wind energy resource evaluation in a site of central italy ... - WindSim

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3.5 Investigation of a flow over a 2D roughly hilly terrainThis paragraph presents an investigation of a flow over a two–dimensional roughlyhilly terrain. Two cases have been realized, to highlight the behavior of an attachedflow and a separated flow, by varying the slope of the hill. A comparison betweenexperimental [3] and numerical data has been done, showing good agreement.The numerical simulations are based on the solution of Reynolds Averaged Navier-Stokes (RANS) equations, by the software WindSim, with the k-ε turbulencemodel. The realized numerical grid is in both cases non orthogonal body fitted type,while the solver which better produces a good level of convergence in the solution isthe segregated, enriched with the “yap” correction of the k-ε turbulence model.3.5.1 Description of the test caseThe experimental data comes from the tests conducted in an open-circuit boundarylayerwind tunnel, having a test section of width, height and length of 1.2, 1.2 and 6meters respectively. A neutrally stratified boundary layer is developed using equallyspaced 0.25 m height triangular spire-type vortex generators and artificial grass of 5mm height. In these experiments, a fully-developed turbulent boundary layer of 0.25m height is generated, and has a typical wind profile over an open flat area (fitting toa log-law profile).The shape of the hill is described by the following equation3.5.1) = ∙ 1+ ∙ ,where:H [m] is the height of the hillL 1 [m] is the half-length of the hill at the upwind mid-height of thehillThe slope of the hill S is defined as the average slope for the top half of the hillupstream of the crest, through the equation37
3.5.2) = ∙.The two models for attached and separated flow are identified as S3H4 and S5H4,where S3 and S5 stand for the hill slope of 0.3 and 0.5 respectively, and H4 stand forthe hill height of 4 centimeters.A sketch of the studied hill is presented in the following figure 3.5.1Figure 3.14: Schematic diagram of the wind flow over a hill.The experimental data, relative to the flow at the inlet of the wind tunnel, havebeen curve-fitted with the following logarithmic functionwith:3.5.3) ( ) = ∗ ∙U * =0,33Z 0 =0,05K=0,41m/smmVon Karman constantThe following figure 3.15 shows the interpolation of the velocity profile.38
Page 1 and 2: UNIVERSITÀ DEGLI STUDI DI CAGLIARI
Page 3 and 4: IndexIndex page IAcknowledgmentsVII
Page 5 and 6: CHAPTER 4: Characteristics of the s
Page 7 and 8: 6.7.1 Mean wind velocity page 1096.
Page 9 and 10: This thesis is the result of a prac
Page 11 and 12: WindSim is a software developed by
Page 13 and 14: CHAPTER 1. Atmospheric Boundary Lay
Page 15 and 16: Figure 1.1: Example of an atmospher
Page 17 and 18: 1.5 The WindSim numerical codeWindS
Page 19 and 20: (κ−ε RNG or the Low Reynolds),
Page 21 and 22: 1.5.4 RESULTSThe Results module all
Page 23 and 24: Figure 1.2: Example of TKE vertical
Page 25 and 26: CHAPTER 2. Simulations over flat te
Page 27 and 28: inlet position (0 meters), station
Page 29 and 30: 2.4 Height distribution factor sens
Page 31 and 32: e decreased, to avoid to build thin
Page 33 and 34: Figure 2.10: Vertical profiles for
Page 35 and 36: CHAPTER 3. Simulations over 2D hill
Page 37 and 38: Table 3.1: Measurement coordinatesS
Page 39 and 40: The results shown above demonstrate
Page 41 and 42: Figure 3.6: Sketch of the 15 km lon
Page 43 and 44: Figure 3.9: Influence of the height
Page 45: Figure 3.13: Zoom of the hill top r
Page 49 and 50: H [m] hill heightν[m 2 /s] air cin
Page 51 and 52: Figure 3.18: Particular of the nume
Page 53 and 54: Finally, the horizontal x velocity
Page 55 and 56: Figure 3.25: Z velocity componentFi
Page 57 and 58: 3.6 RemarksA CFD study of a boundar
Page 59 and 60: Some experimental wind data of this
Page 61 and 62: Both the pictures 4.3 and 4.4 have
Page 63 and 64: Table 4.2: Description of the color
Page 65 and 66: In this periods, data are recorded
Page 67 and 68: In the following pages, a short des
Page 69 and 70: 4.3.2 Mast 5424-15 m Period April-M
Page 71 and 72: 4.3.4 Mast 5424-15 m Period Novembe
Page 73 and 74: 4.3.6 Mast 5428-40 m Period April-M
Page 75 and 76: 4.3.8 Mast 5428-50 m Period Novembe
Page 77 and 78: 4.3.10 Mast 5428-30 m Period Novemb
Page 79 and 80: 4.4.2 Mast 542870
Page 81 and 82: 4.5.2 Mast 542872
Page 83 and 84: CHAPTER 5. Test of the Free Stream
Page 85 and 86: case the wind is blowing from the e
Page 87 and 88: Geometrical modelTable 5.3: Input p
Page 89 and 90: Figure 5.6: Vertical profiles in po
Page 91 and 92: The orthogonalization of the grid h
Page 93 and 94: Figure 5.9: Map of speed-ups for di
Page 95 and 96: Figure 5.30: Speed-2D at 30 m heigh
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Figure 5.12: Speed-2D at 30 m heigh
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CHAPTER 6. Analysis of the wind fie
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Table 6.2: Boundary conditions and
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6.5 Vertical profiles of VelocityTo
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characterized by high wind speed (5
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From the error analysis, it is foun
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Anyhow, the trend of the linear int
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Concerning the CFD simulations, val
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Analyzing RMS error table for tower
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A general overview of the figure 6.
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6.7 Cross Checking of wind dataIn t
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Figure 6.8 a/bFigure 6.8 c/dFigure
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Table 6.11: RMS error for cross che
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Figure 6.9 e/fFigure 6.9 g/hFigure
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Figure 6.10 g/hFigure 6.10 i/lFigur
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to have a better agreement during t
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Figure 7.2: Weibull fitting of the
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Figure 7.5: Perspective view of the
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The calculated AEP has been reporte
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ConclusionsIn this thesis the evalu
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Bibliography[1] CRASTO G. - Numeric
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