Comparison of Zephir and Windcube measurements in the same complex flowfield

Offshore wind is the major growth area in the wind industry sector today. However, there remains a key, fundamental missing element - a thorough understanding of the offshore wind climatology and likely wind resource. In 2008 the EU FP7 funded project NORSEWInD was created with a remit to deliver offshore wind speed data at a nominal project hub height acquired in offshore locations in the North, Baltic and Irish seas. Part of the NORSEWInD project is the use of LiDAR remote sensing (RS) systems mounted on offshore platforms to measure wind velocity profiles. The data acquired from the offshore RS measurements are fed into a large wind speed dataset suitable for use by the wind industry. One significant problem identified was the effect of platform interference effects on the RS data. Another significant effect on the quality of the data produced was the method by which the wind speed and direction was acquired as the method by which LiDARs measure the wind vector is significantly different from a point measurement. Whilst this will have no effect in a homogeneous flow field if there is significant flow distortion, which might be found in close proximity to a large structure or in complex terrain, then the effect of this spatially averaged measurement might cause a significant deviation from a point measurement. This paper reports on the modelling of two different types of LiDAR, the Natural Power ZephIR and the Leosphere Windcube, in a computational fluid dynamics simulation of the flow around a large offshore structure. The paper discusses the difference in the measured wind vector when compared to a point measurement at the measurement height

NORSEWInD Data Report and Correction Data for Berlengas : NORSEWInD Report UoSNW026

The flow field over Berlengas has been simulated on both a sub scale wind tunnel model in a low speed wind tunnel and in a computational fluid dynamics simulation. The CFD model has been validated by the results of the wind tunnel simulation. A simulation of measurements that would be made by a ZephIR LiDAR mounted on the island has been undertaken using the CFD results A method by which the distortion to the flow field over an offshore platform, measured by either a met mast or LiDAR, can be corrected back to the free stream value has been presented and verified. Correction factors have been calculated and are included in the appendix to this report. Based on the CFD and wind tunnel data it is was evident that significant flow distortion exists up to 425m above the island

Fluent User Defined Function: WindCube_comp_sim : NORSEWInD Report UOSNW013

This report describes the Fluent User Defined Function WindCube_comp_sim used to interrogate FLUENT a Fluent data set by simulating the operation of a LeoSphere Windcube LiDAR. The user defined function is contained in the program lidar.c (version 1.06) which has been written in the C programming language. This report contains a listing of the user defined function, describes its method of operation and presents a validation of the analysis process. The report also includes a description of the output data file formats

User Defined Function: lidar_3D : NORSEWInD Report UoSNW006

This report describes the User Defined Function Lidar_3D used to interrogate FLUENT data files to provide the relevant data for the MathCAD LiDAR simulation program. The UDF was written in the C programming language and compiled using Microsoft visual studio 2008. This report contains a listing of the program (version 1.03). This report contains a description of the methodology required to compile the UDF so that it may be called by an "execute on demand" call from FLUENT. The report also includes a description of the input and output data file formats

Computational and Experimental Study on the effect of flow field distortion on the accuracy of the measurements made by anemometers on the Fino3 Meteorological mast

This paper reports on the experimental and computational modelling of the flow field around the FINO3 mast and provides an estimate of the amount of distortion that might be expected on instrumentation mounted on such a large structure. The open source C++ toolbox OpenFOAM was used for the CFD analysis. In order to validate the CFD model, experimental work was carried out in an open section wind tunnel using hot wire anemometry to measure the velocity profile around a sub-scale model of part of the FINO3 mast. The experimental data are in good agreement with the data from the CFD simulatio

Feasibility Study of using a LiDAR in the complex flowfield of an offshore platform, to measure wind shear profile.

