# 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 C _{v} and C_{c},
how the coefficient of discharge calculated?**

Coefficient of discharge = C_{v}
x C_{c}

**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.

• The sum of pressure head, kinetic head and datum head gives the Total Energy Line (TEL).

• 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/m^{2}

*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 10 ^{5}, 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?*

For positive pressure gradient

*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 (H _{m}) of a centrifugal pump?*

Manometer head (H_{m}) = Total
head at outlet - Total head at inlet

**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?*

Yes. The vanes are adjustable

*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.

#### About Sreejith Hrishikesan

Sreejith Hrishikesan Nair is a M-Tech graduate in Communication Systems. He completed B-tech Degree in Electronics and Communication.He is a person who wants to implement new ideas in the field of Technology.

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