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Aerospace Propulsion Study For Shenyang Aerospace University by Lale420 (1)


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This so called PPT for propulsion study for Shenyang Aerospace University. This PPT right protected by Dr. divinder K. Yadav. Its using in SAU by Lale. For all students of Aeronautical Engineering must memorize each & every words from this PPT. If you miss a single words you must fail in the Exam. Remember there is no chance to be creative or use sense you just need to use the power of memorizing.

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Aerospace Propulsion Study For Shenyang Aerospace University by Lale420 (1)

  1. 1. 1 Turbine Engine © Devinder K Yadav
  2. 2. Gas Turbine Theory 1 2
  3. 3. Gas Turbine Cycles • Closed circuit gas turbine powerplant • Open circuit gas turbine powerplant 3
  4. 4. Closed circuit gas turbine powerplant 4
  5. 5. Open circuit gas turbine powerplant 5
  6. 6. Basic Gas Turbines Engines The turbine engine produces thrust by increasing the velocity of the air flowing through the engine. It consists of: • air inlet, • compressor, • combustion chambers, • turbine section, • exhaust section, • accessory section. 6
  7. 7. 7 Basic Gas Turbines Engines
  8. 8. Basic Gas Turbines Engines Turbine engine advantages over a piston engine: • less vibration • increased aircraft performance • reliability • ease of operation. 8
  9. 9. 9
  10. 10. Piston Engines v Turbine Engines 10
  11. 11. 11 How Turbine engine works
  12. 12. Physics applicable to jet engines •Newton’s Third Law of Motion •Charles’ First Gas Law •Charles’ Second Gas Law •Pascal’s Law •Bernoulli’s Theorem •First Law of Thermodynamics •Second Law of Thermodynamics 12
  13. 13. For every action there is an equal and opposite reaction • Turbine engines are known as reaction engine Newton’s Third Law of Motion 13
  14. 14. 14
  15. 15. 15
  16. 16. • When the pressure of a gas remains constant, the volume of the gas will increase as it’s temperature is increased Charles’ First Gas Law 16
  17. 17. 17
  18. 18. Charles’ Second Gas Law • When the volume of a gas is held constant, the pressure of the gas will increase as it’s temperature is increased 18
  19. 19. Pascal’s Law • Pressure always acts at right angles to any confining surface, undiminished throughout the fluid regardless of shape and size of the container 19
  20. 20. 20
  21. 21. • The sum of all energies in a perfect fluid must remain constant • If kinetic energy increases then potential energy must decrease, ie:- velocity is inversely proportional to pressure Bernoulli’s Theorem 21
  22. 22. 22
  23. 23. • Energy can neither be created nor destroyed The First Law of Thermodynamics 23
  24. 24. 24
  25. 25. • Energy will always flow from an area of higher potential to an area of lower potential Second Law of Thermodynamics 25
  26. 26. 26
  27. 27. A convergent duct 27
  28. 28. A divergent duct 28
  29. 29. The Turbine Engine 29
  30. 30. The Brayton Cycle A B C D 30
  31. 31. Pressure vs Temperature Temperature Pressure Atmospheric Pressure 31
  32. 32. Enthalpy vs Entropy Entropy Usability of heat energy Enthalpy Total energy of the gas Atmospheric Pressure A B C D A B C D 32
  33. 33. Temperature, pressure and velocity 33
  34. 34. Force (F) = ma = (weight ÷ gravity) × acceleration Thrust (T) = ma + (pressure × area) T = Where, Wa - weight of air V1 – velocity of airplane V2 – velocity of air at jet nozzle Wf – weight of fuel Aj – area of jet nozzle Pj – static pressure of jet nozzle Pam – ambient static pressure The Jet Engine Equation Pam)Aj(PjVf g Wf V1)(V2 g Wa  34
