bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three Spool High Efficiency Small Scale Gas Turbine Concept
Authors: Malkamäki Matti , Jaatinen-Värri Ahti , Uusitalo Antti , Grönman Aki , Honkatukia Juha , Backman Jari , Hartikainen Toni 
Published: August 2017

Decentralized electricity and heat production is a rising trend in small-scale industry. There is a tendency towards more distributed power generation. The decentralized power generation is also pushed forward by the policymakers.
Reciprocating engines and gas turbines have an essential role in the global decentralized energy markets and improvements in their electrical efficiency have a substantial impact from the environmental and economic viewpoints. This paper introduces an intercooled and recuperated three stage, three-shaft gas turbine concept in 850 kW electric output range. The gas turbine is optimized for a realistic combination of the turbomachinery efficiencies, the turbine inlet temperature, the compressor specific speeds, the recuperation rate and the pressure ratio. The new gas turbine design is a natural development of the earlier two-spool gas turbine construction and it competes with the efficiencies achieved both with similar size reciprocating engines and large industrial gas turbines used in heat and power generation all over the world and manufactured in large production series. This paper presents a small-scale gas turbine process, which has a simulated electrical efficiency of 48% as well as thermal efficiency of 51% and can compete with reciprocating engines in terms of electrical efficiency at nominal and partial load conditions.
Damage Development in SiCf/SiC Composites Through Mechanical Loading
Authors: Bache Martin R. , Jones J. Paul , Quiney Zak , Gale Louise 
Published: August 2017

Sophisticated mechanical characterisation is vital in support of a fundamental understanding of deformation in ceramic matrix composites. On the component scale, “damage tolerant” design and lifing philosophies depend upon laboratory assessments of macro-scale specimens, incorporating typical fibre architectures and matrix under representative stress-strain states.
Standard SiCf/SiC processing techniques inherently introduce porosity between the individual reinforcing fibres and between woven fibre bundles. Subsequent mechanical loading (static or cyclic) may initiate cracking from these stress concentrations in addition to fibre/matrix decohesion and delamination. The localised coalescence of such damage ultimately leads to rapid failure.
Proven techniques for the monitoring of damage in structural metallics, i.e. optical microscopy, potential drop systems, acoustic emission (AE) and digital image correlation (DIC), have been adapted for the characterisation of CMC’s tested at room temperature. As processed SiCf/SiC panels were subjected to detailed X-ray computed tomography (XCT) inspection prior to specimen extraction and subsequent static and cyclic mechanical testing to verify their condition. DIC strain measurements, acoustic emission and resistance monitoring were performed and correlated to monitor the onset of damage during loading, followed by intermittent XCT inspections throughout the course of selected tests.
A 3D Shape Design and Optimization Method for Natural Laminar Flow Nacelle
Authors: Zhong Yongjian , Li Songyang 
Published: August 2017

With the rapid development of high bypass ratio turbofan engine, the proportion of the nacelle drag increases obviously in the total drag of the aircraft with the increase of nacelle surface area. And the frictional resistance is one of the major contributors of drag. Under the same Reynolds number, the friction resistance in turbulent boundary layer is about 10 times larger as that in laminar boundary layer. Therefore, a correctly profiled engine nacelle will delay the transition in the boundary layer and allow laminar flow to extend back, resulting in a substantial drag reduction. In the previous conference paper (9th reference), a 2D nacelle longitudinal profile-line geometry generator, which allows curvature and slope-of-curvature to be continuous was developed and presented. This established an optimization system to minimize nacelle frictional drag. One of the nacelle profile-line is optimized to achieve minimum drag coefficient, and then is stacked with the other original profile-lines to form the 3D isolated nacelle aerodynamic shape. Finally, a total 23% of nacelle outer surface maintains a laminar flow and its frictional drag coefficient is less than initial shape.
This paper proposes a new 2D nacelle longitudinal profile-line design method, based on PARSEC parameterization, with can generate the profile-line rapidly and precisely. Conservation Full Potential Equation was used to calculate the aerodynamic distribution and obtain the transition location. Then adaptive simulated annealing genetic algorithm was adapted to search 2D profiles of low drag, which would be applied to narrow down design space in 3D nacelle optimization. Second, 2D profiles were stacked circumferentially, by NURBS surface generator, to form the 3D nacelle aerodynamic shape, and an optimization system was established, in combination with the 3D nacelle generator, γ–Reθ transition model, Kriging surrogate model and adaptive simulated annealing algorithm, for natural laminar flow nacelle design. Finally, a total 34% of nacelle surface maintains a laminar flow and its frictional drag coefficient is less than initial shape. The generated optimized loft was evaluated by CFD to determine if the low drag of this optimized nacelle shape can be maintained under different Mach numbers and angles of attack.
Effects of Inlet Swirl on Endwall Film Cooling in Neighboring Vane Passages
Authors: Zhang Yang , Li Yifei , Bian Xiutao , Yuan Xin 
Published: August 2017

