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This paper examines the applicability of a triple layer of thermochromic liquid crystals (TLCs) for the determination of local heat transfer coefficients using the transient liquid crystal (LC) technique. The experiments were carried out in a narrow impingement channel, typically used for turbine blade cooling applications. Three types of narrow bandwidth LCs (1??C range) of 35??C, 38??C, and 41??C were individually painted on the target plate of the cooling cavity and the overall paint thickness was accurately determined with an integral coating thickness gauge. The 1D transient heat conduction equation is then implicitly solved for each individual TLC layer on its realistic depth on the painted surface. Local heat transfer coefficients are therefore calculated three times for the same location in the flow improving the measurement accuracy, especially at regions where the LC detection times are too short (stagnation points) or too long (wall-jet regions). The results indicate that if multiple LC layers are used and the paint thickness is not considered, the heat transfer coefficients can be significantly underestimated. [ABSTRACT FROM AUTHOR]

In the present paper, an experimental investigation of the effects of rim seal purge flow on the performance of a highly loaded axial turbine stage is presented. The test configuration consists of a one-and-a-half stage, unshrouded, turbine, with a blading representative of high pressure (HP) gas turbines. Efficiency measurements for various purge flow injection levels have been carried out with pneumatic probes at the exit of the rotor and show a reduction of isentropic total-to-total efficiency of 0.8% per percent of injected mass flow. For three purge flow conditions, the unsteady aerodynamic flow field at rotor inlet and rotor exit has been measured with the in-house developed fast response aerodynamic probe (FRAP). The time-resolved data show the unsteady interaction of the purge flow with the secondary flows of the main flow and the impact on the radial displacement of the rotor hub passage vortex (HPV). Steady measurements at off-design conditions show the impact of the rotor incidence and of the stage flow factor on the resulting stage efficiency and the radial displacement of the rotor HPV. A comparison of the effect of purge flow and of the off-design conditions on the rotor incidence and stage flow factor shows that the detrimental effect of the purge flow on the stage efficiency caused by the radial displacement of the rotor HPV is dominated by the increase of stage flow factor in the hub region rather than by the increase of negative rotor incidence. [ABSTRACT FROM AUTHOR]

An accurate assessment of unsteady interactions in turbines is required, so that this may be taken into account in the design of the turbine. This assessment is required since the efficiency of the turbine is directly related to the contribution of unsteady loss ,necha- nisms. This paper presents unsteady entropy measurements in an axial turbine. The measurements are conducted at the rotor exit of a one-and-one-half-stage unshrouded turbine that is representative of a highly loaded, high-pressure stage of an aero-engine. The unsteady entropy measurements are obtained using a novel miniature fast-response probe, which has been developed at ETH Zurich. The entropy probe has two components: a one-sensor fast-response aerodynamic probe and a pair of thin-film gauges. The probe allows the simultaneous measurement of the total temperature and the total pressure from which the time-resolved entropy field can be derived. The mneasuremnents of the timne- resolved entropy provide a new insight into the unsteady loss mechanismns that are associated ciated with the unsteady interaction between rotor and stator blade rows. A particular attention is paid to the interaction effects of the stator wake interaction, the secondary flow interaction, and the potential field interaction on the unsteady loss generation at the rotor exit. Furthermore, the impact on the turbine design of quantifying the loss in terms of the entropy loss coefficient, rather than the more familiar pressure loss coefficient, is discussed in detail. [ABSTRACT FROM AUTHOR]

