US2463976A

US2463976A - High-pressure compressor

Info

Publication number: US2463976A
Application number: US476735A
Authority: US
Inventors: Kilchenmann Walter
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1942-02-21
Filing date: 1943-02-22
Publication date: 1949-03-08
Anticipated expiration: 1966-03-08

Description

March 8, 1949. w., KILCHENMANN 6 HIGH-PRESSURE COMPRESSOR Filed Feb. 22, 1943 v 3 Sheets-Sheet 1 -INVENTOR [Walter fikfienmazw? ATTORNEYS March 8, 1949. w. KILCHENMANN 2,463,976

-BIGHPRESSURE coirnasson Filed Feb. 22, 1943 s Shoots-Sheet 2 QWT ATTORNEYS March 8, 1949.

. w. KILCH ENMANN 2,463,976 'nxen-rnsssuns courmassax 3 sh ts-sheet 5 Filed F917. 22, 1943 INVENTOR WALTER KILCHENMANN M, ATTORNEYS 1 Patented Mar. 8, 1949 HIGH-PRESSURE COMPRESSOR Walter Kilchenmann, Winterthur, Switzerland, asslgnor to Saint Freres, Socit Anonyme, Winterthur, Switzerland Application February 22, 1943, Serial No. 478,735 In Switzerland February 21, 1942 Claims. (Cl. 230-134) (Granted under the provisions or see. 14, act of March 2, 1927; 357 0. G. 5)

This invention relates to high-pressure compressors whose rotors run with a peripheral speed higher than that of sound and whose blades have radially directed sections in planes normal to the rotor axes to take the centrifugal forces without bending.

Since the rotors, and particularly the blades, of such high-pressure compressors are stressed to the maximum permissible limit under present practice, the rotors have been made with purely radial extension of both the blades and the flow. The blades and the disks connecting them have been shaped as bodies projecting from the hub with uniform resistance to centrifugal forces. The blade passages thereby end in the radial direction. In this way an outlet triangle of velocities is formed in which the absolute velocity oi outlet of the compressed gas is greater than the peripheral speed of the blades, and therefore greater than the velocity of sound.

When the velocity of sound is reached, disturbances caused by Machs pressure waves become observable and have a very detrimental eilect on the efficiency of the compressor. It was therefore necessary in the described high-pressure compressors either to keep the peripheral speed of the rotor blades lower than the velocity 01' sound, being content with the lower pressures generated, or to accept the drawback oi the disturbances which are abruptly introduced at a peripheral speed exceeding the velocity of sound.

According to the present invention, the blade pa sages are set to define a direction of flow obliquely warped with respect to the rotor axis, the blades being bent backwards to such an extent that the absolute velocity of the compressed medium at the outlet does not exceed the velocity of sound, at least not to that extent at which Machs pressure waves are formed.

Since the height of the compression pressure of the product depends on the peripheral components of the absolute outlet speed and the peripheral speed of the rotor, and the peripheral speed of the rotor can be increased very considerably beyond the speed of sound (over 400 m./sec.) when all parts are set exactly radially and are given the appropriate shapes of this invcntion, a compression ratio of at least 2.0 can be reached by the invention in a single-stage machine without adversely affecting its overall eiflciency.

The general semi-axial form of rotor resulting from the application of this invention has been previously known for slow-speed compressors in i which the blades, consisting of sheet iron welded to the hub, are set in such a manner that their cross-sections at right angles to the axis of rotation are directed radially. In this way certain advantages were obtained for the machining of the plate and for the welding. However, for the phenomena of flow taking place far below the velocity of sound this general semi-axial shape is of no significance. It is only with the adoption in a semi-axial rotor of the specific shapes of this invention that, in compressors in which the peripheral speed of the blades exceeds the velocity of sound, the effect is obtained that the occurrence of Machs pressure waves in connection with the velocity of sound is avoided and the efficiency is thereby improved.

In a semi-axial rotor formed according to the invention, intermediate blades may also be arranged or the blades may be discontinuous and staggered. In these ways a further improvement of the rotor efficiency may be obtained, in that they further avoid the increased risk of turbulency which occurs when the velocity of sound is ex eeded.

