Simultaneous Balloon Launches to Investigate Wake Effects on Thermosonde Results

In this paper, we consider the Wind Farm layout optimization problem using a genetic algorithm. Both the Horizontal–Axis Wind Turbines (HAWT) and Vertical-Axis Wind Turbines (VAWT) are considered. The goal of the optimization problem is to optimally place the turbines within the wind farm such that the wake effects are minimized and the power production is maximized. The reasonably accurate modeling of the turbine wake is critical in determination of the optimal layout of the turbines and the power generated. For HAWT, two wake models are considered; both are found to give similar answers. For VAWT, a very simple wake model is employed.

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Wind turbine power prediction considering wake effects with dual laser beam LiDAR measured yaw misalignment

Applied Energy ◽

10.1016/j.apenergy.2021.117308 ◽

2021 ◽

Vol 299 ◽

pp. 117308

Author(s):

Xuyang Li ◽

Yingning Qiu ◽

Yanhui Feng ◽

Zheng Wang

Keyword(s):

Laser Beam ◽

Wind Turbine ◽

Power Prediction ◽

Wake Effects ◽

Dual Laser

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A comprehensive comparative investigation of the Lifting Line Theory and Blade Element Momentum Theory applied to small wind turbines

Journal of Energy Resources Technology ◽

10.1115/1.4053066 ◽

2021 ◽

pp. 1-25

Author(s):

K.A.R. Ismail ◽

Willian Okita

Keyword(s):

Wind Turbines ◽

Power Coefficient ◽

Computational Time ◽

Local Flow ◽

Small Wind Turbines ◽

Wake Effects ◽

Line Theory ◽

Lifting Line ◽

Lifting Line Theory ◽

Blade Element

Abstract Small wind turbines are adequate for electricity generation in isolated areas to promote local expansion of commercial activities and social inclusion. Blade element momentum (BEM) method is usually used for performance prediction, but generally produces overestimated predictions since the wake effects are not precisely accounted for. Lifting line theory (LLT) can represent the blade and wake effects more precisely. In the present investigation the two methods are analyzed and their predictions of the aerodynamic performance of small wind turbines are compared. Conducted simulations showed a computational time of about 149.32 s for the Gottingen GO 398 based rotor simulated by the BEM and 1007.7 s for simulation by the LLT. The analysis of the power coefficient showed a maximum difference between the predictions of the two methods of about 4.4% in the case of Gottingen GO 398 airfoil based rotor and 6.3% for simulations of the Joukowski J 0021 airfoil. In the case of the annual energy production a difference of 2.35% is found between the predictions of the two methods. The effects of the blade geometrical variants such as twist angle and chord distributions increase the numerical deviations between the two methods due to the big number of iterations in the case of LLT. The cases analyzed showed deviations between 3.4% and 4.1%. As a whole, the results showed good performance of both methods; however the lifting line theory provides more precise results and more information on the local flow over the rotor blades.

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The spacecraft wake as a tool to detect cold ions: Turning a problem into a feature

10.5194/egusphere-egu21-2332 ◽

2021 ◽

Author(s):

Mats André ◽

Anders I. Eriksson ◽

Yuri V. Khotyaintsev ◽

Sergio Toledo-Redondo

Keyword(s):

Electric Field ◽

Plasma Parameters ◽

Double Probe ◽

Positive Ions ◽

Collisionless Plasmas ◽

Mass Outflow ◽

Wake Effects ◽

In Situ Observations ◽

Positively Charged

<p>Wakes behind scientific spacecraft caused by supersonic drifting ions is common in collisionless plasmas. Such wakes change the local plasma conditions and disturb in situ observations of the geophysical plasma parameters. We concentrate on observations of the electric field with double-probe instruments. Sometimes the wake effects are caused by the spacecraft body, are minor and easy to detect, and can be compensated for in a reasonable way. We show an example from the Cluster spacecraft in the solar wind. Sometimes the effects are caused by an electrostatic structure around a positively charged spacecraft causing an enhanced wake and major effects on the local plasma. Here observations of the geophysical electric field with the double-probe technique becomes impossible. Rather, the wake can be used to detect the presence of cold positive ions. Together with other instruments, also the cold ion flux can be estimated. We discuss such examples from the Cluster spacecraft in the magnetospheric lobes. For an intermediate range of parameters, when the drift energy of the ions is comparable to the equivalent charge of the spacecraft, also the charged wire booms of a double-probe instrument must be taken into account to extract useful information from the observations. We show an example from the MMS spacecraft near the magnetopause. With understanding of the physics causing wakes behind spacecraft, the local effects can sometimes be compensated for. When this is not possible, sometimes entirely new geophysical parameters can be estimated. An example is the flux of cold positive ions, constituting a major part of the mass outflow from planet Earth, using electric and magnetic field instruments on a spacecraft charged due to photoionization</p><p>&#160;</p>

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