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In the presented work, the lagrangian grid-free vortex element method is used for flow simulation in forced shear layer. Growth rate of instability and eddy formation is well simulated. Also, effect of eddy formation, pairing and the interaction among them are studied. In an unforced shear layer the growth rate is linear depending on the biggest instable frequency but in the forced shear layer other frequencies are taken part. The most important frequency is the forced frequency among other frequencies and the instability growth rate is no longer linear. The results show that the instability would accelerate due to increase of velocity ratio. The wavelength effect is well studied on the instability and is in good agreement with the experimental data.

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A passive scalar is a property that is affected by the flow field without affecting it. In this paper, first, the governing equations on the turbulent flows are solved and the property of a passive scalar in two dimensions is numerically studied. Having the values of the velocity components, the governing equation on transport of a passive scalar is solved. To compute the turbulent velocity field, the Large Eddy Simulation (LES) method using Smagorinsky subgrid scale is invoked. The flow in a cavity has been the basis to validate the accuracy of the generated computer code. To ensure the compatibility between the flow and the transport of passive scalar fields a similar LES approach is used. As a three-dimensional numerical solution for a turbulent flow fields needs a massive computational time and efforts, therefore a two-dimensional simulation used for a proper saving. Instead, to validate the numerical results, the range of the Reynolds number of the flow is kept within the range of the two-dimensional measurements. Comparison of the numerical results and the experimental measurements in two-dimension reveals the high accuracy of the results and compatibility between the flow and passive scalar fields. Ability of developed scheme to accurately handle transport of a passive scalar is promising to extend LES method into the transport of more species and hence to simulate reacting flows.

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In this article sub-grid modeling of Smagorinsky and Localized Smagorinsky Models are investigated. In modeling sub-grid scales, it is necessary to determine the Smagorinsky coefficient which is an experimental constant. Dynamic Models are developed to estimate this value more efficiently. In this research, the test filter is Gaussian, numerical method is based on the finite volume scheme, and a SIMPLE algorithm is used to evaluate the pressure. To perform computations on a personal computer, value of Reynolds number had chosen enough low to make a two dimensional modeling and comparison with respective experimental results possible. Comparison of numerical results shows high accuracy of the localized dynamic models. More numerical investigations reveal that although localized dynamic models need more computing time, but the higher resolution of the method makes it possible to use a coarser grid and hence compensate the extra CPU time.

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A numerical study for the simulation of induced-flow by a two-room compartment fire has been accomplished using a fully-coupled Large Eddy Simulation (LES) model which incorporates Smagorinsky and One-Equation Sub-Grid Scale (SGS) turbulence models. Also, modified Eddy Dissipation Concept (EDC) and Discrete Ordinate Methods (DOM) are used for incorporating combustion and radiation, respectively. The models are applied for a range of total heat release rate (HRR) for fire source in the center and corner of the fire room. Numerical results of prediction by each SGS model are validated and compared against well-known available experimental data. The predicted time-averaged temperature profiles at different location of the compartment for each case have been calculated and found to be in good agreement with the experimental data. The results also show that the accuracy of One-Equation SGS model for the prediction of the characteristics of fire is higher than those obtain by Smagorinsky SGS model. The air mixture at the fire room opening is higher for the centrally located fire source than the corner one.

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A hybrid cooling system encompassing; cooling tower, cooling coil and evaporative cooler have been discussed in ‎present study. Thereinafter, the hybrid system model is used to predict cooling potential of the system under various ‎operational conditions. In order to have an accurate performance prediction of the hybrid cooling system, a numerical ‎simulation was performed and the results validated using experimental measurements. The presented hybrid cooling ‎system provides the necessary pre-cooling effects, enabling a direct evaporative cooler that cools the air even below ‎outdoor air wet-bulb temperature. Besides, the potential of presented hybrid cooling system to provide thermal comfort ‎in various outdoor design conditions evaluated and compared with conventional direct evaporative cooler. Numerical ‎simulation revealed that the hybrid system complements direct evaporative cooling. Based on the simulation results, ‎the overall cooling effectiveness of hybrid system is tangibly magnified 10%-20% and also it is able to fulfill the ‎comfort condition in extended climate conditions rather than stand-alone direct evaporative coolers. Also in present ‎study water loss amount of hybrid system and direct evaporative cooler were verified in various climate conditions of ‎Iran.‎

