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COMPRESSIBLE FLOW 901

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26. For compressible fluid flow the area-velocity relationship is
    (a) dA
    A
    = dVV (1 – M^2 )(b) dAA = dVV (C^2 – 1)

(c) dA

A

= dVV (M^2 – 1) (d) dA

A

= dVV (1 – V^2 ).

27. The sonic velocity is largest in which of the following?
    (a) Water (b) Steel
    (c) Kerosene (d) Air.


28. Which of the following expressions does not represent the speed of sound in a medium?

(a)

K

ρ (b) γRT

(c) K

p

ρ (d)

dp

dρ.

29. The differential equation for energy in isentropic flow is of the form
    (a) dV
    V
    
    
    • dp
      ρ +
    
    
    
    

dA

A

= 0 (b) VdV +

dp

ρ = 0

(c) 2VdV +

dp

ρ = 0 (d) dp + d (ρV

(^2) ) = 0.

30. Which of the following statements is incorrect?
    (a) A shock wave occurs in divergent section of a nozzle when the compressible flow changes abruptly
    from supersonic to subsonic state
    (b) A plane moving at supersonic state is not heard by the stationary observer on the ground until it passes
    him because zone of disturbance in Mach cone trails behind the plane
    (c) A divergent section is added to a convergent nozzle to obtain supersonic velocity at the throat
    (d) none of the above.
    ANSWERS


31. (b) 2. (b) 3. (c) 4. (b) 5. (d) 6. (b) 7. (e)


32. (a) 9. (b) 10. (b) 11. (b) 12. (c) 13. (a) 14. (a)


33. (c) 16. (c) 17. (c) 18. (b) 19. (b) 20. (d) 21. (d)


34. (a) 23. (d) 24. (c) 25. (a) 26. (c) 27. (b) 28. (c)


35. (b) 30. (c).

Theoretical Questions

1. Differentiate between compressible and incompressible flows.


2. Give the examples when liquid is treated as a compressible fluid.


3. When is the compressibility of fluid important?


4. What is the difference between isentropic and adiabatic flows?


5. What is the relation between pressure and density of a compressible fluid for (a) isothermal process
   (b) adiabatic process?


6. Obtain an expression in differential form for continuity equation for one-dimensional compressible flow.


7. Derive an expression for Bernoulli’s equation when the process is adiabatic.


8. How are the disturbances in compressible fluid propagated?


9. What is sonic velocity? On what factors does it depend?


10. What is Mach number? Why is this parameter so important for the study of flow of compressible fluids?