  35. 35. 35
  36. 36. • A common method of determining engine thrust • EPR is the ratio between the total pressure in the exhaust duct and the total pressure at the inlet to the engine Engine Pressure Ratio (EPR) 36
  37. 37. A larger EPR = more thrust Typical EPR values (Boeing 727): NB. EPR is only useful as a measure of thrust on those engines with fixed area exhaust nozzles 37
  38. 38. Thrust versus horsepower • Recall: power = rate of doing work • in other words: – Lift up a one pound weight through 550 feet in one second and you have 1 horsepower • Mathematically: – Power = Force x Distance Time • Propeller torque and RPM are used to calculate horsepower 38
  39. 39. Thrust versus horsepower • Power harder to measure in a jet engine (time and distance elements not always involved) • Once a jet engine is moving forward then a comparison can be made • At an airspeed of 375 mph (325 kts), one lb of thrust = 1 HP • THP = thrust x TAS (kts) 325 • So a B777 engine produces 90,000lbs of thrust – On take off (100kts) = 27690 HP – During climb (300kts) = 83070 HP (assuming full power) 39
  40. 40. Methods of Jet Propulsion 40
  41. 41. A Ram Jet Engine 41
  42. 42. A Pulse Jet Engine 42
  43. 43. A Rocket Engine 43
  44. 44. Gas Turbine Engine 44
  45. 45. Turbojet: Turbofan Turbojet Turboshaft Gas Turbine Engine Types 45
  46. 46. 46 Turbojet engines Also called as the pure jet. The compressor section passes inlet air at a high rate of speed to the combustion chamber. The combustion chamber contains the fuel inlet and igniters for combustion. The expanding air drives a turbine, which is connected by a shaft to the compressor, sustaining engine operation. The accelerated exhaust gases from the engine provide thrust. Turbojet engines are limited on range and endurance. They are also slow to respond to throttle applications at slow compressor speeds.
  47. 47. 47 Turboprop engines A turboprop engine is a turbine engine that drives a propeller through a reduction gear. The exhaust gases drive a power turbine connected by a shaft that drives the reduction gear assembly. Turboprop engines are most efficient at speeds between 250 and 400 m.p.h. and altitudes between 18,000 and 30,000 feet. They also perform well at the slow airspeeds required for takeoff and landing, and are fuel efficient. The
  48. 48. 48 Turbofan engines Turbofan engines are designed to create additional thrust by diverting a secondary airflow around the combustion chamber. The turbofan bypass air generates increased thrust, cools the engine, and aids in exhaust noise suppression. This provides turbojet-type cruise speed and lower fuel consumption. The inlet air that passes through a turbofan engine is usually divided into two separate streams of air. One stream passes through the engine core, while a second stream bypasses the engine core. It is this bypass stream of air that is responsible for the term “bypass engine.” A turbofan’s bypass ratio refers to the ratio of the mass airflow that passes through the fan divided by the mass airflow that passes through the engine core.
  49. 49. 49 Turboshaft engines It delivers power to a shaft that drives something other than a propeller. The biggest difference between a turbojet and turboshaft engine is that on a turboshaft engine, most of the energy produced by the expanding gases is used to drive a turbine rather than produce thrust. Many helicopters use a turboshaft gas turbine engine. In addition, turboshaft engines are widely used as auxiliary power units on large aircraft.
