1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
67
NUMERICAL ANALYSIS OF VELOCITY VECTORS PLOTS AND
TURBULENT KINETIC ENERGY PLOTS OF FLOW OF THE AIR
CURTAIN
Mr Nitin Kardekar, Principal, Jayawantrao Sawant Polytechnic.
Research Scholar, Singhania University.
Dr. V K Bhojwani, Professor, JSPM’s Jayawantrao Sawant College of Engineering, Pune
Dr Sane N K, Research Supervisor, Singhania University
ABSTRACT
A prototype is developed in the laboratory in order to simulate the conditions of the
entrance of the doorway installed with air curtain device. The air curtain blows the air in
downward direction. The flow within the air curtain is simulated with commercial
Computational Fluid Dynamics (CFD) solver, where the momentum equation is modelled
with Reynolds-Average Navier-Stokes (RANS)’ K- ε turbulence model. The boundary
conditions are set up similar to the experimental conditions. The CFD results are compared
and validated against experimental results. The results are obtained in the form of contours;
which are plotted for velocity and turbulent kinetic energy. The velocity vectors are studied
to observe the infiltration through the air curtain and weak velocity zones. High turbulent
zones are identified using the turbulent kinetic energy plots.
Key words: Air curtain, Reynolds-averaged Navier – Stokes equation, K- ε turbulence
model, Velocity vectors, turbulent kinetic energy.
INTRODUCTION
.
Air curtain devices provide a dynamic barrier instead of physical barrier between two
adjoining areas (conditioned and unconditioned) thereby allowing physical access between
them. The air curtain consist of fan unit that produces the air jet forming barrier to heat,
moisture, dust, odours, insects etc. The Air curtains are extensively used in cold rooms,
display cabinets, entrance of retail store, banks and similar frequently used entrances. Study
found that air curtains are also finding applications in avoiding smoke propagation, biological
controls and explosive detection portals. According to research by US department of energy
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
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ISSN 0976 - 6480 (Print)
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2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue
1875 MW energy will be saved
display cabinet air curtains. In 2002 the UK food and drinks
tonnes of oil to power its refrigeration
developing countries like India;
are not only limited to mega cities but they
and small towns. The effects of g
luxury but are necessary part of business development
curtain with respect to Indian climate is necessary to ensure optimise
curtains which would leads to energy conservation
will be always boon for energy starving country like India
METHODOLOGY
The air flow analysis was carried out using c
V13.0 Workbench platform. As
frame. The doorway frame chosen
the frame is 290 mm. There are two slits
pushed by the blower in the domain through these
figure 1) The entire experiment is carried out at isothermal condition
(+- 10
C) at one atmosphere. The velocity of
these conditions are used for CFD
velocity. The flow domain is extended
directions of frame openings. The frame walls are
slip’ walls. It is ensured while choosing the length of extended domain that the direct
transverse flow of air curtain will not cross the boundaries of the domain
configuration is modelled, the mesh
(hexahedron mesh) is used to build the extended domain and flow straightener
portion is meshed with unstructured tetra mesh.
Figure 1 Prototype of model
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
68
MW energy will be saved per year by optimising the performance of
In 2002 the UK food and drinks industry used equivalent of 285
tonnes of oil to power its refrigeration units with most being used in cold storage
the rise in cold storages, super markets, retail store
are not only limited to mega cities but they have also become an integral part of
The effects of globalisation are inevitable. The air curtains are no more
necessary part of business development and economy. Hence study of air
curtain with respect to Indian climate is necessary to ensure optimised performance of air
leads to energy conservation. The saving of energy (Electrical energy)
energy starving country like India.
was carried out using commercial software package
As shown in figure 1 the air curtain is mounted on the top of the
The doorway frame chosen is 2270 mm in height and 900 mm in width, the
There are two slits which open in the air flow domain; the flow
pushed by the blower in the domain through these two slits which are 84 mm
e entire experiment is carried out at isothermal conditions; ambient
he velocity of air leaving the slits is measured
CFD analysis. This velocity is representative of air curtain flow
domain is extended to capture the flow leaving frame boundaries in
The frame walls are treated as impermeable walls, and are ‘no
It is ensured while choosing the length of extended domain that the direct
transverse flow of air curtain will not cross the boundaries of the domain
mesh is generated in the workbench. The structured mesh
(hexahedron mesh) is used to build the extended domain and flow straightener
portion is meshed with unstructured tetra mesh.
