results revealed that combined with the double-layer, dome-shaped turning vanes, the transverse ribs case has the best thermal performance at the tip wall, and the reverse V-shaped ribs case is the best for the leading wall. The pressure drop of the channel with double-layer, dome-shaped turning vanes without any rib turbulator is the lowest, and that of the channel with inclined ribs is significantly higher than that of the channel with transverse ribs.

The superposition of the secondary flow induced by the ribs and the Dean vortex induced by the 180° sharp turn has a marked impact on the flow and heat transfer in the channel. In the double-layer, dome-shaped turning vanes channel, the mass flow distribution of the coolant also affects the heat transfer on the tip wall of the channel, and the ribs can adjust the mass flow distribution. The helical vortex superposed by the mainstream flow and the secondary flow induced by the ribs represents typical flow phenomenon in ribbed channels. The flow and development of the helical vortex are the main factors affecting the heat transfer on the leading/trailing walls.
Thermal History Coatings: Part I — Influence of Atmospheric Plasma Spray Parameters on Performance
Authors: Araguás-Rodríguez Silvia , Ferran-Marqués Marta , Pilgrim Christopher C. , Kamnis Spyros , Feist Jörg P. , Nicholls John R.
Published: January 2021

Firing temperatures in gas turbines have seen a steady increase over the years to allow for higher engine efficiencies and a decrease in hazardous emission levels. Conversely, these harsh conditions severely challenge the component lifetime, requiring a trade-off during the design process. Thus, it is crucial to understand temperature distribution across the majority of a component surface (>80%) to verify the design and component durability. While a range of temperature measurement techniques are available, these are primarily focused on lower temperatures, exhibit low durability (thermal paints), require line of sight (pyrometers), are destructive (thermal crystals) and only provide point measurements (thermocouples, thermal crystals).

To overcome this challenge, Sensor Coating Systems (SCS) have developed Thermal History Coatings (THCs) to measure temperature profiles in the 900–1600°C range. This new temperature profiling capability records the past maximum exposure temperature in such a way that it can be determined once the component has already cooled down.

THCs are comprised of oxide ceramics deposited via Atmospheric Plasma Spraying (APS) to create a robust coating. APS deposition employs several variable parameters; spray settings such as gun power, gas flow or scan rate can affect the particle exposure and thus, the microstructure of the coating and its temperature sensing performance.

This two-part paper covers the THCs principles and demonstrates their capabilities for high-temperature applications. This first part shows, for the first time, the influence of APS parameters on luminescent measurements due to changes in the material microstructure. Extensive calibration data was used to develop a new model to relate the APS spray parameters to the luminescent properties in the as-deposited condition and consequent performance as a temperature sensor. The powder composition and the power and gas flow used during deposition were found to be the most influential parameters. The model identified the optimum spray parameters and was used to demonstrate THCs can achieve measurements in excess of 1600°C.
Analysis of Ignition Processes at Combustors for Aero Engines at High Altitude Conditions With and Without Effusion Cooling
Authors: Martinos Alexios-Dionysios , Zarzalis Nikolaos , Harth Stefan-Raphael
Published: January 2021

The ability to re-ignite at high altitude after a flameout event is critical for flight safety. One reason that makes the relight process of the engine difficult is the low temperature and pressure, which leads to poor atomization, low degree of evaporation and slow reaction rate of the vaporized fuel. For this research work a rectangular, one sector RQL combustion chamber was utilized for experimental investigations at high altitude conditions. The design of the chamber is modular so that experiments for two configurations, i.e. without and with effusion cooling holes can be conducted. The fuel injection and the ignition system are representative of the ones used in commercial aviation.

The investigations were performed in the frame of the European research project SOPRANO at the ISCAR rig. The ISCAR rig is capable of generating low pressure and temperature conditions for flowing kerosene-air mixtures.

The investigation focuses on the characterization of the ignition process, in terms of probability, minimum fuel to air ratio (FAR) and ignition timing for a successful ignition event. In addition, the unsteady flame kernel generation and propagation were analyzed by high-speed imaging recording.

An in-house image processing code was developed in order to derive quantitative spatial information of the flame and overall trends among ignition sequences for the same or different operating conditions.

