US 3181777 A
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May 4, 1965 R. COESTER RANSVERSE-FLOW BLOWER 2 Sheets-Sheet 1 Filed Nov. '27, 1962 May 4, 1965 R. CQESTER 3,181,777
TRANSVERSE-FLOW BLOWER Filed NOV. 27, 1962 2 Sheets-Sheet 2 Fig. 2
United States Patent 3,181,777 'IRANSVERSE-FLOW BLOWER Robert Coester, Haldenstrasse, Zumikon,
Zurich, Switzerland Filed Nov. 27, 1962, Ser. No. 240,310 Claims priority, application Switzerland, Nov. 29, 1961, 13,940/ 61 6 Claims. (Cl. 230-125) This invention relates to a transverse-flow blower in which an approximately radial, inwardly directed supplementary airstream is supplied to the rotor where it enters the low pressure chamber.
By the admission of a supplementary airstream the characteristic of such a blower is stabilized and its efliciency considerably increased, but due to the abrupt change of the flow velocities in the rotor caused by the supplementary airstream, particularly in the vicinity of the point of entry of the rotor into the low pressure chamber, undesirable noise is often produced.
It is an object of the present invention to counteract the generation of noise without, however, surrendering or even impairing the useful characteristic and the excellent efiiciency of the blower. The invention is based on the realization that the transition taking place in the rotor from the outward flow in the zone of the high pressure chamber to the inward flow which prevails in the zone of the low pressure chamber, must be effected gradually, rather than abruptly, but at any rate in such a manner that the inward flow is established at the right time and in sufiicient quantity. Several proposals have already been made for influencing the vortex flow produced between the low pressure chamber and the high pressure chamber in the vicinity of the rotor periphery. T heseproposals have been made after the recognition that the operation and the behaviour of transverse-flow blowers are influenced by the position and concentration of these vortices.
According to one of these proposals the vortex flow in the rotor is more or less substantially retarded in the zone of high flow velocity by guiding devices provided outside of the rotor, in order to reduce the friction losses occurring at high flow velocities and the supplementary stream supplied to the low pressure chamber in immediate proximity to the entry of the rotor, serves to start the rotor flow. This type of construction results in high pressures and good efficiencies. On account of the relatively rapid change in flow velocities in circumferential direction at the point where the supplementary stream is admitted, however, noises are produced which are inadmissible for certain cases of application.
In another case it is started from the idea of producing in the rotor a vortex as concentrated as possible by means of a supplementary stream, in order to obtain high flow velocities in proximity of the vortex center. It is assumed in this case that hereby a particularly high pressure can be produced, especially at low Reynolds numbers. In such arrangements, however, the static pressure is gained more by rnixing, i.e. by turbulent exchange of momentum, than by diffusion, whereby the efiiciency of the machine becomes poor. Moreover, themixing effect referred to is substantially more dependent on the Reynolds number than the dilfusion effect. Finally objectionable noise levels are produced with the concentrated vortex by the high local supervelocities and the rapid change in the direction of flow.
In the transverse-flow blower according to the invention the disadvantages mentioned above are avoided by introducing at least a portion of the supplementary stream into the low pressure chamber at a zone situated upstream with respect to the point of entry of the rotor flow and by producing a continuous vortex distribution in the 3,181,777 Patented May 4, 1965 rotor. To this end a first air passageway or return duct is provided between the high pressure chamber and the low pressure chamber of the transverse-flow blower, in order to produce the supplementary stream. The return duct starts in a diffusor adjacent to the high pressure chamber and spaced a certain distance apart therefrom opens into the low pressure chamber upstream of the point of entry of the rotor. Thereby it is suitable to situate the inlet opening of the return duct in that zone of the diffusor which is poor in energy.
In order to produce a continuous 'vortex formation in the rotor the portion of the housing means or casing remaining between the return duct and the rotor, is formed as a multiply curved guide surface on its side facing the rotor. The slot formed between this guide surface and the rotor periphery has a well-rounded inlet from the high pressure chamber, narrows hereafter to a minimum and subsequently widens again gradually, Thus, the slot may be characterized as convergent-divergent in the,
direction of rotation of the rotor. Finally the guide surface bordering the slot is bent somewhat radially towards the rotor and ends in proximity thereof in a tongue. The inletflow consisting of the already mentioned auxiliary stream and of the air sucked-in from the outside commences afterfthis tongue.
The invention will now be more particularly described by way of example with reference to the accompanying drawing in which:
FIGURE 1 illustrates diagrammatically a partly sectional view of a transverse-flow blower according to the invention.
FIGURE 2 is a diagram showing various 'vortex distributions 7/ just at the inner edge portion of the blade screen.