In this article, various aspects of thermo-fluid modelling for gas turbines are described and the impact on performance calculations and emissions predictions at aircraft system level is assessed. Accurate and reliable fluid modelling is essential for any gas turbine performance simulation software as it provides a robust foundation for building advanced multi-disciplinary modelling capabilities. Caloric properties for generic and semi-generic gas turbine performance simulation codes can be calculated at various levels of fidelity; selection of the fidelity level is dependent upon the objectives of the simulation and execution time constraints. However, rigorous fluid modelling may not necessarily improve performance simulation accuracy unless all modelling assumptions and sources of uncertainty are aligned to the same level.A comprehensive analysis of thermo-fluid modelling for gas turbines is presented, and the fluid models developed are discussed in detail. Common technical models, used for calculating caloric properties, are compared while typical assumptions made in fluid modelling, and the uncertainties induced, are examined. Several analyses, which demonstrate the effects of composition, temperature, and pressure on caloric properties of working media for gas turbines, are presented. The working media examined include dry air and combustion products for various fuels and H/C ratios. The uncertainty induced in calculations by (a) using common technical models for evaluating fluid caloric properties and (b) ignoring dissociation effects is examined at three different levels: (i) component level, (ii) engine level, and (iii) aircraft system level. An attempt is made to shed light on the trade-off between improving the accuracy of a fluid model and the accuracy of a multi-disciplinary simulation at aircraft system level, against computational time penalties. The validity of the ideal gas assumption for future turbofan engines and novel propulsion cycles is discussed. The results obtained demonstrate that accurate modelling of the working fluid is essential, especially for assessing novel and/or aggressive cycles at aircraft system level. Where radical design space exploration is concerned, improving the accuracy of the fluid model will need to be carefully balanced with the computational time penalties involved. [ABSTRACT FROM AUTHOR]

In order to advance the technology for measurements in higher temperature flows, a novel miniature (diameter 2.5 mm) fast response probe that can be applied in flows with temperatures of up to 533 K (500°F) has been developed. The primary elements of the probe are two piezoresistive pressure transducers that are used to measure the unsteady pressure and unsteady velocity field, as well as the steady temperature. Additional temperature and strain gauge sensors are embedded in the shaft to allow a much higher degree of robustness in the use of this probe. The additional temperature sensor in the shaft is used to monitor and correct the heat flux through the probe shaft, facilitating thermal management of the probe. The strain gauge sensor is used to monitor and control probe shaft vibration. Entirely new packaging technology had to be developed to make possible the use of this probe at such high temperatures. Extensive calibration and thermal cycling of the probe used to bind the accuracy and the robustness of the probe. This novel probe is applied in the one-and-½ -stage, unshrouded axial turbine at ETH Zurich; this turbine configuration is representative of a high work aero-engine. The flow condi- tioning stretch upstream of the first stator is equipped with a recently designed hot streak generator~ Several parameters of the hot streak, including temperature, radial and cir- cumferential position, and shape and size can be independently controlled. The interac- tions between the hot streak and the secondary flow present a perfect scenario to verify the probe's capability to measure under real engine conditions. Therefore, measurements with the novel probe have been made in order to prove the principle and to detail the interaction effects with blade row pressure gradients and secondary flows. [DOl: 10.1115/1.4001824] [ABSTRACT FROM AUTHOR]