  50. 50. Turbojet 50
  51. 51. Turbojet 51
  52. 52. Turboprop 52
  53. 53. Turboprop 53
  54. 54. Turbofan 54
  55. 55. 55 Turbofan
  56. 56. 56 Turboshaft engine
  57. 57. 57 Turboshaft engine
  58. 58. High bypass ratio turbofan 58
  59. 59. Low bypass ratio turbofan 59
  60. 60. Fan Bypass Ratio It is the ratio of airflow through the fan duct to the airflow through the engine core For example, if a turbofan has a bypass ratio of 6 to 1, 7 units of air are entering the intake duct with 1 unit entering the engine core and 6 units going through the fan section only 60
  61. 61. 61 Thrust versus A/C speed & drag
  62. 62. Propulsive Efficiency Compares the work done by the engine on the air mass with the work done by the engine on the aircraft. 62
  63. 63. Propulsive Efficiency Thrust (force) = mass x acceleration A turbojet gives a large acceleration to a small mass of air A turboprop gives a small acceleration to a large mass of air 63
  64. 64. Propulsive Efficiency Ratio of exhaust gas velocity to aircraft speed 64
  65. 65. • The turbofan has replaced the turbojet for commercially operated aircraft • For a turbojet and turbofan of the same rated thrust the turbofan will burn less fuel • The turbofan has less wasted kinetic energy after exiting the exhaust (exhaust velocity is closer to aircraft speed) Propulsive Efficiency 65
  66. 66. Propulsive Efficiency 66
  67. 67. Effect of aircraft speed on jet thrust Thrust = M(V2 – V1) Airspeed Ram effect Resultant thrust 250 kts 67
  68. 68. Effect of engine RPM on thrust % Engine RPM 68
  69. 69. Effect of air temperature on thrust Air Temperature 69
  70. 70. Effect of air pressure on thrust Air Pressure 70
  71. 71. Effect of altitude on thrust Altitude Stratosphere 71
  72. 72. 1 Turbine Engine © Devinder K Yadav
  73. 73. Gas Turbine Theory 2 2
  74. 74. Turbine Engine Design and Construction  Entrance Ducts (Intake)  Compressor Section  Compressor-Diffuser Section  Combustion Section  Turbine Section  Exhaust Section 3
  75. 75. Turbine Engine Entrance Ducts Properties Must furnish a uniform supply of air to the compressor in all conditions Contributes to stall-free compressor performance Must create minimal drag 4
  76. 76. Turbine Engine Entrance Ducts 5
  77. 77. Gas Turbine Entrance Ducts A divergent duct from front to back Increased static pressure to the compressor Designed to be efficient at the cruise but must still operate effectively when the aircraft is stationary and before RAM pressure recovery occurs 6
  78. 78. Turbojet inlet duct Single entrance duct 7
  79. 79. Turbojet inlet duct Divided entrance duct 8
  80. 80. Turbojet inlet duct Variable geometry ducts Divergent subsonic inlet duct Supersonic inlet duct 9
  81. 81. Turboprop inlets 10
  82. 82. Turbofan engine inlets 11
  83. 83. Inlet Guide Vanes Direct intake duct air onto the first compressor stage rotor at the correct angle of attack Both stationary and variable angle inlet guide vanes may be used 12
  84. 84. Inlet Guide Vanes 13
  85. 85. Compressor Section It’s function is to supply air in sufficient quantity to satisfy the needs of the combustor Compressors operate on the principle of acceleration of air followed by diffusion to convert the acquired kinetic energy into a pressure rise 14
  86. 86. Compressor Section A secondary purpose of the compressor section is to supply bleed air for use by the engine and aircraft systems Common bleed air uses are Cabin pressurisation Air Conditioning Aircraft pneumatic systems Anti icing, inflating door seals, suction 15
  87. 87. Compressor Section There are two types of compressors Centrifugal flow Axial flow 16
  88. 88. Centrifugal Compressor It consists of an impeller (rotor), a diffuser (stator) and a manifold. 17
  89. 89. The principal differences between the two types of impellers are size and ducting arrangement. The double-entry type has a smaller diameter but is usually operated at a higher rotational speed to ensure enough airflow. The single-entry impeller permits convenient ducting directly to the impeller eye (inducer vanes) as opposed to the more complicated ducting necessary to reach the rear side of the double-entry type. Plenum Chamber This chamber is necessary for a double-entry compressor because air must enter the engine at almost right angles to the engine axis. To give a positive flow, air must surround the engine compressor at a positive pressure before entering the compressor. Single & double entry impellers 18
