Method of enhancing the output efficiency of a propeller and reducing the noise thereof

Abstract

A method of enhancing the output efficiency of a propeller and reducing the noise thereof wherein a plurality of small cavities are formed on the whole or at least a portion of a blade skin of the propeller. When the propeller is rotated and a fluid passes through the small cavities, a plurality of small vortexes are created at the blade skin to form a thin turbulent boundary layer that allows an advantageous interference acting on a turbulence of the fluid at the blade skin. In this way, a portion of fluid is not in contact with the blade skin, and a viscous drag acting on the blade skin is reduced to extend a wake and reduce a drag force of the wake. The aforementioned mechanism can enhance the output efficiency of a propeller and reduce the noise thereof.

1 . A method of enhancing the output efficiency of a propeller and reducing the noise thereof, comprising the steps of:
 a) forming a plurality of small cavities on the whole or at least a portion of an blade skin by a non-destructive measure;   b) producing a plurality of small vortexes at the blade skin to form a thin turbulent boundary layer when a fluid passes through the plurality of small cavities such that a viscous drag acting on the blade skin is reduced to extend a wake and reduce a drag force acting on the wake; and   c) producing a plurality of small vortexes by use of the small cavities by which a thin turbulent boundary layer is created to partially prevent the fluid from contact with the blade skin, thereby reducing the noise.   
     
     
         2 . The method of enhancing the output efficiency of a propeller and reducing the noise thereof as recited in  claim 1 , wherein the plurality of small cavities is in a predetermined shape selected from the collection of a strip shape, a polygonal shape, a circular shape, an elliptical shape and other geometric shapes, and the small cavities are in a concavely arc shape having a lower middle. 
     
     
         3 . The method of enhancing the output efficiency of a propeller and reducing the noise thereof as recited in  claim 2 , wherein the plurality of small cavities are densely distributed, and each small cavity has a depth of 0.001 mm˜10 mm and an area of 0.001 mm 2 ˜100 mm 2 . 
     
     
         4 . The method of enhancing the output efficiency of a propeller and reducing the noise thereof as recited in  claim 3 , wherein the plurality of small cavities of the blade skin attached and fixed onto a thin layer of the blade skin by the paint coating/printing method, and the plurality of small cavities formed by the thin layer has a maximum height (H) not exceeding the thickness (T) of the thin layer. 
     
     
         5 . The method of enhancing the output efficiency of a propeller and reducing the noise thereof as recited in  claim 3 , wherein the small cavities are formed directly on the blade skin by a mold casting method, by a lathe or by a demolding forming method.