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Questionbank : Aerospace Propulsion

Question
1. In the case of supersonic intakes, how is desired mass flow rate is achieved? What are the techniques used to change the back pressure in this case?\n
2. What is high and low frequency aerodynamic \nnoises in jet propulsion? How does Chevron nozzzle help to reduce it?
3. Trends in combustion engines and fuel efficiency.
4. Which thermodynamic properties are also control variables in the given numerical?
5. What are the 4 governing equations for 1-D compressible flow?
6. What is Meyer's Relation?
7. What are calorically perfect gases?
8. How much energy can be stored in each mode?
9. How many different modes of energy storage are available in gases?
10. What are thermally perfect gases?
11. What is the perfect gas equation of state?
12. Explain why there is a contradiction between whether the flow in the compressor of an engine is compressible or incompressible?
13. How to differentiate between turbine and compressor blades?
14. Why are axial compressors more preferred than centrifugal compressors?
15. How is compression achieved in the compressors? Also, explain the compression process.
16. What are the different types of rotary compressors?
17. In which orders should we increase the specific enthalpy, first by increasing pressure then by increasing temperature or vice versa?
18. What are the main functions of intake?
19. What is dual mode scramjet?
20. Explain some different strategies used for injection and flame holding in supersonic combustors?
21. Explain the two main factors and how they effect the heat release in supersonic combustors.
22. Explain 2 important timescales in Scramjets.
23. What is effervescent kerosene or bubbly kerosene and why is it a good fuel?
24. Name some fuels used in Scramjet engine.
25. Which components of gas turbine power plant is main cause of its low efficiency ?\n
26. Why is a double circular arc not suitable for supersonic flows ?
27. explain the loss of stagnation pressure for the combustor.
28. what is general thrust equation for turbojet engine ?
29. What is a DCA profile?
30. How does Multi-Spool technology help to overcome the issue of widely different RPMs required in a Bypass Engine?
31. Why do we do thermodynamic analysis ?\n
32. Why should the fan run at lowest possible RPM in a Bypass Engine?
33. What are the advantages and disadvantages of a Bypass Engine?
34. what is thermodynamic analysis ?
35. How is a fan different from a propeller?
36. What is Bypass Ratio? What is the bypass ratio for commercial aircrafts and military aircrafts?
37. How does a turbo fan help in overcoming the disadvantages of a propeller and jet engine ?
38. The flow turning from smooth corner goes through multiple expansion fans while when it goes through sharp corner it again goes through multiple expansion fan. Why ?
39. Numerical: Determine the thrust, TSFC and nozzle exit areas (cold
40. Compare the slopes of isobars and isochores at lower and higher values of temperature in a t-s diagram for 1D flow?
41. How do you sketch isochores(constant volume contour lines) on a T-S diagram for a 1D flow? Explain how these isochores change with pressure?
42. Why is a reduction in stagnation pressure between two points in a flow is not desirable? How to improve the efficiency of a combustor?
43. Does the stagnation temperature value change at point p2 downstream of a 1D flow from point p1 upstream, when the flow is adiabatic? In what scenarios does the stagnation temperature at p2 differs from p1?
44. Derive the expression of stagnation pressure in terms of Mach number.
45. Explain what is stagnation process?
46. Give the steps for calculating specific thrust.
47. Describe the T-S diagram of an ideal ramjet engine.
48. Even though increasing the number of corners/ramps in the intake makes the compression process more efficient, in real-life applications we do not do so. Why?
49. What are the modes of operation of supersonic intakes?
50. Describe external compression supersonic intakes.
51. What are the strategies we can use to overcome the disadvantages of overspeedng?
52. What are the disadvantages of using overspeeding technique to move the shock in the inlet of the C-D diffuser?
53. What is Mach wave?
54. What is the Zone of action, Zone of silence, and zone of dependence?
55. How do you terminate the shock waves?
56. When does the normal shock wave occur in case of reflected shocks? Can we increase the extent of the normal shock waves?
57. What is a slip line? State if the quantities are continuous or discontinuous (Velocity, Entropy, Static pressure, Temperature).
58. In which case entropy change is more ?\n1. streamline going through normal shock\n2.streamline going through oblique shock wave.
59. What is Mach reflection?
60. Can we see the strong shock solution in both detached and attached shock waves?
61. Mention the Mach numbers for strong, weak solutions and Mach number at the sonic line.
62. In the θ- β- M curve, at which angle of β, the strength of shock wave and loss of stagnant pressure are high? Mention the strong shock solution, weak shock solution, and mach solution in θ- β- M curve.
