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GAS TURBINE ENGINE EXHAUST 13 April, 2017.

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Presentation on theme: "GAS TURBINE ENGINE EXHAUST 13 April, 2017."— Presentation transcript:

1 GAS TURBINE ENGINE EXHAUST 13 April, 2017

2 TABLE OF CONTENTS CHAPTER 1 - CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION S/C: Location S/C: Function CHAPTER 2 - CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES CHAPTER 3 - ENGINE NOISE REDUCTION CHAPTER 4 - THRUST REVERSERS S/C: Principle S/C: Turbo-propellers 13 April, 2017

3 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Location In a single flow turbojet, the exhaust duct is an element located within the engine behind the turbine and by which the gas stream, having undergone the engine thermodynamic cycle, is ejected In the case of a dual-flow turbojet, the hot flow exhaust duct is positioned on the turbine outlet as on a single flow engine; the cold flow exhaust duct is located behind the fan. 13 April, 2017

4 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Location The stations associated with the exhaust ducts of a turbojet: The stations associated with the exhaust ducts of a turbojet : For a single flow turbojet: station 4: exhaust duct inlet station 5: exhaust duct outlet 13 April, 2017

5 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Location The stations associated with the exhaust ducts of a turbojet: For a dual flow turbojet: Hot flow (or primary flow): Cold flow (or secondary flow): station 5: exhaust duct inlet station  15: exhaust duct inlet station 6: exhaust duct outlet station 18: exhaust duct outlet 13 April, 2017

6 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Function The exhaust duct’s function is to convert post-turbine gas energy into kinetic energy. This transformation is an expansion; it is obtained by the shape (convergent in general) of the exhaust duct. It involves an acceleration of gases. This acceleration generates a thrust force. It can be the main thrust of the engine (single flow engines) or a secondary thrust known as "residual thrust" (double flow engine). 13 April, 2017

7 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Function 13 April, 2017

8 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Joining line. It comprises an external casing. Inside, a cone (taper) is fixed by struts. Its role is to channel the hot gases leaving the turbine and to transform their annular flow into circular flow. The taper. Its role is to streamline the rear face of the turbine. It can support the rear bearing of the turbine. Struts. The number of struts is variable, depending on the type of engine. They convey the gas flow in an axial direction. Struts are hollow and can be thus used, due to fresh air circulating inside, to cool the rear face of the turbine or to pressurize the turbine bearing. . 13 April, 2017

9 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Joining line 13 April, 2017

10 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Taper 13 April, 2017

11 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Struts. The number of struts is variable, depending on the type of engine. They convey the gas flow in an axial direction. Struts are hollow and can be thus used, due to fresh air circulating inside, to cool the rear face of the turbine or to pressurize the turbine bearing. Tail pipe. It is a cylindrical conduit intended to ensure the connection between the joining line and exhaust nozzle. Note that it is optional, depending on how the engine is installed in the airframe or in the nacelle. 13 April, 2017

12 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Nozzle. The nozzle enables expansion of gases leaving the turbine to obtain maximum kinetic energy. For a given subsonic speed of gases, the expansion nozzle is convergent in shape. For a given supersonic speed of gases, the nozzle is convergent-divergent in shape. 13 April, 2017

13 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Dual flow turbojet 13 April, 2017

14 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Fixed area convergent nozzle : Mixed flow bi-pass turbojet 13 April, 2017

15 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Variable outlet section convergent nozzle : Eyelids 13 April, 2017

16 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Variable outlet section convergent nozzle : Device with multiple flaps 13 April, 2017

17 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Primary nozzle, convergent, multi-tab nozzle 13 April, 2017

18 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Secondary nozzle, eyelids nozzle 13 April, 2017

19 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Materials Tail pipe. 13 April, 2017

20 CONSTRUCTIONAL FEATURES AND PRINCIPLES OF OPERATION
Materials Exhaust Pipe. 13 April, 2017

21 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Introduction An exhaust duct is composed mainly: of a joining line, including an outer jacket and a cone, the function of which is to assure the continuity of gas flow leaving the turbine, of a tail pipe, ensuring the connection between the joining line and the nozzle. The tail pipe is optional. Its installation depends on how the engine is placed in the frame. of a nozzle of fixed or variable exhaust area, intended to expand and accelerate gases. Nozzle architecture can vary sharply, and is classified in two groups: fixed convergent area ducts, found on most commercial aircraft engines, variable area ducts (convergent or convergent-divergent), found on engines equipped with exhaust reheaters (Concorde or fighter aircraft). 13 April, 2017

22 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Exhaust duct 13 April, 2017

23 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Nozzle types 13 April, 2017

