US2726508A

US2726508A - Aircraft propulsion units of the gas turbine jet type

Info

Publication number: US2726508A
Application number: US273265A
Authority: US
Inventors: Halford Frank Bernard; Moult Eric Stanley; Arscott William Hammett
Original assignee: De Havilland Engine Co Ltd
Current assignee: Bristol Siddeley Engines Ltd
Priority date: 1952-02-25
Filing date: 1952-02-25
Publication date: 1955-12-13
Anticipated expiration: 1972-12-13

Description

1955 F. B. HALFORD ETAL 2,725,508

AIRCRAFT PROPULSION UNITS OF THE GAS TURBINE JET TYPE Filed Feb. 25, 1952 2 Sheets-Sheet 1 Inventors Frank B. Hal-f rd Eric 5, Mom/1f William H. Arsco'H Attorneys Dec. 13, 1955 F. B. HALFORD ET AL 2,726,503

AIRCRAFT PROPULSION UNITS OF THE GAS TURBINE JET TYPE Filed Feb. 25, 1952 2 Sheets-Sheet 2 F/GZ.

I v tor 0 nk B. Ha l fifr d.

I ENC S. Nov/f William H. Arscolrk I Attorneys United States PatefitO AIRCRAFT PROPULSION UNITS OF THE GAS TURBINE JET TYPE Frank Bernard Halford, Edgware, Eric Stanley Moult, Hatch End, and William Hammett Arscott, Harpenden, England, assignors to The De Havilland Engine Company Limited, Edgware, England, a registered company of Great Britain Application February 25, 1952, Serial No. 273,265 8 Claims. 01. 60-356) This invention relates to propulsion units of the gas turbine jet propulsion type including a centrifugal compressor and has for its object to provide a propulsion unit which will be capable of giving a high degree of thrust in relation to its maximum diameter while being of a simple and robust nature.

A propulsion unit of the jet propulsion type according to the present invention comprises a single entry centrifugal compressor having a forwardly facing inlet eye communicating with a coaxial intake passage across which extends a ring of whirl-producing vanes for imparting to the air before it enters the eye rotational motion in the direction of rotation of the impeller of the centrifugal compressor, a main shaft by which the impeller of the centrifugal compressor is connected preferably directly to and driven by a single stage or multi-stage turbine disposed in rear of and spaced from the centrifugal compressor, an annular air transfer passage having an annular entry opening into which the impeller of the centrifugal compressor directly discharges air and an annular exit opening communicating with an annular axial diffuser, an annular combustion chamber or ring of combustion chambers withwhich the outlet end of the axial diffuser communicates, a nozzle ring or the equivalent at the outlet end of the combustion chamber or ring of combustion chambers through which the gases from such chamber or chambers enter the turbine, and a nozzle through which the gases from the turbine are discharged with propulsive effect.

Conveniently the eye of the centrifugal compressor and the intake passage are both annular While, moreover, in any case, the whirl-producing blades or vanes in the intake passage are mounted or formed on an impeller which is arranged to be driven in the same direction as but at a speed considerably lower than, and preferably at about half, or rather less than half, the speed of the main shaft.

Thus in one convenient arrangement the whirl-producing impeller is arranged to be driven through gearing from the main shaft, the gearing being housed for example within the inner circumferential wall of the annular air intake passage.

In an alternative arrangement the means for driving the whirl-producing impeller may comprise a turbine rotor separate from the main turbine rotor and acted upon by the gases from the combustion chamber or chambers, said separate turbine rotor being connected to the whirlproducing impeller.

in any case the whirl-producing impeller is preferably so formed and driven as to impart to the air in advance of the eye of the centrifugal compressor a whirling motion in the form of a free vortex, that is to say a vortex in which the speed of angular movement of the particles of air is inversely proportional to their distance from the axis of rotation, although various forms of forced vortex may be used. Owing to limitations in the design of the vanes 'of the whirl-producing impeller the mean diameter of the part of the annular intake passage across which the vanes of the whirl-producing impeller extend will generally be somewhat greater than the mean diameter of the annular eye of the centrifugal compressor so that the mean diam eter of the part of the intake passage between the whirlproducing impeller and the eye of the centrifugal compressor progressively diminishes from the whirl-producing vanes to the eye with a corresponding axial displacement of the adjacent edges of the whirl-producing vanes and the compressor blades to avoid unduly sharp curvature in the walls of said intake passage.

The axial diffuser is conveniently of the form described in the specification of U. S. Patent application filed December 11, 1950, Ser. No. 200,279, now abandoned, and may or may not be provided with ducts for the passageof air into or out of the inner circumferential wall of the transfer passage for the purpose of boundary layer control to reduce the tendency for turbulence to occur in this transfer passage.

The invention may be carried into practice in various ways but two constructions of propulsion unit according to the invention are shown diagrammatically by way of example in the accompanying drawings, in which.

Figure 1 is a sectional side elevation of one form of propulsion unit the section being in a plane containing the axis of rotation of the main rotary parts of the unit, and

Figure 2 is a similar view to Figure 1 of another form of propulsion unit according to the invention.

