On the scaling of wind turbine rotors

This paper formulates laws for scaling wind turbine rotors. Although the analysis is general, the article primarily focuses on the subscaling problem, i.e., on the design of a smaller-sized model that mimics a full-scale machine. The present study considers both the steady-state and transient response cases, including the effects of aerodynamic, elastic, inertial, and gravitational forces. The analysis reveals the changes to physical characteristics induced by a generic change of scale, indicates which characteristics can be matched faithfully by a subscaled model, and states the conditions that must be fulfilled for desired matchings to hold. Based on the scaling laws formulated here, the article continues by considering the problem of designing scaled rotors that match desired indicators of a full-scale reference. To better illustrate the challenges implicit in scaling and the necessary tradeoffs and approximations, two different approaches are contrasted. The first consists in a straightforward geometric zooming. An analysis of the consequences of zooming reveals that, although apparently simple, this method is often not applicable in practice, because of physical and manufacturing limitations. This motivates the formulation of scaling as a constrained optimal aerodynamic and structural matching problem of wide applicability. Practical illustrations are given considering the scaling of a large reference 10 MW wind turbine of about 180 m in diameter down to three different sizes of 54, 27, and 2.8 m. Results indicate that, with the proper choices, even models characterized by very significant scaling factors can accurately match several key performance indicators. Additionally, when an exact match is not possible, relevant trends can at least be captured.

On the scaling of wind turbine rotors

This article formulates laws for scaling wind turbine rotors. Although the analysis is general, the article primarily focuses on subscaling, i.e. on the design of a smaller size model mimicking a full-scale machine. The present study considers both the steady-state and transient response cases, including the effects of aerodynamic, elastic, inertial and gravitational forces. The analysis reveals the changes to physical characteristics induced by a generic change of scale, indicates which characteristics can be matched faithfully by a sub-scaled model, and states the conditions that must be fulfilled for desired matchings to hold. Based on the scaling laws formulated here, two different strategies to design scaled rotors are considered: in the first strategy the scaled model is simply geometrically zoomed from the reference full-scale one, while in the second strategy the scaled rotor is completely redesigned in order to match desired characteristics of the full-scale machine. The two strategies are discussed and compared, highlighting their respective advantages and disadvantages. The comparison considers the scaling of a reference 10-MW wind turbine of about 180 m of diameter down to three different sizes of 54, 27 and 2.8 m. Simulation results indicate that, with the proper choices, several key performance indicators can be accurately matched even by models characterized by significant scaling factors.

Standard Change Tracking for XML

XML is generally accepted as the default markup language for structured document and data management systems worldwide. But, in spite of the fact that XML document standards have matured over the past decade and despite its widespread use, XML still has a significant shortcoming that limits its usefulness in this role. It has no native ability to track changes. There is rudimentary support for change tracking in some document formats, but a full solution is not available. The consensus emerging is that this is an XML problem rather than a DITA, DocBook or XHTML problem. A generic change-tracking standard would transform the utility of XML. It would allow documents to be moved from one XML editor to another, complete with change history and the ability to roll back to previous versions; it would allow editing applications to track changes in any XML document type; and software designed to handle change in XML could be applied to many different XML document types. The W3C now has a Community Group (W3C Change Community Group http://www.w3.org/community/change/) looking into developing a standard solution. This paper outlines one proposed solution to this important problem. The purpose of the proposed change tracking format is to represent successive changes or edits to an XML document, typically in one or more editing sessions. This paper describes how such changes may be represented in XML markup or in Processing Instructions. The tracked changes are designed to be used either as an independent addition to a file or integrated into the applicable schema.