The aerodynamics and kinematics of flow structures, including the loss generation mechanisms, in the interstage region of a two-stage partially shrouded axial turbine are examined. The nonwcisymmerric partial shroud introduces highly three-dimensional unsteady interactions, the details of which must be understood in order to optimize the design of the blade/shroud. Detailed measurements of the steady and unsteady pressure and velocity fields are obtained using a two-sensor fast response aerodynamic probe and stereoscopic particle image velocimerry. These intrusive and non intrusive measurement techniques yield a unique data set that describes the details of the flow in the interstage region. The measurements show that a highly three-dimensional interaction occurs between the passage vortex and a vortex caused by the recessed shroud platform design. Flow coming from the blade passage suddenly expands and migrates radially upward in the cavity region, causing a localized relative total pressure drop. Interactions of vortex and Wake structures with the second stator row are analyzed by means of the combination of the measured relative total pressure and nondeterminisric pressure unsteadiness. The analysis of the data gives insight on unsteady loss mechanisms. This study provides improved flow understanding and suggests that the design of the blade/shroud and second stator leading edge may be further improved to reduce unsteady loss contribution. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the behavior of leakage flow across shrouded turbine blades. Stereoscopic particle image velocimetry and fast response aerodynamic probe measurements have been conducted in a low-speed two-stage axial turbine with a partial shroud. The dominant flow feature within the exit cavity is the radially outward motion of the main flow into the shroud cavity. The radial migration of the main flow is induced by flow separation at the trailing edge of the shroud due to a sudden area expansion. The radially outward motion is the strongest at midpitch as a result of interactions between vortices formed within the cavity. The main flow entering the exit cavity divides into two streams. One stream moves upstream toward the adjacent seal knife and reenters the main flow stream. The other stream moves downstream due to the interaction with the thin seal leakage flow layer. Closer to the casing wall, the flow interacts with the underturned seal leakage flow and gains swirl. Eventually, axial vorticity is generated due to these complex flow interactions. This vorticity is generated by a vortex tilting mechanism and gives rise to additional secondary flow. Because of these fluid motions combined with a contoured casing wall, three layers (the seal leakage layer, cavity flow layer, and main flow) are formed downstream of the shroud cavity. This result is different from the two-layer structure, which is found downstream of conventional shroud cavities. The seal leakage jet formed through the seal clearance still exists at 25.6% axial chord downstream of the second rotor. This delay of complete dissipation of the seal leakage jet and its mixing with the cavity flow layer is due to the contoured casing wall. Time-averaged flow downstream of the shroud cavity shows the upstream stator's influence on the cavity flow. The time-averaged main flow can be viewed as a wake flow induced by the upstream stator whose separation at the shroud trailing edge induces pitchwise non-uniformity of the cavity flow. [ABSTRACT FROM AUTHOR]

This study aims to illustrate a sequence that optimizes the flight-path trajectory for a hybrid-electric aircraft at mission level, in addition to identifying the respective optimum power management strategy. An in-house framework for hybrid-electric propulsion system modeling is utilized. A hybrid-electric commuter aircraft serves as a virtual test-bench. Vectorized calculations, decision variable count, and optimization algorithms are considered for reducing the computational time of the framework. Performance improvements are evaluated for the aircraft's design mission profile. Total energy consumption is set as the objective function. Emphasis lies on minimizing the average value and standard deviation of the energy consumption and timeframe metrics. The best performing application decreases computational time by two orders of magnitude, while retaining equal accuracy and consistency as the original model. It is employed for creating a dataset for training an artificial neural network (ANN) against random mission patterns. The trained network is integrated into a surrogate model. The latter part of the analysis evaluates optimized mission profile characteristics with respect to energy consumption, against a benchmark flight-path. The combined optimization process decreases the multihour-scale timeframe by two orders of magnitude to a 3-min sequence. Using the novel framework, a 12% average energy consumption benefit is calculated for short, medium, and long regional missions, against equivalent benchmark profiles. [ABSTRACT FROM AUTHOR]

Hybrid-electric propulsion is recognized as an enabling technology for reducing aviation's environmental impact. In this work, a serial/parallel hybrid configuration of a 19-passenger commuter aircraft is investigated. Two underwing-mounted turboprop engines are connected to electrical branches via generators. One rear fuselage-mounted electrically driven ducted fan is coupled with an electric motor and respective electrical branch. A battery system completes the selected architecture. Consistency in modeling accuracy of propulsion systems is aimed for by development of an integrated framework. A multipoint synthesis scheme for the gas turbine and electric fan is combined with physics-based analytical modeling for electrical components. Influence of turbomachinery and electrical power system design points on the integrated power system is examined. An opposing trend between electrical and conventional powertrain mass is driven by electric fan design power. Power system efficiency improvements in the order of 2% favor high-power electric fan designs. A trade-off in electrical power system mass and performance arises from oversizing of electrical components for load manipulation. Branch efficiency improvements of up to 3% imply potential to achieve battery mass reduction due to fewer transmission losses. A threshold system voltage of 1 kV, yielding 32% mass reduction of electrical branches and performance improvements of 1-2%, is identified. This work sets the foundation for interpreting mission-level electrification outcomes that are driven by interactions on the integrated power system. Areas of conflicting interests and synergistic opportunities are highlighted for optimal conceptual design of hybrid powertrains. [ABSTRACT FROM AUTHOR]

