Two commercial Computational Fluid Dynamic (CFD) wind resource assessment tools namely Meteodyn WT and Windsim have been compared for an embankment site named Hjardemål. For comparison of both software, a controlled experiment is carried out for a fixed set-up with same domain size and same number of cells in the X, Y and Z directions. Wind flow has been assessed in the perpendicular upstream direction to the embankment. Vertical wind profiles observed on site at four different towers distributed (-397.69 m) before, (0 m) at, (30.83 m) just after and (199.16 m) after the embankment are compared with both software outputs. Results show that Meteodyn WT predicts closer vertical wind profiles before, at and after whilst wind Windsim predicts a closer wind profile just after the embankment. The discussion of results is based on the limitations of both software tools which have conditioned the comparison.

A annual nergy production analysis was undertaken to compare wind resources and annual energy production as estimated by WAsP and Windsim. Nordex Sverige AB has designed a wind farm with the help of WAsP and this study will involve the examination of this site with Windsim. Two site formations are of interest, one with the same class of turbine and one with a mix of two turbine types. The study is interested in the effect on annual energy production as estimated by the different software of employing a hybrid layout using wind turbines of different height.The results showed that whilst initial estimations of total energy production without wake losses appear very similar between WAsP and Windsim the ways in which the software are treating individual turbines within the planned farm can be quite different because of different physics. The analysis of the „hybrid‟ turbine layout showed significant increases in estimated annual energy production when a turbine with a higher tower and larger rotor diameter was used in a hybrid arrangement. Estimated annual energy losses on the turbines that were not changed in favour of a larger turbine were small. However, no great benefit in estimated turbine efficiency was achieved through the mixing of turbine types with different hub heights. The gains in annual energy production estimated by both software are however significant with increased production of 18 % across the entire farm when comparing the „hybrid‟ layout to a farm based on only the smaller of the two turbine types.

The main aim of this thesis is to compare actual power production from an existing wind farm with power production prediction by WindSim, which is a CFD tool based on the nonlinear flow model. The wind farm that is being worked on is located in Northern Sweden and has high orographic complexity with forested hilly terrain. There is 1 year record of met-mast wind measurements and nearly 2 years record of production data.Firstly roughness and height contours data are put as an input in order to simulate and generate wind fields over the complex terrain. In addition forest model is used to get more detailed roughness height. After generating wind fields existing turbine locations and 1-year wind speed measurement are imported.The results show that how accurate are the CFD calculations to solve turbulence in a complex terrain. Comparison between actual production data with energy production results by simulations is the main approach of this thesis work to validate the simulations.The results indicate that both WAsP and WindSim have overestimated energy production and wind speed as well. However particularly with WindSim forest module CFD calculations have more accurate results than without forest module and WAsP estimations.

No description available.

An accurate wind resource assessment (WRA) is crucial in energy prediction as the power is directly proportional to the wind speed cubed. This thesis analyses the discrepancy between operational assessment and WRA for a wind farm located on a moderately complex terrain in Ireland. As part of this research, a WRA was undertaken and the results were input to two wind farm design tools, WindPro and WindSim, to estimate the annual energy production. Two and a half years of data was available from a 50m met mast. The data was analysed and filtered to ascertain and limit the usage of erroneous data. The dataset was then correlated with an available online dataset utilising the Measure Correlate Predict (MCP) module in WindPro in order to estimate the long term wind resource at the site. The wind resource was then used to determine the annual energy produced at the site using both WindPro and WindSim. A loss of 8% was applied to the energy calculations for comparison with the original WRA. The results demonstrate the energy production from the original energy prediction, undertaken by a leading wind consultancy prior to construction, was overestimated by an average 10.19% over the three years of operation. The averaged wind speed at hub height in the original WRA was 8.2m/s. However, the prediction undertaken using WindPro in this study estimated an average hub height wind speed of 8.0m/s while WindSim estimated an average of 7.36m/s. These differing results had a significant contribution to the difference in Annual Energy Production (AEP). The calculated annual energy results were an overestimation of energy production by an average of 8.10% utilising WindPro, while WindSim underestimated the energy output by just 0.11%.

The aim of this study is to compare the performance of a linear model to a nonlinear model focusing on flow separation based on a critical slope value. Specifically, the WindPRO WAsP model will be compared with the WindSIM CFD model over a simulated terrain to determine the point the two models differ in relation to the inclination of the terrain. The results of this study will verify if the proposed critical slope value of roughly 17 degrees is truly representative of the limitation of the WAsP model in producing accurate results as compared to a CFD model.  Multiple similar studies have been performed using existing sites with actual met mast data as a comparison to the model outputs. Many of these cases have come up with varying results due primarily to the large number of uncontrolled factors influencing the data. This study will be designed in a fully simulated environment where all variables can be controlled, allowing for the manipulation of a single variable to understand its’ specific influence over the model. The primary variable being tested in this study will be the slope of the terrain with all other factors held constant.   Based on the outcome of 7 alternative runs with ridge heights of 100, 120, 140, 160, 180, 200, and 300 meters and respective maximum slope values of 10.31, 12.32, 14.29, 16.23, 18.14, 20, and 28.63 degrees a defined separation point at a hub height of 94 meters could not be found. Each run demonstrated correlation between wind speeds and terrain slope variations but a considerable difference in estimated wind resources was present between the linear and non-linear CFD models where any slope in terrain is present. This, as expected, increases where terrain inclination increases, but a clearly defined difference between the two models is not evident at the previously established critical slope value of approximately 17 degrees (30%).

