GB2105791A

GB2105791A - >Centrifugal fan

Info

Publication number: GB2105791A
Application number: GB08226789A
Authority: GB
Inventors: Heinz Wieland
Original assignee: Wilhelm Gebhardt GmbH
Current assignee: Wilhelm Gebhardt GmbH
Priority date: 1981-09-22
Filing date: 1982-09-20
Publication date: 1983-03-30
Also published as: GB2105791B; FR2513324A1; FR2513324B1; CH662618A5; DE3137554A1

Abstract

To reduce noise the leading and/or trailing edges 10, 11 of the fan blades 2 are serrated. The blades extend between front and back plates 5,4 defining a central region 9 to which air is directed by a stationary guide 6. <IMAGE>

Description

SPECIFICATION Centrifugal fans The present invention is with respect to a centrifugal fan or blower and more specially to a blower having a wheel or impeller having curved - for example backwardly curved - blades placed between a back plate and a front plate designed for working with an inlet guide through which air makes its way axially through an opening in the front plate, the blades each having radially inner leading edges and radially outer trailing edges, the blower having a system for producing an effect on the nature of turbulence at the leading and trailing edges of the blades.

Although responsible for a number of useful effects, centrifugal blowers do have the serious shortcoming of a high noise level, amounting possible to 90 to 100 dB. Furthermore, the nature of the noise spectrum of such blowers is such as to be highly troublesome to persons near the blowers. It is more specially from this point of view that specifications for centrifugal blowers have become tighter and tighter of late, more specially in the case of plant or apparatus which is to be worked near people, as for example in the case of air-conditioners, heat pumps, hot air heating systems, and aspirators for clearing stale air from kitchens and garages. In a number of different cases such blowers have been placed in special, muffled spaces or they have been joined up with the inlet and outlet connections of noise mufflers.While on the one hand such systems may readily be planned for in designing ventilating and conditioning systems, they may, however, in some cases, not be able to be produced using systems presently on the marketplace, quite in addition to the fact that such measures may only be taken in a limited number of uses. In most cases, as needed again and again for certain technical functions, other, backup measures using acoustic insulation and acoustic muffling have been put forward, which, however, make the design complex, the amount of material being greatly increased so that the price of producing systems is high.For example in a suggestion made byJ.l. Petrov in the Soviet Trade Periodical "Vestnik mashinostveniya" no. 11, 1971, pages 40 and 41, for cutting down the noise level of radial fans, turbulence filters or sieves were to be placed at the leading and trailing edges of the blades. While it is true that this system makes the noise level somewhat better, this is at the price of great drop in efficiency and of a poorer aerodynamic performance. Furthermore, in German patent 1,253,402 a suggestion was made for cutting down the noise level of radial fans used for cooling electrical machines by having a certain inequality in the distances between one blade and the next, the inequality being worked out in a special process. The condition in this respect is naturally that the blades are placed radially.In such known systems, however, the overall amount of sound energy coming from the fan was not cut down but only changed so that there was a distribution over a broader frequency spectrum. Furthermore, in another system (see German Offenlegungsschrift specification 2,627,344) for cutting down noise the back plate was to have the form of a truncated cone pointing away from the inlet side, and having its edge running out past the blades and the outer edge of the ring-like plate, this however being responsible for a lower efficiency and a higher price of production.

One purpose of the invention is to take care of this shortcomings.

A further purpose of the present invention is that of cutting down the amount of running noise, more specially the turning sound, of radial fans or blowers by the use of simple design changes in the fan itself.

A still further purpose of the invention is that of cutting down the noise produced by a fan or blower without having an effect on the performance and efficiency.

For effecting these purposes, and still further purposes, in the invention a centrifugal fan or blower having a wheel which is made up of a hub designed to be locked on a driving shaft, of a back plate and of a front plate having generatrices and designed for turning about an axis of said shaft with said generatrices generally in fixed positions in relation to said axis, and of blades running generally along said shaft between said plates, said blades having inner leading edges and outer trailing edges with said leading edges nearer said axis than said outer trailing edges, said blades being joined to said plates for being turned therewith and centrifugally driving air outwards from a space within said inner blade edges formed by said blades ending short of said axis, and an inlet guide being placed on a side of said front plate turned away from said side plate, said fan or blower being designed for producing an effect on turbulence events at said edges of said blades, characterized in that said blade edges, for at least part of the distance between said front and back plates, have teeth with spaces between said teeth forming openings in said blade edges. As has been noted, such a form of the leading edge is responsible for a turbulent boundary layer on the face of the blade helping to put an end, completely or in part, to noise-producing instabilities and shedding of vortices. By designing the trailing edges of the blades on these lines, the pressure field turning with the blades is made more even so that there is a decrease in the periodic transmissions of force at the outer edge of the wheel.The overall outcome of these measures, forming part of the invention, is a drop in the level of the sound produced, more specially at medium and high frequencies, and furthermore the turning sound is very much cut down. The noise on operation of such an impeller or wheel will seem to be less unpleasing than the running noise of an impeller without the design noted. The efficiency and furthermore the pressure-volumetric flow curve will, in this case, be only changed to an unimportant degree. An impeller or wheel with the turbulence producers of the present invention at the edges of the blades does not have to be run in a housing and may be uncovered and without any spiral housing.

