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research-article  
Sajjad Yousefian, Gilles Bourque and Rory Monaghan
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040897
Many sources of uncertainty exist when emissions are modelled for a gas turbine combustion system. They originate from uncertain inputs, boundary conditions, calibration, or lack of sufficient fidelity in the model. In this paper, a non-intrusive polynomial chaos expansion (NIPCE) method is coupled with a chemical reactor network (CRN) model using Python to quantify uncertainties of NOx emission in a premixed burner rigorously. The first objective of the uncertainty quantification (UQ) in this study is the development of a global sensitivity analysis method based on NIPCE to capture aleatory uncertainty due to the variation of operating conditions and input parameters. The second objective is uncertainty analysis of Arrhenius parameters in the chemical kinetic mechanism to study the epistemic uncertainty in the modelling of NOx emission. A two-reactor CRN consisting of a perfectly stirred reactor (PSR) and a plug flow reactor (PFR) is constructed in this study using Cantera to model NOx for natural gas at the relevant operating conditions for a benchmark premixed burner. The results of uncertainty and sensitivity analysis using NIPCE based on point collocation method (PCM) are then compared with the results of advanced Monte Carlo simulation (MCS). Surrogate models are also developed based on the NIPCE approach and compared with the forward model in Cantera to predict NOx emissions. The results show the capability of NIPCE approach for UQ using a limited number of evaluations to develop a UQ-enabled emission prediction tool for gas turbine combustion systems.
TOPICS: Nitrogen oxides, Emissions, Uncertainty quantification, Uncertainty, Sensitivity analysis, Combustion systems, Gas turbines, Modeling, Natural gas, Boundary-value problems, Calibration, Chaos, Polynomials, Flow (Dynamics), Simulation, Uncertainty analysis
research-article  
Sebastian Willeke, Lukas Schwerdt, Lars Panning-von Scheidt and Jörg Wallaschek
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040898
A harmonic mistuning concept for bladed disks is analyzed in order to intentionally reduce the forced response of specific modes below their tuned amplitude level. By splitting a mode pair associated with a specific nodal diameter pattern, the lightly damped traveling wave mode of the nominally tuned blisk is superposed with its counter-rotating complement. Consequently, a standing wave is formed in which the former wave train benefits from an increase in aerodynamic damping. Unlike previous analyses of randomly perturbed configurations, the mode-specific stabilization is intentionally promoted through adjusting the harmonic content of the mistuning pattern. Through a re-orientation of the localized mode shapes in relation to the discrete blades, the response is additionally attenuated by an amount of up to 7.6%. The achievable level of amplitude reduction is analytically predicted based on the properties of the tuned system. Furthermore, the required degree of mistuning for a sufficient separation of a mode pair is derived.
TOPICS: Damping, Disks, Blades, Mode shapes, Traveling waves, Separation (Technology), Standing waves, Wave packets
research-article  
Adam Koscso, Guido Dhondt and Evgeny Petrov
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040900
A new method has been developed for sensitivity calculations of modal characteristics of bladed disks made of anisotropic materials. The method allows the determination of the sensitivity of the natural frequencies and mode shapes of mistuned bladed disks with respect to anisotropy angles that define the crystal orientation of the monocrystalline blades using fullscale finite element models. An enhanced method is proposed to provide high accuracy for the sensitivity analysis of mode shapes. An approach has also been developed for transforming the modal sensitivities to coordinate systems used in industry for description of the blade anisotropy orientations. The capabilities of the developed methods are demonstrated on examples of a single blade and a mistuned realistic bladed disk finite element models. The modal sensitivity of mistuned bladed disks to anisotropic material orientation is thoroughly studied.