Vindkraft för generering av el har under de senaste åren vuxit kraftigt i Sverige och utbyggnaden väntas fortsätta. Ett viktigt steg när nya vindkraftsparker skall byggas är att göra en vindanalys för det aktuella området. Vindanalysen är ett viktigt underlag för att avgöra om en investering i vindkraftverk kommer vara ekonomiskt lönsamt på den aktuella platsen.      Som underlag till vindanalysen sätts vanligen mätutrustning upp i området och vindförhållandena på platsen mäts upp. Att installera och underhålla mätmaster är kostsamt och därför mäts vindarna på ett begränsat antal platser i det intressanta området. Sedan används olika beräkningsprogram för att extrapolera de uppmätta vindresurserna till positioner där mätningar saknas. För närvarande används programmet WAsP som standard av många vindkraftsprojektörer. WAsP:s beräkningsmodell är relativt enkel och tar till exempel inte hänsyn till turbulens som uppkommer då terrängen är kuperad. Som ett alternativ till WAsP har olika CFD-program introducerats på marknaden under senare år. Dessa programs modeller är mer avancerade och de kräver därför längre beräkningstid jämfört med WAsP, men förhoppningen är att de skall ge mer tillförlitliga modelleringsresultat. I denna studie har vindmodelleringar i det linjära modelleringsprogrammet WAsP jämförts med modelleringar i CFD-programmet WindSim. Syftet har varit att undersöka om WAsP ger tillförlitliga modelleringsresultat i svenskt kuperat skogslandskap och om WindSims CFD-beräkningar kan ge en ökad noggrannhet i jämförelse. Prestandan hos respektive program har utvärderats genom att jämföra extrapolerade medelvindar med faktiska mätningar. Vindmätningar har funnits att tillgå från en period av 12 månader från två mätmaster med givare på 60, 80 och 100 meters höjd. Avståndet mellan masterna är cirka 10 kilometer.            Resultaten från studien tyder på att WindSim kan ge en något ökad noggrannhet jämfört med WAsP, men resultaten visar samtidigt att en CFD-modellering inte med automatik ger mer tillförlitliga modelleringsresultat. Studien har visat att resultatet från WindSim är starkt beroende av hur modellen sätts upp och det kan därför vara enklare att göra fel i WindSim jämfört med WAsP. Det blev också tydligt att en modell där den simulerad vindskjuvning (variation av vindhastigheten i höjdled) stämde bra överens med den uppmätta inte behöver betyda att WindSim-modellen gör bra extrapolationer av vindförhållandena från den ena masten till den andra. Vidare visade sig WAsP missbedöma effekter från topografin något och om vindmätningar görs på utmärkande höjder är det sannolikt att WAsP överskattar vindförhållandena i de lågt belägna delarna av terrängen. I WindSim undersöktes två olika modelluppsättningar, en med WindSims skogsmodul där skogen simuleras som 3D objekt och en modell där skogen hanteras med på samma sätt som i WAsP med råhetslängd och nollplansförskjutning. När skogsmodulen användes var det inte möjligt att erhålla en modellerad vindskjuvning som stämde överens med den uppmätta i en neutral atmosfär, vilket är WindSims standardinställning för atmosfärsstabiliteten. I en neutral atmosfär med skogsmodulen överskattades vindhastigheten på låga höjder. Om atmosfären simulerades som stabil i medeltal var det möjligt att få den simulerad vindskjuvning att stämma överens med den uppmätta, men extrapolationerna i horisontalled blev inte bra med denna modell. Om atmosfären skall simuleras som stabil i WindSim tyder resultaten från studien på att vindmätningarna måste delas in efter rådande atmosfärstabilitet för den aktuella tidpunkten för mätningen. Det fungerade inte tillfredställande att använda alla vindmätningar i samma modell och försöka hitta ett passande medelvärde för stabiliteten.  Om vindmätningarna skall delas upp efter rådande stabilitet kommer varje stabilitet kräva en egen modellering vilket betyder att beräkningstiden kommer öka markant. Att simulera skogen i WindSim med en råhetslängd och en nollplansförskjutning visade sig fungera bra. En modellerad vindskjuvning som stämde bra överens med den uppmätta kunde erhållas i en neutral atmosfär och denna modell presterade sammantaget bäst av alla undersökta modeller i den här studien. Det studerade området består övervägande av skog och vindmätningarna som använts är utförda inom skogsområdet. WindSim skogsmodul kan tänkas vara mer användbar och viktig om skog förekommer i begränsade partier och då tänkta vindturbiner inte placeras direkt inom skogsområdet. En förhoppning på CFD-program är att vindmätningar utförda på låg höjd skall kunna användas för att förutse vinden på högre höjder med större noggrannhet jämfört med WAsP. Resultat från den här studien visar dock att det kan vara svårt att uppnå en bra modellerad vindskjuvning i WindSim. Även i WindSim är således viktigt att ha vindmätningar från flera olika höjder för att kunna verifiera modellen mot innan programmet kan förväntas förutse vinden på högre höjder korrekt.    Sammanfattningsvis förefaller en bra inställd WindSim-modell kunna ge en något ökad noggrannhet av extrapolerade vindförhållanden jämfört med WAsP, men om extrapolationer skall göras mellan liknade områden i terrängen, till exempel från en kulle till en annan kulle, är det tveksamt om den lilla ökade noggrannheten ger skäl för den ökade beräkningstiden i WindSim. / An evaluation of wind energy software: a comparison of wind resource calculations made with the software WAsP (linear model) and the CFD software WindSim over a hilly forested area.  Results produced from the wind modeling linear program WAsP were compared with modeling results produced by the CFD program WindSim. The aim was to investigate whether WAsP achieves accurate calculation results over a hilly forested area in Sweden, and if the CFD modeling in WindSim provides more accurate results than WAsP. The performance of each program was evaluated by comparing extrapolated average wind speed data to actual measurements. The study shows that WindSim may achieve an increased accuracy of extrapolated wind conditions compared to WAsP, as well as indicates that a CFD calculation does not automatically provide more reliable extrapolations than linear modeling in WAsP. The accuracy of the WindSim extrapolations was highly dependent on how the model was set up, and hence it may be easier to make errors with WindSim compared to WAsP. A model in WindSim with accurate simulated wind shear did not necessarily mean that the model made good extrapolations of wind conditions horizontally. Furthermore, WAsP was shown to slightly misjudge orographic effects, and when wind measurements are made over hilltops, WAsP most likely overestimates the average wind speed in the lower parts of the terrain.     When a good model was established, WindSim provided slightly more accurate results than WAsP, but if extrapolations are to be made between similar areas in the terrain, for example from one hill to another hill, it is doubtful that the small increase in accuracy gives enough reason for the increased time in calculation required by WindSim.

