Experimental Indirect Determination of Wind Turbine Performance and Blade Element Theory Parameters in Controlled Conditions

2012 ◽  
Vol 36 (6) ◽  
pp. 717-737 ◽  
Author(s):  
David A. Johnson ◽  
Ahmed Abdelrahman ◽  
Drew Gertz
Keyword(s):  
Large Scale ◽  
Radial Direction ◽  
Turbine Blades ◽  
Model Development ◽  
Experimental Studies ◽  
Indirect Determination ◽  
Controlled Conditions ◽  
Power Measurements ◽  
The Impact ◽  
Blade Element

The performance of a three bladed 3.3 m diameter turbine was measured unobtrusively in a large scale, controlled wind, open jet facility. Due to the scale of the facility blockage was very low in comparison to previous studies. The turbine blades utilized NREL S83X airfoils appropriate for the flow conditions and Reynolds number present in the facility. Airfoils were blended along the radial direction in a varying chord, varying twist blade design with a design coefficient of power ( Cp) peak at λ = 5.4. Simultaneous three component velocity measurements were obtained using a purpose built traverse at specific radial locations (segments) upstream and immediately downstream of the rotor plane. These velocities were utilized to determine blade element momentum (BEM) parameters and to predict the performance of the rotor. Comparisons are made to the limited number of experimental studies reported in the literature and with parameters derived from CFD numerical simulations. Measured radial velocities upstream of the rotor were near zero and uniform in the radial direction and were uniform and slightly larger downstream of the rotor indicating the BEM assumption of limited radial interaction between segments was acceptable and that the wake was expanding. Axial induction was most uniform in the radial direction at the design and peak Cp condition and area averaged values approached 1/3 but did not exceed this value. Tangential measured velocities, tangential induction and circulation show the impact of the nacelle and blade root location and the tip. An evaluation of the local angle of attack and two dimensional airfoil data at one radial location gave a reasonable comparison with other measured torque values. Rotor performance determined with this method was compared with electrical power measurements and previous BEM model predictions. The power derived from the BEM method outlined here closely followed electrical turbine power measurements although the method overpredicted the power likely due to the segment discretization in the tip region. The detail of these results should be useful to further understand the flow immediately downstream of a rotor in controlled conditions and provide detailed data for BEM model enhancement and future model development.

scholarly journals Clinical Investigations of the Effect of Citrus unshiu Peel Pellet on Obesity and Lipid Profile

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Seongil Kang ◽  
Sangyeol Song ◽  
Joosang Lee ◽  
Hyekyung Chang ◽  
Sanghun Lee
Keyword(s):  
Lipid Profile ◽  
Total Cholesterol ◽  
Cholesterol Level ◽  
Weight Control ◽  
Large Scale ◽  
Total Cholesterol Level ◽  
Experimental Studies ◽  
Density Lipoprotein ◽  
Citrus Unshiu ◽  
The Impact

Objectives. Several experimental studies have reported antiobesity and lipid-improving effects of Citrus unshiu. However, clinical studies on its effects are lacking. This study was designed to evaluate the impact of Citrus unshiu peel pellet (CUPP) on obesity and lipid profile. Methods. For 118 patients with body mass index (BMI) > 23 who took Citrus unshiu peel pellet (CUPP) for 4 weeks in a Public Health Center, laboratory and biometric readings before and after CUPP administration were analyzed. Results. Mean age of these subjects was 53.8±10.6 years (range: 18-75 years). There were 88 (74.6%) females in the study sample (n = 118). A significant (p < 0.01) decrease in BMI from 27.47±2.24 to 27.27±2.22 was observed in all subjects after CUPP treatment and 65.3% (N = 77) of them lost 1.03±0.83 kg of weight after 4 weeks of treatment. Total cholesterol level was significantly (p < 0.01) decreased from 204.0±37.4 mg/dL to 193.5±36.5 mg/dL. Significant (p < 0.05) decreases in levels of low-density lipoprotein, cholesterol, and triglyceride were also observed. Conclusions. These results suggest that CUPP in practice could help weight control and improve total cholesterol level. Findings of this study provide clinical foundation for future large-scale trials to establish clinical benefits of CUPP.

