# Fluid Mechanics Viva Questions

Fluid Mechanics Lab Viva Questions and Answers

1. What is the unit of Viscosity and kinematic viscosity?

The unit of viscosity is Poise

The unit of kinematic viscosity is Stock

2. With  respect to water column, the measured atmospheric pressure is?

10.3 m

3. How will thou calculate the gauge pressure of a particular point?

The gauge pressure is the difference of absolute pressure and atmospheric pressure.

Gauge pressure = Absolute pressure - Atmospheric pressure

4. How the velocity at a point is measured?

By using a Pilot tube

5. How can you measure the flow rate (discharge) through a pipe?

By a Venturimeter

6. In terms of Cv and Cc, how the coefficient of discharge calculated?

Coefficient of discharge = Cv x Cc

7. What is the use of a current meter?

The main application of the current meter is  for measuring the velocity. Current meter can be used in waterways, channels, rivers and the sea to precisely calculate the current velocity. It is also possible to apply the metre to contaminated water currents.

8. How can you measure the velocity from a current meter?

With the propeller mounted on the rods attached to a wire, the velocity from a current meter  is measured.

9. In a rectangular channel, when the discharge is maximum?

The discharge is maximum through a rectangular channel, when

m = d/2

Where' m' and 'd' are the hydraulic mean depth and the depth of flow

10. Write down the chezy's formula?

The chezy's formula is

Q = AC√(mi)

Where,

A  =  the area of flow of water,

m = the hydraulic mean depth (hydraulic radius),

i = slope of the bed and

'C' =  Chezy's Constant.

The velocity can be calculated as:

V = C√(mi)

11. In a trapezoidal channel, when the discharge is maximum?

The discharge is maximum when, half of top width equals the sloping side.

i.e., Half of top width = Sloping side

12. How will you define the critical depth?

When the specific energy is minimum, the depth of flow can be named as the 'critical depth'.

NOTE:

When the flow depth is 0.81 diameter, the maximum discharge through a circular channel is obtained.

In a v- notch, the rate of flow varies as H5/2.

The kinetic energy per unit weight is V2/2g.

From higher energy to lower energy, the liquid flow takes place.

In a venturimeter, the outlet length is greater than the inlet length.

It is necessary that the liquids using in manometers should have high surface tension.

We know that Kaplan turbine is a propeller turbine in which it is possible to change the vanes fixed to the hub.

The specific gravity of water is equal to 1, and the specific gravity has no unit.

The coefficient of velocity has an average value of 0.97.

The discharge in an open channel is maximum corresponds to its critical depth.

The application of a pilot-tube is for measuring the velocity at a point.

13. How will you define the Reynolds number?

The Reynolds number can be defined as the ratio of inertial force to the viscous force.

Reynolds number =  Inertial force/Viscous force

14. What is the use of a notch?

The main use of a notch is to measure the rate of flow through a small channel.

15. What is the coefficient of contraction?

The ratio between the area of the jet at the vena contracta and the area of the orifice is known as the coefficient of contraction. For a sharp orifice, the standard value may be taken as 0611 (concentric with the flow channel). The smaller the value, the greater the influence of the vena contracta.

16. What is metacentre?

Metacentre is the point, about which a floating body begins oscillating when the body is rotated.

17. What is centre of gravity?

The centre of gravity is the point, about which the weight is acting.

18.What is the use of a differential manometer?

The differential manometer is used to measure the difference between pressure at two points.

19. Define Hydraulic gradient Line (HGL)?

The Hydraulic Gradient Line or Hydraulic Grade Line (HGL) is defined as a line that joins all the liquid levels indicated throughout the pipeline by piezometers, which is linked to the pipeline. If HGL is above the pipeline centre, the pressure is positive and if HGL is below the pipeline centre, then the pressure is negative. The pressure head and the datum head are represented by HGL.

20. What is the unit of surface tension?

Unit of surface tension is Force/unit length

21. How can you convert one poise into MKS unit of viscosity?

For the conversion,

The multiplying factor = 0.1

The dividing factor for the conversion is 98.1

22. Define hydrostatic law?

As per the hydrostatic law, the specific weight of the fluid is equal to the rate of increase of pressure in vertical direction.

23. How will you explain the centre of pressure?

The centre of pressure is the resultant hydrostatic force acting through a point.