Offshore wind is the major growth area in the wind industry sector today. However, there remains a key, fundamental missing element - a thorough understanding of the offshore wind climatology and likely wind resource. In 2008 the EU FP7 funded project NORSEWInD was created with a remit to deliver offshore wind speed data at a nominal project hub height acquired in offshore locations in the North, Baltic and Irish seas. Part of the overall NORSEWInD project was the use of LiDAR remote sensing (RS) systems mounted on offshore platforms to measure wind velocity profiles at a number of locations offshore. The data acquired from the offshore RS measurements was fed into a large and novel wind speed dataset suitable for use by the wind industry. The data was also fed into key areas such as forecasting and MESOSCALE modelling improvements. One significant problem identified was the effect of platform interference effects on the RS data. Therefore, part of the fundamental research incorporated into the NORSEWInD project was an investigation into the possible extent and effect of the interference on the measured data from the various mounting platforms. This paper reports on the Computational Fluid Dynamics (CFD) modelling of the wind flows over the platforms and the verification of the CFD models by the use of sub scale wind tunnel models employing three dimensional Constant Temperature Anemometers (CTAs) to measure local velocity vector data

Feasibility study for estimating the offshore shear layer from on shore measurements

This paper presents an open source computational fluid dynamics (CFD) study of air flow over a complex terrain. The open source C++ toolbox OpenFOAM has been used for the CFD analysis and the terrain considered is a scale model of Berlengas Island, which lies close to the Portuguese coast. In order to validate the CFD model, experimental work has been carried out in an open-section wind tunnel using hot-wire anemometry to measure the wind profiles above the island. In the majority of cases, the OpenFOAM CFD solutions show very good agreement with the experimental wind profile data, confirming that open source CFD solutions are possible for environmental flows over complex terrain. Such an analysis demonstrates the feasibility of estimating offshore boundary layer effects from onshore measurements

Measurement and simulation of the flow field around a triangular lattice meteorological mast

The international standard IEC 61400-12-1 “Wind turbines – Part 12-1: Power performance measurements of electricity producing wind turbines” aims to provide a uniform methodology that will ensure consistency, accuracy and reproducibility in the measurement and analysis of power performance by wind turbines. Annex G of this standard provides a methodology for the appropriate arrangement of instruments on the meteorological mast to ensure accurate measurement. For cup anemometers it provides recommendations about their location relative to the mast so that the effect of mast and boom interference on their output may be minimised. These recommendations are given for both tubular masts and lattice masts.This paper compares the flow distortion predicted by the IEC standard and the results of a 3D Computational Fluid Dynamics (CFD) simulation of a triangular lattice mast. Based on the results of wind tunnel and CFD simulation it was found that the flow distortion surrounding the lattice mast was over predicted by the method suggested in appendix G of IEC61400-12-1. Using the CFD data it was possible to determine, for a range of flow directions and mast heights, the distance from the mast that anemometers would need to be in order to be outside the flow distortion field

Measurement and simulation of the flow field around a triangular lattice meteorological mast

The international standard IEC 61400-12-1 “Wind turbines – Part 12-1: Power performance measurements of electricity producing wind turbines” aims to provide a uniform methodology that will ensure consistency, accuracy and reproducibility in the measurement and analysis of power performance by wind turbines [1]. Annex G of this standard provides a methodology for the appropriate arrangement of instruments on the meteorological mast to ensure accurate measurement. For cup anemometers it provides recommendations about their location relative to the mast so that the effect of mast and boom interference on their output may be minimised. These recommendations are given for both tubular masts and lattice masts. This paper compares the flow distortion predicted by the IEC standard and the results of a 3D Computational Fluid Dynamics (CFD) simulation of a triangular lattice mast. Based on the results of wind tunnel and CFD simulation it was found that the flow distortion surrounding the lattice mast was over predicted by the method suggested in appendix G of IEC61400-12-1. Using the CFD data it was possible to determine, for a range of flow directions and mast heights, the distance from the mast that anemometers would need to be in order to be outside the flow distortion field

A CFD technique for estimating the flow distortion effects on LiDAR measurements when made in complex flow fields

The effect of flow distortion on the measurements produced by a LiDAR or SoDAR in close proximity to either complex terrain or a structure creating localised flow distortion is difficult to determine by analytical means. Also, as LiDARs and SoDARs are not point measurement devices, the techniques they employ for velocity measurements leads to complexities in the estimation of the effect of flow distortion on the accuracy of the measurements they make. This paper presents a method by which the effect of flow distortion on measurements made by a LiDAR in a distorted flow field may be determined using computational fluid dynamics. The results show that the error created by the flow distortion will cause the vector measured by a LiDAR to differ significantly from an equivalent point measurement. However, the results of the simulation show that, if the LiDAR is being used to measure the undisturbed flow field above a structure which creates highly localised flow distortion, the LiDAR results are less affected by the distortion of the local flow field than data acquired by a point measurement technique such as a cup anemometer