US 2841325 A
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July 1, 1958 wElSE AXIAL COMPRESSORS Filed April 29. 1955 3 Sheets-Sheet l ATTORNE Y5 July- 1, 1958 A. WEISE AXIAL COMPRESSORS 3 Sheets-Sheet 2 Filed April 29, 1955 I VENT 0K IRTUR W619i Ami mils A. WEISE AXIAL COMPRESSORS Jul 1, 1958 Filed April 29, 1955 s She ets-Sheet a ATTORNEYS United States Patent Cfilice AXIAL C(EEIPRESSORS Artur Weise, Ruit uber Esslingen, Germany, assignor to secrete Nahonaie dEtude at de Construction tie Moteurs (lAVliifiGn, Paris, France, a French company Application Aprii 29, 1955, Serial No. 504,955 Claims priority, application France P/Iay 4, 1954 1 Claim. (Cl. 230-114) The increase in the outputs of reaction units clearly necessitates a corresponding increase in the output of the various members and in particular of the air compressor which, in the present state of the art, is most frequently of the axial type. Now, the usual types of axial compressors, such as have been constructed in the greater part of reaction motors, are complicated machines, comprising a fairly large number of wheels which act successively on the fluid to be compressed.
The two-fold requirement of increasing the rated output and of reducing the overall dimensions has lead to the development of supersonic compressors. The most simple machines of this kind spring from the following considerations:
As is well known, if the triangles of speed (see Fig. '1) are considered at the intake and at the outlet of an axial compressor Wheel, in which triangle u is the tangential speed at the mean diameter of the blading, v and W1 are the absolute and relative speeds of the fluid at the entry to the Wheel, v and W2 the absolute and relative speeds on the outlet side of the wheel, the specific Work of compression in the wheel may be expressed as follows:
If it is desired to increase the specific work of compression, either 11 or A or Av can thus be varied or both these factors may be varied. The mechanical properties of the metals do not permit of any substantial increase in the peripheral speed 1: with respect to the very high speeds which are already employed; however, the vectorial difierence Av can be considerably increased if the moving wheel works with an average degree of reaction in the vicinity of O, as is the case in the diagram of speed shown in Fig. 1. 'If a wheel of this kind is rotated at the speed employed in the normal types of axial compressors, the speed v of the fluid discharged from the Wheel is supersonic, although the relative speed W2 of the fluid in the wheel remains subsonic.
This supersonic flow thus creates the problem of a suitable construction for the fixed guiding blades, which are located on the delivery side of the moving wheel and act to convert the kinetic energy acquired by the fluid in the wheel into pressure energy. ,7
In accordance with the point of operation of the compressor, compression or expansion waves are formed at the leading edge of these blades, these waves being comprised between two Mach lines which form, as is known, an angle with the direction of flow known as the Mach angle, the value of this being a function of the Mach number of the flow. These perturbations come in contact with the neighbouring blade, or pass in front of it, and are thus propagated towards the upstream side.
In the first case, that is to say when they strike the neighbouring blade and become reflected from it towards the interior of the grid of blades, and thus towards the downstream side of the flow, the conditions of the incident flow are not changed. In the second case, on the other hand, that is to say when the incident flow and 2,841,325 Fatented July 1, 1958 its direction are such that the waves which are produced 'pass in front of the neighbouring blades and propagate themselves towards the upstream side, into the moving wheel from which they are reflected, the result is that the flow becomes uncontrollable. Even if a supersonic compressor does not exhibit such a phenomenon when it operates at the speed for which it is adapted, it will however inevitably be met with while running up to speed from the position of rest.
The present invention has for its object a device for controlling the flow at the entry of a grid of blades which enables these drawbacks to be overcome.
In this device, the blades are combined with shutters or orientable auxiliary blades which precede them and which can either form an extension of them on the upstream side, or be located opposite the spaces between the blades, the orientation of these shutters or auxiliary blades for certain working speeds of the compressor being such that the incidence of the flow with respect to the said auxiliary blades is nil, and thus has a negligible eifect, and that in consequence the disturbances due to the obstacle are also negligible.
In the case of auxiliary blades which preferably have afine and a sharp leading edge, it is convenient to choose a length of chord such that at all the useful speeds of operation of the compressor, a wave of a certain strength caused by a main blade strikes the auxiliary blade and is thus reflected so as to pass into the grid of main blades, thus avoiding a disturbing effect on the upstream side of the flow.
The auxiliary blades may be rigid and may comprise a point of rotation, either on the body of the main blades, or at any point located between two main blades. The auxiliary blades may also be rigidly built-in along their trailing edges, their leading edges being in this case broughtiinto the direction of the indigent flow by an elastic deformation which is preferably such that the first part of these auxiliary blades which directly follows the leading edge, remains straight. The setting of the auxiliary blades may, for example, be obtained automatically, by using the difierence in pressure between the extrados and the intrados of the blades as the controlling force.
The description which follows below with regard to the attached drawings (which are given by way of example only and not in any sense by way of limitation) will make it quite clear how the invention can be carried into effect, the special features which are brought out, either in the drawings or in the text, being understood to form a part or" the said invention.
Fig. 1 is the diagram of composition of speeds in the moving wheel, which has already been referred to in the opening part of the present description.
Fig. 2 is a diagrammatic view in axial cross-section showing the moving wheel of the compressor and the fixed blades which follow it.
