OU BLISS sponsors seminars generally every other Friday from 3-4 pm in room 5600 of the National Weather Center. Members of BLISS, as well as outside guests, will speak on a variety of topics related to boundary layer research, including fieldwork, laboratory simulations, and more. All are welcome.
Jennifer Newman: Optimizing Lidar Scanning Strategies for Wind Energy Turbulence Measurements
Lidars have recently emerged as a valuable tool for wind resource assessment. Unlike cup anemometers on a traditional meteorological tower, which have fixed measurement heights and are limited by the tower height, lidars can measure wind speeds across an entire turbine rotor disk and can be easily deployed at different locations around a wind farm to examine spatial variability of the wind resource. The ability of lidars to accurately measure mean wind speeds has already been well-documented in the literature. However, several questions remain regarding the measurement of turbulence with lidars. Turbulence has profound effects on the amount of power produced by a turbine and can also impact loads on the turbine blades. Thus, lidars must be able to accurately measure turbulence in order to be seen as a viable alternative to meteorological towers.
Most lidar scanning strategies were designed to measure mean wind speeds, not turbulence, and the scanning strategy used by the lidar can actually induce errors in the lidar-measured turbulence. Lidars that use a scanning circle to deduce the three-dimensional wind field require the assumption that the flow is horizontally homogeneous across the lidar scanning circle; when this assumption is invalid, errors are induced in the turbulence components. In addition, lidar measurements from these techniques are affected by variance contamination, which occurs when measurements from different beam positions are combined to calculate the variance of the different velocity components.
In order to improve variance estimates by lidars, two new techniques were evaluated: 1) multi-lidar scanning strategies, which eliminate the use of a scanning circle and 2) the six-beam scanning strategy, which was designed to mitigate variance contamination. Multi-lidar scanning strategies were evaluated at the Southern Great Plains Atmospheric Radiation Measurement site with three research-grade scanning lidars, while the six-beam strategy and two commonly used lidar scanning strategies were evaluated at the Boulder Atmospheric Observatory, which featured a heavily instrumented 300-m tower. Results indicate that the majority of variance errors occur under unstable conditions, when the lower boundary layer is horizontally heterogeneous and variance contamination can overcome the effects of volume averaging. Methods to improve variance estimation under unstable conditions are discussed and evaluated using co-located lidar and sonic anemometer data. In addition, the performance of the two new techniques under different stability conditions is discussed.
03/06/15 - Jennifer Newman: Optimizing Lidar Scanning Strategies for Wind Energy Turbulence Measurements
03/13/15 - Larissa Reames: Title TBA
03/27/15 - Jing Liu: Title TBA
04/10/15 - Jinxin Wang: Title TBA
04/17/15 - Paul Flanagan: Title TBA
04/24/15 - William (Greg) Blumberg: Title TBA
01/16/15 - Dr. Alan Shapiro: A Unified Theory for the Great Plains Nocturnal Low-Level Jet
12/12/14 - Chiel van Heerwaarden: A comparison of heterogeneously heated convective boundary layers with fixed flux and fixed temperature boundary conditions
11/21/14 - Cedrick Ansorge: Study of Stabily Stratified Bounday Layers using Turbulent Ekman Flow
10/31/14 - Tim Bonin: Thermal and Turbulence Characteristics of the Southern Great Plains Nocturnal Boundary Layer
10/24/14 - Mike Buban: The formation of small-scale atmospheric vortices via horizontal shearing instability
10/17/14 - Dr. Alan Shapiro: On the lower boundary condition for pressure in numerical simulations of boundary layer flows driven by surface buoyancy variations
09/26/14 - Dr. Jeremy Gibbs: Step Brothers 2: Revisiting Surface Heat-Flux and Temperature Boundary Conditions in Models of Stably Stratified Boundary-Layer Flows
04/25/14 - Stephen Castleberry: Evaluation of a Microwave Radiometer Thermodynamic Retrieval Algorithm
04/18/14 - Charlotte Wainwright: Sampling the boundary layer with a sodar simulator
04/11/14 - Jinxin Wang: Urban effects on precipitation: a literature review and climatology study for Dallas-Fort Worth
04/04/14 - Kerstin Schaefer: Validation of the mesoscale transport and fluid model METRAS for Berlin based on a measurement campaign in summer 2012
03/28/14 - Nathan Anderson: Vertical Velocity Turbulence Profiles Measured by Two Horizontally Separated Doppler Lidars
02/21/14 - Larissa Reames: The WRF-simulated effects of the Oklahoma City urban area on its environment on the dynamics of a simulated supercell thunderstorm
02/14/14 - Dr. Alan Shapiro: New similarity model solutions for boundary-layer flows
01/31/14 - Dr. Petra Klein: Scaling of Mean Flow and Turbulence in the Urban Canopy Layer
01/17/14 - Jennifer Newman: Optimizing Lidar Scanning Strategies for Turbulence Measurements