GB2062758A

GB2062758A - Suppressing the Noise of Blowers

Info

Publication number: GB2062758A
Application number: GB8029306A
Authority: GB
Original assignee: AOA Apparatebau Gauting GmbH
Current assignee: AOA Apparatebau Gauting GmbH
Priority date: 1979-09-11
Filing date: 1980-09-10
Publication date: 1981-05-28
Also published as: GB2062758B; FR2465105A1

Abstract

A device for suppressing the noise of blowers, fans or like flow machines comprises a flow guide member 4 which encloses the inlet cross-section 7 of the flow machine and has an inlet passage 6 and/or a flow guide member 36 which encloses the outlet cross-section 34 and has an outlet passage. The inlet passage and the outlet passage are sub-divided into a plurality of flow passages by almost radial ribs 12, 38 and annular guide ribs 16, 42. The radial guide ribs 12 of the guide member enclosing the inlet cross-section may be given an S- shaped profile. The guide member enclosing the outlet cross-section may be provided with a hood 39 which forms a sound trap. Sound traps formed by resonant chambers 20, 23 are also provided in the guide member 4. <IMAGE>

Description

SPECIFICATION Device for Suppressing the Noise of Blowers, Fans or Like Flow Machines The invention relates to a device for suppressing the noise of blowers, ventilators or like flow machines.

In use, flow machines s give rise to a considerable noise level caused by the drive, by the rotor as well as by the air current in the passages. This noise is particularly disruptive when such flow machines are used as ventilators in reception or living rooms.

For this reason, a multiplicity of devices have been suggested for the suppression of noise.

For example, DE-PS 937 969 and US-PS 1 69 232 describe concentric guide ribs on the intake side resulting in a speed distribution of the air taken in so as to reduce the noise.

Concentrically disposed guide ribs on the outflow side of flow machines for the purpose of noise suppression are known from GB-PS 444 206 and GB-PS 1196176.

These guide ribs may be provided with cavities so that they act as sound traps (GB-PS 1 445 384).

Further, DE-AS 1 064 191 describes a device which, by means of guide ribs, prevents the separation of the flow and the consequent creation of noise in the hub region of axial flow machines.

However, the disadvantages of all these known devices is that measures must be taken in the vicinity of the flow machine which make it necessary to modify the machine and have a negative influence on the operating behaviour.

It is the problem of the invention to provide a device for suppressing noise that is of low weight and small size, can be connected to existing flow machines without significant modification of said machines and will not detrimentally influence the operating behaviour of the machines.

This problem is solved by a device according to claim 1.

By means of the first guide member, the takein cross-section is continuously increased from the inlet section of the rotor so that the speed of flow at the inlet of the guide member can be lower than at the inlet section of the flow machine, whereby there is a marked reduction in noise. By reason of the plurality of forced direction changes in the air stream that is taken in, one obtains further damping, the selected axial cover of the plurality of flow passages further reducing the emission of noise at the front.

The second guide member strongly damps the jet noise and the rearwardly directed rotor noise, not only by direct screening by reason of covering the plurality of flow passages but also by reducing the speed of flow on account of diffusor effect.

The guide members according to the invention do not require a modification of the blower, fan or flow machine because they are applied to the outside of the rotor zone.

Depending on the nature and design of the flow machine, provision may be made for only a front or a rear guide member or for a front as well as rear guide member.

By using the guide members according to the invention, the operating behaviour of the flow machine is not negatively influenced. On the contrary, the characteristic curve that would be obtained without the guide members of the invention, i.e. the relationship between the mass of the throughput and the pressure, can, by means of the guide members of the invention, be changed at will within certain limits in a manner that appears most suitable for different practical applications: For example, in axial take-in dynamically balanced flow machines, the first guide member of the invention makes it possible to achieve prerotation by the suitable arrangement of the guide ribs in addition to the acceleration that is obtainable for the taken-in air stream in the direction towards the inlet cross-section of the rotor.

Further, for example in the case of flow machines in accordance with claim 8, the operating point of the equipment can, by means of the concentric guide ribs and the enlargement of the outlet cross-section, be transposed to a fully traversed cross-section of the final crosssection of the guide member which may, for example, correspond to the fully traversed circular cross-section or a rectangular cross-section.

Maintaining the angle of divergence by means of the concentric guide ribs makes it possible to diverge the outlet cross-section of the equipment to the full cross-section along a very short distance, so that the guide member can be made very compact. With the aid of the guide member, further unthrottling of the equipment makes it possible to extend the characteristic operating curve towards a larger mass throughput at the same rotary speed.

The invention will now be described in more detail with reference to examples in relation to the drawing, wherein:- Fig. 1 is a part-longitudinal section through an axial intake radial blower having the first guide member according to the invention; Fig. 2 is a section on the line Il-Il in Fig.1 to clarify the profile median line of the radial guide ribs; Figs. 3 and 4 are elevations Ill and IV, respectively, according to Fig. 1 to clarify the radial disposition of the radial guide ribs, and Fig. 5 is a part-longitudinal section through an axial intake radial blower having the second guide member according to the invention.