The form of the teeth or of the serrations on the edges of the blades of the impeller may be different, for example in the form of a meander or U-like form and, on the other hand, zigzag-like, in the form of a letter C, in the form of waves or, lastly, without being regular at all, the joins between the separate teeth or serrations being rounded or pointed, that is to say like corners.

An account will now be given of working examples of the invention to be seen in the Figures.

Figure lisa diagrammatic section of a centrifugal fan (side view) forming part of the invention, the impeller being designed for use with or without a spiral housing.

Figures 2 and 3 are more detailed views of parts of the structure of the invention as seen from the side in section and on a greater scale.

Figures 4to 9 give details of different further possible forms of the invention as seen from the side and with parts in a diagrammatic form.

Figure 10 is a diagrammatic view of curves with respect to the noise properties of a centrifugal fan of known design and a centrifugal fan of the present invention.

A centrifugal fan of the present invention may have a wheel or impeller 1 having curved blades, for example blades which are backwardly curved.

Blades 2, 3 are separately fixed between a back plate 4 and a ring-like plate 5 having its middle opening facing and joined up with an inlet guide 6 so that air may make its way in the direction of arrows 8 after moving axially in along the direction of arrow 7 through the guide 6. The blades have inner leading edges 10 next to the middle space between the blades, and a trailing edge 11, such leading and trailing edges being designed for having an effect on turbulence events at the leading and trailing edges of the blades. The impeller 1 furthermore has a hub 12 for keying the impeller on a driving shaft.

Furthermore, the impeller of Figure 1 is, as a further part of the invention, placed in a spiral housing of known design in which it is turned. However, the design of the present invention makes it possible for the impeller to be run without a spiral housing so that it is uncovered.

As a further part of the invention for producing an effect on turbulence events, at least one of the two edges 10 and 11 of each blade is toothed or serrated for at least part of its breadth, that is to say in the depth or axial direction of the blades. The design may naturally be such that only the trailing or the leading edge of each blade is toothed or serrated in a way dependent on the use to which the fan is to be put and the limit to the noise level.

In the form of the invention to be seen in Figure 2, it will be seen that the full blade breadth bat the blade edges 15 and 16 is toothed or serrated at 17 and 18. In the design of Figure 3 on the other hand, the teeth 20 at the blade trailing edge 19 of blade 21 only go along the middle part of the blade edge, while at the blade's leading edge 22 the teeth 23 will be seen to be on part of the blade edge only which is next to the ring-like plate 24 of impeller 25, the leading edge in fact being toothed for example as far as the middle of the edge or as far as some point short of the middle. It is, however, furthermore possible for the teeth or the serrated part of the blade edge to be next to the back plate 26, this form of the invention not, however, being figured.

The teeth or zigzag form may be in a number of different designs, for example with U-like cutouts as is marked at 27 in the case of impeller 27 of Figure 4.

It is, however, possible for the teeth to have a jagged outline (29) on impeller 30 of Figure 5. On the other hand, the teeth do not have to be regular with respect to their depth, see teeth 31 on impeller 32 in Figure 6. Furthermore, the outline of the teeth or jagged edge may, for example, have a meandering form as will be seen at 33 in the case of impeller 34 (Figure 8). As a possible further example, the teeth or serrated edge may take the form of C-like cutouts as will be seen at 25 on impeller 36 of Figure 9; or, lastly, the teeth may be wavy, see teeth 37 of impeller 38 in Figure 7. In all these cases it will be seen that the joins between the separate teeth or jaggedly cut edges may be rounded (as in Figures 4, 7 and 9) or may be pointed or angled (see Figures 5, 6 and 8).

