US 3536417 A
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Description (OCR text may contain errors)
0a. 27, 1910 STIEFEL ETAL 3,536,417
IMPELLER FOR AXIAL OR RADIAL FLOW COMPRESSORS Original Filed Sept. 19, 1966 2 Sheets-Sheet 1 WALTER STIEFEL Y HANS MERKLE INVENTORS BY (QM-w ATTORNEYS Oct. 27,1970 W.$T|EFEL EI'AL 3,536,417
IMPELLER FOR AXIAL OR RADIAL FLOW COMPRESSORS Original Filed Sept. 19, 1966 2 Sheets-Sheet 2 WALTER STIEFEL HANS MERKLE mvsu roas BY M9 ATTORNEYS United States Patent O 3,536,417 IMPELLER FOR AXIAL R RADIAL FLOW COMPRESSORS Walter Stiefel, Neuhausen, and Hans Merkle, Stuttgart- Frauenkopf, Germany, assignors to Daimler-Benz Aktiengesellschaft, Stuttgart-Unterturkheim, Germany Continuation of application Ser. No. 580,450, Sept. .19, 1966. This application Jan. 30, 1969, Ser. No. 800,336 Claims priority, applicfitigg Gfielrmany, Sept. 22, 1965,
Int. Cl. F04d 19/00, 29/26 US. Cl. 416--223 4 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation of application Ser. No. 580,450, filed Sept. 19, 1966, now abandoned.
BACKGROUND OF THE INVENTION A burbling phenomenon, called rotating stall, occurs at the blades of such compressors-at the rotors as well as at the stators thereofwithin a certain speed range of the engine. This phenomenon is the consequence of a lessening of the amount of flow through the compressor, or an increase in the angle of incidence of the flow on the blades of the compressor and can be considered a preliminary stage of the simultaneous stalling at all blades, known as pumping. However, in contradistinction to pumping, the rotating stall involves stalling at individual blades, and such stalling phenomena can be triggered, at a certain critical magnitude of the angles of incidence, by normal irregularities within the fluid flow. These stalling phenomena, so to speak, result from a damming up of flow at the entrance to the compressor, and a rotating of the fluid therein at a frequency which differs from the frequency of the speed of rotation of the rotor. As a result, this phenomenon is called rotating stall. As a consequence of the pressures created by this effect, blade vibrations and blade breaks can occur, and for this reason, it was heretofore necessary to avoid speeds of rotation or flow quantity located in the vicinity of the critical surge limit, for safety reasons. However, by taking such precautionary measures, the flexibility in speed of rotation or volume of flow of the compressor is substantially impaired.
SUMMARY OF THE INVENTION The present invention is intended to solve the problems of avoiding the above-described disadvantage without having to fulfill the restrictive conditions set out above. In order to solve this problem, the invention starts with the general objective to prevent the occurrence of the rotating stall by intentionally providing irregularities in the blade construction of the impeller. In detail, the invention proposes to make individual blades or blade groups deviate from the other blades of the rotor with respect to shape and/ or position. This inventive idea can also be put into practice by providing certain blades or groups of blades with a blade angle deviating from that of the remaining blades, and/or by providing them with a different basic 3,536,417 Patented Oct. 27, 1970 shape, and/ or by making the pitch of the rotor different. The individual features of the invention can thus be em ployed in combination, in certain individual groupings, or each feature may be utilized by itself.
By means of the above-disclosed inventive concept, there is obtained a differentiation or shift of the fluid flow from laminar to turbulent flow at the individual blades. If, for example, the phenomenon of this interruption of laminar flow occurs at a blade, and the interruption begins to rotate, it then meets with one or several blades having a different shape and/ or position, and thus the fiuid'fiow is advantageously made to engage the blade again. Depending upon the type, number, and magnitude of the irregularities, areas of flow interruption can be completely eliminated, weakened, prevented from rotating, or at least shifted into zones of smaller through flow and different speeds of rotation.
The measures of the invention can, in principle, be provided at any desired location along the circumference of the impeller. However, it is advantageous, particularly in the case of rotors, to make such provisions at opposite or symmetrical points at the diameter of the impeller, in order to avoid imbalances and a concomitant irregular run of the impeller. Thus, in case of an even number of blades, it would be possible, for example, to arrange and/or construct every second blade in a different manner, according to the invention. Of course, it is likewise possible, and definitely within the scope of the invention, to provide the irregularities at random blades and subsequently by other means provide an accurate balancing of the impeller.
The above-mentioned dilferent shaping or positioning of individual blades or groups of blades can, basically, be effected in any desired manner. A main consideration, in this connection, is a change in the blade angle. For this purpose, the invention proposes to provide individual blades or blade groups with a different inlet angle from the remaining blades. This can be done, for example, in such a way that the respective blades are bent somewhat at their roots and thus the inlet angle is reduced in comparison to that of the other blades. However, according to the invention, it is preferred to fashion these individual blades or the blade groups in such a way that they are moved up, or conventionally, cut back at the root. It is also possible to impart to such blades a different curvature at the root area.
In this manner, it is advantageously possible, for example in case of cutback blades, to manufacture all blades identically and then, as a finishing operation, to subject individual blades to this cut-back procedure. As mentioned above, it is advantageous, for example, in order to render flow interruption ineffective as quickly as possible, and preferably at the very next blade, to cut back alternately every second blade. Although it is known to cut back every second blade, this measure heretofore had the purpose of increasing the flow through the compressor. The blades, in the known case, must be cut back beyond the narrowest cross section, while, in accordance with the present invention, the cutting back of the blades is intended to change the angle of flow and has no relationship whatsoever to the narrowest cross section, i.e., the cutback does not have to be beyond such cross section.