63. what is the θ- β- M curve? Draw the θ- β- M curve.
64. What happens to the flow deflection angle as we move far away from the wedge?
65. In case of detached shock in flow over a wedge, what happens to strength of shock ?state the reason why does it become stronger or weaker.
66. In case of flow over a wedge, when do you get attached and detached shocks(in terms of θ and θmax)
67. What are the advantages of using reference states? Describe the two commonly used reference states?
68. Can we calculate the speed of sound in a reacting flow? Justify your answer.
69. Derive the equation for the acoustic wave propagation in ideal gas?
70. In What frame of reference do we apply the governing equations for acoustic wave propagation and why?
71. What is the shape of the wavefront of a small disturbance for air in a room? What is the name of the thermodynamic process of its propagation?
72. how we calculate the entropy change of an irreversible process? Does it depend on the path?
73. Name the different types of combustors.
74. One of the most challenging aspects of manufacturing an engine is controlling the blade tip clearance. How can this be achieved via passive and active control?
75. What is the functionality of the disk of a compressor? What loading is experienced by the disk?
76. What material are blades and disk of the compressor made of?
77. How is stalling of compressors in turbofans overcome?
78. What is the idea behind using actuators to allow for movable guide vanes during off-design operations?
79. Why is the T02 value much higher in ramjet engines compared to turbofan engines or gas turbine engines?
80. How can the off-design operating conditions- as faced while starting the engine, be handled?
81. Plot the T-S curve of an ideal ramjet engine and explain how we can calculate the thrust
82. What problems are faced in the stages of the compressor while operating under off-design conditions?
83. What is the role of the stator of a compressor under design operating conditions?
84. Under what off-design operating condition of the compressor does the relative velocity cause flow separation on the suction side of the airfoil.
85. Explain why mixed compression intakes are designed to operate near its critical point with the help of total pressure recovery vs mass flow rate curve.
86. Using velocity triangles, explain the off-design operating condition when Vx is greater than the design value.
87. When does a compressor operate under off-design conditions?
88. When does an off-design operation condition for the compressor arise?
89. What is the major problem faced while operating the axial compressor under ' off-design conditions ' ?
90. Comment on the variation in the blade height from the first to the last stage of the compressor.
91. What do you understand by- operating an axial compressor under 'design conditions'?
92. What are the three different modes of operation of mixed compression intake?
93. What is the intake buzz problem in external compression intakes?
94. Explain the self correcting mechanism of a CD diffuser with wall openings to control the internal compression intakes.
95. How does CD diffuser with variable area throat help move inside the shock near the inlet?
96. Why is a reciprocating compressor not suitable for aviation?
97. What is the primary function of the intake?
98. What are the cons of using a centrifugal compressor?
99. What is the function of a stator blade in an axial compressor? What are it\'s downsides?
100. What information can you derive from the velocity triangle of a compression machine?
101. What is a blade loading coefficient and how does it relate to the change in the magnitude of relative velocity?
102. Describe shock/wave drag in supersonic intakes.
103. How does normal shock diffuser of axis symmetric supersonic intake works under design and off design operating conditions?
104. Describe supersonic intakes and its functions.
105. What is Chevron nozzle? How does it help in reducing aerodynamic noise?
106. Why can’t we have a Diverging duct for the isolator instead of a constant area duct?
107. What is the function of an Isolator?
108. What are Single-Expansion Ramp nozzles?
109. Why Ramjet technology is not suitable for Mach numbers above 5?
110. How can one find the location of a standing normal shock in a CD nozzle, given po,p_exit,A_throat/A_exit. ?
111. Derive the Hugoniot Equation. What is the speciality of Hugoniot Equation in terms of variables used?
112. Derive the expression for entropy change across a Normal Shock. Explain how subsonic flow and a normal shock cannot coexist using laws of thermodynamics.
113. Draw and explain the T-S diagram and P-V diagram for a flow across a normal shock. Label all the necessary points.
114. What is the characteristic Mach Number? Talk about the Prandtl relation. Also, explain why a1() = a2().
115. Discuss what happens if the Mach Number of flow ahead of a shock tends to 1 and Infinity. Can the infinity limit be used in real life?