Fig. 3 is a developed view of the blades of the wheel and of the fixed blading.
Figs. 4 to 6 show in a similar manner developed views of fixed blades provided with the improvement in accordance with the invention and showing three diiferent forms of embodiment of this improvement.
Fig. 7 is a view to a larger scale of an embodiment in accordance with Fig. 4 and shows a detail of a control device for the auxiliary blades.
I Fig. 8 is a partial cross-section of this device taken along H the line VlllVlH. In this Fig. 8, the line VIIVII shows the outline of the plane from which Fig. 7 is observed.
In Figs. 2 and 3, there is seen at 1 the blading of the moving wheel of an axial compressor, the blades of which have a tangential speed 1: at their mean diameter.
the crests of the leading edges.
-7a of the compressor (see Fig. 8).
the blades form channels between each other, these channels being first of all'convergent-divergent from a to b in order to transform the supersonic flow to a subsonic flow, and are then divergent from b to 0, playing the .part over this portion of the diffusion channels of ordinary compressor and converting the kinetic energy ofthe gas into pressure energy.
The direction of the leading edges 2a is determined in such manner that at the normal speed of working of the compressor, the absolute speed v of the fluid passing out of the wheel is parallel to these leading edges.
If the conditions of working are such that the absolute speed v of the flow makes 'a certain angle of incidence 'with the leading edges 2a, as is the case in Fig. 3, Mach lines shown by the chain-dotted lines 3 are produced at As will be understood withreference to Fig. 3, these Mach lines'are' propagated towards the upstream side of the flow and give rise to the perturbationswhich have been referred to in the preamble to the presentdescription.
In the form of embodiment of the invention which is shown in Fig. 4, this drawback is obviated by constructing the part of each of the blades 2, which is contiguous with the leading edge of these blades, inthe shape of the part 4 which is separated from the blade and is pivotally fixed thereto at 5, so that it can be directed into the direction of the incident flow. The Mach lines 3 represented in chain-dotted lines, and which are produced at the angular transition between each pivoted inlet part 4 and the body 'of the corresponding blade are stopped by the intake part of the next adjacent blade and are thus reflected towards the downstream side of the flow, as
ing edges of which are fixed. In an embodiment of this type, the blades 4:: maybe shorter than the auxiliary blades formed by the pivoted inlet portions 4 of the embodiment shown in Fig. 4.
In the alternative form of embodiment shown in'Fig. 6, the inlet portions 4 of the blades 2 are no longer articulated but are flexible, these parts being made of elastic material to that end; In the case of each blade, the Mach'line is converted into a network of lines 3b, each of which has an intensity which is only a fraction of the corresponding value in the cases previously discussed.
In Fig. '7, two of the inlet portions or auxiliary blades 4 of Fig. 4 have been shown, eachof these'portions'being pivoted with respect to the body of the corresponding blade 2, To this end, each of these portions is fixed on a spindle 7 adapted to pivot in the fixed casing 7a of the compressor (see Fig. 8).
7 One of these auxiliary blades serves as an automatic control for the others. To this end it is provided with two pressure-tapping points 8, 9, located respectively on its intrados and its extrados. These pressure tappings communicate respectively with conduits 12, 13, through the channels 10,11, formed in the auxiliary blade, and orifices 10a, 11a, drilled in the shaft 7. The conduits 12, 13, start from a fixed box 12a which surrounds the.
extremity of the shaft 7 on the outside of the fixed casing One of the conduits 12 terminates in the interior of the sealed pressure capsules 14. The other conduit, 13 terminates on the exterior of these capsules in an. air-tight box 15 which encloses them. a
If the pressure at the intrados at point 8 is greater than the extrados pressure at the point 9, the pressure capsules expand, whilst they contract in the contrary case. They take up a mean volume for the case in which'the pressures'at 8 and 9 are equal, that is to say for the casein which the control auxiliary blade 4 is' directed exactly in the direction .of the relative flow. 7 In this case, the oil-pressure motor 16, the piston 17 of which is coupled .by the circular rod System18 which surrounds the casing of the compressor'to levers 19 rigidly fixed to the various auxiliary blades, remains in the position of rest and leaves the auxiliary blades in the correct position which they occupy. In fact,'the distributor piston-valve 20, rigidly coupled to the pres sure capsule 14' through the medium of the rod 21, is in the position shown at which it shuts-.ofi'the 'conduits 22, 23 which communicate with the respective faces of' the piston 17. An expansion or a contraction of the capsules 14, when the mean line of the auxiliary blades 4 does not coincide with thedirection of the flow, has the elfect -of displacing the distributor 20, either in one direction :01' the other, thus setting the piston, 17 into action in the appropriate sense so as to place the auxiliaryblades 4 in the direction of the relative flowQ By way of alternative, the conduits 10a and 11a,.in-
stead of being drilled side by side in the' shaft 7, could 1 I be drilled one at each end of this shaft, so that in this case'the conduits 12, "13, would be' connected one to, one end of the said shaft, the other to its opposite, end.
It will further be understood that modifications can ing with a sharp supersonic'leading edge and pivoting about an axis extending substantially at the junction between said portions, meansifor adjusting the angular position of the pivotal portions relatively to the stationary portions, and means responsive to the differential pressure on both sides of a pivotal portion for controlling the former-mentioned means. e
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