TOPICS: Anisotropy, Disks, Sensitivity analysis, Blades, Finite element model, Mode shapes, Crystal structure
research-article  
Liang Tang and Allan Volponi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040899
An engine health management (EHM) system typically consists of automated logic for data acquisition, parameter calculation, anomaly detection and eventually, fault identification (or isolation). Accurate fault isolation is pivotal to timely and cost effective maintenance but is often challenging due to limited fault symptom observability and the intricacy of reasoning with heterogeneous parameters. Traditional fault isolation methods often utilize a Single Fault Isolator (SFI) that primarily relies on gas path performance parameters. While effective for many performance related faults, such approaches often suffer from ambiguity when two or more faults have signatures that are very similar when monitored by a rather limited number of gas path sensors. In these cases, the ambiguity often has to be resolved by experienced analysts using additional information that takes many different forms, such as various non-gas path symptoms, FADEC fault codes, comparisons with the companion engine, maintenance records, and quite often, the analyst's gas turbine domain knowledge. This paper introduces an intelligent reasoner that combines the strength of an optimal, physics-based SFI and a fuzzy expert system that mimics the analytical process of human experts for ambiguity resolution. A prototype diagnostic reasoner software has been developed and evaluated using existing flight data. Significant performance improvements were observed as compared with traditional SFI results. As a generic reasoning framework, this approach can be applied not only to traditional snapshot data, but to full flight data analytics as well.
TOPICS: Resolution (Optics), Gas turbines, Ambiguity, Flight, Maintenance, Engines, Physics, Sensors, Computer software, Engineering prototypes, Expert systems, Data acquisition
research-article  
R. Craig McClung, Yi-Der Lee, James Sobotka, Jonathan Moody, Vikram Bhamidipati, Michael P. Enright, D. Benjamin Guseman and Colin B. Thomas
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040901
Recent advances in practical engineering methods for fracture analysis of turbomachinery components are described. A comprehensive set of weight function stress intensity factor (SIF) solutions for elliptical and straight cracks under univariant and bivariant stress gradients has been developed and verified. Specialized SIF solutions have been derived for curved through cracks, cracks at chamfered and angled corners, and cracks under displacement control. Automated fracture models are available to construct fatigue crack growth life contours and critical initial crack size contours for all nodal locations in 2D or 3D finite element models.
TOPICS: Fracture (Materials), Modeling, Turbomachinery, Stress, Weight (Mass), Corners (Structural elements), Displacement, Fatigue cracks, Finite element model
research-article  
Samuel Barak, Erik Ninnemann, Sneha Neupane, Frank Barnes, Jayanta Kapat and Subith Vasu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040904
In this study, syngas combustion was investigated behind reflected shock waves in CO2 bath gas to measure ignition delay times and to probe the effects of CO2 dilution. New syngas data were taken between pressures of 34.58-45.50 atm and temperatures of 1113-1275K. This study provides experimental data for syngas combustion in CO2 diluted environments: ignition studies in a shock tube (59 data points in 10 datasets). In total, these mixtures covered a range of temperatures T, pressures P, equivalence ratios f, H2/CO ratio ?, and CO2 diluent concentrations. Multiple syngas combustion mechanisms exist in the literature for modelling ignition delay times and their performance can be assessed against data collected here. In total, twelve mechanisms were tested and presented in this work. All mechanisms need improvements at higher pressures for accurately predicting the measured ignition delay times. At lower pressures, some of the models agreed relatively well with the data. Some mechanisms predicted ignition delay times which were 2 orders of magnitudes different from the measurements. This suggests there is behavior that has not been fully understood on the kinetic models and are inaccurate in predicting CO2 diluted environments for syngas combustion. To the best of our knowledge, current data are the first syngas ignition delay times measurements close to 50 atm under highly CO2 diluted (85% per vol.) conditions.
