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  • 1.
    Averfalk, Helge
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Werner, Sven
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Pipe Sizing for Novel Heat Distribution Technology2019Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, nr 7, artikkel-id 1276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper assesses pipe sizing aspects for previously proposed, novel, low heat distribution technology with three pipes. Assessment issues include heat loss, pressure loss, and pipe sizing for different typical pipe configurations. This assessment has been provided by the analysis of a case area with single-family houses. Concerning heat loss, the proposed three-pipe solutions have the same magnitude of heat loss as conventional twin pipes, since lower return temperatures compensate for the larger heat loss area from the third pipe. Regarding pressure loss, the main restriction on the size of the third pipe is limited to the pressure loss in the third pipe. Thermostatic valves to manage the flow rate of the third pipe are advocated, since alternative small pumps have not been found to be commercially available. The pipe sizing recommendation is that the third pipe for recirculation purposes can be two to three standard pipe sizes smaller than the corresponding supply and return pipe, if no prosumer is connected in the heat distribution network.

  • 2.
    Ghadirinejad, Nickyar
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Hoseinzade, A.
    University of Sistan and Baluchestan, Zahedan, Iran.
    Experimental Evaluation, Simulation and Statistical Analysis of a Humidification-Dehumidification Solar Desalination System2018Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Inspired by the precipitation cycle, the Humidification-Dehumidification (HDH) method is based on evaporation and consecutive condensation in a natural loop. The heat input to the system is provided by a solar collector, making the system suitable for remote locations with access to sea water and good insolation. In this study investigated parameters included temperatures and flow rates of cooling water, cycled air, and water intake to humidifier, as well as the height of packed bed column. A series of simulations has been performed in the ASPEN Plus software, in order to obtain optimum physical parameters in this desalination system. The experimental results showed that at constant heat flux and optimum air flow rate, three parameters have strong influence on the production of distilled water: the flow rate of cooling water, the flow rate of water inlet and its temperature augmentation. Moreover, although increasing flow rate of cooling water leads to an increase in the distilled water flow rate, this effect is mitigated at high rates. The most reliable Height Equivalent to a Theoretical Plate (HETP) model of random packing has been found by opting for the model of Mangers & Ponter. The estimated error of the model in predicting the height of the packed bed was less than 4%. Regarding closed versus open air flow; the closed air system provided an efficiency of distilled water production up to 15% higher than the open air system for the same conditions. This increase is a result of prevention of the loss of air humidity at the condenser outlet. A regression analysis was performed, which indicates that the HDH system can be well described by a linear model for the logarithm of the rate of desalinated water. The variables used are the saline water flow rate, the heat transfer rate in the solar collector and the air flow rate. The adjusted R-squared of the fit was computed as 89.8%.

  • 3.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Division for Electricity, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Bolin, Karl
    Marcus Wallenberg Laboratory, Department of Aeronautical and Vehicle Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Bååth, L.B.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Maskinteknisk produktframtagning (MTEK).
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Noise directivity from a vertical axis wind turbine2015Inngår i: Proceedings of the 6th International Conference on Wind Turbine Noise 2015, New Brighton: INCE/Europe , 2015Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The directivity of wind turbine noise is of widespread interest and has received attention over an extended period. The reason for this is partly that noise optimization procedures can be implemented in order to increase the efficiency of the power output. Although directivity of horizontal axis wind turbines (HAWTs) are well understood, the directivity pattern around vertical axis wind turbines (VAWTs) are less well investigated.This paper presents measurements of directivity on a 200 kW VAWT, a so called H-rotor, with variable speed and a tower height of 40 m. The turbine, which is situated in a flat agricultural landscape close to Falkenberg at the Swedish west coast, is one of the world’s largest today operational VAWTs. Experimental results as well as a theoretical model based on the turbulent-boundary-layer trailing-edge (TBL-TE) noise suggest higher noise levels upwind of the rotor and the lowest noise levels in the perpendicular directions. Moreover, modulation analysis of the measurements indicates the presence of modulations but the results are inconclusive.

