US2965287A

US2965287A - Radial flow compressor

Info

Publication number: US2965287A
Application number: US616847A
Authority: US
Inventors: Schug Helmut
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1955-11-11
Filing date: 1956-10-18
Publication date: 1960-12-20
Anticipated expiration: 1977-12-20

Description

Dec. 20, 1960 SCHUG 2,965,287

RADIAL FLOW COMPRESSOR Filed Oct. 18, 1956 INVENTOR Helmui Sc/zu BY M WM 2.

ATTORN United States Patent O RADIAL FLOW COMPRESSOR Helmut Schug, Augsburg, Germany, assignor to Maschinenfahrik Augsburg-Nurnberg A.G., Augsburg, Germany, a corporation of Germany Filed Oct. 18, 1956, Ser. No. 616,847

Claims priority, application Germany Nov. 11, 1955 4 Claims. (Cl. 230-134) This invention relates to radial flow compressors and, more particularly, to the structure of impeller blades for radial flow gas compressors.

In designing the shape of impeller blades for radial flow compressors it may be desired to obtain as smooth as possible inlet flow for optimum efiiciency and functioning of the compressor. One may attempt to obtain this characteristic by forming the impeller blades in a twisted configuration radially so that, for each point along the radially extending leading edge of the blade, the angle at which the fluid medium to be compressed enters the blade or impinges thereon corresponds to the direction of relative velocity resulting from the geometric or vectorial sum of the peripheral velocity and the absolute flow velocity. That is, by the absolute flow velocity is meant here the velocity of a fluid particle with respect to its surroundings which are at rest, while by relative velocity is meant the velocity of a moving particle relative to or with respect to the moving impeller blades toward which it is flowing. Also, one may attempt, in developing a radial flow compressor with inducer blades at the inlet thereof, to form the front part of the blade so that it is bent in a peripheral direction along a line which is inclined to a radial plane in the direction of flow.

Such attempts, however, may require, in order to obtain the desired inlet angle at the radially inner edge of the blade adjacent the hub, that the inner blade tip be separated from the hub for a portion of its length. Such undercutting may be quite disadvantageous from the standpoint of strength since the fatigue strength of such an impeller may be greatly reduced by not having the blades fastened to the rotor or hub completely along the full extent of their inner edges, and the notch formedv in such an arrangement may produce a starting point for cracks or other weaknesses.

If it is attempted to eliminate the undercutting and yet adapt the leading edge of the blade to the different relative velocities at various points along the radius of the impeller by providing a blade with different curvatures along different streamlines, the manufacture and formation of such blades may be quite ditficult and expensive.

According to this invention, however, an impeller blade is provided with the desired inlet angles and yet with the blade fastened to the rotor or hub of the compressor throughout its entire radially inner edge. This is accomplished by making the blade so that the surface thereof adjacent the inlet or leading edge is a portion of the surface of a cylinder the axis of which lies in a plane parallel to the axis of the impeller and is inclined at an angle to a radial plane in the direction of fiow. By correlation of the angle of inclination of the cylinder axis and its distance from the leading edge of the blade and the radius of curvature of the cylindrical surface according to this invention, blades are provided having inlet angles corresponding to the directions of the relative velocities at the inlet of the compressor.

One object of this invention is to provide an impeller blade of the character described for a radial flow cornpressor such that the blade has but a single profile curvature and yet provides an inlet angle which corresponds to the direction of relative velocity at various radial points along the inlet edge.

Another object of this invention is to provide an impeller blade of the character described having a single cylindrical surface profile configuration and also being arranged on the hub or rotor of the impeller so that the blade is fastened thereto throughout its radially inner extent, yet has a leading or inlet edge on which the medium to be compressed impinges with optimum smoothness of flow.

A further object of this invention is to provide a radial flow compressor of the character described having blades formed as a portion of a cylindrical surface but with leading edges inclined to the direction of flow to provide inlet flow angles corresponding to the direction of the relative velocity at various radial points along the leading edge of the blade.

Other objects and advantages will be apparent from the following description, the accompanying drawing,

and the appended claims.

In the drawing Fig. l is a geometric representation of the development of the surface of an impeller blade embodying this invention;

Fig. 2 is a partial axial section through a centrifugal compressor embodying this invention;

Fig. 3 is a partial radial section through the impeller of Fig. 2;

Fig. 4 is a section along the line IVIV of Fig. 2; and

Fig. 5 is a section along the line V-V of Fig. 2.

Referring to the drawing, in which like reference characters refer to like elements throughout the several views thereof, the development of the surface of an impeller blade according to this invention is illustrated in Fig. l. The line aa. represents the axis of the impeller, and the plane E is a radial plane perpendicular to E and parallel to axis a-a. An imaginary cylinder Z is located with its axis zz lying in plane E and inclined to radial plane E, at an angle 5i.e. the angle between the cylinder axis zz and the line of intersection d--d of planes E and E The radius of cylinder Z is indicated by r and, in the case of an infinitely thin blade, would be equal to the distance between plane E and rotor axis aa. In such a geometric arrangement, the blade itself is formed as a portion of the surface of cylinder Z, and is indicated at S in Fig. 1 cross-hatched.

Referring to Figs. 2-5, an impeller 1 is indicated for a centrifugal compressor having axial inlet flow and radial outlet flow. The impeller 1 is mounted on a shaft 2.

ing blade portion 3.

