20120130406013 2

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME
118
NUMERICAL ANALYSIS OF TURBULENT KINETIC ENERGY PLOTS,
TURBULENT EDDY DISSIPATION PLOTS AND PRESSURE PLOTS OF
FLOW OF THE AIR CURTAIN
Mr. Nitin Kardekar
Principal, Jayawantrao Sawant Polytechnic
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 Kinetic energy plots, turbulent eddy dissipation plots and pressure variation plots are
generated at predefined planes are analysed 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 spaces (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
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 6, September – October 2013, pp. 118-126
© IAEME: www.iaeme.com/ijaret.asp
Journal Impact Factor (2013): 5.8376 (Calculated by GISI)
www.jifactor.com
IJARET
© I A E M E

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6,
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 oil
most being used in cold storages. In developing countr
markets, retail stores, banks are not only limited to mega cities but they
part of suburban’s and small towns.
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 optimised
which would leads to energy conservation. The saving of energy
boon for energy starving country like India.
Figure 1 Experimental set up without mannequin
(Photograph)
Figure 3 Meshing Details
6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME
119
portals. According to research by US department of energy 1875 MW energy will be saved
super market display cabinet air curtains. In 2002 t
used equivalent of 285 tonnes of oil per year to power its refrigeration
. 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
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 energy starving country like India.
without mannequin Figure 2 Geometry Model with obstacle
eshing Details Figure 4 Experimental set up
(Photograph)
October (2013), © IAEME
MW energy will be saved per year
In 2002 the UK food and
to power its refrigeration units with
like India; the rise in cold storages, super
have also become an integral
The effects of globalisation are inevitable. The air curtains are
necessary part of business development and economy. Hence study of air
performance of air curtains
(Electrical energy) will be always
Geometry Model with obstacle
Experimental set up with mannequin
(Photograph)

Figure 5 Plane Definitions
METHODOLOGY
In order to analyse the behaviour of the flow pattern of air curtain flow, it was decided to
analyse the pressure, turbulent kinetic energy and turbulent eddy dissipation plots of
air flow analysis was carried out using commercial software package ANSYS V13.0 Workbench
platform. As shown in Figure 1 the air curtain is mounted on the top of the doorway frame. The
doorway frame chosen is 2270 mm in height and 900 mm
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 shown in figure 4. The entire
experiment is carried out at isothermal conditions; air at 290C (+ 10C) at one atmosphere. The
velocity of leaving air from slits is 9 m/s, similar conditions are used for CFD an
is representative of air curtain flow velocity. As shown in Figure 2 the domain is extended
(surrounding area) to capture the flow of air leaving frame boundaries in directions of frame
openings. The frame walls are treated as imperme
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 configuration is modelled, the mesh 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. An effort
was made to mesh the entire domain with structured mesh but due to compl
straightener the frame portion has unstructured mesh. The total mesh count is 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
generated in Workbench is internally transferred to CFX
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
Navier-Stokes (RANS), K- ε turbulence model. The default domain is air at 290C. The inlet
boundary condition used is ‘normal speed’ at 9 m/s, since the actual turbulence data a
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 gaug
Pavilion dv6, with Intel CORE i3, 2.4 GHz processor, 8 GB of RAM. The convergence target was
120
Plane Definitions Figure 6 Result Validation
analyse the pressure, turbulent kinetic energy and turbulent eddy dissipation plots of
doorway frame chosen is 2270 mm in height and 900 mm in width, the breadth of the frame is 290
ing the mannequin in the flow of air curtain as shown in figure 4. The entire
velocity of leaving air from slits is 9 m/s, similar conditions are used for CFD analysis, this velocity
openings. The frame walls are treated as impermeable walls and are ‘no slip’ walls. It is ensured
in the workbench. The structured mesh (hexahedron mesh) is used to build the extended
was made to mesh the entire domain with structured mesh but due to complex geometry at the flow
cells falls within this range, as per the CFD Practices this is a good quality mesh. The mesh is
generated in Workbench is internally transferred to CFX-Pre, a CFD solver available with
ics (CFD) solver, where the momentum equation is modelled with Reynolds
turbulence model. The default domain is air at 290C. The inlet
boundary condition used is ‘normal speed’ at 9 m/s, since the actual turbulence data a
domain walls as average static pressure of 0 gauge magnitude. The computational platform is HP
Result Validation
analyse the pressure, turbulent kinetic energy and turbulent eddy dissipation plots of air curtain. The
in width, the breadth of the frame is 290
ing the mannequin in the flow of air curtain as shown in figure 4. The entire
alysis, this velocity
able walls and are ‘no slip’ walls. It is ensured
in the workbench. The structured mesh (hexahedron mesh) is used to build the extended
ex geometry at the flow
the CFD Practices this is a good quality mesh. The mesh is
Pre, a CFD solver available with
ics (CFD) solver, where the momentum equation is modelled with Reynolds-Average
turbulence model. The default domain is air at 290C. The inlet
boundary condition used is ‘normal speed’ at 9 m/s, since the actual turbulence data at inlet is
e magnitude. The computational platform is HP-