TOPICS: High pressure (Physics), Syngas, Shock tubes, Ignition delay, Carbon dioxide, Combustion, Temperature, Diluents, Shock waves, Modeling, Ignition, Probes
research-article  
Peng Wang, Hongyu Ma and YingZheng Liu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040903
In steam turbine control valves, pressure fluctuations coupled with vortex structures in highly unsteady three-dimensional flows make essential contributions to aerodynamic forcing on the valve components, and give rise to flow-induced vibration and acoustic effects. Present study used state-of-the-art data-driven analysis, namely proper orthogonal decomposition (POD) and extended-POD, to extract the energetic pressure fluctuations and dominant vortex structures of the control valve. To this end, typical annular attachment flow inside a control valve was investigated from a detached eddy simulation (DES). Subsequently, the energetic pressure fluctuation modes were extracted from the pressure field's POD analysis. The vortex structures contributing to these energetic pressure fluctuations were extracted by the extended-POD analysis on pressure-velocity coupling field. Finally, dominant vortex structures were revealed directly by POD analysis on valve's velocity field. The results demonstrated that flow instabilities inside the control valve were mainly induced by the wall-attached jet oscillations and the derivative flow separations and reattachments. In pressure field's POD analysis, the axial, antisymmetric and asymmetric pressure modes occupied most of the pressure fluctuation intensity. By further conducting extended-POD analysis, the vortex structures' incorporation with the energetic pressure modes was identified as mainly attributed to the synchronous, alternating and single-sided oscillation behaviors of the annular attachment flow. However for velocity field's POD analysis, the vortex structures, buried in the dominant modes at St=0.017, were primarily resulted from alternating oscillations of the annular wall-attached-jet.
TOPICS: Pressure, Valves, Vortices, Fluctuations (Physics), Steam turbines, Oscillations, Flow (Dynamics), Eddies (Fluid dynamics), Acoustics, Simulation, Flow separation, Principal component analysis, Flow instability, Flow-induced vibrations
research-article  
Ji Ho Ahn, Ji Hun Jeong and Tong Seop Kim
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040866
The demand for clean energy continues to increase as the human society becomes more aware of environmental challenges such as global warming. Various power systems based on high-temperature fuel cells have been proposed, especially hybrid systems combining a fuel cell with a gas turbine, and research on carbon capture and storage technology to prevent the emission of greenhouse gases is already underway. This study suggests a new method to innovatively enhance the efficiency of a molten carbonate fuel cell/micro gas turbine hybrid system including carbon capture. The key technology adopted to improve the net cycle efficiency is off-gas recirculation. The hybrid system incorporating oxy-combustion capture was devised, and its performance was compared with that of a post-combustion system based on a hybrid system. A molten carbonate fuel cell system based on a commercial unit was modeled. Externally supplied water for reforming was not needed as a result of the presence of the water vapor in the recirculated anode off-gas. The analyses confirmed that the thermal efficiencies of all the systems (MCFC stand-alone, hybrid, hybrid with oxy-combustion capture, hybrid with post-combustion capture) were significantly improved by introducing the off-gas recirculation. In particular, the largest efficiency improvement was observed for the oxy-combustion hybrid system. Its efficiency is over 57% and is even higher than that of the post-combustion hybrid system.
TOPICS: Molten carbonate fuel cells, Carbon capture and storage, Micro gas turbines, Combustion, Fuel cells, Gas turbines, Cycles, Renewable energy, Water, Gases, Power systems (Machinery), Anodes, Thermal efficiency, Water vapor, Climate change, Emissions, High temperature
research-article  
Alexander J. Hacks, Sebastian Schuster, Hans Josef Dohmen, Friedrich-Karl Benra and Dieter Brillert
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040861
The paper aims to give an overview over the keystones of design of the turbomachine for a supercritical CO2 (sCO2) Brayton cycle. The described turbomachine is developed as part of a demonstration cycle on a laboratory scale with a low through flow. Therefore the turbomachine is small and operates at high rotational speed. To give an overview on the development the paper is divided into two parts regarding the aerodynamic and mechanical design. The aerodynamic design includes a detailed description on the steps from choosing an appropriate rotational speed to the design of the compressor impeller. For setting the rotational speed the expected high windage losses are evaluated considering the reachable efficiencies of the compressor. The final impeller design includes a description of the blading development together with the final geometry parameters and calculated performance. The mechanical analysis shows the important considerations for building a turbomachine with integrated design of the three major components turbine, alternator and compressor (TAC). It includes different manufacturing techniques of the impellers, the bearing strategy, the sealing components and the cooling of the generator utilising the compressor leakage. Concluding the final design of the TAC is shown and future work on the machine is introduced.