The distribution of film cooling effectiveness of endwall film-cooling holes is considered to be periodic between neighboring high pressure turbine passages in most cascade experiments. In reality, because of the difference in the number of combustors and vanes, the flow fields of neighboring passages are completely different. The secondary flow, especially the passage vortex, is dominated by the upstream inlet rotating flow whose relative flow direction is the reverse between the neighboring vane passages. Specifying the direction of rotation to simulate inlet swirl introduces new challenges in film-cooling design. The present experiment compares five groups of endwall film-cooling with anticlockwise rotating flows at inlet at different clocking positions, and the film-cooling effect is analyzed to investigate the effects of inlet rotating flow. The inlet flow condition of neighboring passages is simulated by switching the position of a swirler fan. Hence, different rotating inlet flow conditions in different positions are achieved.
The GE-E3 airfoil was used in the cascade rig, with a scaled-up factor of 1.95. The inlet Reynolds number is 1.48 × 105 and the Mach number is 0.07. The effects of the blowing ratio and relative positions of the swirler are investigated in the experiment. Adiabatic film-cooling effectiveness is probed by using pressure-sensitive paint (PSP). The coolant is simulated by nitrogen with which a density ratio of around 1.0 can be achieved. Fan-shaped film-cooling holes are introduced into the endwall surface as well as trailing edge discharge holes. The cooling performance of the combustor-turbine gap leakage flow is not considered. Fan-shaped film-cooling holes are introduced into the endwall surface as well as upstream slot. The cooling performance of the combustor-turbine gap leakage flow is considered in this case.
A Pair of nozzle guide vane (NGV) passages are investigated simultaneously by which the film cooling effectiveness can be compared for the same case at the endwall surface. The inlet rotating flow is simulated by an upstream swirler, with five relative positions along the pitchwise direction. According to the experimental results, the inlet rotating flow dominates the film cooling effectiveness distribution at the endwall. The averaged film cooling effectiveness changes substantially with the change in swirler position. The rotating flow at the endwall region mainly interacts with the main flow to modify incidence angle. The influence of the inlet rotating flow is more obvious at the upstream portion. Meanwhile the downstream portion is not as sensitive to rotating flow as the upstream portion.
A High-Loaded Axial Compressor Bifurcate Stator Blade Aerodynamic Design and Vorticity Dynamics Diagnosis for Flow Structure
Authors: Chen Huanlong , Yu Menghan , Li Linxi , Liu Huaping 
Published: August 2017