121
set at 1e-4 RMS; with continuity target error is 1e-4 kg/s. The convergence target achieved after 167
iterations.
RESULT AND DISCUSSION
The Figures 7 show the pressure at plane 1 when obstacle is not placed in the doorway. At
plane 1 the pressure is found continuously increasing from top to bottom in all the areas except at the
slits. The pressure at the slit and the pressure at surrounding are found different. There is very little
variation in the pressure at the door way plane 1. The pressure region entirely changes when the
obstacle is introduced in the door way. The high pressure regions are observed at the head, shoulder,
over the hands and above the ground. The reason behind this is stagnation of flow at these areas. The
flow is restricted resulting in increase of the pressure. Because of flow separation from the body the
low pressure region are observed between two high pressure areas around the head of the mannequin.
The expected low pressures are observed in the area below hand and between legs because of
absence of positive flow in this region. If the pressure is improved in this region then the flow patters
will be smooth and it will result in less infiltration.
Figure 9 and figure 10 show the pressure at plane 2 and plane 3 respectively. The pressure
variation, at plane 2 and at plane 3 occurs in similar pattern. The pressure variation is less in the door
way but high pressure zones are observed at the ground because flow hits the ground. The contour of
pressure can be observed in high pressure stagnation region in the Figure 9. Figure 10 and figure 12
show the pressure at plane 2 and plane 3 respectively when the obstacle is introduced in the door
way. The high pressure zones are observed over the head of mannequin and above the ground. The
high pressure region is observed near knee area and the waist of the mannequin. The high pressure
pocket is also observed at a distance of 0.6 m at waist high on the back side of the mannequin.
In 1937, Taylor and Van Karman proposed the definition of turbulence as ‘an irregular motion which
appears in fluids, gaseous or liquid’. Turbulent kinetic energy means the kinetic energy per unit mass
associated with eddies in the turbulent flow. Using the primed quantities to denote the velocity
fluctuations the Reynolds averaged kinetic energy of turbulent eddies can be written per unit basis as
k = ½ ( u’u’ + v’v’ + w’w’) (1)
Turbulent kinetic energy is produced by the fluid shear, friction or buoyancy or through
external forcing at low frequency eddy scale. Larger the size of turbulent kinetic energy means
higher energy content by eddies. The Turbulent kinetic energy extracted from the main flow to larger
eddies then to smaller the eddies.
Figure 13, Figure 15 and Figure 17 show the variation in turbulent kinetic energy across the
plane 1, plane 2 and plane 3 respectively when the obstacle is not placed in the door way of the air
curtain. Since the air is uniformly distributed and flow is smooth, the turbulent energy in the form of
eddies found on entire flow region with comparatively uniform intensity in flow region and in the
surroundings. Higher values of turbulent kinetic energy are observed at plane 3 in the flow region
below the slit up to 1.2 m from the top. The width of region is maximum 0.065 m at 0.9 m from the
top. This is because the flow from the both slit intermix in this region crossing the mid section area.
The variation in turbulent kinetic energy is found only in upper region when obstacle is introduced in
the door way. Figure 14, Figure 16 and Figure 18 show the variation in turbulent kinetic energy at
plane 1, plane 2 and plane 3 respectively when obstacle is placed in the doorway. Since flow is
unable reach to the ground the turbulent kinetic energy values are found much less below the waist
high area of the mannequin, i.e. below 1.2 m from the top of the doorway.
The dissipation of the kinetic energy of turbulence (the energy associated with turbulent
eddies in a fluid flow) is the rate at which the turbulence energy is absorbed by breaking eddies down

