US3156407A - Supersonic compressors - Google Patents

Description

Nov. 10, 1964 BOURQUARD 3,156,407 ISUPERSONIC couPREssoRs Filed July 6, 1959 s Sheets-Sheet 1 III "'IIIIIIIIIIIIIII' I 1 111/ IIIIIIIIIIIIIIIIII J IIIII/ IIIIIIIIIIIIIIIIIII III, wally/111111111111 Nov. 10, 1964 F. BOURQUARD 3,

SUPERSONIG COIIPRESSORS Filed July 6, 1959 5 Sheets-Sheet 2 Nov. 10, 1964 F. BOURQUARD 3,156,407

' suransonxc couPasssoas Filed. July 6, 1959 3 Sheets-Sheet 3 I V 'IIIIIlI/llllllllllm 3,156,407 SUPERSONIC COMPRESSORS Fernand Eourquard, Courhevoie, France, assignor to Commissariat a lEnergie Atomique, Paris, France, a

French organization Filed July 6, 1959, Ser. No. 825,166 Claims priority, application France July 7, 1958 4 Claims. (Cl. 230-120) The present invention relates to supersonic compressors for gaseous fluids, that is to say to compressors including at least one blading (supersonic blading), either fixed or movable, through which the relative velocity of the fluid with respect to the blades is higher than the local velocity of sound at least in some portions of the passages formed between said blades.

The invention is more especially but not exclusively concerned with compressors of this type including a blading, either fixed or movable, arranged in such manner that the velocity of the fluid at the inlet thereof is supersonic.

The chief object of the present invention is to provide a compressor of this type which is better adapted to meet the requirements of practice than those used up to now, especially concerning the stability of operation.

According to this invention, each of the passages provided between the blades of the supersonic blading, including an intermediate zone in which a normal shock wave is produced (so that the flow in the passage is supersonic upstream of said zone and subsonic downstream thereof), has its portion located upstream of said intermediate zone shaped in such manner as to produce in said last mentioned portion a succession of expansion waves, that is to say of waves creating an acceleration of the fluid on its way toward said shock wave.

Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

FIG. 1 is a part view showing the development of the annular members of a supersonic axial flow compressor made according to the invention, this view being a section by a cylinder coaxial to the compressor and cutting the blades at mid-height thereof.

FIG. 2 is a similar section of a portion of a rotor blading corresponding to a modification.

FIG. 3 shows the velocity triangle characterizing the operation of this compressor.

FIG. 4 is a section of a portion of a centrifugal compressor according to the invention by a plane perpendicular to the axis of said compressor.

The axial flow compressor diagrammatically illustrated by FIG. 1 includes the following elements:

On the one hand, a set of fixed guide blades 1 which are preferably slightly inclined in such manner that the fluid as it leaves said blades has an absolute velocity Va inclined in a given direction, for instance at an angle of approximately 10, and

On the other hand, a rotor including a set of blades 2 located opposite the set of guide blades 1, said blades 2 having a velocity U (at mid-height of said blades 2 in a direction opposed to that toward which the guide blades 1 are inclined, the value of this velocity U being such that the mean relative velocity Vr of the fluid entering the passages between the rotor blades 2 is supersonic.

By way of example, illustrated by the velocity triangle of FIG. 3, if a is the local velocity of sound at the inlet of rotor 2, the velocity Va may be given a value of approximately 0.7a and the velocity U is given a value of about 1.2a.

Thus the velocity Vr of the fluid at the inlet of the passages between blades 2 has a value of about 1.6a, that is to say is supersonic.

} United States Patent 3,156,407 Patented Nov. 10, 1964 It is known that it has already been endeavoured, by a suitable shaping of the blades 2 of such a rotor, in particular by giving a divergent shape to the end portion of every passage P provided between two successive blades, to create during the operation, in each of the respective passages P, a normal shock wave D (recompression wave) downstream of which the velocity of flow becomes subsonic whereas the velocity upstream of said shock wave is supersonic.

In a supersonic blading of this kind, Where normal shock waves are formed, it is advantageous to produce, upstream of the normal shock wave D of every passage, an intermediate transient zone where take place phenomenons which modify the pressure and velocity of the gaseous stream flowing through said transient zone.

