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The dimensionless form of Navier-Stokes equations for two dimensional jet flows are solved using direct numerical simulation. The length scale and the velocity scale of jet flow at the inlet boundary of computational domain are used as two characteristics to define the jet Reynolds number. These two characteristics are jet half-width and centerline velocity. Governing equations are discretized in streamwise and cross stream directions using a sixth order compact finite difference scheme and a mapped compact finite difference method, respectively. Cotangent mapping of is used to relate the physical domain of to the computational domain of . The compact third order Runge-Kutta method is used for time-advancement of the simulation. convective outflow boundary condition is employed to create a non-reflective type boundary condition at the outlet. An inviscid Stuart flow and a completely viscose solutions of Navier Stokes equations are used for the verification of numerical simulations. Results for perturbed jet flow in self-similar coordinates were also investigated which indicate that the time-averaged statistics for velocity, vorticity, turbulence intensities and Reynolds stress distribution tend to collapse on top of each other at flow downstream locations.

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This study was conducted in order to determine the situation and position of Jetstream in the west of Iran and its speed during the rainy synoptic systems in land surface. Therefore, rainfall data of sven synoptic stations in Ilam and Kermanshah provinces during the 1990s, and 60 systems were selected and of the accessible systems the maps 54 were analyzed. The required analyses were carried out by assessing maps on two days before precipitation, beginning of the precipitation day and the days of maximum precipitation. The results showed that Jetstream tracks had anticyclonic curve two days before precipitation which acquire cyclonic curve on the beginning of of precipitation day and the days of maximum precipitation. The value of the Jetstreams meridian gradient is much more, on the days of maximum precipitation than the other days and falls to the minimum rate on the days before precipitation. Jetstream cores were spread on two days before precipitation too which were concentrated in two areas on the beginning and on the maximum precipitation days. The first area was placed in 25-30° north latitude and 32.5-42.5° east longitude (Northern Red Sea) and the second area in 35-39° north latitude and 45-50° north longitude (Southeastern Caspian Sea). There was no linear correlation between Jetstream cores velocity and the volume of system precipitation, because of the effect of many factors on the amount of the systems, precipitation amount. The maximum effect of Jetstream in the studied area was when the Jetstream in the upper levels of troposphere (200 hp) was place of in the south of the lower levels of the Jetstream (300 hp), so that the Jetstream in the lower levels of troposphere was closer to the studied area.

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Abstract: in this article, jet flow from the nozzle exit was considered and calculated numerically in transient two-phase flow and two-dimensional axsymmetric turbulent condition using volume of fluid method (VOF). The hydrodynamical instability for jet flow was analyzed and the breakup length was calculated, the nozzle diameter of 0.11875mm, 0.2375mm and 0.475 mm, the center line velocity of the fluid in the 15.416 m/s and 7.708 m/s and the fluid inside the nozzle used for the calculation are water and gas oil. Fluent 6.3.26 was used for two-phase flow analysis. The results obtained from the present numerical simulation compared with the experimental results of the previous researches, good agreement was obtained. It was concluded that the breakup length decreases as the relative velocity between the phases increase or the liquid density decreases. The nozzle diameter is an important parameter which effect of the nozzle outlet regime and the breakup length.

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This paper discusses about the effects of square wave pulsation on the turbulent flow and heat transfer from slot jet impinging to a concave surface. The RNG k-ε turbulence model is applied for modeling the turbulent flow and heat transfer filed in the present 2-D slot jet flow. The effects of jet Reynolds number, nozzle to surface distance and pulsation frequency on time-averaged Nusselt number distribution are studied carefully. Results show that applying the pulsating jet in the range of 10 Hz to 50 Hz can increase heat transfer from the concave surface in comparison with the steady jet. Increasing jet Reynolds number ranged from 4740 to 9590 significantly increases the time-averaged local Nusselt number. Also, in steady jet, decreasing the nozzle to surface distance, consequences increasing the Nusselt number near the impingement zone. While in pulsating jet, it causes both increasing/ decreasing the Nusselt number all over the concave surface.

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This paper presents a comparative study of turbulence models performance in prediction the oscillating characteristics of naturally excited jet flows. The unsteady averaged Navier-Stoks equations for turbulent incompressible flow and five variant turbulence closures are used in this study. A large family of turbulence models exists in the literature which is far too extensive to be reviewed here. The models are ranged from simple algebraic expressions for the eddy viscosity to more elaborated formulations which introduce a separate transport equation for each component of the Reynolds stresses. The software, FLUENT 6.3.26, was employed for solving the governing equations. Computational results compared with reported experimental data. The standard k-ε and SST k-ω models clearly showed better results than the others. The accuracy of standard k-ε model decreases with decreasing the nozzle inlet velocity and it failed to predict the minimum excitation velocity (minimum excitation kinetic energy) in the self excited fluidic nozzle.

