Unit 3: Axial Flow Compressors - Practice Quiz

1 In an axial flow compressor, the air moves mainly in which direction?

2 What are the two principal blade rows in an axial compressor stage?

3 What is the primary function of the rotor in an axial compressor?

4 What is a primary function of an axial compressor stator?

5 Which velocity represents the motion of a compressor blade?

6 Which relation connects absolute velocity , blade speed , and relative velocity ?

7 In a velocity triangle, the whirl component of velocity acts in which direction?

8 According to the Euler compressor equation, the work input depends mainly on the change in which velocity component?

9 What does the degree of reaction of an axial compressor stage indicate?

10 What does a degree of reaction of represent in an ideal repeating stage?

11 Which symbol is commonly used for degree of reaction?

12 Why is axial compressor flow considered three-dimensional?

13 Where do endwall boundary layers develop in an axial compressor passage?

14 Which relation defines a free-vortex whirl distribution?

15 How does whirl velocity vary with radius in a free-vortex design?

16 What is maintained across the blade span in a constant-reaction design?

17 What is blade solidity in an axial compressor cascade?

18 What does the camber of a compressor blade describe?

19 Which operating condition involves unstable oscillations at low compressor mass flow?

20 Which condition occurs when compressor mass flow is limited by sonic velocity in a passage?

21 An axial compressor rotor operates at a blade speed of . The whirl components at rotor inlet and exit are and , respectively. What is the specific work input?

22 Air enters a compressor stage at . The pressure ratio is , the isentropic efficiency is , and . What is the actual stagnation-temperature rise?

23 At a compressor rotor exit, the axial and whirl velocity components are and . What is the absolute flow angle measured from the axial direction?

24 At rotor inlet, , , and . Using , what is the relative inlet angle measured from the axial direction?

25 For a repeating axial-compressor stage with constant axial velocity, , , and . What is the degree of reaction?

26 In an ideal repeating compressor stage with constant axial velocity, what does a degree of reaction of indicate?

27 If radial velocity is negligible, which radial-equilibrium relation applies to an axisymmetric compressor flow with tangential velocity ?

28 Why do measured compressor-blade exit angles commonly vary near the hub and casing compared with a two-dimensional midspan prediction?

29 In a free-vortex compressor design, both inlet and exit whirl components vary as . Why is the Euler work approximately constant along the blade span?

30 For free-vortex flow with constant axial velocity, how does the magnitude of absolute flow angle generally change from hub to tip?

31 At one radius of a constant-reaction design, , , and . Assuming constant axial velocity, find .

32 For a constant-reaction compressor design with constant axial velocity and angular speed, how must vary with radius?

33 A rotor blade has a metal inlet angle of , while the relative inlet flow angle is under the same sign convention. What is the incidence angle?

34 For a fixed flow turning and blade profile, what is a likely consequence of increasing blade solidity?

35 A rotor passage has relative inlet and exit speeds of and . Using a de Haller limit of , how should the design be assessed?

36 For a rotor, use . If , , , and , what is ?

37 At a fixed corrected speed, what operating limits are normally approached as compressor flow moves below and above the stable range?

38 Which pair correctly represents corrected mass flow and corrected rotational speed, apart from fixed reference-state constants?

39 Which comparison generally explains why centrifugal compressors are favored for compact low-flow applications while axial compressors are favored for large gas turbines?

40 A compressor initially operates at the intersection of its constant-speed characteristic and a system resistance curve. What usually happens when a downstream throttle is partly closed?

41 An axial-compressor stage has , , and . At , take , , and total-to-total efficiency . Neglecting mechanical losses, what is the stage total-pressure ratio?

42 Five identical axial stages each produce an actual stagnation-temperature rise of . The first-stage inlet temperature is , and every stage has and . Assuming no interstage cooling, what is the overall pressure ratio?

43 At a rotor inlet, and . The axial velocity falls from its design value of to while the inlet whirl remains fixed. If , what incidence change results for an unchanged blade metal angle?

44 A repeating -reaction stage has constant axial velocity, flow coefficient , and loading coefficient . Angles are measured as positive magnitudes from the axial direction. Which set of rotor angles is consistent with these conditions?

45 A repeating axial-compressor stage has constant axial velocity, , , and . Neglecting radial velocity and losses, what fraction of the stage static-enthalpy rise occurs in the rotor?

46 In an axisymmetric annulus, radial velocity is negligible and the absolute swirl follows a free vortex, . If density is treated as locally constant, which pressure difference satisfies radial equilibrium between hub radius and tip radius ?

47 An inviscid, adiabatic rotor streamline migrates radially while the rotor angular speed remains constant. Between two points, the quantity increases by . What follows from conservation of rothalpy?

48 At rotor inlet and exit, the whirl distributions are and . For a rotor with , which radial work distribution results?

49 A free-vortex flow has uniform . At mean radius , . What are the approximate absolute flow angles at hub radius and tip radius ?

50 A design must have both radius-independent work and constant reaction . Let , so that . Which pair of whirl distributions satisfies both requirements?

51 At radius , a rotor runs at and provides . If the local reaction is , what are and ?

52 A rotor section has , , whirl change , and solidity . Using , what is its diffusion factor?

53 A zero-inlet-whirl rotor has constant axial velocity, , and loading coefficient restricted to . If the de Haller criterion requires , what is the largest allowable ?

54 For uniform axial velocity and free-vortex inlet swirl , define and . In an annulus where , which blade-twist trend follows as radius increases?

55 A rotor design has diffusion factor at the hub and at the tip. The work distribution and local velocity triangles must remain unchanged. Which modification most directly reduces hub diffusion factor according to Lieblein's expression?

56 A centrifugal impeller has , , backswept exit angle measured from the tangential direction, and slip factor . Using and zero inlet whirl, what is the Euler work?

57 A compressor operates at fixed physical speed and mass flow while inlet total temperature rises and inlet total pressure remains constant. Using and , how does its plotted operating point move?

58 At a compressor-system equilibrium, the local compressor pressure-rise slope is , while the system-resistance slope is . Under a quasi-steady perturbation model, what is the local stability conclusion?

59 During a test, several circumferential pressure probes detect a low-speed cell moving around an axial-compressor annulus. Mean throughflow remains forward, and the plenum shows no large global pressure oscillation. Which phenomenon is present?

60 Which observation most reliably identifies aerodynamic choking on either an axial or centrifugal compressor map?