bluuebunny/crossref_metadata_2025 huggingface dataset:
Metastructure With Piezoelectric Element for Simultaneous Vibration Suppression and Energy Harvesting
Authors: Hu Guobiao , Tang Lihua , Banerjee Arnab , Das Raj
Published: September 2016

Inspired by the mechanism of acoustic–elastic metamaterial (AEMM) that exhibits a stop band gap for wave transmission, simultaneous vibration suppression and energy harvesting can be achieved by integrating AEMM with energy-harvesting component. This article presents an analytical study of a multifunctional system based on this concept. First, a mathematical model of a unit-cell AEMM embedded with a piezoelectric transducer is developed and analyzed. The most important finding is the double-valley phenomenon that can intensively widen the band gap under strong electromechanical coupling condition. Based on the mathematical model, a dimensionless parametric study is conducted to investigate how to tune the system to enhance its vibration suppression ability. Subsequently, a multicell system is conceptualized from the findings of the unit-cell system. In a similar way, dimensionless parametric studies are conducted to optimize the vibration suppression performance and the energy-harvesting performance severally. It turns out that different impedance matching schemes are required to achieve optimal vibration suppression and energy harvesting. To handle this problem, compromising solutions are proposed for weakly and strongly coupled systems, respectively. Finally, the characteristics of the AEMM-based piezoelectric energy harvester (PEH) from two functional aspects are summarized, providing several design guidelines in terms of system parameter tuning. It is concluded that certain tradeoff is required in the process of optimizing the performance toward dual functionalities.
A Linear Feedback Control Framework for Optimally Locating Passive Vibration Isolators With Known Stiffness and Damping Parameters
Authors: Lee Jihyun , Ghasemi Amir H. , Okwudire Chinedum E. , Scruggs Jeffrey
Published: September 2016

This paper investigates the problem of optimally locating passive vibration isolators to minimize unwanted vibration caused by exogenous disturbance forces. The stiffness and damping parameters of the isolators are assumed to be known, leaving the isolator locations, which are nonlinearly related to system states, as unknown optimization variables. An approach for reformulating the nonlinear isolator placement problem as a linear time-invariant (LTI) feedback control problem, by linking fictitious control forces to fictitious measured outputs using a nonzero feedforward term, is proposed. Accordingly, the isolator locations show up within a static output feedback gain matrix which can be optimized, using methods from optimal control theory, to minimize the H2 and/or H∞ norms of transfer functions representing unwanted vibration. The proposed framework also allows well-established LTI control theories to be applied to the analyses of the optimal isolator placement problem and its results. The merits of the proposed approach are demonstrated using single and multivariable case studies related to isolator placement in precision manufacturing machines. However, the framework is applicable to optimal placement of passive isolators, suspensions, or dampers in automotive, aerospace, civil, and other applications.
Immersed Boundary Method for Radiative Heat Transfer Problems in Nongray Media With Complex Internal and External Boundaries
Authors: Łapka Piotr , Furmański Piotr
Published: September 2016

The immersed boundary method (IBM) is gaining attention in the computational fluid dynamics but its applications in the field of a conjugated radiative–conductive or radiative–convective heat transfer seem limited. Therefore, the paper presents extension of this method to heat transfer problems dominated by thermal radiation in a nongray medium. The present model enables simulation of heat and fluid flows in a domain with complex stationary or moving internal and external boundaries on a fixed Cartesian grid (FCG) by applying the finite volume method. The special attention is paid to modeling thermal radiation and optical phenomena at highly curved, opaque, or transparent boundaries which confine the computational domain or separate zones of different thermophysical and optical properties, e.g., different values of a refractive index. The model is limited to a 2D planar or axisymmetric spaces. Detailed verification procedure proves accuracy and correctness of the developed model and shows its potential application field. The model may be used for simulations of a conjugated radiative–conductive or radiative–convective heat transfer in a nongray medium in a complex domain with opaque or transparent curved internal or external boundaries without unstructured or body fitted mesh generation.
Influence of Coolant Jet Pulsation on the Convective Film Cooling of an Adiabatic Wall
Authors: Sultan Qaiser , Lalizel Gildas , Fénot Matthieu , Dorignac Eva
Published: September 2016

