US2398203A - Centrifugal compressor entry vane - Google Patents

Description

April 9, 1946. I Row 2,398,203

CENTRIFUGAL COMPRESSOR ENTRY VANES Filed Nov. 20, 1943 2 Sheets-Sheet l Kermefh A..Brow71e.

ATTORNEY April 9, 1946. K. A. BROWNE 2,398,203

CENTRIFUGAL COMPRESSOR ENTRY VANES Filed Nov. 20, 1943 2 Sheets-Sheet 2 INVENTOR. Kennerh A..Browne.

ATTDHNE? Patented Apr. 9, 1946 CENTRIFUGAL COMPRESSOR ENTRY VANE Kenneth A. Browne, Rillmood, N. 1., alaignor to Wright Aeronautical Corporation, a corporation of New York Application November 20, 1948, Serial No. 511,149

entrance opening in order to provide a large specific capacity. This entrance opening may be as much as 50% of the impeller diameter and, therefore, the inherently large pick-up velocity of the entering fluid considerably reduces the efllciency and pressure head otherwise available from the compressor. Accordingly, it is an object of this invention to provide an entrance vane construction for a centrifugal compressor in which the entrance vanes are designed to gradually convert the rotational pick-up velocity of the entering fluid into static pressure. Furthermore, with a large impeller entrance opening, in the absence of any appreciable conversion of the relative rotational velocity of the entering fluid, there is a low pressure area at the outer periphery of the entrance opening which tends to cause fluid circulation, resulting in non-uniform fluid velocities and even reverse flow conditions, thereby reducing compressor efficiency. In the conventional supercharger impeller, the entrance edges of the impeller vanes are bent in the direction of their rotation primarily in order to improve the compressor efllciency by minimizing the turbulence of the entering fluid. Such conventional bent impeller vanes may to some extent also act as diffusers to convert some of the rotational velocity of the entering fluid into pressure, but these bent vanes are very ineflicient in this respect because a large angle cone is ineflicient as a diffuser as compared to a small angle cone.

It is a further object of this invention to provide a curved entrance vane construction for an impeller of a centrifugal compressor in which the radius of curvature of the entrance vane portions gradually decreases in a downstream direction. It is a further object of this invention to so select the changing radii of the entrance vane portions to produce a gradually increasing char-nel area between the adjacent vanes such that the relation between the cross-sectional area and length of the fluid path between the outer periphery of adjacent vanes is similar to that of a round cone diffuser having an initial diverging cone angle of about 4". Also. because the impeller of an aircraft supercharger rotates at exceptionally high speeds, in the neighborhood of 20,000 R. P. M., it is essential that the major portion of the vanes be radial. For this reason. bending the flat radial vanes of a conventional impeller to obtain the desired diffuser is not suitable or practical.

Other objects of this invention will become apparent from reading the annexed detailed description in connection with the drawings in which: I

Fig. l is a perspective view disclosing a conventional impeller with the entrance vane construction of this invention,

Fig. 2 is a partial radial section illustrating the impeller mounted on its driveshaft,

Fig. 3 is a development of the peripheral curvature of the entrance vanes,

Fig. 4 is a view of an equivalent round cone diffuser,

Fig. 5 is a front view of the entrance section, and

Fig. 6 is a front view of a modification.

Referring to the drawings and particularly to Figs. 1 and 2, a conventional supercharger is illustrated at M comprising an impeller ll having a plurality of vanes l2 and a shroud H. An entrance vane section It is clamped in front of the impeller ll with its vanes i8 terminating in alinement with the impeller vanes H. The impeller H and its entrance section It are both drivably splined to the impeller shaft 20. The vanes ll of the entrance section are curved in the direction of rotation of the impeller and the entrance edge of these vanes are so directed that for a designed rotational speed and entrance velocity the air enters the vanes without shock. In addition, the radius of curvature of vanes 18 gradually decreases in a downstream direction. Accordingly, and as appears in Figs. 1 and 3, the channel area between the vanes it radually increases toward the impeller vanes i2.

Fig. 3 illustrates a development of the outer periphery of the entrance vanes it. The entrance edges of the vanes I! are designed for a particular rotational speed so that the air enters the vanes without shock; that is, so that the tangent to the outer entrance edge of the vanes is substantially parallel to the direction of the relative velocity of the entering air. Furthermore, as illustrated in Fig. 3, the radius of curvature 22 of the outer periphery of the vanes ll gradually decreases in a downstream direction. Considering the area between the outer periphery of the vanes ll, as illustrated in Figure 3, to be of unit height, the change in the radius 22 is large ends of the conical frustum have an area respectively equal to the cross-sectional area normal to the new path at the entrance and discharge ends of the unit height space illustrated in Figure 4 and this conical frustum and unit height space have a similar change in area between these ends. The round cone diimser 24 has an initial cone angle of not more than 10 and preferably the difluser has an initial cone angle of approximately 4 with a small gradual increase in the cone angle toward the discharge end. In order to develop the desired expansion, e. g.. for an impeller having a 12" outer diameter and 22 vanes, the entrance section should be approximately 274" long.

