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Accepted Manuscripts

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research-article  
Hideaki Tamaki
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041003
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.
TOPICS: Diffusers, Vaneless diffusers, Compressor impellers, Flow (Dynamics), Pressure, High pressure (Physics), Surges, Design, Pressure measurement, Compressors, Impellers, Flow visualization
research-article  
Adrien Martin and Fabrice Thouverez
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041001
The search for ever lighter weight has become a major goal in the aeronautical industry as it has a direct impact on fuel consumption. It also implies the design of increasingly thin structures made of sophisticated and flexible materials. This may result in nonlinear behaviours due to large structural displacements. Stator vanes can be affected by such phenomena, and as they are a critical part of turbojets, it is crucial to predict these behaviours during the design process in order to eliminate them. This paper presents a reduced order modelling process suited for the study of geometric nonlinearities. The method is derived from a classical Component Mode Synthesis with fixed interfaces, in which the reduced nonlinear terms are obtained through a STEP procedure using an adapted basis composed of linear modes completed by modal derivatives. The whole system is solved using a harmonic balance procedure and a classic iterative nonlinear solver. The application is implemented on a schematic stator vane model composed of nonlinear Euler-Bernoulli beams under von Karman assumptions.
TOPICS: Weight (Mass), Design, Dynamic analysis, Modeling, Stators, Turbojets, Fuel consumption
research-article  
Patrick Nau, Zhiyao Yin, Oliver Lammel and Wolfgang Meier
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040716
Phosphor thermometry has been developed for wall temperature measurements in gas turbines and gas turbine model combustors. An array of phosphors has been examined in detail for spatially and temporally resolved surface temperature measurements. Two examples are provided, one at high pressure (8 bar) and high temperature and one at atmospheric pressure with high time resolution. To study the feasibility of this technique for full scale gas turbine applications a high momentum confined jet combustor at 8 bar was used. Successful measurements up to 1700 K on a ceramic surface are shown with good accuracy. In the same combustor, temperatures on the combustor quartz walls were measured, which can be used as boundary conditions for numerical simulations. An atmospheric swirl-stabilized flame was used to study transient temperature changes on the bluff body. For this purpose, a high-speed setup (1 kHz) was used to measure the wall temperatures at an operating condition where the flame switches between being attached (M-flame) and being lifted (V-flame) (bistable). The influence of a precessing vortex core (PVC) present during M-flame periods is identified on the bluff body tip, but not at positions further inside the nozzle.
TOPICS: Combustion chambers, Gas turbines, Phosphors, Wall temperature, Flames, Temperature, Temperature measurement, Computer simulation, High pressure (Physics), Resolution (Optics), Transients (Dynamics), Nozzles, Vortices, Boundary-value problems, Atmospheric pressure, Ceramics, Momentum, High temperature, Quartz, Switches
research-article  
Marius Mihailowitsch, Markus Schatz and Damian M. Vogt
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040769
It is well known that the last stage of a turbine and the subsequent diffuser should be viewed at and designed as a coupled system rather than as single standalone components. The turbine outlet flow imposes the inlet conditions to the diffuser, whereas the recovered dynamic pressure in the diffuser directly controls the turbine back pressure. With changing operating point, the turbine outflow can vary significantly. This results consequently in large variations of the diffuser performance. A major role in the coupled system of turbine and diffuser can be attributed to the tip leakage flow. While it is desirable to minimize the tip leakage with regard to the turbine, a higher leakage mass flow can often be beneficial for the diffuser performance. As there is currently a trend towards aggressive and hence shorter diffusers which are particularly prone to separation, the question arises where the optimum for this tradeoff problem lies. To investigate the performance in the coupled turbine / diffuser system, a generic last stage with shrouded rotor and axial exhaust diffuser have been designed. The components are representative for heavy duty stationary gas turbine applications. Results are presented for three different operating points representing part-load, design-load and over-load condition. Three different seal gap widths are taken into account to control the leakage flow. The results indicate that an operating point dependent optimum gap width can be found for the coupled system efficiency whereas the maximum turbine performance is always achieved with a minimum gap width.