On the flow instability caused by large scale boundary-layer flow separation in highly loaded compressor/fan blade passage, a novel bifurcate compressor blade is designed based on pressure gradient control idea for blade passage flow, and a distinctive variable solidity bifurcate blade concept and three-dimensional blade design technology are integrated to achieve this design idea in this paper.
The quantitative flow information for the bifurcate blade passage is obtained by numerical simulation method to investigate the separation flow structure and dynamic mechanism near the wall and in the wake flow area. Besides, the complex influence of vortex structure evolution and the dynamic mechanism of low energy fluid redistribution being controlled in boundary-layer flow area would be revealed by applying the vorticity dynamics theory. The variable law of design parameters is explored in order to decrease aerodynamic loss, to delay flow separation near the wall and corner for the blade surface, to restructure blade aerodynamic loading, to form gentle pressure gradient and to diminish wake flow loss.
The results indicate that although extra aerodynamic loss is generated by the geometric mutation of bifurcate segment, the bifurcate blade effectively restrains the migration of high-entropy secondary flow fluid in the shroud corner area, thus substantially decreasing the loss near endwall/corner, which remarkably promotes the aerodynamic performance, particularly under the condition of positive incidence angle. Moreover, the bifurcate blade skillfully remolds the pressure gradient on the blade surface, and promotes total pressure as well as velocity for the wake area that would be beneficial for the downstream rotor blade. With the introduction of key physical concepts and flow parameters of vortex/vorticity dynamics, such as boundary vorticity flux, vorticity vector, skin-friction vector and tangential pressure gradient, the physical root source and mechanism of gentle pressure gradient formation, wake flow structure being weakened, and flow separation reduction for the endwall and corner are further revealed.
Design and Analysis of a Novel Split Sliding Variable Nozzle for Turbocharger Turbine
Authors: Hu Leon , Sun Harold , Yi James , Curtis Eric , Zhang Jizhong 
Published: August 2017

Variable geometry turbine (VGT) has been widely applied in internal combustion engines to improve the engine transient response and torque at low speed. One of the most popular variable geometry turbine is the variable nozzle turbine (VNT), in which the nozzle vanes can be rotated along the pivoting axis and thus the flow passage through the nozzle can be adjusted to match with different engine operating conditions. One disadvantage of the VNT is the turbine efficiency degradation due to the leakage flow in the nozzle endwall clearance, which is needed to allow the nozzle vanes to rotate without sticking. Especially at small nozzle open condition, there is large loading on the nozzle and high pressure gradient between the nozzle pressure and suction side. Strong leakage flow exists inside the nozzle endwall clearance from pressure side to suction side, leading to large flow loss and turbine stage efficiency degradation.
In the present paper, a novel split sliding variable nozzle turbine (SSVNT) has been proposed to reduce the nozzle leakage flow and to improve turbine stage efficiency. The idea is to divide the nozzle into two parts: one part is fixed and the other part can slide along the partition surface. The mechanism of nozzle flow passage variation in SSVNT is different from that of the traditional pivoting VNT. The sliding vane and the fixed vane together form an integrated vane. The flow of the turbine is determined by the passage of the integrated vanes. When moving the sliding vane to large radius position, the nozzle flow passage opens up and the turbine has high flow capacity. When moving the sliding vane towards small radius position, the nozzle flow passage closes down and the turbine has low flow capacity. As the fixed vane doesn’t need endwall clearance, there is no leakage flow inside the fixed vane and the total leakage flow through the integrated vane can be reduced. Based on calibrated numerical modeling, the analysis results showed that there is up to 12% turbine stage efficiency improvement with the SSVNT design at small nozzle open condition while maintaining the same flow capacity and efficiency at large nozzle open condition, compared to the conventional VNT. The mechanism of efficiency improvement in the SSVNT design has also been discussed.
Investigation of Strip Seal Leakage With Special Focus on Seal Groove Design and Relative Displacement of Sealing Surfaces
Authors: Huber Thomas , Bricaud Cyrille , Zierer Thomas 
Published: August 2017

