O BJECTIVE Q UESTIONS (IES, IAS)
3. Specific volume decreases 4. Temperature decreases
(a) 2, 3 and 4 (b) 1, 2 and 4 (c) 1, 3 and 4 (d) 1, 2 and 3 IES-64. Ans. (d)
IES-65. Assertion (A): A normal shock wave can occur at any section in a convergent-divergent nozzle. [IES-2008]
Reason (R): A normal shock wave occurs only when the flow of the fluid is supersonic and the subsequent flow after the shock is subsonic.
(a) Both A and R are true and R is the correct explanation of A (b) Both A and R are true but R is NOT the correct explanation of A (c) A is true but R is false
(d) A is false but R is true
IES-65. Ans. (d) A shock wave takes place in the diverging section of a nozzle, in a diffuser, throat of a supersonic wind tunnel, in front of sharp-nosed bodies.
IES-66. Consider the curves in the sketch shown below (indicates normal shock)
Out of these curves, those which are not correctly drawn will include
(a) 1 and 2 (b) 3 and 4 (c) 2 and 4 (d) 1 and 5
[IAS-1998]
IES-66. Ans. (c)
IES-67. The given figure represents a schematic view of the arrangement of a supersonic wind tunnel section. A normal shock can exist without affecting the test conditions. [IES-1993]
Compressible Flow
S K Mondal’s Chapter 15
(a) Between sections 4 and 5 (b) At section 4
(c) Between sections 4 and 3 (d) Between sections 1 and 2 IES-67. Ans. (d) A normal shock can exist between 1 and 2 without affecting the test
conditions, as it can be swallowed through the second throat by making it larger than the first.
IES-68. In a perfect gas having ratio of specific heats as 1.4 what is the strength of a normal shock with upstream Mach number equal to 5.0? [IES-2004]
(a) 27 (b) 28 (c) 29 (d) 24
IES-68. Ans. (b) Strength of normal shock = ( ) ( )1
pressre rise across the shock P upstream pressure P
Δ
2 2
1
2 2 1.4
M 1 5 1 28
1 1.4 1
γ γ
⎡ ⎤ × ⎡ ⎤
= + ⎣ − ⎦ = + ×⎣ − ⎦=
IES-69. Assertion (A): A normal shock always makes a supersonic flow of a compressible fluid subsonic, but an oblique shock may not ensure subsonic flow after the shock. [IES-2003]
Reason (R): A normal shock reduces the stagnation pressure and stagnation enthalpy considerably whereas the loss at oblique shock is minimized.
(a) Both A and R are individually true and R is the correct explanation of A (b) Both A and R are individually true but R is not the correct explanation of A (c) A is true but R is false
(d) A is false but R is true IES-69. Ans. (c)
IES-70. Which one of the following is correct for tangential component of velocities before and after an oblique shock? [IES-2009]
(a) Unity (b) Equal (c) Unequal (d) None of the above IES-70 Ans. (b)
IES-71. Introduction of a Pitot tube in a supersonic flow would produce[IES-1994]
(a) Normal shock at the tube nose (b) Curved shock at the tube nose
(c) Normal shock at the upstream of the tube nose (d) Curved shock at the upstream of the tube nose IES-71. Ans. (a)
inlet pressure is given by the relation
( )
/ 1
1
2 1 pB
p
γ γ
γ
− −
⎡ ⎤
= ⎢⎣ + ⎥⎦ [IES-1996]
If the back pressure is lower than PB given by the above equation, then (a) The flow in the nozzle is supersonic.
(b) A shock wave exists inside the nozzle.
(c) The gases expand outside the nozzle and a shock wave appears outside the nozzle.
(d) A shock wave appears at the nozzle exit.
IES-72. Ans. (c)
IES-73. At which location of a converging - diverging nozzle, does the shock- boundary layer interaction take place? [IES-1995]
(a) Converging portion (b) Throat (c) Inlet (d) Diverging portion IES-73. Ans. (d) Shock-boundary layer interaction takes place in diverging portion of
nozzle.
IES-74. A converging diverging nozzle is connected to a gas pipeline. [IES-2006]
At the inlet of the nozzle (converging section) the Mach number is 2. It is observed that there is a shock in the diverging section. What is the value of the Mach number at the throat?