24 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Fixed convergent area nozzle Single flow turbojet. On this type of turbojet the exhaust duct is single. It is composed mainly: of an exhaust cone, including two parts: a casing and an internal cone. The casing is directly attached to the turbine case. Its shape is convergent. The internal cone’s function is to adapt the annular section of the flow in the turbine outlet in circular section. The internal cone is linked to the casing by struts which rectify the flow. of a duct. On some engines, the duct precedes a tail pipe. The duct is a convergent channel in which the expansion of hot gases produces their acceleration. 13 April, 2017

25 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Fixed convergent area nozzle Dual flow turbojet. Double flow turbojets have two ducts. Both flows may be separate: The exhaust duct containing hot flow enables the expansion and the acceleration of the gas stream in the same way as in single flow turbojets. This acceleration, however, represents only one small part of the turbofan’s thrust (about 20% on takeoff), and is called residual thrust. The exhaust duct containing cold flow makes it possible to accelerate the gas stream, which is the main source of a turbofan’s thrust. It is of convergent shape and consists of two partitions. The internal partition is the casing surrounding hot parts of the gas generator. The external partition constitutes the rear part of the engine nacelle. It usually features a thrust reverser. 13 April, 2017

26 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Fixed convergent area nozzle 13 April, 2017

27 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Fixed convergent area nozzle Variable ejector nozzle. Engines equipped with variable area nozzles adjust more easily to their flight envelopes (as broad as possible for fighters). Moreover, engines using re-heaters must be equipped with such nozzles in order to compensate for the increase in mass flow rate. Variable ejector nozzles are classified in two groups: those with a convergent section and those with a convergent – divergent section Convergent shapes limit gas exhaust velocities to Mach 1 (in nozzle throat).. To continue accelerating gases (assuming they still have energy) and reach supersonic exhaust velocities, convergent nozzles must be prolonged with a divergent duct. 13 April, 2017

28 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Variable ejector nozzle 13 April, 2017

29 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Fixed exhaust convergent area nozzle. Space upstream meets the conditions of pressure, temperature, and velocity in the turbine outlet. The downstream space meets conditions of pressure and temperature characteristic of the atmosphere. Pt 5 = pressure turbine outlet and nozzle inlet Tt 5 = temperature turbine outlet and nozzle inlet P 0 = atmospheric pressure T 0 = atmospheric temperature When pressure Pt5 is higher than P0, a flow originates in the upstream space and moves towards the downstream space. The larger the difference between pressures, the greater the flow As the nozzle is convergent, gases are accelerated by expansion. 13 April, 2017

30 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Fixed exhaust convergent area nozzle. If upstream pressure Pt5 continues to increase, gases reach a maximum speed in the nozzle throat. This speed is equal to sonic speed (M=1). As speed is maximum, so is the gas mass flow rate and thrust. The relationship between total pressure and static pressure in the throat, known as critical ratio Rc, takes the value : Rc  1,9. In practice, the real ratio Rr is different from Rc. 13 April, 2017

31 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Fixed exhaust convergent area nozzle. 13 April, 2017

32 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Fixed exhaust convergent area nozzle. 13 April, 2017

33 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Fixed exhaust convergent area nozzle. 13 April, 2017

34 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Fixed exhaust convergent area nozzle. Conclusion: Every constant section nozzle is adapted to a given altitude and to a precise turbojet engine rating. Complete expansion is thus carried out only under well defined conditions. The ideal compromise is thus sought when designing an exhaust duct for an engine intended to propel an aircraft at subsonic speeds. 13 April, 2017

35 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent jet nozzles Variable exhaust convergent area nozzle. For the nozzle to adapt continuously to every engine rating, manufacturers have developed various processes: the bucket (or half-shell) system. the multi-flap system. They allow the adaptation to various engine ratings. They enable, indirectly, the control of turbine temperature 13 April, 2017

36 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Variable exhaust convergent area nozzle: The bucket system 13 April, 2017

37 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Variable exhaust convergent area nozzle: The multi-flap system 13 April, 2017

38 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent - divergent exhaust nozzle The Mach number behind the turbine is lower than 1 (M < 1). The duct behind the turbine always has a convergent shape. Principle of operation By connecting a divergent channel to the convergent nozzl after the throat, the flow can be accelerated (Hugoniot’s Theorem) If the generating pressure Pt5 is sufficient, gases circulate past the nozzle’s throat at Mach 1, and continue expanding in the divergent duct, with an increasing exhaust velocity: M > 1 13 April, 2017

39 CONVERGENT, DIVERGENT AND VARIABLE AREA NOZZLES
Study of convergent - divergent exhaust nozzle The convergent-divergent duct enables supersonic exhaust velocities (past the throat). Because engine ratings are variable, the divergent duct must also be variable. The primary duct is convergent and has a variable section The secondary duct may have a variable section, depending on flight conditions (convergent or divergent). 13 April, 2017

40 ENGINE NOISE REDUCTION
Origin of the noise The streamwise vortices generated in a jet flow, in addition to the azimuthal (or ring type) vortices, have been found to mix fluid streams even more efficiently) Both the azimuthal and streamwise vorticities are of equal importance to jet mixing process and they are not independent of each other. The distortion of azimuthal vortex structure may lead to streamwise vortices under certain conditions. The streamwise vortices in jet mixing flows can be generated by many methods. 13 April, 2017

