Fluid flow phenomenon

1. UREA INDUSTRY

2. Presentation Topic:
Fluid flow phenomenon,
One dimensional flow,
Velocity field
Presented to:
Engr . M Tariq
Presented by:
Makhdoom Ibad Ullah hashmi
Usman tariq

3. PRESENTATION ON FLUID FLOW
PHENOMENA

4. CONTENT
 Fluid
 Behaviour of fluid
 Potential Flow
 Behaviour of fluid stated
 Boundary layer
 For incompressible fluid
 For compressible fluid
 RHEOLOGICAL PROPERITIES OF FLUIDS

5. FLUID FLOW PHENOMENA
Fluid:
In physics a fluid is a substance that continuously deforms under an applied
shear force.
OR
A fluid is a substance that doesn’t permanently resist distortion. An attempt
to change the shape of mass of a fluid results in sliding of the layer of the fluid over
one another.
Behaviour of fluid:
Behaviour of fluid depend upon either the fluid is under the fluid
under the influence of solid bounderies
In the region where the influence of wall is small shear stress is neglible.
Fluid behaviour approach to that of an ideal fluid
The flow of such an ideal fluid is called potential flow and is completely described by
1. Newtonian mechanics
2. Conservation of mass

6. FLUID FLOWPHENOMENA
Potential Flow:
The flow of incompressible fluid with no shear is known as Potential flow
It has some important characteristics-
1. Neither circulation nor eddies forms within the stream.
Hence the potential flow is known as irrotational flow.
2. Friction cannot develop since there is no existence of
shear stress & hence there is no dissipation of mechanical energy into heat energy.
Potential flow can exist since at distance not far from solid boundries
Behaviour of fluid stated by:
A fundamenrtal behaviour of of fluid mechanics is stated by pandtl in 1904 is that of fluid
move at low velocities and high viscoties

7. FLUID FLOW PHENOMENA
Boundary layer :
The effect of solid boundary on the flow is
confined to the layer of the fluid immediately adjacent to the
solid boundary.
This layer is called Boundary Layer & also the shear stress are
confired to this part of the fluid only.
Outside the boundry layer potential flow survives

8. Outside the boundry layer potential flow survives:
Most technical fluid process are studied by considering e
the fluid stream as two parts
Parts of fluid:
(1)Boundary Layer
(2)Remaining fluid
The flow converging to boundry layer is neglected
The flow through pipes and channel fills the entire
channel and there is no potential flow

9. FLUID FLOW PHENOMENA
For incompressible fluid
Within the current of incompressible fluid under the
influence of solid boundries four proper affect appear
1) The coupling of velocity gradient and shear field
2) The onset of turbulence
3) The formation and growth of boundry layer
4) The separation of boundry layer from contact with
solid boundries

10. For compressible fluid :
In the flow of compressible fluids past solid
boundaries, additional effects appear, arising
from the significant density changes that are
charactetistic of compressible fluid

11. RHEOLOGICALPROPERITIES OF FLUIDS
Newtonian fluid – Fluid flow in simple linearity are
called Newtonian fluid. In a Newtonian fluid the
shear stress is proportional to the shear rate ,
and the proportionality constant is called the
viscosity.
where μ = co-efficient of
viscosity
Exmp- Water , Gasses etc
Non-Newtonian fluid-
1. The curve starts from origin & concave
downwards represents Pseudoplastic fluid & this
type of fluid is said to be shear rate –thinning.
Exmp – Polymer solutions , starach
suspensions etc.
2. The curve starts from origin & concave
upwards represents Dilatant fluid & this type of
fluid is said to be shear rate –thickening.
Exmp – Wet beach sand , starch in water etc
3. The straight line having some intercepts in y – axis represents Bingham plastic . This type of fluid
do not flow at all until a threshold shear stress attained & then flow linearly at shear stress
greater than Exmp – Sludge
dy
du
gc

 
FIGURE : Shear stress vs shear rate
for
Newtonian & Non-Newtonian fluid
Newtonian & Non-Newtonian fluid:-
0 0

12. Reynolds stresses :- The stress is much larger in turbulent flow than the laminar flow .
Since the shear stress is higher in turbulent flow Turbulent shear stress are called
Reynolds stresses
Eddy viscosity :- By analogy , he relationship between shear stress and velocity
gradient in a turbulent stream is used to define an eddy viscosity EV .
where E v = eddy viscosity
Also we know ,
μ = co-efficient of viscosity
The above two expression is almost similar .Hence eddy viscosity is analogous to μ .
We know, where ν=kinematic viscosity
And also,
Where =Eddy diffusivity of momentum =
Here kinematic viscosity is analogous to eddy diffusivity.
dy
du
Eg vct 
dy
du
gc