  • 4.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Uppsala University, Uppsala, Sweden.
    Eriksson, Sandra
    Uppsala University, Uppsala, Sweden.
    Goude, Anders
    Uppsala University, Uppsala, Sweden.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Turbulence influence on optimum tip speed ratio for a 200 kW vertical axis wind turbine2016Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 753, artikkel-id 032048Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of turbulence intensity (TI) on the tip speed ratio for maximum power coefficient, here called λCp-max, is studied for a 200 kW VAWT H-rotor using logged data from a 14 month period with the H-rotor operating in wind speeds up to 9 m/s. The TI - λCp-max relation is examined by dividing 10 min mean values in different turbulence intensity ranges and producing multiple CP(λ) curves. A clear positive relation between TI and λCp-max is shown and is further strengthened as possible secondary effects are examined and deemed non-essential. The established relation makes it possible to tune the control strategy to enhance the total efficiency of the turbine.

  • 5.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Gipe, Paul
    Wind-works.org, Bakersfield, CA, USA.
    Beurskens, Jos
    SET Analysis, Schagen, the Netherlands.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    A historical review of vertical axis wind turbines rated 100 kW and above2019Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 105, s. 1-13Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    This paper summarizes and introduces all vertical axis wind turbine (VAWT) projects where 100 kW or larger turbines have been installed. The basis for the review is both existing literature and personal correspondence with people once involved in the different developments. By citing the most relevant work for each project, the paper will also work as an information hub, making information on these projects more accessible.

    Since the 1970s, there have been several VAWT projects with installed turbines of significant size, either as attempts to commercialize VAWTs, or as university led research projects, or as a combination of the two. Most have involved Darrieus turbines built in North America during the 1980s. However, H-rotors, which have always been a favored concept in Europe, have seen a revival during the 2010s.

    The reason VAWTs have never fully challenged the success of the horizontal axis wind turbine (HAWT) is too broad a question to answer here. However, the reasons some VAWT projects have failed are addressed in this paper. Besides the fact that many of the prototypes had terminal failures, most of the installed medium or large-scale VAWTs have to some extent had problems with metal fatigue and durability. Additionally, a lack of long-term interest from governmental or private funders, as well as the introduction of reliable HAWTs, was a recurring theme from those involved in VAWT development, regarding the reason VAWTs so far have failed to succeed. © 2018 The Author(s)

  • 6.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Uppsala University, Uppsala, Sweden.
    Larsson, Sebastian
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET).
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Bååth, Lars
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Maskinteknisk produktframtagning (MTEK).
    Noise Propagation from a Vertical Axis Wind Turbine2014Inngår i: Proceedings of 43rd International Congress on Noise Control Engineering: Internoise 2014 / [ed] John Davy, Charles Don, Terry McMinn, Liz Dowsett, Norm Broner & Marion Burgess, Brisbane, QLD: Australian Acoustical Society , 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Initial noise measurements were performed on a 200kW vertical axis wind turbine (VAWT) and results were compared to that of a Vestas V27, a similar size horizontal axis wind turbine (HAWT). Multiple recording units were placed in line downwind of the turbine to investigate noise propagation. The frequency distribution of the noise were analyzed indicating that the VAWT has lower relative levels for frequencies under 3000 Hz, especially within 600-1200 Hz. Furthermore, VAWT noise seems to occur more around the same frequencies as the natural background noise, increasing masking probability. Results from propagation measurements seemed to indicate that noise declines more rapidly with distance for the VAWT then for the reference HAWT, possibly explained by the lower levels at low frequencies. Further investigation is needed to establish these differences and the 200 kW VAWT creates an opportunity doing so utilizing arguably the largest operational VAWT existing today.

  • 7.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Comparison of inflow-turbulence and trailing-edge noise models with measurements of a 200-kW vertical axis wind turbine2019Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1222, artikkel-id 012028Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Models of inflow-turbulence noise and turbulent-boundary-layer trailing-edge noise are compared to earlier measurements of a 200-kW vertical axis wind turbine so that conclusions regarding the origin of the aerodynamic noise can be drawn. The measurement campaigns, which aimed at establishing the noise emission value and locating the aerodynamic noise sources with a microphone array, are here both compared to further modified versions of the trailing-edge and inflow-turbulence models respectively. Unlike the case for horizontal axis wind turbine, inflow-turbulence noise is deemed as the prevailing noise mechanism. Reducing the self-induced turbulence could then be an effective way of lowering the noise levels for vertical axis wind turbines. Also, looking at the directivity of the inflow-turbulence noise model which indicate most noise in the cross-wind directions, a deviation from the standard downwind measurement position for measuring noise emission is suggested for the VAWT case.