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Turbulent wind flow over buildings occurs due to the complexity like sharp corners, ground effect and different vortexes is one of the best choices to evaluate turbulence methods. DES and DDES are hybrid RANS-LES models for simulating turbulent flow which for their characteristic treat near wall as RANS and farther the wall act as LES model. Consequently computational time will decrease compared to traditional LES models. In this article to evaluate DES and DDES models, turbulent incompressible flow in Re = 22000 over 3D building is simulated using parallel processing facilities. For verification purpose other investigators experiment results are used. Also the mentioned models are compared with classic RANS and LES models, like k-ε and LES-Smagorinsky to depict their performance. Our results illustrate DES model with fine grid has good precision for simulating turbulent incompressible wind flow over building and decline of 26 percentage of computational time compared to LES-Smagorinsky model.

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In this paper a simulation of two fires in a tunnel in which varied arrangements of different sized vehicles at the upstream of fires has been accomplished using FDS. The results reveal that the behavior of two fires is directly influenced by distance between them. The calculated critical velocity is not affected by the variations on the small vehicles arrangement and distance between the vehicles and fires. Interestingly, the presence of medium vehicles leads ventilation flow to strengthen inertial force rather than buoyant force of fire plume in tunnel. Accordingly, when there is a short distance between fires and obstructions, less air ventilation is needed to prevent smoke backlayering. Eventually, far distance between the vehicles and the fires results in vanishing obstruction effects. Consequently, the critical velocity is the same as the case in which there is no vehicle in the tunnel.

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In this study, the effect of inlet supply temperature on energy consumption optimization, thermal comfort and mean local air age has been investigated for a displacement ventilation inside a typical room. Based on the results obtained from this study, an increase in the inlet supply temperature for a displacement ventilation from 17.8 to 25.8 in summer leads to a 50% reduction of consumed energy. Owing to the fact that optimization of consumed energy is an action bound to maintain thermal comfort of occupants, PMV(predicted mean vote) and PPD(predicted percentage of dissatisfied) parameters as two general thermal comfort indices have been investigated. In addition temperature gradient in vertical direction as local thermal discomfort index and mean local air age as air quality index have been probed. All the aforementioned indices except that of mean local air age, lie within the sightly range of ISO7730 standard with an increase in temperature, but air quality index experiences some quality drop in inhalation region, This slight drop is negligible and displacement ventilation system can be used as a suitable ventilation system for summer applications.

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Predicting wind flow pattern around high rise building, because of pedestrian comfort, air pollution in weak wind region and etc. has important position in wind engineering. Turbulent wind flow over buildings due to the complexity like sharp corners, ground effect and different vortexes, is one of the best choices to evaluate turbulence methods. Moreover in a campus due to high velocity region between buildings, simulating wind flow is more complex. Therefore reaching acceptable result needs a fine grid with an accurate turbulence model that increases computational cost. DES is hybrid RANS-LES models for simulating turbulent flow which for their characteristic, treat near wall as RANS and farther the wall act as LES model. Consequently in this hybrid model, computational time will decrease compared to traditional LES models. In this article turbulent 3 dimensional wind flow over Tarbiat Modares University with DES method in different wind velocities is simulated. Because cells number is great, parallel processing has been used. For verification, DES results are compared with traditional LES models such as smagorinsky. The results show good agreement with other traditional methods.