Prototype of model Figure 2 Geometry model
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
June (2013), © IAEME
super market
equivalent of 285
being used in cold storages. In
the rise in cold storages, super markets, retail stores, banks
integral part of suburban’s
The air curtains are no more
Hence study of air
performance of air
The saving of energy (Electrical energy)
ommercial software package ANSYS
mounted on the top of the
the breadth of
domain; the flow jet is
mm apart. (Refer
ambient air at 290
C
measured 7.6 m/s. All
velocity is representative of air curtain flow
to capture the flow leaving frame boundaries in
treated as impermeable walls, and are ‘no
It is ensured while choosing the length of extended domain that the direct
transverse flow of air curtain will not cross the boundaries of the domain. Once the
The structured mesh
(hexahedron mesh) is used to build the extended domain and flow straightener. The frame
Geometry model

3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue
Figure3 model Meshing
The effort was made to mesh the entire domain with structured mesh but due to
complex geometry at the flow straightener
total mesh count is 385443, within
hexahedral cells. The minimum mesh quality is 0.3
as per the CFD Practices this is a good
Workbench is internally transferred to CFX
platform. The flow within the air curtain is simulated within commercial Computational
Fluid Dynamics (CFD) solver, where the momentum equation is modelled
Reynolds-Average Navier-Stokes (RANS)
air at 290
C. The inlet boundary condition us
actual turbulence data at inlet is
uniform turbulence intensity of 5% (medium intensity) is used
turbulence. The outlet condition is assigned to the extended d
static pressure of zero gauge.
The computational platform is HP
processor, 8GB of RAM. The convergence target
target error of 1e-4 kg/s. The convergence target
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
69
model Meshing Figure 4 Details of meshing
The effort was made to mesh the entire domain with structured mesh but due to
complex geometry at the flow straightener the frame portion has unstructured mesh
count is 385443, within which 59589 are tetrahedral cells and 325854
The minimum mesh quality is 0.3, total 708 cells falls within this range,
ractices this is a good quality mesh. The mesh which is created in the
erred to CFX-Pre, a CFD solver available with
The flow within the air curtain is simulated within commercial Computational
Fluid Dynamics (CFD) solver, where the momentum equation is modelled
Stokes (RANS)’ K- ε turbulence model. The default domain is
The inlet boundary condition used is ‘normal speed’ at 7.6 m/s,
at inlet is currently unavailable, for the present simulation the
uniform turbulence intensity of 5% (medium intensity) is used to model the inlet
The outlet condition is assigned to the extended domain walls
The computational platform is HP- Pavilion dv6, with Intel CORE i3
The convergence target is set at 1e-4 RMS; with continuity
convergence target is achieved after 160 iterations
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
June (2013), © IAEME
Details of meshing
The effort was made to mesh the entire domain with structured mesh but due to
the frame portion has unstructured mesh. The
which 59589 are tetrahedral cells and 325854
ls falls within this range,
which is created in the
solver available with workbench
The flow within the air curtain is simulated within commercial Computational
Fluid Dynamics (CFD) solver, where the momentum equation is modelled using
The default domain is
ed is ‘normal speed’ at 7.6 m/s, since the
currently unavailable, for the present simulation the
to model the inlet
omain walls as average
avilion dv6, with Intel CORE i3 2.4GHz
with continuity
achieved after 160 iterations.