Patented Dec. 20, 1960 tion, the various points P P P and P and P are additionally designated with

subscripts

4 and 5 as used in Figs. 4 and 5, respectively. Also the designations r and 6 in Figs. 2 and 5 connote, as in Fig. 1, respectively, the radius of curvature of cylinder Z and the angle of inclination of cylinder axis z-z to radial plane E through the impeller. D and D designate, respectively, the diameter of circles defined by the radially outer and radially inner extremes of the inlet or leading edges 5 of all the blades mounted around the impeller 1. Since the inlet edges 5 are radially or approximately radially disposed, the length of edge 5 is equal or approximately equal to one-half the differences between D and D Since the angle P P P is equal to 6, the blade contours of the radially outer and inner blade edges, shown in Fig. 4, are arcs of an ellipse with semi-axes a 2 a b the circular function r L, tan L,,os (1) For the angle 5 enclosing tangent t, to the ellipse are at the radially inner point P there is obtained in a similar manner L, cos 6 tan B5 Furthermore,

L,,=Li+ -sin6 (3) If the distance L, is selected at least sufliciently large so that the angle 5 is smaller than 90, the imaginary cylinder Z, a portion of the surface of which forms the configuration of blade surface 4, is substantially determined, with its radius and the obliqueness of the inclination of its axis 2-2 to radial plane E by the foregoing functions after the direction of the relative velocity, which should correspond to the direction of tangents 1,, and t; are given or determined for a particular impeller application.

As noted above, the radial or main blade portion 3 and the more axially disposed inducer blade portion 4 can be made integrally of one piece of material. The ease and economy of manufacture, however, may be enhanced by forming these two portions separately and assembling them together, and in such arrangement the juncture between main blade portion 3 and inducer blade portion 4 lies along the line P --P As will be understood, such juncture is a conical surface developed by rotating the line P -P around the cylinder axis a-a. Since line P -P is inclined to a radial plane through the impeller at the angle 6, the angle of this conical juncture surface is 180 26.

As will be seen from the foregoing, an impeller blade according to this invention (or, at least, the inducer portion 4 thereof), has, practically speaking, only a single profile curvature, and that is of a cylindrical surface. Accordingly, such a blade surface is quite simple to manufacture by sheet metal cutting and forming methods, as well as by casting, forging, or molding. Also, notwithstanding that a blade embodying this invention may have only a single profile curvature, different inlet angles result at different radial points along the leading edge since, as formed and mounted on the rotor or hub of the impeller, the cylindrical section actually represents an elliptical arc,

the arc length of which is shorter near the impeller axis.

With the surface of the inducer blade portion 4 developed according to this invention, the remaining blade surface 3 can be developed in any desired or conventional manner. Also, since the deflecting of the entering fluid medium to be compressed corresponds to the increase in the arc length of the elliptical are from radially inner to radially outer points, such deflecting occurs over a longer distance at radially outer points and higher peripheral speeds than at lower peripheral speeds. This situation results in substantial efiiciency of compressors having inducer blades according to this invention.

While the methods and forms of apparatus herein described constitute a preferred embodiment of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

I claim:

1. An impeller blade for mounting around the rotor hub of a radial flow compressor and having an inlet edge, the radially inner end of said blade being fastened substantially through its entire extent to said rotor hub, said blade having an inlet surface portion on which flow impinges upon entering said compressor, said inlet surface portion being a part of the surface of a cylinder, said cylinder having an axis lying in a plane parallel to the axis of said compressor and inclined at an angle to a radial plane perpendicular to said compressor axis in the direction of flow to said blade, and the radius of curvature of said cylinder and the distance of the axis thereof from said inlet edge of said blade all being cor-. related such that the inlet edge of said blade terminates in a plane substantially normal to said axis and lies in a substantially radial plane and the inlet angle of said blade corresponds to the direction of the relative velocities of flow impinging thereon.

2. An impeller blade for mounting around the rotor hub of a radial flow compressor and having an inlet edge, the radially inner end of said blade being fastened substantially through its entire extent to said rotor hub, said blade having an inlet surface portion on which flow impinges upon entering said compressor, said inlet surface portion being a part of the surface of a cylinder, said cylinder having an axis lying in a plane parallel to the axis of said compressor and being inclined at an angle to a radial plane perpendicular to said compressor axis in the direction of flow to said blade, said angle and the radius of curvature of said cylinder being determined by the relations in which L, is determined by the relative inlet flow direction at the radially inner extreme of said leading edge, 5,, is the inlet flow angle at the radially outer extreme of said leading edge, 5 is the inlet fiow angle at the radially inner extreme of said leading edge, r is the radius of said cylinder, L, is one-half the chord length of a circular arc ending at the radially outer extreme of said edge D,, is the diameter of the circle defined by the radially outer extremes of the leading edges of blades mounted on said rotor, D, is the diameter of the circle defined by the radially inner extremes of the leading edges of blades mounted on said rotor, and 6 is the angle of inclination of the axis of said cylinder to said radial plane.

3 An impeller blade according to claim 2 and having a substantially axially disposed inducer blade portion adjacent the inlet of said compressor and a substantially radially disposed main blade portion, the juncture of said inducer and main blade portions lying on the surface of a cone the angle of which is 180 minus 26.

4. An impeller blade according to claim 2 and having a substantially axially disposed inducer blade portion adjacent the inlet of said compressor and a substantially radially disposed main blade portion in which the juncture of said inducer and main blade portions lies on a conical surface having a cone angle of approximately 180 minus twice said angle at which said axis of said cylinder is inclined to said radial plane.

References Cited in the file of this patent UNITED STATES PATENTS Good Oct. 24, 1933 Schubert Dec. 7, 1943 Sollinger Sept. 4, 1945 Campbell et al. May 7, 1946 Millingen et al Mar. 29, 1949 Atkinson Ian. 7, 1958 FOREIGN PATENTS Great Britain of 1895