This document summarizes a study that used computational fluid dynamics (CFD) to analyze air flow velocity streamlines of air curtains. The study developed a prototype to simulate air curtain conditions at a doorway entrance. CFD simulations were conducted and validated against experimental results. The simulations analyzed velocity streamlines at different planes both with and without an obstacle (mannequin) present. Results showed straight downward air particle flow without an obstacle, but complex bending and mixing of streamlines around the obstacle. The study provides insight into air curtain barrier effectiveness under different conditions.

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
150
NUMERICAL ANALYSIS OF AIR FLOW VELOCITY STREAMLINES OF
AIR CURTAINS
Mr Nitin Kardekar
Principal, Jayawantrao Sawant Polytechnic,
Research Scholar, Singhania University, Rajasthan.
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. The air curtain device is mounted above the doorway. An obstacle of human Shape
(mannequin) is placed in the doorway to simulate the real time situation. 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 condition set up is similar to the
experimental conditions. The CFD results are compared and validated against experimental results,
after the validation stage and the air curtain velocity profiles are compared for with obstacle
situations. The results are obtained in the form of velocity streamlines at different planes. The
velocity streamlines are analysed discussed for the two cases reported and discussed in this paper.
Key words: Air curtain, Reynolds-averaged Navier – Stokes equation, K- ε turbulence Model,
velocity streamlines 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
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ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 4, Issue 5, September - October (2013), pp. 150-155
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September
portals. According to research by US department of energy
by optimising the performance of super market display cabinet air curtain
drinks industry used equivalent of 285 tonnes of
used in cold storages. In developing countr
retail stores, banks are not only limited to mega cities but they
suburban’s and small towns. The effects of globalisation are inevitable. The air curtains are no more
luxury but are necessary part of business development and economy. Hence study of air curtain with
respect to Indian climate is necessary to ensure op
leads to energy conservation. The saving of energy (Electrical energy) will be always boon for
energy starving country like India.
METHODOLOGY
In order to analyse the flow of air curtain, it
The study of velocity streamlines is essential to ensure that the air curtain does not get weak or
breaks at any section. The air flow analysis was carried out using commercial software package
ANSYS V13.0 Workbench platform. As shown in Figure 1 the air curtain is
Figure 1 Experimental set up without mannequin
(Photograph)
Figure 3 Meshing Details
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
151
portals. According to research by US department of energy 1875 MW energy will be saved
super market display cabinet air curtains. In 2002 the UK food and
used equivalent of 285 tonnes of oil to power its refrigeration units
. In developing countries like India; the rise in cold storages, super markets,
retail stores, banks are not only limited to mega cities but they have also become an
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 curtains
leads to energy conservation. The saving of energy (Electrical energy) will be always boon for
In order to analyse the flow of air curtain, it was decided to analyse the velocity streamline
The study of velocity streamlines is essential to ensure that the air curtain does not get weak or
The air flow analysis was carried out using commercial software package
Workbench platform. As shown in Figure 1 the air curtain is
without mannequin Figure 2 Geometry Model with obstacle
eshing Details Figure 4 Experimental set up with mannequin
(Photograph)
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
October (2013) © IAEME
MW energy will be saved per year
In 2002 the UK food and
units with most being
like India; the rise in cold storages, super markets,
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
performance of air curtains which would
leads to energy conservation. The saving of energy (Electrical energy) will be always boon for
nalyse the velocity streamlines.
The study of velocity streamlines is essential to ensure that the air curtain does not get weak or
The air flow analysis was carried out using commercial software package
Geometry Model with obstacle
with mannequin
(Photograph)

