SOLICITATION NOTICE
A -- Computational Aeroacoustic Analysis of Wind Turbines
- Notice Date
- 8/7/2002
- Notice Type
- Solicitation Notice
- Contracting Office
- Department of Energy, National Renewable Energy Laboratory - Midwest Research Institute (DOE Contractor), National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO, 80401
- ZIP Code
- 80401
- Solicitation Number
- RAM-2-32246
- Response Due
- 8/30/2002
- Point of Contact
- Neil Wikstrom, Contract Administrator, Phone 303-384-6960, Fax 303-384-6901, - Laura Hughes, Subcontract Administrator, Phone 303-384-7018, Fax 303-384-6901,
- E-Mail Address
-
neil_wikstrom@nrel.gov, laura_hughes@nrel.gov
- Description
- The National Renewable Energy Laboratory (NREL) National Wind Technology Center (NWTC) has undertaken a comprehensive, multi-year research program on the subject of wind turbine aeroacoustics. The goals of this effort are to develop a thorough understanding of the mechanisms for generation, propagation, and mitigation of wind-turbine-blade acoustic emissions; to document and disseminate this information in the form of NREL reports, technical papers, seminars and colloquia; and to support the U.S. wind industry in applying rational acoustic-design principles to the development and deployment of advanced wind turbines. Activities in fiscal year 2000-2001 included a review of previous work, outreach to potential research collaborators, and long-range planning and budgeting. A successful workshop on ?Fundamental of Aeroacoustics with Application to Wind Turbine Noise? was conducted at the NWTC in July 2001. It assembled many wind energy researchers and exposed them, through a series of invited lectures, to the current state of knowledge regarding wind turbine aeroacoustics. Participants also provided their comments and suggestions on NREL?s preliminary aeroacoustics research plan. Several projects were initiated in fiscal year 2001-2002. Wind tunnel tests are underway that will measure the aerodynamic and aeroacoustic performance of 6-8 wind turbine airfoils, with emphasis on those profiles currently deployed or under development. In field tests at the NWTC, acoustic measurements of five small wind turbines were conducted and four other configurations are currently being tested. A review of semi-empirical acoustic prediction methods was completed, and design-optimization codes are being programmed which employ the best features of this previous work. Subsequently, we will attempt to incorporate new methods to analyze specific noise sources. Lastly, a new initiative, which is the subject of this solicitation, is being undertaken to develop computational aeroacoustic (CAA) codes to analyze wind turbine blade noise sources as impacted by important configuration variables. In contrast to the semi-empirical codes that aggregate various airfoil self-noise sources (inflow turbulence, flow separation, trailing-edge bluntness, boundary-layer trailing-edge interaction, and blade-tip vortex), these CAA methods are seen as implementations of the fundamental equations of motion, supplemented by appropriate acoustic analogy. We expect they will capture the basic flow physics and resulting acoustic phenomena, thereby allowing the investigation of noise sources and potential mitigation measures. It is understood that this work is extremely complicated and computationally challenging. Nevertheless, recent progress in the application of CAA methods to propeller, helicopter and airframe noise offers encouragement that application to wind turbine noise will eventually yield useful results. There has been some computational fluid dynamic (CFD) analysis of wind turbines, but virtually no sustained effort in CAA analysis. Therefore, it is unlikely that experienced CAA researchers also have complementary wind energy experience. Because wind turbine aerodynamics per se is quite anomalous, this lack of contemporaneous experience is a potential impediment to research progress. In recognition of this situation, NREL has formulated a two-phase approach for the project. In Phase I, those subcontractors that are selected for award will become familiar with previous research in wind turbine aeroacoustics (and relevant aerodynamics). NREL will assist by providing a comprehensive reference list and copies of documents that are out of print or difficult to procure. With the benefit of the perspective gained by reviewing this previous work, subcontractors will formulate a computational approach to a particular aeroacoustic problem. To enhance the likelihood of success, subcontractors may form teams that, collectively, have the requisite experience in CAA and wind turbine aerodynamics. Researchers at universities, government laboratories and/or private industry are welcome participants. At the conclusion of Phase I, subcontractors will prepare an Interim Report and present their proposed computational approach at an Interim Project Review Meeting attended by key project participants and the NREL review team. The information provided will be used to determine if the proposed approach has sufficient merit to warrant continuation of the project. This decision will be based upon technical accomplishments and programmatic issues. Those subcontractors selected for Phase II will proceed to implement their proposed computational method and use it for selected benchmark validation studies. It is generally believed that the most prominent wind turbine aeroacoustic noise source is the interaction of a turbulent boundary layer with the airfoil (blade) trailing edge. Some airfoils, however, are particularly susceptible to inflow turbulence and may have significant emissions from the leading edge. For this reason, care must be taken in selecting airfoil shape and other configuration variables for downwind turbines. In this case, turbine blades experience significant inflow turbulence as they fly through the tower wake. If leading and trailing edge noise is minimized, blade tip noise may become an important mechanism when trying to reduce acoustic signatures to their lowest possible levels. Researchers are uncertain of the exact mechanism for this blade tip noise. Some speculate it is the result of the interaction of the tip vortex and the trailing edge. Others believe it results from instabilities in the viscous shear layer between the vortex and free stream. With these fundamentals in mind, NREL has identified several wind turbine aeroacoustic problems of interest. Offerors may propose to work on one or more of these problems, or they may propose to work on a different problem if it addresses the specified goals and objectives of the statement of work. Airfoil self noise ? Several researchers have used experimental results to develop semi-empirical methods to predict leading and trailing edge noise. Recent studies investigated a more robust computational approach that may eventually permit the analysis of airfoils of arbitrary shape. Such a method would be useful in evaluating airfoils for use on wind turbines, perhaps obviating time consuming and expensive wind tunnel tests Blade tip noise ? It is desirable that arbitrary blade tip shapes be modeled and their acoustic emissions estimated, at least in a relative sense. Wind turbine blades operate in extremely complex flow situations, with unsteadiness due to inflow turbulence, wind shear, pitching blades, and rotational dynamics. Although it is unlikely that the precise physical properties of this complex flow can be predicted, it may be possible to develop a simplified flow model with estimates of the resulting acoustic emissions. This would allow the detailed comparison of different shapes with the goal of selecting those that produce the lowest acoustic emissions. Rotating blades ? A more complex effort involves the modeling of the entire rotor, including twist, taper and airfoil shapes. Further refinement would involve the use of a turbulent inflow model. This approach has been used (with varying degrees of success) in computational fluid dynamic (CFD) models to predict blade aerodynamic forces. Extending this approach to include predictions of the aeroacoustic field is an extremely challenging problem, but one that is worth attempting. Full system model ? A logical extension of the rotating blades (rotor) problem is to model the complete wind turbine, including the tower. This is particularly important for downwind turbines, where the flow field is made more complex by the shedding of coherent vortices in the tower wake. This is a recognized problem that has discouraged the development of downwind turbines, which have a reputation for broadband ?tower shadow? noise as well as low-frequency impulsive noise. The value of a CAA model of this situation is in its potential use to adjust configuration variables to avoid these problems. The purpose of this pre-solicitation notice is to obtain an indication of the level of interest by potential participants. Therefore, expressions of interest are sought from potential respondents to the forthcoming Request for Proposal (RFP). Expressions of interest should include 1) the names, addresses, telephone numbers, facsimile numbers, and email addresses of the primary contact persons; and 2) a statement indicating that you request access to the RFP document. Expressions of interest should be received at NREL no later than August 30, 2002. This is not a Request for Proposals.
- Record
- SN00135065-W 20020809/020808084729 (fbodaily.com)
- Source
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