TOPICS: Diffusers, Gas turbines, Exhaust systems, Turbines, Stress, Pressure, Flow (Dynamics), Leakage flows, Leakage, System efficiency, Outflow, Tradeoffs, Separation (Technology), Design, Rotors
research-article  
Torsten Heinze, Lars Panning-von Scheidt, Jörg Wallaschek and Andreas Hartung
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040843
Considering rotational speed-dependent stiffness for vibrational analysis of friction-damped bladed disk models has proven to lead to significant improvements in nonlinear frequency response computations. The accuracy of the result is driven by a suitable choice of reduction bases. Multi-model reduction combines various bases which are valid for different parameter values. This composition reduces the solution error drastically. The resulting set of equations is typically solved by means of the harmonic balance method. Nonlinear forces are regularized by a Lagrangian approach embedded in an alternating frequency/time domain method providing the Fourier coefficients for the frequency domain solution. The aim of this paper is to expand the multi-model approach to address rotational speed-dependent contact situations. Various reduction bases derived from composing CMS methods will be investigated with respect to their applicability to capture the changing contact situation correctly. The methods validity is examined based on small academic examples and large-scale industrial blade models. Coherent results show that the multi-model composition works successfully, even if multiple different reduction bases are used per sample point of rotational speed. This is an important issue in case that contact situations for specific values of speed are uncertain forcing the algorithm to automatically choose a suitable representation. Additionally, the randomized singular value decomposition (RSVD) is applied to rapidly extract a multi-model basis. This approach improves the computational performance by orders of magnitude compared to the standard SVD, while preserving the ability to provide a best rank approximation.
TOPICS: Dynamics (Mechanics), Blades, Computation, Errors, Frequency response, Stiffness, Friction, Algorithms, Disks, Approximation
research-article  
Timo Zornek, Thomas Mosbach and Manfred Aigner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040908
A FLOX®-combustion system was developed to couple a fixed-bed gasifier with a micro gas turbine. The two-staged combustor consists of a jet-stabilized main stage adapted from the FLOX®-design combined with a swirl stabilized pilot stage. It was operated in a Turbec T100 test rig using an optically accessible combustion chamber, which allowed OH*-chemiluminescence and OH-PLIF measurements for various fuel compositions. In particular, the hydrogen content in the synthetically mixed fuel gas was varied from 0 % to 30 %. The exhaust gas composition was additionally analysed regarding CO, NOx and unburned hydrocarbons. The results provide a comprehensive insight into the flame behaviour during turbine operation. Efficient combustion and stable operation of the Turbec T100 was observed for all fuel compositions, while the hydrogen showed a strong influence. It is remarkable, that with hydrogen contents higher than 9 % no OH radicals were detected within the inner recirculation zone, while they were increasingly entrained below hydrogen contents of 9 %. Without hydrogen, the inner recirculation zone was completely filled with OH radicals and the highest concentrations were detected there. Therefore, the results indicate a different flame behaviour with low and high hydrogen contents. Although the flame shape and position was affected, pollutant emissions remained consistent below 10 ppm based on 15 % O2. Only in case of 0 % hydrogen, CO emissions increased to 43 ppm, which is still meeting the emission limits. Thus, the combustor allows operation with low calorific syngases having hydrogen contents from 0 % to 30 %.
