US3173604A

US3173604A - Mixed flow turbo machine

Info

Publication number: US3173604A
Application number: US173437A
Authority: US
Inventors: Herman E Sheets; Lawrence Kurt
Original assignee: General Dynamics Corp
Current assignee: General Dynamics Corp
Priority date: 1962-02-15
Filing date: 1962-02-15
Publication date: 1965-03-16
Anticipated expiration: 1982-03-16
Also published as: DE1428105A1; CH422213A; GB1033502A

Description

March 16, 1965 H. E. SHEETS ETAL 7 MIXED FLOW TURBO MACHINE Filed Feb. 15, 1962 2 Sheets-Sheet l INVENTOR HERMAN E. SHEETS KUPT LAWRENCE H. E. SHEETS ETAL 3,173,604

MIXED FLOW TURBO MACHINE 2 Sheets-Sheet 2 March 16, 1965 Filed Feb. 15, 1962 INVENTOR HERMAN E. 5HEETS KURT LAWRENCE BY @Mv, fi mg m @mw i nited States Patent Qftice arises i- ?atented. Mar. 16, 1365 3,173,604 MIXED FLOW TURBO MACHINE Herman E. Sheets and Kurt Lawrence, New London County, Conn., assignors to General Dynamics Corporation, New York, N.Y., a corporation of Delaware Filed Feb. 15, 1962, Ser. No. 173,437 13 Claims. (Cl. 23012ll) This invention relates generally to mixed flow turbomachines and more particularly to mixed flow turboiachines having a unique blade configuration resulting in improved operating efficiency as compared to previous mixed flow turbo-machines, an increased pressure output and a blade inexpensive to manufacture.

Mixed flow turbo-machines heretofore designed or operated have generally been of the nonaxial flow discharge type, i.e., the fluid left the impeller or rotor in a direction other than concentric with the axis of impeller or rotor rotation. The principal disadvantage of this type of machine resulted from the fact that extra energy was required to take the non-axially discharged fluid and direct it in an axial flow path. Additionally, a machine of increased size and fluid ducts, and consequently lOl'C weight, was required to receive and redirect the fluid in an axial flow path. Another disadvantage of this type of machine was the amount of noise generated during their operation.

Mixed flow turbo-machines of the axial flow discharge type have been previously built in small numbers. All of these machines were designed on the premise that one rad to have either constant or accelerated flow through the blades on the impeller or rotor for proper operation. All of these machines had a common drawback in that they were relatively inefficient in operation. Some small improvement in operation has been achieved but only through a substantial increase in the cost of manufacture of the impeller or rotor blades.

The basic Euler equation for energy transformation shows that the amount of pressure produced in turbomachines is proportional to the amount of pressure pro duced in the rotor or impeller as a result of centrifugal force (represented by the term, U U and the deceleration of flow through the rotor or impeller (represented by the term, IVE-W and through the stator or outlet guide vanes (represented by the term, C C however. heretofore it was believed that in the case of mixed flow turbo-machines having high deflection angles of flow through the rotor, it would not be possible to permit decelerated flow through the rotor since stalling would inevitably occur. As a consequence, with accelerated flow through the rotor the term. W W became negative in the Euler formula thereby decreasing the actual amount of pressure otherwise produced by the clfects of centrifugal force and deceleraied flow through the stator. Of course, by having accelerated flow through the rotor it Was possible to obtain higher pressures than in the case of straight axial fiow turbo-machines but only at a substantial loss in operating efiiciency. Since the friction or drag losses within a turbo-machine vary with the square of the relative velocity of fluid through the rotor and the absolute velocity of the fluid through the stator, the respective aforesaid velocities must be kept to the minimum required to produce the desired pressure. With the discovery that decelerated flow can be permitted through the rotor of a mixed flow turbo-machine, Without danger of stalling, even where large deflection angles are necessary to produce the desired pressure, it now becomes possible to pass the fluid through the rotor and stator at smaller velocities and thereby increase the operating efficiency of the machine since the friction losses have been decreased. It has been found that the improved efficiency is obtainable For Slotted Rotor 'v'nues For Solid Rotor Varies (a) The ratio of the relative mean exit. velocity of flow at the trailing edge of the airfoil or blade on the rotor or impeller to the relative mean inlet velocity of flow at. the leading edge of the airfoil or blade on the rotor or impeller must fall within a range 0L- (b) The ratio of the relative huh exit; velocity of flow at the trailing edge of the airfoil or blade on the rotor or impeller to the relative hub inlet velocity of flow at the leading edge of the airfoil or blade on the rotor or impeller must fall within a range of (c) The ratio of the relative tip exit; velocity of flow at the trailing edge of the airfoil or blade on the rotor or impeller to the relative tip inlet velocity of flow at the leading edge of the airfoil or blade on the rotor must; fall within a range of 0. G0 to 0. 0. 45 to 0. 85

