Unit 1: Concepts of compressible flow - Practice Quiz

1 Which statement best describes an isentropic flow?

2 In compressible-flow analysis, which fluid property is allowed to vary significantly?

3 For steady, adiabatic flow with no shaft work and negligible potential-energy change, which quantity remains constant?

4 Which principle states that the net force on a flowing fluid equals its rate of momentum change?

5 Which velocity is commonly used as a reference when defining Mach number?

6 What is stagnation temperature?

7 Compared with its static temperature, the stagnation temperature of a moving adiabatic fluid is generally:

8 What does the local speed of sound represent?

9 For a perfect gas, which expression gives the local speed of sound?

10 At the critical state of a compressible flow, the local Mach number is:

11 How is Mach number defined?

12 A flow with is classified as:

13 What is the critical Mach number of an aircraft?

14 Which wave causes pressure, temperature, and density to increase across it?

15 Which wave commonly forms when a supersonic flow turns around a convex corner?

16 When does a moving disturbance produce a Mach cone?

17 Which relation gives the Mach angle for supersonic flow?

18 What is the Mach angle when ?

19 Which Mach-number range is commonly classified as subsonic?

20 Above which approximate Mach number are compressibility effects usually considered important in gas flow?

21 Air flows isentropically with at Mach . What is the stagnation-to-static temperature ratio ?

22 For air with flowing isentropically at , approximately what is the ratio ?

23 A gas stream accelerates from Mach to Mach . Which modeling decision is most appropriate?

24 In a steady, adiabatic nozzle with no shaft work and negligible potential-energy change, the gas velocity increases. What happens to its static enthalpy?

25 A steady one-dimensional stream has a mass flow rate of and accelerates from to . If inlet and exit pressure forces balance, what net force acts on the fluid in the flow direction?

26 For a perfect gas, the maximum theoretical velocity is . If and , what is ?

27 The critical-speed Mach parameter is defined as . For air with , what is when the ordinary Mach number is ?

28 Air at has a static temperature of . Assuming isentropic deceleration and , what is its stagnation temperature?

29 The stagnation pressure of an air stream at Mach is . Assuming and isentropic flow, what is the static pressure?

30 Calculate the speed of sound in air at using and .

31 If the absolute temperature of a perfect gas increases by a factor of four while its composition remains unchanged, how does its speed of sound change?

32 Air has a stagnation temperature of . What is its critical temperature at the sonic state, using ?

33 For an isentropic air flow with , which value most closely represents the critical pressure ratio ?

34 An aircraft travels at where the local speed of sound is . What is its Mach number?

35 An airfoil has a critical Mach number of . What first occurs when its free-stream Mach number reaches this value?

36 A supersonic stream turns smoothly around a convex corner, away from itself. Which wave pattern is produced?

37 Which set of changes occurs when an adiabatic perfect-gas flow passes through a normal shock?

38 A point disturbance moves through still air at Mach . What is the half-angle of the resulting Mach cone?

39 A Mach wave makes an angle of with the direction of a uniform supersonic flow. Approximately what is the flow Mach number?

40 An aircraft flies at a free-stream Mach number of . Which description best characterizes the likely flow around its airfoil?

41 A steady, one-dimensional, isentropic flow passes through a duct at a section where . If the area decreases slightly downstream, which statement correctly accounts for the two possible isentropic solutions at that section?

42 Air with flows isentropically from a free stream at to a location where . Using , estimate the local density change relative to the free stream.

43 A stationary normal shock occurs in air with and upstream Mach number . What is the nondimensional pressure rise ?

44 For a calorically perfect gas, define and let be the sonic speed associated with the same stagnation state. For air with , what is ?

45 Air at passes through an adiabatic normal shock. Neglecting external work, which pair correctly describes the downstream-to-upstream stagnation-property ratios?

46 For a small, high-frequency pressure disturbance in a chemically reacting gas whose composition remains frozen during propagation, which expression defines the appropriate local sound speed?

47 For isentropic air flow with , which set of critical-state ratios is correct at ?

48 The dimensionless velocity parameter is , where corresponds to the same stagnation state. For air with , what Mach number corresponds to ?

49 An airfoil has an incompressible minimum pressure coefficient . Estimate its critical Mach number by combining the Prandtl–Glauert approximation with the exact isentropic sonic pressure coefficient for .

50 Which statement correctly distinguishes finite compression and expansion waves in inviscid supersonic flow of a perfect gas?

51 An aircraft flies horizontally at at an altitude of where the sound speed is . Assuming steady motion and no atmospheric refraction, how long after passing directly overhead does its Mach cone reach the observer?

52 A uniform supersonic stream has a measured Mach angle of . If its static temperature doubles while its velocity and gas properties remain unchanged, what is the new Mach angle?

53 An airfoil operates at , but local acceleration produces a region with terminated by a shock. How should the overall flow regime be classified?

54 A converging nozzle has throat area and receives air at and . With and , the back-pressure ratio is reduced from to . What happens to the ideal mass flow rate?

55 A stationary propulsion control volume ingests at and discharges it at through an area of . The exit pressure is and ambient pressure is . With inlet and ambient pressure forces already balanced, what is the thrust?

56 Which relation correctly connects Mach number to the reference velocity ratio for a calorically perfect gas?

57 A Pitot probe is placed in an air stream at with . A normal shock stands ahead of the probe. What ratio of measured Pitot pressure to upstream static pressure, , should be expected?

58 Along an isentrope, a fluid obeys . If its pressure increases by a factor of four, by what factor does its local sound speed increase?

59 For fixed stagnation pressure and temperature, the isentropic mass flux can be written as . At which Mach number is maximized?

60 Two geometrically similar airfoils have incompressible minimum pressure coefficients and under their respective operating conditions. Under the same perfect-gas assumptions, which comparison of their critical Mach numbers is correct?