In the construction shown in Figure l the propulsion unit comprises a casing or frame A which is of generally tubular form and of tapering cross section from its front to its rear as shown, and carries bearings indicated at A1 and A2 adjacent to its front and rear ends supporting a tubular main shaft assembly B. Secured to the front end of the casing A is the casing C of a centrifugal compressor of the single entry type the rear wall of which is, as shown, substantially fiat while its front wall C1, which includes the entry eye C2 is of curved form viewed in cross sections containing the axis of the compressor so as to provide a smooth combined axial and radial flow for the air through the compressor in known manner. The'main shaft B carries at its forward end the combined axial and radial flow impeller D of the centrifugal compressor while its rear end carries the rotor E of a turbine E1 which as shown is of the single stage type but may equally be of the multi-stage type.

Rigidly mounted or formed on the front wall C1 of the compressor and forming in effect a continuation of the wall of the inlet eye C2 is a wall F constituting the outer wall of an annular intake passage F1 which extends from an inlet opening F2 at its forward end to the eye C2 and is formed, as shown, so that its diameter first increases progressively from the inlet opening F2 to a point F3 and then decreases progressively to the eye C2.

The inner wall of the intake passage F1 is formed partly by a fixed casing G, carried by the outer wall by means of suitable webs and provided with a nosepiece G2, and partly by a rotary wall G1 carried as hereinafter re ferred to, the form of the inner wall G, G1 being such in relation to that of the outer wall F that the mean diameter of the annular intake passage F1 as a whole increases progressively up to the point P3 and then decreases'progressively to the eye C2.

Extending across the annular intake passage F1 at the point P of largest mean diameter are the blades H of a whirl-producing impeller H1 which is supported on a hub member H2 carried in hearings in the casing G and also supporting the rotary part G1 of the inner wall of the annular intake passage F1 which thus rotates as a unit with the impeller H1. I Y

The impeller H1 and wall part G1 are arranged to be driven at about half or rather less than half the speed of the impeller D of the centrifugal compressor through reduction gearing comprising a relatively small sun wheel K connected by a shaft K1 to the impeller D and meshingwith relatively large planet wheels K2 secured to shafts K3 supported in stationary bearings, the shafts K3 also carrying further relatively small sun wheels K4 which mesh with a relatively large sun wheel K5 on the hub H2.

Immediately surrounding the casing of the centrifugal compressor C is an annular transfer passage L, which viewed in the cross section shown resembles a right angle bend of comparatively small mean radius. This radius is chosen to be as small as is practicable without risk of causing undue turbulence in the air due to separation of the fluid flow from the inner wall of the bend. Passages (not shown) for the inflow or outflow of air through appropriately placed ducts in the inner wall of the bend for boundary layer control purposes may be provided as described in the specification of U. S. patent application No. 200,272, now abandoned, so as to enable a smaller radius of curvature to be used then would otherwise be possible.

The annular inlet opening L1 of the transfer passage L receives air direct from the impeller D while the annular outlet opening L2, which faces rearwardly, communicates directly with the forward end of an annular axially extending diffuser M in the form of an annular passage containing a set or two or more sets of guide vanes indicated at M1 which convert at least the major portion of the rotational energy of the air entering the diffuser into pressure energy, thus acting as straighteners. The diffuser is thus conveniently of the kind described in the specification of U. S. patent application No. 200,279, now abandoned.

The rear end of the axial diffuser M communicates with an annular air delivery passage M2 or series of air delivery passages by which the air is led to a series of substantially axially extending combustion chambers N lying around the smaller diameter part of the casing A so that the over all diameter of this part of the unit is not greater than, and is preferably somewhat less than the over all diameter of the diffuser. The combustion chambers N, which may be of known form and may be supplied with fuel in any convenient manner, communicate at their rear ends with a nozzle ring N1 through which the hot gases from the combsution chambers are directed onto the blades of the turbine rotor E, the gases after passing through the turbine being led by a suitably formed annular duct NZ to a propulsion nozzle N3.

In the alternative construction shown in Figure 2 the arrangement is generally similar to that shown in Figure 1 and similar parts have therefore been given similar reference letters to the corresponding parts in Figure l and will not be again described.

The principal difference between the construction shown in Figure 2 and that shown in Figure l is that, instead of the whirl-producing impeller H1 being driven through gearing from the impeller D of the centrifugal compressor it is driven by a separate turbine rotor. Thus, in the construction shown in Figure 2, the whirl-producing impeller H1 is mounted upon or provided with a hub H3 rigidly supported on the front end of a shaft 0 which passes through a suitably modified main shaft Bl carrying the impeller D and the turbine rotor E and carries at its rear end a turbine rotor P disposed in rear of the rotor E and on which the gases from the combustion chambers impinge after leaving the rotor E and after passing through a set of stationary vanes P1 so as to cause rotation of the shaft 0 in the same direction as the main shaft B1 but at about half or somewhat less than half the speed of the main shaft Bl.