This study investigates the effects of sinusoidal pulsations externally imposed to an oblique round jet. The effectiveness of film coverage of an adiabatic wall onset for a thermally uniform bulk flow is presented in the perspective of gas turbine film cooling. For the injectant fluid, both the temperature and the mass flow rate are controlled prior to entrance to the periodic forcing system using a loudspeaker drive. The characteristic film cooling parameters including the blowing ratios and the temperature ratio are maintained at M=ρiUi/ρ∞U∞ = 0.65, 1, and 1.25, and Ti/T∞=2 respectively. The injection fluid is pulsated to a nondimensionalized frequency of St=f⋅d/U = 0, 0.2, 0.3, and 0.5. In the present investigation, the impact of injectant film modulation is figured out by analyzing the velocity fields measured by a system of time-resolved particle image velocimetry (TR-PIV), as well as analyzing the adiabatic wall temperature and the convective heat transfer coefficient measured by a system of infrared thermography. The overall film-cooling effectiveness is revealed by the time-averaged analysis, in which altered time-averaged jet trajectories and wake behavior are focused. It is observed that the pulsations tend to result in lower effectiveness when the flow remained attached to the wall in steady blowing case. In steady blowing cases with jet liftoff, such as for M= 1.25, rendering low-frequency pulsation helps in increasing film-cooling effectiveness due to the discharge of lower mass flow rate coolant during the significant time interval of the respective pulse cycle.
Direct Numerical Simulation and RANS Comparison of Turbulent Convective Heat Transfer in a Staggered Ribbed Channel With High Blockage
Authors: Marocco Luca , Franco Andrea
Published: September 2016

A turbulent convective flow of an incompressible fluid inside a staggered ribbed channel with high blockage at ReH ≈ 4200 is simulated with direct numerical simulation (DNS) and Reynolds-averaged Navier–Stokes (RANS) techniques. The DNS results provide the reference solution for comparison of the RANS turbulence models. The k–ε realizable, k–ω SST, and v2¯–f model are accurately analyzed for their strengths and weaknesses in predicting the flow and temperature field for this geometry. These three models have been extensively used in literature to simulate this configuration and boundary conditions but with discordant conclusions upon their performance. The v2¯–f model performs much better than the k–ε realizable while the k–ω SST model results to be inadequate.
Exponential Passivity Results for Singular Networked Cascade Control Systems Via Sampled-Data Control
Authors: Santra Srimanta , Sakthivel R. , Mathiyalagan K. , Marshal Anthoni S.
Published: September 2016

This paper addresses the issues of admissibility analysis and exponential passivity using sampled-data control for a class of singular networked cascade control systems (NCCSs) with time-varying delays and external disturbances. Based on the new augmented Lyapunov–Krasovskii functional which considers all the available information about the actual sampling pattern, a new set of delay-dependent condition is obtained to ensure the singular networked cascade control systems to be regular, impulse-free, stable, and exponentially passive. Based on the derived condition, the sampled-data control problem is solved and an explicit expression for the desired cascade controller is given. If the given linear matrix inequalities are feasible, then corresponding gain parameters of the designed cascade control will be determined. Finally, a numerical example based on a power plant boiler–turbine system is provided to demonstrate the effectiveness of the developed technique.
Numerical Analysis on the Swirl Flows in the Exhaust Hood of Steam Turbine and Optimization Design
Authors: Yin Mingyan , Yang Chen , Meng Liu , Yan Wei , Zhuhai Zhong , Li Jun , Feng Zhenping
Published: September 2016

A well-designed exhaust hood of large steam turbines would recover some kinetic energy from the flow between the last stage blades and condenser, which improves the efficiency of the cylinder. The internal flow field of the exhaust hood was firstly numerical investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions based on the ANSYS-CFX. Then, the effects of the dimensions of the cylinder, bearing cone, diffuser guide, and diffuser ribs on the static pressure recovery performance of the exhaust hood were numerically conducted. The numerical results show that the cylinder length has significantly impact on the static pressure recovery coefficient of the exhaust hood by comparison of the cylinder section area at the fixed bearing cone and diffuser size. The bearing cone and diffuser were optimized to improve the aerodynamic performance of the exhaust hood. The rotationally symmetrical and enlarged diffusers show the different static pressure recovery performance of the exhaust hood. The optimized exhaust hood shows the improved aerodynamic performance by comparison of the initial design. The detailed flow pattern of the initial and optimized exhaust hood is also illustrated and discussed. This paper explicitly shows the interaction, and offers a good strategy for optimization, which has not been thoroughly discussed.
Experimental Investigation on the Influence of Inclination Angle on the Film Cooling Performance of Diffuser Shaped Holes
Authors: Liu Cun-liang , Zhu Hui-ren , Wu A-sai , Zhai Ying-ni
Published: September 2016

