Comparison of Flow Analysis through Sudden Contraction and Enlargement of Pipes by Providing Smooth Corners

1. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 205
Comparison of Flow Analysis through Sudden Contraction
and Enlargement of Pipes by Providing Smooth Corners
S. Sambhu Prasad1
, G. Satish2
, G.Panduranga3
1
Professor & Principal, 2,3
Assistant Professor, Department of Mechanical Engineering, Pragati Engineering
College, Andhra Pradesh, India
Abstract— This project deals with the computational fluid
dynamics analysis of flow in sudden enlargement and
contraction pipes. This project describes an analytical
approach to describe the areas where Pipes (used for flow)
are mostly susceptible to damage. In this project we
discussed to know the pressure values and velocity values at
sudden contraction and sudden enlargement of pipes. The
software used for this purpose are GAMBIT and FLUENT.
The 2D model of the both the pipes are made by GAMBIT
and analysis is to be carried out by FLUENT. The models
are first generated using the data and then are meshed and
then various velocity and pressure contours are to be drawn
and graphs to analyze the flow through the pipes. Various
graphs indicating the variation of velocity, pressure and
temperature along the stream length of the pipes are given.
Comparisons were made with the sharp corners and smooth
corners for the pipe..
Keywords-Gambit, Fluent, 2D model..,
I. INTRODUCTION
Flow through ducts with sudden (sharp-edged)
contractions occurs in many industrial applications.
The flow separation in the vicinity of the contraction
plane causes an increase in pressure loss, which
affects erosion rates and heat and mass transfer rates at
the separation. Pipe contractions exist in a variety of
process and chemical plants. In order to determine the
overall pumping power in a piping system, it is
essential to have reliable design procedures to predict
pressure losses. It is also important to know the flow
details of the separations upstream and downstream of
the contraction plane to avoid placing sensitive
equipment in these regions.
The pressure loss through the contraction is caused by
two consecutive processes:
(1) Contraction of the flow to the vena contract, and
(2) Expansion to the wall of the small pipe.
The latter is an ―uncontrolled‖ expansion against an
adverse pressure gradient. Vena contracta is the point
in a fluid stream where the diameter of the stream is
the least, and fluid velocity is at its maximum, such as
in the case of a stream issuing out of a nozzle,
(orifice).The maximum contraction takes place at a
section slightly downstream of the orifice, where the
jet is more or less horizontal.
The effect is also observed in flow from a
tank into a pipe, or a sudden contraction in pipe
diameter. Streamlines will converge just downstream
of the diameter change, and a region of separated
flow occurs from the sharp corner of the diameter
change and extends past the vena contracta.
The reason for this phenomenon is that fluid
streamlines cannot abruptly change direction. In the
case of both the free jet and the sudden pipe diameter
change, the streamlines are unable to closely follow
the sharp angle in the pipe/tank wall. The converging
streamlines follow a smooth path, which results in the
narrowing of the jet (or primary pipe flow) observed.
Sudden expansions are when the area of the pipe
increases suddenly along the length of the pipe (at a
90 degree angle). The downstream velocity will be
lower than the upstream velocity. In Energy lost is
because of turbulence. Amount of turbulence depends
on the differences in pipe diameters.
II. PROCEDURE
A. Modeling of the 2d geometry:
The modeling of the pipe is done by considering
the following cases to do the flow analysis.
Case1: The pipe with sudden contraction with sharp
corners.
Figure 2.1: Meshed profile Sudden Contraction pipe
with sharp corners generated in GAMBIT.
Case2: The pipe with sudden contraction with round
corners
Figure 2.2: Meshed profile Sudden Contraction pipe
with round corners generated in GAMBIT.
Case3: The pipe with sudden enlargement with sharp
corners

2. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 206
Figure 2.3: Meshed profile Sudden Enlargement pipe
with sharp corners generated in GAMBIT.
Case4: The pipe with sudden enlargement with round
corners
Figure 2.4: Meshed profile Sudden Enlargement pipe
with round corners generated in GAMBIT.
B. Fluent Analyses.
FLUENT is the software used for modeling fluid
flow and heat transfer in complex geometries. It
provides complete mesh flexibility, including the
ability to solve your flow problems using unstructured
meshes that can be generated about complex
geometries with relative ease. It is written in the C
computer language and makes full use of the
flexibility and power offered by the language.
Consequently, true dynamic memory allocation,
efficient data structures, and flexible solver control are
all possible. All functions required to compute a
solution and display the results are accessible in
FLUENT through an interactive, menu-driven
interface.
The basic procedural steps for solving a problem in
FLUENT include:
1) Define the modeling goals.
2) Create the model geometry and grid.
3) Set up the solver and physical models.
4) Compute and monitor the solution.
5) Examine and save the results
6) Consider revisions to the numerical or physical
model parameters, if necessary
C. Solver, Material Selection & Operating Condition
Defining in Fluent:
The solver is defined first. Solver is taken as
pressure based and formulation as implicit, space as
2D and time as unsteady. Velocity formulation as
absolute and gradient options as Green-Gauss Cell
based are taken. Energy equation is taken into
consideration. The viscous medium is also taken. First
the analysis is carried using laminar flow and then the
k-epsilon is considered. 2 results are to be found out.
The selection of material is done. Material selected is
water-liquid. The properties of
Water -liquid is taken as follows-
i. Density = 998.2 kg/m3
ii. Cp (specific heat capacity) = 4182 J/kg K
iii. Thermal conductivity = 0.6W/m K
iv. Viscosity =0.001003 kg/m s
The analysis is carried out under operating conditions
of 101325 Pascal. Gravity (981 mm/sec2
) is taken into
consideration.
D. Boundary Conditions:
1. Fluid
Fluid is taken as water-liquid.
2. Inlet
Velocity inlet was taken for the nozzle inlet and the
value of velocity inlet was taken as 2m/sec. Initial
gauge pressure was taken as 101325 Pascal.
Temperature was taken as 500K.
3. Outlet
The diffuser was set as outflow and the flow rate as 1.
4. Wall
In wall, the motion of wall is selected as stationary
wall.
5. Controls Set Up
The solution is set as listed below. The under
relaxation factor was set as given-
Pressure-0.3
Density-1
Body forces-1
Momentum-0.7
Pressure Velocity Coupling was taken as
SIMPLE
Discretization Equation are selected as given-
Pressure- Standard
Momentum- First Order Upwind
Energy- First Order Upwind (For turbulent
flow Power Law was taken into
Consideration)
6. Initialization
Solution initialization is done. Initial values of
velocity are taken as 2m/sec along all zones of
direction. Temperature is taken as 500K.
Residual Miniaturization is done and convergence
criteria are set up. The convergence
Criteria of various parameters are listed below.
Continuity- 0.001
X-Velocity- 0.001
Y-Velocity- 0.001

3. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 207
Z-Velocity- 0.001
Energy- 1e-06
The number of iterations is then set up and iterations
starts. The iteration continues till convergence is
reached.
III RESULTS
A. Flow Analysis in Sudden Contraction:
(With Sharp corners):
Figure 3.1: Sudden Contraction (Velocity
Behaviour)
Figure 3.2: Sudden Contraction (Velocity Behaviour)
Figure 3.3: Vena Contracta.
Figure 3.4: Sudden Contraction (Pressure Behaviour)
Figure 3.5: Sudden Contraction (Pressure Behaviour).
Figure 3.6: Sudden Contraction (Turbulent Behaviour)
Figure 3.7: Sudden Contraction (Turbulent Behaviour).
Table 3.1: Parameters.
S.No. Parameter Min. Max.
1
Pressure
(pascal)
92151.74 112316.3
2 Velocity (m/s) 0 5.021684
3
Turbulent K.E
(k)
0.003131546 1

4. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 208
Table 3.2: Mass Flow Rate.
MASS FLOW RATE (Kg/s)
Default-Interior 79557.105
Inlet 79856.001
Outlet -79854.269
Wall 0
Net 1.7317627
B. Flow Analysis in Sudden Contraction:
(With round corners of radius 5mm):
Figure 3.8: Sudden Contraction (Velocity Behaviour)
Figure 3.9: Sudden Contraction (Velocity Behaviour)
Figure 3.10: Sudden Contraction (Pressure Behaviour)
Figure 3.11: Sudden Contraction (Pressure Behaviour).
Figure 3.12: Sudden Contraction (Turbulent
Behaviour)
Figure 3.13: Sudden Contraction (Turbulent
Behaviour).
Table 3.3: Parameters.
S.No. Parameter Min. Max.
1
Pressure
(pascal)
96756.22 110142.2
2 Velocity (m/s) 0 4.407094
3
Turbulent K.E
(k)
0.004398072 1
Table 3.4: Mass Flow Rate.
MASS FLOW RATE (Kg/s)
Default-Interior 104506.82
Inlet 79856.001
Outlet -79855.961
Wall 0
Net 0.039694196
C. Flow Behaviour in Sudden Enlargement
(With Sharp corners):
Figure 3.14: Sudden Enlargement (Velocity Behaviour)

5. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 209
Figure 3.15: Sudden Enlargement (Velocity Behaviour)
Figure 3.16: Sudden Enlargement (Pressure Behaviour)
Figure 3.17: Sudden Enlargement (Pressure
Behaviour).
Figure 3.18: Sudden Enlargement (Turbulent
Behaviour)
Figure 3.19: Sudden Enlargement (Turbulent
Behaviour).
Table 3.5: Parameters.
S.No. Parameter Min. Max.
1
Pressure
(pascal)
100426.9 101375.1
2 Velocity (m/s) 0 2.109524
3
Turbulent K.E
(k)
0.002080848 1
Table 3.6: Mass Flow Rate.
MASS FLOW RATE (Kg/s)
Default-Interior 199345.33
Inlet 39928
Outlet -39928.963
Wall 0
Net -0.96245855
D. Flow Analysis in Sudden Enlargement:
(With round corners of radius 5mm):
Figure 3.20: Sudden Enlargement (Velocity Behaviour)
Figure 3.21: Sudden Enlargement (Velocity Behaviour)

6. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 210
Figure 3.22: Sudden Enlargement (Pressure Behaviour)
Figure 3.23: Sudden Enlargement (Pressure
Behaviour).
Figure 3.24: Sudden Enlargement (Turbulent
Behaviour)
Figure 3.25: Sudden Enlargement (Turbulent
Behaviour).
Table 3.7: Parameters.
S.No. Parameter Min. Max.
1 Pressure
(pascal)
99371.92 101325.8
2 Velocity (m/s) 0 2.115486
3 Turbulent K.E
(k)
0.002659606 1
Table 3.8: Mass Flow Rate.
MASS FLOW RATE (Kg/s)
Default-Interior -398294.2
Inlet 39928
Outlet -39928.772
Wall 0
Net -0.77170309
E. Comparison Of Velocity’s For Different
Geometry’s:
Figure 7.5.1: Comparison
A Sudden Contraction with sharp corners.
B Sudden Contraction with round corners.
C Sudden Enlargement with sharp corners.
D Sudden Enlargement with round corners.
IV THEORITICAL CALCULATIONS
(Sudden Contraction Pipes):
Let,
D1 be the diameter of cross-section area 1 =
0.04m
D2 be the diameter of cross-section area 2 =
0.02m
The inlet velocity V1 =2m/sec
Area A1=1.257*10-3m
Area A2 =0.314*10-3m
Outlet velocity V2=?
By applying Continuity equation
A1V1=A2V2
V2= A1V1/ A2
V2 =8.0063 m/sec
Head loss =
= 0.5
= m of water.
Experimental Calculations:
By using FLUENT software,
Velocity outlet = 4.58 m/sec.

7. International Journal of Engineering Trends and Technology (IJETT) – Volume 25 Number 4- July 2015
ISSN: 2231-5381 http://www.ijettjournal.org Page 211
Velocity inlet = 2 m/sec.
Head loss =
= 0.5
= 0.53 m of water.
After making Round Corners
Velocity inlet = 2 m/sec.
Velocity outlet = 4.33 m/sec
Head loss =
=0.5
= 0.47 m of
water.
V. CONCLUSION:
From the above analysis, it is observed that
the flow is severely disrupted if there are contour
changes occurring in the downstream flow in the pipe.
Sudden enlargement creates more severe formation of
flow eddies than sudden contraction. Also, the losses
are more at the point where the enlargement in the
pipe begins.
In the sudden contraction, vena contracta’s
are formed at the point of contraction and this point is
the most susceptible point for pipe damage. So, to
increase the life of the pipe in cases of sudden
contraction the pipes must be designed in view of the
above observations making the corners more rounds
so as to minimize the losses in the pipes
To conclude, this examination results
indicate that FLUENT can be used with high degree of
accuracy to visualize the minor or singular head losses
due to minor appurtenances and accessories present in
a pipe network.
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