The invention is explained in detail below with the help of the accompanying drawings, in which:

Fig. 1 shows in a simplified manner one exampl of execu ion of a high-pressure compressor according to the invention in longitudinal section;

Figs. 2 and 3 show the rotor of the high-pressure compressor according to Fig. 1 in plan and in cross-section;

Figs. 4 and 5 illustrate. in posit ons similar to Figs. 2and 3, a rotor with intermediate blades:

Figs. 6 and '7 illustrate likewise a rotor with discontinuous and staggered blades; and

Figs. 8 and 9 are geometrical f gures to illustrate the manner of deriving the blade curvature.

The compressor according to Fig. 1 has a rotor l with integral blades 2, made up from the solid, for instance by forging and milling, and arranged overhung on shaft 3. The air or other gas to be compressed is drawn in from the passage 4 and discharged in the compressed state through the spiral casing 5.

In service the blades 2 (Figs. 2 and 3) 01' the rotor I run with a peripheral speed which exceeds the velocity of sound at least at the outlet edges 0. In order to be able to withstand the elevated centrifugal forces thus produced without bending. the blades 2 are made in such a way that all sections lying at right angles to the axis of the rotor e. g. II, II-II III-III, extend exactly in a radial direction, e. g. in the direction of the radii r1, rs, rs, respectively. The sections taken on the lines 1-1, 11-11, III-III of Fig. 3 give the plane blade sections marked 1, II and II, respectively, in Fig. 2.

The direction of flow in the passages between the blades is not radial but is inclined with respect to the rotor axis X in the direction of the arrow l. Because of this, it is possible to so bend the blades backwards with respect to the direction of rotation 8, that the absolute velocity of the compressed medium at the outlet does not exceed the velocity of sound.

The shape which the middle surface of the blade then assumes is one of a screw surface with a pitch either constant or changeable along the rotor, one requirement being that the middle line of the blade shall be curved backwards with respect to the directions of the flow and the rotation. By middle line of the' blade" is to be understood a line drawn on the middle surface of the blade in the middle between the inner limit of the blade at the hub and the outer limit of the blade, this line consequently running in the direction of the flow, i. e. somewhat like the arrow 1 in Fig. 3.

This shape results, at service rotation speeds in which the blade tip speed exceeds the velocity of sound, in an outlet angle for the blades (with relation to the peripheral direction) whose cosine is greater than the ratio of the relative velocity of the medium to twice the peripheral velocity of the blade tip. In order to show how a screw line of constant or variable pitch and of constant or variable diameter may be employed to define the middle line of the blade on an actual rotor, reference is made to Figs. 8 and 9, which apply common geometrical construction methods to a rotor of this invention: The middle lines of the blades of the rotors illustrated in Figs. 1-7 lie on a surface of revolution, whose axis of revolution is identical with the axis of rotation X of the rotor. A cone tangential to this surface in the radius r is drawn in Fig. 8. It is tangential to one of the blade middle lines at the point A and has, as half apex angle, the angle '7 (gamma). In cylindrical coordinates the locus of the point A is defined by the point of intersection F in which the transverse plane--containing the point A and situated at a right angle to the axis of rotation X-cuts the axis of rotation, further by the radius r and finally by the angle which the meridian plane containing the radius r makes with a meridian plane chosen as initial plane.

Now, if the transverse plane is displaced by the differential value d1: in the X direction, the radius 7' turns through the differential angle value do: (:1 alpha) and thereby generates a small part of the screw surface through which the middle surface of the blade is formed.

If this screw surface were continued with a constant pitch and cut with a coaxial cylindrical surface, the ordinary screw-line, drawn dashed in Fig. 8, would be obtained. If it were cut with the conical surface drawn in Fig. 8, the conical screw line of constant pitch would be obtained; it is drawn solid. If the transverse plane is moved further in the X direction through the distance s/2, not only the screw surface has completed a 4 half turn, but the same holds good for'the ordinary screw line, and for the conical screw line,

as it is' shown in the drawing, whereby 3 defines itself as the screw pitch prevailing at the point A of the middle line of the blade, which middle line is not drawn in Fig. 8.

4 Thus the diflerentlal equation of the screw surface,

is obtained, in which a may be variable in the a: direction and r does not appeansince 1' has the value AF only for the point A, but, for all parts of the screw surface that lie outside the point A, remains still free to be chosen as desired.