TOPICS: Design, Turbomachinery, Supercritical carbon dioxide, Compressors, Impellers, Bearings, Leakage, Compressor impellers, Manufacturing, Sealing (Process), Flow (Dynamics), Cooling, Machinery, Design engineering, Turbines, Brayton cycle, Cycles, Generators, Geometry
research-article  
Nicolas Guerin, Anders Thorin, Fabrice Thouverez, Mathias J. Legrand and Patricio Almeida
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040858
Turbomachinery rotor-stator unilateral contact induced interactions play a growing role in lifecycle analysis and thus motivate the use of accurate numerical prediction tools. Recent literature confirmed by ongoing in-house experiments have shown the importance of thermomechanical coupling effects in such interactions. However, most available (possibly reduced-order) models are restricted to the sole mechanical aspects. This work describes a reduction technique of thermomechanical models involving unilateral contact and frictional contact occurrences between rotor and stator components. The proposed methodology is grounded on Guyan and Craig--Bampton methods for the reduction of the structural dynamics in conjunction with Krylov subspace techniques, and specifically the Craig--Hale approach, for the reduction of the thermal equations. The method has the capability to drastically reduce the size of the model while preserving accuracy. It stands as a reliable strategy to perform simulations of thermomechanical models with localized mechanical and thermal loads.
TOPICS: Simulation, Engineering simulation, Rotors, Stators, Thermomechanics, Turbomachinery, Stress, Structural dynamics, Life cycle assessment
research-article  
Andrea Tanganelli, Francesco Balduzzi, Alessandro Bianchini, Francesco Cencherle, Michele De Luca, Luca Marmorini and Giovanni Ferrara
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040864
In centrifugal compressor design, the volute plays a key role in defining the overall efficiency and operating range of the stage. Due to the high flow speed at the volute inlet, the capability of ensuring the lowest amount of total pressure loss is pivotal to ensure good efficiency. Moreover, the flow conditions change when the volute operates far from its design point: at mass flow rates lower than the design one, the flow becomes diffusive, while at higher mass flow rates the fluid is accelerated, thus leading to different loss-generation mechanisms. These phenomena are particularly relevant in turbocharger applications, where the compressor needs to cover a wide functioning range; moreover, the design is often driven also by space limitations imposed by the vehicle layout, leading to a variety of volute shapes. The present paper reports an analysis on the sources of thermodynamic irreversibilities occurring inside different volutes applied to a centrifugal compressor for turbocharging applications. Three demonstrative geometrical configurations are analyzed by means of 3D numerical simulations using common boundary conditions to assess the overall volute performance and the different loss mechanisms, which are evaluated in terms of the local entropy generation rate. The modification of the loss mechanisms in off-design conditions is also accounted for by investigating different mass flow rates. It is shown that the use of the entropy generation rate for the assessment of the irreversibilities is helpful to understand and localize the sources of loss in relation to the various flow structures.
TOPICS: Compressors, Turbochargers, Flow (Dynamics), Design, Entropy, Fluids, Computer simulation, Vehicles, Boundary-value problems, Shapes, Pressure
research-article  
Cécile Dumartineix, Benjamin Chouvion, Fabrice Thouverez and Marie-Océane Parent
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040865
The improvement of efficiency in the design of turbomachines requires a reliable prediction of the vibrating behavior of the whole structure. The simulation of blades vibrations is decisive and this is usually based on elaborated finite element model re- stricted to the bladed-disk. However the blades dynamic behavior can be strongly affected by interactions with other parts of the engine. Global dynamic studies that consider these other parts are required but usually come with a high numerical cost. In the case of a bi-rotor architecture, two coaxial rotors with different rotating speed can be coupled with a bearing system. The me- chanical coupling between the shafts generates energy exchange that alters the dynamic behavior of the blades. The equations of motion of the whole structure that take into account the coupling contain periodic time-dependent coefficients due to the difference of rotational speed between both rotors. Equations of this kind, with variable coefficients, are typically difficult to solve. This study presents a preprocessing method to guarantee the elimi- nation of time-dependent coefficients in the bi-rotor equations of motion. This method is tested with a simplified finite element model of two bladed-disks coupled with linear stiffnesses. We obtain accurate results when comparing frequency analysis of preprocessed equations with time-integration resolution of the initial set of equations. The developed methodology also offers a substantial time saving.