For this purpose, it has been suggested to shape the supersonic blades, in their portions located upstream of the normal shock wave, in such manner as to create, in every passage, upstream of said normal shock wave, one or several oblique shock waves (recompression waves) intended to slow down the gaseous flow and to increase its pressure before it reaches said normal shock wave.

Such an arrangement, which has the advantage of increasing the pressure of the gaseous flow gradually from the first recompression oblique wave to the normal shock wave, involves a lack of stability of said normal shock wave for some conditions of operation, in particular in the case of a sudden increase of the How in the downstream direction, this lack of stability preventing the normal shock wave from being maintained in the vicinity of the supersonic throat.

The object of the present invention is to overcome this drawback at the cost of a small supplementary loss of pressure in the gaseous flow.

According to this feature, blades 2, in the portion of each of them limiting the transient zone of every passage P and located upstream of the normal shock wave D are arranged in such manner as to produce in said transient zone, instead of recompression waves, expansion waves d d d (only some of which are shown on FIG. 1). The effect of these expansion waves is to accelerate the flow of fluid upstream of the normal shock wave D (whereas the recompression waves according to prior devices slowed down the flow in the transient zone) thus further permitting, at the place of said normal shock wave, a distribution of velocities of regular divergence.

It results therefrom that the normal shock wave D has a convexity turned toward the downstream direction, such a convexity being favorable to the stabilization of said shock wave. When shock wave D is urged in the downward direction by an increase of the flow rate of the gaseous stream, it moves slightly in this downstream direction, thus increasing the suction produced immediately upstream of said normal shock wave by the successive actions of expansion waves d d d etc.

Shock wave D having been moved toward higher velocities, a more violent shock is produced at the passage through said shock wave D, so that there is an increased pressure drop which compensates for the increase of suction in the downward direction.

The normal shock wave D is thus stabilized in its new position.

It will be understood that such an operation is inherent in the presence of expansion waves upstream of the normal shock wave because, when the transient zone is occupied by recompression waves, the pressure drop at the passage through the normal shock wave is the lower as the shock wave is moved a greater distance in the downward direction by suction. Therefore in this case, the normal shock wave is unstable in case of sudden suction thereof in the downward direction.

Concerning now the means to be provided'for creating, in said transient zone, the expansion waves that are to accelerate the gaseous fluid flow through said zone, they may be obtained by giving at least the suction face E of every blade, in the portion thereof located in the transient zone, a suitable convexity, the portion of the suction face located upstream of this convex portion being preferably rectilinear and extending substantially in the direction of the inlet velocity Vr of the gaseous fluid stream.

Thus the suction face E of every blade 2 includes a substantially rectilinear flat area starting from the blade leading edge, parallel to the velocity Vr of the gaseous stream entering the passages between the blades, this flat area extending from the leading edge A of the blade to the point B from which an expansion wave d starting from the suction face of the blade that is considered reaches the next blade at the leading edge A thereof. After this flat area, the suction face E of blade 2 includes a slightly convex portion BC (the respective tangents at B and C making an angle of approximately 7 with each other). This convex portion BC pr ferably has a constant curvature and its end C is advantageously at the point where an oblique shock wave A C starting from the leading edge A of the next blade reaches the blade suction face that is being considered. Finally the blade suction face E includes, after this convex portion BC, a rectilinear portion CD extending at least as far as the place where the normal shock wave D is located. This rectilinear portion increases the deflection produced by convex portion BC (the angle between the tangent at C to BC and the rectilinear portion having advantageously the same order of magnitude as the dihedral angle of the leading edge of the blade). This rectilinear portion CD extends beyond point D possibly as far as the trailing edge F of the blade. It may also be followed by a curvilinear portion arranged in accordance with the laws of subsonic aerodynamics so as to obtain the desired result at the ou let of the blading.

As for the pressure face I of the blade, it may be given a substantially rectilinear shape from the leading edge A to the trailing edge F.

According to the modification illustrated by FIG. 2, the convexity of 7 above referred to with reference to FIG. 1 may be distributed between the two opposite walls that limit the transient zone, these two walls including for instance'convex portions BC and BC, each of which correspond to a change of direction of 3.5". Each of said convex portions may be followed by rectilinear portions forming the divergent diffuser passage.