  90. 90. Centrifugal Compressor Impellers 19
  91. 91. Centrifugal Compressor 20
  92. 92. Centrifugal Compressor 21
  93. 93. Centrifugal Compressor Air enters the impeller at the hub and then flows outward through impeller blades The impeller imparts rotational and outward velocity to the air which then flows into the diffuser where divergent ducts convert velocity into pressure 22
  94. 94. Centrifugal Compressor 23
  95. 95. Centrifugal Compressor 24
  96. 96. Advantages of Centrifugal Compressor High pressure rise (10:1) Good efficiency over a wide rotational speed range Robust Low cost 25
  97. 97. Disadvantages of Centrifugal Compressor Large frontal area More than two stages is not practical because of the energy losses between stages 26
  98. 98. Two stage centrifugal compressors Single stage 27
  99. 99. Two stage centrifugal compressor 28
  100. 100. Centrifugal Compressor Most common in rotorcraft and turboprop aircraft because of their robustness – more reliable on gravel runways 29
  101. 101. Axial Compressor The airflow and compression occur parallel to the rotational axis of the compressor Air Flow 30
  102. 102. Axial Compressor 31
  103. 103. Axial Compressor 32
  104. 104. Axial Compressor 33
  105. 105. 34
  106. 106. Axial Compressor 35
  107. 107. Axial Compressor 36
  108. 108. Axial Compressor 37
  109. 109. Axial Compressor 38
  110. 110. Variable stator vanes operation: They are operated by fuel pressure and scheduling is done by main engine control (fuel control unit). 39
  111. 111. Axial Compressor The air flows axially through a number of rotating rotor blades and fixed intervening stator vanes Each set of rotating blades and stator vanes is known as a compressor stage 40
  112. 112. 41
  113. 113. 42
  114. 114. Vector Diagram – complete engine 43
  115. 115. 44
  116. 116. Axial compressor roots and tips Vibration is a problem with any rotational machinery The root of the compressor disk is often only loosely fitted to the hub As the compressor rotates centrifugal loading locks the blade in its correct position and the air stream over the airfoil provides a shock mounting or cushioning effect 45
  117. 117. To avoid energy losses (including shock waves) over the tips of the rotor blades, the clearance between the rotor and the surrounding shroud must be kept to a minimum Newer engines are designed to rotate within a shroud strip of abradable material Sometimes during coastdown a high pitched noise can be heard if the blade tip and shroud strip are touching 46
  118. 118. Advantages of Axial Flow Compressors Higher compression available by addition of compression stages Small frontal area and lower drag 47
  119. 119. Disadvantages of Axial Compressors High cost of manufacture Relatively high weight Higher starting power requirements Lower pressure rise per stage Good compression in the cruise and take off power settings only 48
  120. 120. Combination Compressors Popular in many small turbine engines (Pratt and Whitney PT 6) 49
  121. 121. Axial Compressor There are three designs of axial flow compressors Single spool Double spool Triple spool 50
  122. 122. Axial Compressor (N1) (N2) Spools are not mechanically linked together 51
  123. 123. Multi Spool Compressors For any given power setting the high pressure compressor speed is held constant by the fuel control unit The low pressure compressor(s) will speed up and slow down with changes in engine inlet conditions resulting from atmospheric changes 52
  124. 124. Trent 900 triple spool compressor 53
  125. 125. Advantages of multi-spool axial compressors Less power required for starting Less prone to compressor stalling Quicker acceleration 54
  126. 126. Compressor Stall & Surge Compressor blades, being aerofoils, can stall at too high an angle of attack the close proximity of blades in different stages means that if one stage stalls, so may the next 55
  127. 127. Angle of Attack and compressor stall Compressor stalls cause air flowing through the compressor to slow down, stagnate or reverse direction this is then know as an engine surge Any change to the design airflow will have an effect to all other sections of the gas turbine engine 56
  128. 128. 57
