GB2149016A

GB2149016A - Air control system

Info

Publication number: GB2149016A
Application number: GB08422469A
Authority: GB
Inventors: Rollin George Giffin
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1983-10-31
Filing date: 1984-09-05
Publication date: 1985-06-05
Also published as: IT1178575B; IT8423209A0; JPS60125732A; GB8422469D0; FR2554169A1; IT8423209A1; DE3439108A1

Abstract

An air control system providing relatively high pressure air from an airstream for use external to the engine, includes inner airfoils 16 connected to a rotor, a shroud 18 attached to the outer end of each inner airfoil, and outer airfoils 24 extending outwardly from the shroud defining a tip compressor. The shroud divides the airstream into inner and outer flowpaths 28,30 with the outer flowpath 30 containing the high pressure air. The tip compressor may have different numbers of blades, blade orientation or shape compared with the inner section. <IMAGE>

Description

SPECIFICATION Air control system The present invention relates in general to an air control system in a turbine engine for providing high pressure air for use external to the engine. More particularly, the invention relates to a novel fan tip compressor for producing such high pressure air.

BACKGROUND OF THE INVENTION The development of aircraft capable of vertical or short take-offs and landings has presented a number of challenging problems.

One of these is how to efficiently maintain aircraft pitch, yaw and roll control during takeoffs and landings when normal control surfaces are inoperative due to lack of forward motion.

One means of controlling the aircraft during such periods is by providing small nozzles or jets at strategic locations on the aircraft. By suppling relatively high pressure air to these nozzles, sufficient control of the aircraft can be achieved.

In the past, air for these nozzles has been obtained from the compressor. Typically, a collection manifold is located around holes in the compressor casing for bleeding high pressure air from the compressor airstream. This compressor bleed system is adequate for relatively low volume requirements. However, as the quantity of air demanded increases, significant engine performance deterioration occurs.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an efficient means for obtaining high pressure air from and airstream.

It is another object of the present invention to provide a new and improved fan blade configuration.

It is a further object of the present invention to provide a new and improved fan tip compressor.

SUMMARY OF THE INVENTION In one form of the present invention, an air control system in a gas turbine engine provides relatively high pressure air from an airstream for use external to the engine. The air control system comprises a plurality of inner airfoils connected to a rotor, a shroud attached to the outer end of each of the inner airfoils, and a plurality of outer airfoils extending outwardly from the shroud. The shroud divides the airstream into inner and outer flowpaths with the outer flowpath containing the high pressure air BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of an air control system according to one form of the present invention.

Figure 2 is a view taken along the line 2-2 in Fig. 1.

Figure 3 is a similar view of that of Figure 2 according to an alternative form of the present invention.

DETAILED DESCRIPTION OF THE INVEN TION Fig. 1 shows a view of the forward end of a gas turbine engine 10 with an air control system 1 2. Air control system 1 2 includes a fan 14 with inner airfoils 1 6 connected to a rotor 25. System 1 2 further includes a shroud 1 8 attached to the outer end 20 of airfoil 16, and a fan tip compressor 22 with outer airfoils 24. Airfoils 24 extend outwardly from shroud 18 and are attached thereto so that fan 14, shroud 18, and compressor 22 are driven by rotor 25.

Shroud 1 8 divides airstream 26 into inner flowpath 28 and outer flowpath 30. Flowpaths 28 and 30 may be separated upstream of shroud 1 8 by fairing 32 as shown in the embodiment of Fig. 1. Downstream of shroud 18, these flowpaths are separated by outer engine casing 34. Flowpath 28 is further divided downstream of fan 14 into bypass duct 36 and core duct 38. However, it will be clar that many different downstream configurations of flowpath 28 are possible without departing from the scope of the present invention.

Air control system 1 2 may further include variable inlet guide vanes 40 located within outer flowpath 30 and upstream of fan tip compressor 22. In a like manner, outlet guide vanes 42 may be included in outer flowpath 30 aft of compressor 22. Collection manifold 44 is located in outer flowpath 30 downstream of outer airfoils 24 and outlet guide vanes 42. Outlet means 46 direct the air in outer flowpath 30 for use external to engine 10. For example, this air may be ducted to nozzles on an aircraft wing for pitch, yaw and roll control.

Fig. 2 is a view taken along the line 2-2 in Fig. 1 and shows in more detail the blading arrangement of fan 14 and tip compressor 22. Inner airfoils 16, shown by dashed lines, have a slight bend or camber. -As airfoils 1 6 rotate in the direction shown by arrow 48, the pressure of air in inner flowpath 28 is increased. A quantitative measure of pressure increase resulting from blade rotation is the difference between air pressure aft of the blade and air pressure forward of the blade.

This pressure rise is typically on the order of .3 to 1.0 atmospheres.

Outer airfoils 24 have more camber than inner airfoils 16, particularly near the trailing edge 50. Such increased camber, in combination with the higher speed of outer airfoils 24 over inner airfoils 16, provides an increased pressure rise in outer flowpath 30. This pres sure rise due to tip compressor 22 exceeds the pressure rise in inner flowpath 28 due to fan 1 4. For purposes of supplying relatively high pressure air to wing tip nozzles according to one embodiment of the present invention, the pressure rise in the outer flowpath 30 is at least 25% higher than the pressure rise in the inner flowpath 28.

