scholarly journals Using the SWEPT Methodology for a Preliminary Wind Potential Estimation

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Jean-Luc Menet
Keyword(s):  
Wind Turbine ◽  
Characteristic Curve ◽  
Rayleigh Distribution ◽  
Mean Velocity ◽  
Technical Data ◽  
Wind Potential ◽  
Order Of Magnitude ◽  
General Data ◽  
The Mean ◽  
A Site

The implantation of wind turbines generally follows a wind potential study which is made using specific numerical tools; the generated expenses are only acceptable for great projects. The purpose of the present paper is to propose a simplified methodology for the evaluation of the wind potential, following three successive steps for the determination of (i) the mean velocity, either directly or by the use of the most occurrence velocity (MOV); (ii) the velocity distribution coming from the single knowledge of the mean velocity by the use of a Rayleigh distribution and a Davenport-Harris law; (iii) an appropriate approximation of the characteristic curve of the turbine, coming from only two technical data. These last two steps allow calculating directly the electric delivered energy for the considered wind turbine. This methodology, called the SWEPT approach, can be easily implemented in a single worksheet. The results returned by the SWEPT tool are of the same order of magnitude than those given by the classical commercial tools. Moreover, everybody, even a “neophyte,” can use this methodology to obtain a first estimation of the wind potential of a site considering a given wind turbine, on the basis of very few general data.

scholarly journals On the cooling and evaporative powers of the atmosphere, as determined by the kata-thermometer

1919 ◽  
Vol 90 (632) ◽  
pp. 438-447 ◽  
Keyword(s):  
Body Temperature ◽  
Skin Temperature ◽  
Cross Section ◽  
Cooling Power ◽  
Mean Velocity ◽  
Cross Section Area ◽  
Section Area ◽  
Order Of Magnitude ◽  
The Mean ◽  
A Current

In a paper published in ‘Phil. Trans.’ (B, vol. 207, 1916, pp. 183-220) by L. Hill, O. W. Griffiths, and M. Flack, there was detailed the theory and use of an instrument, the kata-thermometer, a large-bulbed alcohol thermometer, for determining the cooling power of the atmosphere on a surface at body temperature. A formula H/ θ = 0⋅27 + 0⋅36 √V, where H = heat lost in mille-calories per square centimetre per second, θ = (36⋅5— t )°C., where t = temperature of enclosure, and V = velocity of air current in metres per second, was obtained for the loss of heat of the dry kata-thermometer in a current of air; 36⋅5° C. was chosen as the skin temperature. This is a variable, and only reaches that figure in warm atmospheres. The constant 0⋅36 in the above formula was determined from experiments which were carried out with the apparatus then available in a tube of which the cross-section area was of the same order of magnitude as that of the kata. Therefore, in calculating the velocity of the air current i.e ., the mean velocity of the air striking the kata, the area of cross-section of the kata was subtracted from that of the tube.

scholarly journals An Analytical Model for the Effect of Vertical Wind Veer on Wind Turbine Wakes

Energies ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1838 ◽  
Author(s):  
Mahdi Abkar ◽  
Jens Sørensen ◽  
Fernando Porté-Agel
Keyword(s):  
Wind Turbine ◽  
Input Parameter ◽  
Mass Conservation ◽  
Wake Flow ◽  
Mean Velocity ◽  
Gaussian Shape ◽  
Velocity Deficit ◽  
Proposed Model ◽  
The Mean ◽  
Wake Model

In this study, an analytical wake model for predicting the mean velocity field downstream of a wind turbine under veering incoming wind is systematically derived and validated. The new model, which is an extended version of the one introduced by Bastankhah and Porté-Agel, is based upon the application of mass conservation and momentum theorem and considering a skewed Gaussian distribution for the wake velocity deficit. Particularly, using a skewed (instead of axisymmetric) Gaussian shape allows accounting for the lateral shear in the incoming wind induced by the Coriolis force. This analytical wake model requires only the wake expansion rate as an input parameter to predict the mean wake flow downstream. The performance of the proposed model is assessed using the large-eddy simulation (LES) data of a full-scale wind turbine wake under the stably stratified condition. The results show that the proposed model is capable of predicting the skewed structure of the wake downwind of the turbine, and its prediction for the wake velocity deficit is in good agreement with the high-fidelity simulation data.

scholarly journals Analysis and correlation of fluid motions in natural thermal convection in a cylindrical vessel

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 859-865
Author(s):  
Wei Wang ◽  
Xin-Lei Guan ◽  
Li-Jun Wang ◽  
Chu-Wen Guo
Keyword(s):  
Temperature Gradient ◽  
Thermal Convection ◽  
Vertical Direction ◽  
Space Time ◽  
Cylindrical Vessel ◽  
Mean Velocity ◽  
Time Correlations ◽  
Characteristic Points ◽  
Order Of Magnitude ◽  
The Mean

