Добавил:
Upload Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
Aircraft_design.pdf
Скачиваний:
641
Добавлен:
03.06.2015
Размер:
15.01 Mб
Скачать

10.6 Formulation and Theory: Isentropic Case

329

Figure 10.13. Afterburning turbojet and T-s diagram (real cycle)

Thus:

 

 

 

 

(m˙ p + m˙ s ) × (Veq V) = m˙ p × (Vep V) + m˙ s × (Ves V)

 

or

(1 + BPR) × (Veq V) = (Vep V) + BPR × (Ves V)

 

or

(1 + BPR) × Veq = (Vep V) + BPR × (Ves V) + V× (1 + BPR)

 

= Vep + BPR × Ves

 

or

Veq = [Vep + BPR × Ves]/(1 + BPR)

(10.18)

Then, turbofan propulsive efficiency:

 

 

ηpf =

2V

(10.19)

 

Veq + V

 

Large engines could benefit from weight savings by installing short-duct turbofans; some smaller aircraft also use short-duct nacelles.

10.6.3 Afterburner Engine: Formulation

Figure 10.13 is a schematic diagram showing the station numbers for an AB jet engine. To keep numbers consistent with the turbojet numbering system, there is no difference between Stations 4 and 5, which represent the turbine exit condition. Station 5 is the start and Station 6 is the end of AB. Station 7 is the final exit plane. Figure 10.13 also shows the isentropic AB cycle in a T-s diagram.

AB is deployed only in military aircraft (except in the civil supersonic Concorde) as a temporary thrust-augmentation device to meet the mission demand at takeoff and/or fast acceleration and maneuvers to engage or disengage in combat. AB is applied at full throttle by activating a fuel switch. The pilot can feel the deployment by the sudden increase in the g-level in the flight direction. A ground observer

Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]