4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
70
Figure 5 Experimental and Velocity Result
Comparison (Plane2)
Figure 6 Mid Plane Locations
RESULTS AND DISCUSSIONS
The objective of the air curtain is to restrict the infiltration of outside air and thus save
the energy and keep the comfort conditions inside the space as it is. The addition of air
curtain which serves as an interface/partition between two spaces, it is very complicated flow
pattern observed in close vicinity of the air curtain device. The analysis of such a
complicated flow
Figure 7 Velocity contour (Plane 1) Figure 8 Cross flow velocity crossing
the air curtain at middle space

5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
71
Figure 9 Velocity Vector (Plane 2) Figure 10 Turbulent kinetic energy contour
Figure 11 Turbulent Kinetic Energy (plane 2) Figure 12 Velocity Streamlines (plane 1)
is difficult with experiments, whereas CFD can be handful tool to analyse the flow patterns
when validated. The velocity matrix generated with experiments at the centre plane is in
good agreement with the CFD results. The figure 5 shows the result comparison. The
validation result justifies the CFD results, and thus extends our belief for other flow results
generated which are impossible to judge experimentally. The CFD plots associated with 3
mid planes are as shown in the figure 6. Figure 7 shows transverse velocity contour on plane
3 positioned at right angle to air curtain passing through the slit. It reveals that the flow
velocity of air curtain reduces to 2.3 m/s from initial velocity 7.6 m/s till it reaches ground
and diverts sideways. The figure 9 shows velocity vector at the same plane which indicates
that the velocity vectors from both sides of the air curtain are not crossing the barrier.
This satisfies the condition of separation of environment on the either side of the
curtain. The cross flow velocities are found in the range of 0 to 1m/s. It is clear from figure
7 that cross velocity vectors on plane 1 are attracted towards low pressure zone of air jet and

6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
72
then directed downside because of high momentum of air jet which assures non cross flow
conditions. But, when cross flow velocity vectors were observed at plane 2 passing through
the space between the slits, revealed that the velocity vectors of the magnitude 0.1 to 0.83 m/s
are passing through small dead portion between 2 slits (Below motor support base). This is
the portion where air curtain is weak barrier. Figure 8 also supports this finding, that the flow
in this region is not a downward barrier flow but, it is diffused flow due to the geometry of
the air curtain. This may be the reason why air curtain is breached marginally. Hence it is
concluded to avoid separation of air entry slits if possible and if not from manufacturing point
of view, then should be kept minimal to improve the barrier effectiveness.
Figure 10 shows that turbulence kinetic energy contour at YZ plane across the air
curtain. It is observed that initially turbulence is less and as it approaches at the ground the
turbulent kinetic energy (TKE) increases, the range of TKE is of 0.39 m2
/s2
to 0.43 m2
/s2
.
This represents smooth air curtain flow initially and disturbances occur in the flow when it
reaches the ground. When jet of air curtain strikes the ground it is diverted sideways, which
causes higher TKE. When kinetic turbulence energy plots were observed from front
maximum TKE was observed near ground. However when observed in the plane 2 (figure
11) the higher turbulence kinetic energy is observed between height of 200 mm to 800 mm
from the top. The air curtain expands in XZ plane may be the reason of higher values of
TKE. Figure 12 shows the velocity streamlines starting at inlet which are smooth flow line
reaching the ground and diverting on either sides. The flow of air is found continuous,
straight and without break. This is the desired function of air curtain. In many applications
especially in refrigerated air curtains the need is to divert the flow only on one side (Inside
conditioned space). This can be accomplished by varying the jet angle with the help of guide
vane in the air curtain.
CONCLUSION
A numerical study of air curtain flow over door way was performed using CFD code
Ansys CFX 13.0. The study found the model is in good agreement with the experimental
results. The flow over curtain was found continuous, straight and without break, as per
requirement of the air curtain. The plot of turbulent kinetic energy shows the higher turbulent
region of the flow of the air curtain. The cross flow is the cause due to dead zone and not
because of flow behaviour. The region is the area of air curtain where flow is blocked
because of the base of air curtain motor. The velocity vectors of magnitude 0-0.83 m/s are
found crossing air curtain. It is recommended to avoid separation of air entry slits if possible
and if not from manufacturing point of view, then should be kept minimal.
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[1] Zhikun Cao Hua Han, Bo Gu, ‘A novel optimization strategy for the design of air
curtains for open vertical refrigerated display cases.’ Applied Thermal Science
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[3] Homayun K Navaz, Dabiri, D. & R. Faramarzi, M. Gharib, D. Modarress, ‘The
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7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME
73
[4] Brandon S Field and Erich Loth, ‘An air curtain along a wall with high inlet
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