. Preferably the shroud i4 is provided with a nozzle-like entrance portion l4 and the entrance vanes ll extend into this nozzle-like entrance portion. That is, the upstream ends of the outer periphery of the entrance vanes l8 may flare radially outwardly into the nozzle entrance as seen-in Fig. 2. 'This construction results in a reduction in the axial length which would otherwise be necessary if minimum diameter of the nozzle-area entrance portion were located in front of or at the impeller entrance as is the dial. This construction is quite'desirable becausev of the high rotational speeds of air craft supercharger impellers and the consequent bending stres that develops unless the blades are radially disposed. For this reason, any appreciable bending of the flat radial vanes of a conventional impeller is not practical. The impeller of this invention is made in two sections: the conventional impeller section ii, and the entrance vane section i6. These two section are clamped together on the impeller drive shaft with the vane i8 forming a continuation of the vanes I2. Obviously, these two sections could be made in one piece. If desired, the downstream end of the impeller vanes it may be curved slightly with the entrance vanes i8 shaped to form a substantially smooth continuation of such bent vanes.

The entrance section it may be a single casting as illustrated in Fig. 5, or the entrance vanes may be separately formed as in Fig. 6. In Fig. 6 the hub 26 is provided with splines or gear teeth 28 out along a curved path corresponding to the radial projection of the outer periphery of the vanes ll. It is also satisfactory to cut the splines 28 on a path having a constant heli cal angle so chosen that the helix corresponds as closely as possible to the true radial projection of the outer periphery of the vane i8, thereby I struction insures an accurate fit between the root end of the blades 29 and the helical splines 2| on the hub 28. The-whole assembly is then copper-brazed or bonded by other suitable means to produce a virtually integral assembly. In general, brazing methods require a very close nt of the parts to be secured together in order to provide a strong bond and this condition is obtained by the above-described gear cutting method.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications and changes.

I claim as my invention:

1. An entrance vane section adapted to be cured in front of an annular impeller of a centrifugal compressor for rotation therewith, said entrance section comprising a plurality of radially extending vanes and being adapted to form a substantially smooth axial continuation of the impeller, said entrance vanes being curved in the direction of rotation of the impeller with a radius of curvature which decreases in the direction of flow therethrough, the outer periphery of said entrance vanes defining a surface diverging in an upstream direction at the entrance end of the impeller.

2. In combination, a centrifugal fluid impeller having a plurality of circumferentially spaced radial vanes, each of said vanes having an entrance vane portion curved in the direction of rotation of the impeller with a radius of curvature which gradually decreases in the direction of flow through the impeller thereby providing a flow path between said entrance vane portions of gradually increasing cross-sectional area in the direction of the flow, the increase in the crosssectional area of the flow path between the outer periphery of the entrance vane portions being similar to the increase in area of a rou d conical frustum whose angle of divergence is not more than 10 3. In combination, a centrifugal fluid impeller having aplurality oi circumferentially spaced radial vanes, each of said vanes having an entrance vane portion curved in the direction of rotation of the impeller with a radius of curvature which gradually decreases in the direction of flow through the impeller thereby providing a flow path between said entrance vane portions of gradually increasing cross-sectional area in the direction of the flow, the increase in the crosssectional area of theflow path between the outer periphery of the entrance vane portions being similar to the increase in area of a round conical frustrum whose angle of divergence is not more than 10, said entrance vane portions being radially disposed.

4. In combination, a centrifugal fluid impeller having a hub portion and a plurality of circumferentially spaced vanes extending therefrom. each of said vanes having a curved entrance vane portion, said entrance portions being radially disposed, said entrance portions from their outer periphery to and including the intersection of their root ends with said hub portion being curved in the direction of rotation of the impeller, the radius of said curvature gradually decreasing in a downstream direction to provide a flow path between said entrance vane portions of gradually increasing cross-sectional area in the direction in the direction 0! rotation of the impeller, the radius of said curvature gradually decreasing in a downstream direction to provide a flowpath between said entrance portions of gradually increasing cross-sectional area in the direction of the flow, the increase in the cross-sectional area of the flow path between the outer periphery of the entrance vane portions being similar to the increase in area of a round conical irustum whose in angle oi divergence is not more than 10.

. KENNETH A. BROWNE.

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