US2331076A - Turbine nozzle ring - Google Patents

Description

4 A. MELDA HL ,33 6

' TURBINE NOZZLERING Filed May 11, 1940 s Sheets-Sheet i Ira/endow; flrelfifslak,

' 169mm 19%) .s'

Oct. 5, 1943. N I A. MELDAHL 2,331,076

TURBINE NOZZLE RING Filed May 11, 1940 3 Sheets-Sheet 2 1943- A. MELDAHL TURBINE NOZZLE RING 3 SheetIs-Sheet 3 Filed May 11, 1940 M I WA,

Patented Oct. 5, 1943 The present invention relates to the. design and manufacture of turbine nozzle rings,

An object of the invention is topro'vide turbine nozzle rings in which the-blades are of such profile that the nozzle section may be readily -atljusted to meet the requirements of a barticular case. In other words, an object of the "invention is to provide turbine 'n'ozzle rings tnatfmaybe manufactured in a single stock design-and thereafter altered by finishing operations to obtain for particular installations.

the difie'rent nozzle sections that are best suited A further object is to provide turbine nozzle 7 rings the blades of which'aieso 'sha'ped that the nozzle section will increase as the outlet edges 5 of the blades are cut away as'bya machining or the blades Will Still give an fiicint Stiih passage with low losses.

A further object is to proviaenezzle rings with 3.

blades that. are long'compared with their mean diameter, said nozzle rings impartingapproximately non-rotating movem nt of the'powerfiuid in spite of the fa'ct that cylindrical shape. I a 7 When designing turbines it is often necessary to adapt the nozzle section to the prevailing con- 'di-tions 'encounte'redwhen the installation is coinpleted and tested under normal operating conditions. This may be jd'one'by partial admission i. e. by closing a certain number of nozzles, but this gives a poor efiicie'ncy. It may alsobe done by changing the lengthiof the blades, iulladmis, sion being maintained. This'gives a better efiiciency, but the cost of manufacture is increased,

and any modification of nozzle section that may become necessary on an existing ftu'rbin'e is very expensive, as the nozzle ring andru'nning blades must be changed. i

7 Experience has shown that itis possible to change considerably the nozzle section without changing the running blades, and still obtain good eificiencies. The degree of reaction of course varies with the nozzle section and the turbine speed, but this is not of serious. importance and in practice'fican be tolerated.

According to the present invention the nozzle blades or guide vanes are so shapedthat, by cutting away their outlet edges, the nozzle section will be increased and the remaining parts of the blades will suffice to givea good nozzle with high efliciency. The increasein axial'clearance between nozzle outlets and running blades has no the" nozzle 'b1ades are of N grinding operation and the remaining parts of detrimental'eil'ect' onth'e turbiheelficlency; .The I I nozzle blades are easily aneri-by fixing-thema- "zl'e" ring in alathe" and turning off "the outlet edges until the desired nozzle section is obtained. In order to facilitate this operation the spaces between the blades can be filledwith a suitable mass, for instance rosin. The blades can also be ground instead 'of being turned oil. In cases where the blades arenot all to be alteredto thesame extent, the blades can be milled 0r filed downbyhand. g i 1 The advantages obtained by such a nozzle ring si n a a 11) For one single turbine typelolnly O e nozzle ring model is needed." Thedifferent'nozzle sec: tions required are all obtained'from the same model by cutting .away the outlet ed-gesof the nozzle "bladesuntil the desired nozzle section is attained, I g I v (2) Only one single rotor bladingislnecessary for'each type of turbine. f

7(3) If experience shows that it is necessary to modify the nozzle section 'of a turbine inserv ice, thenlonlyfthe nozzle ring need be changed. If an increase in'nozzle section needed, then it is only necessary to cut away the outlet edges of the nozzleblades. If the nozzle section must be diminished; then the nozzle ring must be replaced by a new nozzle ring, made to the same model, theblades of which have not been cut away or 'have'been cut away to a lesser extent.

In any case this means a considerable simplification of manufacturefoff stock kee iing and of necessary modification in service."

The present invention is especiallyvaluable in the design of singlejsta'ge exhaust gas turbines for driving the charging blowers of internal com bustion engines. In this case it is essential. that "the nozzle sectionflbe exactlyadapted to the working conditions of the internal combustion engine,

and on the other-handit is not possible to determine beforehand exactly which nozzle section will ive the best results in operation, andthe correctfnozzle 'seotionmust therefore be tried out in service." In this case it is especially'valuable to be able totry different nozzle sections with as 'little ecstand as few modifications to the turbirielaspossible. g g v To'ensure a good efiicienc'y, the blades should have such a, profile that the envelope of a series of circles inscribed in the passage between the blades when they are setup on a straight line of centers is convex and continuously converging, in the direction of the nozzle outlet towards said straight line of. centers, the convergence being such that the distance betweentne center iofj th e smallest inscribed 'ciicle and the centerof that inscribed circle having twice the diameter is more than 0.8 times the nozzle blade pitch and less than 1.25 times the nozzle blade pitch.

