US2405048A - Centrifugal compressor - Google Patents

Description

July 30, 1946; W. T. NMZKERSQN CENTRIFUGAL COMPRESSOR Filed Nov. 18, 1944 2 Sheets-Sheet l Nickeraon July 30, 194 6. w, Ng s 2,405,048

CENTRIFUGAL COMPRES SOR Filed Nov. 18, 1944 2 Sheets-Sheet 2 WWW c A I 4 p bu U a q Q Patented July 30, 1946 CENTRIFUGAL COMPRESSOR Winfield '1. Nickerson, Lynn, Mass, assignor to General Electric Company, a corporation of New York Application November 18, 1944, Serial No. 554,024

4 Claims.

The present invention relates to centrifugal compressors having an impeller for impelling medium to be compressed, a diiiuser for receiving medium impelled by the impeller and converting part of its velocity energy into pressure energy. and a scroll or discharge chamber for receiving medium from the diiiuser and discharging it into a consumer.

The overall dimensions of such centrifugal compressors are in part determined by the radial dimensions of the diffuser and also by the particular arrangement of the diffuser and the dis charge scroll. It i desirable, particularly in aircraft when used as part of a turbosupercharger, to keep these overall dimensions of the compressor as small as possible in order to bring them within the general limits of the overall dimensions of the particular turbine driving the col.-- pressor and thereby to produce a compact design relatively light in weight. In the past, this has been accomplished in part by the provision of saw-toothed diffusers having sidewalls with sawtoothed outer portions to permit lateral discharge from the diffuser passages through the openings in the sidewalls and by providing the discharge scroll substantially laterally of the diffuser. With such arrangements it has been possible to reduce the outer dimensions of the discharge scroll substantially to the outer dimensions of the diffuser. An arrangement of this kind is disclosed in Patent No. 2,289,231 to C. H. Auger et al., issued on July 7, 1942, and assigned to the same as'signee as the present application.

The object of my invention is to provide an improved construction and arrangement of turbosuperchargers in which the outer overall dimensions of the compressor are substantially equal to or of the order of the outer overall dimensions of the turbine.

Another object of my invention is to provide an improved centrifugal compressor in which the difiuser and the discharge scroll form a unitary, compact structure of the small outer dimension.

A third object of my invention is the provision of an improved construction and arrangement of diffusers for centrifugal compressors with relatively long diffuser passages of relatively small radial length. Broadly, this is accomplished in. accordance with my invention by a diiiuser in which the diffuser passages curve gradually outwardly and axially from their inlets or entrances toward their exits or discharge openings. In a preferred embodiment, the entrances of a plurality of circumferentially spaced diffuser pas sages are located on a cylinder or cylindrical surface as in any other diffuser, but, in contrast to the normal diffuser arrangement, the exit or discharge openings of my difiuser'pas'sages are located in circumferentially spaced, substantially radial planes through the compressor and the outlet portion of each passage is located on top of the inlet or intermediate portion of an adjacent passage.

For a better understanding of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawings.

In the drawings, Fig. 1 illustrates a turbosupercharger, partly in section, embodying my invention for use on aircraft to supply compressed me dium such as air to an internal combustion engine, a cabin or like consumer for 'ompressed medium; Fig. 2 is a perspective, fragmentary view of Fig. 1; Fig. 3 i a sectional view of a modification according to my invention; Fig. 4 is a sec-- tion along lines i-4 of Fig. 3; Fig. 3 is in part a section along line 3-3 of Fig. 4;; Figs. 5 and are sections along lines 5-5 and 3'45, respectively, of Fig. l; and Fig. T is a perspective fragmentary view of Fig. 3.

The turbosupercharger comprises a turbine I having a bucket wheel 2 secured to an overhung portion of a shaft 3 and a nozzle box 4 or conducting gases to the bucket wheel 2 and having a flanged inlet portion 5 for receiving such gases from a suitable source, for example, the exhaust manifold of an internal combustion engine (not shown). The turbine constitutes a power agency for driving a centrifugal compressor having impeller 5 secured to a shaft 3 and located with in a casing which has two flanged halves l, 8 e cured together by a row of bolts 9. The casing forms an inlet conduit l0, an impeller chamber I l, a diffuser chamber l2 and a scroll or discharge chambe l3. The impeller chamber l! i formed between the two case halves l and 3, whereas the inlet conduit l0 and the other chambers, that the diffuser chamber and the scroll, are all formed solely by the casing half 3.

