EP0086785B1

EP0086785B1 - Propeller particulary for pneumatic blower use

Info

Publication number: EP0086785B1
Application number: EP82901126A
Authority: EP
Inventors: Heikki Vartiala
Original assignee: FOEHN Oy
Current assignee: FOEHN Oy
Priority date: 1981-03-27
Filing date: 1982-03-29
Publication date: 1987-07-22
Also published as: WO1982003430A1; FI74115B; DE3276831D1; JPS58500449A; NO823967L; AU8332382A; FI810946L; FI74115C; EP0086785A1

Abstract

Propeller, comprising a hub (1) and at least two cocentral vanes (2) radially projecting from the hub. The aim is to solve the problem created by high noise level occuring in propellers of prior art, mainly in blowers. It is a further aim to provide a propeller of higher efficiency than propellers known in the art, mainly for blower use but also for use in liquids. In the propeller of the invention, on the front side of each vane (2) of the propeller has been disposed a centric front louver element (7) substantially parallelling the vane and alar in shape and constituting a slot (8) between the front louver element and the vane. On the backside of each vane (2) it is possible, if desired, to place one or several centric sound suppressor fins (9, 11) substantially parallelling the vane and alar in shape and constituting slots (10, 12) between the vane and the sound suppressor fin, respectively fins. The front louver element (7), the vane (3) and the sound suppressor fins (9, 11), if any, constitute preferably a vane configuration that is concave as viewed from the pressure side of the vane.

Description

The present invention concerns a propeller particularly for pneumatic blower use as defined in the preamble of the main claim.
The noisiness of blowers causes a problem in blowers difficult to solve. Endeavours have been made to eliminate the noise of propellers in blowers by means of mufflers, e.g. by trumpet-like sound insulating chambers and sound traps continuing in the flow direction behind the blower. Moreover, mufflers of prior art are not satisfactory. Trumpet-like (flared) or tubular sound insulating chambers require great space and in addition their manufacturing and mounting costs are high. Mufflers cannot be installed at nearly all necessary points. The mufflers reduce the output of the blower.
In addition, blowers known in the art are not satisfactory as to their output. Raising the output and input power of the blower and the pitch angle of the propeller and/or increasing the propeller diameter causes in most instances the noise level of the propeller to become intolerable.
From US-A-3,075,743 a propeller for a turbo-machine is known wherein each blade consists of e.g. two vanes forming a slot between them. The flow output (m³/h), the pressure difference (mm H₂0) and especially the noise level (dB) obtained with said known propeller are not satisfactory.
The object of the present invention is to eliminate the drawbacks mentioned. The object of the invention is to provide a propeller especially for blower use which is substantially more quiet than any propeller known in the art, that is, of which the sound level is substantially lower than that of propellers known in the art. It is a further object of the invention to provide a propeller particularly for blower use, which is more efficient referred to its size and noise level than those of prior art.
Regarding the characteristic features of the invention, reference is made to the claims part.
Compared with the propeller of US-A-3,075,743 the propeller of the present invention gives better output and pressure difference results at remarkably (30%) lower noise level (same diameter, same number of revolutions, same number of blades).
The invention is described in the following in detail with the aid of embodiment examples and referring to the drawing attached, wherein:-

Fig. 1 presents a blower according to the invention, reproduced in perspective and sectioned in part, and
Fig. 2 shows the section along line II-II of the vane of the propeller according to Fig. 1.