  129. 129. 58
  130. 130. 59
  131. 131. Angle of Attack and compressor stall Causes Excessive fuel flow changes Turbulent air Contaminated or damaged compressors Contaminated or damaged turbine blades Engine operation outside design RPM Too rapid movement of throttles 60
  132. 132. Angle of Attack and compressor stall Can occur during a cross wind take-off Can occur during a steep turn Detected by Audible noise and/or vibration Fluctuating RPM Increased EGT 61
  133. 133. Angle of Attack and compressor stall Reverse air flow may result in the compressor blades bending and contacting the stator vanes Sophisticated engines use: bleed air to reduce the possibility of compressor stall, or variable incidence guide vanes 62
  134. 134. 63
  135. 135. Turbine Engine © Devinder K Yadav 1
  136. 136. Gas Turbine Theory 3 2
  137. 137. The Combustion Section The combustion process must ideally be able to efficiently convert chemical energy to heat energy under all operating situations from engine start to engine shut down A chemically correct (stoichiometric) mixture is approximately 15:1 air/fuel 3
  138. 138. The Combustion Process The temperature of the gases released by combustion can be well in excess of 15000C which will destroy the combustion chamber and turbine section About 60% of the air entering the combustion chamber is used for cooling only 4
  139. 139. The Combustion Process 5
  140. 140. 6
  141. 141. The Combustion Process To function properly the combustion chamber must 1. Provide a proper environment for the mix of air and fuel 2. Cool the hot gases to a temperature the turbine section components can withstand To accomplish this the airflow through the combustor is divided into primary and secondary paths 7
  142. 142. The Combustion Process Air from the compressor may enter the combustion chamber in excess of 500 feet per second (300 knots) The axial flow of the primary airflow must be reduced to about 5 feet per second (3 knots) Because of the slow flame propagation rate of jet fuels if the primary velocity were too high it would blow the flame out (flame out) 8
  143. 143. The Combustion Process The reduction in axial velocity is achieved by swirl vanes which create radial motion and retard axial motion The air from the swirl vanes and secondary air holes interact and create a region of low velocity circulation This forms a toroidal vortex similar to a smoke ring stabilising and anchoring the flame 9
  144. 144. The Combustion Process 10
  145. 145. The Combustion Process 11
  146. 146. The Combustion Process The combustion process is complete in the first one third of the combustion liner In the remaining two thirds of the combustor length the combusted and uncombusted gas is mixed to provide an even heat distribution at the turbine nozzle 12
  147. 147. Flame Out Although uncommon in modern engines they still occur Some common causes are Turbulent weather High altitude Violent flight maneuvers 13
  148. 148. The Combustion Process ** Be careful when quoting air/fuel ratios** 14
  149. 149. Flame Out Flame out (lean) Usually occurs at low fuel pressures at low engine speeds in high altitude flight Flame out (rich) Usually occurs during fast engine acceleration in which an over rich mixture causes combustion pressure to increase until compressor flow stagnates Turbulent inlet conditions can also cause stalls15
  150. 150. Flame Out To minimise the possibility of flame out it is essential to have a correct matching of compression ratio, mass airflow and engine speed 16
  151. 151. Combustion Chamber Types The various combustion chambers in use include Multiple can Can Annular Annular reverse flow Annular 17
  152. 152. Multiple Can 18
  153. 153. Multiple Can This type of combustion chamber is more common with centrifugal flow compressors and earlier types of axial flow compressors The separate flame tubes are interconnected to allow a constant pressure and also propagate combustion around the flame tubes during starting 19
  154. 154. Can Annular 20
  155. 155. Annular 21
  156. 156. Annular Reverse Flow 22
  157. 157. Annular Reverse Flow Common in turboprop engines as this arrangement provides shorter engine length and also a weight reduction 23
  158. 158. Garrett TPE 331 Reverse Flow Combustion Chamber 24