In ordinary straight axial flow turbo-machines, the use of very large relative fluid inlet angles ([3 results in stalling because of the extremely large deceleration of flow that takes place. However, it has been discovered that by special contouring of the hub of the impeller it is possible to obtain a range of specific values of decelerated flow through the impeller even for large relative fluid inlet angles (5 This means that in the case of the mixed flow turbo-machine, it is now possible to define a specific performance characteristic in terms of the pres sure flow relationship. This relationship is a function of the specific value to the relative fiuid outlet angle (8,). which is that angle measured betwen the relative outlet velocity and the circumferential wheel speed. A mixed fiow turbo-machine can now be designed having a steeper pressure characteristic with less pressure variation from the design Operation point to shutoff conditions.

The contour of shape of the hub of the impeller, as has already been indicated, is important if high acrodynamic rotor efficiency at subsonic flow is to be achieved. For the best aerodynamic rotor efiiciency, the hub shape should provide a controlled rate of rotor fluid deceleration or acceleration without any sudden increases or decreases in the rate of change.

The discovery that a specific range of decelerated fluid flow can be permitted through the rotor of a mixed flow turbo-machine at any relative fluid inlet angle (5 without stalling, coupled with the fact that the effect of decreasing the cross-sectional area from rotor inlet to rotor exit results in a reduction of variation in turning angles at the various stations along the rotor blade height and thereby approaches the condition of constant camber, makes it thus possible to select a proper decreasing crosssectional area in the rotor zone by selecting the proper hub shape which under certain conditions can be so designed as to permit the use of an airfoil or blade having a constant camber. This constant camber feature discovery is quite important since the use of a constant camber blade does not appreciably adversely affect the overall performance of the mixed flow turbo-machine and such a blade is less expensive to manufacture than one with a variable camber. Additionally important is the discovery that it is possible to use an airfoil or blade which does not have any twist throughout its height. Ordinarily, without the loss of substantial efiiciency, a non-twisted blade can be used only where the stagger angle or angle of incidence (5) is constant. However, it has been discovered that the stagger angle,

B1+, where {3 is the angle at which the fluid enters the rotor and a is the blade angle of attack) may, depending upon the operating characteristics of the particular airfoil or vane, vary as much as 25 from the values calculated according to the well known free vortex design theory without any appreciable eflect on the pressure output and ethciency of operation of the mixed flow turbo-machine. By this change in stagger angle, the flow conditions in impeller and stator are changed from those of a free vortex to a forced vortex. The import of this particular discovery is that for the first time it is now possible to construct a mixed flow turbo-machine having blades of constant camber and without any twist throughout the height thereof which is as efiicient as the straight axial flow turbomachines and which is substantially less expensive to manufacture. correspondingly, the invention consists of a combination of forced vortex flow through the rotor together with such a predetermined shape of the hub contour that according to the usual flow calculations, blades without twist and constant camber can be used.

It has been discovered that when a mixed flow turbomachine is built in accordance with the invention described herein that an impeller or rotor efliciency of ninety-three percent (93%) can be obtained which is substantially higher than the efliciency of any previously known mixed flow turbo-machine, and that such high efliciency is obtained with blades or vanes which are simple in design and very inexpensive to manufacture.