As shown the shaft 0 is supported in bearing D in a plate D within the casing G and in bearings O mount ed inthe ends of the shaft B1.

being arranged with their axes parallel to the axis of the shaft B their axes may have a tangential component and in this case the dijfuser blades M1 maybe so formed as to cause the air to leave them in a similar combined axial and tangential direction so that the air can enter the combustion chambers with as little change in direction as possible.

It is, moreover, to be understood that, although in the arrangement shown a series of combustion chambers are provided the invention is also applicable to arrangements in which a single annular combustion chamber surrounds the main casing.

Moreover, in modified arrangements according ot the invention the centrifugal compressor may have an impeller the blade carrying disc of which instead of havhelix.

ing a substantially flat outer portion hasan outer portion of approximately frusto-conical form so that the air leaves it in a direction having a substantial rearward axial component, thus reducing the angle through which the air has to be deflected by the transfer passage to enter the diffuser.

It will be seen that with each of the arrangements shown according to the invention the whirl-producing impeller H1, by causing the air delivered to the eye C2 to rotate in the same direction as the impeller D, enables a higher rate of mass flow to be obtained through the centrifugal compressor without exceeding the permissible Mach number of the fluid flow relatively to the blades of the impeller D. Moreover, the air will leave the centrifugal impeller D with a high rotational component of motion and will thus readily be able to pass through the transfer passage L in spite of the apparent sharpness of the bend in that passage when viewed in the cross sections shown since each particle of air will be passed through the bend in a path resembling a spiral The rotational energy of the particles of air can then be converted into pressure in the axial diffuser M, which itself is of small over all diameter compared with a radial flow diffuser of similar capacity, and the maximum diameter and weight of the unit can thus be maintained small for the maximum rate of mass flow through it and hence the maximum thrust which can be obtained from it.

What we claim as our invention and desire to secure by Letters Patent is:

1. An aircraft propulsion unit of the jet propulsion type comprising a single entry centrifugal compressor having a forwardly facing inlet eye, a rotary whirl-producing impeller arranged in an entry passage in advance of the entry eye of the compressor and driven in the same direction as but at a lower speed than the centrifugal impeller, the whirl-producing impellerhaving an annular ring of rotary vanes which have a mean diameter appreciably greater than the diameter of the entry eye of the compressor, while the diameter of the entry passage progressively diminishes from the whirl-producing impeller vanes to the entry eye of the compressor, a turbine disposed in rear of and spaced from the centrifugal compressor, a main shaft by which the impeller of the centrifugal compressor is connected to and driven by said turbine, an annular axial diffuser in rear of said compressor, an annular air transfer passage leading from the compressor to said annular axial diffuser, the transfer passage regarded in cross-sections containing the axis of the compressor being bent through a substantial angle from a generally radial direction to a generally axial direction, and being unencumbered with any blades upstream of the axial portion of the transfer passage which would tend to convert the circumferential component of the velocity of the gas into a radial or axial component, at least one combustion chamber with which the outlet end of the axial diffuser communicates, a nozzle ring at the outlet end of the combustion chamber through which the gases from such chamber enter the turbine, and a nozzle through which the gases from the turbine are discharged with propulsive effect.

2. A propulsion unit as claimed in claim 1, in which the Whirl-producing impeller is arranged to impart rotation to the air passing through the entry passage Without exercising upon it any appreciable compressing effect.

3. A propulsion unit as claimed in claim 1 in which the bend in the transfer passage between the centrifugal compressor and the axial diffuser occurs at or closely adjacent to the circumferential tips of the centrifugal compressor blades.

4. A propulsion unit of the jet propulsion type as claimed in claim 1 in which the means for driving the Whirl-producing impeller comprises transmission gearing connecting the Whirl-producing impeller to the main shaft.

5. A propulsion unit of the jet propulsion type as claimed in claim 4 in which the transmission gearing is housed within the inner circumferential Wall of the annular intake passage.

6. A propulsion unit of the jet propulsion type as claimed in claim 5 in which the whirl-producing impeller is formed and driven at such speed as to impart to the air in advance of the eye of the centrifugal compressor a whirling motion in the form of a substantially free vortex.

7. A propulsion unit of the jet propulsion type as claimed in claim 1 including a subsidiary turbine rotor separate from the turbine rotor which drives the impeller of the centrifugal compressor and acted upon by the gases from the combustion chamber, and transmission means between the subsidiary turbine rotor and the Whirlproducing impeller.

8. A propulsion unit of the. jet propulsion type as claimed in claim 7 in which the whirl-producing impeller and the turbine rotor driving it are so formed that the Whirl-producing rotor imparts to the air in advance of the eye of the centrifugal compressor a whirling motion in the form of a substantially free vortex.

References Cited in the file of this patent UNITED STATES PATENTS 2,405,919 Whittle Aug. 13, 1946 2,423,634 Berliner July 8, 1947 2,446,552 Redding Aug. 10, 1948 2,458,600 lrnbert et al Ian. 11, 1949 2,464,724 Sdille Mar. 15, 1949 2,548,465 Burdett et al Apr. 10, 1951 2,575,682 Price Nov. 20, 1951 FOREIGN PATENTS 611,447 Great Britain Oct. 29, 1948