This set of Aircraft Design Multiple Choice Questions & Answers focuses on “Propulsion – Jet-Engine Integration-4”.
1. What is the function of a typical nozzle?
a) To expand exhaust flow
b) To reduce flow velocity
c) To generate lift to fly
d) To increase pressure
Explanation: Function of nozzle is to expand flow. Nozzle is used to increase flow velocity by decreasing pressure and temperature of the flow. Lift is generated by wings primarily. Pressure can be increased by using compressor.
2. Performance of engine can be controlled by nozzle.
Explanation: Velocity of exhaust can be altered by using nozzle. Nozzle expands exhaust flow. This will reduce pressure and temperature of the flow. By altering the shape of Nozzle we can alter the velocity and performance parameters.
Explanation: A typical convergent nozzle is shown in the above figure. The illustrated fixed convergent nozzle Increases velocity of the flow for subsonic condition. For supersonic expansion divergent section is required.
4. Only convergent section will be used for supersonic speeds.
Explanation: Convergent section alone can be used to increase flow velocity if flow is in subsonic speed. However at supersonic speeds only convergent section of the nozzle cannot provide required velocity. At supersonic speeds, convergent section works as the diffuser.
5. Consider a flow with 0.5M. Now, as area decreases, velocity of the flow inside convergent section _____________
c) reduces by half always
d) velocity is independent of area
Explanation: Given, Mach number = 0.5. The flow is in subsonic speed region.
For subsonic speed, as area decreases the flow velocity will increase for convergent nozzle.
Explanation: Preliminary sizing of capture area is shown in the above diagram. It provides typical guidelines and values to get preliminary sizing of capture area. Drag polar is used to provide relationship between lift and drag.
7. Our designed Mach number is 0.8. Find the required area ratio for the design. Assume isentropic relation is valid.
Explanation: Given, Mach number M=0.8
Now, area ratio is given by, A/A* = (1/M)*(1+0.2M2)3*0.5787 = (1/0.8)*(1+0.2*0.82)3*0.5787
A/A* = 0.7233*1.1283 = 1.038.
8. If area ratio is 1.110 then, at which mach number flow is flowing?
Explanation: Given, area ratio A/A* = 1.110
Now, as we know, A/A* = (1/M)*(1+0.2M2)3*0.5787
For given problem, we will substitute different values of Mach number from the options.
Let’s consider M = 0.68
Hence, for assumed value of Mach number,
A/A* = (1/0.68)*(1+0.2*0.682)3*0.5787
A/A* = 0.8510*1.092483 = 1.110.
The evaluated area ratio is equal to the given area ratio.
Hence, correct value of Mach number is 0.68.
9. ____________ is the most common type of boundary layer diverter used for supersonic applications.
a) Channel diverter
Explanation: Channel diverter is considered as most common type of boundary layer diverter used for supersonic applications. It offers high performance among the other types. Empennage is tail section of the aircraft.
Explanation: Above diagram is representing concept of C-D nozzle. Cd nozzle consists of both convergent and divergent section. It is used for rocket propulsion where high speed is required. Typical cd nozzle consists a throat area. At throat Mach number is 1. Hence at throat flow is in sonic condition. Above diagram is illustrating a typical bell nozzle geometry.
11. At exhaust of nozzle temperature is 200k and density of the flow is 1.01 kg/m3. If back pressure is 1 bar then, nozzle is ______________
a) nozzle can be under or over expanded
b) under expansion
c) over expanded
d) design condition
Explanation: Given, temperature t 200k, density d 1.01 kg/m3
Now, exit pressure p = d*R*T = 200*287*1.01 = 57974 = 0.57 bar < 1 bar
Since exit pressure p < back pressure, the nozzle is over expanded.
Sanfoundry Global Education & Learning Series – Aircraft Design.
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