Modem steam turbines need to operate efficiently and safely over a wide range of operating conditions. This paper presents a unique unprecedented set of time-resolved steam flowfield measurements from the exit of the last two stages of a low pressure (LP) steam turbine under various volumetric massflow conditions. The measurements were performed in the steam turbine test facility in Hitachi city in Japan. A newly developed fast response probe equipped with a heated tip to operate in wet steam flows was used. The probe tip is heated through an active control system using a miniature high-power cartridge heater developed in-house. Three different operating points (OPs), including two reduced massflow conditions, are compared and a detailed analysis of the unsteady flow structures under various blade loads and wetness mass fractions is presented. The measurements show that at the exit of the second to last stage the flow field is highly three dimensional. The measurements also show that the secondary flow structures at the tip region (shroud leakage and tip passage vortices) are the predominant sources of unsteadiness at 85% span. The high massflow operating condition exhibits the highest level of periodical total pressure fluctuation compared to the reduced massflow conditions at the inlet of the last stage. In contrast at the exit of the last stage, the reduced massflow operating condition exhibits the largest aerodynamic losses near the tip. This is due to the onset of the ventilation process at the exit of the LP steam turbine. This phenomenon results in three times larger levels of relative total pressure unsteadiness at 93% span, compared to the high massflow condition. This implies that at low volumetric flow conditions the blades will be subjected to higher dynamic load fluctuations at the tip region. [ABSTRACT FROM AUTHOR]

The lower fuel burn and pollutant emissions of hybrid electric vehicles give a strong motivation and encourage further investigations in this field. The know-how on hybrid vehicle technology is maturing, and the reliability of such power schemes is being tested in the mass production. The current research effort is to investigate novel configurations, which could achieve further performance benefits. This paper presents an assessment of a novel hybrid configuration comprising a micro-gas turbine, a battery bank, and a traction motor, focusing on its potential contribution to the reduction in fuel burn and emissions. The power required for the propulsion of the vehicle is provided by the electric motor. The electric power is stored by the batteries, which are charged by a periodic function of the micro-gas turbine. The micro-gas turbine starts up when the battery depth of discharge exceeds 80%, and its function continues until the batteries are full. The performance of the vehicle is investigated using an integrated software platform. The calculated acceleration performance and fuel economy are compared with those of conventional vehicles of the same power The sensitivity of the results to the variation in the vehicle parameters such as mass, kinetic energy recovery, and battery type is calculated to identify the conditions under which the application of this hybrid technology offers potential benefits. The results indicate that if no mass penalties are incurred by the installation of additional components, the fuel savings can exceed 23%. However~ an increase in the vehicle's weight can shrink this benefit especially in the case of light vehicles. Lightweight batteries and kinetic energy recovery systems are deemed essential, enabling technologies for a realistic application of this hybrid system. [ABSTRACT FROM AUTHOR]

This work is a feasibility study of a 19-passenger hybrid-electric aircraft, to serve the short-haul segment within the 200-600 nautical miles. Its ambition is to answer some dominating research questions, during the evaluation and design of aircraft based on alternative propulsion architectures. The potential entry into service (EIS) is foreseen beyond 2030. A literature review is performed to identify similar concepts under research and development. After the requirements' definition, the first level of conceptual design is employed. The objective of design selections is driven by the need to reduce CO2 emissions and accommodate aircraft electrification with boundary layer ingestion engines. Based on a set of assumptions, a methodology for the sizing of the hybrid-electric aircraft is described to explore the basis of the design space, incorporating a parametric analysis for the consideration of boundary layer ingestion effects. Additionally, a methodology for the energy storage positioning is provided to highlight the multidisciplinary aspects between the sizing of an aircraft, the selected architecture (series/parallel partial hybrid), and the storage characteristics. The results show that it is not possible to fulfill the initial design requirements (600 nmi) with a fully-electric aircraft configuration, due to the far-fetched battery necessities. It is also highlighted that compliance with airworthiness standards is favored by switching to hybrid-electric aircraft configurations and relaxing the design requirements (targeted range, payload, battery technology). Finally, the lower degree of hybridization (40%) is observed to have a higher energy efficiency (-12% energy consumption) compared to the higher degree of hybridization (50%) and greater CO2 reduction, with respect to the conventional configuration. [ABSTRACT FROM AUTHOR]

