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Unit 6: Elementary Turbine Design - Practice Quiz

ASE202 — Propulsion-I 60 Questions
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1 What is the primary function of a gas turbine?

Introduction Easy
A. Convert shaft work into gas pressure
B. Convert gas energy into shaft work
C. Convert liquid fuel into electricity
D. Convert electrical energy into heat

2 Which turbine component directs the gas flow toward the rotor blades?

Introduction Easy
A. Shaft support bearings
B. Fuel injection nozzles
C. Stationary nozzle guide vanes
D. Rotating compressor blades

3 In an ideal impulse turbine stage, where does the pressure drop mainly occur?

Impulse and reaction turbine Easy
A. Across the turbine shaft
B. Across the moving blades
C. Across the stationary nozzles
D. Across the exhaust duct

4 In a reaction turbine stage, the pressure decreases through which blade rows?

Impulse and reaction turbine Easy
A. Neither stationary nor moving rows
B. Only the final exhaust row
C. Only the stationary blade row
D. Both stationary and moving rows

5 What is the main purpose of turbine compounding?

Compounding of turbine Easy
A. Increase fuel temperature before combustion
B. Reduce rotor speed to practical values
C. Eliminate the need for turbine blades
D. Raise compressor pressure in one row

6 In pressure compounding, the total pressure drop is divided among:

Compounding of turbine Easy
A. Several shaft bearings
B. Several turbine stages
C. Several combustion chambers
D. Several exhaust pipes

7 Turbine isentropic efficiency compares actual turbine work with:

Efficiency of turbine Easy
A. Ideal isentropic turbine work
B. Mechanical loss in bearings
C. Heat supplied during combustion
D. Compressor work at inlet

8 Which condition generally indicates a more efficient turbine?

Efficiency of turbine Easy
A. Actual work approaches ideal work
B. Blade leakage increases rapidly
C. Exhaust losses become larger
D. Bearing friction increases steadily

9 In a turbine velocity diagram, blade speed is directed:

Velocity diagrams Easy
A. Tangentially to the rotor
B. Radially toward the shaft
C. Normally to the casing
D. Axially through the rotor

10 Which velocity component acts parallel to the turbine axis?

Velocity diagrams Easy
A. Blade velocity component
B. Radial velocity component
C. Whirl velocity component
D. Axial velocity component

11 For constant blade speed, turbine specific work is commonly expressed as:

Work and efficiency Easy
A.
B.
C.
D.

12 Turbine power output equals mass flow rate multiplied by:

Work and efficiency Easy
A. Gas static pressure
B. Rotor angular position
C. Specific turbine work
D. Turbine blade area

13 The degree of reaction is the ratio of rotor static enthalpy drop to:

Degree of reaction Easy
A. Compressor static pressure rise
B. Total stage static enthalpy drop
C. Exhaust kinetic energy loss
D. Combustor total temperature rise

14 What is the degree of reaction of an ideal impulse turbine stage?

Degree of reaction Easy
A.
B.
C.
D.

15 Why are multiple turbine stages used?

Turbine multi staging and stage performance Easy
A. To eliminate the working fluid
B. To divide energy extraction among stages
C. To prevent all rotor rotation
D. To maintain constant gas pressure

16 A turbine stage normally consists of:

Turbine multi staging and stage performance Easy
A. One compressor and one diffuser
B. One stator row and one rotor row
C. One bearing and one exhaust pipe
D. One combustor and one fuel pump

17 Which factor commonly limits the maximum turbine inlet temperature?

Factors limiting turbine design Easy
A. Shaft paint color selection
B. Bearing housing surface finish
C. Exhaust pipe external shape
D. Blade material temperature capability

18 Increasing turbine rotational speed mainly increases which blade load?

Factors limiting turbine design Easy
A. Hydrostatic load
B. Magnetic load
C. Centrifugal load
D. Buoyancy load

19 In internal convection cooling, cooling air flows through:

Cooling of turbine blade Easy
A. Passages inside the blade
B. Fuel lines near the combustor
C. Nozzles inside the compressor
D. Bearings outside the casing

20 What is the purpose of film cooling on a turbine blade?

Cooling of turbine blade Easy
A. Raise the blade metal temperature
B. Increase friction along the surface
C. Block airflow through the turbine
D. Form a cool layer over the surface

21 In an axial-flow turbine stage, what is the primary function of the stator followed by the rotor?

Introduction Medium
A. The stator cools the gas, and the rotor maintains constant velocity
B. The stator accelerates the gas, and the rotor extracts shaft work
C. The stator extracts shaft work, and the rotor raises gas pressure
D. The stator compresses the gas, and the rotor reduces its entropy

22 A turbine operates at a fixed angular speed. If its mean blade radius is increased, what is the most likely direct effect?

