US1136098A - Fluid-impelling device of the screw-propeller type. - Google Patents

Description

C. H. CAMPBELL. FLUID lMPELLlNG DEVICE OF THE SCREW PROPELLER TYPE.

' APPLICATION man MAR. 21, 1913.

Patented Apr. 20, 1915.

9 I v l M INVENTOR 4! WITNESSES:

W By A ztomeys,

THE NORRIS PETERS coy. F'HGTCLITHQ. WASHINGTON, 2v c4 CHARLES H. CAMPBELL, OF NEW YORK, N. Y.

FLUID-IMPELLING DEVICE OF THE SCREW-PROPELLER TYPE.

Application filed March 21, 1913.

To all whom it may concern Be it known that 1, CHARLES H. CAMP- BELL, a citizen of the United States, residing in the borough of Manhattan, city, county, and State of New York, have invented certain new and useful Improvements in Fluid- Impelling Devices of the Screw-Propeller Type, of which the following is a specification.

This invention relates to screw propellers applicable for the pumping or circulating of liquids or gases, for the propulsion of ships in water, for the propulsion of flying machines, and for other analogous purposes. Such devices for impelling air are commonly known as propeller fans or disk fans. With any such screw impeller it is the outermost parts of the blades that are most effective, the portions near the hub or axis having little or no effect; and in the operation of such a screw impeller it is found that a reverse flow occurs on the discharge side in the region of the central or axial portion, due apparently to the setting up of eddy currents. Such reverse flow occurs within an approximately conical or conoidal space having its apex approximately coincident with the rotative axis and some distance removed from the screw on its discharge side. Within this conoidal space the screw is doing no useful work, this space being filled with a confusion of currents flowing partly backward and serving largely to obstruct and retard the flow of the main currents set up by the efiective outer portions of the blades. This is perhaps most apparent in the case of a marine propeller wherein there exists a wasteful churning of the water near the axis and for some distance behind the screw. These confused and conflicting currents detract seriously from the efficiency of the propeller.

Efforts have been made to improve screw impellers by enlarging the hub so as to eliminate the ineflective portions of the blades near the axis, but this does not avoid the disturbing effect of the eddy currents which are formed on its discharge side. It has even been proposed to make the hub in conical or conoidal form, but this also has proved ineffective.

The present invention aims to overcome the disadvantages heretofore encountered, and to this end it provides the screw impeller with an enlarged hub so as to eliminate the inefiective central portions of the- Specification of Letters Patent.

Patented Apr. 20, 1915.. Serial No. 755,881.

blades, and this hub is made hollow and cup-shaped, the cup being closed on the fluid inlet side and open on the fluid discharge side. It results from this construction that the back flow due to eddy currents is directed into the hollow of the cup, the currents being turned therein and directed parallel with the main external current and finally discharged thereinto so as to join such current and augment it, instead of existing as confused conflicting currents which oppose the main flow. It results also that the conical or conoidal space in which the eddy or reverse currents exist is prolonged and more sharply difierentiated from the main fiow, and so that by the reaction existing between the currents within such space and the main currents exterior thereto, a steadying effect is produced whereby the screw impeller revolves in more perfect alinement, and with greater steadiness and uniformity than with impellers of the screw propeller type heretofore constructed. The invention markedly improves the efiiciency of impellers of this type.

The accompanying drawings show one suitable embodiment of the invention.

Figure 1 is a side elevation; Fig. 2 is an end elevation; Fig. 3 is a longitudinal midsection accompanied by a diagrammatic representation of the flow.

Upon the driving shaft A is mounted a cup-shaped structure B carrying the blades C C. The shaft A enters an enlargement or hub portion a which may be prolonged within the cup as shown in Fig. 3, and to which the shaft is keyed or attached by setscrews or otherwise in any suitable manner. The device may rotate openly in the fluid medium, or it may turn within a tubular shield or conduit D, the latter being shown in Fig. 3. The direction of its rotation is shown by the arrow in Fig. 1. The blades C C may be of any desired number, and of any shape or conformation which is customary or desirable. Numerous shapes for such blades are known as applied to screw propellers, aeroplane propellers, propeller fans or the like, and all such shapes are available in connection with my invention.

The peculiar feature of my invention is the provision of the hollow cup-shaped part B which is closed on the fluid inlet side and is open on the fluid discharge side. On the fluid inlet side it is preferably rounded gently somewhat as shown so as to smoothly divide the entering fluid and direct it outside of the cup. On the fluid discharge side the cup is best made as thin as is consistent with strength, and it should have a. smooth symmetrical open edge or rim. In the illustration a considerable portion of the hub is of hollow cylindrical formation, the cylindrical portion being shown extending forwardly and rearwardly of the blades. The inner or rearward side of the closed front end of the hub, in radial section, is shown presenting a curve extending forwardly from the central region and then ba kwardly and merging with the surface of the cylindrical portion. In the operation of any screw impeller there exists a I tendency to a return or back flow coincident with the center or axis of rotation. This is shown in Fig. 3 by the arrows b b. In ordinary propellers these reverse currents are very confused, traveling in varied directions and becoming constantly entangled with and opposing the main currents. By merely enlarging the hub so as to eliminate the comparatively ineffective portions of the blades nearest the axis, these backward currents may be rendered less confused and conflicting, but nevertheless at some point they must encounter the main flow, and by eddying thereagainst they obstruct and retard it, thus wasting power in useless churning of the fluid. The region in which such reverse flow and confusion of conflicting currents or eddies occurs, is found to have an approach to a conical or conoidal form, as indicated approximately in Fig. 3 bythe dotted lines 0 c which circumscribe a conoidal figure of greater or less length, converging to an axis which I may be located approximately at the point d. lVithin this figure the main flow tends to occur in a backward direction, but in screw impellers as heretofore constructed the flow within this space has been so confused, conflicting and variable that it would be impossible to lay down for it any'definite direction or tendency.

