Blade for a rotary machine

Abstract

A blade for use in rotary machines such as a wind turbine blade has a plurality of dimples distributed over an area of a low pressure or suction surface of the blade which preferably extends from immediately adjacent to a leading edge of the blade at least partially towards a rear or trailing edge of the blade.

What is claimed is: 
     
         1 . A blade having a plurality of dimples distributed over an area of at least one surface of the blade which extends from at or adjacent a leading edge of the blade at least partially towards a rear edge of the blade. 
     
     
         2 . A blade according to  claim 1 , comprising an aerofoil blade. 
     
     
         3 . A blade as claimed in  claim 1 , comprising a low pressure or suction surface and an opposed high pressure or pressure surface, and the dimples are distributed over at least an area of the low pressure surface. 
     
     
         4 . A blade as claimed in  claim 2 , in which the aerofoil is asymmetric. 
     
     
         5 . A blade as claimed in  claim 1 , in which the leading edge is rounded and the trailing edge is sharp. 
     
     
         6 . A blade as claimed in  claim 1 , wherein the area of dimples extends along at least a major part of the length of the blade. 
     
     
         7 . A blade as claimed in  claim 1 , wherein the dimples are generally teardrop-shaped with a wider end facing towards the leading edge of the blade. 
     
     
         8 . A blade as claimed in  claim 1 , wherein the dimples vary in distribution density. 
     
     
         9 . A blade as claimed in  claim 1 , wherein the dimples vary in depth. 
     
     
         10 . A blade as claimed in  claim 1 , wherein the dimples vary in cross section with depth. 
     
     
         11 . A blade as claimed in  claim 1 , wherein the plurality of dimples comprises dimples of different size. 
     
     
         12 . A blade as claimed in  claim 1 , wherein the trailing edge of the blade has a localised rearward or downstream extension. 
     
     
         13 . A blade as claimed in  claim 12 , wherein the localised rearward extension is at a free end of the blade. 
     
     
         14 . A blade as claimed in  claim 1 , wherein the blade is a rotary machine blade. 
     
     
         15 . A blade as claimed in  claim 1 , wherein the blade is a wind turbine blade. 
     
     
         16 . A blade as claimed in  claim 3 , wherein dimples are also provided on the pressure surface of the blade. 
     
     
         17 . A wind turbine comprising at least one blade according to  claim 1 . 
     
     
         18 . An air displacement system comprising at least one blade according to  claim 1 . 
     
     
         19 . An air displacement system according to  claim 18  comprising a fan comprising the at least one blade.