When such blades are used for nozzle rings having a ratio of mean diameter to nozzle blade length of less than 6:1, a further advantage is obtained. It is known that to obtain non-rotational flow behind a nozzle ring, the exit angle must increase with increasing radius. For incompressible fiuids the tangent of the exit angle must increase in proportion to the radius, for elastic fluids the increase is less, according to the speed, the increase becoming zero, i. e. the exit angle being constant at the speed of sound.

In a nozzle ring according to the present invention it is now possible to adjust the nozzle section on each radius in such a way that the relation between outlet angle and radius which will give non-rotational movement, is actually realized.

If the blades are placed in a position perpendicular to the axis of the nozzle ring, and if the blades are altered on each individual radius so as to realize the desired non-rotational movement, then the altered outlet edges will generally not lie in a plane perpendicular to the axis, but approximately on a conical surface, it having, for instance, been necessary to cut away the outlet edges of the blades more at their roots than at their tips. In such a case it may be convenient to tilt the blades axially so as to bring the altered edges back into a plane perpendicular to the axis.-

The accompanying drawings show embodiments of the invention.

Fig. 1 is a diagram illustrating two adjacent blades of a nozzle ring embodying the invention, the blades being shown in cross-section normal to their horizontal axes, with a seriesof circles inscribed in the fluid passage and tangent to the blade profiles; v

Fig. 2 is a similar diagrammatic view of adjacent blades of the nozzle ring after the outlet edges of the blades have been cut back to increase the nozzle section;

Fig. 3 is a diagram for the analysis of the blade profiles on the basis of the inscribed circles of Fig. 1;

Fig. 4 is a sectional view on the section line l4 of Fig. 5 through three adjacent blades, the sections of blades I51; and I5 being through the tips thereof and the section of blade l5b being through the root of the blade;

Fig. 5 is a perspective view, viewed from the outlet side of the ring, and

Fig. 6 is a vertical section on the line 66 of Fig. 5, of a portion of a nozzle ring in which the outlet edges of the blades are in a plane perpendicular to the axis of the ring;

Fig. '7 is a perspective view, viewed from the outlet side of the ring, and V Fig. 8 is a vertical section on the line 8-8 of Fig. 7, of a portion of a nozzle ring'in which the outlet edges of the blades have been cut away more at the tips than at the roots without any tilting of the blades, thereby leaving the outlet edges lying in an imaginary frustro-conical surface which is concave toward the inlet side of the ring;

Fig. 9 is a perspective view, viewed from the outlet side of the ring, and

Fig. 10 is a vertical section on the line Ill-l0 of Fig. 9 of a nozzle ring in which the outlet edges of the blades have been cut away more at the roots than at the tips without any'tilting of the blades, thereby leaving the outlet edges lying in an imaginary frustro-conical surface which is convex toward the inlet side of the ring.

In order to simplify the disclosure of the invention, non-essential and well known features such as the shape and mounting of the roots and tips of the blades have not been illustrated. It will be understood, however, that the nozzle ring is of the conventional ring shape, that the blades may be suitably mounted between inner and outer cylindrical and concentric supports l6 and H (see Figs. 5 to 10, inclusive), and that the blades extend radially from the axis of the ring and are curved in the direction parallel to the axis of the ring. The edge of each blade adjacent the axis is referred to hereinafter as the root of the blade and the opposite edge which is remote from the axis of the ring is referred to as the tip of the blade. The other two edges of the blade are referred to as the inlet and outlet edges. The four edges of the blades referred to above are identified on the drawing as follows: 18 marks the inlet edges of blades, I 9 marks the outlet edges, 20 marks the roots, and 2i marks the tips.

In Fig. l of the drawings, adjacent radial blades I5, l5a of the nozzle ring, as originally manufactured, are shown in section as seen when out through by a cylindrical surface concentric with the axis of the nozzle ring at the mean diameter of the blades (section line l-| on Fig.

"7) where they are spaced circumferentially by the blade pitch p. The blade profile is such, as will be explained hereinafter with reference to Fig. 3, that the outlet nozzle section is increased by any removal of material from the outlet end or edge of the blades. This efiect will be apparent from an inspection of Fig. 2 in which the residual portions of blades l5, I5a are shown in section after substantial portions [5' of the outlet edges of'the blades have been removed by machining, grinding or filing.

