GB2424927A

GB2424927A - A pre-swirl nozzle ring and a method of manufacturing a pre-swirl nozzle ring

Info

Publication number: GB2424927A
Application number: GB0507075A
Authority: GB
Inventors: Volker Herzog
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2005-04-06
Filing date: 2005-04-06
Publication date: 2006-10-11
Also published as: GB0507075D0

Abstract

A method of manufacturing a pre-swirl nozzle ring 6 for a gas turbine; said method comprising the steps of providing a flow metering ring having a plurality of pre-swirl nozzle flow passages 20 therein; measuring the actual flow rate of the flow metering ring; comparing the said measured flow rate with a pre-determined required flow rate; determining whether the said measured flow rate is within acceptable limits of the said required flow rate, and, if not: adjusting the flow rate of the said ring in accordance with the said comparison by increasing the flow cross-sectional area of one or more of the said pre-swirl nozzle passages 20 and/or increasing the number of pre-swirl nozzle flow passages 25 in the ring.

Description

A PRE-SWIRL NOZZLE RING AND A METHOD OF MANUFACTURING

A PRE-SWIRL NOZZLE RING

The present invention relates generally to a pre-swirl nozzle carrier for a gas turbine and particularly to the control of fluid flow through the carrier.

In the field of gas turbine engines it is known to use a proportion of air from one or more compressors to provide cooling of various static and rotating components. In particular, the turbine rotor blades are cooled by airflow bled from the compressor section of the engine. Cooling air is supplied into a pre-swirl chamber located upstream of the turbine rotor by pre-swirl nozzles provided on an annular pie-swirl nozzle carrier, typically a ring or a plurality of circumferentially spaced segments that together form a ring.

The cooling airflow required to cool the turbine rotor blades is determined by the engine cycle for which the blades are designed. In order to achieve optimum cooling efficiency the flow area of the pie- swirl nozzles is matched as closely as possible to a required flow rate for a particular engine.

It is known, for example, from US 4,730,978, to form an annular carrier body with pre- swirl nozzles and to adjust the overall flow rate of the carrier body by blanking one or more pre-swirl nozzles to reduce the actual flow rate approximately to a required flow rate. However, the blanking of one or more pre-swirl nozzles does not allow fine-tuning of the flow rate and, moreover, can lead to an uneven circumferential flow distribution over the rotor blades which can in turn lead to uneven cooling of the rotor.

The present invention seeks to address the problems with known pre-swirl nozzle rings.

According to a first aspect of the present invention there is provided a method of manufacturing a pre-swirl nozzle ring for a gas turbine; said method comprising the steps of: providing a flow metering ring having a plurality of pie-swirl nozzle flow passages therein; measuring the actual flow rate of the flow metering ring; comparing the said measured flow rate with a pre-determined required flow rate; determining whether the said measured flow rate is within acceptable limits of the said required flow rate, and, if not: adjusting the flow rate of the said ring in accordance with the said comparison by Increasing the flow cross-sectional area of one or more of the said pie- swirl nozzle passages and/or increasing the number of pre-swirl nozzle flow passages in the ring.

Therefore, whilst in known systems a nozzle ring with a flow rate in excess of a required flow rate is produced and is reduced to achieve an approximate required flow rate, the present invention seeks to form a nozzle ring the flow rate of which is equal to or less than a required flow rate and, following a flow rate checking step, to use designated tuning pre-swirl nozzles to increase the flow rate to a required flow rate. The present invention achieves a required flow rate without the need to block off one or more nozzles and therefore can provide a ring which delivers an even airflow distribution, is easily made and is easily tuned to achieve a desired airflow. Moreover, the accuracy to which a flow rate can be fine-tuned is far greater then a system in which one or more holes are entirely blanked off.

The first step of the method involves forming a nozzle ring with one or more pre-swirl nozzles Subsequently the flow rate of the ring is measured and compared to a required flow rate. The pre-swirl nozzles initially formed with the ring are designed to give a flow rate less than or equal to a required flow rate so that if any adjustment is required it is an increase in flow rate which is required. Once the measured flow rate has been compared to the required flow rate and the required increase in flow rate is calculated, one or more pre-swirl nozzles are used to increase the flow rate.