By the enlargement of the hub or support for the blades to approximately the extent indicated, and by making this in the form of a hollow cup, provision is made for separating the reverse currents within such conoidal figure from the main current, thereby preventing any conflict between them, and any opposition by the reversed or eddy currents to the main flow induced by the blades. What appears to occur is that the return flow indicated by arrows b b is concentrated and straightened out, so that it becomes a continuous reverse current approximately concentric with the axis of rotation (denoted by the dotted line 02), and this flow enters the cup and on reaching the closed side thereof is divided and sweeps outwardly in all directions, following the curved inner wall of the cup, as denoted by the arrows c c, and thence travels along the outer wall of the cup as denoted by the arrows f, being thus turned parallel with the main flow which is shown by the arrows g g. The rapid whirling of the cup also whirls the fluid currents whichtraverse this wall (carrying .them along partly by skin friction and partly by induction), and when these currents reach the open edge of the cup they tend by reason of the centrifugal force thus generated to fly outwardly in a direction which is the resultant of their directly outward tendency due to centrifugal stress, and their momentum in the forward or axial direction. The dotted arrow It may be taken as illustrating approximately the direction in which these currents tend to flow out from the cup; but this tendency is resisted and overcome by the far greater volume and force of the main annular current 57 g, which in practice must nearly suppress the expansive direction of the currents from within the cup, with the result that these expand but little if any, as for example to the slight extent indicated by the arrow 6. This expansive tendency however has the effect of widening the region which otherwise would be circumscribed by the limiting lines 0 0, displacing it, for example, approximately to the extent denoted by the dotted lines 7' 1', and thus establishing a conical region having a larger base than would otherwise occur. This region also is prolonged to greater axial length by reason of the forward direction thus imparted to the currents f i discharged from within the cup, the prolongation of these currents being indicated at 7c 70. Hence the internal ineffective region is prolonged into an approximately conical or conoidal space or greater length than would otherwise result; but what is most important, this region, instead of being filled with confused and conflicting eddies, is now occupied by comparatively regular parallel streams of fluid which instead of becoming tangled with and opposing the main stream,

are separated therefrom by the cup, and are retained in an orderly course and directed into or merged with the main flow, so that all churning or confusion of currents where they come together is avoided, with the re suit that the impeller delivers fluid much more efficiently than with the former construetions.

The prolonged conical or conoidal region inclosed within the converging tubular stream constituting the main flow, has an advantageous effect in that it tends to steady the rotary impeller in a manner somewhat analogous to what would occur if the hub were prolonged as a solid cone of similar contour and turning in an approximately rigid bearing. This effect is thought to be due to the reaction between the outer main flow and the inner reverse current which on returning to the cup expands within it and fills it, thereby acquiring a bearing or abutment within the cup. The result is that under rapid rotation if the bearing carrying the shaft be turned so as to deflect the axis of rotation, the impeller resists such deflection to a perceptible extent. It is further noticeable that the screw under rapid rotation accompanied by more or less whirling in spiral direction of the discharged fluid, has a gyroscopic effect, whereby also a tendency is generated to resist any efl'ort to divert the axis of rotation. These effects are most marked when the impeller is inclosed within a tubular envelop or casing such as that indicated in Fig. 3 at D. This may more or less closely embrace the impeller, provided only that clear space is aflorded around it.

The construction may be materially changed and the proportions modified to any practicable extent without departing from the novel principle introduced by this invention. It is to be understood that the embodiment shown in the drawings is illustrative merely, being of the preferred construction and proportions.

I claim as my invention 1. A fluid impeller havingscrew blades, and a hollow cup open at the discharge side disposed within such blades and located in such position relatively thereto that the dis charge from the blades freely enters the hollow hub and freely leaves the same, the walls of the hub being of such formation that the fluid upon leaving the cup forms a solid cone extending rearwardly for filling the normal rearward void and steadying the impeller, and effecting orderly movement of the discharged fluid.

2. A fluid impeller having screw blades, and a hollow cup open at the discharge side disposed within and carrying such blades and located in such position relatively thereto that the discharge from the blades freely enters the hollow hub and freely leaves the same, the walls of the hub being of such formation that the fluid upon leaving the cup forms a solid cone extending rearwardly for filling the normal rearward void and steadying the impeller and effecting orderly movement of the discharged fluid.

3. A fluid impeller having screw blades, and a hollow cup open at the discharge side occupying the ineffectual central portion within and carrying such blades and located in such position relatively thereto that the discharge from the blades freely enters the hollow hub and freely leaves the same, the walls of the hub being of such formation that the fluid upon leaving the cup forms a solid cone extending rearwardly for filling the normal rearward void and steadying the impeller and'effecting orderly movement of the discharged fluid.

4:. A fluid impeller having screw blades, and a hollow cup open at the discharge side disposed within and carrying such blades and located in such position relatively thereto that the discharge from the blades freely enters the hollow hub and freely leaves the same, the Walls of the hub being of hollow cylindrical formation and extending forwardly and rearwardly of the blades, the inner rearward side of the front end of the hub presenting, in radial section, a curve extending forwardly from the central region and from thence rearwardly and merging with the surface of the cylindrical portion whereby the fluid upon leaving the cup forms a solid cone extending rearwardly for filling the normal rearward void and steadying the impeller and effecting orderly movement of the discharged fluid.

In witness whereof, I have hereunto signed my name in the presence of two subscribing witnesses.

CHARLES H. CAMPBELL.

Witnesses:

THOMAS F. WALLACE, FRED WHITE.

Copies of this patent may be obtained for five centseach, by addressing the Commissioner of Patents, Washington, D. 0.

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