Optimizing Dual-Doppler Lidar Measurements of Surface Layer Coherent Structures with Large-Eddy Simulations


Book Description

Coherent structures are patterns in the wind field of the atmospheric boundary layer. The deployment of two scanning Doppler lidars facilitates the measurement of the horizontal wind field, but the inherent averaging processes complicate an interpretation of the results. To assess the suitability of this technique for coherent structure detection large-eddy simulations are used as a basis for virtual measurements, and the effects of the lidar technique on the wind field structure are analyzed.




Optimizing Dual-Doppler Lidar Measurements of Surface Layer Coherent Structures With Large-Eddy Simulations


Book Description

Coherent structures are patterns in the wind field of the atmospheric boundary layer. The deployment of two scanning Doppler lidars facilitates the measurement of the horizontal wind field, but the inherent averaging processes complicate an interpretation of the results. To assess the suitability of this technique for coherent structure detection large-eddy simulations are used as a basis for virtual measurements, and the effects of the lidar technique on the wind field structure are analyzed. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.




Coherent Doppler Wind Lidars in a Turbulent Atmosphere


Book Description

Radiophysical tools for measuring atmospheric dynamics include sodars, Doppler radars, and Doppler lidars. Among these, coherent Doppler lidars (CDLs) have been considered the best for remote measurement of wind turbulence. This is important not only for understanding the exchange processes in the boundary layer, but also in the applied aspect, such as aviation safety. CDLs significantly extend possibilities of experimental investigation of not only wind turbulence, but also coherent structures such as aircraft wake vortices. The authors of this book conducted field tests of the developed methods of lidar measurements of the wind velocity, atmospheric turbulence parameters, and aircraft wake vortices. This valuable resource, containing over 500 equations based on original results from the authors’ work, gives professionals a comprehensive description of the operating principles of continuous wave and pulsed coherent Doppler lidars. This book studies the possibilities of obtaining information about wind turbulence from data measured by continuous wave and pulsed CDLs. The procedures for estimation are described, as well as algorithms for numerical simulation. Results on the vortex behavior and evolution are then presented.




Evolution Within the Atmospheric Boundary Layer of Coherent Structures Generated by Wind Turbines


Book Description

Wind turbine wakes undergo complex dynamics varying as a function of the incoming wind conditions, which are modulated by the atmospheric static stability and terrain characteristics. Accurate evaluation of the wind velocity components over the rotor disc represent the relevant input for the wind turbine aerodynamics. Power extraction exerted by the turbines on the atmospheric boundary layer leads to the generation of wind turbine wakes, which are flow regions characterized by a velocity deficit and the presence of coherent vorticity structures evolving downstream. Therefore, wind turbulence and dynamics of these vorticity structures produced by utility-scale wind turbines need to be characterized accurately. In this work, a field measurement campaign is described where different remote sensing instruments were assessed to retrieve the wind velocity components with different levels of accuracy. This campaign provided an unique opportunity to retrieve the wind velocity components with different technologies and perform inter-comparison studies in terms of both first and second order turbulent statistics. The results show that Doppler LiDARs have capability to retrieve mean wind speed with high accuracy and turbulent fluctuations with certain limitations. Besides the development of experimental measurement techniques for probing vorticity dynamics within the atmospheric boundary layer, research endeavors were focused in performing analyses based on Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) to identify coherent structures within wind turbine wakes. Different data-sets, which include Large Eddy Simulation (LES) of single wind turbine with and without tower and nacelle were analyzed. Careful analysis enabled the detection of different instability modes of the helicoidal tip vortices, namely elliptical instability and leap-frogging due to the self rotation and mutual induction among the vortex cores.










Airborne/Space-Based Doppler Lidar Wind Sounders Sampling the Pbl and Other Regions of Significant Beta and U Inhomogeneities


Book Description

This final report covers the period from April 1994 through March 1998. The proposed research was organized under four main tasks. Those tasks were: (1) Investigate the vertical and horizontal velocity structures within and adjacent to thin and subvisual cirrus; (2) Investigate the lowest 1 km of the PBL and develop algorithms for processing pulsed Doppler lidar data obtained from single shots into regions of significant inhomogeneities in Beta and U; (3) Participate in OSSEs including those designed to establish shot density requirements for meso-gamma scale phenomena with quasi-persistent locations (e.g., jets, leewaves, tropical storms); and (4) Participate in the planning and execution of an airborne mission to measure winds with a pulsed CO2 Doppler lidar. Over the four year period of this research contract, work on all four tasks has yielded significant results which have led to 38 professional presentations (conferences and publications) and have been folded into the science justification for an approved NASA space mission, SPARCLE (SPAce Readiness Coherent Lidar Experiment), in 2001. Also this research has, through Task 4, led to a funded proposal to work directly on a NASA field campaign, CAMEX III, in which an airborne Doppler wind lidar will be used to investigate the cloud-free circulations near tropical storms. Monthly progress reports required under this contract are on file. This final report will highlight major accomplishments, including some that were not foreseen in the original proposal. The presentation of this final report includes this written document as well as material that is better presented via the internet (web pages). There is heavy reference to appended papers and documents. Thus, the main body of the report will serve to summarize the key efforts and findings. Emmitt, Dave Marshall Space Flight Center WIND VELOCITY MEASUREMENT; DOPPLER RADAR; OPTICAL RADAR; REMOTE SENSING; PLANETARY BOUNDARY LAYER; METEOROLOGICAL RADAR; ATMOSPHERIC S...