116. Derive mathematical expressions for Static and stagnation pressures, static and stagnation temperatures, Mach number, density across a normal shock
117. Formulate the efficiency for the turbine using the TS diagram of the process in the turbine.
118. Explain the common thread in all the definitions of efficiencies (turbine, combustor, compressor, nozzle and inlet)
119. Formulate the efficiency of the nozzle.
120. Why do we need to think about the exit pressure in the nozzle?
121. Explain the complication with the nozzle and how we solve that?
122. State the loss of stagnation pressure metric for the combustor.
123. Define the efficiency of the compressor.
124. In the inlet, there was no work condition then why are we going for the same kind of definition for this compressor and there was no energy transfer but here is a transfer?
125. Define the efficiency of the subsonic inlet.
126. Explain the effect of irreversibility on the ideal turbojet cycle.
127. What are the different types of combustor designs?
128. Why is it necessary to maintain the blade tip clearance and how is it done?
129. What is the need for a variable stator blade or movable guide vanes?
130. How can the above mentioned off-design problem be rectified with the help of the stator or any other method?
131. What happens when the axial velocity across the rotor is higher than or lesser than the operating conditions?
132. State an example of off-design operating condition of an engine and why it is happening?
133. Why does even small departures in design conditions of inlet creates a major variation and thus creating a major problem in off-design operation of compressors?
134. In the PV diagram for normal shock, why state 2 can not be in the 1st, 3rd and 4th quadrant taking state1 point as an origin?
135. Under design conditions how does the axial velocity and pressure varies across the compressor?
136. In axial compressor why does the height of the blade decreases from first to last stage?
137. What is the significance of a stator?
138. For Rayleigh flow, write the resulting expression for the change in density, pressure, static temperature, entropy, velocity, and Mach number?
139. Write the differential form of governing equations?
140. how can we define thrust in terms of \
141. what is impulse function (or) how can we define the formula of the impulse function ?
142. what are the governing equations under quasi 1-d assumption and varing area duct ?
143. what is quasi one dimension assumption ?
144. why Rayleigh flow is a continuous solution?
145. Describe continuity, momentum, and energy equation and draw PV diagram for state1 and state 2 in Normal shock wave solution
146. What is the exit pressure when the nozzle is i) not choked ii) choked?
147. What is the Overall Pressure Ratio, Fan Pressure Ratio and Bypass ratio for Ramjet Engine?
148. Why is Specific Thrust a more important performance parameter than Total thrust?
149. What is intake momentum Drag?
150. What is Pressure thrust?
151. What is Momentum Thrust?
152. Why does ambient pressure matter while calculating Thrust force?
153. Briefly describe the different zones of a typical combustion chamber?
154. Why significant amount of cooling air is required in a compressor?
155. What is the common material used for the combusters? Specify the requirements for the material needed for that purpose
156. With the help of the emission vs combustion temperature curve, figure out the optimal range where an aircraft engine operates?
157. Why air-fuel ratio is as high as 60:1 in a premixed jet?
158. Explain blade cooling and the need for it?
159. Explain thermal barrier coating (TBC)?
160. Why does the axial compressor has almost replaced the centrifugal?
161. Why does the LP or IP turbine not require cooling?
162. Why the centrifugal compressor is better than the radial compressor?
163. Write the Euler turbo-machinery equation and its definition.
164. In the intake process of gas turbine engine, why does the air enter axially and leave radially? Why the vice - versa can not happen in a radial compressor?
165. In propulsion, why does the order of increasing pressure first then increasing temperature matters?
166. How the external compression in intake is achieved?
167. What is the purpose of having holes in the liner of a gas turbine engine?
168. What are the two modes in which intake generally try to achieve compression
169. What are the major components of a gas turbine engine?
170. How are theta and beta measured? (symbols have their usual meanings)
171. What is the flow deflection angle? How is it denoted?
172. Why are the normal shocks named so?
173. How is the study of Oblique shocks and normal shocks similar? How is this likeness put to use?
174. How to determine thrust (cold and hot) for static conditions for a CF6-50C2 Turbofan engine?
175. What are the types of losses that can occur in a combustor when fuel is burned in it?
176. How much fuel do you actually burn to take a stream of air from stagnation temp T03 to stagnation temp T04 in a combustor?
177. How much fuel do you need to burn ideally to take a stream of air from stagnation temp T03 to stagnation temp T04 in a combustor?