Tight sealing lines are vital in large gas turbines (GT) to achieve high performance and efficiency. Leakage including rim purge air can sum up to 30% of the total cooling and leakage air consumption of a gas turbine. Leakage through static strip seals contributes about 1/3 to all leakage air. Considering the seal design as on drawings, sealing quality is generally influenced by the seal type, sealing groove curvature and the sealing groove roughness. In addition the sealing quality depends strongly on the geometric deviation of the groove compared to ideal design. This is caused by manufacturing deviations or relative movements of the grooves during operation of the parts containing the sealing.
In the article at hand, different seal designs and pertinent sealing quality is discussed. More in detail, it is discussed the geometric relation of seal, groove and misalignment to predict the seal position relative to its groove confinements. The risk of seal clamping can be judged and adaptation of seal or groove geometry can be derived. The effect of leakage increase due to misalignment is investigated by a test matrix varying seal length and curvature radius of groove as well as radial misalignment.
Aerodynamic Excitation Analysis of Radial Turbine Blades due to Unsteady Flow From Vaneless Turbine Housings
Authors: Netzhammer Stephan , Vogt Damian M. , Kraetschmer Stephan , Leweux Johannes , Koengeter Andreas 
Published: August 2017

Turbocharger turbine blades are subjected to resonant excitation that can lead to High Cycle Fatigue (HCF). In vaneless turbines the excitation primarily stems from asymmetries in the turbine housing such as the volute and the tongue. Given the nature of such asymmetries, the excitation is of a Low Engine Order (LEO) type.
The present study deals with the effect of radial turbine housing design on LEO resonant excitation of turbine blades. The study focuses on two geometrical key design parameters of a twin-scroll turbine housing for a radial turbine which is the rotor-tongue distance and the circumferential angle between both tongues. The generalized force approach is used to identify the critical blade surface regions in order to understand the excitation mechanism of each specific design and to assess the differences of design variants with respect to the baseline design. The presented approach is highly practicable, because it is less expensive than full FSI-simulations.
This approach is validated on tip timing test data from full-scale experiments. Correlation to test data shows that the presented approach is capable of capturing the relative trends reliably and hence can efficiently be employed in an industrial design process such as to minimize blade vibration amplitudes. It is shown that a reduction of blade vibration amplitudes by a factor of 10 could be achieved.
Experimental Investigation of an Inverted Brayton Cycle Micro Gas Turbine for CHP Application
Authors: Agelidou Eleni , Monz Thomas , Huber Andreas , Aigner Manfred 
Published: August 2017

Decentralized heat and power (CHP) production constitutes a promising solution to reduce the primary energy consumption and greenhouse gas emissions. Here, micro gas turbine (MGT) based CHP systems are particularly suitable due to their low pollutant emissions without exhaust gas treatment.
Typically, the electrical power demand for single houses ranges from 1 to several kWel. However, downsizing turbocharger components of a conventional MGT CHP system can reduce electrical efficiencies since losses like seal and tip leakages, generally do not scale proportionally with size. By introducing an inverted Brayton Cycle (IBC) based MGT this potential can be exploited. The IBC keeps the volumetric flows constant while mass flow and thermodynamic work are scaled by the ratio of pressure level. Since the performance of turbocharger components is mainly driven by the volumetric flow they should be applicable for both cycles. Hence, smaller power outputs can be achieved.
The overall aim of this work, is the development of a recuperated inverted MGT CHP unit for a single family house with 1 kWel. This paper presents an experimental study of the applicability and feasibility of a conventional MGT operated in IBC mode. The demonstrator was based on a single shaft, single stage conventional MGT. Reliable start up and stable operation within the entire operating range from 180 000 rpm to 240 000 rpm are demonstrated. The turbine outlet pressure varied between 0,5 bar (part load) and 0,3 bar absolute (full load). All relevant parameters such as pressure losses and efficiencies of the main components are investigated.
Moreover, the power output and the mechanical and thermal losses were analyzed in detail. Although the results indicated that the mechanical and heat losses have a high influence on the performance and economic efficiency of the system, the prototype shows great potential for further development.
Heat Transfer in a Rotating Rib-Roughened Wedge-Shaped U-Duct
Authors: Ding Liang , Tian Shuqing , Deng Hongwu 
Published: August 2017

