Fan Blade Noise Reducer

Abstract

The leading edge method improves fan blade aerodynamics, which reduces energy lost into the airflow as acoustic noise. This results in a quieter fan, with no significant change to air moving capability. This is accomplished by increasing the radius of the fan blade leading edge, and by ensuring that any laminar boundary layer existing over the fan blade is tripped into a more energetic, and less likely to separate, turbulent boundary layer. Most fan blades are not fabricated with aerodynamic (airfoil) cross sections. Typically, they are either stamped from sheet stock, or molded out of thin material, in both cases with “sharp” leading edges with small leading-edge radius compared to fan blade chord length. Airfoils designed to operate at the Reynolds-numbers applicable to fan blades eschew sharp leading edges for large, rounded leading edges to control the surface pressure distributions and permit operation over a wide angle of attack range without boundary layer separation. The leading edge treatment in this patent application serves the purpose of increasing the fan leading edge radius without scrapping the entire fan blade and replacing it with a proper low Reynolds-numbers airfoil shape.

I claim: 
     
         1 . Altering the geometric shape and size with various materials or by production methods of the leading edge of a fan blade will change the aerodynamics and harmonics of the fan thus significantly reducing fan noise with insignificant loss of cfm or rpm. 
     
     
         2 . The process in  claim 1  wherein a piece of 0.250D/0.125 ID round rubber tubing is split on one side and attached to the leading edge of all fan blades of a fan to achieve said results. 
     
     
         3 . The process in  claims 1  and  2  wherein various materials shaped so they increase the leading edge radius can be substituted to achieve said results. 
     
     
         4 . The process in  claim 1  wherein the fan blade manufacture can alter the fan blade to achieve said results.