Fig. 2 shows an embodiment wherein inner airfoils 1 6 and outer airfoils 24 are connected to a continuous shroud ring 18. Depending on the application, airfoils 24 and 1 6 may either be detachable from shoud 1 8 or integrally formed therewith. It should be noted that Fig. 2 shows a corresponding number of inner and outer airfoils 24 and 1 6 with the same axial projection 62. However, the number of airfoils and their axial projection may vary.

In order to further increase pressure rise in outer flowpath 30, the total chord length of outer airfoils 24 can be made greater than the total chord length of inner airfoils 1 6. Two ways of increasing total chord length are by increasing the chord length 64 of each airfoil 24 or by increasing the number of outer airfoils 24.

Fig. 3 shows an alternative embodiment wherein the number of outer airfoils is increased. In addition, each shroud 1 8 is divided into shroud segments 52. Each segment 52 contains an inner airfoil 16, shown by dashed lines, and a first outer airfoil 24a. The center of mass of inner airfoil 1 6 is located at first position 54. Position 54 may be located in space relative to the engine centerline by an axial-radial-circumferential coordinate system. Likewise, first outer airfoil 24a has a center of mass located at position 56. As fan 14, shroud 18, and tip compressor 22 rotate, a bending moment due to the offset of center of mass at position 56 relative to center of mass at position 54 will be induced. Since shroud 18 is segmented, all such bending moments are transmitted through inner airfoils 16.

Thus, for a segmented shroud according to the embodiment shown in Fig. 3, a second outer airfoil 24b, added to increase total chord length, may be advantageously positioned relative to airfoils 1 6 and 24a. Airfoil 24b will have a center of mass at position 58.

First outer airfoil 24a and second outer airfoil 24b, taken together, have a center of mass located at a second position 60. By proper placement of outer airfoils 24a and 24b, second position 60 can be made to substantially correspond with first position 54 or the chord of airfoil 1 6 thereby minimizing the bending moment on inner airfoils 16.

In operation, air control system 1 2 is capable of providing relatively high pressure air from airstream 26 for use external to primary engine propulsion. The number and aerodynamic shape of outer airfoils 24 of fan tip compressor 22 are configured so as to provide a pressure rise in excess of that attainable by fan 1 4. If desired variable inlet guide vanes 40, together with fairing 32, may be employed to modulate the pressure rise and flow characteristics in outer fiowpath 30. After reaching collection manifold 44. the air is then available to do work or produce thrust wherever required.

In order to incorporate the present invention on an existing turbofan engine, changes external to the bypass and core ducts are required.

However, structural modifications internal to the engine need not be made. Consenquently, the tip compressor 22 is an economic means by which relatively high pressure air for purposes such as described herein may be delivered. Moreover, it may more efficiently deliver such air than compressor bleed systems with more extensive ducting.

It will be clear to those skilled in the art that the present invention is not limited to the specific embodiments described and illustrated herein. Nor is the invention limited to tip compressors on fan blades or for application on turbofan engines. Rather, it applies equally to tip compressors on any rotatable blade as, for example, found on turbojet engines.

It will be understood that the dimensions and proportional and structural relationships shown in the drawings are iilustrated by way of example only and these illustrations are not to be taken as actual dimensions or proportional structural relationships used in the fan tip compressor of the present invention.

Claims

1. In a gas turbine engine, an air control system for providing relatively high pressure air from an airstream for use external to said engine comprising: a plurality of inner airfoils connected to rotor; a shroud attached to the outer end of each of said inner airfoils; and a plurality of outer airfoils extending outwardly from said shroud; wherein said shroud divides said airstream into inner and outer flowpaths, said outer flowpath containing said high pressure air.

2. An air control system, as recited in claim 1, wherein the rotation of said inner and outer airfoils induces a pressure rise of said air in said inner andn outer flowpaths, respectively; and wherein said pressure rise in said outer flowpath exceeds said pressure rise in said inner flowpath.

3. An air control system, as recited in claim 2, wherein said pressure rise in said outer flowpath is at least 25% higher than said pressure rise in said inner flowpath.

4. An air control system, as recited in claim 1, wherein the total chord length of said outer airfoils is greater than the total chord length of said inner airfoils.

5. An air control system, as recited in claim 1, further comprising: a plurality of variable inlet guide vanes located within said outer flowpath and upstream of said outer airfoils.

6. An air control system, as recited in claim 1, further comprising a collction manifold located in said outer flowpath, downstream of said outer airfoils.

7. In a gas turbine engine including a fan with a plurality of inner airfoils connected to a rotor, and a shroud attached to the outer end of each of said inner airfoils; a fan tip compressor comprising: a plurality of outer airfoils extending outwardly fro.m said shroud.

8. A fan tip compressor, as recited in claim 7, wherein the total chord length of said outer airfoils exceeds the total chord length of said inner airfoils.

9. In a gas turbine engine including a fan with an inner airfoil connected to a rotor, and a shroud segment attached to the outer end of said inner airfoil, said inner airfoil having its center of mass located at a first position; a fan tip compressor comprising: a first outer airfoil extending outwardly from said shroud segment; and a second outer airfoil extending outwardly from said shroud segment, said first and second outer airfoils having a center of mass located at a second position.

10. A fan tip compressor, as recited in claim 9, wherein said second position substantially corresponds with said first position.

11. An air control system of fan tip compressor substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2 or Fig. 3 of the drawings.