Effect of humanoid shaped obstacle on the velocity

INTERNATIONAL Mechanical Engineering and Technology (IJMET), ISSN 0976 –
International Journal of JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
IJMET
Volume 3, Issue 3, September - December (2012), pp. 511-516
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2012): 3.8071 (Calculated by GISI)
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EFFECT OF HUMANOID SHAPED OBSTACLE ON THE VELOCITY
PROFILES OF FLOW OF AIR CURTAIN
Mr Nitin Kardekar, Research Scholar, Singhania University
Principal JSPM’s Jayawantrao Sawant Polytechnic. Pune.

Dr Sane N K, Research Supervisor, Singhania University
Professor Emeritus, JSPM’s JSCOE, Pune
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 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
contours for velocity profile at different planes. The contour plots of velocity profile are
analysed and are discussed for the two cases are reported and discussed in this paper. This
paper also highlights the gray areas in the flow domain where effect of air curtain is weak.
Key words: Air curtain, Reynolds-averaged Navier – Stokes equation, K- ε turbulence
model, turbulent kinetic energy
INTRODUCTION

Air curtains are the devices that provide a dynamic barrier instead of physical barrier between
two adjoining areas thereby allowing easy physical access between them. The air curtain
consist of fan unit that produces the jet forming barrier to heat, moisture, dust, odours 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 energy1875MW energy will be saved
per year if super market display cabinet air curtain will be operated at optimised performance.
In 2002 the UK food and drinks industry used equivalent of 285 tonnes of oil to power its
refrigeration industry, with most being used in cold storage. In developing countries like
India; the rise in cold storages, super markets, retail stores, banks are not only limited to

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

mega cities but they are the integral part of suburban’s and small towns as well. The effects
of globalisation are inevitable. The air curtains are no more luxury but they are the necessary
part of business development and the economy. Hence the study of air curtain with respect to
Indian climate is upmost necessary to ensure optimised performance of air curtains which
leads to energy conservation. The saving of energy (Electrical energy) will be always boon
for energy starving country like India.
METHODOLOGY

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 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 domain; the flow jet is pushed by the
blower in the domain through these slits. The slits are 84 mm away as shown in the Figure 9.
This area is referred as midsection. The entire experiment is carried out at isothermal
conditions; air at 240C ( + 10C) 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. The domain is extended to capture the flow of air leaving frame boundaries in
directions of frame openings. The frame walls are treated as impermeable walls, and are ‘no
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. Ones the
configuration is modelled, the mesh is generated 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. The total mesh count is 385443, within 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-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
modelled with Reynolds-Average Navier-Stokes (RANS), K- ε turbulence model. The
default domain is air at 240C. 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 computational platform is HP- Pavilion dv6, with Intel CORE i3
2.4GHz processor, 8GB of RAM. The convergence target set at 1e-4 RMS; with continuity
target error is 1e-4 kg/s. The convergence target achieved after 167 iterations.

RESULTS AND DISCUSSION
Figure 5 shows the velocity profile at the plane when a person is passing through the air
curtain. The image of humanoid is clearly distinguishable in the door way. From the Figure 7
it is clear that the smooth flow of air curtain is totally disturbed because of presence of the
obstacle. The smooth layers of velocities are no more seen as observed in the velocity profile
without obstacle. In the range 0.3 m from the top the velocity changes from 9 m/s to 6.3 m/s
without any pattern. The effect of midsection is also clearly visible in the Figure 7. The
velocities in this area are slightly improved to the range 4.50 m/s to 5.40 m/s. The no velocity
or low velocity (0 m/s to 0.76 m/s) zone which was observed up to 0.3 m is reduced to 0.1 m

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because of presence of the obstacle which is positive effect on air curtain performance. The
flow in the range of 3.65 m/s to 6.38 m/s is observed around the humanoid. The flow of 6.38
m/s to 8.21 m/s is also noticed on the side of the ‘head’ and ‘shoulder’ of the humanoid. The
bottom velocities are found improved with presence of obstacle. The velocities near ground
are now in the range of 2.70 m/s to 3.65 m/s against the range observed of 0.9 m/s to 1.8 m/s
without obstacle. The stagnation effect is observed at the top of obstacle in very small area.
The areas of concern with regards to flow of air curtain with obstacle are the areas below the
hand and legs of the obstacle. The velocity in the 0.0 m/s to 0.9 m/s range is observed in this
section. This shows no air curtain or very weak air curtain. Every time a person passes
through the air curtain the air curtain will become weak in this section and will lose its
purpose. The infiltration between inside and outside environments will not be effectively
blocked by these low velocity sections resulting in reduction in effectiveness of air curtain.

Figure 1 Experimental set up (Photograph)
Figure 3 meshing Details

Figure 2 Geometry Model with obstacle

Figure 4 Validation of the model

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Figure 5 Velocity Profile at plane 1 with
obstacle

Figure 7 Velocity Profile at plane 3 with
obstacle

Figure 6 Velocity Profile at plane 2 with Figure 8 Velocity Profile at plane 2 and plane 3
above obstacle
obstacle

Figure 9 Location of midsection.

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Figure 8 reveals the details of the velocity profile at plane 2 and plane 3. As plane 2 and plane
3 passes through the midsection where there is no input of air and slit where direct air enters
in the door way respectively. The velocities are accordingly found to be lowest and highest in
the region respectively. The red area represents the highest velocity at plane 3 over the top of
obstacle whereas maximum velocity recorded over the top of obstacle at plane passing
through midsection ( plane 2) is found in the range 3.21 m/s to 3.81 m/s as compare to
maximum velocity (input velocity) of 9 m/s.
Figure 6 and Figure 6 shows the velocity profile at the door way when obstacle is introduced
in the door way. As shown in figure the smooth profile obtained is clearly disturbed. The
Velocity profile at plane 2 shows much distorted pattern as compared to plane 3 because of
indirect flow. The velocities are found increasing at distance of 1.3 m from the top because of
flow movement of the air but at plane 3 very little effect was found at the back of obstacle
near the waist height region. As found at plane 1 no high velocity region was found near the
obstacle at plane 2 and plane 3. The velocity near the obstacle was found decreasing as
compared to the surrounding in the range of 0 m/s to 0.6 m/s because of boundary layer
effect. This is because the air curtain is perpendicular to plane 2 and plane 3, and width of air
curtain is small as compare to width of the obstacle.

CONCLUSION

A numerical study of flow of air curtain over door way with and without insertion of human
shape obstacle 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 the air curtain was
observed continuous, straight and without break, as per requirement of the air curtain. The
study reveals that the midsection area has large influence over velocity profile of the air
curtain. A good high velocity flow was observed below midsection when obstacle is
introduced. But when obstacle is introduced the low velocity regions were observed below
hands and between legs of the human shape obstacle which leads to mixing of air between
two environments thereby weakening air curtain effect.
REFERENCE

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Effect of humanoid shaped obstacle on the velocity

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