Introduction Medium
A. Blade speed increases while centrifugal stress decreases
B. Blade speed and centrifugal stress both decrease
C. Blade speed decreases while work capacity increases
D. Blade speed and centrifugal stress both increase

23 For an ideal impulse turbine stage, where does the static pressure drop occur?

Impulse and reaction turbine Medium
A. Equally in the stator and rotor
B. Almost entirely in the moving rotor
C. Only in the downstream diffuser
D. Almost entirely in the stator nozzle

24 An axial turbine stage has equal static enthalpy drops in its stator and rotor. What type of stage does this most closely represent?

Impulse and reaction turbine Medium
A. A zero-work stage
B. A 50% reaction stage
C. A pure impulse stage
D. A fully reaction stage

25 Which arrangement characterizes a velocity-compounded Curtis turbine stage?

Compounding of turbine Medium
A. One nozzle row followed by multiple moving rows and guide rows
B. Multiple nozzle rows followed by one moving blade row
C. Alternating compressors and turbines on separate shafts
D. One moving row followed by multiple exhaust diffusers

26 Why is pressure compounding used in a Rateau turbine?

Compounding of turbine Medium
A. To concentrate the full pressure drop in one rotor
B. To eliminate all stationary nozzle blade rows
C. To divide a large pressure drop among several stages
D. To maintain constant pressure through every stage

27 A turbine has an actual stagnation enthalpy drop of and an isentropic stagnation enthalpy drop of . What is its total-to-total isentropic efficiency?

Efficiency of turbine Medium
A.
B.
C.
D.

28 A turbine has an internal efficiency of and a mechanical efficiency of . Neglecting other losses, what fraction of the isentropic work appears as shaft work?

Efficiency of turbine Medium
A.
B.
C.
D.

29 A turbine rotor has blade speed , inlet whirl velocity , and exit whirl velocity . What is the specific work output?

Velocity diagrams Medium
A.
B.
C.
D.

30 At turbine-rotor inlet, the axial velocity is and the whirl velocity is . What is the absolute flow angle measured from the axial direction?

Velocity diagrams Medium
A.
B.
C.
D.

31 For a simple ideal impulse turbine with symmetrical moving blades, the nozzle angle is measured from the wheel direction. Which blade-speed ratio gives maximum diagram efficiency?

Work and efficiency Medium
A.
B.
C.
D.

32 A turbine stage produces of Euler work from an available isentropic enthalpy drop of . What is its diagram efficiency?

Work and efficiency Medium
A.
B.
C.
D.

33 The static enthalpy drops across the stator and rotor of a turbine stage are and , respectively. What is the degree of reaction?

Degree of reaction Medium
A.
B.
C.
D.

34 A turbine stage has a total static enthalpy drop of and a degree of reaction of . What is the rotor static enthalpy drop?

Degree of reaction Medium
A.
B.
C.
D.

35 A four-stage turbine is designed with equal ideal enthalpy drops and a total ideal drop of . What is the ideal drop per stage?

Turbine multi staging and stage performance Medium
A.
B.
C.
D.

36 A turbine stage has a stagnation enthalpy drop of and a blade speed of . What is its stage-loading coefficient ?

Turbine multi staging and stage performance Medium
A.
B.
C.
D.

37 If turbine blade speed is increased by , approximately how does centrifugal stress change when other relevant quantities remain constant?

Factors limiting turbine design Medium
A. It increases by about
B. It increases by about
C. It remains approximately unchanged
D. It increases by about

38 As gas expands through an axial turbine, its density decreases. If mass flow and axial velocity remain nearly constant, how should the annulus flow area change?

Factors limiting turbine design Medium
A. It should decrease through the turbine
B. It should increase through the turbine
C. It should first decrease and then vanish
D. It should remain constant throughout

39 Which blade-cooling method forms a protective layer of cooler air over the external blade surface?

Cooling of turbine blade Medium
A. Internal convection through ribbed passages
B. Thermal conduction through the blade root
C. Film cooling through surface holes
D. Radiative cooling from the trailing edge

40 Cooling effectiveness is defined as . If , , and , what is the blade metal temperature ?

Cooling of turbine blade Medium
A.
B.
C.
D.

41 For an adiabatic axial turbine stage with negligible clearance losses, which statement correctly describes the ideal energy transformations through the stationary and rotating blade rows?

Introduction Hard
A. Static enthalpy remains constant through the stator, increases through the rotor, and rothalpy is conserved through the stator
B. Stagnation enthalpy decreases through the stator, remains constant through the rotor, and rothalpy decreases through the rotor
C. Stagnation enthalpy remains constant through the stator, decreases through the rotor, and rothalpy is conserved through the rotor
D. Rothalpy decreases through the stator, stagnation enthalpy increases through the rotor, and static enthalpy remains constant

42 Which pressure and energy distribution most accurately distinguishes an ideal impulse stage from an ideal reaction stage?