The nozzles used to tune the flow rate may be pre-formed in the ring prior to measuring the flow rate. In this case the tuning operation would involve increasing the size of existing nozzles to increase the flow rate of the carrier body. Accordingly, the pre-swirl nozzles selected for tuning may comprise some of the pre-swirl nozzles formed in the carrier body prior to measuring of the ring flow rate. Alternatively, designated tuning nozzles may be created only following the flow checking step.

The step of adjusting the flow rate of the ring may comprise the step of increasing the flow cross-section of one or more of the pre-swirl nozzles pre-designated as flow tuning holes, and/or machining at least one additional pre-swirl nozzle flow passage at a pre- determined position or positions on the ring.

The at least one additional flow passage may be provided at an angular position on the ring which improves the circumferential uniformity of the air flow distribution through the ring.

The ring may be formed by a casting operation. By using a casting operation the accuracy of the pre-swirl nozzles formed in the ring is limited and although the measured flow rate of the ring can be close to the required flow rate, some tuning is required.

The pre-swirl nozzles may be formed by casting. Accordingly the pre-swirl nozzles may be formed in the casting operation which forms the ring.

The pre-swirl nozzles may be formed by spark erosion. Spark erosion, such as electro- discharge machining (EDM) may be used to form the pre-swirl nozzles in a pre-cast ring. Spark erosion may also be used to form additional tuning pre-swirl nozzles after flow measurement.

The additional nozzles may be formed or increased in size by a drilling operation.

The step of adjusting the flow rate of the ring may comprise the step of drilling at least one additional pre-swirl nozzle passages and/or drilling at least one existing pre-swirl nozzle to increase the flow cross-section thereof. The size of the drill bit used in the drilling operation can be carefully selected to provide a required increase in flow rate.

Typically the achievable tolerance of the drilling operation is much more accurate than standard casting or EDM processes.

The nozzle formation in the ring of the present invention can therefore be thought of as a two-stage process. In the first stage nozzles are formed in a ring to give a flow rate which is as close as possible to a required flow rate. Following a flow measurement step a secondary nozzle forming operation is used to create more nozzles or increase the size of existing nozzles in order to increase the overall flow rate of the ring to a required flow rate.

According to a further aspect of the present invention there is provided a pre-swirl nozzle ring for a gas turbine engine, the said ring comprising: one or more primary nozzle flow passages having an inlet and/or outlet with a non-circular flow cross- section; and one or more tuning nozzles having an inlet and/or outlet with a circular flow cross-section.

According to a further aspect of the present invention there is provided a pre-swirl nozzle ring for a gas turbine engine, the said ring comprising: one or more primary nozzle flow passages having an inlet and/or outlet with an elongate flow cross-section; and one or more tuning nozzles having an inlet and/or outlet with a circular flow cross- section.

According to a further aspect of the present invention there is provided a pre-swirl nozzle ring for a gas turbine engine, the said ring comprising: one or more primary nozzle flow passages having an inlet with an elongate flow cross-section; and one or more tuning nozzles having an inlet with a circular flow cross-section.

Nozzle rings with nozzles having a circular section are known, for example from US 4,708,5088. However, in some cases because of restrictions on the height of the carrier body round holes cannot deliver sufficient airflow. Accordingly, rings with nozzles having a non-circular, such as an elongate, flow section are produced. It is difficult to produce elongate nozzles within very close tolerances to achieve a required dimension, shape, and surface finish and it is also difficult to adjust the size of such nozzles once formed. Accordingly, achieving a required flow rate with a ring having elongate nozzles by fine tuning has previously not been possible.