Another embodiment of the invention, likewise relating to the variation in individual angles of incidence (stagger angles), provdes that individual blades or blade groups have a different basic shape. Sometimes, it is suflicient to provide an increase in the relative thickness and/or a thickening at the entrance (root) portion of the select blades. Finally, it is also possible to utilize a variation in the postionng of the blade for changng the angle of incidence. For this purpose, according to the invention,
3 individual blades or groups thereof are provided on the impeller so that they are twisted about their radially extending axis with respect to the other blades. Here, again, all blades can be identically manufactured and must only be attached to the impeller body in varying positions.
According to the invention, another positional change can be provided by arranging individual blades or blade groups at a different pitch along the impeller. This measure per se is conventional, for example, in hydrodynamic clutches, but there it serves for entirely different purposes, namely, for preventing a coincident blow or knock in the clutch.
It is an object of the present invention to provide an impeller for compressors, particularly for use in aircraft engines, which avoids or otherwise completely eliminates the inherent probems relating to so-called rotating stall in known arrangements.
It is another object of the present invention to solve the abovementioned problems of the prior art in a relatively simple and economical manner.
It is a further object of the present invention to prevent the occurrence of rotating stall by intentionally providing irregularities in the blade construction of the impeller so as to dissolve interruptions in the laminar fluid flow therethrough.
It is another object of the present invention to provide an impeller wherein individual blades or blade groups deviate from the other blades of the rotor with respect to shape or position so as to eliminate as quickly as possible rotating irregularities in the laminar fluid flow.
BRIEF DESCRIPTION OF THE DRAWING These and other objects, features and advantages of the present invention will become clearer from the following detailed description thereof when taken in connection with the accompanying drawings, which illustrate several embodiments of the invention, and wherein:
FIGS. 1, 2 and 4 show various embodiments of blade arrangements according to the invention in a schematic view; and
FIG. 3 shows an impeller of a radial flow compressor having a blade arrangement according to FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, wherein like reference numerals are utilized throughout the several views to designate corresponding parts wherever possible, and particularly to FIG. 1, blades 10 and 11 form a cascade of blades wherein certain blades, for example, the alternate blades 11, are of a stronger curvature at the root 12 than the blades 10 and thus are provided with a larger entrance angle than the blades 10. The dot-dash line 13 at the blades 11 indicates the shape of all other blades 10. There is thus obtained with respect to a given fiow direction, a different angle of incidence (stagger angle) at the blades 11, so that the effect of generating irregularities in the fluid fiow at these blades according to the invention is achieved.
The same efiect as in the embodiment of FIG. 1 may be obtained by the embodiment of FIG. 2. In this figure, every second blade 11a is cut back in length at the root 12 with respect to the normal blades 10. This embodiment is also shown in FIG. 3, wherein there is illustrated in side view an impeller 14 of a radial flow compressor of basically known type. This embodiment of FIG. 3 has the advantage that the blades 10 and 11a can be manufactured identically. Cutting back every second blade 11a can then be conducted as a finishing step.
In the embodiment of FIG. 4, a varying angle of incidence is obtained by rotating every second blade 11b about its radial axis.
The dot-dash line 15 corresponds to the position of all other blades 10. Thus, the blades 10 and 1112 can be of identical configuration; they need only be attached at the impeller body in varying positions to attain the objectives of the present invention.
While we have shown and described several embodiments in accordance with the present invention, it is understood that the sarne is not limited thereto, but is susceptible of numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and decsribed herein; but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.
What is claimed is:
1. A compressor impeller having a plurality of blades mounted adjacent to one another in a substantially annular array with their leading and trailing edges being respectively annularly aligned in common planes and with some of the blades exhibiting a different characteristic from that of the remaining blades of the array to resist the formation of rotating stall, wherein the improvement comprises each of some of said blades of the array having their leading edge portions inclined in the same direction as the remaining blades, with respect to a plane passing through the axis of the impeller and its longitudinal axis, but to a greater extent, thus defining larger inlet angles than said remainig blades, wherein all of said blades have substantially identical trailing edge portions.
2. The compressor impeller according to claim 1, wherein. all of said blades have substantially identical cross-sections except for only the leading edge portions of said some of the blades having a greater curvature to form their larger inlet angles.
3. The compressor impeller according to claim 1, wherein said some of the blades and said remaining blades alternate in the annular array.
4. The compressor impeller according to claim 1, wherein all of said blades have substantially identical cross-sections except for only the leading edge portions of said some of the blades having a greater curvature to form their larger inlet angles.
References Cited UNITED STATES PATENTS 1,087,995 2/1914 Sturtevant 230134.5 1,534,721 4/1925 Lasche 25339 1,639,274 8/1927 Zoelly et a1. 25377 1,893,184 1/1933 Smellie 230-134 2,570,155 10/1951 Redding 25377 2,798,661 7/1957 \Villenbruck et al. 230122 2,870,958 1/1959 Pinsley 253-77 3,347,520 10/1967 Owezov 25377 FOREIGN PATENTS 83,294 6/ 1920 Austria.
685,979 12/1939 Germany.
830,542 2/ 1952. Germany. 1,177,277 9/1964 Germany.
HENRY F. RADUAZO, Primary Examiner U.S. Cl X.R. 230l20