GB2448320A

GB2448320A - Aircraft engine variable area nozzle having expandable rear section

Info

Publication number: GB2448320A
Application number: GB0706856A
Authority: GB
Inventors: Pericles Pilidis; Vasileids Kyritsis
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-10
Filing date: 2007-04-10
Publication date: 2008-10-15
Anticipated expiration: 2027-04-10
Also published as: GB2448320B; GB0706856D0

Abstract

A variable area nozzle / jet-pipe comprises a front 1 and a rear part 3 which are split along a line 5 which runs circumferentially around the nozzle. The rear part 3 of the nozzle is able to expand in diameter and therefore increase inlet 2 and outlet 4 areas. The split line 5 may be regular or irregular, and may comprise chevrons which induce vortex generation when the variable geometry feature is deployed. The vortices enhance the mixing of the jet and ambient air. Ideally, the rear section of the nozzle is made of shape memory alloys (SMA) and is attached to the front section by several supports 6. The expansion of the shape memory material is maximised between consecutive supports, and minimised at the support areas itself (see figure 4). When the rear jet-pipe section has expanded, a secondary inlet is created, which allows external air to be entrained into the jet flow, which reduces the jet speed and noise of a jet engine.

Description

Aircraft Engine Variable Nozzle for Silencing and Performance

Enhancement

Background

Modern aero gas turbine engines are constantly optimized. Continuously larger difficulties are being encountered during their development, due to the increasingly conflicting requirements on noise and performance. Further-more, for civil turbofans, fan stability becomes an increasingly important issue, as Bypass Ratio rises. A solution to these problems can be found through the use of a variable nozzle.

The stability issue is mainly pronounced at low flight Mach numbers.

which are experienced during ground operation, take-off and the initial seg ments of climb. It can theoretically be encountered by an increase of the non-dimensional flow capacity of the nozzle downstream of the fan, which can be achieved by an enlargement of its area. The application of ejector nozzles is excluded in civil engines due to their low efficiency, while iris noz-zles utilizing overlapping, hydraulically adjustable "petals" are characterized by prohibited weight and complexity, when considering the low bypass nozzle Pressure Ratio.

Furthermore, noise restrictions in the airport perimeters are becoming more stringent with time. The reduction of specific thrust is in favour of the jet noise reduction. Constant geometry chevrons are also applied to nozzles to enhance the turbulent mixing of the jet with the ambient air. Although they do contribute to noise reduction, they negatively affect Specific Fuel Consumption, which is major importance at cruise conditions.

Statement of invention

The invention consists of a novel variable nozzle configuration, which: 1. helps jet noise reduction at take-off conditions while eliminating the mixing losses imposed by the constant geometry chevrons at cruise conditions, 2. enhances stable operation of the fan at low flight Mach numbers and 3. augments thrust at low flight speeds by utilizing the entrainment effect.

Generally, for an aero gas turbine application, the precise nominal geom-etry of the nozzle, shown in Figure 1, depends on the engine cycle and the aerodynamic interference of the engine with the airframe. Moreover, when variable geometry is deployed, the exact opening of the nozzle secondary inlet 2 and the increase of the nozzle exit area 4 at take-off are determined by the operating condition of the components upstream and the trade-off between thrust augmentation and jet noise reduction.

The mechanical actuation of the nozzle is considered to be an applica-tion of smart materials and shape memory alloys, which are currently under investigation for use in gas turbine engines.

Consequently, the invention focuses on the variable geometry concept, rather than exact figures, which are application specific.

In general terms, the novel variable nozzle geometry described herein incorporates the following features: 1. The splitting of the nozzle into two parts, the front 1 and the rear 3, along a chevron or undulating line 5, which extends all around the perimeter at a defined distance from the nozzle exit. The expansion of the diameter at the entry of the rear part of the nozzle 3 creates an opening 2, which digests air moving externally to the nozzle surface upstream and acts as an additional secondary nozzle inlet 2.