The present invention proposes that a nozzle ring with non-circular, in particular elongate, flow-section primary nozzles for providing a majority of the airflow and one or more circular tuning nozzles, which are more easily formed and re-sized, can be used in order to allow tuning of the airflow of the carrier body to a required rate. The present invention may therefore provide a nozzle ring with elongate and circular flow-section nozzles on the same component.

The primary nozzles may have an outlet with an elongate flow crosssection.

Accordingly the inlet and outlet of the nozzles are elongate.

The tuning nozzles may have an outlet with a circular flow cross-section. Alternatively the tuning nozzles may have an outlet with an elongate flow cross-section forming a conical nozzle extending from a circular inlet to an elongate outlet.

The flow cross-section may be uniform from the inlet to the outlet of each of the nozzles or may vary from the inlet to the outlet.

A ring in which all of the nozzle outlets are of uniform flow crosssection may be formed so as to give evenly distributed cooling flow.

The ring may have a plurality of equally spaced primary pre-swirl nozzles. In one embodiment the ring has twenty-eight primary nozzles. Equally spaced pre-swirl nozzles provide even cooling of the rotor disc and blades.

The ring may have a plurality of equally spaced tuning nozzles. In one embodiment the ring has four tuning nozzles.

Because the tuning nozzle inlets have a circular flow cross-section they are much easier to adjust in size than elongate nozzles. By forming tuning nozzles in a ring or increasing the size of already present tuning nozzles the airflow of the carrier body can be adjusted to a required airflow rate. The airflow adjustment is achieved without the requirement for any nozzles to be blanked and consequently without compromising the exit flow pattern of the ring.

The ring may comprise a plurality of arcuate segments; alternatively the ring may comprise a complete annulus such as a hoop-continuous annular structure.

The primary nozzles may be circumferentially elongate in section on the ring.

One to four tuning nozzles may be formed in the ring and used for finetuning of the ring airflow. In one embodiment, four tuning nozzles are provided, each being positioned at 90-degree intervals on an annular ring.

The primary and/or tuning nozzles may follow an oblique path through the ring. Oblique nozzles can be used to direct the airflow and pre-swirl the air in the same direction as the rotor disc and blades are rotating to reduce friction as the air hits the rotating components.

The inlet and/or outlet of the primary nozzles may have an oval section. Primary nozzles with an inlet and/or outlet having a "racetrack" configuration have been shown to be particularly suitable.

According to a further aspect of the present invention there is provided a pre-swirl nozzle ring for a gas turbine engine, the ring being formed by casting and having a plurality of primary nozzle flow passages cast therein, and having one or more tuning nozzle flow passages machined therein post-casting.

Accordingly, this aspect of the present invention provides a ring having nozzles formed by casting and nozzles formed after the casting operation. The nozzles formed after the casting operation can be used to tune the airflow through the carrier body to achieve a required airflow rate.

The present invention may comprise a pre-swirl nozzle carrier, ring or ring segment as described herein formed by a method as described herein.

The present invention may provide a gas turbine engine having a pre-swirl nozzle ring as described herein.

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial sectional view of a high pressure turbine section of a gas turbine engine; Figure 2A is a plan view of a carrier body nozzle ring section formed according to a first step of a method according to the present invention; Figure 2B shows the nozzle section of Figure 2A following a tuning step according to the method of the present invention; Figure 3A shows a plan view of a nozzle section formed according to an alternative first step of a method according to the present invention; Figure 3B shows the nozzle section of Figure 3A following a tuning step according to the method of the present invention; Figure 4 is an internal perspective view illustrating the inlet and outlet sides of a fixed-flow nozzle and a tuning nozzle forming part of a nozzle ring according to the present invention; Figure 5 is a perspective internal view illustrating the inlet and outlet sides of a fixed-flow pie-swirl nozzle and tuning nozzle formed according to an alternative embodiment; and Figure 6 is a perspective view of an outlet side of a nozzle ring formed according to the present invention.

Referring first to Figure 1 there is shown a partial section of the high pressure turbine section of a gas turbine engine for use, for example, in the aerospace industry.

