Numerical analysis of velocity vectors plots and turbulent kinetic energy

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Numerical analysis of velocity vectors plots and turbulent kinetic energy

  1. 1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME67NUMERICAL ANALYSIS OF VELOCITY VECTORS PLOTS ANDTURBULENT KINETIC ENERGY PLOTS OF FLOW OF THE AIRCURTAINMr Nitin Kardekar, Principal, Jayawantrao Sawant Polytechnic.Research Scholar, Singhania University.Dr. V K Bhojwani, Professor, JSPM’s Jayawantrao Sawant College of Engineering, PuneDr Sane N K, Research Supervisor, Singhania UniversityABSTRACTA prototype is developed in the laboratory in order to simulate the conditions of theentrance of the doorway installed with air curtain device. The air curtain blows the air indownward direction. The flow within the air curtain is simulated with commercialComputational Fluid Dynamics (CFD) solver, where the momentum equation is modelledwith Reynolds-Average Navier-Stokes (RANS)’ K- ε turbulence model. The boundaryconditions are set up similar to the experimental conditions. The CFD results are comparedand 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 studiedto observe the infiltration through the air curtain and weak velocity zones. High turbulentzones are identified using the turbulent kinetic energy plots.Key words: Air curtain, Reynolds-averaged Navier – Stokes equation, K- ε turbulencemodel, Velocity vectors, turbulent kinetic energy.INTRODUCTION.Air curtain devices provide a dynamic barrier instead of physical barrier between twoadjoining areas (conditioned and unconditioned) thereby allowing physical access betweenthem. 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. Studyfound that air curtains are also finding applications in avoiding smoke propagation, biologicalcontrols and explosive detection portals. According to research by US department of energyINTERNATIONAL JOURNAL OF ADVANCED RESEARCH INENGINEERING AND TECHNOLOGY (IJARET)ISSN 0976 - 6480 (Print)ISSN 0976 - 6499 (Online)Volume 4, Issue 4, May – June 2013, pp. 67-73© IAEME: www.iaeme.com/ijaret.aspJournal Impact Factor (2013): 5.8376 (Calculated by GISI)www.jifactor.comIJARET© I A E M E
  2. 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue1875 MW energy will be saveddisplay cabinet air curtains. In 2002 the UK food and drinkstonnes of oil to power its refrigerationdeveloping countries like India;are not only limited to mega cities but theyand small towns. The effects of gluxury but are necessary part of business developmentcurtain with respect to Indian climate is necessary to ensure optimisecurtains which would leads to energy conservationwill be always boon for energy starving country like IndiaMETHODOLOGYThe air flow analysis was carried out using cV13.0 Workbench platform. Asframe. The doorway frame chosenthe frame is 290 mm. There are two slitspushed by the blower in the domain through thesefigure 1) The entire experiment is carried out at isothermal condition(+- 10C) at one atmosphere. The velocity ofthese conditions are used for CFDvelocity. The flow domain is extendeddirections of frame openings. The frame walls areslip’ walls. It is ensured while choosing the length of extended domain that the directtransverse flow of air curtain will not cross the boundaries of the domainconfiguration is modelled, the mesh(hexahedron mesh) is used to build the extended domain and flow straightenerportion is meshed with unstructured tetra mesh.Figure 1 Prototype of modelInternational Journal of Advanced Research in Engineering and Technology (IJARET), ISSN6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME68MW energy will be saved per year by optimising the performance ofIn 2002 the UK food and drinks industry used equivalent of 285tonnes of oil to power its refrigeration units with most being used in cold storagethe rise in cold storages, super markets, retail storeare not only limited to mega cities but they have also become an integral part ofThe effects of globalisation are inevitable. The air curtains are no morenecessary part of business development and economy. Hence study of aircurtain with respect to Indian climate is necessary to ensure optimised performance of airleads to energy conservation. The saving of energy (Electrical energy)energy starving country like India.was carried out using commercial software packageAs shown in figure 1 the air curtain is mounted on the top of theThe doorway frame chosen is 2270 mm in height and 900 mm in width, theThere are two slits