The analysis of the blade profile is facilitated, as shown in Fig. 1, by inscribing between the blades a series of circles, identified by reference numerals l to 12, inclusive, at their centers, that are tangent to surfaces of the blades at their pitch diameters. The centers of adjacent circles are equally spaced and the diameters of the successive circles increase at a more than linear rate, as is indicated by the continuous curvature and convexity of, the envelope lines I3 of the circles l-l2 towards the linear center line M on which the several circles are redrawn in Fig. 3. The rate of change in the cross section of the fluid, passage is such that, when the smallest circle I at the nozzle outlet has a diameter a, the distance A from the nozzle outlet to the nozzle section of radius a or, diameter 2a, is more than 0.8 of the blade pitch p and less than 1.25 times the blade pitch p.

The bladesmay be individually formed as castings and secured to the support in any desired manner, but, for small turbines having a ratio of mean blade diameter to blade length of not more than 6 to 1, the blades are preferably cut or stamped from sheet metal, bent to shape, and then secured to the support.

In Fig. 4, the blades l5 and [5a are shown in section as viewed on a cylindrical surface passing through the tips of the blades, and the blade l5b is shown in section as viewed on a cylindrical surface through.the root of that blade. Assuming that the blades have a ratio of mean diameter to blade length of 5:1, the blade pitches 2J1, p2 at the root and tip of the blades, respectively, have a ratio of 4:6.

this means that the tangents of the efiective exit.

angles at .the root and the tip of the blades should have the ratio of 4:6. Ih the blades are cut back on. a plane normal to the axis of the nozzle ring, the exit angles (11, 12 at the blade root and blade tip, respectively, are defined by sin az=azlpz In the particular example illustrated in Fig. 4, a1 is 930" and a2 is 1215. This increase in the exit angle toward the tip of the blade does not satisfy the stated requirement for non-rotational movement of an incompressible fluid as the exit angle at the tip of the blade should have the value of about 1415". This larger exit angle a: can be obtained by cutting back the tip portion of the blade to increase the nozzle section at thatpoint to a value az at which I Sll'l 272 In the case of an elastic fluid, the outlet section should be smaller according to compressibility, as the pressure behind the nozzle ring is higher at the tip than at the root. If 15% compression is assumed, then the nozzle section a2 will be correct.

If the nozzle blade outlet edge 'are cut away at the tip corresponding to the nozzle section or (incompressible fluid) the altered outlet edges will lie in an imaginary conical surface (see Fig.

8) which is concave toward theinlet side of the ring. This may be avoided by tilting the nozzle blades axially by the amount 0 at the tip of the nozzle blades so that the altered outlet edges of the nozzle blades will again lie in a plane perpendicular to the axis of the nozzle ring (Fig. 6).

On the other hand, if the outlet edges of the blades are cut away more at the roots than at the tips and the blades are not tilted to bring the resulting edges into a plane perpendicular to the axis, the resulting edges of the blades will lie in an imaginary conical surface (see Fig. 10) which is convex toward the inlet side of the ring.

I claim:

1. A turbine nozzle ring comprising radial blades associated to define a curved fluid passage between each adjacent pair of blades, the opposed surfaces of each adjacent pair of blades being so shaped and relatedthat when developed with reference to a straight line representing the" 5 mean fluid path they are convex throughout their" lengths'towards said straight line and continuously approach the'straight line in the direction of the nozzle outlet, whereby the effective outlet section of the blading may be increased by cutting away the outlet ends of the blades.

2. A turbine nozzle ring with blades so shaped and arranged that the envelope of a series of circles inscribed in the passage between said blades, when said circles are set up on a straight line of centers, is convex toward said straight line of centers and continuously converging. in the direction of the nozzle outlet, the convergence be-' ing such that the distance between the center of the smallest inscribed circle and the centerof that inscribed circle having twice the diameter of said smallest inscribed circle is more than 0.8

. times the nozzle blade pitch and less than 1.25

the nozzle blade pitch at the mean diameter of .7

the blades.

3. A turbine nozzle ring as claimed in claim 2, the ratio of the mean diameter of the nozzle ring and the length of the nozzle blades being less than 6:1.

4. A turbine nozzle ring as claimed in claim 2, wherein the axial dimensions of said blades at the roots and at the tips, respectively, are dif,-

ferent and the outlet edges of the blades lie in a conical surface.

5. A turbine nozzle ring as claimed in claim 2, wherein said blades are wider axially of the ring at the roots than at the tips, the outlet edges of the blades defining a conical surface that is concave towards the inlet side of the nozzle ring and the decrease in width of said blades towards the 0 tips thereof being. such that the efiective exit angles increase radially of the blade edge at a rate corresponding to non-rotational movement of the power fluid through the nozzle ring.

/ 6. A turbine nozzle ring as claimed in claim 2,

5 wherein said bladeshave outlet edges in a plane normal to the axis of the nozzle ring, the blades being tilted axially to increase the effective exit angle towards'the tips of the blades at a rate? corresponding to non-rotational movement of the power fluid through the nozzle ring.

AXEL MELDAHL.

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