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Abstract: In this paper the experimental study of the flow pattern around a round wall jet has been carried out to investigate the effect of the bed roughness on the turbulence characteristics, including Reynolds stress and turbulence intensities. Measurements were conducted using the three-dimensional velocimeter, ADV and time series of the velocity components are used to investigate the variation of the turbulent flow parameters along the measuring domain. The results showed that by increasing the bed roughness, the streamwise and vertical turbulence intensities increase by downstream distance and for a specific bed roughness the streamwise turbulence intensity is higher than the vertical one. Furthermore, by going downstream from the jet entrance the bed shear stress reduces and by increasing the bed roughness, the bed shear stress has an increasing trend along the jet centerline. Location of the maximum bed shear stress does not change by changing the bed roughness.

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Abstract- In this paper, it is shown how to use the recently developed Firefly Algorithm to optimize abrasive water-jet cutting as a nonlinear multi-parameter process. Back propagation neural network were developed to predict surface roughness in abrasive water-jet cutting (AWJ) process. In the development of predictive models, machining parameters of traverse speed, water-jet pressure, standoff distance and abrasive flow rate were considered as model variables. Firefly Algorithm by using back propagation neural network optimizes glass surface roughness in abrasive water-jet cutting and proposes appropriate parameters for minimum surface roughness. Testing results demonstrate that the model is suitable for predicting the response parameters. However this algorithm has not be tested for practical problems, the results showed this algorithm applicable for processes with complex nature.

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In this research, grey cast iron scraps were recycled into powders and were then used in combination with iron powder for producing iron based powder metallurgy parts. Design of experiments was conducted by response surface method for both the green and sintered parts. For the green properties, the parameters cast iron powder percentage and compaction pressure, and for the sintered parts, the mentioned parameters in addition to sintering temperature and sintering time were selected each in five levels as the input process parameters. Transverse rupture strength and elastic modulus were measured as the responses. Regression analysis and analysis of variance were used to investigate the effect of input parameters, develop the mathematical models and evaluate the validity of the models. Scanning electron microscopy and optical microscopy micrographs were provided to better understanding. The obtained results, in addition to determine the effects of the input parameters, demonstrated the adequate mechanical properties of the produced parts in industrial scales and the validity of the proposed models. Also, the proposed method demonstrated its good capability for estimation of elastic modulus of powder metallurgy parts.

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In this research, the machinability of iron-recycled grey cast iron powder metallurgy parts is investigated. For this purpose, grey cast iron swarfs were transformed to powders by target jet milling method and were then used to prepare powder metallurgy parts in combination with commercial iron powder. Green compacts were prepared with the variables of cast iron powder percentage and compaction pressure. Design of experiments was conducted by response surface method for sintered parts with the variables of cast iron powder percentage, compaction pressure, sintering temperature and sintering time each in five levels. Regression analysis and analysis of variance were used to investigate the effect of input parameters, develop the mathematical models and evaluate the validity of the models. In the green section, machinability was qualitatively investigated in drilling. For sintered parts, machinability was evaluated by measuring the thrust and torque forces and the obtained surface finish in drilling. The obtained results certificated the accuracy of the extracted regression equations for predicting the machining properties of the parts. Also, the results demonstrated that the addition of jet milled grey cast iron improves the machinability of iron-based powder metallurgy parts.

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Abrasive water jet cutting process can produce tapered edges on cutting kerf. This problem can limit the applications of abrasive water jet cutting process and in some cases it is necessary another edge preparation process. In this paper, an experimental investigation kerf characteristics of Ti-6Al-4V titanium alloy under abrasive water jet cutting is presented. In this regards, it is shown how to use the hybrid approach of Taguchi method and principal component analysis to optimize abrasive water jet cutting are used in this paper. The abrasive water jet cutting process input parameters effect on material removal rate and the characteristics of the surface. A considerable effort was made in understanding the influence of the system operational process parameters such as water jet pressure, traverse speed, abrasive flow rate, and standoff distance. Due to appropriate selecting abrasive water jet cutting process parameters leads to optimizing of kerf characteristics include top kerf width, kerf tapper and kerf deviation, therefore it is important to select appropriate input parameters. The obtained results from this method show that the hybrid approach of Taguchi method and principal component analysis is a suitable solution for optimizing of abrasive water jet cutting process.