FIGURE 3 shows the ratio Cm/Cu along said inner edge portion, symmetrical vortex and velocity distributions only being taken into consideration, and
FIG. 4 shows velocity triangles. Referring to FIGURE 1 of the drawing the blower,
rather the interior space thereof is divided into two chambers 2 and 3 by the rotor 1. The latter is made in wellknown manner of discs 4 (in the drawing only one such disc is shown) between which blades 5 arearranged and transversely fastened on the periphery of the disc at a predetermined angle of incidence. Upon rotation of the rotor 1 in the direction of the arrow P the air passes, as indicated by the arrow L, out of the chamber 2, i.e. out of the low pressure or inlet chamber through the rotor into the chamber 3, i.e. into the high pressure or outlet chamber, and is carried away from there by a diffuser 6, as this is indicated by another arrow L.
A duct 7 arranged in the direction of rotation of the rotor 1 between the low pressure chamber 2 and the high pressure chamber 3, communicates at one end with the low pressure chamber 2 and at the other end with the rotor 1 previous to the entry thereof into the high pressure chamber. It serves to improve the flow conditions in the rotor at the point where the latter enters the low pressure chamber. This arrangement needs no closer discussion in connection with the present subject.
At the side of the rotor about diametrically opposite to the duct 7 the housing means of the blower designated as a whole by the numeral 8, is provided with a further duct or first air passageway 9 one end of which extends into the diffusor 6 in the zone of the inwardly curved wall 6' of the latter for a supply of air under pressure. The other end of the duct 9 communicates with the suction chamber 2, whereby the opening 9 of the duct 9 in the lowpressure chamber 2 is arranged upstream with respect to the point of entry 10 of the rotor 1 into the low pressure chamber 2. The direction of the section of duct 9 adjacent to the opening 9' is selected so that the supplementary stream issuing from the duct 9 flows about tangentially to the housing walls 11 and 12 limiting the inlet flow towards the point of entry 10 of the rotor 1 into the low pressure chamber. This supplementary stream originates, as it is evident, in the high pressure chamber 3, particularly in the relatively energy-poor zone along the inner wall of the diffusor. 'Attention is called again here to the fact that thereby at the same time an improvement in the pressure conversion in the diffusor is obtained.
The convergent-divergent slot 13 defined or delimited on the one hand by the rotor periphery and on the other hand by the guide surface 14 formed by the housing means 8, which surface extends from the inlet at point 16 to the end at tongue 1% beyond a point 15 at which the slot width reaches a minimum, serves to produce a continuous vortex distribution in the rotor as shall be explained in more detail hereafter. At 16, i.e. at the inlet or transition of the slot 13 into the pressure chamber 3 the wall of the guide surface 11 is strongly rounded and extends generally away from the rotor periphery as shown. The recess between point 15 and point 10 is connected to the side 8' of the duct 9 by means of a second air passageway or bypass 17. Thus, the said passageway or bypass communicates at its discharge end with the divergent portion of the slot 13. In an additional construction of the transverse-flow blower this bypass 17 is omitted.
As mentioned, upon rotation of the rotor in the sense of the arrow P the air flows in the direction of the arrow L from the low pressure chamber through the rotor into the high pressure chamber 3 and through the ditfusor 6. A small portion of the air from the high pressure chamber 3 can penetrate through the slot 13, where the air will be considerably deflected towards the periphery of the rotor by the wall 14 shortly before reaching point 10. There is formed thereby in the vicinity of the rotor periphery counter-clockwise vortices, as it is indicated by the continuously returning lines W and W By means of these vortices or vortex distributions the velocity conditions in the rotor are influenced, whereby the described formation with respect to noise production as well as with regard to energy losses due to internal friction is very advantageous. The duct 17 from duct 9 opening into the slot 13 shortly ahead of point 10 serves to supply energy-rich air to compensate frictional losses occurring in slot 13.
The supplementary air stream which, as mentioned, is taken from the relatively energy-poor zone along the inner wall of the diffusor and which passes through duct 9 into the low pressure chamber, flows along the wall 12 at the point 10 of entry of the rotor 1 into the low pressure chamber, whereby the supplementary stream can mix with the remaining incoming air prior to arriving at the rotor. Thereby abrupt velocity changes along the rotor periphery are avoided.
Already previously the inventor has theoretically proved that, as soon as the relative velocity at the inner edge portion of the rotor blade screen is everywhere radial, a potential flow in the interior of the rotor must consist of vortices, the centers of which lie on the inner edge of the blade screen. An arbitrary, thus also a continuous distribution of such vortices is possible with the sole limitation that the sum of the vortex forces result in a flow velocity on the inner edge portion of the blade screen that equals the peripheral rotor velocity existing just on that point.
FIGURE 3 shows various calculated velocity distributions on the inner edge portion of the blade screen resulting from the associated vortex distributions max according to FIGURE 2 just at this inner edge portion. The peripheral component of flow Cu is constant.
FIGURE 3 shows the ratio Cm/Cu (Cm=radial component of the flow velocity) along the circumferential angle a. Symmetrical vortex and velocity distributions only are taken into consideration. In the same manner, however, asymmetrical distributions may also be realized.