The casing half 1 has an inner flange-d porti" 14 secured to a ring 15 by a plurality of bolts The ring 15 may form part of the of bearing ii for supporting the intermednte portion of the shaft 3, and the inner rim of the ring !5 is sealed to the shaft by a suitable packing E3 to preclude leakage of oil from the bearing 1? into the impeller chamber. annular baifie 59 with an outer extension is located between the compressor casing and the nozzle box 4 to support the latter on the compressor casing and to reduce heat radiation from the turbine to the compressor. The upper end of the shaft 3 in the present example is supported on a bearing 2! centrally disposed within the compressor inlet conduit l and held thereon by a plurality of circumferentially spaced webs 0r vanes 22, which latter also serve properly to direct air or like medium through the inlet conduit l9 towards the eye of the impeller 6.

The diffuser, according to my invention, as previously stated, forms an integral part of the compressor casing, or one half thereof, and has a plurality of spaced diifuser passages which curve gradually outwardly and axially from th inlets toward their respective exits. Fig, 2 shows in perspective two diffuser passages 23 and 24. These two passages are formed between circumferentially spaced vanes or partitions 25, 26 and 21. In addition to these vanes which form sidewalls of the passages 23, 24, each passage has a bottom and a top. Thus, the passage 23 has a bottom 28 and a top 29, The adjacent or succeeding passage 24 has a bottom 36 and a top 3!. From a consideration of Fig. 2, it will be readily seen that the bottom 28 of the first diffuser passage 23 merges gradually into the top 3! of the adjacent or second diffuser passage 24. In other words, the bottom of each diffuser passage forms part of the top of a succeeding passage or, vice versa, the top of each diffuser passage forms-a part of the bottom of a preceding diffuser passage. Furthermore, each vane 25, 26, 21 merges gradually into and forms part of, or is partly formed by the outer wall of the scroll or discharge casing. The bottom of each passage also merges into and forms part of the scroll. In other words, each passage has a sidewall and a bottom merging into and forming part of the scroll. Each diffuser vane, as pointed out above, has an inner portion separating two adjacent passages, an outer portion merging into the wall of the scroll and, in addition, each vane has an inner upper portion or extension which forms an inner sidewall of a passage. Thus, in Fig. 2, the vane 26 has an inner portion separating the passages 23, 24. The same vane has an outer portion merging into the wall of the scroll and, in addition, the vane 26 has an inner upper portion or extension which forms the inner sidewall of the passage 23. The exit or discharge opening of each diffuser passage is located substantially in a radial plane through the compressor axis. Also, the exit of each diffuser passage is axially spaced from and located at least partly above an intermediate part of a succeeding passage. The center lines f diffuser passages of the kind described are three-dimensional curves of skewed or helical character. The curvature is substantially gradual from the inlet towards the outlet of each passage. A particle passing through a passage moves from the entrance radially outward and simultaneously circumferentially and axially,

In a diffuser of this kind the outer dimensions of the scroll may be made substantially equal to the outer dimensions of the diffuser and the passages of the latter merge gradually into the scroll and are of comparative short radial length.