The principal object of this invention is to provide an inexpensive mixed flow turbo-machine having a substantially improved operating efficiency.

Another object of this invention is to provide a mixed fiow turbo-machine of the axial flow discharge type in which the relative velocity of fluid flow through the im peller and the absolute velocity of fluid flow through out let guide vanes are kept to a minimum to obtain the desired pressure output.

Another object of this invention is to provide a mixed flow turbo-machine in which the blades or vanes on the impeller or rotor have a constant camber and the ratio of relative mean exit velocity at the trailing edge of each said blade or vane to the relative mean inlet velocity of flow at the leading edge of each said blade or vane is less than one.

Another object of this invention is to provide a mixed flow turbo-machine impeller in which said impeller has two or more airfoils or blades projecting generally radially therefrom, each said air foil or blade having a substantially constant camber and chord, each said airfoil or blade being constructed substantially without any twist throughout the height thereof, and the ratio of relative mean exit velocity of flow at the trailing edge of each said airfoil or blade to the relative mean inlet velocity of flow at the leading edge of each said airfoil or vane is less than one.

Another object of this invention is to provide a mixed flow turbo-machine impeller in which said impeller has two or more airfoils projecting generally radially thercfrom, each said airfoil having a substantially constant camber, the fluid flow at the tip of each said airfoil being substantially concentric with the axis of rotation of said impeller, the fluid flow at the hub of each said airfoil being substantially a mixture of axial and radial (three dimensional) flow, the ratio of the relative tip exit velocity of flow at the trailing edge edge of each said airfoil to the relative tip inlet velocity of flow at the leading edge of each said airfoil being less than 0.85 and the ratio of the relative hub exit velocity of the flow at the trailing edge of each said airfoil to the relative hub inlet velocity of flow at the leading edge of each said airfoil being less than 1.].

Still another object of this invention is to provide a mixed flow turbo-machine impeller having airfoils pro jecting generally radially therefrom in which the ratio of the relative mean exit velocity of flow at the trailing edge of each said airfoil to the relative mean inlet velocity at the leading edge of each said airfoil varies within a range of 6.7 to .95.

Other objects will appear from the following descriptic-n, appended clain s and accompanying drawings.

The above objects are accomplished by the means illustrated in the accompanying rawings in which- PEG. 1 is a schematic, longitudinal sectional View of a mixed flow turbo-machine, including a rotor and stator, having blades of the present invention;

FIG. 2 is a schematic, longitudinal sectional view of a mixed flow turbo-machine, including a rotor and a slotted blade stator positioned in a zone of increasing axial flow area, having blades of the present invention;

FIG. 3 is a schematic, longitudinal sectional view of a mixed flow turbdmachine, including a rotor and a stator positioned in a zone of increasing axial flow area having vanes of the present invention;

FIG. 4 is a vector flow diagram of a typical mixed flow turbomachine constructed .in accordance with this invention taken at the hub station.

FIG. 5 is a vector flow diagram of a typical mixed flow turbo-machine constructed in accordance with this invention taken at the tip station.

In FIGS. 1-3, a mixed flow turb0-machine 10 is shown comprising a cylindrical housing 12 in which is positioned an impeller or rotor 14 having blades or vanes 16, an inner casing 18 having outlet guide vanes 20 and an electrical motor 22 positioned within said inner casing 18 and connected by a shaft to the rotor 14. In FIGS. 2 and 3, the inner casing 18 is shown as providing an 1ncreasing axial flow area in the downstream direction. The rotor blade 16 in FIG. 1 and the outlet guide vane 20 in FIG. 2 has a slot 24 extending generally longitude nally in a downstream direction with respect to the chord of the rotor blade 16 and guide vane 20 from the lower surface to the upper surface of the airfoil and having its exit positioned in the upper surface and its gap and overlap dimensions generally as specified in United States patent application Serial No. 768,490 (filed October 2 1958), now Patent No. 3,075,743. In FIGS. 1 and 2, the airfoils or blades 16 and guide vanes 20 are being shown as contoured, and having substantially constant camber and chord and without any substantial twist throughout the airfoil or blade height. In FIG. 3 the vanes 16 and guide vanes 20 are shown as having constant thickness as is normally the case Where sheet metal vanes are used and having constant camber and chord and being constructed without any substantial twist throughout the vane height. FIGS. 4 and 5 are vector diagrams of a typical mixed flow turbo-machine constructed in accord ance with this invention. In these figures the various symbols have the following definition:

C is equal to the absolute inlet velocity of the air at station 1.

