GB2203494A - Jet propulsion fluid duct - Google Patents

Abstract

The large ducted fan gas turbine powerplants now being designed for use in the next decade, are capable of mass flows which are far in excess of that required for part of the flight regime. The physical dimensions by the fan duct of such a powerplant also creates problems by way of frontal area, the magnitude of which can only be reduced by making the wall structure as thin as possible. To this end and at the same time with a view to catering for the excess flow, the present invention provides a propulsive fluid duct (such as the fan duct of a ducted fan engine) having a downstream end portion 12a which is axially translatable relative to the remainder of the duct and which includes a plurality of flaps 20. Ram mechanisms 22, and a telescopic arrangement of channels 26, 28, with pins 30, engaging slots 32, enable the end portion 12a to be translated, translation of the end portion to be stopped, and thereafter the flaps 20 to be pivoted to a position in which they extend across the duct thereby reducing its cross sectional flow area. During rearward translation of the end- portion 12a a gap 38 opens up through which air from the fan duct can exit. <IMAGE>

Description

PROPULSION FLUID DUCT The present invention relates to a duct through which in operation a propulsive fluid flows.

The invention has particular efficacy when utilised in the fan duct of a ducted fan gas turbine engine which needs that ability to cater for differing flow requirements. This should not be regarded as limitive, since provided the appropriate heat resistant materials are used for the construction of the invention, it may be incorporated in the jet pipe of a gas turbine engine.

The present trend in the design of ducted fan gas turbine engines, is to increase the bypass ratio ie. the quantity of air passed through the fan duct relative to the air passed through the associated core gas generator.

There results during the cruise portion of the flight of an associated aircraft, improvements in the specific fuel consumption (S.F.C) ie. the number of pounds weight of fuel used, per pound of thrust produced, per hour of flight of the aircraft is reduced.

There are drawbacks however. One such drawback is that whilst the design is aimed at optimum conditions during cruise of the associated aircraft, because this is by far the longest lasting part of the flight regime, the bypass ratio does not provide a suitable configuration for take off and landing.

The invention seeks to provide an improved structure for a high bypass ratio ducted fan gas turbine engine.

According to the present invention a propulsion fluid duct has a bounding wall provided with a downstream end portion which is translatable relative to the remainder of the duct wall and includes a plurality of pivotable flaps, means for effecting the translation, further means for halting the translation and wherein on halting of the translation of the end portion, the first means on command can apply a force to cause the flaps to pivot to an operative position across the duct.

Preferably the flaps when non operative provide inner and outer flow surfaces of the bounding wall.

The peripheral opening which results from the translation of the downstream is defined by walls which are orientated so as to allow a gas flow therethrough the longitudinal axis which will not change the original direction of flow thereof by more than an angle of 200 relative to the axis of the duct.

Preferably, though not restrictively, the upstream portion of the duct wall has first channel members extending downstream therefrom and the downstream translatable portion has further channel members which are adapted to telescope over the first channel members so as to enable support thereof during translation.

The translation halting means may comprises a pin on one or more either the first or further channel members slidably engaging in a co-operating, closed ended slot in the other of the channel members.

Preferably the translating and pivoting movements are achieved by common extendable ram rods.

The invention will now be described by way of example and with reference to the accompanying drawings in which: Fig 1 is a diagrammatic view of a ducted fan gas turbine engine in accordance with the present invention.

Fig 2 is an enlarged sectional part view on line 2-2 of Fig 1.

Fig 3 is a view in the direction of arrow 3 in Fig 2.

Fig 4 is a cross sectional view on line 4-4 in Fig 3.

Referring to Fig 1. A ducted fan gas turbine engine 10 includes a wall in the form of a cowl 12 which surrounds a stage of fan blades (not shown). The cowl 12 also surrounds the upstream end of the core gas generator 14 and the former, with the latter define a fan duct 16 which terminates in a thrust nozzle 18.

The thrust nozzle 18 consists of the downstream portion 12a of the cowl 12 and includes in its structure a plurality of equi angulary spaced flaps 20. The flaps 20 provide inner and outer flow surfaces of the nozzle 18 ie.

a fan air flow surface and an ambient air flow surface respectively. Further, the nozzle 18 and its associated flaps 20 are translatable en mass relative to the remainder of the cowl 12, in a direction axially thereof.

The translatory movement is brought about by actuation of ram mechanisms 22.

Referring now to Fig 2. The downstream nozzle portion 12a and its associated flaps 20 have upstream faces 22 which are inclined at a common shallow angle to the axis of the cowl 12. The maximum magnitude of the angle is 200 for reasons which are explained later in this specification. The downstream end of the main portion of the cowl 12 has a complementary face 24 so that when the two portions abut as shown in full lines, a considerable area of engagement between them is achieved.