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In this study, the effects of discharge angle from an air curtain’s jet have been investigated on aerodynamic sealing of a room with positive pressure ventilation system. For this reason, the modeling of flow, heat transfer and species diffusion has been performed by using OpenFoam® numerical solver. The results show that the jet discharge angle has significant effects on the distribution of parameters such as temperature, concentration of pollutants and occupants’ thermal sensation index. So, by varying the jet discharge angle from +10 (towards the indoor space) to -10 (towards the outdoor space), the average temperature difference between two spaces is reduced to 2.5°C. Also, the mentioned varying in discharge angle causes a significant reduction in the mean concentration of pollutants at the indoor space, from 25ppm to 5ppm. On the other hand, the results indicated that for the discharge angle of -10, the average of occupant’s thermal sensation index is shifting to the cool feeling. Therefore, the mentioned discharge angle can reduce the impacts of outdoor warm conditions on the indoor’s. In other words, the discharge angle of -10 demonstrates the best performance of the air curtain device in thermal and aerodynamic separating of two indoor and outdoor spaces.

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Air entrainment in liquids via a fluid jet, is a complex phenomenon that has important applications in industry and the environment. The impact of a vertical laminar water jet translating over the quiescent pool of water at constant velocity was studied empirically, and the penetration depth as well as distribution of the bubbles formed by this jet was measured for both fresh and sea water with two different optical methods. This experiment was conducted at different flow rates (corresponding to different vertical velocities). In each case, the jet was moved at different horizontal velocities relative to the pool surface. As the jet started its horizontal translation, air began entering the pool from the bottom of the point of impact. Bubbles penetration depth was measured through a high-speed imaging technique, and pulse shadowgraphy was used for measuring the bubbles distribution. Increasing the vertical velocity of the jet while simultaneously decreasing the horizontal velocity of the same led to increased bubble penetration depths, and similar results were obtained for fresh water and sea water. This result was obtained in spite of the fact that the number and size of the bubbles formed in sea water were dramatically different from those formed in fresh water. Moreover, the significant role of buoyant forces in the distribution of the bubbles was obvious. The penetration depth and distribution of the bubbles were measured and reported for various jets with different diameters at different vertical and horizontal velocities.

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Effects of secondary sonic jet injection in divergent part of supersonic nozzle on flow field structure and thrust vector control performance has been numerically analyzed. Three dimensional multi-blocks extended numerical code has been used to model the complexity of turbulence flow by k-ω SST model. Structured computational domain has been applied and initial results of simulation validated with previous experimental results. The obtained numerical results are compared with the experimental ones, and the outcome shows acceptable agreement between the two. Different injection power generates by varying the injection surface and pressure ratio with respect to throat pressure. Injection power increment make changes in performance and also sometimes it lowers the performance. In the current research aside from complete complex flow features description, allowable power range to increase system performance has been presented. In this range, increasing the injection mass flow rate, decreases the amplification factor, but increases the deflection angle and axial thrust augmentation as most important performance parameters. Out of estimated range for allowable mass power injection, performance parameters different behavior differently that shows a drastic drop in performance.

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In this research, a numerical simulation of liquid jet ejecting from elliptical orifices into gaseous phase with different aspect ratios, at Rayleigh regime is performed. The range of the Weber number and the aspect ratio of the orifice are from 20 to 300 and 0.25 to 0.66, respectively. The volume of fluid (VOF) method and large eddy simulation are used to simulate the liquid interface dynamics and the jet breakup utilizing the OpenFoam software. In order to achieve the most accurate results for axis-switching phenomenon and jet breakup length, the dynamic mesh refinement is used for all the examined cases. The results, which are validated with recent experimental and numerical works, indicate that the jet breakup length raises by increasing the Weber number. Also, it is shown that the jet breakup length declines as the aspect ratio of orifices decreases. Finally, it is observed that for the orifices with lower aspect ratios, jet is breaking into droplets with uniform sizes with almost no satellite droplets which always present in the circular jet breakup.

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In this paper the coupled lattice Boltzmann model is developed for simulation of multi-step combustion mechanism of a methane jet diffusion flame. The lattice Boltzmann scheme employs the double-distribution-function model, one distribution function for solving flow field and another for temperature and species concentration fields. The density and temperature fields are coupled through low Mach number flow field. The solution parameters such as species properties and rate of chemical reactions adjust in every time step according to temperature and concentration of species variations. Using combustion mechanisms instead of one step fast chemistry reaction and considering effect of temperature and species concentration on solution parameters are the main advantages of the developed model. For validation of the model, a four-step reduced mechanism with six species is used for simulation of combustion in a methane jet diffusion flame configuration. Agreement between the present results and experimental data confirms that this scheme is also an efficient numerical method for more detailed combustion simulations.