(a) < 1 (b) Equal to 1 (c) > 1 (d) ≥1 IES-74. Ans. (b)
IES-75. Shock waves in nozzles would occur while turbines are operating (a) At overload conditions (b) At part load conditions (c) Above critical pressure ratio (d) At all off-design conditions IES-75. Ans. (d)
Oblique Shock Wave
IES-76. For oblique shock, the downstream Mach number: [IES-1997]
(a) Is always more than unity (b) Is always less than unity (c) May be less or more than unity (d) Can never be unity.
IES-76. Ans. (c) If M > 1, then weak shock wave, If M < 1, then strong shock wave.
Fanno Line
IES-77. Assertion (A): In the case of Fanno line flow, in the subsonic region friction causes irreversible acceleration. [IES-1997]
Reason (R): In the case of Fanno line, flow, decrease in entropy is not possible either for supersonic or subsonic flows.
(a) Both A and R are individually true and R is the correct explanation of A (b) Both A and R are individually true but R is not the correct explanation of A (c) A is true but R is false
(d) A is false but R is true IES-77. Ans. (c)
IES-78. During subsonic, adiabatic flow of gases in pipes with friction, the flow properties go through particular mode of changes. Match List-I (Flow
Compressible Flow
S K Mondal’s Chapter 15
properties) with List-II (Mode of changes) and select the correct
answer: [IES-2002]
List-I List-II
A. Pressure 1. Increase in flow direction
B. Density 2. Decreases with flow direction
C. Temperature
D. Velocity
Codes: A B C D A B C D
(a) 1 1 2 2 (b) 2 2 2 1
(c) 2 2 1 2 (d) 2 1 1 2
IES-78. Ans. (d)
IES-79. The prime parameter causing change of state in a Fanno flow is:
[IES-1998]
(a) Heat transfer (b) Area change (c) Friction (d) Buoyancy IES-79. Ans. (c)
IES-80. Fanno line low is a flow in a constant area duct: [IES-1997]
(a) With friction and heat transfer but in the absence of work.
(b) With friction and heat transfer and accompanied by work.
(c) With friction but in the absence of heat transfer or work.
(d) Without friction but accompanied by heat transfer and work.
IES-80. Ans. (c) Fanno line flow is the combination of momentum and continuity equation. For constant area duct fanno line flow with friction but in the absence of heat transfer and work.
IES-81. In the Fanno line shown in the given figure
(a) Subsonic flow proceeds along PQR.
(b) Supersonic flow proceeds
along PQR.
(c) Subsonic flow proceeds along PQ and supersonic flow proceeds along RQ.
(d) Subsonic flow proceeds along RQ and supersonic flow
proceeds along PQ. [IES-1994]
Fanno Line Representation of Constant Area Adiabatic Flow
IES-82. Which one of the following statements is correct about the Fanno flow?
(a) For an initially subsonic flow, the effect of friction is to decrease the Mach
number towards unity [IES-2007]
(b) For an initially supersonic flow, the effect of friction is to increase the Mach number towards unity
(c) At the point of maximum entropy, the Mach number is unity (d) Stagnation pressure always increases along the Fanno line IES-82. Ans. (c)
IES-83. Which one of the following is the correct statement? [IES-1999]
(a) The Mach number is less than 1 at a point where the entropy is maximum whether it is Rayleigh or Fanno line.
(b) A normal shock can appear in subsonic flow
(c) The downstream Mach number across a normal shock is more than one (d) The stagnation pressure across a normal shock decreases
IES-83. Ans. (d)
IES-84. The effect of friction on flow of steam through a nozzle is to:
(a) Decrease the mass flow rate and to increase the wetness at the exit (b) Increase the mass flow rate and to increase the exit temperature (c) Decrease the mass flow rate and to decrease the wetness of the steam (d) Increase the exit temperature, without any effect on the mass flow rate IES-84. Ans. (c) The effect of friction of flow of steam through a nozzle is to decrease the
mass flow rate and to decrease the wetness of the steam.
Rayleigh Line
IES-85. Rayleigh line flow is a flow in a constant area duct: [IES-1997]
(a) With friction but without heat transfer (b) Without friction but with heat transfer (c) With both friction and heat transfer (d) Without either friction or heat transfer
IES-85. Ans. (b) Reyleigh line flow in a constant area duct without friction but with heat transfer. Fanno line flow is a flow in a constant area duct with friction but in the absence of heat transfer and work.
Compressible Flow
S K Mondal’s Chapter 15
IES-86. Which of the following assumptions/conditions are true in the case of
Rayleigh flow? [IES-2005]