Anyway, there is obtained in every passage P, upstream of the normal shock wave .0 thereof, an increasing velocity gradient for the air stream, accompanied by an expansion, then, after the shock wave, a recompression and fan-like distribution of the velocities, which are suddenly reduced by the passage of the fluid through the shock wave, such an arrangement making it possible to stabilize the normal shock wave.

FIG. 4 shows a centrifugal compressor made according to the present invention. This compressor includes a bladed rotor 3 delivering a gaseous fluid at supersonic relative velocity to a fixed diffuser blading.

Preferably, at the inlet of every passage P formed between two successive blades, there is obtained for the flow of the fluid a movement of permanent velocity such that the surfaces of equal velocities and equal pressures are of revolution about an axis of rotor 3. For this purpose, the inlet portion AB of the suction face of every blade is given the shape of a concave spiral arc producing recompression waves directed toward rotor 3, the end point B of this are corresponding to the last compression wave BA capable of reaching said rotor without being stopped by the leading edge A of the next blade.

After point B, the suction face E of the blade include a convex area intended to create, in the transient zone located upstream of the normal shock wave D", expansion waves capable of accelerating the flow of the fluid, the end point C of this convex portion (the curvature of which may, as above, correspond to a deflection of 7) being preferably the point where the oblique shock wave starting from the leading edge A of the next blade reaches the pressure face E of the blade that is being considered. After this convex area, there is provided a rectilinear flat area which increases the deflection by an angle approximately equal to the angle of the leading edge, this last mentioned flat area extending as far as the trailing edge of the blade.

Thus point B constitutes an inflexion point whereas point C constitutes an angular point in the profile of the lade.

As for the pressure face I of every blade, it may include a rectilinear fiat area starting from the leading edge and continued by a convex portion limiting, together with the oppositely disposed suction face of the next blade, a subsonic diffuser in which may possibly be disposed a guide blade 5.

Whatever be the type of compressor made according to the invention, the passages P between the blades may be either of rectangular transverse section or of ovoid or circular transverse section.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and cflicient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there m'ignt be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended Within the scope of the accompanying claims.

What I claim is:

1. A supersonic axial flow compressor for a gaseous fluid which comprises, in combination, a casing, two coaxial annular members mounted in said casing adjacent to each other in the axial direction and defining an annular flow duct for said gaseous fluid through said two members successively in said axial direction, the downstream member being a rotor, blades carried by said rotor and extending across said flow duct to form between them a plurality of passages for said gaseous fluid, and guide blades carried by the upstream member and arranged to guide said fluid, fed thereto at a predetermined velocity to give it as it leaves said guide blades a velocity represented by a given vector, each of said rotor blades comprising on the suction face thereof a substantially flat area extending from its leading edge and parallel to the vector which is the resultant of the above mentioned vector and of a vector representing the relative velocity of said rotor blade leading edge at working speed with respect to said upstream member, the velocities represented by the two last mentioned vectors being such that the resultant velocity is supersonic, the fore portion of each of said passages being convergent and the rear portion divergent in the direction of the gaseous fluid flow, with a throat region between said portions, so as to produce a normal shock wave rearwardly of said convergent portion, downstream of which shock wave the fluid flow is subsonic, said suction face of each of said rotor blades comprising, after said flat area, a slightly convex area extending from said flat area to said throat portion, said flat and convex areas being arranged to produce, in said convergent portion of said passage, a succession of expansion waves creating an acceleration of the gaseous fluid flowing past them to reach said throat region, said convex area beginning at the points from which an expansion wave starting from said suction face reaches the leading edge of the next blade facing said suction face.