24. Which theorems deals with the law of conservation of energy and law of conservation of mass?

Law of conservation of energy - Bernoulli's theorem

Law of conservation of mass - Continuity equation

25. What is the use of pelton turbine?

The pelton turbine is used when the head on the turbine is greater than 300 m.

26. Name the fluid, which is incompressible and non-viscous (in viscid)?

The ideal fluid

27.What is the ratio of dynamic viscosity to density?

Kinematic viscosity

Kinematic viscosity = dynamic viscosity / density

28. How will you measure the discharge of liquids?

By using a notch.

29. What is the application of a critical depth meter?

The main application of a critical depth meter is to measure the hydraulic jump.

30. Which force passes through  the centroid of the liquid displaced by the body in a floating body?

The buoyant force.

31. What is the necessary and sufficient condition for the steady flow?

The necessary condition for the steady flow is that the velocity should be constant at a point with respect to time.

32. What is the use of pilot-tube?

The main use of pilot tube is to measure the velocity at a particular point.

33. What is the shape of the stress-strain graph for a Newtonian fluid?

It is a straight line

State true or false:

34. The convergent-divergent mouthpiece has maximum coefficient of discharge?

True

35. Water is a Newtonian fluid?

True

36. The similarity of motion signifies the kinematic similarity between model and a prototype?

True

NOTE:

■ One that has a hydraulic average depth equal to 1/2 depth is the most economical component of a trapezoidal channel.

■ The pressure head loss for the laminar flow through pipes varies directly as the velocity  varies.

■ In a moving liquid, the forces are viscous force, gravity force and inertia force.

■ By using Mach number, the model analysis of aeroplanes and projectiles moving at supersonic speed takes place.

■ When the area of flow increases, then the velocity also increases for a supersonic flow.

■ One poise = 0.1 Ns/m2

37. Name the flow, if the fluid particles move in layers parallel to the boundary?

Laminar flow

38. The force exerted by a flowing fluid on a solid body perpendicular to the direction of flow is termed as?

Lift Force

39. If the surface of the body doesn't coincide with the streamlines, then the body is termed as?

Bluff Body

40. For a fluid at what condition, the shear stress becomes zero?

The shear stress becomes zero when the fluid is at rest

41. Name the point through which the Buoyant force is acting?

Centre of Buoyancy

42. At what condition, the equilibrium of a floating body becomes unstable?

when metacentre falls below the centre of gravity

43. At what condition, the equilibrium is stable for a sub-merged body?

When centre of buoyancy falls above the centre of gravity.

44.  When we can say the flow is steady?

If the pressure, density, velocity, etc.. do not change with respect to time at a particular point, then we can say that the flow is steady.

45. Distinguish between  uniform flow,  compressible flow and laminar flow?

In a fluid flow, if the velocity doesn't change with respect to the length of direction of flow, then the flow is termed as uniform flow.

If the density of a fluid varies from point to point in a flow region, then the flow is termed as compressible flow.

If all the lines are parallel to the surface and the fluid particles moves in straight lines, then the flow is termed as laminar flow.

46. What is a turbulent flow?

When the fluid particles moves in a zig-zag way, the flow is termed as turbulent flow.

47. What you know about kinematics of fluid flow?

Kinematics of fluid flow is the study of fluid motion without considering the forces causing the flow.

48. which device is used for measuring the discharge?

Orifice Meter

49. When the mach number becomes less than unity, the flow is known as?

Sub-sonic flow

50. How rate of flow is measured?

By using Mouthpieces

51. What is co-efficient of velocity?

Co-efficient of velocity is defined as the ratio of actual velocity of a jet of water at vena-contracta to the theoretical velocity.

52. What is inertia force?

Inertia force is the product of mass and acceleration of a flowing liquid.

53. What you understand about velocity of approach?

Velocity of approach is the velocity with which the water approaches a notch.

54. What is the maximum efficiency of power transmission through a pipe?

66.67%

55. What is the application of bulk modulus?

For determining the mach number of a fluid.

56. Write the formula for mach number?

Mach Number = (Inertia Force / Force due to compressibility)1/2

57. What is the use of a Froude number?

Froude number is used for the model analysis of free surface flows.

58. For what types of fluids, the boundary-layer takes place?

For real fluids

59. When the Reynolds number is greater than 5 x 105, the boundary layer is called as?

Turbulent boundary layer.

