Diffuser arrangement
A diffuser arrangement is provided in which a wall surface of the diffuser arrangement incorporates an upstream part and a downstream part with an aperture between them. There is a step displacement between the upstream part and the downstream part along with specific shaping of the leading edge of the aperture whereby fluid air flow is drawn into the aperture from a fluid flow whilst avoiding undue disturbance to that flow. The present diffuser arrangement allows incorporation within an engine without complex fabrication or structural requirements.
1. A diffuser arrangement of a combustor for an engine, the diffuser arrangement located upstream of the combustor and comprising a wall surface in a fluid flow conduit formed with an aperture between an upstream part of the wall surface and a downstream part of the wall surface, the downstream part having a step displacement away from a projected profile projected in the downstream direction of the upstream part of the wall surface whereby in use flow momentum in a fluid flow past the wall surface facilitates flow bleed into the aperture; wherein the step displacement is between 0.05 to 0.12 of either the conduit radius or half the conduit cross-sectional width; the aperture has a width at the wall surface between 0.04 to 0.07 of either the conduit radius or half the conduit cross-sectional width.
2. An arrangement as claimed in claim 1 wherein the upstream part has a leading edge to the aperture shaped to enhance flow momentum thereabout towards the aperture.
3. An arrangement as claimed in claim 2 wherein the leading edge is curved into the aperture.
4. An arrangement as claimed in claim 3 wherein the leading edge has a curvature dependent upon expected flow rate and cross-section of the conduit including the wall surface.
5. An arrangement as claimed in claim 3 wherein the leading edge will have a radius between 0.05 to 0.15 of the conduit inlet passage height.
6. Apparatus as claimed in claim 5 wherein the leading edge has a radius between 0.09 to 0.11 of the conduit inlet passage height.
7. An arrangement as claimed in claim 1 wherein the downstream part has a trailing edge to the aperture which is angularly presented.
8. An arrangement as claimed in claim 1 wherein the downstream part is at an angle up to 35° to the principal axis of fluid flow in the conduit.
9. Apparatus as claimed in claim 8 wherein the angle is 30° to the principal axis of fluid flow in the conduit.
10. Apparatus as claimed in claim 1 wherein the step displacement is between 0.06 to 0.1 of either the conduit radius or half the conduit cross-sectional width.
11. An arrangement as claimed in claim 1 wherein the aperture is divergent away from an opening in the wall surface.
12. An arrangement as claimed in claim 1 wherein the width is between 0.05 to 0.06 of either the conduit radius or half the conduit cross-sectional width.
13. An arrangement as claimed in claim 1 wherein the aperture has an aperture wall upon the side towards the downstream part which is substantially perpendicular to the principal axis of fluid flow in the conduit.
14. An arrangement as claimed in claim 1 wherein the combined length of the wall surface is three to four times a conduit inlet passage height.
15. An arrangement as claimed in claim 1 wherein the aperture is coupled to a cooling system of an engine.
16. An engine incorporating a diffuser arrangement as claimed in claim 1 .
17. An arrangement as claimed in claim 1 wherein the upstream part of the wall is divergent.