2. A supersonic axial flow compressor for a gaseous fluid which comprises, in combination, a casing, two

coaxial annular members mounted in said casing adjacent to each other in the axial direction and defining an annular flow duct for said gaseous fluid through said two members successively in said axial direction, the downstream member being a rotor, blades carried by said rotor and extending across said flow duct to form between them a plurality of passages for said gaseous fluid, and guide blades carried by the upstream member and arranged to guide said fluid, fed thereto at a predetermined velocity to give it as it leaves said guide blades a velocity represented by a given vector, each of said rotor blades comprising on the suction face thereof a substantially flat area extending from its leading edge and parallel to the vector which is the resultant of the above mentioned vector and of a vector representing the relative velocity of said upstream member at Working speed with respect to said rotor blade leading edge, the velocities represented by the two last mentioned vectors being such that the resultant velocity is supersonic, the fore portion of each of said passages being convergent and the rear portion divergent in the direction of the gaseous fluid flow, with a throat region between said portions, so as to produce a normal shock wave rearwardly of said convergent portion, downstream of which shock wave the fluid iiow is subsonic, said suction face of each of said rotor blades comprising, after said flat area, a slightly convex area extending from said flat area to said throat portion, and, after said convex area, a flat area extending at least as far as the place where said normal shock wave is produced, said flat and convex areas being arranged to produce, in said convergent portion of said passage, a succession of expansion waves creating an acceleration of the gaseous fluid flowing past them to reach said throat region, said convex area beginning at the points from which an expansion wave starting from said suction face reaches the leading edge of the next blade facing said suction face.

3. A supersonic axial flow compressor for a gaseous fluid which comprises, in combination, a casing, two coaxial annular members mounted in said casing adjacent to each other in the axial direction and defining an annular flow duct for said gaseous fluid through said two members successively in said axial direction, the downstream member being a rotor, blades carried by said rotor and extending across said flow duct to form between them a plurality of passages for said gaseous fluid, and guide blades carried by the upstream member and arranged to guide said fluid, fed thereto at a predetermined velocity to give it as it leaves said guide blades a velocity represented by a given vector, each of said rotor blades comprising on the suction face thereof a substantially flat area extending from its leading edge and parallel to the vector which is the resultant of the above mentioned vector and of a vector representing the relative velocity of said upstream member at working speed with respect to said rotor blade leading edge, the velocities represented by the two last mentioned vectors being such that the resultant velocity is supersonic, the fore portion of each of said passages being convergent and the rear porat least as far as the place where said normal shock wave is produced, said flat and convex areas being arranged to produce, in said convergent portion of said passage, a succession of expansion waves creating an acceleration of the gaseous fluid flowing past them to reach said throat region, the pressure faces of said rotor blades being of flat rectilinear shape from the leading edge to the trailing edge of each of said blades, said convex area beginning at the points from which an expansion wave starting from said suction face reaches the leading edge of the next blade facing said suction face.

4. A supersonic axial flow compressor for a gaseous fluid which comprises, in combination, a casing, two coaxial annular members mounted in said casing adjacent to each other in the axial direction and defining an annular flow duct for said gaseous fluid through said two members successively in said axial direction, the downstream member being a rotor, blades carried by said rotor and extending across said flow duct to form between them a plurality of passages for said gaseous fluid, and guide blades carried by the upstream member and arranged to guide said fluid, fed thereto at a predetermined velocity to give it as it leaves said guide blades a velocity represented by a given vector, each of said rotor blades comprising on the suction face thereof a substantially flat area extending from its leading edge and parallel to the vector which is the resultant of the above mentioned vector and of a vector representing the relative velocity of said upstream member at working speed with respect to said rotor blade leading edge, the velocities represented by the two last mentioned vectors being such that the resultant velocity is supersonic, the fore portion of each of said passages being convergent and the rear portion divergent in the direction of the gaseous fluid flow, with a throat region between said portions, so as to produce a normal shock wave rearwardly of said convergent portion, downstream of which shock wave the fluid fiow is subsonic, said suction face of each of said rotor blades comprising, after said flat area, a slightly convex area extending from said flat area to said throat portion, and, after said convex area, a fiat area extending at least as far as the place where said normal shock wave is produced, said flat and convex areas being arranged to produce, in said convergent portion of said passage, a succession of expansion tion divergent in the direction of the gaseous fluid flow,

with a throat region between said portions, so as to produce a normal shock wave rearwardly of said convergent portion, downstream of which shock wave the fluid flow is subsonic, said suction face of each of said rotor-blades comprising, after said flat area, a slightly convex area extending from said flat area to said throat portion, and, after said convex area, a flat area extending waves creating an acceleration of the gaseous fluid flowing past them to reach said throat region, the pressure faces of said rotor blades being of convex shape from the leading edge to a point upstream of} said throat region, said convex area beginning at the points from which an expansion wave starting from said suction face reaches the leading edge of the next blade facing said suction face.