Impulse and reaction turbine Hard
A. An impulse stator has negligible static-pressure drop, whereas a reaction stator receives all of the stage static-enthalpy drop
B. An impulse rotor has the entire stage pressure drop, whereas a reaction rotor operates at approximately constant static pressure
C. An impulse rotor has negligible static-pressure drop, whereas a reaction rotor converts part of its static-enthalpy drop into relative kinetic energy
D. An impulse stage produces no rotor work, whereas a reaction stage produces work only through centrifugal pressure forces

43 An ideal single-stage impulse turbine has at measured from the wheel tangent. The blade speed is . The rotor blades are symmetrical, and the relative speed is unchanged. What is the specific work?

Velocity diagrams Hard
A.
B.
C.
D.

44 In an axial turbine stage, , , , and , where absolute-flow angles are measured from the axial direction and whirl is signed. Determine the specific work and the rotor-inlet relative angle from the axial direction.

Velocity diagrams Hard
A. and
B. and
C. and
D. and

45 A turbine stage has constant axial velocity, blade speed , rotor-inlet whirl , and rotor-exit whirl . Neglecting losses, what is the degree of reaction?

Degree of reaction Hard
A.
B.
C.
D.

46 For a constant-axial-velocity stage, define , with signed absolute-flow angles measured from the axial direction. Which condition produces reaction?

Degree of reaction Hard
A.
B.
C.
D.

47 An ideal two-row Curtis stage has two identical moving rows separated by an ideal fixed redirecting row. The inlet whirl is , axial velocity is constant, and each moving row reverses the relative tangential component without loss. Which blade-speed ratio gives maximum total work?

Compounding of turbine Hard
A.
B.
C.
D.

48 A single ideal impulse stage is replaced by three identical Rateau pressure-compounded stages having equal isentropic enthalpy drops. Each stage is operated at its own optimum speed ratio. Relative to the original optimum wheel speed , what wheel speed is required, and how does the ideal total work change?

Compounding of turbine Hard
A. , with unchanged ideal total work
B. , with unchanged ideal total work
C. , with one-third the ideal total work
D. , with three times the ideal total work

49 A turbine produces of actual shaft work. At the same inlet state and outlet pressure, the isentropic total-to-total and total-to-static enthalpy drops are and , respectively. What are and ?

Efficiency of turbine Hard
A. and
B. and
C. and
D. and

50 A single impulse rotor receives flow at from the wheel tangent. Its speed ratio is , its relative-speed ratio is , and its inlet and outlet blade angles are equal. Neglecting nozzle loss, what is its diagram efficiency?

Work and efficiency Hard
A.
B.
C.
D.

51 A multistage turbine has a common stage isentropic efficiency of . Its reheat factor, defined as the sum of individual isentropic stage drops divided by the overall isentropic drop, is . What is the overall turbine isentropic efficiency?

Turbine multi staging and stage performance Hard
A.
B.
C.
D.

52 Three turbine stages have isentropic drops of , , and and stage efficiencies of , , and . The overall isentropic drop between the turbine end states is . Which pair gives the overall efficiency and reheat factor?

Turbine multi staging and stage performance Hard
A. and
B. and
C. and
D. and

53 The first rotor of a multistage turbine discharges at . An interstage blade row can recover of this kinetic energy as useful availability for downstream work. Relative to complete loss of the discharge velocity, what is the maximum work improvement?

Turbine multi staging and stage performance Hard
A.
B.
C.
D.

54 A uniform, untapered turbine blade has density , hub-to-tip radius ratio , and allowable root centrifugal stress . Neglecting gas bending and stress concentration, what is the maximum tip speed?

Factors limiting turbine design Hard
A.
B.
C.
D.

55 A turbine nozzle receives a perfect gas with at stagnation pressure . Neglecting losses, below what back-pressure ratio will further reduction of back pressure fail to increase mass flow through the minimum area?

Factors limiting turbine design Hard
A.
B.
C.
D.

56 A stage requires at loading coefficient . Structural stress limits to , while a relative-Mach constraint with limits it separately. Which constraint governs, and what is the maximum work at fixed ?

Factors limiting turbine design Hard
A. Structural stress governs;
B. Relative Mach number governs;
C. Relative Mach number governs;
D. Structural stress governs;

57 Film-cooling effectiveness is defined by . If , , and , what blade-metal temperature is implied?

Cooling of turbine blade Hard
A.
B.
C.
D.

58 A blade surface is exposed to gas at with . Coolant enters at , and the metal must not exceed . Neglect wall resistance and assume equal gas-side and coolant-side areas. What minimum coolant-side coefficient is required?

Cooling of turbine blade Hard
A.
B.
C.
D.

59 At a film-cooling hole exit, and . The mainstream has and . What is the coolant blowing ratio ?

Cooling of turbine blade Hard
A.
B.
C.
D.

60 A flat blade wall separates gas at from coolant at . Given , , wall thickness , and conductivity , determine the hot-side and cold-side wall temperatures.

Cooling of turbine blade Hard
A. and
B. and
C. and
D. and
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