• Evaluate three novel latent heat storage designs for cogeneration application. • Conduct 3-D simulation to study secondary flow effect in spiral coil heat exchanger. • Test scaled-down prototype to infer heat transfer rate in novel encapsulated designs. • Compare storage thermal performance and costs between designs for integration. Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A one-dimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46–72 °C and a HTF supplying flowrate range of 4.2–8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spiral coil design (1830 kWh). The ellipsoid capsule design shows a slightly lower accumulated storage capacity (700 kWh) than the slab design for 3-hr charge and an equivalent accumulated storage capacity/depth of discharge (250 kWh/14%) as the latter. Furthermore, the storage power cost of the slab capsule design is the lowest, by 6–12% lower than the spiral coil design and by 2–3% lower than the ellipsoid capsule design. However, with the highest design flowrate of 8.4 m3/h, the low state of charge (below 40%) after three hours and the low depth of discharge (below 14%) after one hour indicate that redesigning the heat transfer boundary conditions and the configurations of the three units are necessary to meet desirable storage performance in cogeneration applications. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a time-domain equivalent source method (ESM) for acoustic scattering prediction is suggested, based on acoustic velocity formulations. Incident and scattered acoustic predictions are realized by acoustic velocity formulation V1A of Ghorbaniasl. Formulation V1A is based on the FW-H equation and allows direct evaluation of the boundary condition, without requiring acoustic pressure gradient computation. The scattering approach is implemented and validated by the analytical case of scattering of a pulsating monopole source by a rigid sphere. The developed methodology is efficient for scattering problems where broadband noise sources are considered. [ABSTRACT FROM AUTHOR]

In this paper, a convected frequency-domain approach for acoustic scattering prediction is suggested, for sources and scattering surfaces in a uniform constant flow. Frequency-domain moving-medium formulations are used for prediction of the incident acoustic pressure and acoustic pressure gradient. The latter is required for evaluation of the hardwall boundary condition in a moving medium and allows a convected definition of the equivalent sources. The scattering approach is validated by the analytical case of scattering of a pulsating monopole source by a rigid sphere. The applicability of the methodology to moving-medium problems is demonstrated for rotating and pulsating monopole point sources in a uniform flow, located near an infinite flat scattering surface. The suggested approach allows frequency-domain scattering predictions for sources in a uniform constant flow of any subsonic velocity, enabling direct inclusion of convection effects on incident and scattered acoustics. The hardwall boundary condition is thus evaluated directly in a moving medium. The need for a Lorentz transform is obviated, overcoming the complexity it introduces and the limitations it imposes. [ABSTRACT FROM AUTHOR]

Abstract: This paper is founded on a statistical wind data analysis for two interconnected wind farms in Greece. Specifically, after the acquisition of a representative set of climatology data by two meteorological masts installed in two different mountainous regions, an annual power output prediction is carried out in order to estimate the performance and viability of the selected wind turbines in the parks. Two alternative power output simulation models are used; one empirical and one computational, the results of which are examined in a comparative manner. Furthermore, a wake losses’ estimation is performed via the application of two different wake models, while a simple noise emission impact analysis is implemented. The study ends with a brief financial assessment of the two wind energy projects. The main outcome of the energy calculations is that the empirical numerical tool underestimates the total annual energy production of the two wind farms as well as their capacity factors. The wake models’ comparative overview indicates a low percentage of wake losses for both the wind parks, which ensures the maximum power yield achievement. Finally, the results of the noise emission analysis prove that the turbines’ predicted noise signals fall within the limits of recent regulation protocols. [Copyright &y& Elsevier]