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September
Figure 5 Plane Definitions
mounted on the top of the frame. The doorway frame chosen is 2270 mm in height and 900 mm in
width, the breadth of the frame is 290 mm. There are two slits opens in the
pushed by the blower in the domain through these slits. The experimentation without insertion of
mannequin are carried out first then repeated after placing the mannequin in the flow of air curtain as
shown in figure 4. The entire experiment is carried out at isothermal conditions; air at 2
at one atmosphere. The velocity of l
CFD analysis, this velocity is representative of air curtain flow velocity.
domain is extended (surrounding area)
directions of frame openings. The frame walls are treated as impermeable wa
walls. It is ensured while choosing the length of
air curtain will not cross the boundaries of the domain.
is generated (Figure 3) in the workbench. The structured mesh (hexahedron mesh) is used to build
the extended domain and flow straightener. The frame portion is meshed with unstructured tetra
mesh. 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.
385443 of which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh
quality is 0.3, total 708 cells falls within this range, as per the CFD Practices this is a good quality
mesh. The mesh which is created in t
solver available with workbench platform. The flow within the air curtain is simulated within
commercial Computational Fluid Dynamics (CFD) solver, where the momentum equation is
modelled with Reynolds-Average Navier
domain is air at 290
C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual
turbulence data at inlet is currently unavailable, for the present simulation the
intensity of 5% (medium intensity) is used to model the inlet turbulence. The outlet condition is
assigned to the extended domain walls as average static pressure of 0 gauge magnitude. The
computational platform is HP- Pavilion dv6, with
The convergence target set at 1e-4 RMS; with continuity target error is 1e
target achieved after 167 iterations.
RESULT AND DISCUSSION
The objective of the air curtain is to restri
energy and keep the comfort conditions inside the space as is. The addition of
serves as a partition between two spaces
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
152
Plane Definitions Figure 6 Result Validation
on the top of the frame. The doorway frame chosen is 2270 mm in height and 900 mm in
frame is 290 mm. There are two slits opens in the domain; the flow jet is
pushed by the blower in the domain through these slits. The experimentation without insertion of
mannequin are carried out first then repeated after placing the mannequin in the flow of air curtain as
xperiment is carried out at isothermal conditions; air at 2
at one atmosphere. The velocity of leaving air from slits is 9 m/s, similar conditions are used for
analysis, this velocity is representative of air curtain flow velocity. As shown
(surrounding area) to capture the flow of air leaving frame boundaries in
directions of frame openings. The frame walls are treated as impermeable walls and are
walls. It is ensured while choosing the length of extended domain that the direct transverse flow of
he boundaries of the domain. Once the configuration is modelled, the mesh
is generated (Figure 3) in the workbench. The structured mesh (hexahedron mesh) is used to build
xtended domain and flow straightener. The frame portion is meshed with unstructured tetra
mesh. 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. The total mesh count is
which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh
quality is 0.3, total 708 cells falls within this range, as per the CFD Practices this is a good quality
mesh. The mesh which is created in the Workbench is internally transferred to CFX
solver available with workbench platform. The flow within the air curtain is simulated within
commercial Computational Fluid Dynamics (CFD) solver, where the momentum equation is
Average Navier-Stokes (RANS), K- ε turbulence model. The default
C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual
turbulence data at inlet is currently unavailable, for the present simulation the uniform turbulence
intensity of 5% (medium intensity) is used to model the inlet turbulence. The outlet condition is
assigned to the extended domain walls as average static pressure of 0 gauge magnitude. The
Pavilion dv6, with Intel CORE i3, 2.4 GHz processor, 8
4 RMS; with continuity target error is 1e-4 kg/s. The convergence
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 is. The addition of air curtain which
partition between two spaces. Very complicated flow pattern is observed in close vicinity
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
October (2013) © IAEME
Result Validation
on the top of the frame. The doorway frame chosen is 2270 mm in height and 900 mm in
domain; the flow jet is
pushed by the blower in the domain through these slits. The experimentation without insertion of
mannequin are carried out first then repeated after placing the mannequin in the flow of air curtain as
xperiment is carried out at isothermal conditions; air at 290
C ( + 10
C)
similar conditions are used for
As shown in Figure 2 the
to capture the flow of air leaving frame boundaries in
lls and are ‘no slip’
extended domain that the direct transverse flow of
the configuration is modelled, the mesh
is generated (Figure 3) in the workbench. The structured mesh (hexahedron mesh) is used to build
xtended domain and flow straightener. The frame portion is meshed with unstructured tetra
mesh. The effort was made to mesh the entire domain with structured mesh but due to complex
The total mesh count is
which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh
quality is 0.3, total 708 cells falls within this range, as per the CFD Practices this is a good quality
he Workbench is internally transferred to CFX-Pre, a CFD
solver available with workbench platform. The flow within the air curtain is simulated within
commercial Computational Fluid Dynamics (CFD) solver, where the momentum equation is
turbulence model. The default
C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual
uniform turbulence
intensity of 5% (medium intensity) is used to model the inlet turbulence. The outlet condition is
assigned to the extended domain walls as average static pressure of 0 gauge magnitude. The
GHz processor, 8 GB of RAM.
4 kg/s. The convergence
ct the infiltration of outside air and thus save the
air curtain which
observed in close vicinity

