The dynamic inflow effect describes the unsteady aerodynamic response to fast changes in rotor loading due to the inertia of the wake. Fast changes in turbine loading due to pitch actuation or rotor speed transients lead to load overshoots. The phenomenon is suspected to be also relevant for gust situations; however, this was never shown, and thus the actual load response is also unknown. The paper’s objectives are to prove and explain the dynamic inflow effect due to gusts, and compare and subsequently improve a typical dynamic inflow engineering model to the measurements. An active grid is used to impress a 1.8m diameter model turbine with rotor uniform gusts of the wind tunnel flow. The influence attributed to the dynamic inflow effect is isolated from the comparison of two experimental cases. Firstly, dynamic measurements of loads and radially resolved axial velocities in the rotor plane during a gust situation are performed. Secondly, corresponding quantities are linearly interpolated for the gust wind speed from lookup tables with steady operational points. Furthermore,simulations with a typical blade element momentum code and a higher-fidelity free-vortex wake model are performed. Both the experiment and higher-fidelity model show a dynamic inflow effect due to gusts in the loads and axial velocities. An amplification of induced velocities causes reduced load amplitudes. Consequently, fatigue loading would be lower. This amplification originates from wake inertia. It is influenced by the coherent gust pushed through the rotor like a turbulent box. The wake is superimposed on that coherent gust box, and thus the inertia of the wake and consequently also the flow in the rotor plane is affected. Contemporary dynamic inflow models inherently assume a constant wind velocity. They filter the induced velocity and thus cannot predict the observed amplification of the induced velocity. The commonly used Øye engineering model predicts increased gust load amplitudes and thus higher fatigue loads. With an extra filter term on the quasi-steady wind velocity, the qualitative behaviour observed experimentally and numerically can be caught. In conclusion, these new experimental findings on dynamic inflow due to gusts and improvements to the Øye model enable improvements in wind turbine design by less conservative fatigue loads.
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The dynamic inflow effect denotes the unsteady aerodynamic response to fast changes in rotor loading due to a gradual adaption of the wake. This does lead to load overshoots. The objective of the paper was to increase the understanding of that effect based on pitch step experiments on a 1.8 m diameter model wind turbine, which are performed in the large open jet wind tunnel of ForWind – University of Oldenburg. The flow in the rotor plane is measured with a 2D laser Doppler anemometer, and the dynamic wake induction factor transients in axial and tangential direction are extracted. Further, integral load measurements with strain gauges and hot-wire measurements in the near and close far wake are performed. The results show a clear gradual decay of the axial induction factors after a pitch step, giving the first direct experimental evidence of dynamic inflow due to pitch steps. Two engineering models are fitted to the induction factor transients to further investigate the relevant time constants of the dynamic inflow process. The radial dependency of the axial induction time constants as well as the dependency on the pitch direction is discussed. It is confirmed that the nature of the dynamic inflow decay is better described by two rather than only one time constant. The dynamic changes in wake radius are connected to the radial dependency of the axial induction transients. In conclusion, the comparative discussion of inductions, wake deployment and loads facilitate an improved physical understanding of the dynamic inflow process for wind turbines. Furthermore, these measurements provide a new detailed validation case for dynamic inflow models and other types of simulations.
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Dynamic inflow effects occur due to the rapid change of the rotor loading underconditions such as fast pitch steps. The paper presents a setup suitable for the investigation ofthose effects for non-axisymmetric rotor conditions, namely individual pitch steps. Furthermore, insights into the relevant phenomena are gathered. An individual pitch control capable model wind turbine is set up in a wind tunnel in order to conduct measurement under controllable conditions. During the execution of the collective and individual pitch steps, the loads and the operational parameters are recorded by the onboard sensors. Meanwhile, simulations engineering aeroelastic codes are run in order to evaluate their accuracy for predicting the relevant phenomena. Results show distinct behaviour of the rotor loads during an individual pitch step, which differs from the loads under collective steps. The free vortex wake simulations are able to predict the turbines’ response satisfactory while the blade element momentum tools show deviations from the measurements. The findings serve as a basis for discussion and future work.
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Dynamic stall phenomena bring risk for negative damping and instability in wind turbine blades. It is crucial to model these phenomena accurately to reduce inaccuracies in predicting design driving (fatigue) loads. Inaccuracies in currentdynamic stall models may be due to the facts that they are not properly designed for high angles of attack, and that they do not 10 specifically describe vortex shedding behaviour. The Snel second order dynamic stall model attempts to explicitly model unsteady vortex shedding. This model could therefore be a valuable addition to DNV GL’s turbine design software Bladed. In this thesis the model has been validated with oscillating airfoil experiments and improvements have been proposed for reducing inaccuracies. The proposed changes led to an overall reduction in error between the model and experimental data. Furthermore the vibration frequency prediction improved significantly. The improved model has been implemented in Bladed and tested 15 against small scale turbine experiments at parked conditions. At high angles of attack the model looks promising for reducing mismatches between predicated and measured (fatigue) loading. Leading to possible lower safety factors for design and more cost efficient designs for future wind turbines.
