Patent Publication Number: US-2007104934-A1

Title: Lightweight nacelle for turbines and methods for making same

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to methods for manufacturing of nacelles for turbines and for nacelles made by such methods. Configurations of the present invention are applicable to many different types of turbines, and are particularly advantageous for wind turbines.  
      At least one known nacelle configuration introduces substantial weight at the top of each wind turbine tower. The high weight at the top of the wind tower tends to increase cost and decrease reliability and life of wind turbines. In addition, this nacelle configuration includes a large cutout to accommodate a power shaft. This cutout introduces flexibility to the structure and requires local reinforcing and/or stiffening members.  
     BRIEF DESCRIPTION OF THE INVENTION  
      One aspect of the present invention therefore provides a lightweight nacelle that includes a plurality of wound carbon fibers embedded in an epoxy matrix around a hollow region, and having rounded corners.  
      Another aspect of the present invention provides a method for making a nacelle that includes winding a plurality of carbon fibers embedded in an epoxy matrix around a mandrel.  
      It will thus become apparent that configurations of the present invention provide a low-cost, structurally efficient nacelle.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a pictorial schematic drawing representing the winding of carbon fibers embedded in an epoxy matrix as in some configurations of the present invention.  
       FIG. 2  is a pictorial drawing of a nacelle representative of some configurations of the present invention.  
       FIG. 3  is a partial planar cross-section of the nacelle of  FIG. 2  taken in plane  3  of  FIG. 2 .  
       FIG. 4  is a configuration of wind turbine using the nacelle of  FIGS. 2 and 3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Some configurations of the present invention utilize an automated process in which a composite pre-impregnated tape/tow winding is used to fabricate a pitch-based carbon fiber epoxy nacelle for turbine engines. Pitch-based carbon fibers are inexpensive and readily available in a wide variety of strengths and stiffness, thereby allowing the structural response of the nacelle to be tuned to any of various preselected design criteria.  
      In some configurations of the present invention and referring to  FIG. 1 , carbon fibers embedded in a low-cost epoxy matrix in either tape or tow format are wound around a mandrel. Suitable carbon fibers include, but are not necessarily limited to, pre-impregnated pitch-based carbon fibers. Fiber architecture can be tuned for predetermined strength and stiffness requirements. For example, the fibers can be wound +/−10-degree orientation for axial strength and stiffness (0-degrees is not possible with the winding process due to the winding poles), ±/−45-degree orientation for torsional stiffness and strength, and 90-degree orientation for lateral strength and stiffness. A thicker, dome (i.e., pole) region is a byproduct of some configurations of the present invention and provides natural reinforcement for the shaft cutout. Also, in some configurations of the present invention, rounded corners result from limitations in composite material winding. These rounded corners are also advantageous because they result in aerodynamic surfaces that are less likely to produce flow separation or vortex trails, which are vibration drivers, in high wind gusts. The winding can be performed using an automated process to produce a lighter weight, higher quality, nacelle structure due to well-controlled manufacturing conditions.  
      Thus, and referring to  FIG. 1 , some configurations of the present invention comprise a lightweight nacelle  10 . Nacelle  10  itself comprise a plurality of carbon fibers  12  embedded in an epoxy matrix  14  and wound around a mandrel  16 , which is subsequently removed to leave behind a hollow region  60  (best seen in  FIGS. 2 and 3 ). Mandrel  16  may comprise an inflatable elastomeric to facilitate removal. Wound carbon fibers  12  in some configurations are pre-impregnated, pitch-based carbon fibers, which may be selected to satisfy predetermined strength requirements, stiffness requirements, or both.  
      Carbon fibers  12  in some configurations include fibers oriented to provide axial strength and stiffness. For example, in some configurations, fibers  12  include fibers  50  that are wound in a θ=±10 degree orientation. In some configurations, carbon fibers  12  include fibers oriented to provide torsional stiffness and strength, which may, for example, include fibers  52  wound in a θ=±45 degree orientation. And in some configurations, fibers  12  include fibers  54  oriented to provide lateral strength and stiffness. For example, nacelle  10  may include fibers  12  wound at a 90 degree orientation.  
      In many configurations and referring to  FIGS. 2 and 3 , nacelle  10  has a thickened dome region  18  and rounded corners  20 .  
      Referring to  FIG. 4 , nacelle  10  configurations of the present invention are particularly suitable for use in wind turbines  22  which have a rotor  24  having a least one blade  26 , and a generator (not shown, but inside nacelle  10 ). In many configurations, three blades  26  are provided for aerodynamic efficiency.  
      In some configurations, a method for making a nacelle  10  is provided that comprises winding a plurality of carbon fibers  12  embedded in an epoxy matrix  14  around a mandrel  16 . The plurality of carbon fibers  12  can comprise pre-impregnated, pitch-based carbon fibers. In some configurations, the method further includes preselecting the fibers in accordance with predetermined strength requirements, stiffness requirements, or both.  
      The winding a plurality of carbon fibers  12  in some configurations further comprises orienting and winding fibers to provide axial strength and stiffness. For example, orienting and winding the fibers to provide axial strength and stiffness can comprise winding the fibers in a ±10 degree orientation.  
      Winding a plurality of fibers  12  in some configurations comprises orienting and winding fibers to provide torsional stiffness and strength. For example, orienting and winding fibers to provide torsional stiffness and strength can comprise winding the fibers in a ±45 degree orientation.  
      Winding a plurality of fibers  12  ins some configurations comprises orienting and winding fibers to provide lateral strength and stiffness. For example, orienting and winding fibers to provide lateral strength and stiffness can include winding fibers in a 90 degree orientation.  
      While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.