Experimental investigation has been performed to investigate the influence of inclination angle on the film cooling performance of two typical diffuser shaped hole configurations, including laidback hole and laidback fanshape hole, using transient liquid crystal measurement technique. Under very small blowing ratio, increase of inclination angle has very small influence on the film cooling effectiveness of laidback fanshape hole configuration. With the increase of blowing ratio, large inclination angle notably reduces its film cooling effectiveness, especially in the upstream region. For film cooling of laidback hole configuration, the increase of inclination angle reduces the film cooling effectiveness under small blowing ratio due to the lift-off of film jets, while produces better film coverage and higher film cooling effectiveness under larger blowing ratios in the downstream region due to the reattachment of lift-off film jets. The increase of inclination angle reduces the heat transfer coefficient for film cooling of laidback fanshape hole configuration in the upstream region. For film cooling of laidback hole configuration, heat transfer coefficient is higher in the upstream region for large inclination angle case due to the enhancement effect of strong counter-rotating vortex pair, while laidback hole with small inclination angle has relatively higher heat transfer coefficient in the downstream region. Under very large blowing ratio, the counter-rotating vortex pair produce two intensely enhanced heat transfer region of spindle shape for film cooling of holes with large inclination angle. From the aspect of heat flux ratio, increase of inclination angle is beneficial to the thermal protection of laidback hole film cooling under large blowing ratio. For both diffuser shaped hole configurations, holes with large inclination angle have larger discharge coefficient due to smaller aerodynamic loss in the hole.
Optimization of a Steam Turbine Blade’s Double-T Root Through Contact Surface Convexity
Authors: Ehlers Johanna , Ressing Henning , von Karstedt Wulf-Christof , Rixen Daniel , Gadala Mohamed S.
Published: September 2016

The turbine blade is one of the most critical components of a steam turbine. The high thermal loads and large centrifugal forces cause extreme stresses on the blade, especially on its root.

This paper focuses on improving the double-T root of a turbine blade of the control stage by decreasing the root’s peak equivalent von-Mises stress. An 18% reduction was achieved in the peak stress by changing the convexity of the contact surface between the root and the groove. The equivalent von-Mises stress was determined in a static structural analysis of a three dimensional finite element model (3D FEM-model) using ANSYS Workbench. This numerical model was developed to include one blade and the associated part of the shaft, whereas the complete circle of blades was considered by applying cyclic symmetry. Furthermore, this paper includes a modal analysis comparing the natural frequencies of the initial FEM-model with the frequencies of the optimized one. The results were established by an investigation of the influence of the FEM-model’s parameters, its material properties, thermal effects, and an additional damping wire in the shroud.
Two Years of Improvement and Experience in PEMS for Gas Turbines
Authors: Bainier Francis , Alas Pascal , Morin Florian , Pillay Tony
Published: September 2016

Due to environmental regulations, Nitrogen oxides (NOx), Carbon Monoxide (CO) and Sulfur Dioxide (SO2) emissions are key issues for gas turbine plants. Regulators are becoming more and more involved and they often require complete and real-time emission information.

The measurements can be done with gas analyzers, this technology is called CEMS: Continuous Emissions Monitoring System. An alternative method [1][2] is to use a calculation based on the turbine instrumentation. This technology is called PEMS: Predictive Emissions Monitoring System. But these technologies do not provide all the information required by the regulator.

GRTgaz, the main gas transmission company in France managing 44 turbines spread over 27 stations across France, has decided to monitor its emissions by PEMS for many years. Two years ago, GRTgaz developed successfully its own PEMS equations, organized answers to regulators around this technology and decided to spread the technology across its gas turbine fleet. The complete intellectual path followed is described in the paper GT2014-25242. This 2016 3-part paper describes the PEMS project steps forward.

In the first part of the paper, a review is done of the PEMS equations used at GRTgaz for NOx and CO concentrations. The various lean premixed combustion turbines differ in terms of combustion design, control and instrumentation. These differences are analyzed considering their influence on combustion and their impact on the PEMS results accuracy.

In order to comply with regulators requirements a calibration of the PEMS results is done every quarter. The results of the first 2 stations equipped with PEMS are described in this first part.

The second part of the paper introduces the smoke developed and the neutral air flow to complete the real time calculation required by the regulators: SO2 concentration and the mass flowrates for NOx, CO and SO2. The final calculation integrates the mass flowrate in order to elaborate the total mass emitted into the atmosphere over different time periods.