A natural thermal convection system is set up in a cylindrical vessel with aspect ratio of 2 having a temperature gradient in the vertical direction, and the fluid motions due to convection are investigated. The 2-D velocity field along the plane passing through the diameter of the vessel is obtained using particle image velocimetry. The results indicate that the convection is in the transition stage and the mean velocity fields show two pairs of counter-rotating circulations. The mean motions are predominant in the vertical direction under the influence of the temperature gradient, while the fluctuations in the x- and y-directions have the same order of magnitude. Probability density functions of fluctuation velocities at seven characteristic points show different behaviors. The space-time correlations in the regions where the circulations interact exhibit the iso-correlation-lines predicted by the elliptical approximation hypothesis. The space-time correlations of the streamwise and vertical fluctuations show distinct movements which imply the existence of anisotropy around the interaction region.

scholarly journals Cloud motions on Mars

1971 ◽  
Vol 40 ◽  
pp. 320-328
Author(s):  
W. A. Baum ◽  
L. J. Martin
Keyword(s):  
High Elevation ◽  
Daily Basis ◽  
Martian Surface ◽  
Mean Velocity ◽  
Mapping Procedure ◽  
Topographic Features ◽  
Bright Spots ◽  
Order Of Magnitude ◽  
Photographic Survey ◽  
The Mean

A search of several thousand plates in the Lowell Observatory collection yielded 28 groups of plates on which the positions of well-defined transient bright spots (often assumed to be clouds) could be followed on a nearly daily basis. These groups of plates were from 15 different oppositions of Mars, starting from 1907 and ending with 1958. All but two of these spanned four nights or more, and the maximum interval covered was thirty nights. Whether they appeared to show motion or not, the successive positions and shapes of all apparently associated bright spots or clouds were plotted on Mercator projections with the use of a projection plate reader especially designed at the Planetary Research Center for planet image studies of this kind. Clouds near the limb were avoided.The 28 groups of plates yielded 95 cloud histories. More than half appeared to be relatively stationary. Others showed definite motion well in excess of observational error but sometimes followed paths that partly doubled back upon themselves. The mean velocity for non-stationary clouds was found to be 5.6 km per hour, and the most commonly occurring direction of motion was eastward, particularly at high latitudes. The range of velocities found by this mapping procedure is nearly an order of magnitude smaller than values that have been estimated earlier by others from visual observations. These earlier observations are evidently in error, unless there exist clouds at high elevation, visible only on the limb, that can move much faster than those that were mapped from this photographic survey. More clouds were found in the northern hemisphere than in the southern, and there seemed to be an avoidance of the relatively darker areas of the Martian surface. Certain regions seem to be more favored than others. A few recurrences at identical positions suggest the existence of related topographic features.

scholarly journals The structure of turbulence in a rapid tidal flow

2017 ◽  
Vol 473 (2204) ◽  
pp. 20170295 ◽  
Author(s):  
I. A. Milne ◽  
R. N. Sharma ◽  
R. G. J. Flay
Keyword(s):  
Numerical Models ◽  
Tidal Flow ◽  
Tidal Energy ◽  
Tidal Channels ◽  
Mean Flow ◽  
Mean Velocity ◽  
Simple Geometry ◽  
The Mean ◽  
The Uk ◽  
A Site

The structure of turbulence in a rapid tidal flow is characterized through new observations of fundamental statistical properties at a site in the UK which has a simple geometry and sedate surface wave action. The mean flow at the Sound of Islay exceeded 2.5 m s −1 and the turbulent boundary layer occupied the majority of the water column, with an approximately logarithmic mean velocity profile identifiable close to the seabed. The anisotropic ratios, spectral scales and higher-order statistics of the turbulence generally agree well with values reported for two-dimensional open channels in the laboratory and other tidal channels, therefore providing further support for the application of universal models. The results of the study can assist in developing numerical models of turbulence in rapid tidal flows such as those proposed for tidal energy generation.

The intermediate wake of a body of revolution at high Reynolds numbers

2010 ◽  
Vol 659 ◽  
pp. 516-539 ◽  
Author(s):  
JUAN M. JIMÉNEZ ◽  
M. HULTMARK ◽  
A. J. SMITS
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Stress Distributions ◽  
Body Of Revolution ◽  
Self Similarity ◽  
Mean Velocity ◽  
High Reynolds Numbers ◽  
Order Of Magnitude ◽  
The Mean ◽  
High Reynolds

Results are presented on the flow field downstream of a body of revolution for Reynolds numbers based on a model length ranging from 1.1 × 106 to 67 × 106. The maximum Reynolds number is more than an order of magnitude larger than that obtained in previous laboratory wake studies. Measurements are taken in the intermediate wake at locations 3, 6, 9, 12 and 15 diameters downstream from the stern in the midline plane. The model is based on an idealized submarine shape (DARPA SUBOFF), and it is mounted in a wind tunnel on a support shaped like a semi-infinite sail. The mean velocity distributions on the side opposite the support demonstrate self-similarity at all locations and Reynolds numbers, whereas the mean velocity distribution on the side of the support displays significant effects of the support wake. None of the Reynolds stress distributions of the flow attain self-similarity, and for all except the lowest Reynolds number, the support introduces a significant asymmetry into the wake which results in a decrease in the radial and streamwise turbulence intensities on the support side. The distributions continue to evolve with downstream position and Reynolds number, although a slow approach to the expected asymptotic behaviour is observed with increasing distance downstream.

