Fluid machenics Flashcards
What are the laws affecting fluid motion?
(ESE 2009
(a) The principle of conservation of mass.
(b) Newton’s laws of motion and viscosity.
(c) The first and second laws of thermodynamics.
Why mercury is preferred for use in barometer
and in other pressure measuring devices?
The low vapour pressure along with its high
density.
1.25 Define kinematic viscosity and ~ .. ‘
viscosity.
Kinematic V1scos1ty is the mea . su~ ~ ~e
resist1ve flow of a fluid under the .
1
nfl . uence of
gravity. It may also be defined as the ab
1
t . f fl . sou e viscosity o a Uld divided by its denslt .
Absolute viscosity is the resistance t~ flow
encountered when one layer or plane of fluid
attempts to move over another identical layer
of plane of fluid at a given speed, Absolute
viscosity is also called dynamic viscosity
Differentiate between solid and liquid?
(ESE 2012
Solid, which is a state of matter that has a fixed
volume and shape with atoms that are bound
tightly to each other that makes It resistant to
change. They can only change if they are cut or
broken by force,
Liquid,which is another state of matter that .has
no shape and takes the shape of the conta1ner
that holds it.’ Atoms in a liquid, although also
bound together but are temporary thus allowing
them to move freely and flow.
What is hydraulic engineering?
Hydraulic engineering is a sub-discipline of civil
engineering and is concerned with the flow and
conveyance of fluids, principally water and
sewage. One feature of these systems is the
extensive use of gravity as the motive force to
cause the movement of the fluids. This area of
civil engineering is intimately related to the design
of bridges, dams, channels, canals, and levees
and to both sanitary and environmental
engineering
What is viscosity?
ESE 2016
It is the property of fluid by virtue of which it
offers resistance to the movement of one layer
to adjacent layer. It occurs mainly due to
cohesion between the fluid particles and the
exchange of momentum between the fluid
layers.
It is expressed as shear stress per unit rate of
change of shear strain i.e.
‘t
J.l = dv!dy
Its Sl unit is N.s/m2 or Pa.s.
How viscosity varies with velocity?
ESE 2016
Viscosity is the property of a fluid which is
independent of fluid velocity. However it
depends on the fluid temperature.
Explain various properties of fluid?
ESE 2016
The various properties of fluid are as under:
Mass density: It is the mass of fluid per unit
its volume i.e.
Mass density {p) = Mass of the fluid (M) I
Volume of the fluid (V).
Its Sl unit is kglm3.
Specific weight: It is the weight of fluid per
unit volume of the fluid i.e.
Specific weight (w) = Weight of the fluid (W) I
Volume of the fluid (V)
Its Sl unit is Nlm3.
Specific volume: It is the volume of the fluid
per unit weight of the fluid i.e.
Specific volume = Volume of fluid (V)I Weight
of the fluid (W)
Its Sl unit is m3IN.
Viscosity: It is the property of fluid by virtue of
which it offers resistance to the movement of
one layer to adjacent layer. It occurs mainly due
to cohesion between the fluid particles and the
exchange of momentum between the fluid
layers.
It is expressed as shear stress per unit rate of
change of shear strain i.e.
‘t
11 = dv! dy
Its Sl unit is N.slm2 or Pa.s.
Surface tension: It is the property of fluid film
by virtue of which it exerts tension and Is
expressed as,
Surface tension (a)= Force (F)Ilength(L)
Its Sl unit is N/m.
What Is Pascal’s law?
ESE 2012
According to Pascal’s law the intensity of
pressure at any point in a static fluid is same In
all directions.
What Is stable equilibrium?
If centre of buoyancy lies directly above the
centre of gravity.
What do you understand by, stagnation
pressure and dynamic pressure?
Stagnation pressure: The point where the fluid
is at rest is called as stagnation point (like in
Pitot’s tube) and the pressure at that point is
called as stagnation pressure.
Dynamic pressure: The pressure anywhere in
the flowing fluid is called as dynamic pressure.
What is velocity potential function?
It is a scalar function of space and time, its
negative derivative with respect to any direction
gives the fluid velocity in that direction.
What Is convective acceleration?
It is the rate of change of velocity due to the
change of position of fluid particles in a fluid
flow.
How can you say that the fluid flow is
irrotational?
If velocity potential exists, the flow should be
irrotational or if stream function satisfies the
Laplace equation, then also the fluid flow is
irrotational
What is a stream function?
It is that function whose partial derivative with
respect to any direction gives the velocity
component at right angles to that direction.
What is flow net?
A grid obtained by drawing a series of
equipotential lines and stream lines is called
flow net
What is streamlined and bluff body?
A body whose surface coincides with the
streamlines, when the body is placed in a ftow
is called streamlined body. If the surface of the
body does not coincide with the stream lines,
the body is called bluff body.
Is the flownet analysis applicable to
rotational flow? If not, why?
Flow net analysis is applicable to rotational ftow
as well however if the flow is irrotational then
the problem can be solved graphically. Flow
net is very useful in analyzing two dimensional
irrotational flow problems.
A cylindrical tank half filled with a liquid is
rotated about its vertical axis with a certain
constant speed. If the liquid at the sides
reaches at the top of the tank, what would
be the level of water at the axis of rotation?
In this case, the depth of water at the middle
on the vertical axis of rotation is equal to twice
the rise of liquid on the sides
What is Euler’s equation of motion?
ESE 2012
Euler’s equation of motion considers only two
forces, namely the pressure force and the fluid
weight or the body force.
How can you determine the flow rate?
ESE 2008
The numerical difference in stream function
between two streamlines is equal to the flow
rate per unit width passing between them.
What is forced vortex?
ESE 2016
When a fluid is rotated about a vertical axis at
constant speed, every particle of it has the same
angular velocity and the fluid moves as if it were
a solid. This type of motion is known as forced
vortex.
What is continuity equation?
ESE 2012
Continuity equation is a mathematical
expression of conservation of mass . This
equation is based on the principle that the mass
of any matter can neither be created nor be
destroyed.
What are assumptions of continuity
equation?
(ESE 2016)
In continuity equation, It is assumed that flow
rate is constant. It Is based on principle of
conservation of mass I.e. mass can neither be
created nor be destroyed.