The right-hand portion of Fig. 1 shows the front end or take-in side of a radial blower having a rotor 1, a blower housing 2 and an outlet passage 3. A guide member 4 according to the invention is flange-connected to the blower housing at 5. This guide member is rotationally symmetric or dynamically balanced with respect to the rotary axis of the rotor 1 and has an inlet passage 6 which is curved to S shape in the axial direction, substantially has the shape of an S line on its side and continuously diverges outwardly from the inlet cross-section 7 of the rottottotor towards an inlet plane 8, the curvature being selected so that there is cover in the axial direction, i.e. there is no axially rectilinear throughgoing flow path.A radially inwardly disposed guide face 10 of the inlet passage Is at its front zone, i.e. in the region of the front S curve 11, connected by at least substantially radial guide ribs 12 to a concentric radially outwardly disposed guide face 13 of the inlet passage. The radial guide ribs 12 have a substantially S-shaped profile median line as shown in Fig. 2, care being taken that they cover at least one pitch 14. These ribs 12 have an inclination greater than zero, e.g. of 370 to a respective radial plane or a radial line 1 5 (see Figs. 3 and 4), so that they produce circuitous passages 9 between the individual ribs that could possibly also be utilised to produce prerotation in a direction towards the rotor 2.Between the inner and outer guide face 10 and 13, there are annular guide ribs 16 which are likewise curved corresponding to the inlet passage 6 so that axial covering is achieved, i.e. no axially directed flow path is possible in the throughflow zone.

Concentrically and radially inwardly of the guide face 10 there is an annular chamber 20 in the region of the front S curve; it is open towards the inlet passage 6 by means of apertures 21 and serves as a sound trap. A further annular chamber 23 which is likewise open towards the inlet passage 6 and likewise serves as a sound trap is disposed at the rear S curve 22 at the side of the outer guide face 13 radially beyond said guide face and axially offset from the chamber 20. The length of the chambers is tuned to the wave length of the rotational tone of the blower.

By means of the upstream first guide member according to the invention, the front side of the blower Is screened from the outside, the special cross-sectional shape of the flow passage bringing about a slower take-in flow at the inlet and an accelerated flow, possibly with prerotation, at the outlet of the guide member so that, apart from effective noise damping by means of screening or partitioning and multiple flow deflectlon, an improvement can be achieved in the efficiency.The accessory according to the invention increases the scope of use of otherwise conventional blowers to particularly noise sensitive applications, the construction in the form of attachments to be connnnnected by flanges making it possible to employ conventional blowers or fans or the like which can be used In the normal manner if the additional guide members are left off.

Fig. 5 likewise illustrates a radial blower with the annular outlet passage 3 enclosing its drive 31, the passage terminating In an outlet cross section 34 which is normal to the rotary axis 33 of the blower. In the plane of the outlet cross section 34, the blower housing 2 has a connecting flange for a downstream guide member 36 which has a cylindrical or rectangular outer housing 37 axially extending the blower housing. With the aid of radial or almost radial guide ribs 38, the inside of the outer housing 37 carries a substantially parabolic outwardly converging hood 39 which covers the drive 31 surrounded by the outlet cross-section 34 and uniformly increases the outflow cross-section from the outlet cross-section 34 to the full circular diameter 40, i.e. the largest internal diameter of the outlet cross-section 34.The hood is preferably perforated as illustrated to assume the soundproofing function of a sound trap.

Annular or part-annular concentric guide ribs 42 are disposed between the hood 39 and the outer housing 37 of the guide member, only a single concentric guide rib being provided in the case of the present example. There may be a plurality, the number of the rings depending on the largest diameter of the outer housing, the angle of divergence or the required structural length. If there were to be no concentric ribs 42, the hood would have to converge by maintaining a suitable angle of divergence so as to avoid separation of the flow paths.This angle can, however, be increased by using the concentric guide ribs 42, i.e. one can considerably shorten the total length over which the hood converges from its largest to its smallest diameter, it merely being necessary to take care that the ribs 42 are so inclined to the rotary axis 43 of the blower that the overall angle of divergence of the flow passages 43 formed between the ribs 42 and 38 remains smaller than the aerodynamic limiting values. The inclination of the ribs 42 partially covers the opening cross-section of the guide member so that the direct axial passage of sound can be reduced. Similarly, the hood also screens the back of the drive unit 31.

The end edges of the radial guide ribs 38 are preferably set inwardly as illustrated whereas the concentric guide ribs extend up to the end faces of the outer housing. In the case of an advantageous development, corresponding concentric guide ribs 44 may be provided in the outlet passage 32 of the blower as a continuation of the respective guide ribs 42 of the guide member. However, it is also possible to extend the guide ribs 42 beyond the connecting plane towards the blower so that they can be inserted in the outlet passage 3 when the guide member is flange connected.