On using one of the forms of edges forming part of the present invention, the useful effects noted will be produced inasfar as a toothed or serrated form of the leading edge of the blades is a help in cutting down noise-producing instabilities and shedding of vortices while such teeth or serrations at the trailing edge of a blade are responsible for a more even pressure field turning with the blades and, for this reason, for a decrease in the regular changes in forces at the impeller. All in all there is, for this reason, a decrease in the sound or noise level, more specially at medium and high frequencies and there is a great decrease in the level of turning sound or rotary noise without having any effect on the efficiency or, to a marked degree, on the pressure volumetricflow curve.The running noise of an impeller of the present invention will generally seem to be less unpleasing than the running noise of a known design of impeller. Figure 10 makes a comparison between the noise produced by an impeller of the present invention, which is plotted as curve 50 in dB against frequency, while curve 51 is representative of the noise level or frequency spectrum of an impeller not producing turbulence, that is to say a known design of impeller.

It is furthermore to be underlined that the way of cutting down noise as used in the present invention, and which is responsible for a very marked effect, as may be seen from Figure 10, that is to say about 5 to 10%, may be produced with a very simple change in design and in fact the fan or the way of producing it are in no way made any more complex. Furthermore, an impeller of the present invention designed for producing turbulence at the edges of the blades may be used without a housing, that is to say in an uncovered condition.

The teachings of the invention may be used with an equally good effect in the case of fans with radial blades or with blades which are forwardly curved.

Claims

1. A centrifugal fan or blower comprising a wheel adapted to be coaxially mounted on a driving shaft, and including a pair of plate members spaced apart along the axis and blades extending between the plate members for rotation therewith, said blades having inner leading edges and outer trailing edges with said leading edges nearer the axis than said outer trailing edges for centrifugally driving air outwards from a space within said inner blade edges formed by said blades ending short of the axis, and said blade edges, for at least part of the distance between said plate members, having teeth with spaces between said teeth forming openings in said blade edges, for producing an effect on turbulence events at said edges of said blades.

2. A fan or blower as claimed in claim 1, wherein the trailing edge of each blade is toothed.

3. Afan or blower as claimed in claim 1 or claim 2, wherein the leading and trailing edges of each blade are toothed.

4. A fan or blower as claimed in any of claims 1 to 3, wherein the or each edge of each blade is toothed for the full distance between said plate members.

5. A fan or blower as claimed in any of claims 1 to 3, wherein a middle part of the length of the or each edge of each blade is toothed.

6. A fan or blower as claimed in any of claims 1 to 3, wherein the or each edge of each blade is toothed along a length of each edge starting next to one of said plate members and ending short of the other plate member.

7. A fan or blower as claimed in any of claims 1 to 3, wherein the or each edge of each blade is toothed along a length thereof starting at and next to a back one of the plate members, said toothed length of each said edge ending short of a front one of the plate members.

8. A fan or blower as claimed in any of the preceding claims, wherein said teeth are in the form of meanders.

9. A fan or blower as claimed in any of claims 1 to 7, wherein said teeth are U-shaped.

10. A fan or blower as claimed in any of claims 1 to 7, wherein said teeth are zig-zag in form.

11. A fan or blower as claimed in any of claims 1 to 7, wherein the toothed edges have C-like cutouts between said teeth.

12. Afan or blower as claimed in any of claims 1 to 7, wherein said teeth are responsible for forming a wavy edge.

13. Afan or blower as claimed in any of claims 1 to 7, wherein said teeth on said plate edge are irregular.

14. Afan or blower as claimed in any of claims 1 to 7, wherein said teeth are joined together by rounded off parts of said blade edges.

15. A fan or blower as claimed in any of claims 1 to 7, wherein said teeth are joined up by sharp, angle-like parts of said blade edges.

16. A fan or blower as claimed in any of the preceding claims, wherein a spiral housing is provided for the wheel.

17. A fan or blower as claimed in any of claims 1 to 15, wherein said wheel is designed for running without a housing.

18. A fan or blower substantially as hereinbefore described with reference to the accompanying drawings.

19. A centrifugal fan or blower having a wheel which is made up of a hub designed to be locked on a driving shaft, of a back plate and of a front plate having generatrices and designed for turning about an axis of said shaft with said generatrices generally in fixed positions in relation to said axis, and of blades running generally along said shaft between said plates, said blades having inner leading edges and outertrailing edges with said leading edges nearer said axis than said outer trailing edges, said blades being joined to said plates for being turned therewith and centrifugally driving air outwards from a space within said inner blade edges formed by said blades ending short of said axis, and an inlet guide for guiding air axially into said space, said guide being placed on a side of said front plate turned away from said side plate, said fan or blower being designed for producing an effect on turbulence events at said edges of said blades, characterised in that said blade edges, for at least part of the distance between said front and back plates, have teeth with spaces between said teeth forming openings in said blade edges.