The portion 12a has a plurality of equi angularly spaced 'U' shaped channels 26 fixed thereto and these telescopically engage further channels 28 which are affixed to the upstream portion of the cowl 12 and project therefrom in a downstream direction. Each channel 26 has a pin 30 which projects radially inwardly of the portion 12a and engages in a closed ended slot 32 in a respective channel 28. This features is more clearly seen in Fig 3.

The flaps 20 are each pivotably attached to and between a pair of respective adjacent channels 26, so as to be pivotable about an axis 34. Translating of the portion 12a and the flaps 20 enmass and pivoting of the flaps per se are achieved as follows: At the start of the take off run of an associated aircraft (not shown) the rams 22 (Fig 1) are actuated so that the ram rods 36 (Fig 2) extend and so move the portion 12a in a downstream direction to the position in dotted lines. In so doing the channels 26 slide along the channels 28 until the pins 30 abut the downstream closed end of their slots 32 whereupon translation is halted by not increasing the ramforce. Gap 38 has now been created in the cowl 12, which allows air from the fan duct to exit therefrom.Since the fan nozzle 18 is still available for the outward passage of fan air, the total fan air outlet area has been increased and this ensures that the considerable flow of air through the fan duct 16 is enabled, without generating conditions which without the annular gap, would cause the fan to surge.

On attaining cruise altitude, the engine 10 is throttled back with the result that the airflow through the fan duct 16 is reduced. The rams 22 are then activated to move the portion 12a upstream, into abutting engagement with the main portion of the cowl 12.

When the aircraft lands, then in order to enable it to lose forward speed, the rams 22 (Fig 1) are activated again, but now, on the pegs 30 engaging the closed ends of their respective slots 32, the ram loads are continued.

Since translation of the downstream portion 12a is prevented, the loads are transmitted to the flaps 20, which are thus caused to pivot about their pivot axis 34 which of course, are now in a position further downstream than hitherto, as shown in chain dotted lines in Fig 2.

The flaps 20 pivot to the position shown in chain dotted lines in Fig 2 which results in some of the fan air being deflected radially outwardly of the fan duct.

On the present example, the flaps 20 are so proportioned and pivoted, that on reaching a flow deflecting position as depicted in Fig 2, they do not reach the casing of the core gas generator 1A. The fan duct 16 therefor is not entirely blocked. This is merely a design choice in the particular instance. The flap 20 could be arranged so as to extend into contact with the core gas generator 14, without departing from the spirit of the present invention, and thus deflect all of the air radially outwards.

Referring briefly to Figs 3and 4. In the former the pivotable connection of one of the flaps 20 to the tut shaped channel 26 is clearly seen, pivoting occuring about the axis 34 as described hereinbefore. In the latter figure, one of the pins 30 is seen projecting radially inwardly from the 'U' shaped channel 26, through the slot 32 in the channel 28.

Having read this specification, the skilled man will realise that mechanisms such as ball screws and co-operating nuts (not shown) may be substituted for the ram mechanisms 22.

Claims (9)

Claims:

1. A propulsive fluid duct, a bounding wall structure of which comprises a downstream end portion which is translatable relative to the remainder thereof and includes a plurality of pivotable -flaps, means for effecting the translation, means for halting the translation and wherein on said halting of the translation of the end portion, the means for effecting translation can on command apply a force to cause the flaps to pivot to an operative position across the duct.

2. A propulsive fluid duct as claimed in claim 1 wherein the flaps when in a non operative position provide inner and outer flow surfaces of the bounding wall.

3. A propulsive fluid duct as claimed in claim 1 or claim 2 wherein on said translation occurring a peripheral gap is opened in said bounding wall, said gap being defined by walls which are orientated so as to allow a fluid flow therethrough without changing its original direction of flow by more than 200 relative to the axis of the duct.

4. A propulsive fluid duct as claimed in any previous claim and including first channel members protuding from the downstream end of the fixed bounding wall structure and further channel members fixed to the translatable end portion and fitting in telescopic manner with the first channel members s as to enable support'of the downstream translatable portion during said translation.

5. A propulsive fluid duct as claimed in claim 4 wherein the translation halting means comprises a pin protruding from each of either the first or further channel members, into a respective closed ended slot in a respective co-operating channel.

6. A propulsive fluid duct as claimed in any previous claim wherein the translation effecting means comprises common extendable ram mechanisms which are connected between the translatable portion and the remainder of the duct wall.

7. A propulsive fluid duct as claimed in any previous claim wherein the propulsive fluid duct is the fan duct gas turbine powerplant.

8. A propulsive fluid duct substantially as described in this specification and with reference to the accompanying drawings.

9. A ducted fan gas turbine engine including a propulsive fluid duct as claimed in any of claims 1 to 8.