Assessing young learners’ foreign language abilities

2020 ◽  
Vol 54 (1) ◽  
pp. 1-37 ◽  
Author(s):  
Marianne Nikolov ◽  
Veronika Timpe-Laughlin
Keyword(s):  
Foreign Language ◽  
Language Learning ◽  
Language Proficiency ◽  
Large Scale ◽  
Experimental Studies ◽  
Language Abilities ◽  
Language Programs ◽  
Young Learners ◽  
Foreign Language Programs ◽  
The Impact

AbstractGiven the exponential growth in the popularity of early foreign language programs, coupled with an emphasis of evidence-based instruction, assessing young learners’ (YLs) foreign language abilities has moved to center stage. This article canvasses how the field of assessing young learners of foreign languages has evolved over the past two decades. The review offers insights into how and why the field has developed, how constructs have been defined and operationalized, what language proficiency frameworks have been used, why children were assessed, what aspects of their foreign language proficiency have been assessed, who was involved in the assessment, and how the results have been used. By surveying trends in foreign language (FL) and content-based language learning programs involving children between the ages of 3 and 14, the article highlights research into assessment of and for learning, and critically discusses areas such as large-scale assessments and proficiency examinations, comparative and experimental studies, the impact of assessment, teachers’ beliefs and assessment practices, young learners’ test-taking strategies, age-appropriate tasks, alternative and technology-mediated assessment, as well as game-based assessments. The final section of the article highlights where more research is needed, thus outlining potential future directions for the field.

scholarly journals The Effect of Youth Entrepreneurship Education Programs: Two Large-Scale Experimental Studies

SAGE Open ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 215824402095697
Author(s):  
Gayoung Kim ◽  
Dohyeon Kim ◽  
Woo Jin Lee ◽  
Sunyoung Joung
Keyword(s):  
Large Scale ◽  
Experimental Studies ◽  
Entrepreneurship Education ◽  
Entrepreneurial Intention ◽  
Social Problem Solving ◽  
Entrepreneurial Intentions ◽  
Comparison Groups ◽  
Quasi Experimental ◽  
Matched Comparison ◽  
The Impact

Recent years have witnessed the worldwide growth of entrepreneurship education (EE) as entrepreneurship is regarded as the key driver of innovation and economic growth. Most extant studies on EE have focused on its impact on entrepreneurial intentions. However, the application of the same EE measurements for both adults and adolescents has long been criticized; the indices developed for potential adult entrepreneurs may not be suitable for young entrepreneurs, considering the large time gap before they enter the workforce. This study aims to develop appropriate indicators for the assessment of youth EE in Korea and to examine the effectiveness of youth EE. Two large-scale quasi-experimental studies were conducted with pre- and posttest matched-comparison groups for verification. This study suggests six common variables for measuring the impact of youth EE: opportunity discovery, opportunity exploitation, entrepreneurship, creativity capacity, social problem solving, and entrepreneurial intention. The analyses showed that all these indicators positively influenced youth EE. We also proposed practical suggestions for the development of EE programs.

scholarly journals A numerical model for the time-dependent wake of a pedalling cyclist

2019 ◽  
Vol 233 (4) ◽  
pp. 514-525
Author(s):  
Martin D Griffith ◽  
Timothy N Crouch ◽  
David Burton ◽  
John Sheridan ◽  
Nicholas AT Brown ◽  
...  
Keyword(s):  
Drag Force ◽  
Large Scale ◽  
Aerodynamic Drag ◽  
Experimental Studies ◽  
Wake Flow ◽  
Time Dependent ◽  
Navier Stokes ◽  
Streamwise Vorticity ◽  
Leg Cycling ◽  
The Impact

A method for computing the wake of a pedalling cyclist is detailed and assessed through comparison with experimental studies. The large-scale time-dependent turbulent flow is simulated using the Scale Adaptive Simulation approach based on the Shear Stress Transport Reynolds-averaged Navier–Stokes model. Importantly, the motion of the legs is modelled by joining the model at the hips and knees and imposing solid body rotation and translation to the lower and upper legs. Rapid distortion of the cyclist geometry during pedalling requires frequent interpolation of the flow solution onto new meshes. The impact of numerical errors, that are inherent to this remeshing technique, on the computed aerodynamic drag force is assessed. The dynamic leg simulation was successful in reproducing the oscillation in the drag force experienced by a rider over the pedalling cycle that results from variations in the large-scale wake flow structure. Aerodynamic drag and streamwise vorticity fields obtained for both static and dynamic leg simulations are compared with similar experimental results across the crank cycle. The new technique presented here for simulating pedalling leg cycling flows offers one pathway for improving the assessment of cycling aerodynamic performance compared to using isolated static leg simulations alone, a practice common in optimising the aerodynamics of cyclists through computational fluid dynamics.