In Fig. 1 is depicted a blower provided with a propeller according to the invention. The propeller comprises a hub 1, centrally and rotatably carried in a trumpet-like frame 13, with vanes 2, 2'. The vanes 2, 2' project radially from the hub and have an oblique pitch a against the plane placed at right angles to the axis of the hub (visible in Fig. 2). The propeller has been disposed to rotate with the aid of an electrical motor 14 located on the extension of the hub 1 in the frame 13 centrally and carried by supports 15. With the propeller rotating in a fluid - in air in the present case - the side 3 of the vane which first meets the fluid is the leading edge 3 and the opposite side is the trailing edge 4. The side of the vane 2 which when rotating meets the fluid is the pressure side 5 and the opposite side is the vacuum side 6.
In front of each vane 2 of the propeller shown in Figs. 1 and 2, in the direction of rotation of the vane partly in front of its leading edge 3, has been disposed a front louver element 7, substantially parallelling the vane and vane-shaped. The front louver in part dips into the vacuum side 6 of the vane and it forms a slot 8 with the vane 2.
The front louver element 7 is thinner and more narrow in the cross section then the vane 2. The front louver element 7 guides the fluid which the vane meets partly behind the vane to the vacuum side thereof and strongly reduces the turbulent flow in the region of the leading edge 3 of the vane. The decrease of turbulent flow reduces the fluid resistance as the vane rotates in the fluid, simultaneously reducing the intensity (that is the power) of the noise generated.
In the embodiment presented, the front louver elements 7 are fastened to the hub of the propeller similarly as the vanes of the propeller. The front louver elements have substantially the same shape as the vanes 2 of the propeller, with a pitch angle smaller than the pitch angle of the propeller vane, positive or negative, e.g. in the range from 0 to 25°C. If desired, the front louver element 7 may be fastened exclusively to the vane 2, e.g. by pin attachment, and/or to a vane circle which may be provided, encircling the vane tips, together with the vanes and the sound suppressor fins to be mentioned below.
According to the invention, as shown in Figs. 1 and 2, partly behind the trailing edge 4 of each vane 2 has been disposed a sound suppressorfin 9, which extends radially from the hub and substantially parallel to the vane and forms a slot 10 with the vane. The sound suppressor fin is vane-shaped, substantially smaller in thickness and width than the vane. The sound suppressor fin is affixed to the hub 1 of the propeller in the manner of the vane 2. If desired, it is possible to use the pin attachment mentioned, as sole mounting of the sound suppressor fin, and/or the vane circle mentioned above.
In the present embodiment there has been disposed another sound suppressor fin 11 partly behind the trailing edge of the sound suppressor fin 9 of each vane 2, this fin 11 extending radially from the hub equally, substantially parallel to the vane and to the preceding sound suppressor fin, and each such fin forming a slot 12 with the preceding sound suppressor fin. The latter sound suppressor fin 11 is substantially smaller than the vanes in its dimensions (width and thickness) and in the embodiment depicted also smaller than the first sound suppressor fin. The latter sound suppressor fin 11 may be affixed by pin attachment to the preceding sound suppressor fin 9 or to the vane 2 or, like the vane, to the hub 1. Possibly, a vane circle may be used as sole or additional mounting, as mentioned above with reference to the vane, the front louver element and the preceding sound suppressor fin.
The placement with reference to each other of the propeller vane 2, front louver element 7 and sound suppressor fins 9, 11 according to Fig. 1 is best revealed in Fig. 2, according to which the front louver element, vane and sound suppressor fins constitute a vane configuration which is substantially concave as viewed from the pressure side 5. Furthermore, the front louver element 7, the vane 2 and the sound suppressor fins 9, 11 are each concave as viewed from the pressure side 5. The front louver element 7 is located mainly on the vacuum side 6 of the vane, the first sound suppressor fin on the pressure side 5 of the vane, and the second sound suppressor fin 11 on the pressure side of the vane 2 and of the preceding sound suppressor fin 9. The front louver element 7, the vane 2 and the sound suppressor fins 9, 11 have greater thickness in their part adjacent to the leading edge and taper down towards the trailing edge.

Example 1

In order to determine the properties of the propeller of the invention, a propeller as shown in Fig. 1 was tested side by side with propeller of equal size but of conventional design. The number of vanes on each tested propeller was 8, the propeller diameter about 30 cm, the area of the propeller vane was substantially the same. During the test both propellers were run at 1400 r.p.m. In the test, the quantity of air transported by the propeller was measured, as well as the over-pressure generated on the propeller's positive pressure side at a constant distance from the propeller; the noise level of the propeller was furthermore aurally assessed.
The results of measurement are presented in the table below.