References Cited in the tile of this patent UNITED STATES PATENTS 2,435,236 Redding Feb. 3, 1948 2,659,528 Price Nov. 17, 1953 2,934,259 Hausmann Apr. 26, 1960 2,935,246 Roy May 3, 1960 FOREIGN PATENTS 459,043 Italy Aug. 23, 1950 687,338 Great Britain Feb. 11, 1953 687,365 Great Britain Feb. 11, 1953 776,676 France Jan. 31, 1935 1,106,834 France July 27, 1955

Claims (1)

1. A SUPERSONIC AXIAL FLOW COMPRESSOR FOR A GASEOUS FLUID WHICH COMPRISES, IN COMBINATION, A CASING, TWO COAXIAL ANNULAR MEMBERS MOUNTED IN SAID CASING ADJACENT TO EACH OTHER IN THE AXIAL DIRECTION AND DEFINING AN ANNULAR FLOW DUCT FOR SAID GASEOUS FLUID THROUGH SAID TWO MEMBERS SUCCESSIVELY IN SAID AXIAL DIRECTION, THE DOWNSTREAM MEMBER BEING A ROTOR, BLADES CARRIED BY SAID ROTOR AND EXTENDING ACROSS SAID FLOW DUCT TO FORM BETWEEN THEM A PLURALITY OF PASSAGES FOR SAID GASEOUS FLUID, AND GUIDE BLADES CARRIED BY THE UPSTREAM MEMBER AND ARRANGED TO GUIDE SAID FLUID, FED THERETO AT A PREDETERMINED VELOCITY TO GIVE IT AS IT LEAVES SAID GUIDE BLADES A VELOCITY REPRESENTED BY A GIVEN VECTOR, EACH OF SAID ROTOR BLADES COMPRISING ON THE SUCTION FACE THEREOF A SUBSTANTIALLY FLAT AREA EXTENDING FROM ITS LEADING EDGE AND PARALLEL TO THE VECTOR WHICH IS THE RESULTANT OF THE ABOVE MENTIONED VECTOR AND OF A VECTOR REPRESENTING THE RELATIVE VELOCITY OF SAID ROTOR BLADE LEADING EDGE AT WORKING SPEED WITH RESPECT TO SAID UPSTREAM MEMBER, THE VELOCITIES REPRESENTED BY THE TWO LAST MENTIONED VECTORS BEING SUCH THAT THE RESULTANT VELOCITY IS SUPERSONIC, THE FORE PORTION OF EACH OF SAID PASSAGES BEING CONVERGENT AND THE REAR PORTION DIVERGENT IN THE DIRECTION OF THE GASEOUS FLUID FLOW, WITH A THROAT REGION BETWEEN SAID PORTIONS, SO AS TO PRODUCE A NORMAL SHOCK WAVE REARWARDLY OF SAID CONVERGENT PORTION, DOWNSTREAM OF WHICH SHOCK WAVE THE FLUID FLOW IS SUBSONIC, SAID SUCTION FACE OF EACH OF SAID ROTOR BLADES COMPRISING, AFTER SAID FLAT AREA, A SLIGHTLY CONVEX AREA EXTENDING FROM SAID FLAT AREA TO SAID THROAT PORTION, SAID FLAT AND CONVEX AREAS BEING ARRANGED TO PRODUCE, IN SAID CONVERGENT PORTION OF SAID PASSAGE, A SUCCESSION OF EXPANSION WAVES CREATING AN ACCELERATION OF THE GASEOUS FLUID FLOWING PAST THEM TO REACH SAID THROAT REGION, SAID CONVEX AREA BEGINNING AT THE POINTS FROM WHICH AN EXPANSION WAVE STARTING FROM SAID SUCTION FACE REACHES THE LEADING EDGE OF THE NEXT BLADE FACING SAID SUCTION FACE.

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