60. Where the laminar sub-layer exists?

In turbulent boundary layer region

61. In which case, the separation of boundary layer takes place?

62. Due to which parameters, the drag force is exerted by a fluid on a body immersed in the fluid?

Pressure and viscous force

63. At what condition, the flow in open channel becomes turbulent?

The flow in open channel becomes turbulent when the Reynolds number is greater than 2000.

64. Differentiate  sub-critical flow, critical flow and shooting flow?

When the Froude number in open channel flow is less than 1.0, then we can say that the flow is sub-critical flow.

When the Froude number in open channel flow is equal to 1.0, then we can say that the flow is critical flow.

When the Froude number in open channel flow is greater than 1.0, then we can say that the flow is shooting flow.

65. Define specific speed of a turbine?

The specific speed of a turbine can be defined as the speed of turbine in which the turbine produces unit power at unit head.

66. Name the device that converts mechanical energy into hydraulic energy?

Pump

67. Name the device that converts hydraulic energy into mechanical energy?

Turbine

68. Define a reaction turbine?

If the total energy is kinetic energy and pressure energy at the inlet of the turbine, then  the turbine is called as reaction turbine.

69. Which turbine is a reaction radial flow turbine?

Francis Turbine

70. Which turbine is an axial flow reaction turbine?

Kaplan Turbine

71. Which tube is used for discharging water from the exit of Francis turbine and Kaplan turbine?

Draft Tube

72. Define unit speed of a turbine?

The unit speed of a turbine is the speed of the turbine, when it is working under unit head.

73. What you understand about curves at constant head of a turbine?

Main characteristic curves of a turbine

74. What you understand about curves drawn at constant speed?

Operating characteristic curves of a turbine

75. Name the curve at constant efficiency?

Muschel Curves

76. Write the equation of the manometer head (Hm) of a centrifugal pump?

77. For what reason the impellers are connected in series and parallel?

For producing a high head by multistage centrifugal pumps, the impellers are connected in series.

For discharging large quantity of liquid by multi-stage centrifugal pump, the impellers are connected in parallel.

78. At what condition, cavitation takes place?

At any point, if the pressure of the flowing fluid is less than the vapour pressure of the fluid, then cavitation takes place. Cavitation takes place in case of Francis turbine.

79. Write down the equation for the discharge through a single-acting reciprocating pump?

Q = ALN/60

80. What is the use of air vessel in reciprocating pump?

For obtaining a continuous supply of water at uniform rate.

81. By fitting an air vessel to a double acting reciprocating pump, the work saves is?

39.2%

82. What is the limiting value of separation pressure head for water?

2.5 m (abs.)

83. When the separation takes place during suction stroke and delivery stroke of a reciprocating pump?

At the beginning of suction stroke and At the end of delivery stroke.

84. What is the use of hydraulic accumulator?

The hydraulic accumulator is used for storing the energy of a fluid in the form of pressure energy.

85. What is the working principle of a hydraulic ram pump?

Water-hammer principle

86. What is the use of a hydraulic coupling device?

For transmitting same torque to the driven shaft.

87. What is the use of a torque converter?

It is used for transmitting increased or decreased torque towards the driven shaft.

88. Is it possible to adjust the vanes fixed on the hub in a Kaplan turbine?

89. What you know about the run-away speed of a Pelton wheel?

Run-away speed is the no load speed with no governor mechanism

90. What is spouting velocity?

Spouting velocity is the ideal velocity of a jet.

91. What is the use of surge tank in a pipe line?

For relieving the pressure due to water hammer, surge tank is used.

92. Which turbine is suitable for low head and high discharge?

Kaplan Turbine

93. What is free vortex flow?

Free vortex flow can be defined as the flow of water leaving the impeller in a centrifugal pump casing.

94. What is the use of a rotameter?

The rotameter is used for measuring the discharge of fluids.

95. What is the use of a hot wire anemometer?

Hot wire anemometer is used for measuring the velocity of gases.

96. When the total loss of head is same as in each pipe?

If the pipes are connected in parallel

97. What is incompressible flow?

From point to point, if the density of a fluid is constant in a flow region, the flow is called as incompressible flow.

98. What is the equation of the weight of the body, when a falling body has attained terminal velocity?

Equal to drag force plus the buoyant force

99. In laminar flow through a circular pipe, the velocity distribution follows which law?

Parabolic Law

100. Which diagram shows the variations of pressure head in the cylinder for one complete revolution of crank?

Indicator Diagram

101. Force on the projection of curved surface on a vertical plane for a submerged surface is indicated by?

Horizontal component of force due to static liquid.