  159. 159. Fuel Supply Fuel is supplied to the combustion chamber by one of two methods The most common is the injection of a fine atomised spray into the re-circulating airstream through spray nozzles 25
  160. 160. The Combustion Process 26
  161. 161. Fuel Supply The second fuel supply method is based on the pre-vaporisation of the fuel before it enters the combustion zone The fuel/air mix is carried in a vaporising tube which passes through the primary flame area of the combustion chamber More common in low power engines 27
  162. 162. The Turbine Section The turbine section is bolted onto the combuster and contains nozzle guide vanes, turbine rotors and turbine stators The turbine functions to transform a portion of the kinetic and heat energy in the exhaust gases into mechanical work to drive the compressor, propeller, fan and accessories 28
  163. 163. The turbine section 29
  164. 164. The turbine section Turbine Stator Turbine Rotor 30
  165. 165. The turbine section • Since energy is extracted from the airflow through a turbine section, pressure decreases across the turbine section • Hence the boundary layer is much more likely to remain attached than in the compressor section • Each stage of the turbine section can support several stages of compressor 31
  166. 166. The turbine section 32
  167. 167. The turbine section 33
  168. 168. The turbine section 34
  169. 169. The turbine section 35
  170. 170. The turbine section 36
  171. 171. The turbine section 37
  172. 172. The turbine section 38
  173. 173. The turbine section 39
  174. 174. The turbine section 40
  175. 175. 41
  176. 176. 42
  177. 177. Turbine Blades Turbine blades extract energy from the gas stream in two ways Reaction Impulse 43
  178. 178. Reaction turbine blades Reaction drives the blades via an aerodynamic reaction The gas stream is accelerated by convergent nozzle guide vanes and directed to flow over the turbine blades producing an aerodynamic reaction 44
  179. 179. Impulse turbine blades Impulse turbine blades rotate via impact of high velocity gas on the blades The blades of a pure impulse turbine are bucket shaped to maximise the conversion of kinetic energy to mechanical energy 45
  180. 180. 46
  181. 181. Turbine Blades Most turbine blades combine both impulse and reaction principles The degree of reaction depends on the type of engine 47
  182. 182. Turbine Blades Turbojets require high exhaust velocities to produce thrust so they use high reaction turbine blades to produce maximum acceleration Turboprops and APUs use impulse turbine blades because they are concerned with power extraction and not thrust 48
  183. 183. Turbine Blades Turbofans use reaction/impulse blades to extract energy to drive the fan while maintaining reasonably high exhaust velocity for core engine thrust 49
  184. 184. Turbine Blades • Higher entry pressure at the blade tips means that, to create a uniform exit flow, blade profiles are adjusted to a reaction profile at the tip 50
  185. 185. 51
  186. 186. Turbine Blade Creep Turbine blades are subject to enormous stress loads A blade weighing only 8 grams may have to resist a centrifugal force of over 2000 kg This causes turbine blades to lengthen with continued use – known as creep 52
  187. 187. 53
  188. 188. 54
  189. 189. Turbine Blade Creep If manufacturer’s temperature or rpm limits are exceeded the creep rate increases and blade life is drastically reduced Overhauls are timed to ensure that blades are replaced before tertiary creep begins 55
  190. 190. Turbine Temperature Measurement Ideally temperature probes should be placed in the turbine inlet to measure turbine inlet temperature (TIT) The temperature at the turbine inlet is usually too hot to place temperature probes 56
  191. 191. Turbine Temperature Measurement Temperature probes are usually placed in an intermediate stage (ITT) or at the turbine outlet stage (TOT) ITT and TOT readings are often compensated to give an indication of the temperature at the most critical point – the turbine inlet 57
  192. 192. Turbine blade cooling • Cooled by internal air cooling system 58
  193. 193. Exhaust Section The exhaust section is located behind the turbine section and usually consists of a convergent cone to convert pressure energy to kinetic energy 59
  194. 194. Exhausts 60
  195. 195. Exhausts 61
  196. 196. Exhausts 62
  197. 197. Engine Exhausts 63