TOPICS: Rotors, Blades, Finite element model, Equations of motion, Disks, Bearings, Design, Engines, Simulation, Resolution (Optics), Turbomachinery, Vibration
research-article  
Joseph Beck, Jeffrey Brown, Alex Kaszynski and Emily Carper
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040869
The impact of geometry variations on integrally bladed disk eigenvalues is investigated. A large population of industrial Bladed Disks (Blisks) are scanned via a structured light optical scanner to provide as-measured geometries in the form of point-cloud data. The point cloud data is transformed using Principal Component Analysis that results in a Pareto of Principal Components (PCs). The PCs are used as inputs to predict the variation in a Blisk's eigenvalues due to geometry variations from nominal when all blades have the same deviations. A large subset of the PCs are retained to represent the geometry variation, which proves challenging in probabilistic analyses because of the curse of dimensionality. To overcome this, the dimensionality of the problem is reduced by computing an active subspace that describes critical directions in the PC input space. Active variables in this subspace are then fit with a surrogate model of a Blisk's eigenvalues. This surrogate can be sampled efficiently with the large subset of PCs retained in the active subspace formulation to yield a predicted distribution in eigenvalues. The ability of building an active subspace mapping PC coefficients to eigenvalues is demonstrated. Results indicate that exploitation of the active subspace is capable of capturing eigenvalue variation.
TOPICS: Manufacturing, Disks, Eigenvalues, Dynamic light scattering, Geometry, Optical scanners, Principal component analysis, Blades
research-article  
Anders Thorin, Nicolas Guerin, Mathias J. Legrand, Fabrice Thouverez and Patricio Almeida
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040857
In turbomachinery, it is well known that tighter operating clearances improve the efficiency. However, this leads to unwanted potential unilateral and frictional contact occurrences between the rotating (blades) and stationary components (casings) together with attendant thermal excitations. Unilateral contact induces discontinuities in the velocity at impact times, hence the terminology nonsmooth dynamics. Current modeling strategies of rotor-stator interactions are either based on regularizing penalty methods or on explicit time-marching methods derived from Carpenter's forward Lagrange multiplier method. Regularization introduces an artificial time scale in the formulation corresponding to numerical stiffness which is not desirable. Carpenter's scheme has been successfully applied to turbomachinery industrial models in the sole mechanical framework, but faces serious stability issues when dealing with the additional heat equation. This work overcomes the above issues by using the Moreau--Jean nonsmooth integration scheme within an implicit theta-method. This numerical scheme is based on a mathematically sound description of the contact dynamics by means of measure differential inclusions and enjoys attractive features. The procedure is unconditionally stable opening doors to quick preliminary simulations with time-steps one hundred times larger than with previous algorithms. It can also deal with strongly coupled thermomechanical problems.
