Andrew Oldroyd

An eight month test campaign of the Qinetiq ZephIR system : Preliminary results

The Beatrice Windfarm Demonstrator project is a major part of the European Union sponsored DOWNVInD programme (Distant Offshore Wind farms with No Visual Impact iN Demonstrator) that will install two multi megawatt wind turbines (of type REpower 5M) in the Moray Firth Scotland, adjacent to the Beatrice Alpha oil platform, owned and operated by Talisman Energy. As part of the project, a programme has been designed and instigated over the last eight months to thoroughly examine the performance and capabilities of the QinetiQ ZephIR LiDAR system as well as to establish its suitability for being the primary wind data acquisition instrument on the Beatrice project. This paper represents a first look at the results of this programme.

Hub Height Ocean Winds over the North Sea Observed by the NORSEWInD Lidar Array: Measuring Techniques, Quality Control and Data Management

In the North Sea, an array of wind profiling wind lidars were deployed mainly on offshore platforms. The purpose was to observe free stream winds at hub height. Eight lidars were validated prior to offshore deployment with observations from cup anemometers at 60, 80, 100 and 116 m on an onshore met mast situated in flat terrain. The so-called “NORSEWInD standard” for comparing lidar and mast wind data includes the criteria that the slope of the linear regression should lie within 0.98 and 1.01 and the linear correlation coefficient higher than 0.98 for the wind speed range 4–16 m∙s−1. Five lidars performed excellently, two slightly failed the first criterion and one failed both. The lidars were operated offshore from six months to more than two years and observed in total 107 months of 10-min mean wind profile observations. Four lidars were re-evaluated post deployment with excellent results. The flow distortion around platforms was examined using wind tunnel experiments and computational fluid dynamics and it was found that at 100 m height wind observations by the lidars were not significantly influenced by flow distortion. Observations of the vertical wind profile shear exponent at hub height are presented.

The Myres Hill remote sensing intercomparison study: preliminary results

Two remote sensing techniques (SODAR and LIDAR) have been developed for measuring wind speed and turbulence from ground level up to altitudes of 300 m or higher. Although originally developed in the defence sector, these techniques are now generating considerable interest in the renewable energy and meteorological sectors. Despite the benefits of these instruments they are not yet generally accepted for due diligence measurements by wind energy developers and financial institutions. There is a requirement for a series of independent assessments of these new metrology techniques, comparing their measurements with the approved cup-type anemometer readings. This is being addressed at TUV NELs Myres Hill wind turbine test site in a measurement programme supported by the DIUS National Measurement Systems Measurement for Innovators scheme and a consortium of 21 industrial collaborators. Data from SODAR and LIDAR systems are being compared with results from cup-type anemometers mounted at different heights on an 80m meteorological mast. An ultrasonic sensor is also mounted on the mast. The objective of the test programme is to assess the effectiveness of SODAR and LIDAR wind speed measurement techniques under different operating regimes and atmospheric conditions. Results from the measurements will provide definitive data on the performance of the remote wind speed sensing techniques under test on complex terrain typical of many wind farm sites. Preliminary measurements based on data acquired during the initial measurement campaign are presented.

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

Abstract 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.

Particle image velocimetry studies of bubble growth and detachment by high-speed photography

An understanding of bubble flows is important in the design of process equipment, particularly in the chemical and power industries. In vapor-liquid processes the mass and heat transfer between the phases is dominated by the liquid-vapor interface and is determined by the number, size, and shape of the bubbles. For bubble flows these characteristics are often controlled by the generation mechanisms and, since bubble flows are often generated at an orifice, it is important to determine the controlling parameters which dictate how bubbles grow and detach. For bubbles growing at orifices the liquid displacement is an important feature and affects the pressure distribution acting on the bubble and the heat and mass transfer that may occur at the bubble interface. Therefore, in this study, the characteristics of the liquid velocity field are studied experimentally using Particle image Velocimetry (PIV) during growth, detachment and translation of a bubble being generated at an orifice supplied with a constant mass flow rate of air. The process is transient and occurs over a period of approximately 50 msecs. In order to map the transient flow field a combination of high speed cine and cross correlation PIV image processing has been used to determine the liquid velocity vector field during the bubble growth process. The paper contains details of the PIV technique and presents several of the velocity vector maps calculated.