TOPICS: Optical measurement, Fuels, Combustion chambers, Micro gas turbines, Hydrogen, Flames, Emissions, Combustion, Gaseous fuels, Chemiluminescence, Design, Turbines, Syngas, Exhaust systems, Shapes, Pollution, Nitrogen oxides
research-article  
Violette Mounier, Cyril Picard and Jurg Schiffmann
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040845
Domestic scale heat pumps and air conditioners are mainly driven by volumetric compressors. Yet the use of reduced scale centrifugal compressors is reconsidered due to their high efficiency and power density. The design procedure of centrifugal compressors starts with pre-design tools based on the Cordier line. However, the optimality of the obtained pre-design, which is the starting point of a complex and iterative process, is not guaranteed, especially for small-scale compressors operating with refrigerants. This paper proposes a data-driven pre-design tool tailored for small-scale centrifugal compressors used in refrigeration applications. The pre-design model is generated using an experimentally validated 1D code which evaluates the compressor performance as a function of its detailed geometry and operating conditions. Using a symbolic regression tool, a reduced order model that predicts the performance of a given compressor geometry has been built. The proposed pre-design model offers an alternative to the existing tools by providing a higher level of detail and flexibility. Particularly, the model includes the effect of the pressure ratio, the blade height ratio and the shroud to tip radius ratio. The analysis of the centrifugal compressor losses allows identifying the underlying phenomena that shape the new isentropic efficiency contours. Compared to the validated 1D code the new pre-design model yields deviations below 4% on the isentropic efficiency, while running 1500 times faster. The new pre-design model is therefore of significant interest when the compressor is part of an integrated system design process.
TOPICS: Compressors, Design, Refrigeration, Geometry, Heat pumps, Refrigerants, Shapes, Air conditioners, Integrated systems, Power density, Blades, Pressure
research-article  
Luis San Andres, Bonjin Koo and Sung-Hwa Jeung
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040902
Piston rings (PRs) and O-rings (ORs), commonly used as end seals in SFDs for commercial and military gas turbine engines, respectively, amplify viscous damping in a short physical length and while operating with a modicum of lubricant flow. This paper presents experimental force for two identical geometry SFDs with end seals. A computational model reproducing the test conditions delivers force coefficients in agreement with the test data. Archival literature calls for measurement of a single pressure signal to estimate SFD reaction forces. The paper presents force coefficients estimated from (a) measurements of the applied forces and ensuing displacements, and (b) the dynamic pressure recorded at a fixed angular location and "integrated" over the journal surface. Identified damping and inertia coefficients from dynamic pressures show a marked difference from one pressure sensor to another, and vastly disagreeing with test results from the first method or predictions. The rationale for the discrepancy relies on local distortions in the dynamic pressure fields that show zones of oil vapor cavitation at a near zero absolute pressure and/or with air ingestion producing high frequency spikes from bubble collapsing; both phenomena depend on the magnitude of the oil supply pressure. An increase in lubricant supply pressure suppresses both oil vapor cavitation and air ingestion which produces an increase of both damping and inertia force coefficients. Supplying lubricant with a large enough pressure (flow rate) is crucial to avoid the pervasiveness of air ingestion.
TOPICS: Seals, Piston rings, Dampers, Pressure, Lubricants, Damping, Inertia (Mechanics), Flow (Dynamics), Vapors, Cavitation, Bubbles, Pressure sensors, Gas turbines, Geometry, Military systems, Signals
research-article  
Donghyuk Jung, Haksu Kim, Seungwoo Hong, Yeongseop Park, Hyungbok Lee, Donghee Han, Manbae Han and Myoungho Sunwoo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040578
This paper proposes three different methods to estimate the low-pressure cooled exhaust gas recirculation (LP-EGR) mass flow rate based on in-cylinder pressure measurements. The proposed LP-EGR models are designed with various combustion parameters, which are derived from (1) heat release analysis, (2) central moment calculation, and (3) principal component analysis (PCA). The heat release provides valuable insights into the combustion process, such as flame speed and energy release. The central moment calculation enables quantitative representations of the shape characteristics in the cylinder pressure. The PCA also allows the extraction of the influential features through simple mathematical calculations. In this paper, these approaches focus on extracting the combustion parameters that are highly correlated to the diluent effects of the LP-EGR, and the parameters are used as the input states of the polynomial regression models. Moreover, in order to resolve the effects of cycle-to-cycle variations on the estimation results, a static model based Kalman filter is applied to the combustion parameters for the practically usable estimation. The fast and precise performance of the proposed models was validated in real-time engine experiments under steady and transient conditions. The proposed LP-EGR mass flow model was demonstrated under a wide range of steady states with an R2 value over 0.98. The instantaneous response of the cycle-basis LP-EGR estimation was validated under transient operations.