Heat transfer in a rotating two-pass trapezium-shaped channel, with staggered 90-deg ribs on both leading and trailing surfaces is experimentally investigated. The hydraulic diameter of the first and second pass is 24.5 mm and 16.9 mm, respectively. The inlet Reynolds number and rotational speed range from 10000 to 50000 and zero to 1000 rpm, respectively, which results in the inlet rotation number varying from zero to 1.0. The heated copper plate technique is employed to measure the regional averaged heater transfer coefficients. Pressure drops are measured by newly designed rotating pressure measurements module. Both ribbed cases and smooth cases are compared to present rib enhancement effect.
For non-rotating result, the results show that the trailing surface presents much higher heat transfer than other cases due to the special wedge-shaped geometry. The ribbed wedge-shaped achieves enhanced regional heat transfer performances than the smooth case at all locations. Compared with the non-rotating results in the first pass, heat transfer on both trailing and leading surfaces is enhanced except for the position near the turn region, but weakened on outer surface in stream-wise direction. And at high rotation numbers, the highest maximum heat transfer on railing surface happens at a location of approximately X/D = 10. In the first pass, rotation always enhances heat transfer on the trailing surface as rotation number increases and the rotation-to-stationary Nusselt number ratio reaches to 2.0 at the rotation number of 0.5. The leading and outer surfaces both have a critical rotation number located at Roc = 0.05.
Gas Thermometry Using Two-Thermocouple Radiation Correction
Authors: Martin Christopher , LePera Stephen , Vandsburger Uri 
Published: August 2017

The current work is the first in a series of investigations to develop a method for high-temperature thermometry of gaseous flows using thermocouple pairs with disparate convective properties to infer the contribution of radiation. Two thermocouples of deliberately dissimilar bead geometry are placed side-by-side in a flow while the two beads are heated by surface radiation. Their dissimilar responses to radiation cause a predictable divergence between the two temperature measurements.
The current approach improves upon others found in literature owing to its in-situ measurement for convection coefficients rather than dependence on empirical estimation. Each bead is deliberately overheated, and the time constant of the thermal decay back to equilibrium indicates the intensity of convection. Here, we perform this measurement in air while varying velocity, duration of overheat, and intensity of overheat. We compare the calculated temperature correction against the known air temperature.
Heat transfer through the probe wires to the ceramic probe support was found to have a strong effect on the correction, although corrected values were always closer to the actual gas temperature than the original uncorrected value. In conditions of mild radiation loading, the effect was sufficiently symmetric between the two beads to allow effective correction. All measurements indicated that if additional information about the probe body temperature was collected in addition to the thermocouple measurements, the correction could be improved significantly.
EBFOG: Deposition, Erosion and Detachment on High Pressure Turbine Vanes
Authors: Casari Nicola , Pinelli Michele , Suman Alessio , Montomoli Francesco , di Mare Luca 
Published: August 2017

Fouling and erosion are two pressing problems that severely affect gas turbine performance and life. When aircraft fly through a volcanic ash cloud the two phenomena occur simultaneously in the cold as well as in the hot section of the engine. In the high pressure turbine, in particular, the particles soften or melt due to the high gas temperatures and stick to the wet surfaces. The throat area, and hence the capacity, of the HP turbine is modified by these phenomena, affecting the engine stability and possibly forcing engine shutdown.
This work presents a model for deposition and erosion in gas turbines and its implementation in a three dimensional Navier-Stokes solver. Both deposition and erosion are kept into account, together with deposit detachment due to changed flow conditions. The model is based on a statistical description of the behaviour of softened particles. The particles can stick to the surface or can bounce away, eroding the material. The sticking prediction relies on the authors’ EBFOG model. The impinging particles which do not stick to the surface are responsible for the removal of material.
The model is demonstrated on a high pressure turbine vane. The performance deterioration and the throat area reduction rate are carefully monitored. The safe-to-fly time through a cloud can be inferred from the outcome of this work as important piece of on-board information for the flight crew.