into smaller and smaller eddies until it is ultimately
expressed as the kinetic energy per unit mass per second, with units of velocity squared per second
(m2/s3). The kinetic energy of the turbulence is usually involved directly as a conserved property of
the flow. The rate of dissipation of turbulence kinetic energy is a little more complicated and we
must rely on some empirically based model. The various turbulence models differ mainly in the way
the dissipation rate is derived. In some cases the rate of dissipati
of the flow, for example a length
Figure 7 Pressure variations at plane 1
without obstacle
Figure 9 Pressure variations at plane 2
without obstacle
122
into smaller and smaller eddies until it is ultimately converted into heat by viscous forces. It is
The rate of dissipation of turbulence kinetic energy is a little more complicated and we
the dissipation rate is derived. In some cases the rate of dissipation is derived from other properties
Pressure variations at plane 1 Figure 8 Pressure variations at plane 1
with obstacle (mannequin)
Pressure variations at plane 2 Figure 10 Pressure variations at plane 2
converted into heat by viscous forces. It is
The rate of dissipation of turbulence kinetic energy is a little more complicated and we
on is derived from other properties
Pressure variations at plane 1
Pressure variations at plane 2

123
Figure 11 Pressure variations at plane 3 Figure 12 Pressure variations at plane 3
without obstacle with obstacle (mannequin)
Figure 13 Turbulent Kinetic Energy Variation Figure 14 Turbulent Kinetic Energy Variation
at plane 1 without obstacle at plane 1 with obstacle
Figure 17 Turbulent Kinetic Energy Variation Figure 18 Turbulent Kinetic Energy Variation
at plane 3 without obstacle at plane 3 with obstacle (mannequin)

124
Figure 19 Turbulent Eddy Dissipation Figure 20 Turbulent Eddy Dissipation

125
scale. In the widely used k-ε turbulence model the dissipation rate (ε) is modelled as if it were itself a
conserved property. Figure 19, Figure 21 and figure 23 show the turbulent eddy dissipation at plane
1, plane 2 and plane 3 respectively when obstacle is not placed in the door way. The gradually
decreasing turbulent eddy dissipation can be observed at plane 1 with the effect of midsection below
which, the turbulent eddy dissipation values attend higher values as compared in horizontal plane.
The places where higher turbulent energy is observed, the higher turbulent energy dissipation rates
are observed at the same places. Figure 20; figure 22 and Figure 24 shows the turbulent eddy
dissipation at plane 1, plane 2 and plane 3 respectively when obstacle is placed in the door way
reveals similar observation as discussed above only with the difference in the magnitude.
Conclusion ; It is observed from the graph that in addition to velocity profile streamlines turbulent
kinetic energy and turbulent eddy dissipation parameters can also give insight in air curtain flow
performance. The experiments performed during this work confirm higher turbulent kinetic energy
signifies effective barrier where as lower turbulent kinetic energy indicates a weak air barrier.
Turbulent eddy dissipation is higher in the region where turbulent kinetic energy values are high and
are negligible in low turbulent kinetic energy region. Introduction of mannequin showed weak barrier
characteristics under arms and between legs. The turbulent kinetic energy results without mannequin
indicate (figure 17) weak barrier at the centre
REFERENCES
[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 Engineering, Volume 31,
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2003, pp. 273–279.
[3] Homayun K Navaz, Dabiri, D. & R. Faramarzi, M Gharib, D Modarress,’The application of
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[12] Appropriate indoor climate for environmentally sustainable Supermarket, measurements and
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