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In this study, by cooling coil load calculation in under floor air distribution systems, the effect of separate location of the return and exhaust vents and return vent height on energy consumption, thermal comfort conditions and indoor air quality have been investigated. Based on the results obtained from this study, when the height of return vent is equal to 2.0, 1.3, 0.65 and 0.3 m, the amount of energy usage reduction compared to no return vent is equal to 10.9, 15.3, 18.9 and 25.7 percent respectively. Limiting factors in the amount of this reduction are thermal comfort of occupants and indoor air quality. To this end, thermal comfort indices (Predicted Mean Vote and Predicted Percentage of Dissatisfied), local thermal discomfort index (Temperature gradient in vertical direction), and indoor air quality index (Mean Local Air Age) have been probed with changing return vent height by CFD methods (AirPak software with SIMPLE algorithm by using Indoor Zero Equation turbulence model). Based on the results, by reducing the height of return vent from ceiling to floor, the exhaust air temperature increased, which causes to temperature gradient increase in vertical direction. The survey was conducted that choosing the location of 1.3 m(upper boundary of occupied space in seated mode) for return vent, causes to 15.3 percent reduction in the amount of energy consumption while maintaining the states of thermal comfort conditions and indoor air quality.

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Investigations of the phenomena associate with the Fluid-Structure interactionin transonic turbomachines due to the presence of unstable flow behaviors have double significance. Severe restrictions of the experimental methods, has developed researchers approach in this field to Numerical methods. Nevertheless, using simple two-dimensional model to investigate the phenomenon of quality is inevitable because of high computational cost of numerical methods in aerodynamic and aeroelastic simulation of full model of turbomachines. In this paper transonic flow in fixed fan cascade and fan cascade with central blade vibration in Forced harmonic pattern is simulated and variations of turbulence characteristic patterns are studied. In order to prevent divergence of the solution and achieve more accurate results, the step by step algorithm is developed. On the other hand, spring methodology with linear torsional springs is used for movement of dynamic grid around the oscillating blade. Mesh quality is assessed by examining maximum Mach number and y+ variation. Compare the results with the available experimental data indicated a significant difference in the position of the vortices are detached and re-attached. This difference proves need to use a turbulence model is more accurate in terms of the wide separation. In this paper, effect of blade geometry, flow separation and central blade oscillation on flow pattern and turbulence characteristics of transonic flow have been investigated. Obtained results explain the effect of mentioned parameters on the turbulence kinetic energy and dissipation frequency.

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Hybrid cooling systems is used to increase the cooling effectiveness of direct evaporative coolers. In this study, a hybrid cooling system including cooling tower, cooling coil and evaporative cooler have been discussed. The major aim of hybrid systems using is to reduce the energy consumption compare to the other cooling methods. So in this research, optimization of hybrid system was investigated. In order to have an accurate performance prediction of hybrid cooling system, a numerical simulation was performed and the results validated using experimental measurements. Moreover, genetic algorithm is used to determine the optimal design parameters. Minimizing the operation cost including water and electricity costs is considered as the objective function. All design constraints and standards were considered in optimization process. Investigated case study indicates that the optimal design can significantly reduce the operation costs. Optimization results revealed that in optimal case, air mass flow of cooling tower is lower than water mass flow. Also, the velocity of air through evaporative pad was obtained the minimum allowable value and the cross section of cooling tower was obtained the highest possible value according to the constraints. Finally, importance of water and electricity in the optimum system design was investigated due to lack of water in some areas.

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In this paper, the flow field and mass transfer characteristics were evaluated numerically via Large Eddy Simulation in the presence and absence of the electric field in flat channel that is included cavity containing water. Comparison of the numerical results with the experimental data were in a good agreement with experimental data at prediction of flow field and mass transfer. Then, the effect of the Reynolds number variations in the different applied voltage on the water evaporation rate is investigated. The results indicate that applying the high voltage at the wire electrode can generate vortex and produce perturbation on the water surface. It is shown that at constant Reynolds number with the presence of the electric field, the Sherwood number will be increased but in constant applied voltage the Sherwood number will increase to the Reynolds of 3391 and then will decrease due to reduction in the size of generated vortex. Also, a linear relationship was obtained relationship exists between the Sherwood number factor and the EHD number at Reynolds numbers greater than 3391. Finally, a relationship between dimensionless numbers like the relative Sherwood number, the Reynolds number and the EHD number was obtained.

