“Two cases were considered: a worst-case orientation with one of the blades in the vertical position, and a low-backscatter case with one blade tip pointed at the radar and the other two blades oriented away.”
Editor’s note: Remcom, a developer of electromagnetic modeling and simulation software, recently released a whitepaper titled “Modeling the Effects of Wind Turbines on Radar Returns.” In it, authors R. Ryan Ohs, Gregory J. Skidmore, and Dr. Gary Bedrosian use Remcom’s XGtd software to predict how wind turbine interference affects nearby radar installations. The abstract and introduction of the white paper are presented here. For the full paper, click here.
Abstract
Wind turbines located near radar installations can significantly interfere with a radar’s ability to detect its intended targets. In order to better understand and mitigate the adverse effects of wind turbines on radar, the government and wind farm community need tools that can be used to analyze the radar returns from wind turbines. Remcom’s XGtd software is a high frequency solver capable of calculating the radar cross section of electrically large objects. In this paper, interference from wind turbines is predicted using XGtd simulations and new post-processing algorithms that calculate Doppler shift quantities based on points of interaction with the rotating turbine blades. Results of the analysis are used to calculate the bistatic radar cross section and Doppler shift from two blade orientations. In addition, the time-varying monostatic radar cross section and Doppler shift for a single wind turbine are analyzed and shown to agree well with measured data from actual wind turbines.
Introduction
Several studies and reports have documented the adverse effect that wind turbines and wind farms have on radar returns, including long range radar, air traffic control, and weather radar. Their impact can be summarized by three major effects:
- Large Size: wind turbine heights can reach 198 meters, including max blade height. This results in large radar cross-section, and potential for detection at long ranges.
- Rotational velocity similar to aircraft: with rotor diameters between 40 and 126 meters spinning at 12- 34 RPM (typically at the lower end for larger blades), blade tip velocities can exceed 150 Knots, comparable to a slower aircraft such as a Cessna.
- Wind Farm Sizes: with the number and size of farms growing (some now exceed 1,000 turbines), potential radar clutter can be very significant.
As a result of this problem, many wind farm projects are delayed or denied pending long-term assessments of radar impacts. The New York Times recently reported the results of a survey by the American Wind Energy Association (AWEA) indicating that approximately 9,000 megawatts of wind projects were delayed or abandoned in 2009 due to radar concerns by the military and FAA, and that this was nearly equal to the amount of wind capacity actually built that year. Two recent examples include a 130 wind turbine project in Nantucket Sound and a 300- plus wind turbine project in Oregon. As future wind farm developers attempt to mitigate the problem with new designs, special materials, and relocation of problematic wind turbines, there will be a need for accurate and reliable modeling and simulation of the wind turbine radar returns.
In this paper, we present the results of an effort to develop a new capability to model the impact of wind turbines on radar signals, including the complex and time-varying nature of the impact of spinning turbine blades on radar returns. Our approach builds on Remcom’s existing XGtd software, adding new specialized post-processing capabilities to handle the unique nature of Doppler shift for rotating turbine blades. The study includes analysis of turbine blade materials and the impact of varying blade positions on RCS and Doppler shift, concluding with a comparison between predicted and measured Doppler and RCS for a wind turbine with blades in motion. The ultimate objective is to demonstrate a new capability to accurately model the impact of wind turbines on radar returns.
By: R. Ryan Ohs, Gregory J. Skidmore and Dr. Gary Bedrosian
Remcom
www.remcom.com/
Filed Under: News, Software, Turbines