From FIGURES 2 and 3 it results that fiat velocity distributions having low supervelocities and only gradual velocity changes along the periphery, which distributions are essential not only for lowest noise occurrence but also for a good efficiency of the pressure generation by diffusion, can be obtained only with continuous vortex distributions. Such vortex distributions occur, when the housing surrounding the rotor is formed so that outside of the rotor at flow pattern is rendered possible, which conforms to the type of flow calculated on the inner edge portion of the blade screen according to the laws of continuity and energy economy. For the configuration of the housing section between outlet difiusor and low pressure chamber, the velocity triangles shown in FIGURE 4 have to be considered: In order to obtain an admission from the outside upon the forwardly curved blades 1, as free as possible from shocks, the flow medium must be supplied at low meridian velocity Cm to the rotor at low velocity and with a velocity component in the direction of the peripheral velocity. In this zone the flow medium must have an increased total pressure relatively to the low pressure chamber, so that the total pressure in the interior of the rotor remains constant throughout. As soon as the meridian velocity shall increase to Cm, the direction of admission must change in such a manner that the velocity component slowly disappears in the direction of the direction of the peripheral velocity and finally the medium will be supplied with opposed vortex. The conformation of the slot 13 in FIGURE 1 from point 15 to point 10 and the wall 12 follows these conclusions. However, the zone over which vortices are distributed along the inner edge portion of the screen, may be further extended by connecting a longer well rounded inlet ahead of the slot whereby a shape of slot is produced according to FIGURE 1. This slot is characterised by a well rounded inlet until a certain minimum distance from the rotor, which may be relatively small, e.g. also smaller than /3 of the blade depth in radial direction. This rounded admission affords for a continuous vortex and velocity distribution between the points 16 and 10 even for working conditions of the blower far deviating from the point of optimum output. Thereby it is attained that the described blower in contradistinction to herefore known constructions operates with a low noise level in a wide zone of its characteristic. The losses occuring in this section of the rotor are covered by the energy of the medium supplied shortly before termination of the feeding operation. In those cases where this does not suffice, a small channel 17 is provided, through which additional medium from a farther downstream portion of the dilfusor may be supplied to the rotor.
The essential portion of the energy still required for covering losses and for stabilizing the entire field of flow, however, is taken from the supplementary stream issuing from duct 9, which at least partly opens upstream into the low pressure chamber tangentially to the incoming stream. The mouth of the fiow at an upstreamlocation, thus not in immediate proximity to the rotor, is pro vided, in order that eventual velocity differences between supplementary airstream and drawn-in medium may be compensated or flattened out by intermixing, and that abrupt changes in velocity on the periphery of the rotor edge, which produce noise, may no longer occur.
1. The combination in a transverse-flow blower of a rotor rotatable in one direction and a housing means, said housing means defining a low pressure inlet chamber for a generally radial supply flow of air into the rotor and a high pressure outlet chamber for a generally radial flow of air outwardly from the rotor, said housing means serving also to define with the rotor and adjacent its periphery an arcuate convergent-divergent slot, said slot being convergent-divergent in the direction of rotation of the rotor and being disposed adjacent and in communication with said high pressure chamber at a portion of the later whereat the rotor leaves the same in rotation, said housing means serving also to define a rounded inlet surface for said slot which extends generally away from the rotor periphery in the high pressure chamber, said housing means serving also to define a first air flow passageway which communicates with said low pressure chamber so as to discharge a supplementary air stream thereto approximately tangentially with respect to supply air flow therein and which is connectible with a supply of air under pressure, and said housing means serving also to define a second air flow passageway having a discharge end in communication with said slot and whichis connectible with a supply of air under pressure, said discharge end of said second passageway being in communication with the slot in the divergent portion of the latter.
2. The combination in a transverse-flow blower as set forth in claim 1 wherein said first air passageway communicates with said high pressure chamber for its supply of air under pressure.
3. The combination in a transverse-flow blower as set forth in claim 2 wherein said second air flow passageway is arranged to communicate with and receive air under pressure from said first air flow passageway.
4. The combination in a transverse-flow blower as set forth in claim 1 wherein said housing means also defines a relatively deep recess communicating with the divergent portion of said slot and which is bounded by an arcuate housing means surface which curves inwardly from said divergent slot portion to approximately a radial line.
5. The combination in a transverse-flow blower as set forth in claim 4 wherein said first air passageway communicates with said high pressure chamber for its supply of air under pressure.
6. The combination in a transverse-flow blower as set forth in claim 5 wherein said second air flow passageway is arranged to communicate with and receive air under pressure from said first air flow passageway.
References Cited by the Examiner FOREIGN PATENTS 935,340 2/48 France. 830,362 3/60 Great Britain. 876,611 9/61 Great Britain.
JOSEPH H. BRANSON, IR., Primary Examiner.
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