Example 2

In order to measure the efficiency of the propeller of the invention and the level of the noise generated by the propeller, a measurement was carried out. An axial blower as shown in Figs. 1 and 2 was used in the measurements. The propeller's speed of rotation was 1462 r.p.m., the temperature of the blown air was -8°C. The efficiency was calculated from the power drawn by the electromotor of type Str6mberg HXUR 208 C2 B3, 2.2 kW 1420 r.p.m. The principle of the test set-up was that of BSS 848: Part 1: 1982, connected to a duct, blowing free.

Example 3

In order to compare the noise levels of a propeller, intended for an axial blower, according to the invention and of that of a Woods axial blower with identical diameter, a measurement was carried out in which the sonic power level was determined in a duct-test set-up as in Example 2, propeller diameters 50 cm, speed 1480 r.p.m.
The power level of the propeller of the invention has been entered on line dB₁ in the table and that of the referenced propeller, on line dB₂.
It is possible, in a pneumatic blower, to use to advantage a second sound suppressor fin with 90° pitch angle known e.g. from centrifugal blowers, in which case the tubular frame of the blower may be outwardly flared at said second sound suppressor fin, in order to boost the blower's output. The sound suppressor fins may, if desired, be placed equally on the vacuum side of the vane; similarly, the front louver element may be placed mainly on the pressure side of the vane. Furthermore, the number of propeller vanes and accordingly of louver elements and sound suppressor fins may vary to be proper for instance for a propeller with 2, 3, 4, 5, 6, 7, 8 or more vanes. Furthermore, the vanes and preferably the front louver elements, and possibly the sound suppressor fins, belonging to a propeller according to the invention may be constructed each to be turnable about its axis, these axes being radial with reference to the hub of the propeller. Thus, the vanes and preferably the front louver elements and the sound suppressor fins, may all be turnable jointly and/or separately and placeable in desired position, towards controlling the pitch angles of the vanes, front louver elements and/or sound suppressor fins jointly and/or, if desired, separately.

Claims

1. A propeller particularly for pneumatic blower use, comprising a hub (1) and at least two vanes (2) radially projecting from the hub and having an oblique pitch angle (a), the side of the vane which, when the propeller is rotating, first meets the fluid being the leading edge (3) and the opposite side being the trailing edge (4) and the side of the vane which meets the fluid being the pressure side (5) and the opposite side being the vacuum side (6), wherein, in the direction of rotation, partly in front of the leading edge of each vane there is disposed a radially extending front louver element (7) substantially parallelling the vane and being vane-shaped, dipping partly into one side of the vane, and forming a slot (8) with the vane characterized in that, partly behind the trailing edge (4) of each vane (2) there is disposed radially extending suppressorfin (9) substantially parallelling the vane and being vane-shaped and forming a slot (10) with the vane both the front louver element (7) and the sound suppressor fin (9) being substantially smaller in thickness and width than the vane.

2. Propeller according to claim 1, characterized in that, partly behind the suppressor fin (9) of each vane (1) there is disposed another, possibly several sound suppressor fins (11), the latter extending radially and substantially parallelling the vane and each forming a slot (12) with the preceding sound suppressor fin.

3. Propeller according to claim 1 and 2, characterized in that the sound suppressor fins (9, 11) are disposed at least in part on the pressure side (5) of the vane (2).

4. Propeller according to any one of claims 1 to 3, characterized in that the front louver element (7), the vane (2) and the sound suppressor fin (9) and next sound suppressor fin (11), if any, form a vane configuration which is concave as viewed from the pressure side (5).

5. Propeller according to any one of claims 1 to 4, characterized in that the vane (2) is concave as viewed from the pressure side (5).

6. Propeller according to any one of claims 1 to 5, characterized in that the front louver element is concave as viewed from the pressure side (5).

7. Propeller according to any one of claims 1 to 6, characterized in that the sound suppressor fins (9, 11) belonging to the propeller are concave as viewed from the pressure side.