which open in the air flow domain; the flowpushed by the blower in the domain through these two slits which are 84 mme entire experiment is carried out at isothermal conditions; ambienthe velocity of air leaving the slits is measuredCFD analysis. This velocity is representative of air curtain flowdomain is extended to capture the flow leaving frame boundaries inThe frame walls are treated as impermeable walls, and are ‘noIt is ensured while choosing the length of extended domain that the directtransverse flow of air curtain will not cross the boundaries of the domainmesh is generated in the workbench. The structured mesh(hexahedron mesh) is used to build the extended domain and flow straightenerportion is meshed with unstructured tetra mesh.Prototype of model Figure 2 Geometry modelInternational Journal of Advanced Research in Engineering and Technology (IJARET), ISSNJune (2013), © IAEMEsuper marketequivalent of 285being used in cold storages. Inthe rise in cold storages, super markets, retail stores, banksintegral part of suburban’sThe air curtains are no moreHence study of airperformance of airThe saving of energy (Electrical energy)ommercial software package ANSYSmounted on the top of thethe breadth ofdomain; the flow jet ismm apart. (Referambient air at 290Cmeasured 7.6 m/s. Allvelocity is representative of air curtain flowto capture the flow leaving frame boundaries intreated as impermeable walls, and are ‘noIt is ensured while choosing the length of extended domain that the directtransverse flow of air curtain will not cross the boundaries of the domain. Once theThe structured mesh(hexahedron mesh) is used to build the extended domain and flow straightener. The frameGeometry model
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, IssueFigure3 model MeshingThe effort was made to mesh the entire domain with structured mesh but due tocomplex geometry at the flow straightenertotal mesh count is 385443, withinhexahedral cells. The minimum mesh quality is 0.3as per the CFD Practices this is a goodWorkbench is internally transferred to CFXplatform. The flow within the air curtain is simulated within commercial ComputationalFluid Dynamics (CFD) solver, where the momentum equation is modelledReynolds-Average Navier-Stokes (RANS)air at 290C. The inlet boundary condition usactual turbulence data at inlet isuniform turbulence intensity of 5% (medium intensity) is usedturbulence. The outlet condition is assigned to the extended dstatic pressure of zero gauge.The computational platform is HPprocessor, 8GB of RAM. The convergence targettarget error of 1e-4 kg/s. The convergence targetInternational Journal of Advanced Research in Engineering and Technology (IJARET), ISSN6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME69model Meshing Figure 4 Details of meshingThe effort was made to mesh the entire domain with structured mesh but due tocomplex geometry at the flow straightener the frame portion has unstructured meshcount is 385443, within which 59589 are tetrahedral cells and 325854The 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 theerred to CFX-Pre, a CFD solver available withThe flow within the air curtain is simulated within commercial ComputationalFluid Dynamics (CFD) solver, where the momentum equation is modelledStokes (RANS)’ K- ε turbulence model. The default domain isThe inlet boundary condition used is ‘normal speed’ at 7.6 m/s,at inlet is currently unavailable, for the present simulation theuniform turbulence intensity of 5% (medium intensity) is used to model the inletThe outlet condition is assigned to the extended domain wallsThe computational platform is HP- Pavilion dv6, with Intel CORE i3The convergence target is set at 1e-4 RMS; with continuityconvergence target is achieved after 160 iterationsInternational Journal of Advanced Research in Engineering and Technology (IJARET), ISSNJune (2013), © IAEMEDetails of meshingThe effort was made to mesh the entire domain with structured mesh but due tothe frame portion has unstructured mesh. Thewhich 59589 are tetrahedral cells and 325854ls falls within this range,which is created in thesolver available with workbenchThe flow within the air curtain is simulated within commercial ComputationalFluid Dynamics (CFD) solver, where the momentum equation is modelled usingThe default domain ised is ‘normal speed’ at 7.6 m/s, since thecurrently unavailable, for the present simulation theto model the inletomain walls as averageavilion dv6, with Intel CORE i3 2.4GHzwith continuityachieved after 160 iterations.
