GB2411698A - Coolant flow control in gas turbine engine - Google Patents

Abstract

A coolant passage 100 is provided with a flow control feature 103 having a lateral extent to limit the cross-sectional area available for flow 101 within the passage. The passage may be in the trailing edge of a turbine aerofoil and the flow control feature may be rectangular, triangular, tear-drop shaped, or racetrack shaped and may give rise to laminar flow or turbulent flow downstream of the feature, dependent upon the shape used. The feature may be cast or formed with the coolant passage, or a separate insert.

Description

241 1698

A FLOW CONTROL ARRANGEMENT

The present invention relates to flow control arrangements and more particularly to flow control arrangements utilised within cooling passages of a turbine engine such as those in the trailing edge of a turbine blade or guide vane.

Referring to Fig. 1, a gas turbine engine is generally indicated at 10 and comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high pressure compressor 14, a combustor 15, a turbine arrangement comprising a high pressure turbine 16, an intermediate pressure turbine 17 and a low pressure turbine 18, and an exhaust nozzle 19.

The gas turbine engine 10 operates in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 which produce two air flows: a first air flow into the intermediate pressure compressor 13 and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high pressure compressor 14 is directed into the combustor 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines 16, 17 and 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low pressure turbines 16, 17 and 18 respectively drive the high and intermediate pressure compressors 14 and 13 and the fan 12 by suitable interconnecting shafts.

It will be understood from the above that particularly the turbine stages of a turbine engine become relatively hot due to the combustion temperatures of the gas flows through those turbine stages. These high temperatures are present whether the engine is used for aircraft propulsion or as other power plant for driving ships or generating electricity, etc. Nevertheless, engine efficiency is closely related to operating temperatures so that it is normal to provide cooling of particular components within a turbine engine to enable high operating temperatures. With particular components such as the trailing edge of the gas turbine aerofoil, it will be appreciated that it is difficult to accommodate cooling passages. For example, trailing edge cooling passages are restricted by the minimum dimensions available from the casting and forming processes to fabricate the component. These minimum dimensions subsequently dictate the minimum flow level that can pass through the coolant passage. It will be understood in certain circumstances it is desirable to reduce the flow rate further without increasing manufacturing cost.

Reducing flow rate may allow more efficient use of coolant flows for heat transfer and potential improvements in operating efficiency both in terms of turbine efficiency and combustion emissions.

In accordance with the present invention there is provided a flow control feature for a coolant passage arrangement in a turbine engine, the flow control feature having a lateral presence when positioned within a coolant passage to limit thereby available cross-sectional area for flow within the passage and the lateral presence being shaped for desired aerodynamic effect upon any such flow in use.

Further in accordance with the present invention there is provided a flow control arrangement for a coolant passage in a turbine engine wherein the arrangement includes a flow control feature as described above.

Typically, the flow control feature is symmetrical in a direction to allow symmetry with regard to any flow in a coolant passage. Typically, the feature is rectangular or triangular or racetrack or tear drop shaped.

Possibly, the feature is an insert for subsequent fitting within a coolant passage. Preferably, the flow control feature is cast or formed with a coolant passage.

Generally, the aerodynamic effect is to facilitate substantially laminar flow downstream of the feature in use.

Alternatively, the aerodynamic effect is to create turbulence downstream of the feature to facilitate heat exchange.

Normally, the control feature is positioned centrally within a coolant passage in use.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which, Fig. 2 is a schematic perspective view of a flow control arrangement in accordance with the present invention; and, Fig. 3 illustrates alternative forms of flow control feature in accordance with the present invention.

Referring to Fig. 2 providing a schematic perspective view of a trailing edge of a component such as a turbine engine aerofoil in accordance with the present invention.

Thus, the trailing edge 100 incorporates a number of passages such that a coolant air flow in the direction of arrowhead 101 passes through those passages in order to provide cooling in the relatively thin section of the trailing edge 100. As indicated above, generally the trailing edge 100 will be relatively thin so that formation of passages within that trailing edge 100 must be carefully performed such that these passages achieve the desired performance. As can be seen the width 102 of the trailing edge defines the available cross-section of that trailing edge 100 within which the passages can be formed. It will be understood that there should be a minimum wall thickness for structural integrity within the component formed whilst accurately casting narrow passages of consistent dimensions is normally difficult but is further exacerbated by the relatively thin nature of the trailing edge 100.

Cooling air within a turbine engine is generally taken from the compressor stages of that engine and so can be considered parasitic upon engine performance such that cooling flow for desired cooling effect should be minimised wherever possible.

Returning to Fig. 2, the illustrative passage with trailing edge section 100 incorporates flow control features 103 in order to block flow by reducing the available cross- sectional area to the flow 100 within the passage. In such circumstances coolant flow 100 may be reduced such that there is less parasitic effect upon engine performance.

Furthermore, it may be more convenient to form coolant passages which are oversized in particular situations with regard to trailing edges such that flow control features 103 in accordance with the present invention may be incorporated either during the casting phase or where possible by insertion subsequent to casting. The flow control features 103 then reducing flow rate to that required operationally.