The last part deals with developing personnel involvement, managing the data and compiling the results given to regulators. These aspects were more difficult to implement than expected. The importance of these aspects should not be underestimated because the scientific credibility of PEMS cannot be confirmed without them.
Application of S-PIV for Investigation of Round and Shaped Film Cooling Holes at High Density Ratios
Authors: Watson Travis B. , Nahang-Toudeshki Sara , Wright Lesley M. , Crites Daniel C. , Morris Mark C. , Riahi Ardeshir
Published: September 2016

Hot section turbine engine components are often cooled through the use of a cool film of air on the component wall. The source of the air used for film cooling comes from the compressor of the gas turbine engine and may be 800°C, or more, cooler than the hot gas path air. The temperature differential between the hot mainstream gas and the film coolant results in a large difference in density between the two gases. In order to investigate the effect of high density ratios on film cooling performance, a traditional, round hole (θ = 30°) and a laidback, fan shaped hole (θ = 30°, α = γ = 10°) were observed using Stereo-Particle Image Velocimetry (S-PIV). Flowfield measurements were performed on various planes downstream of the film cooling hole (x/d = 0, 1, 3 and 10 for the round hole and x/d = 0, 3, and 10 for the shaped hole). At each location the coolant-to-mainstream interaction was captured at multiple density ratios (DR = 1, 2, 3, 4) and blowing ratios (M = 0.5, 1.0, 1.5). Using S-PIV, the three-dimensional flow field was measured. Distributions of the flow vorticity were derived from the high speed velocity measurements taken during S-PIV testing. For the simple angle, round holes, the results show at the elevated density ratios, the coolant spreads laterally near the hole; while at DR = 1, the coolant trace is limited to the width of the film cooling hole. Furthermore, as the cooling jet exits from the round hole, the vorticity within the jet is very strong, leading to increased mixing with the mainstream. However, as the density ratio increases (at a given blowing ratio), this mixing was reduced. For a given flow condition, the rotation was reduced with the jet exiting the shaped hole (compared to the round hole), and this led to enhanced protection on the surface. While investigating both round and shaped holes, it was shown the S-PIV method is a valuable tool to observe and quantify the jet–to–mainstream interactions near the film cooled surface.
Measurements Versus Predictions for a Hybrid (Hydrostatic Plus Hydrodynamic) Thrust Bearing for a Range of Orifice Diameters
Authors: Childs Dara W. , Esser Paul
Published: September 2016

A fixed-geometry hybrid thrust bearing is investigated with three different supply-orifice diameters, (1.63, 1.80, and 1.93 mm). The test rig uses a face-to-face thrust bearing design, with the test bearing acting as the rotor loading mechanism. A hydraulic shaker applies the static axial load, which is reacted by a second (slave) thrust bearing. The rotor is supported radially by two water-lubricated fluid film journal bearings and is attached to a 30,600 rpm motor via a high speed coupling with very low axial stiffness. Thrust bearings are tested for a range of supply pressures (5.17, 10.34, 17.34 bars), fluid film thicknesses, and speeds (7.5, 12.5, and 17.5 krpm). The water-lubricated test bearings have eight pockets, with feed orifices located centrally in each pocket. Experimental results are comparted to predictions found using the bulk-flow model HYDROTHRUST®.

Analysis of the data reveals generally good agreements between predictions and measurements. Thrust-bearing inlet supply and inner radius flow rates all decreased with decreasing orifice diameters and bearing axial clearances. In most cases, the bearings with larger orifice diameters exhibit higher recess pressure ratios, operating clearances, and flow rates. The 1.93 mm orifice diameter configuration does not display higher recess pressure ratios or operating clearances at high speeds for some supply pressures, but it does continue to require additional lubricant flow rate compared to the smaller orifice bearings. In these cases, the results are not reflected in predictions, which otherwise correlate very well with experimental measurements. Estimations of static loading axial stiffness are obtained using experimental results.

An optimum hybrid thrust bearing orifice diameter will depend on the conditions of individual applications. Larger orifices generally provide larger operating clearances and higher stiffnesses, but also require higher flow rates. For most applications, a compromise of bearing performance parameters will be desired. The test results and comparisons presented will aid in sizing orifice diameters for future hybrid thrust bearing designs and in validating and improving models and predictions.
Micro-Turbojet to Turbofan Conversion via Continuously Variable Transmission: Thermodynamic Performance Study
Authors: Kadosh K. , Cukurel B.
Published: September 2016

In this study, the viability, performance, and characteristics of a turbojet-to-turbofan conversion through the use of a continuously variable transmission (CVT) are investigated. By an in-house thermodynamic simulation code, the performance of the simple cycle turbojet, a direct shaft joined turbofan, and a CVT coupled turbofan with variable bypass are contrasted. The baseline turbojet and turbofan findings are validated against a commercial software. The comparison indicates high quantitative agreement.