Comparison of Mann Turbulence and atmospheric turbulence as inflow conditions on a wind turbine in large-eddy simulations (LES)

2021 ◽  
Author(s):  
Linus Wrba ◽  
Antonia Englberger
Keyword(s):  
Wind Turbine ◽  
Atmospheric Surface Layer ◽  
Turbine Blades ◽  
Potential Temperature ◽  
Large Eddy Simulations ◽  
Wind Turbine Blades ◽  
Large Eddy ◽  
The Impact ◽  
Inflow Conditions ◽  
Blade Element

&lt;p&gt;This study deals with different inflow conditions on wind-turbines in LES in order to analyse the impact on the wake. The wind turbine regarded in this study has a hub height of 57.19 m while the radius of the blade measures 40m. Furthermore, the blade element momentum method (BEM) is used to calculate the development forces of the wind turbine blades on the flow. First, the syntheticly generated turbulence of a Mann[1] box generator is considered. Second, atmospheric boundary layer simulations from Englberger and D&amp;#246;rnbrack (2018) are applied as inflow conditions for the three wind components and the potential temperature to calculate the wake of the wind turbine. The distribution of turbulent kinetic energy in eddys of different sizes is worked out in their energy spectrum.The inflow conditions represent the -5/3 Kolmogorov spectrum. The wake characteristics are evaluated for both inflow datasets and the arising differences are discussed in this study&lt;/p&gt;&lt;div&gt;&lt;br&gt;&lt;div&gt; &lt;p&gt;[1] Mann, J. (1994). The spatial structure of neutral atmospheric surface-layer turbulence. Journal of fluid mechanics 273&lt;/p&gt; &lt;/div&gt; &lt;/div&gt;&lt;div&gt;&lt;br&gt;&lt;div&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;/div&gt; &lt;/div&gt;

scholarly journals Performance Evaluation of an Object Management Policy Approach for P2P Networks

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Dario Vieira ◽  
Cesar A. V. Melo ◽  
Yacine Ghamri-Doudane
Keyword(s):  
Large Scale ◽  
Scalable Video Coding ◽  
Experimental Studies ◽  
Management Policy ◽  
P2p Systems ◽  
Object Management ◽  
Web Cache ◽  
High Scalability ◽  
Management Policies ◽  
The Impact

The increasing popularity of network-based multimedia applications poses many challenges for content providers to supply efficient and scalable services. Peer-to-peer (P2P) systems have been shown to be a promising approach to provide large-scale video services over the Internet since, by nature, these systems show high scalability and robustness. In this paper, we propose and analyze an object management policy approach for video web cache in a P2P context, taking advantage of object's metadata, for example, video popularity, and object's encoding techniques, for example, scalable video coding (SVC). We carry out trace-driven simulations so as to evaluate the performance of our approach and compare it against traditional object management policy approaches. In addition, we study as well the impact of churn on our approach and on other object management policies that implement different caching strategies. A YouTube video collection which records over 1.6 million video's log was used in our experimental studies. The experiment results have showed that our proposed approach can improve the performance of the cache substantially. Moreover, we have found that neither the simply enlargement of peers' storage capacity nor a zero replicating strategy is effective actions to improve performance of an object management policy.

The Reduction of Over Tip Leakage Loss in Unshrouded Axial Turbines Using Winglets and Squealers

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Zbigniew Schabowski ◽  
Howard Hodson
Keyword(s):  
Flow Pattern ◽  
Large Scale ◽  
Turbine Blades ◽  
Suction Side ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Gap Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Axial Turbines ◽  
The Impact

The possibilities of reducing the over tip leakage loss of unshrouded rotors have been investigated using a linear cascade of turbine blades and computational fluid dynamics (CFD). The large-scale blade profile is the same as that of the tip profile of a low-speed high-pressure research turbine facility. The impact of various combinations of squealer and winglet geometries on the turbine performance has been investigated. The influence of the thickness of the squealers has also been assessed. It was found that a 22% reduction in loss slope was possible, when compared to the flat tip blade, using simple tip modifications. The results obtained with the suction side squealer and cavity tip agreed well with the work of other researchers. Three winglet-based tip geometries were tested. One was a plain winglet, the other two had squealers applied. A significant impact of the squealers and their shape on the tip gap flow pattern and loss generation was found. The physical processes occurring within the tip gap region for the tested geometries are explained using both numerical and experimental results. The impact of the flow pattern within the tip gap on the loss generation is described. Good agreement between CFD and the experimental data was found. This shows that CFD can be used with confidence in the design process of shroudless turbines.