C represents the absolute average exit velocity leaving the impeller at station 2.

W represents the relative fluid velocity measured with respect to the impeller blade at station 1 and W represents the relative fluid exit velocity measured with respect to the impeller blade at station 2.

C represents the absolute fluid velocity entering the inlet guide vane section at station 2.

U represents the impeller blade circumferential velocity at station 1.

U represents the impeller blade circumferential velocity at station 2.

[3 represents the fluid relative entrance angle at station 1.

B represents the fluid relative exit angle at station 2.

0 represents the fluid turning angle Within the impeller blade.

AC represents the change of the whirl velocity or rotational velocity component resulting by the action of the impeller.

The subscript (/1) refers to a condition occurring at the hub and the subscript (t) refers to a condition occurring at the tip of the impeller blade. Station one (1) is located immediately ahead of the leading edge of the impeller blade. Station two (2) is located immediately downstream of the trailing edge of the impeller blade.

From the vector diagrams shown in FIGS. 4 and 5, it can be shown by simple geometric relationships that Eulers basic equation for energy transformation within the rotor and stator of the turbo-machine:

can be reduced to the following form: 2 u m1 m2 From this equation it can be seen that inlet hub speed (U can be changed without directly affecting the pressure (H) produced; however, any change in the inlet hub speed (U produces a corresponding change in the inlet absolute fluid velocity (C Therefore, by considering the vector diagram in conjunction with equation B above, it is noted that any decrease in C will require an increase in AC if the same pressure (H) is to be maintained. This decrease in C with a corresponding decrease in U will reflect a reduction in W However, for the same pressure (H) output, AC must increase, resulting in a corresponding decrease in the magnitude of W In this manner it can be seen that the ratio of W W can be controlled and selected to stay within the desired limits.

It can also be seen from FIGS. 4 and 5 that in order to proportion the vector diagram initially to achieve the proper W /W ratios, it is necessary to define limits of outlet and inlet hub/tip diameter ratios. The first limiting criteria will be that Since the flow coefficient equals C,,,/ U, it can be shown that Since the inlet tip flow coefficient (41 must be smaller than the outlet tip flow coefficient (m the minimum and maximum values for can easily be determined. By using the above design criteria, it is possible to pro portion initially the fluid flow vector diagram in order to achieve a proper design for a mixed flow turbomachine.

As previously indicated, for a turbo-machine having subsonic flow through its rotating and stationary blades, a decrease in inlet hub diameter (D will result in a decreased relative inlet velocity (W and, in turn, results in a decreased relative outlet velocity (W The decrease of (W is caused by a required increase in the circumferential whirl velocity (AC in order to obtain the desired pressure (H). This inc rease in AC actually causes a change in deflection of fluid by tlie impeller as the fluid passes through it. A decrease in C causes a corresponding decrease in the inlet hub diameter (D with blade velocity (U remaining constant resulting in a decreased tip relative inlet velocity (W however, AC must still increase in order to obtain the desired pressure (H). This effect therefore increases the fluid deflection at the tip at a rate different than at the hub section. Hence, the relative deflection (6) at both hub and tip sections can be controlled by a proper choice of inlet hub diameter. It is well known in the basic art of turbo-machine design that blade profiles producing a particular deflection of fluid are chosen (in a particular manner) from the test data reported by such agencies as NASA. Hence, the proper choice of inlet hub diameter will produce deflections at all stations that can be satisfied by an impeller blade having constant camber. Constant chord can also be achieved by combining the two requirements (constant chord and constant camber) when choosing the inlet hub diameter.