Analyzing the results of the turbofan engine equipped with a variable bypass and CVT, it is observed that both the thrust and the efficiency are increased. The augmented thrust is observed to be an artifact of enhanced component matching and wider operational range introduced by variable bypass capability. On the other hand, the introduction of CVT contributes to the reduction in fuel consumption. Therefore, the current research suggests that adaptation of a micro-turbojet into a variable cycle micro turbofan will greatly improve the performance and efficiency of existing engines, in addition to providing a pathway towards extended use in various applications.
Duffing’s Vibration of a Rotor Supported on Gas Foil Bearings With Base Excitation: Measurements and Model Predictions
Authors: Kim Tae Ho , Kim Young Min , Lee Jongsung , Park Moon Sung , Ha Kyoung-Ku , Lee Changha , Kim Chimyung
Published: September 2016

The widespread application of gas foil bearings (GFBs) to high-performance microturbomachinery requires accurate predictions for their physical models based on experimental test data. This paper presents the experimental measurements and model predictions of Duffing’s vibration in a rotor supported on GFBs with base excitation, implemented for small oil-free turbomachinery. The rotor consisted of an impeller at one end and a thrust collar at the other end. Two gas foil journal bearings (GFJBs) located between the impeller and thrust collar supported the rotor, and one pair of gas foil thrust bearings (GFTBs) supported the thrust collar. A series of dynamic excitation tests on the rotor-GFBs system was conducted with increasing dynamic load and excitation frequency, with the rotor operating at 20,000 rpm. An electromagnetic shaker provided dynamic sine sweep loads at excitation frequencies of 10–200 Hz to the test rig base in the axial and horizontal directions. An accelerometer installed on the test rig measured the acceleration due to the dynamic loads and provided it to the shaker controller for use as a reference signal. The acceleration level was controlled to ensure a constant value, while the excitation frequency increased. During the excitation tests, two sets of orthogonally positioned eddy current sensors and one axially positioned eddy current sensor recorded the rotor’s horizontal, vertical, and axial vibrations. The test measurements demonstrated that the rotor’s vibrational motions synchronous to the shaker excitation were the most dominant. At a constant dynamic load, as the excitation frequency increased, the amplitude of the rotor motion gradually increased until it reached a certain frequency, after which it jumped down at the higher frequencies. This amplitude jump-down phenomenon became more pronounced as the dynamic load increased. In general, both the peak amplitude and jump-down frequency increased nonlinearly with the increasing dynamic loads, thus revealing the typical Duffing’s vibration. For benchmarking against the test measurements, a previously developed numerical integration of a nonlinear equation of motion (EOM) was modified to predict the rotor’s vibrational motions with base excitations to an acceleration of 9 G (gravity). This nonlinear equation uses a third-order polynomial equation that best fits the measured structural foil bearing deflection versus static load. Comparisons of the predicted synchronous amplitude and acceleration of the rotor for the increasing excitation frequencies and the predicted waterfall plot of the amplitude of the rotor motion with the test measurements showed excellent agreements, thus validating the predictive model of the rotor-GFB system with base excitation.
Rotating Heat Transfer Measurements on a Multi-Pass Internal Cooling Channel: II — Experimental Tests
Authors: Pagnacco Fabio , Furlani Luca , Armellini Alessandro , Casarsa Luca , Davis Anthony
Published: September 2016

The present contribution is focused on heat transfer measurements on internal cooling channels of a high pressure gas turbine blade in static and rotating conditions.

A novel rig designed for the specific purpose was used to assess the heat transfer coefficients on a full internal cooling scheme of an idealized blade. The channel has a multi-pass design. Coolant enters at the blade hub in the leading edge region and move radially outwards inside a two-sided ribbed channel. The second passage is again a two-sided ribbed channel with a trapezoidal cross section of high aspect ratio, while inside the third leg low aspect-ratio cylindrical pin fins are arranged in a staggered configuration to promote flow turbulence. Inside the third passage, the coolant is progressively discharged at the blade trailing edge and finally at the blade tip. The test model differs with respect to the real design only because there is no curvature due to the blade camber. Conversely, the correct stagger angle of the real blade with respect to the rotation axis is preserved.

Experiments were performed for static and rotating conditions with engine similar conditions of Re=21000 and Ro=0.074, both defined at the channel inlet. Transient liquid crystal technique was used for the measurement of the heat transfer coefficient (HTC) on both pressure and suction sides internal surfaces of the channel. From the spatially resolved HTC maps available, it is possible to characterize the thermal performances of the whole passage and to highlight the effect of rotation.
Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Authors: Diefenthal Mathias , Hopfinger Michael , Rakut Christian , Wirsum Manfred , Heuer Tom
Published: September 2016

In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial turbine wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the turbine wheel came more into focus. In order to account for the thermally induced stresses in the turbine wheel as a part of the standard design process, a fast method is required for predicting metal temperatures.

In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures.