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
153
of the air curtain device. The analysis of such a complicated flow is difficult with experiments,
whereas CFD can prove 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 can
extend our belief for other flow results which are impossible to judge experimentally. The CFD
plots are associated with 3 mid planes, as shown in the Figure 5.
To reveal the details of movement of air particle, the streamline are drawn at planes 1, 2 and 3 with
and without mannequin. Figure 7, 8 and 9 shows the streamline at plane 1, plane 2 and plane 3
respectively when mannequin is not introduced in the flow path. Straight flow of air particle from top
to bottom is observed in all the planes. Above 150 mm from the ground the particles move sideways
because the flow hits the ground. The velocity gradually decreased from top to bottom. The air
particles from surrounding area gain momentum and get attracted towards the air curtain flow. This
is because of higher velocity of air curtain particles; the low
Figure 7 Velocity streamline at plane 1 Figure 8 Velocity streamline at plane 2
without obstacle without obstacle
Figure 9 Velocity streamline at plane 3 Figure 10 Velocity streamline at plane 1
without obstacle with obstacle (mannequin)

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME
154
Figure 11 Velocity streamline at plane 2 Figure 12 Velocity Streamline at plane 3
with obstacle (mannequin) (3D View)
pressure region is created and surrounding air particles move towards this region to minimise the
pressure difference. The velocity of surrounding particles is very low of the order of 0.0056 m/s. The
particles from both surrounding are attracted towards the flow but do not cross the air curtain. Thus
air curtain forms a perfect barrier. The surrounding particles leave the flow in their respective
surrounding along with air curtain flow. Figure 8 and 9 explains this phenomenon at plane 2 and
plane 3 respectively. Figure 10 shows the velocity streamline at plane 1 with obstacle located at the
doorway. The streamline are found bend over the mannequin in all the directions. The concentration
of streamline is observed on the sideways and rarefaction over front and backside of the mannequin.
This explains the high velocity zone on the side of mannequin and low velocity region on front and
backside of mannequin. The streamlines get crossed in the region below hands and the legs of the
mannequin representing the mixing of surrounding particles and absence of effective air curtain
barrier. At the bottom because the flow hits ground and absence of positive air curtain flow, the
particle movement is complex. The particles, especially at the front and back of the mannequin are
moving in all directions forming spiral movement perpendicular to mannequin instead of flowing
downwards straight to ground. The particles on the side of the mannequin escape to sideways
forming rouged barrier for both the environments. The boundary layer on the sideways is totally lost
because of high velocity and concentration of air particles, and a narrow path between mannequin
and side of the doorway. Figure 11 and Figure 12 show the streamlines at plane 2 and plane 3
respectively. At both the planes the streamlines move sideways and again turn back towards the
mannequin. The deviation of air particles are found more at plane 2 as compared to plane 3 because
of higher velocities and hence higher momentum of air particles at plane 3. No intermixing of air
particles is observed up to half way i.e. up to waist height of the mannequin. Thereafter because of
no positive flow between legs of the mannequin, the particles tend to cross the mannequin causing
weakening of the air curtain barrier. Figure 11 show the Velocity streamline at plane 2 with
obstacle. Figure 12 shows the three dimensional view of streamlines at plane 3. The sides of the
doorway and the surrounding are hidden from the view. From these figures the location the
streamlines can be understood within the flow domain.

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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CONCLUSION
Numerical analysis of velocity streamlines of flow of air curtain provides valuable data for
analysing the performance of air curtain. Functioning of air curtain was found smooth and reliable
when the obstacle is not introduced as per the basic need of air curtain. Such performance will
definitely ensure the effective separation of two environments. But when obstacle in the form of
mannequin is introduced, the streamlines are observed to cross on the other side of the barrier. The
crossover of the particle is also observed at the bottom side of door. Thus air curtain performance
deteriorates when a person passes through it. From above discussion, it is clear that the air curtain
purpose to separate the two environments will not be successful until this crossover of the particles is
prevented. If air curtain is installed at the entrance of the shopping mall and daily thousands of
customer are passing through the curtain then every time the air curtain barrier is breached causing
crossover of air particles. The present paper is highlighting this issue which must be solved. A little
improvement in the effectiveness of the air curtain will save the loss of valuable conditioned air. And
thus the operating expenses on air conditioning system will be saved. Considering the numbers of
installations of air curtain in the entire world, millions of dollars would be saved in energy bills
globally.
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