In order to achieve comparability between the investigated configurations (liners without and with effusion cooling), the pressure drop across the nozzle and the liners was the same depending on the operating condition. Results show that both pressure and temperature affect the ignition process, with the former being the dominant parameter in the investigated conditions. In both configurations, the minimum FAR increased as long as the conditions in the chamber became more adverse, indicating that at high altitude low-pressure situations, the performance of the airblast atomizer deteriorated causing poor ignition. This is overcome by creating a richer fuel-air mixture in the primary zone. Finally, the air injected through the effusion cooling holes near the spark seems to create favorable conditions for the ignition process.
The Feasibility of an Euler-Lagrange Approach for the Modelling of Wet Steam
Authors: Wittmann Tim , Bode Christoph , Friedrichs Jens
Published: January 2021

This study investigates the applicability of an Euler-Lagrange approach for the calculation of nucleation and condensation of steam flows. Supersonic nozzles are used as generic validation cases, as their high expansion rates replicate the flow conditions in real turbines. Experimental and numerical validation data for these nozzles are provided by the International Wet Steam Modelling Project of Starzmann et al. (2018). In contrast to most participants of that project, an Euler-Lagrange approach is utilized for this study. Therefore, the classical nucleation theory with corrections and different droplet growth laws is incorporated into the Discrete Phase Model of ANSYS Fluent. Suggestions for an efficient implementation are presented. The Euler-Lagrange results show a good agreement with the experimental and numerical validation data. The sensitivities of the Euler-Lagrange approach to modelling parameters are analysed. Finally, an optimal parameter set for the calculation of nucleation and condensation is proposed.
Experimental and Numerical Researches in a Four-Stage Low Speed Research Compressor Facility
Authors: Zhu Mingmin , Qiang Xiaoqing , Ju Zhenzhou , Ma Yuchen , Teng Jinfang
Published: January 2021

The flow fields in rear stages of multi-stage axial compressor is difficult to measure in detail owing to the limited height and space. Thus, low speed research compressor (LSRC) facilities which are modelled from rear stages have been widely used to explore the internal flow fields and improve compressor design. A newly-designed vertical LSRC facility is established and put into used in Shanghai Jiao Tong University. The construction and design features of this LSRC facility are introduced in this paper. A cantilevered stage has been tested in this test rig. Compressor performance, inter-stage parameters distributions and contours are measured at design point and near stall point. Steady single passage simulations for four-stage compressor are carried out to validate numerical methods and further interpret the internal flow fields in test stages.

This vertical LSRC facility consists of inlet guide vane (IGV) and four repeated stages with an external diameter of 1.5 meter and a rotating speed of 900 RPM. The third stage is the mainly tested one, while the first and second stages provide the inlet conditions and the fourth stage provides the outlet conditions. Complete measuring methods and systems are established for this newly-built LRSC facility. The measurements of overall performance and inter-stage flow fields are carried out for test stage with cantilevered stator rows. The simulation for four-stage compressor are also performed for cantilevered configuration. The results of steady single-passage simulation have a similar trend with experimental ones, in terms of overall performance and parameters distributions.
Performance Characteristics of a Centrifugal Compressor With Capacity Control by Variable Diffuser Vanes
Authors: Im Kangsoo , Jeong Jongsik
Published: January 2021

A study of a variable diffuser vane capacity control method was done for the delivery of air into degasser of a SRU (Sulfur Recovery Unit) in a refinery process which requires a wide operating range and high head rise. Rig tests were made with diffuser vanes with various diffuser turning angles to evaluate performance of the compressor with variable diffuser vane. The compressor running on the test rig consisted of inlet bell mouth venturi, unshrouded impeller and vaned diffuser with tip clearance and scroll. To evaluate performance of the impeller and diffuser, static pressure was measured on the shroud side through 30 pressure tabs. The performance characteristics of the compressor stage, such as head coefficient, work coefficient, impeller exit flow condition and diffuser pressure recovery, are evaluated for 3 diffuser vanes and speeds. All performance characteristics are expressed as dimensionless form for each diffuser turning angle and speed. For the stage performance, compressor capacity is reduced as diffuser turning angle increase. For the impeller and diffuser performance, impeller exit flow coefficient is used for impeller exit flow condition and its performance. Based on the rig test, 6 customized single stage compressors with the variable diffuser vane capacity control system for the degasser of SRU were made and shop test were performed on each compressor. It was found that surge of the compressors can be controlled by variable diffuser vane and largely depends on the diffuser geometry.
Effect of Initial Surface Roughness on Water Erosion Resistance of Last Stage Blade Substrate of Steam Turbine
Authors: Li Fang , Wang Shunsen , Di Juan , Feng Zhenping
Published: January 2021