  4. 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME70Figure 5 Experimental and Velocity ResultComparison (Plane2)Figure 6 Mid Plane LocationsRESULTS AND DISCUSSIONSThe objective of the air curtain is to restrict the infiltration of outside air and thus savethe energy and keep the comfort conditions inside the space as it is. The addition of aircurtain which serves as an interface/partition between two spaces, it is very complicated flowpattern observed in close vicinity of the air curtain device. The analysis of such acomplicated flowFigure 7 Velocity contour (Plane 1) Figure 8 Cross flow velocity crossingthe air curtain at middle space
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME71Figure 9 Velocity Vector (Plane 2) Figure 10 Turbulent kinetic energy contourFigure 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 patternswhen validated. The velocity matrix generated with experiments at the centre plane is ingood agreement with the CFD results. The figure 5 shows the result comparison. Thevalidation result justifies the CFD results, and thus extends our belief for other flow resultsgenerated which are impossible to judge experimentally. The CFD plots associated with 3mid planes are as shown in the figure 6. Figure 7 shows transverse velocity contour on plane3 positioned at right angle to air curtain passing through the slit. It reveals that the flowvelocity of air curtain reduces to 2.3 m/s from initial velocity 7.6 m/s till it reaches groundand diverts sideways. The figure 9 shows velocity vector at the same plane which indicatesthat 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 thecurtain. The cross flow velocities are found in the range of 0 to 1m/s. It is clear from figure7 that cross velocity vectors on plane 1 are attracted towards low pressure zone of air jet and
  6. 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME72then directed downside because of high momentum of air jet which assures non cross flowconditions. But, when cross flow velocity vectors were observed at plane 2 passing throughthe space between the slits, revealed that the velocity vectors of the magnitude 0.1 to 0.83 m/sare passing through small dead portion between 2 slits (Below motor support base). This isthe portion where air curtain is weak barrier. Figure 8 also supports this finding, that the flowin this region is not a downward barrier flow but, it is diffused flow due to the geometry ofthe air curtain. This may be the reason why air curtain is breached marginally. Hence it isconcluded to avoid separation of air entry slits if possible and if not from manufacturing pointof view, then should be kept minimal to improve the barrier effectiveness.Figure 10 shows that turbulence kinetic energy contour at YZ plane across the aircurtain. It is observed that initially turbulence is less and as it approaches at the ground theturbulent kinetic energy (TKE) increases, the range of TKE is of 0.39 m2/s2to 0.43 m2/s2.This represents smooth air curtain flow initially and disturbances occur in the flow when itreaches the ground. When jet of air curtain strikes the ground it is diverted sideways, whichcauses higher TKE. When kinetic turbulence energy plots were observed from frontmaximum TKE was observed near ground. However when observed in the plane 2 (figure11) the higher turbulence kinetic energy is observed between height of 200 mm to 800 mmfrom the top. The air curtain expands in XZ plane may be the reason of higher values ofTKE. Figure 12 shows the velocity streamlines starting at inlet which are smooth flow linereaching 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 applicationsespecially in refrigerated air curtains the need is to divert the flow only on one side (Insideconditioned space). This can be accomplished by varying the jet angle with the help of guidevane in the air curtain.CONCLUSIONA numerical study of air curtain flow over door way was performed using CFD codeAnsys CFX 13.0. The study found the model is in good agreement with the experimentalresults. The flow over curtain was found continuous, straight and without break, as perrequirement of the air curtain. The plot of turbulent kinetic energy shows the higher turbulentregion of the flow of the air curtain. The cross flow is the cause due to dead zone and notbecause of flow behaviour. The region is the area of air curtain where flow is blockedbecause of the base of air curtain motor. The velocity vectors of magnitude 0-0.83 m/s arefound crossing air curtain. It is recommended to avoid separation of air entry slits if possibleand if not from manufacturing point of view, then should be kept minimal.REFERENCE[1] Zhikun Cao Hua Han, Bo Gu, ‘A novel optimization strategy for the design of aircurtains for open vertical refrigerated display cases.’ Applied Thermal ScienceEngineering, Volume 31, Issue 16, November 2011, pp. 3098-3105.[2] Tassou, S. A. and Pappas, T. C., ‘Numerical Investigations into the Performance ofDoorway 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, ‘Theapplication of Advanced methods in analysing the performance of the air curtain in arefrigerated display case’, Journal of fluid Engineering, Vol. 124, September 2002,pp. 756- 764.
  7. 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME73[4] Brandon S Field and Erich Loth, ‘An air curtain along a wall with high inletturbulence’ Journal of Fluid Engineering, May 2004, pp 126/391.[5] 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’, American Institute ofAeronautics and Astronautics Vol 35, No. 9, 2009[6] Durbin, P.A. and Pittersson Reif, B.A, Stastistical Theory and modelling forTurbulent flows, Wiley, New York 2001.[7] Samir R Traboulsi, Ali Hammoud, M Farid Khalil, ‘Air curtain Integrity whenMisusing the Refrigerated Display Cabinets’, ISSN, 1790-5087 Issue 2, Volume 4April 2009.[8] Nitin Kardekar and Dr Sane N K, “Effect of Humanoid Shaped Obstacle on theVelocity Profiles of Flow of Air Curtain”, International Journal of MechanicalEngineering & Technology (IJMET), Volume 3, Issue 3, 2012, pp. 511 - 516, ISSNPrint: 0976 – 6340, ISSN Online: 0976 – 6359.[9] Nitin Kardekar, Dr. V K Bhojwani and Dr Sane N K, “Experimental PerformanceAnalysis of Flow of Air Curtain”, International Journal of Mechanical Engineering &Technology (IJMET), Volume 4, Issue 2, 2013, pp. 79 - 84, ISSN Print: 0976 – 6340,ISSN Online: 0976 – 6359.

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