The guide member constitutes a multiple diffuser by which the outlet cross-section 34 of the blower is, for example, enlarged to the full circular cross-section 40 which forms the end section 45 of the guide member. Basically, enlargement is possible to practically any desired cross-sectional size, which could also be rectangular. In this way the operating or functional point of the blower can be selectively set or varied by simple means, e.g. made the same as the end section 45 which, in the present example, corresponds to the full circular crosssection through which the flow penetrates. The blower is thereby unthrottled and the characteristic operating curve is extended to give a larger mass throughout at the same rotary speed. The jet noise and the rearwardly directed noise of the rotor are considerably damped, namely by direct screening as well as by a reduction in the speed of flow.

A suitable material for the guide member is an extrudable plastics material. Without the guide member according to the invention, the fan can be used and installed in conventional manner, e.g.

in pipes or other locations which are less noise sensitive. The guide member also permits one to fulfil the function of an adaptor for different connecting cross-sections, e.g. mains conduit cross-section. Further, suitable materials may be employed for additionally increasing the soundproofing; also, the faces that are swept by the flow may be entirely or partially lined with soundproofing material.

Claims

1. A device for suppressing the noise of blowers, fans or like flow machines, characterised in that a first guide member is provided which encloses the inlet cross-section of the rotor and has an inlet passage curved in the flow direction to provide axial cover and with a cross-section converging inwardly to the inlet cross-section in the flow direction, and/or a second guiddidiiddiddidiggu guide member is provided which encloses the outlet cross-section and has an outlet passage diverging in the flow direction, and that the inlet or outlet passage is sub-divided by radial or almost radial and concentric annular or partially annular and annular guide ribs into a plurality of flow passages which are at least partially radially and/or axially covered by the guide ribs.

2. A device according to claim 1, characterised in that the radial guide ribs of the first guide member have a substantially S-shaped profile median line covering at least one pitch.

3. A device according to claim 2, characterised in that the radial guide ribs of the first guide member are inclined to the radial line to cover at least one pitch and include an angle larger than zero with the respective radial line.

4. A device according to claim 3, characterised in that the angle is about 370.

5. A device according to any preceding claim for axial take-in dynamically balanced flow machines with an annular inlet cross-section, characterised in that the axial direction the throughflow section of the first guide member has the shape of an 'S' lying on its side and axially diverging outwardly in trumpet formation.

6. A device according to any preceding claim, characterised in that the first guide member is provided with cavities for soundproofing radially inwardly of the front S curve and concentrically radially outwardly of the rear S curve.

7. A device according to claims 5 and 6, characterised in that the radial and concentric guide ribs of the first guide member extend from the inlet end of the guide member substantially beyond the front S curve.

8. A device according to claim 1 for flow machines with a drive unit which is disposed radially inwardly of the outlet cross-section and the drive axis of which is normal to the outlet cross-section, characterised in that a hood which covers the drive unit and tapers substantially parabolically in the downstream direction at a larger angle than the limiting angle of flow separation forms together with the second guide member the annular outlet passage which diverges to a full outflow cross-section in the flow direction and which is sub-divided by the guide ribs into a plurality of flow passages of which the flow section diverges in the downstream direction at a smaller angle than the limiting angle of the flow separation.

9. A device according to claim,8, characterised in that the hood is perforated.

10. A device according to claim 8 or 9, characterised in that the hood is integrally connected to the guide member by way of the radial or almost radial guide ribs.

11. A device according to claim 8 or 9, characterised in that the hood is releasably connected to the guide member by way of the radial or almost radial guide ribs.

12. A device according to any one of claims 8 to 11, characterised in that the concentric guide ribs are extended into the outlet cross-section.

13. A device according to any preceding claim, characterised in that the swept faces of the guide members are at least partially lined with soundabsorbing material.

14. A device according to any preceding claim, characterised in that the first and/or second guide member can be substantially flange-connected to conventional blowers, fans or like flow machines.

15. A device for suppressing the noise of fluid flow creating apparatus, comprising a housing which includes a passage and which is engageable with the apparatus such that an end of the passage overlies a fluid opening of the apparatus, the passage converging towards said end and being curved whereby to damp fluid flowing therethrough.

1 6. A device for suppressing the noise of fluid flow creating apparatus, comprising a housing which contains a passage and which is engageable with the apparatus such that an end of the passage ovelies a fluid opening of the apparatus, the passage converging towards said end and being sub-divided into a plurality of portions by ribs extending longitudinally of the passage.

17. A device for suppressing noise substantially as herein particularly described with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

18. A device for suppressing noise substantially as herein particularly described with reference to and as illustrated in Figure 5 of the accompanying drawings.

1 9. Fluid flow creating apparatus including a device as claimed in any preceding claim.