A turbine rotor disc I carries a plurality of rotor blades 2 and is rotatable about a horizontal rotational axis in an arrangement which will be well known to the skilled man.

Upstream of the disc 1 is a pre-swirl chamber 3 which receives cooling air from a plurality of pre-swirl nozzles 5 formed on a nozzle ring 6 of a pre-swirl nozzle carrier body generally indicated 7 and shown in solid lines. In this embodiment the ring 6 is formed as an integral part of the carrier body 7.

Airflow exiting the turbine compressor section (not shown) bypasses the combustion chamber (not shown) and is ducted to the nozzle ring 6 via a duct 8. Air from the duct 8 is therefore fed into the pre-swirl chamber 3 through the nozzles 5 (which are holes passing through the nozzle ring 6. The nozzles 5 are used to impart swirl on the airflow entering the chamber 3. The nozzles 5 are arranged so that the swirl direction of the cooling airflow is co-directional with the direction of rotation of the rotor disc 1 so that air is fed onto the disc 1 and blades 2 with a directional component corresponding to the direction of rotation in order to reduce frictional forces generated as the air hits the rotor assembly.

A method of manufacturing a pre-swirl nozzle ring of the type shown in Figure 1 will now be described in relation to Figures 2A and 2B.

Referring first to Figure 2A there is shown the air inlet face of a nozzle ring generally indicated 6 of the type forming part of the pre- swirl nozzle carrier body 7 shown in Figure 1. The nozzle ring 6 comprises an annular body 15 in the form of a plate forming part of a carrier body. The body 15 has a plurality of axially extending, circumferentially spaced fixed-flow pre-swirl nozzles 20. By fixed-flow is meant a nozzle whose flow rate is not adjusted following initial formation. The nozzles 20 comprise holes passing through the body 15 and having a generally oval or "racetrack" section such that they are circumferentially elongate.

The radial thickness I of the nozzle section body 15 is such that the required flow rate cannot be achieved with a series of nozzles having a circular section. Accordingly, the nozzles 20 are elongate to provide the required flow rate of air as well as a more even air supply flow distribution.

The nozzle ring 6 is formed by a metal casting operation. In this embodiment the casting operation is used to form the nozzles 20. In other embodiments (not shown) the body 15 is formed solid and nozzles 20 are formed using a post-casting step such as spark erosion.

Having formed the carrier body a flow check is carried out in order to measure the overall flow rate provided by the body 15. The number, size and distribution of the flow- metering nozzles 20 is chosen to provide a particular flow rate and flow distribution which is suited for a particular gas turbine engine.

The flow rate of the ring 6 is measured by any convenient means as will be well known to the skilled man. The measured flow rate is compared to a required flow rate. The nozzles 20 are formed in the carrier body so that the measured flow rate is equal to or less than the required flow rate so that if adjustment is required it is an increase in flow rate which must be achieved.

Whilst forming the nozzles 20 as elongate satisfies the level of flow rates required approximately, adjusting the flow rate by adjusting the size of the nozzles 20 is problematic.

In order to increase the flow rate to the required flow rate the ring 6 is tuned by forming two or more diametrically opposed tuning nozzles 25 in the body 15 as shown in Figure 2B. The tuning nozzles 25 comprise circular-section holes passing axially through the - 10- body 15. Because the elongate nozzles 20 provide a majority of the required flow rate the tuning nozzles 25 can be circular as they are not required to contribute greatly to the flow rate but rather to fine-tune. The size, number and distribution of tuning nozzles provided is determined by the level of increase in flow rate necessary to achieve the required flow rate. Because the tuning nozzles 25 are circular in section their formation is relatively easy and can be achieved, for example, a drilling operation.

Subsequent to formation of the tuning nozzles 25 a further flow calculation step may be used to check that the tuning operation has been successful. Further increases to the flow rate could be provided by increasing the number or size of the tuning nozzles 25, which could also easily be achieved, for example by using a larger dnll bit on an existing hole.

In an alternative embodiment (not shown) the body 15 is provided with twenty eight equally spaced elongate nozzles and four equally spaced tuning nozzles.