By considering the effects resulting from reducing the inlet hub diameter to a value less than the outlet hub diameter and keeping the outlet hub/tip diameter ratio greater than 0.60, the angular location of the inlet relative velocity (W at all stations can be controlled. This controlled angular location in conjunction with standard profile angles of attack, which are very well known in the art of turbo-machine design, can provide blades or vanes of profiles with little or no twist throughout the blade or vane height.

Taking the above effects into account and utilizing the results of various experiments and analyses, the use of non-twisted blades is now possible for mixed flow impellers of high efficiency. These vanes or airfoils operate under a free vortex flow, or a modification thereof, namely, a forced vortex flow.

The present invention has been described generally in connection with impeller or rotor blades, but is also applicable to stationary or guide vanes. with moving blades, the movement of the fluid flow relative to the moving blades must be considered while with stationary blades or vanes there is only the absolute fluid movement to be considered.

The specified embodiment of blades which has been shown and described is to be understood to be illustrative only. As has been fully discussed above, the blades may be modified within the limitations specified to meet different conditions and requirements. We therefore contemplate such variations as corne within the spirit and scope of the appended claims.

We claim:

1. A turbo-machine of the mixed flow type, comprising: a substantially cylindrical housing, a casing in said housing substantially co-axial therewith, an impeller in said housing mounted for rotation on said casing, said impeller including a contoured hub with at least two cambered vanes projecting generally radially outwardly therefrom, each of said vanes being positioned on said impeller such that the hub diameter at the intersection of the hub and the leading edge of the vane is smaller than the hub diameter at the intersection of the hub and the trailing edge of the same vane, the annulus area between the hub and the housing at said leading edge intersection being susbtantially greater than a corresponding annulus area at said trailing edge intersection, the resultant flow of air through said impeller including a substantial radial component mixed with a substantial axial component, the contour of said hub being such that a predetermined controlled rate of change of resultant flow velocity through said impeller is induced without loss of efficiency while the ratio of the relative means exit velocity of flow at the trailing edge of each vane t0 the relative mean inlet velocity of flow at the leading edge of each vane is less than one.

2. The turbo-machine of claim 1 further characterized in that the ratio of relative mean exit velocity of flow at the trailing edge of each vane to relative mean inlet velocity of flow at the leading edge of each vane varies within a range of 0.7 to 0.95.

3. The turbo-machine of claim 1 further characterized in that the ratio of relative tip exit velocity of flow at the trailing edge of each vane to relative tip inlet velocity of flow at the leading edge of each vane is less than 0.85 and the ratio of relative hub exit velocity of flow at the trailing edge of each vane to relative hub inlet velocity of flow at the leading edge of each vane is less than 1.1.

4. The turbo-machine of claim 1 further characterized in that each of said vanes has substantially constant camber and chord throughout its length.

5. The turbo-machine of claim 4 further characterized in that each of said vanes is substantially untwisted throughout its length.

6. A turbo-machine of the mixed flow type, comprising: a substantially cylindrical housing, a casing in said housing substantially co-axial therewith, an impeller in said In connection housing mounted for rotation on said casing, said impeller including a contoured hub with a cascade of cambered vanes projecting generally radially outwardly therefrom, each of said vanes being positioned on said impeller such that the hub diameter at the intersection of the hub and the leading edge of the vane is smaller than the hub diameter at the intersection of the hub and the trailing edge of the same vane, the annulus area between the hub and the housing at said leading edge section being substantially greater than a corresponding annulus area at said trailing edge intersection, the fluid flow at the tip of each vane being substantially concentric with the axis of rotation of said impeller and the fluid flow at the hub of each vane being substantially a mixture of axial and radial flow components, the contour of said hub being such that a predetermined controlled rate of change of re sultant flow velocity through said propeller is induced without loss of efficiency while the ratio of relative mean exit velocity of flow at the trailing edge of each vane to relative means inlet velocity of flow at the leading edge of each vane is less than one.