scholarly journals Wind tunnel experiments on wind turbine wakes in yaw: effects of inflow turbulence and shear

2018 ◽  
Vol 3 (1) ◽  
pp. 329-343 ◽  
Author(s):  
Jan Bartl ◽  
Franz Mühle ◽  
Jannik Schottler ◽  
Lars Sætran ◽  
Joachim Peinke ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Laser Doppler Anemometry ◽  
Vortex Pair ◽  
Wake Flow ◽  
Turbulent Shear ◽  
Mean Velocity ◽  
Inflow Turbulence ◽  
The Mean ◽  
Inflow Conditions ◽  
Wake Characteristics

Abstract. The wake characteristics behind a yawed model wind turbine exposed to different customized inflow conditions are investigated. Laser Doppler anemometry is used to measure the wake flow in two planes at x∕D = 3 and x∕D = 6, while the turbine yaw angle is varied from γ=-30∘ to 0∘ to +30∘. The objective is to assess the influence of grid-generated inflow turbulence and shear on the mean and turbulent flow components. The wake flow is observed to be asymmetric with respect to negative and positive yaw angles. A counter-rotating vortex pair is detected creating a kidney-shaped velocity deficit for all inflow conditions. Exposing the rotor to non-uniform highly turbulent shear inflow changes the mean and turbulent wake characteristics only insignificantly. At low inflow turbulence the curled wake shape and wake center deflection are more pronounced than at high inflow turbulence. For a yawed turbine the rotor-generated turbulence profiles peak in regions of strong mean velocity gradients, while the levels of peak turbulence decrease at approximately the same rate as the rotor thrust.

scholarly journals Wind tunnel experiments on wind turbine wakes in yaw: Effects of inflow turbulence and shear

2018 ◽  
Author(s):  
Jan Bartl ◽  
Franz Mühle ◽  
Jannik Schottler ◽  
Lars Sætran ◽  
Joachim Peinke ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Laser Doppler Anemometry ◽  
Vortex Pair ◽  
Wake Flow ◽  
Mean Velocity ◽  
Inflow Turbulence ◽  
The Mean ◽  
Center Deflection ◽  
Inflow Conditions ◽  
Wake Characteristics

Abstract. The wake characteristics behind a yawed model wind turbine exposed to different customized inflow conditions are investigated. Laser Doppler Anemometry is used to measure the wake flow in two planes at x/D = 3 and x/D = 6 while the turbine yaw angle is varied from −30° and 0° to +30°. The objective is to assess the influence of grid-generated inflow turbulence and shear on the mean and turbulent flow components. The wake flow is observed to be asymmetric with respect to negative and positive yaw angles. A counter-rotating vortex pair is detected creating a kidney-shaped velocity deficit for all inflow conditions. Exposing the rotor to non-uniform shear inflow changes the mean and turbulent wake characteristics only insignificantly. At low inflow turbulence the curled wake shape and wake center deflection are more pronounced than at high inflow turbulence. For a yawed turbine the rotor-generated turbulence profiles peak in regions of strong mean velocity gradients, while the levels of peak turbulence decrease at approximately the same rate as the rotor thrust.

scholarly journals Scaling of the turbulent/non-turbulent interface in boundary layers

2014 ◽  
Vol 751 ◽  
pp. 298-328 ◽  
Author(s):  
Kapil Chauhan ◽  
Jimmy Philip ◽  
Ivan Marusic
Keyword(s):  
Boundary Layer ◽  
Outer Part ◽  
Tangential Velocity ◽  
Reynolds Numbers ◽  
Momentum Balance ◽  
Normal Velocity ◽  
Mean Velocity ◽  
Order Of Magnitude ◽  
Theoretical Reasoning ◽  
The Mean

AbstractScaling of the interface that demarcates a turbulent boundary layer from the non-turbulent free stream is sought using theoretical reasoning and experimental evidence in a zero-pressure-gradient boundary layer. The data-analysis, utilising particle image velocimetry (PIV) measurements at four different Reynolds numbers ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\delta u_{\tau }/\nu =1200\mbox{--}14\, 500$), indicates the presence of a viscosity dominated interface at all Reynolds numbers. It is found that the mean normal velocity across the interface and the tangential velocity jump scale with the skin-friction velocity$u_{\tau }$and are approximately$u_{\tau }/10$and$u_{\tau }$, respectively. The width of the superlayer is characterised by the local vorticity thickness$\delta _{\omega }$and scales with the viscous length scale$\nu /u_{\tau }$. An order of magnitude analysis of the tangential momentum balance within the superlayer suggests that the turbulent motions also scale with inner velocity and length scales$u_{\tau }$and$\nu /u_{\tau }$, respectively. The influence of the wall on the dynamics in the superlayer is considered via Townsend’s similarity hypothesis, which can be extended to account for the viscous influence at the turbulent/non-turbulent interface. Similar to a turbulent far-wake the turbulent motions in the superlayer are of the same order as the mean velocity deficit, which lends to a physical explanation for the emergence of the wake profile in the outer part of the boundary layer.

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