Referring now to Figures 3A and 3B a nozzle ring 106 having a nozzle section body according to an alternative embodiment is shown. The body 115 shown in Figure 3A is similar to the body 15 shown in Figure 2A in that a ring-like structure is formed by casting and includes a plurality of elongate pre- swirl nozzles 120. However, in this embodiment the body 115 is also formed with two designated tuning nozzles 125 i.e. the tuning nozzles 125 are pre-formed in the carrier body prior to a flow checking operation.

The flow rate of the body 115 is checked and compared to the required flow rate.

Adjustment of the flow rate is achieved by increasing the size of the existing tuning nozzles 125 as shown in Figure 3B rather than by forming new nozzles.

In other embodiments (not shown) in which there is not a constraint to use elongate nozzles a ring with a plurality of circular flow-section nozzles may formed and following a flow measurement step the size of some or all of the nozzles may be increased, or further circular flow-section nozzles may be formed, to increase flow.

Referring now to Figures 4 and 5 there is shown two alternative arrangements for elongate fixed-flow pre-swirl nozzles and tuning preswirl nozzles of the type which could be used on the nozzle rings 6, 106 shown in Figures 2 and 3.

Referring first to Figure 4 there is shown part of a nozzle ring body 215 with the airflow inlet side of the body generally indicated 230 and the airflow outlet side generally indicated 235. An elongate, fixed-flow nozzle is indicated 220 and has an elongate, generally oval shape inlet 221 and an identical elongate, oval shape outlet.

Accordingly, the walls of the nozzle 220 are parallel.

Adjacent the nozzle 220 is a tuning nozzle generally indicated 225. The nozzle 225 has a circular inlet 226 and an elongate, oval outlet 227. Accordingly the nozzle is generally conical in form. By having both outlets 222, 227 as elongate the flow distribution passing through the body 215 is spread evenly into a pre-swirl chamber.

The rate of airflow which can be achieved through the tuning nozzle 225 can be increased by drilling from the outlet side 230 to increase the bore of the circular inlet 226. Because the nozzle 225 is conical in form it would be easy to produce the ring shown in Figure 4 by casting both the fixed-flow nozzle 220 and the tuning nozzle 225.

Referring now to Figure 5 a nozzle section body 315 is formed with a fixed-flow elongate nozzle 320 identical to the nozzle 220 of Figure 4 such that it has an elongate, oval inlet 321 and outlet 322. A tuning nozzle 325 is provided adjacent the nozzle 320 and has a circular inlet section and a circular outlet section 327. Accordingly, the nozzle 325 comprises a hole with a cylindrical flow section.

The bore of the hole forming the nozzle 325 could be increased using a drill bit of increased diameter. The nozzle 325 would be suitable either for formation together with the body 315 or in a post-forming operation before or after an initial flow checking step. - 12-

Referring now to Figure 6 there is shown a perspective view of a segment of the outlet side of a carrier body nozzle ring 406 comprising a body 415. The body 415 includes two elongate, fixed-flow nozzles 420 which flank a circular-section tuning nozzle 425.

Claims

A method of manufacturing a pre-swirl nozzle ring for a gas turbine; said method comprising the steps of: providing a flow metering ring having a plurality of pre-swirl nozzle flow passages therein; measuring the actual flow rate of the flow metering ring; comparing the said measured flow rate with a pre-determined required flow rate; determining whether the said measured flow rate is within acceptable limits of the said required flow rate, and, if not: adjusting the flow rate of the said ring in accordance with the said comparison by increasing the flow cross- sectional area of one or more of the said pre-swirl nozzle passages and/or increasing the number of pre-swirl nozzle flow passages in the ring.
2 A method as claimed in Claim 1, in which the step of adjusting the flow rate of the ring comprises the step of increasing the flow cross-section of one or more of the said pre-swirl nozzles pre-designated as flow tuning holes, and/or machining at least one additional pre-swirl nozzle flow passage at a pre-determined position or positions on the said ring.