  • 8.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Uppsala University, Uppsala, Sweden.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Goude, Anders
    Uppsala University, Uppsala, Sweden.
    Eriksson, Sandra
    Uppsala University, Uppsala, Sweden.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Bernhoff, Hans
    Uppsala University, Uppsala, Sweden.
    Turbulence influence on wind energy extraction for a medium size vertical axis wind turbine2016Inngår i: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 19, nr 11, s. 1963-1973Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The relation between power performance and turbulence intensity for a VAWT H-rotor is studied using logged data from a 14 month (discontinuous) period with the H-rotor operating in wind speeds up to 9 m/s. The turbine, designed originally for a nominal power of 200 kW, operated during this period mostly in a restricted mode due to mechanical concerns, reaching power levels up to about 80 kW. Two different approaches are used for presenting results, one that can be compared to power curves consistent with the International Electrotechnical Commission (IEC) standard and one that allows isolating the effect of turbulence from the cubic variation of power with wind speed. Accounting for this effect, the turbine still shows slightly higher efficiency at higher turbulence, proposing that the H-rotor is well suited for wind sites with turbulent winds. The operational data are also used to create a Cp(λ) curve, showing slightly lower Cp compared with a curve simulated by a double multiple streamtube model. Copyright © 2016 John Wiley & Sons, Ltd.

  • 9.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Division for Electricity, Department of Engineering Sciences, Uppsala University, PO Box 534, SE - 751 21 Uppsala, SwedenDivision for Electricity, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Bernhoff, Hans
    Division for Electricity, Department of Engineering Sciences, Uppsala University, PO Box 534, SE - 751 21 Uppsala, SwedenDivision for Electricity, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Avoidance of resonances in a semi-guy-wired vertical axis wind turbine2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Resonance analysis for a vertical axis wind turbine is performed. The turbine may be described as semi-guy wired, being bolted stiffly to the ground as well as supported by guy wires. The influence of the first mode eigen frequency of the guy wires and how it is affected by wind load is examined. Using beam theory, an analytical model for calculating the first mode eigen frequency of the guy wire for different wind loads is derived. The analytical model is verified with FEM-simulations and then used to assemble a diagram showing how to combine the wire size, inclination angle and pre-tension for an eigen frequency range over the 3P load for nominal rotational speed and for a certain effective spring force acting on the tower. This diagram, here called an EA-T diagram, may be used as a quick tool for comparing wire setups and a similar diagram can be used for other guy wired structures.

  • 10.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Bernhoff, Hans
    Uppsala Universitet.
    Eigen Frequencies of A Vertical Axis Wind Turbine Tower Made of Laminated Wood and the Effect Upon Attaching Guy Wires2014Inngår i: Wind Engineering: The International Journal of Wind Power, ISSN 0309-524X, E-ISSN 2048-402X, Vol. 38, nr 3, s. 277-290Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Eigen frequencies of a vertical axis wind turbine tower made out of laminated wood which are both bolted to the ground and supported by guy wires are studied and compared. Using beam theory, an analytical model taking the guy wires into account for calculating the first mode eigen frequency of the tower has been derived. The analytical model is then evaluated by comparing with FEM-simulations and measurements performed on the actual tower. The model is found to be reasonably accurate keeping in mind that the estimated masses and second moments of area are somewhat rough. Furthermore the model can be used to give an indication of the magnitude of change in eigen frequency when modifying a tower or guy wire property.

  • 11.
    Möllerström, Erik
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Uppsala University, Uppsala, Sweden.
    Ottermo, Fredric
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik.
    Bernhoff, Hans
    Uppsala University, Uppsala, Sweden.
    Noise Emission of a 200 kW Vertical Axis Wind Turbine2016Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, nr 1, artikkel-id 19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The noise emission from a vertical axis wind turbine (VAWT) has been investigated. A noisemeasurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result hasbeen compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE) noise.The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to96.2 dBA. At this wind speed, the turbine was stalling as it was run at a tip speed lower than optimaldue to constructional constraints. The noise emission at a wind speed of 6 m/s, 10 m above groundwas measured while operating at optimum tip speed and was found to be 94.1 dBA. A comparisonwith similar size horizontal axis wind turbines (HAWTs) indicates a noise emission at the absolutebottom of the range. Furthermore, it is clear from the analysis that the turbulent-boundary-layertrailing-edge noise, as modeled here, is much lower than the measured levels, which suggests thatother mechanisms are likely to be important, such as inflow turbulence.

