Axial flow impeller
A low noise axial flow impeller has a multi cellular form of construction comprising a multiplicity of individual axial flow channels disposed in a circumferential and radial 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. For high total flow area coupled with low structural weight the channels are arranged in tessellating rings of equal numbers of channels, with channel cross sections based on hexagons (or truncated hexagons in the case of the channels in the innermost and outermost rings). In another embodiment each channel also extends from a respective channel inlet to a respective channel outlet which is offset from the respective inlet in the radial direction of the impeller, and involves an increase in the internal dimension of the respective channel in the direction radial 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. An axial flow impeller comprising a multiplicity of individual axial flow channels disposed in a circumferential and radial array with respect to the axis of rotation of the impeller, wherein the array of flow channels is in the form of a radial succession of coaxial rings of such channels, with the channels in each such ring being offset in the circumferential direction from the channels in the adjoining ring(s), and with the same number of channels in each such ring.
2. An impeller according to claim 1 wherein at least a plurality of said flow channels are of generally hexagonal cross-section.
3. An impeller according to claim 1 wherein at least a plurality of said flow channels are of generally quadrilateral cross-section.
4. An impeller according to claim 1 wherein said rings of flow channels tessellate in the radial direction.
5. An impeller according to claim 4 wherein there are at least three said rings of flow channels and the channels in at least that or those ring(s) which are not the radially innermost or outermost ring are of generally hexagonal cross-section.
6. An impeller according to claim 1 wherein the number of channels in each said ring is a prime number.
7. An axial flow impeller comprising a multiplicity of individual axial flow channels disposed in a circumferential and radial 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 radial direction of the impeller, and involve an increase in the internal dimension of the respective channel in the direction radial to the axis of rotation of the impeller.
8. An impeller according to claim 7 wherein at least a plurality of said flow channels are of generally hexagonal cross-section.
9. An impeller according to claim 7 wherein at least a plurality of said flow channels are of generally quadrilateral cross-section.
10. An impeller according to claim 7 wherein the array of flow channels is in the form of a radial succession of coaxial rings of such channels, with the channels in each such ring being offset in the circumferential direction from the channels in the adjoining ring(s).
11. An impeller according to claim 10 wherein there are the same number of flow channels in each said ring.
12. An impeller according to claim 11 wherein said rings of flow channels tessellate in the radial direction.
13. An impeller according to claim 12 wherein there are at least three said rings of flow channels and the channels in at least that or those ring(s) which are not the radially innermost or outermost ring are of generally hexagonal cross-section.
14. An impeller according to claim 10 wherein the number of channels in each said ring is a prime number.
15. A fluid dynamic machine incorporating an impeller according to claim 1 .
16. A fluid dynamic machine incorporating an impeller according to claim 7 .