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The correct placement of supply air inlets and pollution extraction outlets play an important role in increasing indoor air quality and reducing the amount of pollution in enclosed car parks. In this paper the effect of exhaust locations, exhaust height and parking dimensions on indoor air quality of car park is investigated with numerical simulation. For this purpose conservation equations are solved with openFoam. For validation, air flow and pollution is simulated in a simple car park and compared with experimental results. In the next section, the effect of exhaust vent locations on increasing indoor air quality is investigated and is compared with other solutions. The result of numerical simulation indicates that, if inlets and exhausts are located in end sides of car park and if exhaust vent locations are in the optimized height, the indoor air quality in the car park is increased.in this paper, the graph of CO concentration in different heights is explained and by using it, the optimum range for exhaust vent locations is proposed. Moreover the standard criteria for using jet fans is expressed and the results showed that, for ventilation of car parks with length more than criterion, jet fans should be used.

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Mine ventilation is one of the important functions in mining. The purpose of mine ventilation is providing enough oxygen to breath, create comfortable working conditions and dilute and remove the gases and dust from mine. Methane gas released from minerals while extraction in coal mines. To prevent the accumulation of this gas and intense explosions, the use of auxiliary ventilation beside main ventilation is essential. Auxiliary ventilation in room and pillar coal mining is used generally two methods of stopping and brattice.In this study, the equations of conservation of mass, momentum, species and energy is discrete by using computational fluid dynamics and the results have been validated with experimental work and then several scenarios have been predicted to improve mine ventilation. Results show that concentration of methane decreases 47 % using stoppings, but the concentration is still higher than the standard level. By using brattice the level of methane concentration decreased to 74.2%, but methane concentration in side walls of coal face is 3.4% that is still higher than the level of standard. Optimized case was simulated by using stoppings and brattice simultaneously and quality of air improved 88.8% and concentration of methane has been fully respected and mine safety and explosive gas concentration are desirable.

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Heat and mass transfer in textiles are usually simulated using models that consider sorption and condensation. But in electrolyte solutions, ions existed in fluid passing the textile can cause a phenomenon called electric double layer. Charges on the textile pores will attract the ions with opposite charge which will affect the fluid flow. To investigate this effect, Poisson-Boltzmann equation is solved beside the other governing equations of the phenomenon. Net electric charge density is computed from this equation and is applied to liquid diffusion coefficient. In this research, the influence of electric double layer is shown and then the factors affecting the strength of this phenomenon have been studied. One side of the textile is thoroughly in contact with liquid and other side is in contact with air. To validate the obtained results, temperature variations in the outer side of the textile are computed and compared with the available experimental works. There is a good agreement between the results. According to the results, applying electric double layer effect in equations cause temperature difference to 20 percent in the outer surface of textile to lack of consideration this. In addition, time for textile full saturation when the electric double layer is considered, increased more than fivefold. The results show that by reducing the viscosity of fluid. The effect of electric double layer on the textile's outer surface temperature has increased. Porosity and zeta potential are other influential factors which according to calculations, increasing each effect can be accelerated electric double layer.

