Centrifugal impeller

Abstract

A low noise centrifugal fan impeller has a multi cellular form of construction comprising a multiplicity of individual radial flow channels disposed in a circumferential and longitudinal array with respect to the axis of rotation. This increases the “blade passing frequency” as compared to a conventional impeller and since higher frequencies have lower energy for a given flow output the total amplitude of the noise generated can be reduced. Each channel extends from a respective channel inlet to a respective channel outlet which is offset from the respective inlet in the longitudinal direction of the impeller, and involves an increase in the internal dimension of the respective channel in the direction parallel to the axis of rotation, thus assisting deceleration and compression of the air or other medium being conveyed as it flows through the channels.

1 . A centrifugal impeller comprising a multiplicity of individual radial flow channels disposed in a circumferential and longitudinal array with respect to the axis of rotation of the impeller, wherein at least a plurality of said channels are configured to extend from a respective channel inlet to a respective channel outlet which is offset from the respective inlet in the longitudinal direction of the impeller, and involve an increase in the internal dimension of the respective channel in the direction parallel to the axis of rotation of the impeller. 
   
   
       2 . An impeller according to  claim 1  wherein the flow channels are so configured that their inlets collectively define an inlet array of dished form surrounding the axis of rotation, the radius of which array decreases with increasing distance in the longitudinal direction of the impeller from a main inlet to the impeller at one end thereof. 
   
   
       3 . An impeller according to  claim 2  further comprising a profiled body located around the axis of rotation within said dished inlet array, the radius of which body increases with increasing distance in the longitudinal direction of the impeller from said main inlet. 
   
   
       4 . An impeller according to  claim 1  wherein the flow channels are so configured that their inlets collectively define an inlet array lying in a generally radial plane with respect to the axis of rotation. 
   
   
       5 . An impeller according to  claim 1  wherein at least a plurality of said flow channels are of generally hexagonal cross-section. 
   
   
       6 . An impeller according to  claim 1  wherein at least a plurality of said flow channels are of generally quadrilateral cross-section. 
   
   
       7 . An impeller according to  claim 1  wherein the array of flow channels is in the form of a succession of circumferential rows of such channels arranged along the impeller, with the channels in each such row being offset in the circumferential direction from the channels in the adjoining such row(s). 
   
   
       8 . An impeller according to  claim 7  wherein there are at least three such rows and the flow channels in at least that or those row(s) which are not at the longitudinal ends of the array are of generally hexagonal cross section. 
   
   
       9 . An impeller according to  claim 1  wherein the array of flow channels is in the form of a succession of circumferential rows of such channels arranged along the impeller, with the same number of channels in each such row. 
   
   
       10 . An impeller according to  claim 9  wherein said number is a prime number. 
   
   
       11 . A fluid dynamic machine incorporating an impeller according to  claim 1 .