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Shaped charges are explosive devices with a high penetration capability and are used for both civilian and military purposes. In civilian applications shaped charge devices are used in demolition works, oil drilling and mining. In the military applications, shaped charges are used against different kinds of armors and Protective Structures. Analysis of forming and penetration of shaped charge projectiles issue is so complex that include explosion of charge, propagation of the shock wave in the charge, hitting the shock wave to the liner, liner deformation, projectile formation and finally striking projectile to target until it stops. According to the complexity of Behavior of the concrete during the Penetration of the Jet, the material models shoude be able to model the effect to large deformation, high hydrostatic pressure, high strain rate and failure. Although there are many references about Numerical simulation of shaped charge Jet in the armor targets, however it was not found any comprehensive sources about penetration of shaped charge in the reinforced concrete targets. Experimental results suggest that both kinetic energetic projectile and shaped charge are capable of destroying concrete targets, but the magnitudes of damage due to them are different. Compared with a kinetic energy projectile, a shaped charge has more significant effect of penetration into the target, and causes very large spalling area. In this paper, AUTODYN software was used to numerical simulation of shaped charge jet formation and target penetration. Different solver and modeling alternatives of AUTODYN were evaluated for jet formation and penetration problems. Euler solver of the AUTODYN was used to jet formation simulations and Lagrange solver was used for penetration simulations and both models were 2D axisymmetric. To simulate the penetration performance of the RPG – 7 charge, both the jet and the target were modeled by Lagrangian elements. The results of jet formation simulations, performed by the Euler solver were used to determine the properties of the jet. Penetration simulations were performed for a fixed 2 CD standoff distance. The jet material distribution obtained by the Euler solution at 2 CD standoff distance was mapped onto the Lagrange solver. The quality of this Euler-to-Lagrange mapping was limited to the mesh resolution of the Lagrangian jet part. The first goal of this research is presentation of a reliable method to numerical simulation of Penetration of shaped charge of RPG – 7 into the concrete targets by use of available software tools. Therefore, simulation results were compared to the experimental results in three stages that Include the jet formation, jet Penetration in armor targets and behavior of concrete target against Penetration. The second goal is determination of the safe thickness of conventional concrete targets against the Penetration of RPG – 7 weapen and investigation of the behavior of this concrete type of target in terms of penetration depth, hole diameter and failure of the front and rear surfaces of the target.

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In this paper, breakup of liquid jet is simulated using smoothed particle hydrodynamics (SPH) which is a meshless Lagrangian numerical method. For this aim, flow governing equations are discretized based on SPH method. In this paper, SPHysics open source code has been utilized for numerical solutions. Therefore, the mentioned code has been developed by adding the surface tension effects. The proposed method is then validated using dam break with obstacle problem. Finally, simulation of two-dimensional liquid jet flow is carried out and its breakup behavior considering one-phase flow is investigated. Length of liquid breakup in Reyleigh regime is calculated for various flow conditions such as different Reynolds and Weber numbers and the results are validated by an experimental correlation. The whole numerical solutions are accomplished for both Wendland and cubic spline kernel functions and Wendland kernel function gave more accurate results. Effect of fluid viscosity is investigated in the breakup length of the fluid as well. The accomplished modeling presented that smoothed particle hydrodynamics (SPH) is an efficient method for simulation of liquid jet breakup phenomena.

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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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Electrospray is a branch of the scientific area of electrohydrodynamics which is based on electrical charging of liquids. The electrospray governing equations are a combination of hydrodynamic and electrostatic equations to which the addition of liquid breakup process escalates their complexity. This research work aims at developing a numerical solver to simulate the electrospray process in an emitter-disc configuration using Heptane as a working liquid under various electrical potentials. The simulation results in comparison with CFD and experimental data show good agreements both quantitatively and qualitatively. The results clearly have captured the formation of liquid flow profiles at the emitter exit demonstrating various electrospray modes. These modes initiate a microdripping mode at the lowest voltage, i.e. 3.5kV, prompting consecutively to spindle and pulsating cone-jet modes and ending in a stable cone-jet mode at the highest charging voltage, i.e. 6.5kV. In addition, it is also observed that the liquid cone and the vortex shaped within it would shrink as an increase in the electric potential is imposed. Although the increase in electric potential results in rise of the maximum magnitudes of electric field and velocity, the electric charge accumulation at all electric potential values occurs on the outer surface of the liquid flow implying its electrical conductivity.

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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.