7. The turbo-machine of claim 6 further characterized in that each of said vanes has substantially constant camber and chord throughout its length.

8. The turbo-machine of claim 7 further characterized in that each of said vanes is substantially untwisted throughout its length.

9. The turbo-machine of claim 8 further characterized in that the ratio of relative tip exit velocity of flow at the trailing edge of each vane to relative tip inlet velocity at the leading edge of each vane is less than 0.85 and the ratio of relative hub exit velocity of flow at the trailing edge of each vane to the relative hub inlet velocity of flow at the leading edge of each vane is less than 1.1.

10. A turbo-machine of the mixed flow type comprising: a substantially cylindrical housing, a casing in said housing substantially co-axial therewith, an impeller in said housng mounted for rotation on said casing, said impeller including a contoured hub with a least two cambered air foils projecting generally radially outwardly therefrom, each of said air foils being positioned on said impeller such that the hub diameter at the intersection of the hub and the leading edge of each air foil is smaller than the hub diameter at the intersection of the hub and the trailing edge of same air foil, the annulus area between the hub and the housing at said leading edge intersection being substantially greater than a corresponding annulus area at said trailing edge intersection, the resultant fiow of air through said impeller including a substantial radial component mixed with a substantial axial component, the contour of said hub being such that a predetermined controlled rate of change of resultant fiow velocity through said impeller is induced without loss of efficiency while the ratio of relative mean exi-t velocity of flow at the trailing edge of each vane to relative mean inlet velocity of flow at the leading edge of each vane is less than one.

11. The turbo-machine of claim 10 further characterized in that each of said air foils has substantially constant camber and chord throughout its length.

12. The turbo-machine of claim 10 further characterized in that each of said air foils is substantially untwisted throughout its length.

13. The turbo-machine of claim 10 further characterized in that each of said air foils is slotted along its length, the ratio of relative mean exit velocity of flow at the trailing edge of each slotted air foil to relative mean inlet velocity of flow at the leading edge of each slotted air foil varying within a range of 0.55 to 0.95.

References Cited in the file of this patent UNITED STATES PATENTS 2,084,111 Schicht June 15, 1957 2,806,645 Stalker Sept. 17, 1957 2,936,948 Eck May 17, 1960 3,059,834 Hausammann Oct. 23, 1962 3,075,743 Sheets Jan. 29, 1963 FOREIGN PATENTS 107,876 Australia July 13, 1939 223,071 Australia July 29, 1959 564,336 Great Britain Sept. 22, 1944 622,415 Great Britain May 2, 1949 628,263 Great Britain Aug. 25, 1949 786,448 Great Britain Nov. 20, 1957 OTHER REFERENCES The Slotted-Blade Axial Blowerby H. E. Sheets (8 pp.), received U.S.P.O. Sept. 19, 1957.

Claims

1. A TURBO-MACHINE OF THE MIXED FLOW TYPE, COMPRISING: A SUBSTANTIALLY CYLINDRICAL HOUSING, A CASING IN SAID HOUSING SUBSTANTIALLY CO-AXIAL THEREWITH, AN IMPELLER IN SAID HOUSING MOUNTED FOR ROTATION ON SAID CASING, SAID IMPELLER INCLUDING A CONTOURED HUB WITH AT LEAST TWO CAMBERED VANES PROJECTING GENERALLY RADIALLY OUTWARDLY THEREFROM, EACH OF SAID VANES BEING POSITIONED ON SAID IMPELLER SUCH THAT THE HUB DIAMETER AT THE INTERSECTION OF THE HUB AND THE LEADING EDGE OF THE VANE IS SMALLER THAN THE HUB DIAMETER AT THE INTERSECTION OF THE HUB AND THE TRAILING EDGE OF THE SAME VANE, THE ANNULUS AREA BETWEEN THE HUB AND THE HOUSING AT SAID LEADING EDGE INTERSECTION BEING SUBSTANTIALLY GREATER THAN A CORRESPONDING