An Additively Manufactured Four Sensor Fast Response Aerodynamic Probe

The current work describes the design, development and testing of a miniature fast response aerodynamic probe (FRAP) with 4 sensors (4S), able to perform measurements in unsteady three-dimensional flow field. Moreover, the calibration and first results with the newly developed probe is also provided. The miniature FRAP-4S demonstrates a 3 mm tip diameter, which represents a 25% reduction in diameter size, in comparison to a first generation FRAP-4S, without any loss in terms of measurement bandwidth. The 3 mm outer casing of the probe is additively manufactured with a high-precision binder jetting technique. In terms of aerodynamic performance, the probe demonstrates high angular sensitivity up to at least ± 18° incidence angle in both directions. To evaluate the measurement accuracy of the newly developed FRAP-4S, measurements are performed at the Laboratory for Energy Conversion (LEC) in both a round axisymmetric jet and an one-and-a-half stage, unshrouded and highly-loaded axial turbine configuration. Turbulence measurements performed with the miniature FRAP-4S are compared against hot-wire studies in round free-jets found in the literature. Good agreement in both trends but also absolute values is demonstrated. Moreover, the performance of the probe is compared against traditional instrumentation developed at LEC, namely miniature pneumatic and FRAP-2S probes. The results indicate that the FRAP-4S, despite its larger size in comparison to the other probes tested, can resolve the main flow patterns, while the highest deviations occur in the presence of highly skewed and sheared flows. Furthermore, the additively manufactured probe was proven to be robust after more than 50 hours of testing in representative turbine environment configuration. Finally, it should be highlighted that the newly developed FRAP reduces measurement time by a factor of three in comparison to FRAP-2S, which directly translates to reduced development time and thus cost, during turbomachinery development phase.

Joint Wavelet Transform and Time Synchronous Averaging Source Separation Method and its Application on Aero-Engine

The reliability and safety of aero-engine are often the decisive factors for the safe and reliable flight of commercial aircraft. Hence, the vibration source location and fault diagnosis of aero-engine are of prime importance to detect faults and carry out fast and effective maintenance in time. However, the vibration signals collected by the sensors arranged on the casing of the aero-engine are generally the mixed signals of the main vibration sources inside the engine, and the components are extremely complicated. Therefore, the vibration source identification is a big challenge for a fault diagnosis and health management of the engine. In order to separate the key vibration sources of rotating machinery such as aero-engine, a Joint Wavelet Transform and Time Synchronous Averaging based algorithm (JWTS) is proposed in this paper. Based on the fact that the fundamental frequency and its harmonic and sub-harmonic components are generally included in the vibration spectrum of shaft fault signal of rotating machinery, wavelet transform and time synchronous averaging algorithm are combined to extract them. The algorithm completes separating the main vibration sources with three steps. First, the source number and fundamental frequency of each source are estimated using the wavelet transform. Second, every source is extracted from each observed signal by the time synchronous averaging method. Time synchronous averaging method can effectively extract a signal of cycle and harmonic rotor components and can suppress noise. Third, the optimal estimation of each source is determined according to signal’s 2-norm. Since the extracted source with a larger energy is closer to the real source, and signal’s 2-norm is a good indicator of the signal energy. Hence, the key vibration sources related to rotary speeds of the engine are obtained separately. The method is verified by synthetic mixed signals first. Three periodic signals of different frequencies are used to simulate the vibration sources of the aeroengine. The fundamental, harmonic and sub-harmonic components of them, as well as Gaussian white noise, are randomly mixed. The results show that the JWTS algorithm can estimate the number of the main sources and can extract each source effectively. Then the method is demonstrated using vibration signals of a real aero-engine. The results indicate that the proposed JWTS method has extracted and located the main sources within the aero-engine, including sources from the low-pressure rotor, high-pressure rotor, combustion chamber and accessory. Therefore, the proposed method provides a new fault diagnosis technology for rotating machinery, especially for a real aero-engine.

Error Considerations for Turbine-Generator Torsional Vibration Monitoring

Turbine-generator torsional vibration is linked to electrical events in the power grid by the generator air-gap torque. Modern power systems are subject to gradual transformation by increasing flexibility demands and incorporation of renewable resources. As a result, electrical transient events are getting more frequent and thus torsional vibration is getting more and more attention. Especially in the case of large steam and gas turbines torsional vibration can cause material fatigue and present a hazard for safe machine operation. This paper freely builds on previous work, where a method for torsional vibration evaluation using an incremental encoder measurement was presented, in that it supplements error considerations to this methodology. Measurement errors such as precision of the rotor encoder manufacturing, choice of the proper sensor, its signal to noise ratio and the error of instantaneous velocity computation algorithm are analyzed. The knowledge of these errors is essential for torsional vibration as there is an indirect and relatively complicated path from the measurement to the final torsional vibration results compared to other kinds of vibration. The characteristics of particular errors of the processing chain are validated both on experimental data from a test rig as well as field data measured on turbine-generators in power plants.

