PROPELLER

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: PROPELLER The present invention concerns a propeller as defined in the preamble of the main claim. In particular, I the invention concerns propellers intended for blowers. 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 satis¬ factory. Trumpet-like (flared) or tubular sound insulating chambers require great space and in addition their manu¬ facturing 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. The object of the present invention is to eliminate the drawbacks mentioned. The object of the invention is to provide a propeller especially for blov/er 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 blowers, 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. The invention is described in the following in detail with the aid of embodiment examples and referring to the drawing attached, wherein: - O PI Fig. 1 presents a blower according to the in- vention, 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. 6 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 a oblique pitch against the plane placed at right angles to the axis of the hub (visible in Fig. 2) . The propeller has been dis¬ posed 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 and the opposite side is the trailing edge. 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 part¬ ly in front of its leading edge 3, has been disposed a front- louver element 7, substantially parallelling the vane and alar in shape. The front louver in part dips into the vacuum side 6 of the vane and it constitutes a slot 8 between the front louver element and the vane 2. The front louver element 7 is thinner and more narrow in the cross section than the vane 2. The front louver element 7 guides the fluid which the vane meets partly in 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 similar¬ ly 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 . 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. In the embodiment of the invention depicted in Figs 1 and 2, on the trailing side 4 of each vane 2 has been disposed a sound suppressor fin 9, which is centric, substantially parallel to the vane and alar and constitutes a slot 10 between the sound suppressor fin and the vane. The sound suppressor fin is alar in shape, substantially- inferior in thickness and width to 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 on the trailing side of the sound suppressor fin 9 of each vane 2, this latter being equally centric, substantially parallel to the vane and to the preceding sound suppressor fin, and each such fin con¬ stituting a slot 12 between the preceding sound suppressor fi s and the latter sound suppressor fin 1. 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 suppres¬ sor 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. Table 1 Conventional Propeller of propeller the invention Diameter 31cm 30 cm Speed of rotation 1400 r.p.m. 1400 r.p.m. Output 1500 m 3 /hr 1500 m 3 /hr Pressure differential 7 mm H-O 380 nun H,0 Noise level Noisy Virtually noiseless (noise level equivalent to quiet talk) 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 Strδmberg HXUR 208 C2 33, 2.2 kW 1420 r.p.m. The principle of the test set-up was that of BS2843:Part 1:1982, connected to a duct, blowing free. Table 2 Measurement 1 Volumetric flow rate 4 . 45 m /sec Static pressure 34 mm .*. . C. Total pressure 420 Pa Measurement 2 Efficiency calculated for volumetric flow rate 14733 m /hr; power take-up then 1.9 w Total pressure 420 Pa Efficiency 91% Total sonic pressure 76-78 dB 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 identi¬ cal 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.o. . Table 3 Sonic power level in duct, p 3 = 160 Pa Hz 63 125 250 500 1000 2000 4000 8000 dB 84 82 85 83 81 80 80 72 dB. 97 98 98 96 96 96 96 74 The power level of the propeller of the invention has been entered on line dB.. in the table and that of the reference propeller, on line dB-. The invention is not confined to the embodiment example and its embodiments may vary within the scope of the claims stated below. For instance, the shapes, pitch angles, placement with reference to each other and number of the vanes, front.louver elements and sound suppressor fins may vary. It is then 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 louver elements, vanes and sound suppressor fins may in their cross section be plate-like, arcuate or have the shape of curved plates; 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. Furehermore, the number of propeller vanes anji 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. The propeller of the invention is applicable not only in blowers but also in liquid fluids such as for propellers on boats or ships, or for transporting and agitating liquids. 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, the possibly the sound suppressor fins, may ail 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: CLAIMS .. A propeller, comprising a hub (1) and at least two coσentral vanes (2) radially projecting from the hub and having an oblique pitch angle (0.. , 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), c h a r a c t e r i z e d in that on the front side, in the direction of rotation, of each vane (2) partly in front of the leading edge (3) thereof has been disposed a centric front louver element (7) substantially parallel¬ ling the vane and alar in shape, dipping partly into the vacuum side (6) of the vane, and constituting a slot (8) between the front louver element and the vane. 2. Propeller according to claim. ' 1 , c h a r a c t e r i z e d in that on the backside of each vane (2) has been disposed a centric sound suppressor fin (9) substantially parallelling the vane and alar in shape and constituting- a slot ( 10) between the sound suppressor fin and the vane. 3. Propeller according to claim 2, c h a r a c t e r i z e d in that on the backside of the sound suppressor fin (9) of each vane (1) has been placed another, possibly several sound suppressor fins (11), the latter being centric, substantially parallelling the vane and each constituting a slot (12) between the preceding sound suppressor fin (9) and the latter sound suppressor fin (11). ' 4. Propeller according to claim 2 or 3, c h a r a c t e r i z e d in that the sound suppressor fins (9, 11) have been disposed at least in part on the pressure side (5) of the vane(2). 5. Propeller according to any one of claims 1 to 4, c h a r a c t e r i z e d in that the front louver element (7) , the vane (2) and the sound suppressor fin (9) and the latter, if any, and next sound suppressor fins (11) constitute a vane configuration which is concave as viewed from the pressure side (5) . 6. Propeller according to any one of claims 1 to 5, c h a r a c t e r i z e d in that the vane (2) is concave as viewed from the pressure side (5) . 7. Propeller according to any one of claims 1 to 6, c h a r a c t e r i z e d in that the front louver element is concave as viewed from the pressure side (5). 8. Propeller according to any one of claims 1 to- 7, c h a r a c t e r i z e d in that the sound suppressor fins (9, 11) belonging to the propeller are concave as viewed from the pressure side.

Inventors: VARTIALA HEIKKI
Applicants: FOEHN OY, VARTIALA HEIKKI
Application year: 1982
Main classification: F04D29
IPC codes: F04D29