With this understanding, a fast method to calculate the transient temperatures in a radial turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.
Design and Performance Evaluation of an Economical Vertical Axis Wind Turbine
Authors: Himri Abdelghani , Göttlich Emil
Published: September 2016

Nowadays, ensuring access to energy is one of the serious challenges the world confronts. For those who live in poverty, a shortage of access to energy services desperately influences and undermines health, affects education and development. The problem of energy access for the poor countries has become even more intense because of the impacts of climate change, the global financial crisis and volatile energy prices. Then a use of another sources of energy such as wind power could be a good alternative in these countries.

This paper represents a design of a vertical axis wind turbine that will produce an output power of 883 W for 9 m/s wind speed from a synchronous generator. The project involves the design and the sizing of all the components of this wind turbine. Oil barrels will be used as blades, Filippini was one of the first ones who developed a wind turbine architecture with half cylinders. Later, some modifications were introduced which leads to Thiès rotor and C-rotor.

A simple design was established to facilitate its implementation and reduce its cost. This wind turbine was designed to be used in developing countries. These facts had led to think about an uncomplicated conception and use accessible and cheap equipment which could be available all over the world.

Afterwards, a scaled prototype was realized to make some tests in order to examine its efficiency, some modifications were done to observe the feedback. The procedure of the design of the wind turbine was accomplished from the beginning to the end, no step has been skipped. Later, an estimation of cost was completed. The initial cost remains lower than the cost of a wind turbine in the market. Finally, this wind turbine could be constructed easily with accessible materials. An implementation of this machine in developing countries could help people in their lives. An economical model applied to an African country shows that using one turbine could save about 1400 € per year.
Large Eddy Simulation of Conjugate Heat Transfer Around a Multi-Perforated Plate With Deviation
Authors: Lahbib Dorian , Dauptain Antoine , Duchaine Florent , Nicoud Franck
Published: September 2016

To improve gas turbine efficiency, engine manufacturers increase both the overall compressor pressure ratio and the turbine inlet temperature, resulting into a higher thermal load of the combustion chamber walls. Cooling systems such as multi-perforated plates are in this context good candidates to lower the thermal constraints on the liners. Such technological devices consist in introducing, through submillimetric holes, a cold air flow into the boundary layer of the chamber wall. Though commonly used in industrial applications, perforations with an angle of deviation, i.e. not aligned with the main flow, have not been studied in most experimental and numerical studies. The deviation angle impacts the liner temperature by modifying the flow structure around the plate. Conjugate heat transfer computations coupling Large Eddy Simulation and heat conduction are performed on streamwise and 45 angled configurations composed of 12 rows at an operating point representative of helicopter combustors to analyze the effect of the deviation. The flow organization around the plate is modified, yielding different heat flux distribution and plate temperature. The major differences are observed within the perforations where the heat flux coefficient increases up to 54% in the configuration with deviation.
Structural Optimization of Fir-Tree Root and Groove for Turbine Blade With Splines and Genetic Algorithm
Authors: Yu Deqi , Li Fengwei , Yang Jiandao , Cheng Kai , Shu Weilin , Lv Kai , Li Ming
Published: September 2016

The wide use of fir-tree root and groove in turbine structures prompts the expectation to find optimum configurations, which ensure that stresses are in the safe limits to avoid mechanical failure. To perform the optimization, the reasonable characterization of root configuration is required. The existing researches characterized the fir-tree root with straight line, arc or even elliptic fillet, then the parameters of these features were defined as design variables to perform root profile optimization. However, this feature-based optimization technique yields configuration which is only optimal under the feature assumption, the question why choose these feature and whether there is a better feature modeling technique is difficult to answer. In this work, instead of the feature-based method, spline curves technique is involved to characterize the root and groove configuration, and the horizontal coordinates of the control points are selected as design variables, which are modified in the vicinity of their initial values during optimization process. The objective function is to minimize the peak stress in the root and groove regions. With the Multi-island genetic algorithm, the optimal fir-tree root configuration can be obtained with better stress distributions and low stress concentrations. The proposed spline-based optimization approach may shed lights on the conceptual design of blade root and can be easily extended to other industrial equipment design.
Experimental and Numerical Investigation of Quick Closing Buffer Performance of Steam Turbine Admission Valve
Authors: Xiao Lei , Xu Sihua , He Jin , Hu Zhiqiang , Zhou Xiaogang
Published: September 2016

