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20120130406013 2

  1. 1. 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
  2. 2. 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 International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 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) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 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)
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, 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 International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME 120 Plane Definitions Figure 6 Result Validation 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 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 experimentation without insertion of mannequin are carried out first then ing 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 analysis, this velocity 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 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. Once 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. An 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 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 is generated in 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 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 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, 2.4 GHz processor, 8 GB of RAM. The convergence target was International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – October (2013), © IAEME Result Validation 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 curtain. 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 doorway frame. The 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 experimentation without insertion of mannequin are carried out first then ing 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 alysis, this velocity 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 able 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. Once 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. An effort ex geometry at the flow 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 the CFD Practices this is a good quality mesh. The mesh is Pre, a CFD solver available with workbench platform. The flow within the air curtain is simulated within commercial Computational 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 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 e magnitude. The computational platform is HP- Pavilion dv6, with Intel CORE i3, 2.4 GHz processor, 8 GB of RAM. The convergence target was
  4. 4. 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 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
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, 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 International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME 122 into smaller and smaller eddies until it is ultimately converted into heat by viscous forces. It is 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 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 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 with obstacle (mannequin) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – October (2013), © IAEME converted into heat by viscous forces. It is 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 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 on is derived from other properties Pressure variations at plane 1 with obstacle (mannequin) Pressure variations at plane 2 with obstacle (mannequin)
  6. 6. 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 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)
  7. 7. 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 124 Figure 19 Turbulent Eddy Dissipation Figure 20 Turbulent Eddy Dissipation at plane 1 without obstacle at plane 1 with obstacle (mannequin) Figure 21 Turbulent Eddy Dissipation Figure 22 Turbulent Eddy Dissipation at plane 2 without obstacle at plane 2 with obstacle (mannequin) Figure 23 Turbulent Eddy Dissipation Figure 24 Turbulent Eddy Dissipation at plane 3 without obstacle at plane 3 with obstacle (mannequin)
  8. 8. 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 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, issue 16, November 2011 pp. 3098-3105 [2] Tassou, S. A. and Pappas, T. C., “Numerical Investigations into the Performance of Doorway Vertical Air Curtains in Air-Conditioned Spaces,” ASHRAE Transactions, Vol. 109, No. 1, 2003, pp. 273–279. [3] Homayun K Navaz, Dabiri, D. & R. Faramarzi, M Gharib, D Modarress,’The application of Advanced methods in analysing the performance of the air curtain in a refrigerated display case’, Journal of fluid Engineering, September 2002.Vol. 124, pp. 756- 764. [4] Julian E Jaramillo, Carles D Perez-Segarra, Orial Lehmkuhl, Assensi Oliva, ‘Detail Numerical study of Turbulent flows in air curtain’ V European Conference on Computational Fluid Dynamics, ECCOMAS CFD 2010, Lisbon Portugal. June 10 [5] Enrico Nino, Rocco Fasanella, Rocco. Mario Di Tommaso, ‘Characterisation of a two dimensional air curtain, Journal of Engineering and Technology 902.pdf. 2010. [6] Brandon S Field and Erich Loth, ‘An air curtain along a wall with high inlet turbulence’ Journal of fluid engineering, May 2004 126/391. [7] Frank K. Lu, Vijay A. Chauhan, Adam J Pierce, Takayuki Yajin and J Craig Dutton, ‘Numerical model of doorway flow induced by an air curtain’, Vol 35, No. 9, 2009 American Institute of Aeronautics and Astronautics [8] Dr. Homayun K. Nawaz, Dr. Dana Dabiri Mazyar Amin and Ramin Faramarzi ‘Past, Present and future Research towards air curtain performance optimisation, OR-05-16-4. [9] 'Durbin, P.A. and Pittersson Reif, B.A, 'Stastistical Theory and modelling for Turbulent flows', Wiley, New York 2001. [10] Samir R Traboulsi, Ali Hammoud, M Farid Khalil, ‘Air cirtain Integrity when Misusing the Refrigerated Display Cabinets’ ISSN 1790-5087 issue 2, Volume 4 April 2009 [11] Pedro Dinis Gaspar, L.C. Carriho Goncalves and R A Pitarma, ’Three dimensional CFD modelling and analysis of the thermal entrainment in the open refrigerated display cabinets, ASME Journal 2008.
  9. 9. 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 126 [12] Appropriate indoor climate for environmentally sustainable Supermarket, measurements and Questionnaires Air curtain manual, Thermozone Technology. 2003. [13] Nitin Kardekar and Dr Sane N K, “Effect of Humanoid Shaped Obstacle on the Velocity Profiles of Flow of Air Curtain”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 3, 2012, pp. 511 - 516, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [14] Nitin Kardekar, Dr. V K Bhojwani and Dr Sane N K, “Experimental Performance Analysis of Flow of Air Curtain”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 79 - 84, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [15] Nitin Kardekar, Dr. V K Bhojwani and Dr. Sane N K, “Numerical Analysis of Velocity Vectors Plots and Turbulent Kinetic Energy Plots of Flow of the Air Curtain”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 4, 2013, pp. 67 - 73, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

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