178. Illustrate the phenomenon of adding more heat that required q* in case of supersonic flow on a P-V diagram?
179. What happens when we add more heat than the permitted heat (q*) in case of supersonic flow?
180. What happens when we add more heat than the permitted heat (q*) in case of subsonic flow?
181. What is Thermal Choking?
182. Prove that the point where Rayleigh line is tangential to the heat curve is the sonic point.
183. How to find where the downstream state would be on the P-V diagram of the Rayleigh line?
184. How does the P-V diagram corresponding to the Rayleigh line look like?
185. What information can be obtained from the T-S diagram of a Rayleigh Flow?
186. What are the basic requirements for the material choice of nozzle ? What are the commonly used material for that purpose ?
187. Purpose of nozzle
188. Explain the sequence of events that occur while varying the stagnation pressure over a convergent nozzle using a TS diagram.
189. What are the basic requirements for the material choice of Turbine blades ? What are the commonly used material for that purpose ?
190. Why single crystal made turbine blade is more preferable ?
191. What are the metallurgical issues faced by HP Turbine blades due to its critical operating conditions?
192. Explain the significance of film impingement cooling in Blade turbine cooling technology ?
193. Explain the need of Blade cooling in HP turbine and how it is done ?
194. Based on HP Turbine operating environment, what are the most essential requirements for the turbine blades ?
195. How a single turbine stage differs from a single compressor stage ?
196. Explain physically why the flow upstream of the nozzle is completely insensitive to any changed (reduced) pressure conditions downstream?
197. What are the basic requirements for the material choice of combustor and combustor liner ? What are the commonly used material for that purpose ?
198. Explain the role of Fuel Staging in handling the reduction of emissions from a gas turbine engine ?
199. How the emissions of CO and NOx products vary with the combustion temperature ?
200. How Turbine Inlet Temperature and Pressure ratio are related to the NOx formation and efficiency of a gas turbine engine ?
201. What type of stresses are faced by a combustor and the HP turbine blades in a gas turbine engine ?
202. What are the air-fuel ratios in the premixed jet (overall) and in the combustion chamber ?
203. State the percentage distribution of the compressed jet of air (after compressor stage) according to its purposes.
204. Mention the different zones of a typical combustion chamber along with its functions
205. What are some advese effects that could be observed by increasing the bypass ratio of a turbofan engine.?
206. How do you distinguish between pushing or pulling the flow through the nozzle?
207. What happens if we increase the bypass ratio in a turbofan engine?
208. what is meant by an under-expanded jet at the exit of a convergent nozzle?
209. How does the flow through a convergent nozzle behave when the ambient pressure is lower than the sonic pressure conditions?
210. Explain using a TS diagram, the characteristics of the flow through a convergent nozzle when the ambient pressure is lowered to the sonic pressure condition?
211. What changes are observed in fuel flow rate and thrust when the turbine inlet temperature is kept constant.
212. how does the loss of stagnation pressure effect the mass flow rate?
213. what is the max mass flow rate that can be achieved by controlling the downstream conditions?
214. On which quantities does the mass flow rate of a chocked passage depend on?
215. What is the need for less diameter fans in low bypass ratio engine ?
216. Why large bypass ratio leads to less thrust ?
217. How to improve the efficiency of an aircraft engine ? Elaborate on better aerodynamics.
218. What factors effect the thrust produced by a fan nozzle
219. What is a geared turbo fan engine ? What is the advantage and disadvantage of using it ?
220. Is the assumption that Darcy Friction Factor remains constant from inlet to outlet, a reasonable approximation, since velocity of flow may vary from inlet to outlet?
221. What is the “hydraulic diameter” used in Fanno Flow?
222. What are the Governing Equations for Fanno Flow?
223. We know Fanno Flow is one-dimensional flow with friction. However while deriving the governing equations of Fanno Flow, we assume that the fluid is inviscid. In that case, how do we incorporate frictional effects in the flow?
224. Suppose we initially add q amount of heat at the inlet of the duct in Rayleigh Flow. Now we increase the amount of heat added by q’. Will any change(s) in inlet conditions occur to accommodate this change(s)? If so what are they?
225. What is the effect of heat addition on static pressure in Rayleigh Flow?
226. What is the effect of heat addition on stagnation pressure in Rayleigh Flow?
227. Given the ratios of upstream and downstream stagnation pressures and stagnation temperatures in Rayleigh Flow, can we solve for upstream and downstream Mach Numbers analytically? What can be one possible difficulty?
228. How does stagnation pressure loss vary across different possible solutions of theta-beta-M curve ? And how to calculate its amount?