TOPICS: Simulation, Engineering simulation, Thermoelasticity, Blades, Turbomachinery, Thermomechanics, Contact dynamics, Excitation, Stators, Stiffness, Modeling, Non-smooth dynamics, Rotors, Algorithms, Stability, Heat, Doors
research-article  
Ward De Paepe, Massimiliano Renzi, Marina Montero Carrero, Carlo Caligiuri and Francesco Contino
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040859
With the current shift from centralized to more decentralized power production, new opportunities arise for small-scale Combined Heat and Power (CHP) production units like micro Gas Turbines (mGTs). However, to fully embrace these opportunities, the current mGT technology must become more flexible in terms of operation and in terms of fuel utilization. Cycle humidification is a possible route to handle these problems. Current simulation models can correctly assess the impact of humidification on the cycle performance, but they fail to provide detailed information on the combustion process. To fully quantify the potential of cycle humidification, more advanced numerical models are necessary, capable of handling the complex chemical kinetics in the combustor. In this paper, we compared and validated such a model (in-house MATLAB model) with a typical steady-state model (Aspen Plus) of the steam injected mGT based on the Turbec T100. Both models were compared considering steam injection in the compressor outlet or in the combustor, focussing only on the global cycle performance. Simulation results showed some differences between the models; however, the general trends observed are consistent. Additionally, the numerical results of the injection in the compressor outlet were validated with steam injection experiments, indicating that the MATLAB model overestimates the efficiency improvement by 25% to 45%. The results show the potential of simulating the humidified cycle using more advanced models; however, in future work, special attention should be paid to the experimental tuning of the model parameters in general and the recuperator in particular.
TOPICS: Cycles, Steam, Micro gas turbines, Compressors, Combustion chambers, Combined heat and power, Matlab, Simulation models, Simulation results, Steady state, Chemical kinetics, Combustion, Fuels, Computer simulation, Energy generation
research-article  
Nikola Kovachev, Christian U. Waldherr, Jürgen F. Mayer and Damian M. Vogt
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040856
Resonant response of turbomachinery blades can lead to high cycle fatigue (HCF) if the vibration amplitudes are excessive. Accurate and reliable simulations of the forced response phenomenon require detailed CFD and FE models that may consume immense computational costs. In the present study, an alternative approach is applied, which incorporates nonlinear harmonic (NLH) CFD simulations in a one-way fluid-structure interaction (FSI) workflow for the prediction of the forced response phenomenon at reduced computational costs. Five resonance crossings excited by the stator in a radial inflow turbocharger turbine are investigated and the aerodynamic excitation and damping are predicted using this approach. Blade vibration amplitudes are obtained from a subsequent forced response analysis combining the aerodynamic excitation with aerodynamic damping and a detailed structural model of the investigated turbine rotor. A comparison with tip timing measurement data shows that all predicted values lay within the range of the mistuned blade response underlining the high quality of the utilized workflow.
TOPICS: Rotors, Turbines, Vibration, Blades, Resonance, Simulation, Computational fluid dynamics, Damping, Engineering simulation, Workflow, Fluid structure interaction, High cycle fatigue, Excitation, Inflow, Turbochargers, Finite element model, Stators, Turbomachinery
research-article  
Thomas Krummrein, Martin Henke and Peter Kutne
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040855
Steady state simulations are an important method to investigate thermodynamic processes. This is especially true for innovative micro gas turbine (MGT) based cycles as the complexity of such systems grows. Therefore, steady state simulation tools are required which ensure large flexibility and computation robustness. As the increased system complexity result often in more extensive parameter studies also a fast computation speed is required. While a number of steady state simulation tools for micro gas turbine based systems are described and applied in literature, the solving process of such tools is rarely explained. However, this solving process is crucial to achieve a robust and fast computation within a physically meaningful range. Therefore, a new solver routine for a steady state simulation tool developed at the DLR Institute of Combustion Technology is presented in detail in this paper. The solver routine is based on Broyden's method. It considers boundaries during the solving process to maintain a physically and technically meaningful solution process. Supplementary methods are implemented and described which improve the computation robustness and speed. Furthermore, some features of the resulting steady state simulation tool are presented. Exemplary applications of a hybrid power plant, an inverted Brayton cycle and an aircraft auxiliary power unit show the capabilities of the presented solver routine and the steady state simulation tool. It is shown that the new solver routine is superior to the standard Simulink algebraic solver in terms of system evaluation and robustness for the given applications.