In order to study the effect of initial surface roughness on water droplet erosion resistance of last stage blade substrate of steam turbine, eight 17-4PH samples were grounded and velvet polished by different mesh metallographic sandpaper to establish sample with different initial surface roughness. The water droplet erosion experiments were carried out in the highspeed jet water erosion experiment system, and the mass and micro-morphology of each sample were measured by using precision electronic balance and ultra-depth of field microscope respectively at each experimental stage, and the measurement of water erosion trace width and maximum water erosion depth were also completed at the same time. On the basis of experiments, LS-DYNA was used for numerical simulation to verify the reliability of experimental results again. Results show that the smoother the initial surface of sample, then the smaller the mass loss, the stronger its water erosion resistance. On the contrary, the rougher the initial surface of sample, the more severe the surface irregularity, the more times the water droplets concentrated at the lowest point of pit when water droplets flow laterally after impact is completed, thus accelerating the formation of initial crack and lateral expansion, the poorer the water erosion resistance of sample. At same water erosion time, the smoother the sample surface, the later the complete erosion trace appear, the narrower the water erosion trace width. However, the maximum water erosion depth of sample is not affected by the initial surface roughness. The numerical simulation results are in good agreement with the experimental results.
Influence of Equation-of-States on Supercritical CO2 Combustion
Authors: Manikantachari K. R. V. (Raghu) , Martin Scott M. , Rahman Ramees K. , Velez Carlos , Vasu Subith S.
Published: January 2021

Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that, using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict-Webb-Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.
Applying Advanced Ultrasonic In-Line Inspection Technologies to Effectively Manage Hook Cracks
Authors: Wargacki Cory , Forshner Wade , Guajardo Rogelio , Hennig Thomas
Published: January 2021

Axial cracking inspections have become common place on a global level within pipeline operator’s integrity management programs. As technology continues to improve, operators are presented with more accurate assessments of the assets that are in current operation. However as more information is collected more threats are being identified and need to be assessed in a manner that is more applicable to their specific morphology. It is well known that vintage ERW manufacturing techniques can suffer from a wide range of potential threats such as lack of fusion or inclusions within the steel forming hook cracks during the rolling and welding process. Current In-line inspection technologies that are designed to detect, Identify and size cracklike flaws in pipelines are very proficient at doing so. However, due to the physical principals of the Ultrasonic pulse echo technology, deep features approaching, or above pulse echo saturation amplitudes pose challenges in determining accurate depth sizing.

In 2015 a Canadian pipeline operator determined the need to inspect one of their 16” assets for axial crack-like indications. During the analysis of this inspection data set, a number of saturated crack-like indications were reported. Saturated cracklike signals present a challenge to operators as they have to be considered in a conservative manner as 4mm or deeper which in turn leads to difficulties in the prioritization of resources associated with the excavation program.

The operator approached NDT Global in 2017, after the release of NDT Global’s Enhanced sizing depth algorithm to reevaluate the features that were present in the previous crack inspection data set. Working together with the operator, NDT Global applied the Enhanced sizing methodology to all features of significance in the pipeline segment and compared the results to lab measurements and in field NDE measurements.

The outcome of the reanalysis using the most up to date software algorithms utilizing enhanced sizing showed great benefits by increasing the accuracy of the crack depth sizing as NDT Global was now able to report full through wall depth sizing, however there were still some limitations on the ability to accurately size crack-like features as the primary threat is believed to be a result of hook cracks.

As a final step in this program NDT Global was provided sample spools that were cut out of the pipeline segment to perform a pull testing campaign utilizing the newest crack detection technology that was specifically targeted towards accurately sizing tilted and skewed crack like features.

The authors will briefly discuss the pipeline system and inspection campaign and in detail will discuss the benefits of using technology that has been developed to help pipeline operators better understand the threats in their integrity management program.