JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year AEROSPACE PROPULSION I Previous Question Paper (February - 2022 - R13)

A turbofan engine is a type of air-breathing jet engine that combines the characteristics of a turbojet with a ducted fan. It consists of a core engine (compressor, combustor, and turbine) surrounded by a large fan at the front. The intake air is split into two streams: the core flow, which passes through the engine core to generate thrust, and the bypass flow, which is accelerated by the fan and bypasses the core.

Operationally, the fan draws in a large mass of air. A portion of this air enters the core compressor, where it is compressed, mixed with fuel in the combustion chamber, and ignited. The resulting high-energy gases expand through the turbine, which extracts power to drive the compressor and the front fan. The remaining bypass air is accelerated by the fan and exits through a separate nozzle or mixes with the core exhaust, providing the majority of the engine's total thrust.

The bypass ratio, defined as the ratio of the mass flow rate of the bypass air to the mass flow rate of the core air, is a critical parameter. High bypass ratio engines are more efficient at subsonic speeds.

Advantages include:

• Higher propulsive efficiency due to the acceleration of a larger mass of air to a lower velocity.
• Significantly lower noise levels compared to pure turbojets, as the high-velocity core exhaust is shielded by the slower bypass air.
• Improved fuel economy, particularly for long-range commercial transport.

Disadvantages include:

• Increased engine diameter and frontal area, leading to higher aerodynamic drag.
• Greater weight and mechanical complexity due to the large fan and bypass ducting.
• Limited performance at supersonic speeds compared to low-bypass or turbojet engines.

Gas turbine engines are classified primarily based on the method of energy extraction and the path of the working fluid. The main types include:

• Turbojet: All air passes through the core; thrust is generated entirely by the high-velocity exhaust jet.
• Turbofan: A portion of the air bypasses the core, providing additional mass flow at lower velocities, increasing efficiency.
• Turboprop: Most energy is extracted by the turbine to drive a propeller, with minimal jet thrust.
• Turboshaft: Similar to turboprop but used for helicopters or industrial applications, where the output is mechanical shaft power rather than thrust.

Given data: Exit velocity (V_e) = 650 m/s, Mass flow rate (ṁ) = 40 kg/s, Flight velocity (V_a) = 250 km/h = 69.44 m/s.

1. Thrust developed (F):

2. Thrust power (P_T):

3. Propulsion efficiency (η_p):