One of the main functions of the steam turbine admission valve is to provide a very fast closing to intercept the supply of mass flow rapidly from the steam entering the turbine and cause destructive overspeed. In order to quickly close the admission valve, at the beginning of the stroke the moving parts of the valve should be accelerated to a high speed; when the stroke ends, a lot of kinetic energy is converted to impact energy. To prevent damage to valve parts, a quick closing buffer system is required to absorb the most of the impact energy. The quick closing buffer system plays an important role in the admission valve as an influencing factor of the dynamic characteristics of the valve. In the past, considering the complex internal structure, the research about quick closing buffer system relied on confirmatory experimental study or analytic method to get a quick closing buffer process. This paper focus on the quick closing process of a high pressure steam admission valve of Shanghai Turbine Plant. The dynamic characteristic of the quick closing buffer system is investigated by means of method of CFD numerical simulation for the first time, in order to find a more convenient and effective way to get the key factors that affect the dynamic characteristics, and the accuracy of the of CFD numerical simulation is verified by test, which are valuable for building an accurate dynamic characteristic analysis model of steam turbine admission valve.
Numerical and Experimental Investigation of Axial Gap Variation in High Pressure Steam Turbine Stages
Authors: Bellucci Juri , Rubechini Filippo , Arnone Andrea , Arcangeli Lorenzo , Maceli Nicola , Paradiso Berardo , Gatti Giacomo
Published: September 2016

This work aims at investigating the impact of axial gap variation on aerodynamic performance of a high-pressure steam turbine stage.

Numerical and experimental campaigns were conducted on a 1.5-stage of a reaction steam turbine. This low speed test rig was designed and operated in different operating conditions. Two different configurations were studied, in which blades axial gap was varied in a range from 40% to 95% of the blade axial chord. Numerical analyses were carried out by means of three-dimensional, viscous, unsteady simulations, adopting measured inlet/outlet boundary conditions. Two set of measurements were performed. Steady measurements, from one hand, for global performance estimation of the whole turbine, such as efficiency, mass flow, stage work. Steady and unsteady measurements, on the other hand, were performed downstream of rotor row, in order to characterize the flow structures in this region.

The fidelity of computational setup was proven by comparing numerical results to measurements. Main performance curves and span-wise distributions shown a good agreement in terms of both shape of curves/distributions and absolute values. Moreover, the comparison of two dimensional maps downstream of rotor row shown similar structures of the flow field.

Finally, a comprehensive study of the axial gap effect on stage aerodynamic performance was carried out for four blade spacings (10%, 25%, 40% and 95% of S1 axial chord), and five aspect ratios (1.0, 1.6, 3, 4 and 5). The results pointed out how unsteady interaction between blade rows affects stage operation, in terms of pressure and flow angle distributions, as well as of secondary flows development. The combined effect of these aspects in determining the stage efficiency is investigated and discussed in detail.
The Influence of Hydrodynamic Bearing Configuration on Morton Effect
Authors: Tong Xiaomeng , Palazzolo Alan
Published: September 2016

The Morton effect (ME) results from the synchronous, thermal excitation of a rotating shaft because of the uneven viscous shearing in hydrodynamic bearings and the asymmetric temperature distribution in shafts. The temperature difference bends the rotor, reducing the film thickness and increasing the thermal unbalance, which may cause excessive vibration level and unsteady phase angle. To predict the potential thermal instability from the ME, the finite element method is used to solve the transient rotordynamics and temperature distribution in the lubricant, bearing and shaft. The conventional thermal unbalance method is replaced by a more accurate thermal shaft bow model for rotordynamic analysis and the three-dimensional energy equation is utilized for the lubricant temperature prediction. Considering that the temperature change in the shaft and bearing occurs quite slowly relative to the shaft vibration deflection change, a staggered scheme is employed to assign a longer period to update the system temperature distribution and a shorter period to update the vibration orbits. Verified by a real overhung compressor model, the ME instability onset speed predicted by simulation coincides with the tested speed, at which large vibration level is observed. The hysteresis phenomenon, which is quite typical for thermal-induced vibration problems, can be caused by the ME and is demonstrated by the simulation. A stability recovery speed is confirmed, above which the vibration level and the rotor temperature difference will decrease to an acceptable level and the system will become stable. To investigate the influence of bearing configuration on ME, different bearing types including fixed pad bearings (FPBs) and tilting pad bearings (TPBs) with various pad numbers are analyzed. Meanwhile, the bearing clearance and preload intentionally remain unchanged in the comparison. Results show that despite similar critical speeds, the TPBs are better at suppressing the ME with lower average temperature and larger film thickness in the lubricant, especially at high speeds. This is due to the self-tilting ability for the TPBs to maintain a satisfactory bearing clearance. The four-pad TPBs outperform the five-pad TPBs with both lower average temperature and smaller temperature difference in the shaft considering that the effective load-carrying area is larger in the 4-pad bearings. Moreover, the asymmetric pivot offset of 0.6 is simulated to demonstrate its superiority in mitigating the ME compared with the common 0.5 offset. Considering that the ME instability occurs in the vicinity of the critical speeds in most cases, the bearing diameter-length ratio should be carefully designed to achieve a larger separation margin.
Design and Numerical Analysis of a New Type of Pre-Swirl Nozzle
Authors: Liu Yuxin , Liu Gaowen , Kong Xiaozhi , Feng Qing
Published: September 2016