229. What is the role of flame holder?
230. What kind of nozzle do we require in case of a turbojet with a afterburner and why?
231. Mention the disadvantages of a propeller
232. What is the difference in the operation of a gas turbine in case of a propeller and jet engine?
233. How does a jet engine produce thrust?
234. On what principle does a propeller work?
235. What is the main advantage of using wide-chord blades in an engine fan?
236. What happens to theta-beta-M curve when we increase mach number and how does this affect (theta)max ?
237. What happens to shock wave when theta > (theta)max in theta-beta-Mach number curve?
238. What is the Standout distance and how does it vary with the Deflection angle and the freestream Mach Number?
239. When is a detached shock formed? Also, explain the flow direction behind the detached shock wave
240. How are the Normal Shock Tables used in solving Oblique Shock Problems?
241. Why are oblique shock waves used for compression instead of compressors in ramjet and scramjet engines? (Similar to the mixed compression intake)
242. What is a slip line?
243. Briefly Explain the Boundary conditions used in solving a Problem of Oblique Shocks in the Exit.
244. Briefly Explain the Effects of Back Pressure Variation in a CD Nozzle.
245. How do you define the direction of an Oblique Shock Wave ?
246. Elaborate on why modern airliner engines are necessarily multi-spooled.
247. Why should the HP compressor spin at the higher speed than IP and LP compressors?
248. Why should the HP compressor spin at the higher speed than IP and LP compressors?
249. Give two reasons why the fan in turbofan engines should run at the lowest possible RPM.
250. Would you pick a high bypass turbojet engine to power high-altitude (50k-60k ft MSL) aircraft? Why or why not?
251. What is fan blade containment in turbofan engines?
252. Discuss a possible reason for why General Electric's CF6 has far fewer HP turbine stages than the coupled compressor stages while still managing to run them.
253. Why is an extremely wide range of flammability very important in a scramjet combustor?
254. What are the fundamental issues in developing a supersonic combustor?
255. What are the different strategies that have been used in the past for injection and flame holding and what are the principles behind them? (cavity, ramp, strut)
256. What are the different metrics that we used to assess the performance of the combustor?
257. On what factors does the combustion process depend and what are the challenges that come along? (injection, mixing flame holding in detail)
258. What are the limiting factors in heat release in combustors?
259. Explain the important timescales in scramjet propulsion and how they pose an issue?
260. Why is low density of hydrogen considered a disadvantage?
261. How is effervescent kerosene made, and why has it gained popularity recently?
262. What are the different kinds of fuels used in the past? Describe the pros and cons of each type of fuel?
263. Why is the choice of fuel very crucial for a scramjet engine?
264. What is the difference between a normal shock and an oblique shock?
265. What is the theta - beta - M relationship? Derive it.
266. Which property of the oblique shocks makes it more suitable than the normal shock in practical compressive devices?
267. What are some of the practical uses of oblique shock waves?
268. How does the stagnation pressure vary across a normal shock and an oblique show for the same given freestream mach number? Why so?
269. Why cannot the flow deflect away from the wave by a 'finite angle', say theta, through an expansion wave?
270. Why do conventional propeller aircraft lose their power plant efficiency beyond nearly M 0.4-0.5?
271. What percentage of the total thrust provided by a turbofan engine can be attributed to the core flow?
272. The Eurofighter Typhoon has a passive engine part that helps maintain the kernel of the afterburner flame. Which component is this and how does it work?
273. What features of the propeller engine and the turbo jet engine does a turbofan engine combine into one unit ?
274. Deescribe using a TS diagram the flow through a CD nozzle.
275. Describe rayleigh flow pressure behavior in the supersonic entry conditions.
276. Describe some of the technologies being used for Turbine blade cooling ?
277. Show the steps in solving the oblique shock angles for flow over a 2D wedge.
278. How does the Hugoniot curve shift when heat is added to a flow ?
279. What are the metallurgical issues faced with HPT turbine blades under high temperature, pressure and centrifugal load conditions ?
280. Describe the TS plot Vs PV plot.
281. What happens when a axial compressor works in off-design conditions ?
282. Describe in detail the properties of the isobars and the isochors in the TS and the PV diagrams ?
283. Describe what you mean by compressibility of a fluid ? How does it affect processes in the gas turbine combustor ?
284. Describe how pressure, temperature and axial velocity vary station to station in a gas turbine engine ?