The modification illustrated in Figs. 3 to 7 inclusive comprises a casing having two halves 3| and 32 corresponding to the two halves 8 and 7 p v ly o Fig. 1. The casing half 32 forms an inlet 33 and a combined discharge scroll and section 34. An impeller 35 secured to a shaft 36 is disposed in the casing and supported on a bearing 31 held by guide vanes 38 in the inlet 33 of the casing. The diffuser for conducting compressed medium discharged from the impeller into the scrol1 and converting part of its velocity energy into pressure energy comprises a plurality of circumferentially spaced, overlapping diffuser passages 39, 40, M. The passages are formed between vanes 42, 43 (Fig. '7). The inlet ends of the diffuser passages are located on a cylinder like those in Figs. 1, 2 but the inlet edges of the vanes 42, 43 are inclined whereas the inlet edges of the vanes in Fig. 2 are substantially perpendicular to the casing or parallel to the axis of the impeller. The inclined vanes 42, 43 assure a smooth flow of compressed medium int the inlets of the diffuser passages and their inclination relative to the exit edges of the impeller blades reduces pulsations, that is, sudden flow changes during operation as the impeller exit edges pass the diffuser vane inlet edges. The inclination of the diffuser vanes towards the axis decreases from the inlets towards the outlets of the diffuser passages as best seen from a comparison between Figs. 5, 6, '2'. The inclination is a maximum at the inlet and a minimum at the outlet of the diffuser passages where the vanes merge into the wall of the scroll. At the outlets of the diffuser passages the vanes "are substantially axial and merge gradually into the bottom and top parts of the passages. The corners between these parts and the vanes are rounded (Fig. 3). In the arrangement of Fig. 1, adjacent passages overlap each other partly only near their outlets whereas in the modification of Figs. 3 to 7, as best shown in Fig. 7, each diffuser passage has an outlet overlapping completely a succeeding passage and having an intermediate part overlapped completely by a preceding passage. The elimination of sharp corners between the diffuser vanes and top and bottom walls reduces friction losses of fluid passing therethrough.

Having described the method of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a centrifugal compressor, a casing having two halves secured together and defining an impeller chamber therebetween, one of the halves defining a central axially extending compressor inlet conduit and a diffuser and discharge scroll, said scroll being axially spaced from the impeller exit and located entirely on the compressor inlet side of the diffuser, said scroll at its largest crosssection merging into and being partly formed by the wall of the compressor inlet conduit, said diffuser including a plurality of overlapping diffusing passages arranged to direct fluid discharged from the impeller exit into the scroll with a velocity having substantial tangential and axial components, said diffusing passages having circumferentially spaced inlets and outlets, the

inlets of the diffusing passages being located sub--' stantially on a cylinder surrounding and adja-'- cent the impeller exit, and the outlets of the pas-' sages being axially and radially spaced from their respective inlets and lying within the discharge scroll, the outlets being also located in circumferentially spaced planes substantially parallel to the compressor axis.

A diffuser for a centrifugal impeller having walls forming a plurality of separate diffusing passages arranged to receive fluid from the impeller and discharge it with a velocity having substantial tangential and axial components, each passage having an inlet and an outlet with the inlet located on a cylinder around the axis of the diffuser and the outlet radially and axially spaced from the inlet and located substantially in a plane parallel to the axis of the diffuser, the outlet portion of each passage being axially adjacent and overlapping completely an intermediate portion of the next succeeding passage,

3. A diffuser for a centrifugal impeller, comprising walls forming a plurality of separate overlapping diffusing passages for receiving fluid from the impeller, each passage having an inlet lying on a cylinder adjacent and surrounding the impeller exit and an outlet circumferentially and radially and axially spaced from the inlet and arranged to discharge fluid into the scroll with a velocity having substantial tangential and axial components, each passage having circumferentially and radially spaced inner and outer sidewalls, a bottom, and a top axially spaced from the bottom, the inner sidewall of each passage merging gradually into and forming a portion of the outer sidewall of the next succeeding passage, and the bottom of each passage merging gradually into and forming part of the top of the next succeeding passage.

4. A diffuser for a centrifugal impeller having walls forming a plurality of separate overlapping diifusing passages, each passage having an inlet lying on a cylinder adjacent and surrounding the impeller exit and an outlet ciroumferentlally and radially and axially spaced from the inlet, each passage having circumferentially spaced substantially radially extending walls inclined to the axis of the diffuser, a radially inner sidewall extending axially and tangentially from the inlet to the outlet and .being substantially perpendicular to said inclined walls, and an outer sidewall radially spaced from the inner sidewall and forming a portion of the scroll, the inne portion of said inclined walls being common to adjacent diffusing passages.

WINFIELD T. NICKERSON.

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