41 ENGINE NOISE REDUCTION
Exhaust noise 13 April, 2017

42 ENGINE NOISE REDUCTION
Solutions Flow mixture. Design enabling flow mixture before their backward ejection. Significant reduction in exhaust gas noise, and in some cases, an improvement in nacelle aerodynamics. 13 April, 2017

43 ENGINE NOISE REDUCTION
Solutions Lobed nozzles. A lobed nozzle used to generate large-scale streamwise vortices in a jet flow has been considered to be a promising method for jet mixing enhancement. 13 April, 2017

44 ENGINE NOISE REDUCTION
Turbofan Lobed Mixer Nozzle 13 April, 2017

45 ENGINE NOISE REDUCTION
Turbofan Lobed Mixer Nozzle 13 April, 2017

46 THRUST REVERSERS Function
Reverse the whole or part of the propelling flow in order to create an aerodynamic braking force. This makes it possible to assist the braking of the aircraft. They improve deceleration on slippery runway. They reduce brake wear. 13 April, 2017

47 THRUST REVERSERS Location
Generally, thrust reversers are located in the rear part of a single flow turbojet and in an intermediate position in a modern dual flow turbojet. Single flow turbojet 13 April, 2017 Dual flow turbojet

48 THRUST REVERSERS Study of the gas stream
When analysing the formula, we realize that in order to obtain an effective opposite thrust, are required: a high aircraft speed (i.e. as soon as possible after landing), a re-orientation of the ejected flow as forward as possible (manufacturers limit the angle  to 45° forward to avoid engine stall and runway remains ingestion). 13 April, 2017

49 THRUST REVERSERS Principle
Thrust reversers obey the same principle: to try and redirect the propelling flow ahead for it to hit atmospheric air head-on. So as to avoid interferences between the air sucked by the engine and the reversed flow, the ejection angle of reversed flow is generally limited to 45°. The unfolding of thrust reversers occurs when engine idles. Engine rating increases only when the spreading out sequence is completed. The resulting reversed thrust is about 40% of takeoff thrust (full power). 13 April, 2017

50 THRUST REVERSERS Various types Eyelid (shell) type thrust reversers.
13 April, 2017

51 THRUST REVERSERS Various types Cascade type thrust reversers.
13 April, 2017

52 THRUST REVERSERS Various types Petal (prop-fan) type thrust reversers.
13 April, 2017

53 THRUST REVERSERS Turbo-propellers
The thrust reversing on a turbo-propeller is carried out by inverting the pitch of the propeller. This is done thanks to the propeller governor: when thrust reversing is engaged, it swivels each blade ; when engine power increase, a thrust force opposite to the direction of aircraft motion is created. 13 April, 2017

54 Reversers spreading out
THRUST REVERSERS Reversers spreading out As soon as levers are switched: The reverse system opens, driven by jacks, Indicators describing the system unlocked state light up (amber warning lights): [REV UNLK]. Indicators describing the system opened state light up (green lights) : [REV ] Amber lights [ REV UNLK ] go out Reverse thrust levers are then free of movement. Reverse thrust can be increased by pulling the reverse levers backwards 13 April, 2017

55 Thrust reverse lever and indicators
THRUST REVERSERS Thrust reverse lever and indicators 13 April, 2017

56 THRUST REVERSERS Interfaces
The thrust reverse assembly on an aircraft equipped with turbojet is often connected to the brake system. Thus the aerodynamic brake system, called " Ground Spoilers " function (which acts on the automatic deployment of slowing down surfaces on the ground) can be activated as soon as the reverse lever has its deployment position unlocked, For that purpose it is necessary of course that all the usual operation conditions of such a system should be met (aircraft on ground, throttle control levers in idling position,...). The thrust reverser assembly on an aircraft equipped with turbojet is often connected to the anti-stall control system. The VBV position can be affected by the use of the thrust reverse assembly. Thus the theoretical opening surface of the valves can be increased up to reaching a fixed value when reversers are used 13 April, 2017

57 THRUST REVERSERS V.B.V. 13 April, 2017

58 THRUST REVERSERS Maintenance
The forces actuating thrust reversers are very significant in order to ensure the correct operation in spite of the aerodynamic and mechanical stresses. The greatest precaution is required when inspecting or repairing this system. It is important for the system to be deactivated when work is to be done on it, so as to prevent any risk of accident. It may also be deactivated and set in locked position in order to allow the departure of an aircraft: thrust reversers would be inoperative : 13 April, 2017

59 THRUST REVERSERS Maintenance 13 April, 2017

60 THRUST REVERSERS Maintenance 13 April, 2017

61 THRUST REVERSERS Maintenance 13 April, 2017


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