  • 12.
    Ottermo, Fredric
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Bio- och miljösystemforskning (BLESS), Energiteknik. Division for Electricity, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Bernhoff, Hans
    Division for Electricity, Department of Engineering Sciences, Uppsala University, Uppsala, Sweden & Swedish Centre for Renewable Electric Energy Conversion, Uppsala, Sweden.
    An upper size of vertical axis wind turbines2014Inngår i: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 17, nr 10, s. 1623-1629Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The scaling behaviour of a straight-bladed vertical axis wind turbine is considered. A scaling scheme is described that, in the presence of a wind shear profile, aims at leaving the material stresses of the scaled construction unchanged. On the basis of a recent 200 kW three-bladed H-rotor design, a structural upper size of the turbine is proposed, this size being the scale at which the gravitational force starts to become important. As gravity has a much worse scaling behaviour than the aerodynamic and centrifugal forces, the construction work will become increasingly more difficult above this scale. The upper size is estimated to be around 30 MW. © 2013 John Wiley & Sons, Ltd.

  • 13.
    Ottermo, Fredric
    et al.
    Uppsala University.
    Bernhoff, Hans
    Uppsala University.
    Resonances and Aerodynamic Damping of a Vertical Axis Wind Turbine2012Inngår i: Wind Engineering: The International Journal of Wind Power, ISSN 0309-524X, E-ISSN 2048-402X, Vol. 36, nr 3, s. 297-304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamics of a straight-bladed vertical axis wind turbine is investigated with respect to oscillations due to the elasticity of struts and shaft connecting to the hub. In particular, for the three-bladed turbine, a concept is proposed for dimensioning the turbine to maximize the size of the resonance free rpm range for operation. The effect of aerodynamic damping on the struts is also considered. The damping of these types of oscillations for a typical turbine is found to be good.

  • 14.
    Ottermo, Fredric
    et al.
    Uppsala University.
    Eriksson, Sandra
    Uppsala University.
    Bernhoff, Hans
    Uppsala University.
    Parking Strategies for Vertical Axis Wind Turbines2012Inngår i: ISRN Renewable Energy, ISSN 2090-746X, Vol. 2012, s. 904269-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strategies for parking a vertical axis wind turbine at storm load are considered. It is proposed that if a directly driven permanent magnet synchronous generator is used, an elegant choice is to short-circuit the generator at storm,since this makes the turbine efficiently damped. Nondamped braking is found to be especially problematic for the case of two blades where torsional oscillations may imply thrust force oscillations within a range of frequencies.

  • 15.
    Ottermo, Fredric
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Möllerström, Erik
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS). Uppsala University, Uppsala, Sweden.
    Nordborg, Anders
    Sound View Instruments, Borrby, Sweden.
    Hylander, Jonny
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Rydberglaboratoriet för tillämpad naturvetenskap (RLAS).
    Bernhoff, Hans
    Uppsala University, Uppsala, Sweden.
    Location of aerodynamic noise sources from a 200 kW vertical-axis wind turbine2017Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 400, s. 154-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Noise levels emitted from a 200 kW H-rotor vertical-axis wind turbine have been measured using a microphone array at four different positions, each at a hub-height distance from the tower. The microphone array, comprising 48 microphones in a spiral pattern, allows for directional mapping of the noise sources in the range of 500 Hz to 4 kHz. The produced images indicate that most of the noise is generated in a narrow azimuth-angle range, compatible with the location where increased turbulence is known to be present in the flow, as a result of the previous passage of a blade and its support arms. It is also shown that a semi-empirical model for inflow-turbulence noise seems to produce noise levels of the correct order of magnitude, based on the amount of turbulence that could be expected from power extraction considerations.

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