Enhanced Early Warning Diagnostic Rules for Gas Turbines Leveraging on Bayesian Networks

The monitoring and diagnostics of Industrial systems is increasing in complexity with larger volume of data collected and with many methods and analytics able to correlate data and events. The setup and training of these methods and analytics are one of the impacting factors in the selection of the most appropriate solution to provide an efficient and effective service, that requires the selection of the most suitable data set for training of models with consequent need of time and knowledge. The study and the related experiences proposed in this paper describe a methodology for tracking features, detecting outliers and derive, in a probabilistic way, diagnostic thresholds to be applied by means of hierarchical models that simplify or remove the selection of the proper training dataset by a subject matter expert at any deployment. This method applies to Industrial systems employing a large number of similar machines connected to a remote data center, with the purpose to alert one or more operators when a feature exceeds the healthy distribution. Some relevant use cases are presented for an aeroderivative gas turbine covering also its auxiliary equipment, with deep dive on the hydraulic starting system. The results, in terms of early anomaly detection and reduced model training effort, are compared with traditional monitoring approaches like fixed threshold. Moreover, this study explains the advantages of this probabilistic approach in a business application like the fleet monitoring and diagnostic advanced services.

A Novel SOFC Thermal Management Strategy of SOFC-GT Hybrid System With Anode and Cathode Control Loops

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.

Uncertainty Evaluation on Multi-Hole Aerodynamic Pressure Probes

In the frame of a continuous improvement of the performance and accuracy in the experimental testing of turbomachines, the uncertainty analysis on measurements instrumentation and techniques is of paramount importance. For this reason, since the beginning of the experimental activities at the Laboratory of Fluid Machines (LFM) located at Politecnico di Milano (Italy), this issue has been addressed and different methodologies have been applied. This paper proposes a comparison of the results collected applying two methods for the measurement uncertainty quantification to two different aerodynamic pressure probes: sensor calibration, aerodynamic calibration and probe application are considered. The first uncertainty evaluation method is the so called “Uncertainty Propagation” method (UPM); the second is based on the “Monte Carlo” method (MCM). Two miniaturized pressure probes have been selected for this investigation: a pneumatic 5-hole probe and a spherical fast response aerodynamic pressure probe (sFRAPP), the latter applied as a virtual 4-hole probe. Since the sFRAPP is equipped with two miniaturized pressure transducers installed inside the probe head, a specific calibration procedure and a dedicated uncertainty analysis are required.

CFD–Aided Design Methodology for PCHE-Type Recuperators in Supercritical CO2 Recompression Power Cycles

The supercritical carbon dioxide (sCO2) cycle has emerged as a promising power cycle for various types of power conversion systems, based on its high thermal efficiency, (approaching 60%), small-size and compactness. The recompression Brayton cycle with sCO2 is based on high capacity regenerators processing a large amount of heat making their effectiveness critical for the overall cycle efficiency. Printed Circuit Heat Exchangers (PCHEs) are used in these cycles because of their high attainable effectiveness values. The design process for these regenerators is demanding, considering the peculiarities of variation of CO2 density and thermal properties near the critical temperature. On the other hand, a reduced computation time is necessary for the quick assessment of alternative design options. A hybrid design methodology for the high-temperature and the low-temperature recuperator (HTR and LTR) is presented in this paper, which employs 3D CFD conjugate heat transfer computation of the performance of a small two-channel module of the PCHE type. The results of the module computation are deployed in a 1D segmental method for the performance computation of the full heat exchanger’s channel length. Thus, the thermal effectiveness and pressure drop characteristics for the full heat exchanger are computed fast and with high accuracy. Application of the proposed methodology is carried out for the HTR and LTR computation in a recompression sCO2 Brayton cycle of a 600 MWth size power plant.

Integration Options for Nuclear Steam Cycle Using Liquid Air Energy Storage

To facilitate the energy transition, the conventional baseload nuclear power must be equipped with flexibility. By integrating grid-scale energy storage systems to the existing nuclear plants, they can curtail their load to avoid surplus generation. Liquid air energy storage (LAES) has been steadily investigated for their advantages, and this paper suggests an integrated layout using mechanical drive steam turbine and packed bed energy storage systems. Possible options for integration of LAES to the existing nuclear steam cycle are considered. The performance of packed bed storage systems is analyzed using transient modeling, and the results are fed into the overall cycle design using an in-house code. The results of the analysis suggests that the concept can reach up to 45.7–59.8% in round-trip efficiency, under much simplified cycle layout than the reference LAES layouts.

Aero Engine Concepts Beyond 2030: Part 2 — The Free-Piston Composite Cycle Engine

Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. Part one focuses on the steam injecting and recovering aero engine concept. This second part presents the free-piston composite cycle engine concept. A third publication, building upon those two concepts, presents the project which aims for demonstrating the proof of concept with numerical simulation and test-bench experiments up to a technology readiness level of three. The free-piston composite cycle engine concept is composed of a gas turbine topped with a free-piston system. The latter is a self-powered gas generator in which the internal combustion process drives an integrated air compressor. Here, several free-piston engines replace the high-pressure core of the gas turbine. Through the ability to work at much higher temperatures and pressures, the overall system efficiency can be increased significantly, and fuel burn as well as CO2 emissions reduce. The proposed free-piston composite cycle engine design is described in detail, and the sources of thermodynamic benefits are stated. Concrete engineering solutions consider the implementation into an aircraft. The free-piston design enables lower weight and size compared to a crankshaft-bound piston engine, as no mechanical transmission and lubrication system is required. The absence of a crankshaft and connecting rods eliminates reactive forces, reduces mechanical losses, and allows higher mean piston velocities. Facilitated through air lubrication, higher cylinder temperatures are viable. The reduction of heat losses enables cooling of the piston-cylinder with core fluid. The use of a sequential combustion chamber can enhance operability and tailor the production of NOx in low-altitude operation. A discussion of emissions affecting the environment shows the potential to reduce the climate impact of aviation.

Thermo-Economic Assessment Under Electrical Market Uncertainties of a Combined Cycle Gas Turbine Integrated With a Flue Gas-Condensing Heat Pump

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.