  198. 198. Exhausts 64
  199. 199. Engine exhausts • Convergent exhaust duct 65
  200. 200. Exhausts 66
  201. 201. Exhausts 67
  202. 202. Exhausts 68
  203. 203. Exhausts 69
  204. 204. Exhausts 70
  205. 205. Exhausts 71
  206. 206. Accessory Section The primary function is to provide space for the mounting of accessories necessary for operation and control of the engine. It also includes accessories concerned with the aircraft, such as electric generators and fluid power pumps. Secondary functions include acting as an oil reservoir and/or oil sump, and housing the accessory drive gears and reduction gears. Accessories are usually mounted on common pads either ahead of or adjacent to the compressor section. 72
  207. 207. Accessory Section 73
  208. 208. Accessory Section Accessory Section 74
  209. 209. Accessory Section 75
  210. 210. Accessory Section 76
  211. 211. Accessory Section 77
  212. 212. Accessory Section 78
  213. 213. Accessory Section 79
  214. 214. Auxiliary Power Units 80
  215. 215. Auxiliary Power Units A gas turbine powerplant Supplies the aircraft with Bleed air Electrical power Hydraulic power 81
  216. 216. Auxiliary Power Units Used mainly during ground operations, take-off and landing Most can be used in flight as a back up supply source but usually have an operating altitude limit 82
  217. 217. Auxiliary Power Units APUs have the following features: Operate at a constant RPM Start sequence is fully automatic Vital parameters are automatically monitored Automatic shutdown with any faults 83
  218. 218. Auxiliary Power Units A typical cockpit panel consists of: Start and stop button Turbine temperature indicator (EGT) RPM indicator Control switches for bleed air, hydraulic and electrical generation 84
  219. 219. 85
  220. 220. Many turbofan engines have two or more spools to A. improve the cooling of the combustion chamber walls resulting in a lower turbine temperature B. assist the compressor sections to rotate closer to their ideal RPM C. reduce vibration within the engine core D. increase spool up time required when compared to a single spool And….. the answer is……….. 86
  221. 221. An ideal jet intake delivers air to the compressor in which state? A. No turbulence and pressure lower than ambient B. Increased radial velocity and temperature higher than ambient C. Increased temperature and velocity compared ambient conditions D. No turbulence and pressure higher than ambient And….. the answer is……….. 87
  222. 222. The row of stator blades after each row of compressor blades in n axial flow compressor is designed to A. longitudinally balance the engine B. convert axial flow to radial flow before the next rotating compressor section C. convert kinetic energy to pressure energy D. Convert pressure energy to pressure energy And….. the answer is……….. 88
  223. 223. Of a turbofan’s total air passing through the intake 21% goes through the engine core. The bypass ratio is closest to A. 4:1 B. 5:1 C. 1:5 D. 1:4 And….. the answer is……….. 89
  224. 224. Which of the following would increase the maximum possible performance of a jet engine? A. introduce the air into the engine at a lower speed B. introduce the air into the engine at a lower temperature C. introduce the air into the engine at a higher temperature D. introduce the air into the engine at a lower pressure And….. the answer is……….. 90
  225. 225. Gas decreases in velocity and increases in pressure when A. flowing through a convergent duct B. it is within the last two thirds of the combustion chamber C. it is within the nozzle guide vanes prior to the first turbine rotor section D. flowing through a divergent duct And….. the answer is……….. 91
  226. 226. What is meant by tertiary creep in a turbine blade of a gas turbine engine? A. blade creep experienced on the test bench by the manufacturer B. normal blade creep during the acceptable working life of the turbine blade section C. blade creep that could be detrimental to continued use of the turbine section D. an unruly university aviation student And….. the answer is……….. 92
  227. 227. For a given engine RPM, thrust output from a gas turbine engine will be greatest A. At MSL in ISA conditions B. At high altitude in ISA conditions C. At high altitude in ISA + conditions D. At MSL in ISA + conditions And….. the answer is……….. 93
  228. 228. 94