The flow control features 103 depicted in Fig. 2 are illustrated as of a block nature. In such circumstances the flow 100 generally meets a substantially flat surface in the trailing edge 100 passage and this may create turbulence, etc. Fig. 3 illustrates four alternative forms of flow control feature in accordance with the present invention.

These features are referred to respectively as 203a, 203b, 203c, 203d with the flow direction 201 illustrated by an arrowhead. It can be seen that a rectangular flow control feature 203a can be formed, but this feature 203a presents a substantially flat front surface 204 which will create turbulence and other aerodynamic effects when presented with a coolant flow 201a. This turbulence may be advantageous in terms of enhancing heat transfer, but in other circumstances could present problems.

Control feature 203b is of a triangular nature such that an apex 205 is presented to a coolant flow 201b. The effect of the apex 205 is to more clinically cleave the flow 201b, but at the base side 206 a pressure disturbance will be created particularly about the edges which again will induce turbulence and possibly detrimental effects upon the flow 201b.

As indicated above the alternative control features 203a, 203b create aerodynamic turbulence effects which may be advantageous in terms of heat transfer, but could also cause problems. In such circumstances in order to achieve controlled substantially laminar flow through the trailing edge passage, an aerodynamically streamlined flow control feature 203c is normally preferred. Thus, the control feature 203c still provides a lateral presence defined by the width 207 of the feature 203c, but a presented coolant flow 201c slips passes about the control feature 203c with limited if any turbulent effect. In such circumstances the flow control feature 203c essentially blocks any coolant passage in terms of the available cross-sectional area for coolant flow 201c, but without introducing potentially detrimental or operationally variable turbulence. The control feature 203c is of a substantially teardrop cross- section such that there is a flow reduction due to a blockage or closure equivalent to the width 207 within the coolant flow passage. A further alternative control feature 203d may also be used. This feature 203d takes the shape of a typical race track with an oval profile to again block free flow but with smoothed corners and edges to avoid creation of turbulence. It will be noted the race track shape is substantially partially rectangular and or partially oval with fillet radii at the corners for smooth flow.

As indicated above, any reduction in coolant flow will reduce the parasitic effect upon engine performance of extracting that coolant flow from compressor stages of a turbine engine.

As illustrated, particularly in Fig. 2, the control features in accordance with the present invention may be presented in a parallel relationship across the coolant passage. Alternatively, flow control features in accordance with the present invention may be arranged in side- by-side spaced banks of parallel features as depicted in Fig. 2, and at respective spaced downstream positions in the coolant passage. Clearly, these control features in respective adjacent banks will normally not be aligned with each other and so will be blocking effectively different sections of the coolant passage in order to reduce flow and therefore parasitic effects upon engine performance. It will also be understood that any turbulent effects of adjacent control features in accordance with the present invention may be utilised in order to further constrict free flow of the coolant flow by creating a turbulent wash barrier or wake emanating from each flow control feature which acts across the coolant flow to restrict its free movement.

As indicated above, generally flow control features in accordance with the present invention will be cast or moulded with the component incorporating the coolant passage. It would be appreciated that in such circumstances the flow control features in accordance with the present invention within an arrangement provide structurally reinforcing pillars within the coolant passage such that thinner walls may be possible in the trailing edge section than previously acceptable such that more conveniently formed wider coolant passages may be made with the reduction in available cross sectional area provided by the control features to ensure coolant flow is acceptable in terms of parasitic effects upon engine performance.

The distribution, size and configuration of the particular control features used in a coolant passage will be determined by operational requirements. Thus the distribution may vary across the width of a trailing edge or within a coolant passage dependent upon particular localised features or operational requirements in terms of cooling efficiency, etc. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims (12)

1. A flow control feature for a coolant passage arrangement in a turbine engine, the flow control feature having a lateral presence when positioned within a coolant passage to limit thereby available cross- sectional area for flow within the passage and the lateral presence being shaped for desired aerodynamic effect upon any such flow in use.

2. A feature as claimed in claim 1 wherein the flow control feature is symmetrical in a direction to allow symmetry with regard to any flow in a coolant passage.

3. A feature as claimed in claim 1 or claim 2 wherein the feature is rectangular or triangular or tear drop shaped or racetrack shaped.

4. A feature as claimed in any of claims 1, 2 or 3 wherein the feature is an insert for subsequent fitting within a coolant passage.

5. A feature as claimed in any of claims 1, 2 or 3 wherein the flow control feature is cast or formed with a coolant passage.

6. A feature as claimed in any preceding claim wherein the aerodynamic effect is to facilitate substantially laminar flow downstream of the feature in use.

7. A feature as claimed in any of claims 1 to 5 wherein the aerodynamic effect is to create flow turbulence downstream of the feature to facilitate heat exchange.

8. A feature as claimed in any preceding claim wherein the control feature is positioned centrally within a coolant 3 0 passage in use.

9. A flow control feature substantially as hereinbefore described with reference to the accompanying drawings.

10. A flow control arrangement for a coolant passage in a turbine engine wherein the arrangement includes a flow control feature as claimed in any preceding claim.

11. A turbine engine incorporating a flow control arrangement as claimed in claim 10.

12. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.