 



 DVDVDV
NRE 
mvv
RE
DV
E
DV
E
DV
N




m

vE

13. BOUNDARY LAYERS
 Here the flow of fluid is parallel
to a thin plate . A boundary is
define as the part of a moving
fluid in which a fluid is
influence by a solid boundary .
The velocity of the fluid as
solid-liquid interface is zero.
The velocity increases with
distance from the plate as
shown in figure.
Each of the curve represents the velocity profile for definite value of
x , the distance from the leading edge of the of the plate. The curves
changes slope rapidly near the plate . Line OL represents an
imaginary surface , which separates the fluid stream into two parts ,
one in which fluid velocity is constant and the other where the
velocity varies from zero to a velocity substantially equal to that of
un disturbed fluid.

14. LAMINAR & TURBULANT FLOW IN BOUNDARY LAYER
Flow near the
boundary layer is
laminar flow. Since
velocity is very low as
we move further from
the solid boundary the
velocity is fairly large
and hence the floe
become turbulance.
There are three
layers:-
1. Viscous
sublayer
2. Buffer layer
3. Turbulent

15. BOUNDARYLAYERFORMATIONIN STRAIGHT TUBUES
Considering a straight, thin-walled tube with fluid entering it at a
uniform velocity. As shown in the above fig. A boundary layer begins
to form at the entrance to the tube and as the fluid move to the first
part of the channel , the boundary layer thickens. During this stage the
boundary layer occupies only a part of the tube & total stream consists
of a core of fluid moves like a road like manner . But the velocity of
fluid is constant. In the boundary layer , the velocity varies from zero
to constant velocity existing in the core . As we further move down to
the tube , the boundary layer occupies an increasing portion of the
cross-section of the tube.
At this point , the velocity distribution in the tube reaches
its final point & remains unchanged for the remaining part of the fluid .
Such flow with an unchanging velocity distribution is called ‘Fully
Developed Flow' .

16. VELOCITY FIELD
When a stream of fluid is flowing in bulk past a
solid at the actual interface adhere between
solid and fluid.
The adhesion is a result of the force field at the
boundary, which are also responsible for the
interfacial tension between solid and fluid.
If the wall is at rest in the reference frame
chosen for the solid system ,the velocity of the
fluid at the interface is zero.

17. CON..
But at the distance away from the solid velocity
is not zero there must be variation in velocity
from point to point in the flowing system.
The velocity also vary with time

18. MATHEMATICALLY
Velocity field implies a distribution of velocity in a given region
.It is denoted in a functional form as V(x,y,z,t) .
It is useful to recall that we are studying fluid flow under the
Continuum Hypothesis which allows us to define velocity at a
point.
Further velocity is a vector quantity i.e., it has a direction
along with a magnitude. This is indicated by writing velocity
field as

19. Velocity may have three components, one in
each direction, i.e, u,v and w in x,
y and z directions respectively. It is usual to
write as

20. STEADY FLOW
If a flow is such that the properties at every
point in the flow do not depend upon time, it is
called a steady flow.
Mathematically speaking for steady flows,
where P is any property like pressure, velocity
or density. Thus

21. UN STEADY FLOW
Flow is one where the properties do depend on
time.

22. USES OF VELOCITY FIELD
The flow velocity of a fluid effectively describes
everything about the motion of a fluid.
Many physical properties of a fluid can be
expressed mathematically in terms of the flow
velocity

23. CON….
For steady flow the representation will be
For incompressible the representation will be
For ir rotational flow

24. ONE DIMENSIONAL FLOW
Term one, two or three dimensional flow refers to the
number of space coordinated required to describe a
flow.
It appears that any physical flow is generally three-
dimensional.
But these are difficult to calculate and call for as much
simplification as possible.
This is achieved by ignoring changes to flow in any of
the directions, thus reducing the complexity.
It may be possible to reduce a three-dimensional
problem to a two-dimensional one, even an one-
dimensional one at times.

25. EXAMPLE OF ONE DIMENSIONAL FLOW

26. Consider flow through a circular pipe. This flow is
complex at the position where the flow enters the
pipe.
But as we proceed downstream the flow simplifies
considerably and attains the state of a fully developed
flow.
A characteristic of this flow is that the velocity
becomes invariant in the flow direction as shown in
Fig

27. Velocity for this flow is given by
It is readily seen that velocity at any location depends
just on the radial distance from the centre line and is
independent of distance, x or of the angular position .
This represents a typical one-dimensional flow