TOPICS: Cylinders, Pressure, Exhaust gas recirculation, Direct injection spark ignition engines, Combustion, Cycles, Transients (Dynamics), Flow (Dynamics), Heat, Pressure measurement, Engines, Flames, Kalman filters, Polynomials, Principal component analysis, Regression models, Shapes, Steady state, Diluents
research-article  
Anastasios O. Koskoletos, Nikolaos Aretakis, Alexios Alexiou, Christoforos Romesis and Kostas Mathioudakis
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040909
Propulsion Diagnostic Method Evaluation Strategy (ProDiMES) offers an aircraft engine diagnostic benchmark problem where the performance of candidate diagnostic methods is evaluated while a fair comparison can be established. In the present paper, the performance evaluation of a number of gas turbine diagnostic methods using the ProDiMES software is presented. All diagnostic methods presented here were developed at the Laboratory of Thermal Turbomachinery of the National Technical University of Athens (LTT/NTUA). Component, sensor and actuator fault scenarios, that occur in a fleet of deteriorated twin-spool turbofan engines are considered. The performance of each diagnostic method is presented through the evaluation metrics introduced in the ProDiMES software. Remarks about each methods performance as well as the detectability and classification rates of each fault scenario are made.
TOPICS: Aircraft engines, Computer software, Performance evaluation, Turbomachinery, Turbofans, Sensors, Engines, Propulsion, Actuators, Gas turbines
research-article  
Rahul Rajasekharan-Nair and Evgeny Petrov
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040906
Single crystal blades used in high pressure turbine bladed disks of modern gas-turbine engines exhibit material anisotropy. In this paper the sensitivity analysis is performed to quantify the effects of blade material anisotropy orientation on deformation of a mistuned bladed disk under static centrifugal load. For a realistic, high fidelity model of a bladed disk both: (i) linear, and (ii) non-linear friction contact conditions at blade roots and shrouds are considered. The following two kinds of analysis are performed: (i) local sensitivity analysis, based on first order derivatives of system response w.r.t design parameters, and (ii) statistical analysis using polynomial chaos expansion. The polynomial chaos expansion is used to transfer the uncertainty in random input parameters to uncertainty in static deformation of the bladed disk. An effective strategy, using gradient information, is proposed to address the "curse of dimensionality" problem associated with statistical analysis of realistic bladed disk.
TOPICS: Deformation, Friction, Crystals, Anisotropy, Chaos, Polynomials, Disks, Blades, Sensitivity analysis, Statistical analysis, Uncertainty, High pressure (Physics), Design, Gas turbines, Turbines, Engines, Stress
research-article  
Angelo Grimaldi and Vittorio Michelassi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040907
This paper discusses the impact of inlet flow distortions on centrifugal compressors based upon a large experimental data base in which the performance of several impellers in a range of corrected flows and corrected speeds have been measured after been coupled with different inlet plenums technologies. The analysis extends to centrifugal compressor inlets including a side stream, typical of Liquefied Natural Gas (LNG) applications. The detailed measurements allow a thorough characterization of the flow field and associated performance. The results suggest that distortions can alter the head by as much as 3% and efficiency of around 1%. A theoretical analysis allowed to identify the design features that are responsible for this deviation. In particular, an extension of the so-called "reduced-frequency", a coefficient routinely used in axial compressors and turbine aerodynamics to weigh the unsteadiness generated by upstream to downstream blade rows, allowed to determine a plenum-to-impeller reduced frequency that correlates very well with the measured performance. The theory behind the new coefficient is discussed together with the measurement details, and validate the correlation that can be used in the design phase to determine the best compromise between the inlet plenum complexity and impact on the first stage.
TOPICS: Compressors, Flow (Dynamics), Liquefied natural gas, Impellers, Design, Turbines, Blades, Databases, Theoretical analysis, Aerodynamics
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  
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

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