- 14 -
3 A method as claimed in Claim 2, in which the said at least one additional flow passage is provided at an angular position on the ring which improves the circumferential uniformity of the air flow distribution through the ring.
4 A method as claimed in any preceding claim, in which the metering ring is formed by casting.
A method as claimed in any preceding claim, in which the pre-swirl nozzles are formed by casting.
6 A method as claimed in any of Claims 1 to 4, in which the pre-swirl nozzles are formed by spark erosion.
7 A method as claimed in any preceding Claim, in which the additional nozzles are formed by spark erosion.
8 A method as claimed in any of Claims 1 to 7, in which the step of adjusting the flow rate of the ring comprises the step of drilling at least one additional pre-swirl nozzle passages and/or drilling at least one existing pre-swirl nozzle to increase the flow cross-section thereof.
9 A pre-swirl nozzle ring for a gas turbine engine, the said ring comprising: one or more primary nozzle flow passages having an inlet with an elongate flow cross-section; and one or more tuning nozzles having an inlet with a circular flow cross- section.
A pre-swirl nozzle ring as claimed in Claim 9, in which the primary nozzles have an outlet with an elongate flow cross-section.
11 A pre-swirl nozzle ring as claimed in Claim 9 or Claim 10, in which the tuning nozzles have an outlet with a circular flow cross-section.
12 A pie-swirl nozzle ring as claimed in Claim 9 or Claim 10, in which the tuning nozzles have an outlet with an elongate flow cross-section.
13 A pre-swirl nozzle ring as claimed in any of Claims 9 to 12, comprising a plurality of equally spaced primary pre-swirl nozzles.
14 A pre-swirl nozzle ring as claimed in any of Claims 9 to 13, in which the ring comprises a plurality of arcuate segments.
A pre-swirl nozzle ring as claimed in any of Claims 9 to 14, in which the ring is a hoop-continuous annular structure.
16 A pre-swirl nozzle ring as claimed in any of Claims 9 to 15, in which the or each primary nozzle is circumferentially elongate in section on the ring.
17 A pre-swirl nozzle ring as claimed in any of Claims 9 to 16, in which the radial thickness of the ring is approximately 7mm.
18 A pre-swirl nozzle ring as claimed in any of Claims 9 to 17, in which the axial thickness of the ring is approximately 30mm.
19 A pre-swirl nozzle ring as claimed in any of Claims 9 to 18, in which the ring has twenty-eight primary nozzles.
A pre-swirl nozzle ring as claimed in any of Claims 9 to 19, in which one to four tuning nozzles are provided in the ring.
21 A pie-swirl nozzle ring as claimed in any of Claims 9 to 20, in which the primary and/or tuning nozzles follow an oblique path through the carrier body.
22 A pie-swirl nozzle ring as claimed in any of Claims 9 to 21, in which the inlet and/or outlet of the primary nozzles have an oval section.
23 A pre-swirl nozzle ring for a gas turbine engine, the said ring comprising: one or more primary nozzle flow passages having an inlet and/or outlet with a non- circular flow cross-section; and one or more tuning nozzles having an inlet and/or outlet with a circular flow cross-section.
24 A pre-swirl nozzle ring for a gas turbine engine, the said ring comprising: one or more primary nozzle flow passages having an inlet and/or outlet with an elongate flow cross-section; and one or more tuning nozzles having an inlet and/or outlet with a circular flow cross-section.
A pre-swirl nozzle ring for a gas turbine engine, the ring being formed by casting and having a plurality of primary nozzle flow passages cast therein, and having one or more tuning nozzle flow passages machined therein post-casting.
26 A pie-swirl nozzle ring as claimed in any of Claims 9 to 25, in which the ring is formed by a method according to any of Claims 1 to 8.
27 A gas turbine engine having a pre-swirl nozzle ring according to any of Claims 9 to 26.
28 A method of manufacturing a pre-swirl nozzle ring substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.
29 A pie-swirl nozzle ring substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.