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Wind turbines are usually clustered in wind farms which causes the downstream turbines to operate in the turbulent wakes of upstream turbines. As turbulence is directly related to increased fatigue loads, knowledge of the turbulence in the wake and its evolution are important. Therefore, the main objective of this study is a comprehensive exploration of the turbulence evolution in the wind turbine’s wake to identify characteristic turbulence regions. For this, we present an experimental study of three model wind turbine wake scenarios that were scanned with hot-wire anemometry with a very high downstream resolution. The model wind turbine was exposed to three inflows: laminar inflow as a reference case, a central wind turbine wake, and half of the wake of an upstream turbine. A detailed turbulence analysis reveals four downstream turbulence regions by means of the mean velocity, variance, turbulence intensity, energy spectra, integral and Taylor length scales, and the Castaing parameter that indicates the intermittency, or gustiness, of turbulence. In addition, a wake core with features of homogeneous isotropic turbulence and a ring of high intermittency surrounding the wake can be identified. The results are important for turbulence modeling in wakes and optimization of wind farm wake control
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The environment of the(Dutch) building industry is increasingly turbulent. There are many cges for the building industry. Innovative tendering, better marketing, openness and transparency are examples of this. A strong reduction in failure costs (estimated at between 10 and 25% of the total costs) and an increase in quality are also necessary. Lastly, the declining inflow of young people has to be mentioned. The image of the building industry is not particularly good and students prefer to choose other industries. The building industry therefore has to change and, so far, everyone agrees. Evidently both the building industry and its environment are very keen to change; the sincere will is there, and money and energy are available, but it seems that efforts are not proceeding in a very planned or coordinated manner at present. And this is causing fragmentation and, therefore, sub optimisation. How does sectoral change proceed and how is this process to be managed? That is the central question in this paper.
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Electrohydrodynamic atomization (EHDA) is a technique which uses the influence of strong electric fields to manipulate the break-up of a liquid, pumped through a capillary nozzle, into droplets. In this work, an extended description of a specific high flow EHDA mode, known as the simple-jet mode, is presented. In it, a review of different works published about the mode is presented as well as results about the droplet population generated with varicose and whipping break-up using water as the atomized liquid. Additionally, experiments were conducted to investigate whether such atomization method could be used to improve the efficiency of droplet inair evaporation, using a single effect evaporation chamber coupled with a EHDA multinozzle system functioning as a shower head. The liquid used in these experiments was a solution of water and NaCl (35 g L−1) to simulate sea water average concentrations. The results have shown that, the manipulation of the droplet diameter, droplet size distribution and spray angle, provided by EHDA, could improve the droplet evaporation efficiency by up to 40% when combinedwith, e.g. forced convection and higher inlet temperatures.
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This report maps different programs that supportrefugees on the road to entrepreneurship. The municipality of The Hague, along with the refugee and migrant support organization EnterStart (MigrantINC) asked for an evaluation of the program The Hague Test Garden (from now on called The Test Garden) where refugees can ask for help starting their own businesses. The evaluation is not just based on the experiences in The Test Garden; other programs have been included in the evaluation to come to a broader view of the road to entrepreneurship and the obstacles encountered. The increased inflow of refugees in Dutch society and on the Dutch labor market has generated different support programs for starting-up a business. Some of these programs already existed but shifted to accommodate the needs of this specific target group. Other programs were initiated to support refugees because of perceived barriers in Dutch society. Most programs are private initiatives, funded on a project basis. In the Netherlands, refugees that hold a residence permit are called ‘status holders’. Upon arrival, they received a temporary permit for at least five years. They need to follow a civic integration and language program and they are expected to be part of the (regular) education system or labor market as soon as possible. The Test Garden started in 2016, a time when multiple support systems for refugee-entrepreneurs began their programs. This report starts with a short overview ofrefugee flows to the Netherlands. The main part of the report consists of the comparison and evaluation of the different programs. The information was gathered through literature, websites, and in-depth interviews with program managers and others involved. Interviews with the participants are only included for The Test Garden (Appendix 1 gives an overview of the meetings and interviews). LinkedIn: https://www.linkedin.com/in/karijn-nijhoff-89589316/
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This paper seeks to contribute to sustainable business model innovation (SBMI) literature. It aims to do so by putting forward a relatively simple tool that simultaneously calculates the financial value alongside sustainability impact based on the Sustainable Development Goals (SDGs) of a proposed business model innovation. For small businesses to validate the outcome of a proposed SBMI, some form of sustainability measurement will be necessary. Simple tooling specifically aimed at small businesses do not exist. We address this gap in how to predict or create a prognosis of the combined financial and sustainability effect of a proposed business model (BM) in a frugal (easy, time and knowledge effective) and effectual (allowing for iterations, available means and calculating affordable loss) manner. The tool is called the Pos-FSBC (Positive Financial and Sustainability Business Case). The instrument is a calculation model in Excel where users insert a limited number of numerical variables. Alongside financial variables the tool uniquely links the key variable ∆ SDG to the expected quantity sold, it then calculates the contribution to the SDGs in a relevant and measurable unit. By being successful with a sustainable innovation, the tool helps businesses drive out nonsustainable competitors. The tool has been iteratively developed and tested in several students’ projects and in a pilot with practitioners. Based on the findings we propose more iterations to develop an understanding whether the tool inspires business change and if so how.
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This paper presents the results of an exercise to assess the effects of metaphors on knowledge management. Knowledge is an abstract phenomenon with no direct referent in the real world. To think and talk about knowledge we use conceptual metaphors. The exercise shows that these metaphors greatly influence the problems we identify related to knowledge in organizations and the type of knowledge management solutions we propose. The knowledge as water metaphor used in this exercise – which reflects the dominant way of thinking in Western knowledge management literature – leads to the thingification of knowledge, resulting in a discourse about ways to formalize, manage and control knowledge. This discourse primarily serves the interests of management. In contrast, the knowledge as love metaphor used in this exercise – which reflects more an Asian way of thinking about knowledge – shifts the discourse from the topic of knowledge as a thing to the underlying preconditions for good knowledge work. These conditions include the facilitation of knowledge professionals, the quality of the relationships in the organization, and the quality of the organizational culture. This discourse is aimed at humanizing the organization instead of formalizing it and is more in the interest of employees.
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