The middle line of the blade lies on this screw surface thus defined which forms the middle surface of the blade, and it now remains to investigate what relations must exist between the pitch .9, the radius r of the middle line of the blade and the angle 7 as half apex angle of the cone touching this middle line, in order that this middle line may have the required backwards curving. For this purpose, in Fig. 8 at the point A on the conical screw line shown non-dotted, and thus also on the middle line of the blade not shown there, the tangent AD is drawn, the length AD being considered to be infinitely small, so that the perpendicular dropped from the point D on to the meridian plane passing through A represents the tangent at the point A to the paralleleircle passing through A. This tangent DB consequently represents the direction of the peripheral velocity at the point A, while the tangent AD represents the direction of the middle line of the blade and therefore the direction of the relative velocity of the delivered medium led along both sides of the blade. These two tangents include the angle 5 (beta) (see Fig. 9). AB is the generating line of the cone, AC the generating line of the cylinder, and the angle BAC is therefore the angle 7 as half apex angle of the cone. AE is the tangent at the point A to the cylindrical screw line, drawn in broken lines. BCED is a rectangle, and the angles BCA and DEA are right angles. The angle CEA is marked ,9. From Fig. 9 the following trigonometrical relations are obtained:

If the cylinder is developed in a lowing relations are obtained:

a tan d 2 where r=radlus of the cylinder.

Substituting this relation into the formula tan B'=tan /3.cos 7 we have plane, the fol- I planer is passed through before the transverse planez, the requirement must be fulfilled that ,62 B1 or that tan ,Bz tan [31 Consequently also the following relations hold good:

and the formula:

T2 (-08 Yg T 1 CO8 71 is obtained.

If on the other hand, the rotor is conical, i. e. the angle 7 is constant, the form of the equation:

is obtained.

This backwards bending makes it possible to have a compression ratio of more than 2.0 within a single stage, without having to put up with disturbances through Machs pressure waves, which occur in the region above the velocity of sound.

The rotor according to Figs. 4 and 5 has additional intermediate blades 9 arranged between the main blades 2; the intermediate blades give a better guiding to the fiow of the medium which is to be compressed, and thereby prevent, within the fiow passages, a non-uniform distribution of the medium which is to be compressed.

The rotor according to Figs. 6 and 7 has blades l6 which are interrupted at the spaces II and are continued in staggered arrangement. In this way turbulence, which could very well occur at the high speeds used, is prevented.

It is possible under certain conditions of working to let the velocity of flow of the compressedmedium increase slightly beyond the velocity of sound without any disturbances being caused by Machs pressure waves.

I claim:

1. A rotor for a centrifugal gas compressor to be operated at peripheral velocities above the speed of sound for fitted rotation about an axis, one end of said rotor being of smaller diameter than the other, the outer surface of said rotor having longitudinally-extending channels obliquely warped with respect to the rotor axis arranged to receive gas to be compressed at the 6 smaller end of said rotor and to discharge .compressed gas at the larger end of said rotor, said channels being defined in part by blades which have radially extending cross-sections and in the fiow direction curve backwards from the direction of rotation to form angles to planes of revolution at right angles to the rotor axis decreasing toward the larger end of said rotor, the middle lines of said blades forming a surface of revolution, the middle surfaces of said blades conforming substantially to a surface having the equation:

I da nix-a and the dimensions of the rotor being such that 2.2L 83 T1 COS 'Y| 1 in which dx is a distance along the rotor axis toward said larger end, s is the lead or pitch, do: is i 3. A rotor as claimed in claim 1, the rotor body of which is formed as a cone such that:

4. A rotor as claimed in claim 1 in which the blades extend from substantially the small end of the rotor to substantially the large end of the rotor.

5. A rotor as claimed in claim 1 in which the blades which define in part the longitudinallyextending peripheral passages of the rotor are discontinuous and staggered.

WALTER KILCHENMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 991,134 Capell May 2, 1911 1,029,554 Neumayer June 11, 1912 1,717,694 Kraut June 18, 1929 1,839,126 Sperry Dec. 29, 1931 1,959,703 Birman May 22, 1934 2,407,469 Birman Sept. 10, 1946