Pre-swirl nozzle is regarded as an important part of preswirl system. Theoretical analysis shows that the temperature drop of pre-swirl system directly relates to the pre-swirl effectiveness of nozzle. When the inlet and outlet pressure are given, there are three ways to improve the nozzle pre-swirl effectiveness. Firstly, increase the discharge coefficient by optimizing the geometry of nozzle; secondly, decrease the preswirl angle; thirdly, minimize the deviation angle of outlet flow to decrease the actual throat area and then increase the tangential velocity.

A new kind of pre-swirl nozzle called vane shaped hole (VSH) nozzle was presented and designed in this paper. The vane height/ pitch ratio of VSH nozzle could be adjusted to an appropriate value, which made its performance of acceleration and deflection better than that of cascade vane nozzle. With the same throat area, radial location and pre-swirl angle (15°), the performance of VSH nozzle was numerically analyzed and compared with three other traditional ones at pressure ratio range 1.1∼1.9, and Reynolds number range 1×105∼5×105. The three traditional nozzles were the simple drilled nozzle, aerodynamic nozzle and cascade vane nozzle. To consider the mixing and rotating influence in the pre-swirl cavity downstream of nozzle, the rotating pre-swirl cavity and receiver hole were included in the computational models. Entropy generation analysis was also made for each nozzle to assess the source of irreversibility.

Numerical results show that the discharge coefficient of aerodynamic nozzle increase 13.7% compared with that of simple drilled nozzle owing to the smaller pressure gradient at nozzle inlet. For cascade vane nozzle, pressure gradient generated in the course of acceleration and deflection would decrease due to the well-designed vane profile. The discharge coefficient of cascade vane nozzle can be as high as 0.97, whereas the preswirl effectiveness is only 0.86 because of a large deviation angle ( 2.42°). For VSH nozzle, higher vane height/pitch ratio and close to zero trailing edge radius lead to a further decrease of endwall secondary flow loss and trailing edge loss, which results in a very small deviation angle ( 0.56°). Consequently, the pre-swirl effectiveness of VSH nozzle is about 8% higher than that of cascade vane nozzle, though the discharge coefficient is about 5% lower. Since the volume of solid block in VSH is bigger than the volume of vane in cascade vane nozzle, which could reduce the difficulty in manufacturing but increase the total weight. Thus, the final nozzle design should comprehensively consider the aerodynamic performance, cost, manufacturing, and stress constraints.
CFD Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions
Authors: Rutledge James L. , Polanka Marc D. , Greiner Nathan J.
Published: September 2016

The hostile turbine environment requires that film cooling designs are tested in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods is best suited to provide scaled film cooling performance. Furthermore, precise matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched.

A computational simulation of an engine scale film cooled leading edge geometry at high temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low temperature experimental conditions with a 10x scale model. Matching was performed with three common coolant types used in low temperature film cooling experiments — room temperature air, CO2, and cold air to match density ratio. Results indicate that matched momentum flux ratio is the most appropriate for matching adiabatic effectiveness for the case of room temperature air coolant, but also matching density ratio through either CO2 or cold coolant has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches density ratio.
Large Eddy Simulation of Inclined Jet in Cross Flow With Cylindrical and Fan-Shaped Holes
Authors: Zhong Lingxu , Zhou Chao , Chen Shiyi
Published: September 2016

A large eddy simulation (LES) investigation of the inclined jet in crossflow is presented in this paper. The angle between the hole and the main flow is 35 degrees, which represents a typical film cooling application. Two different geometries, namely the cylindrical hole and the fan-shaped hole, are investigated at a blowing ratio of 0.5, which is a representative value for film cooling. The numerical tool is first validated and then used to study the flow and the film cooling effectiveness of the cooling holes. Both the time averaged and the instantaneous flow characteristics are analyzed. In the time averaged results, the counter-rotating vortex pair has large effects on the mixing of the coolant with the main flow. The instantaneous results show that the mixing of the injected flow with the main flow is highly related to the unsteady coherent vortices. The difference in the cooling effectiveness distribution for the two holes is due to the different coherent vortices. The relationship between the coherent vortices and the temperature distribution is explained in detail. These results show that the vortices distribution at the exit of the hole has important influence on the later development of the hairpin vortices, thus affecting the temperature distribution and the cooling effectiveness.