Unit 1: Fundamentals of Gas Turbine - Practice Quiz

1 What is the correct basic sequence of processes in a gas turbine engine?

2 What is the primary function of the compressor in a gas turbine engine?

3 Which component normally supplies the power required to drive the compressor?

4 Which equation represents the basic net thrust of a jet engine?

5 In the thrust equation, what does represent?

6 When the nozzle exit pressure equals ambient pressure , what is the pressure-thrust term?

7 If all other conditions remain constant, how does increasing engine mass flow rate affect thrust?

8 If flight speed remains constant, what generally happens when exhaust velocity increases?

9 For fixed nozzle exit pressure and area, what happens to pressure thrust when ambient pressure increases?

10 At the same inlet temperature, what is the usual effect of increasing compressor inlet pressure?

11 What happens to the static pressure of inlet air as it slows down in an ideal diffuser?

12 At constant pressure, how does a rise in compressor inlet temperature usually affect air density?

13 Which thrust-augmentation method burns additional fuel downstream of the turbine?

14 Why can water injection increase gas turbine thrust?

15 Which engine type is generally most efficient for aircraft flying at low to moderate subsonic speeds?

16 Which component produces most of the thrust in a typical turboprop engine?

17 What does the bypass ratio of a turbofan compare?

18 What is a common advantage of a high-bypass turbofan during subsonic flight?

19 Which statement best describes airflow through a basic turbojet?

20 Compared with a turboprop, a turbojet is generally better suited to which operating condition?

21 Which sequence correctly represents the principal energy-conversion processes in a simple turbojet engine?

22 In a steady-running turbojet, the turbine extracts only part of the combustion-gas energy primarily because the remaining energy is needed to:

23 An ideal diffuser slows the air entering a gas turbine without heat or shaft work. Which change should occur?

24 Which equation gives the uninstalled net thrust of a single-stream jet engine when fuel mass flow is included?

25 A turbojet processes of air. Neglect fuel flow and pressure thrust. If and , what is the net thrust?

26 A nozzle has an exit area of and an exit pressure above ambient pressure. What pressure thrust does it produce?

27 For a perfectly expanded nozzle, which term in the thrust equation becomes zero?

28 If exhaust velocity and mass flow remain constant while aircraft speed increases, what directly causes net momentum thrust to decrease?

29 For an engine with constant mass flow of and constant exhaust velocity, flight speed increases from to . Neglecting pressure thrust, by how much does net thrust change?

30 Two engines produce the same ideal momentum thrust. Engine X accelerates a large mass of air by a small velocity increment, while Engine Y accelerates a small mass by a large increment. Which generally has higher propulsive efficiency at subsonic speed?

31 An aircraft operates at the same speed and inlet temperature but moves to a region of lower ambient pressure. What is the most likely effect on uncorrected engine thrust?

32 On a hot day, an engine runs at the same physical rotational speed and ambient pressure as on a cold day. Why does its thrust generally decrease?

33 An inlet suffers a larger total-pressure loss because of flow separation. At otherwise similar operating conditions, what is the expected engine response?

34 For an adiabatic inlet, increasing flight velocity increases the inlet stagnation temperature according to . If static temperature is unchanged, what follows?

35 Why does an afterburner increase turbojet thrust?

36 Water or water-methanol injection at the compressor inlet is most useful during hot-day takeoff because it:

37 A turbojet afterburner raises thrust from to while fuel flow rises from to . Which statement is correct?

38 Which engine is generally most suitable for an aircraft requiring high propulsive efficiency at low-to-medium subsonic speed and strong takeoff performance?

39 A turbofan has a core mass flow of and a bypass mass flow of . What is its bypass ratio?

40 Which comparison among turbojets, low-bypass turbofans, and high-bypass turbofans is generally valid?

41 Which description correctly represents the energy and pressure changes through a practical single-spool turbojet operating steadily?

42 A turbojet compressor raises the stagnation temperature from to . The turbine inlet temperature is , compressor and turbine specific heats are equal, and shaft mechanical efficiency is . If the turbine drives only the compressor, what is the turbine exit stagnation temperature?

43 A turbojet ingests of air and adds of fuel. It flies at and exhausts at . The nozzle exit area is and . Neglect inlet pressure forces. What is the net thrust?

44 An underexpanded nozzle operates with unchanged exit mass flow, velocity, pressure, and area while ambient pressure decreases by . If , how does net thrust change under these assumptions?

45 An engine ingests of air at and discharges at . Its nozzle has and . Which pair gives gross thrust and net thrust, respectively?

46 A geometrically fixed turbojet operates at the same corrected speed and turbine temperature ratio at two altitudes. Inlet stagnation temperature is unchanged, but inlet stagnation pressure at the second condition is of the first. Neglect Reynolds-number effects. What approximate thrust ratio is expected?

47 A compressor runs at unchanged physical shaft speed when its inlet stagnation temperature rises from to . By approximately what percentage does corrected speed change?

48 Air at enters an ideal adiabatic intake at . Using , what stagnation temperature reaches the compressor face if intake heat transfer and velocity there are negligible?

49 An inlet distortion or loss reduces compressor-face stagnation pressure by without changing stagnation temperature. If the compressor remains at the same corrected operating point, which first-order result is most appropriate?

50 Why does an afterburning turbojet generally require a variable-area exhaust nozzle when afterburner fuel is scheduled?

51 Which statement best explains how water or water-methanol injection can augment takeoff thrust on a hot day?

52 A static turbojet produces dry momentum thrust with and . With afterburning, these become and . If both nozzles are perfectly expanded, what is the thrust increase?

53 At , an ideal turboprop produces an effective slipstream speed of , while an ideal turbojet has . Using , which comparison is correct?

54 An unmixed turbofan has core airflow , fuel flow , and bypass ratio . At flight speed , core and bypass exit velocities are and . With both streams perfectly expanded, what is net thrust?

55 For a high-supersonic aircraft where small frontal area and high specific thrust dominate over subsonic fuel economy, which engine characteristic most strongly favors a turbojet over a high-bypass turbofan?

56 Two ideal engines produce the same thrust at the same subsonic flight speed. One accelerates a large mass flow by a small velocity increment; the other accelerates a small mass flow by a large increment. Which conclusion follows from momentum and kinetic-energy considerations?

57 For an ideal, perfectly expanded jet with negligible fuel mass, show the rate of jet kinetic-energy increase per unit thrust as . If and , what is this ratio?

58 A convergent nozzle remains choked while upstream stagnation conditions and throat area are fixed. Ambient pressure decreases, but the nozzle exit remains at the critical pressure. What happens to ideal one-dimensional nozzle thrust?

59 A turbojet ingests airflow and adds fuel flow . If pressure thrust is zero, by how much does the approximation underestimate the exact momentum thrust? Use and .

60 Compressor inlet stagnation pressure rises by and stagnation temperature rises by , while physical shaft speed and physical mass flow remain unchanged. What happens to corrected speed and corrected flow ?