Improving turbine endwall cooling uniformity by controlling near-wall secondary flows

2016 ◽  
Vol 231 (14) ◽  
pp. 2689-2705 ◽  
Author(s):  
Mitra Thomas ◽  
Thomas Povey
Keyword(s):  
Mass Flux ◽  
Large Scale ◽  
Guide Vane ◽  
Pressure Ratio ◽  
Experimental Studies ◽  
Pressure Profile ◽  
Design Guidelines ◽  
Secondary Flows ◽  
The Impact ◽  
Endwall Cooling

In this paper, we propose a design philosophy for cooling high-pressure nozzle guide vane endwalls, which exploits the momentum of cooling jets to control vane secondary flows thereby improving endwall cooling uniformity. The impact of coolant-to-mainstream pressure ratio, hole inclination angle, hole diameter, vane potential field, and overall mass flux ratios are considered. Arguments are developed by examining detailed experimental studies conducted in a large-scale low-speed cascade tunnel with engine-realistic combustor geometry and turbulence profiles. Computational fluid dynamics predictions validated by the same are used to extend the parameter space. We show that the global flow field is highly sensitive to the inlet total pressure profile, which in turn can be modified by introducing relatively low mass flow rates of cooling gas at engine realistic coolant-to-mainstream pressure ratios and mass flux ratios. This interaction effect must be understood for successful design of optimised endwall cooling schemes, an effect which is not sufficiently emphasized in much of the literature on this topic. Design guidelines are given that we hope will be of use in industry.

The Reduction of Over Tip Leakage Loss in Unshrouded Axial Turbines Using Winglets and Squealers

2007 ◽  
Author(s):  
Zbigniew Schabowski ◽  
Howard Hodson
Keyword(s):  
Flow Pattern ◽  
Large Scale ◽  
Turbine Blades ◽  
Suction Side ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Gap Flow ◽  
Axial Turbines ◽  
The Impact ◽  
Good Agreement

The possibilities of reducing the over tip leakage loss of unshrouded rotors have been investigated using a linear cascade of turbine blades and CFD. The large-scale blade profile is the same as that of the tip profile of a low-speed HP research turbine facility. The impact of various combinations of squealer and winglet geometries on the turbine performance has been investigated. The influence of the thickness of the squealers has also been assessed. It was found that a 22% reduction in loss slope was possible, when compared to the flat tip blade, using simple tip modifications. The results obtained with the suction side squealer and cavity tip agreed well with the work of other researchers. Three winglet-based tip geometries were tested. One was a plain winglet, the other two had squealers applied. A significant impact of the squealers and their shape on the tip gap flow pattern and loss generation was found. The physical processes occurring within the tip gap region for the tested geometries are explained using both numerical and experimental results. The impact of the flow pattern within the tip gap on the loss generation is described. Good agreement between the CFD and the experimental data was found. This shows that the CFD can be used with confidence in the design process of shroudless turbines.

The deformation of solids by liquid impact at supersonic speeds

1961 ◽  
Vol 263 (1315) ◽  
pp. 433-450 ◽  
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Impact Load ◽  
Turbine Blades ◽  
Stress Waves ◽  
Liquid Jet ◽  
High Speeds ◽  
Liquid Impact ◽  
The Impact ◽  
Very High

A study has been made of the deformation of solids at high rates of strain which are produced by the impact of a small cylinder or jet of liquid on the surface of the solid. A method is developed for projecting this jet against the solid at velocities up to 1200 m/s. The subsequent deformation of the solid under impact and the behaviour of the liquid is observed by high-speed photographic methods. The magnitude and duration of the impact load are also measured by using a piezo-electric transducer. The mode of deformation of the solid has been investigated for plastic, elastic and brittle materials. There is evidence that the liquid jet, on impact, behaves initially in a compressible manner. Part of the deformation is due to these compressible effects and part to the shearing action of the liquid flowing at very high speeds across the surface. If the head of the jet has an appropriate shape (e.g. wedge shaped) the velocity of flow across the surface may be much greater than the velocity of approach. It is found that there are five general types of deformation produced in the solid. There are (i) circumferential surface fractures, (ii) subsurface flow and fractures, (iii) large-scale plastic deformation, (iv) shear deformation around the periphery of the impact zone, and (v) fracture due to the reflexion and interference of stress waves. The predominating mode of deformation depends primarily on the mechanical properties of the solid and on the velocity of impact. The observations have a bearing on the practical problem of the erosion of aircraft flying at high speed through rain and on the erosion of turbine blades.

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