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2009

Wind farm assessment is a costly and time consuming process when it is planned by traditional methods such as a met mast. Therefore, new models have been established and used for the wind farm assessment to ease the process of wind farm planning. These models are Global-regional models which add to cost efficiency and time saving. There are several types of these models in the market that have different accuracy. This thesis discusses and uses in simulations Global – regional model data outputs from European Centre for Medium-Range Weather Forecasts (ECMWF), Weather Research Forecast WRF and ECMWF, which is currently producing ERA-Interim, global reanalysis of the data-rich period since 1989 .The goal of the master's thesis is to see whether it is useful and efficient to use Global – regional weather model data such as the Era Interim Global Reanalysis Model data for wind assessment by comparing it with the real data series (met mast) located in Maglarp, in the south of Sweden.The comparison shows that in that specific area (hindcast) at Maglarp, in the south of Sweden, very promising results for planning a wind farm for a 100m, 120m and 38m heights.

As wind industry is developing steadily oshore, the wind turbine spacing remainsa key element for maximizing revenues and reducing loading from turbineswake interaction. In the case of relatively close to shore oshore wind farms, orlarge arrays onshore, the turbulence intensity coming from dierent sectors canhave an eect on wake growth and decay. In an attempt to obtain wind featuresat site, some boundary conditions for micro-siting simulation are found, using acommercial RANS ow solver CFD software was used. The approach in this workcould be described more practical than theoretical and could be more useful fordevelopers than pure CFD specialists.By simulating with three dierent roughness length for open sea, with theappropriate and contextual assumptions, for the oshore Lillgrund wind farm,vertical proles and turbulence intensity were extracted from the WindSim softwareat the meteorological mast position and enabled measurement comparison.In a second attempt to compare the eect of the wind and turbulence prolespreviously obtained, a sector of interest is simulated with the actuator disc model.In general, the site conditions over the large-scale domain evaluated by thecommercial software are satisfactory after adjusting the roughness length for theopen sea. The turbulence intensity trend for various in ow angle is capturedby the simulations and computed wind proles are for the most part adequately.A comparison of spring and winter ltered measurements enable discussion uponsome sectors disagreement. As for the small-scale actuator disc model using thedeveloped site conditions, the result is over-estimated by the simulations, especiallyfor the second row downstream.