TOPICS: Cycles, Steady state, Micro gas turbines, Simulation, Computation, Robustness, Hybrid power systems, Thermodynamic processes, Brayton cycle, Aircraft, Combustion technologies, Algebra
research-article  
Jens S. Müller, Finn Lückoff and Kilian Oberleithner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040862
The fundamental impact of the precessing vortex core (PVC) as a dominant coherent flow structure in the flow field of swirl-stabilized gas turbine combustors has still not been investigated in depth. In order to do so, the PVC needs to be actively controlled to be able to set its parameters independently to any other of the combustion system. In this work, open-loop actuation is applied in the mixing section between the swirler and the generic combustion chamber of a non-reacting swirling jet setup to investigate the receptivity of the PVC with regard to its lock-in behavior at different streamwise positions. The mean flow in the mixing section as well as in the combustion chamber is measured by stereoscopic particle image velocimetry and the PVC is extracted from the snapshots using proper orthogonal decomposition. The lock-in experiments reveal the axial position in the mixing section that is most suitable for actuation. Furthermore, a global linear stability analysis is conducted to determine the adjoint mode of the PVC which reveals the regions of highest receptivity to periodic actuation based on mean flow input only. This theoretical receptivity model is compared with the experimentally obtained receptivity data and the applicability of the adjoint-based model for the prediction of optimal actuator designs is discussed.
TOPICS: Stability, Vortices, Flow control, Actuators, Flow (Dynamics), Combustion chambers, Locks (Waterways), Particulate matter, Principal component analysis, Swirling flow, Combustion systems, Gas turbines
research-article  
Giacomo Fantozzi, Mats Kinell, Sara Rabal Carrera, Jenny Nilsson and Yves Kuesters
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040868
Recent technological advances in the field of additive manufacturing have made possible to manufacture turbine engine components characterized by controlled permeability in desired areas. These have shown great potential in cooling application such as convective cooling and transpiration cooling and may in the future contribute to an increase of the turbine inlet temperature. This study investigates the effects of the pressure ratio, the thickness of the porous material and the hatch distance used during manufacturing on the discharge coefficient. Moreover, two different porous structures were tested and in total 70 test objects were investigated. Using a scanning electron microscope, it is shown that the porosity and pore radius distribution, which are a result from the used laser power, laser speed and hatch distance during manufacturing, will characterize the pressure losses in the porous sample. Furthermore, the discharge coefficient increases with increasing pressure ratio, while it decreases with increasing thickness to diameter ratio. The obtained experimental data was used to develop a correlation for the discharge coefficient as a function of the geometrical properties and the pressure ratio.
TOPICS: Pressure, Porous materials, Discharge coefficient, Lasers, Manufacturing, Cooling, Permeability, Temperature, Gas turbines, Turbines, Scanning electron microscopes, Porosity, Transpiration, Additive manufacturing
research-article  
Alessandro Bianchini, Giulia Andreini, Lorenzo Ferrari, Dante Tommaso Rubino and Giovanni Ferrara
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040863
Recent studies showed that a prompt detection of the stall inception, connected with a specific model to predict the associated aerodynamic force, could provide room for an extension of the left margin of the operating curve of centrifugal compressors. In industrial machines working in the field, however, robust procedures to detect and identify the phenomenon are still missing, i.e. the operating curve is cut preliminary by the manufacturer by a proper safety margin; moreover, no agreement is found in the literature about a well-defined threshold to identify the onset of the stall. In some cases the intensity of the arising subsynchronous frequency is compared to the revolution frequency, while in many others it is compared to the blade passage frequency. A large experience in experimental stall analyses collected by the authors revealed that in some cases unexpected spikes could make this direct comparison not reliable for a robust automatic detection. To this end, a new criterion was developed based on an integral analysis of the area subtended to the entire subsynchronous spectrum of the dynamic pressure signal of probes positioned just outside the impeller exit. A dimensionless parameter was defined to account for the spectrum area increase in proximity to stall inception. This new parameter enabled the definition of a reference threshold to highlight the arising of stall conditions, whose validity and increased robustness was verified based on a set of experimental analyses of different full-stage test cases of industrial centrifugal compressors at the test rig.
TOPICS: Diffusers, Compressors, Stall inception, Impellers, Fluid-dynamic forces, Blades, Experimental analysis, Probes, Robustness, Signals, Pressure, Aerodynamics, Machinery, Safety

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