2. an increase of the nozzle exit area 4, which accommodates the mass-flow increase and favours a reduction of jet speed.

3. the existence of chevrons or of an undulatory shaped line 5 at the leading edge of the secondary nozzle inlet 2, which operate as vortex creators to enhance the mixing of the ambient stream with the jet downstream.

4. support structures 6, which are needed for the mechanical support of the nozzle component 3 downstream. These could be either external or internal. The figures show external support structures.

Drawings For the description of the variable nozzle geometry concept, the following figures are attached: 1. Side view of the nozzle at the nominal operating condition.

2. Side view of the nozzle with deployed areas.

3. Rear view of the nozzle at the nominal operating condition.

4. Rear view of the nozzle with deployed areas.

The figures show regular chevrons 5, but other regular or irregular shapes are possible. This comment is applicable hereafter, when reference to "chevron" is made.

Figure 1 graphically presents the side view of the nozzle, when being op-erated at its nominal condition at high flight Mach number, such as cruise.

At this position, its external surface is smooth and identical to a constant ge-ometry nozzle shape, which is used for example at current, conventional civil turbofan engines. Additional features include a number of support structures 6, which undertake the mechanical support of the rear part of the nozzle 3.

At this position the clievrons 5 do riot interfere with the flow internally or ex-ternally of the nozzle, thus contributing to a high efficiency for the expansion and the external aerodynamics. Still, the dashed chevron outline 5 reveals where the separation between the front 1 and rear part 3 of the nozzle takes place, when the nozzle Variable Geometry is deployed.

In Figure 2 the side view of the deployed nozzle is provided. The surfaces of the front 1 and rear 3 part of the nozzle are separated along the chevron outline 5. The increased diameter of the secondary nozzle inlet 2 allows for the digestion of mass-flow moving externally to the nozzle surface upstream, according to the principle of the entrainment effect applied to an unchoked bypass nozzle at low flight Macli numbers. The additional mass flow entering from the secondary nozzle inlet 2 can be further augmented by an increase of the nozzle exit area 4. The latter can be such that, the effect of mass-flow increase is compensated and accordingly the nozzle Pressure Ratio and jet velocity drop. As a consequence of the improved propulsive efficiency and the increased mass flow, time deployed nozzle configuration acts as a thrust augmentor or jet pump. Moreover, taking into consideration the reduction of the back-pressure experienced by the fan, its operating point moves toward a reduced Fan Pressure Ratio and an increased Surge and Flutter Margin.

At the same time the reduced jet speed positively affects jet noise reduction.

The latter is further promoted by the use of chevrons 5, which are exposed to the external flow and act as vortex generators that enhance the mixing of the jet stream with the ambient air downstream of the nozzle exit 4.

Figure 3 shows the rear view of the nominal nozzle geometry, whose side view was initially presented in Figure 1. The dashed line corresponds to the outline of the chevrons, which at this operating point do not interfere with the flow either internally or externally of the nozzle.

The rear view of the deployed nozzle geometry is provided in Figure 4. The comparison between the solid and the dashed line of the chevrons 5 makes evident the local increase of the diameter, at the area where the front and rear nozzle parts are separated. The same comment also applies for the increased nozzle exit diameter 4. Due to the application of smart materials, the increase of diameter is maximized at the center between two successive support structures, but it is minimized at the area of the support structures.

Claims

Claims 1. A nozzle geometry which is split into two parts, the front

and the rear along a line, which extends all around the perimeter at a defined distance from the nozzle exit and allows for the expansion of the rear nozzle part in terms of diameter and therefore inlet and exit areas.
2. A nozzle geometry according to claim 1, in which the split of the nozzle surface is done along a regular or irregular undulatory shaped line to allow for vortex generation, when variable geometry is deployed.
3. A nozzle geometry according to claim 1, in which the rear part of the nozzle is mechanically supported by a finite number of support structures.