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A practical method for improving the COP of an air-cooled chiller is pre-cooling the entering air of its condenser via a water mist system. This article studies a water mist system with hollow-cone spray nozzles and investigates the effects of water flow rate, water droplet diameter and the number of spray nozzles on system performance. Simulations were run by software FLUENT applying Eulerian-Lagrangian method. Solution grid independency was obtained and it was validated with experimental data. According to the results, in a constant air flow rate of 8.3 (kg/s), with increasing the water flow rate from 0.05 to 0.4 (kg/s), percent increase of COP increases from 3 to about 14, but the percentage of evaporated water decreases from 12.13 to 7.62 (however the value of evaporated water increases). Besides, decreasing the water droplets’ diameter from 200 to 50 micrometer, results in percent increase of COP from 4 to 24. Due to less water evaporation in higher flow rates, the number of spray nozzles was raised in a constant total flow rate that according to the results, increasing the number of nozzles improves the system performance. Also with other simulations it was observed that increasing the number of nozzles is more effective in higher flow rates and less drop diameters. Finally by the case study, it was demonstrated using sufficient number of nozzles, it is possible to achieve higher COPs in lower flow rates and therefore in addition to energy consumption decline, the water consumption could be lowered.

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The management of air quality in enclosed parking lots has many challenges such as increasing pollution concentration and pollution movement between floors. In this article, the complete calculation of ventilation system in multilevel parking lots is presented and the effect of supply and exhaust vents height on pollution concentration and movement is investigated by using numerical simulation. Also a new criterion for recognition of flow pattern is presented. In the numerical simulation, the conservation equations are solved by using openFoam. For validating the numerical simulation, the results are compared with available experimental results. The comparison of results is showed good accuracy of numerical simulation. After that, the common multilevel parking lots are introduced and the effect of supply and exhaust vent heights on the amount of pollution in these parking lots are investigated. The results showed that, if the supply vents are installed on the non-dimensional heights of about 0.55 and exhaust vents are installed on the non-dimensional heights of about 0.55 to 0.7, the best ventilation flow pattern in the multilevel parking lots is obtained. Furthermore, by using the novel method of this paper, the ideal bulk flow velocity for development of piston flow in parking lot is obtained and the flow pattern is tend to piston flow by optimizing the supply and exhaust vent heights.

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Stenosis in coronary artery and the other cardiac diseases such as Atherosclerosis is major cause of death in the world. Numerical simulation of blood flow can help medical evaluation to curve arteries have been stenosis. The purpose of this paper is to find the effect of arteries stenosis on the hemodynamic parameters by simulation of blood flow in LAD branch of coronary artery. The computational domain has been determined from CT images of human heart. In this study, blood is assumed to be homogeneous, Newtonian and the blood flow assumed to be pulsatile. In order to more realistic modeling of flow and pressure, Seven–element lumped model has been used in coronary artery outlet, in order words the 0D and 3D models are coupled together. The results indicate that the calculated flow wave is the minimum in systolic phase and maximum in diastolic phase in coronary artery, in contrast with Aorta. On the other hand, by increasing the stenosis percent from 30 to 60 percent, no significant drop of flow has been observed in the state of rest, and it has been validated with experimental results. The results indicate that with increasing stenosis, time average wall shear stress in the stenosis region increases, while it decreases before and after the stenosis, also the investigation of oscillating shear index indicates that in the state of 60% of stenosis and in the main downstream branch, it has the maximum value, that is indicative of the presence of turbulent flow in this region.

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With recent developments in sprinkler technology, water mist system is becoming more and more useful in fire suppressions. The computational method is an efficient way to investigating effect of Nozzle parameter of water mists and optimize them. In this research, a open source fire dynamic simulator (FDS) is used to numerically investigating the different nozzle parameter on the fire suppression and extinguishment mechanism.The range of droplet size was determined based on the NFPA 750 standard. Extinguishing mechanisms in water mist systems and their effect on extingushing time and nozzle parameter such as droplet size, water flow rate and spray cone angle were investigated. The simulation concluded that droplet sizes I hollow cone angle smaller than 121 μm and larger than 600 μm were appropriate for fire extingushment. With a full cone angle nozzle and 1/5 flowrate compared with hollow cone nozzle, fire extingush time reduce from 26 second to 7.4 second. Spray cone angle in fine droplets does not much affect the duration of fire extinguishing, however, for large droplets, the desired result can be achieved by reducing the spary cone angle. So with recognition of nozze parameter and its effects on fire extingushing time could rich the optimum design.
Keywords
m design.