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With the advancements of numerical upstream and central difference methods in modeling the subsonic and supersonic flows in different paths including the flow inside turbine blades, employing the numerical CUSP technique in the Jameson’s finite volume method can simultaneously benefit from the positive features of both mentioned methods. The novelty of this paper is first, improving Jameson’s finite volume method in modeling a 2D supersonic flow between the blades of a steam turbine using the CUSP method, and second, defining the most optimum control function mode using the Marquardt-Levenberg inverse method and by accounting for the mass conservation equation. By considering the importance of the shock regions in the blade’s surface suction side, the focus of the mentioned method is on this part which results in the significant improvement of the pressure ratio in Jameson’s finite volume method. The results of the first combined method (Jameson and CUSP) at the shock region of the blade’s suction surface desirably agree with the experimental data, and a decrease of numerical errors at this region is resulted. Furthermore, the results of the second combined method (Jameson, CUSP and inverse method) shows that in comparison with original Jameson’s method and the first combined method, by average, the conservation of mass condition is improved 15% at the shock region of the blade’s suction surface.

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The significance of research on the specifications of the supercritical fluids becomes more evident with respect to the increase of their application in different food, chemical, polymer, oil, and gas industries. One of the major specification, is the coefficient of thermal expansion (β) where the ideal gas model was used in most of the processes in which this component is applied; the weakness of this model is that it is unable to make an accurate prediction of this parameter within the range of critical point. For this reason, in this study to determine the coefficient of thermal expansion, Redlich–Kwong equation of state is used and a new relation as a function of temperature, pressure, and compressibility is obtained. Comparing behavior of the curves obtained from this relation with experimental data, exhibits a favorable consistency. Moreover, natural convection heat transfer of the supercritical fluid in a vertical channel at constant temperature walls conditions were considered numerically. The governing equations were solved using the finite-volume method (FVM) and based on the SIMPLE Algorithm. After validation with the earlier studies. Then, the flow and heat transfer characteristics based on the obtained coefficient of thermal expansion were compared with the ideal gas assumptions. Finally, the trend of change in heat transfer coefficient away from the critical point was studied.

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Supercritical fluids have substituted non-super critical fluids in some areas of industry because of their unique characteristics and have been the subject of numerous experimental, numerical and analytic studies since their discovery. In this study laminar natural convection between a hot vertical tube with constant temperature and supercritical carbon dioxide with uniform temperature at inlet is simulated by utilizing a numerical model. The simulation is a two-dimensional, pseudo-transient numerical model based on finite volume method. The main objective of this study is to investigate and analyze the effect of severe property variations of supercritical carbon dioxide on the flow and temperature field of natural convection that ultimately affect heat transfer rates with respect to non-critical natural convection. Numerical simulations have been carried out for temperature and pressure ranges of 305K to 312K and 7.5MPa to 9MPa respectively. Span and Wanger’s multi-parameter equation of state have been used directly to determine carbon dioxide properties around pseudo critical temperature for the first time. Results indicate an increased rate of total heat transfer up to 160% near pseudo-critical temperature and 118% in other temperatures for supercritical natural convection with respect to ideal gas assumption.

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One of the disadvantages of drag driven vertical axis wind turbines, is low aerodynamic performance of the turbine which is mainly due to adverse torque of the returning blade. A recently introduced design suggests using opening/closing blades for the rotor to eliminate the negative torque of the returning blade. In this study, the aerodynamic performance of the newly proposed turbine has been investigated experimentally and numerically. The experimental measurements are performed in a subsonic open-jet type wind tunnel facility. However, the numerical simulations are performed using the Ansys-Fluent commercial software, using the Multiple Reference Frame model (MRF). The effects of the number of blades (3, 4 and 6-bladed), end plates and turbulence intensity on the torque and power coefficients are examined in details, in several Reynolds numbers. Results show that the new rotor has no negative torque in one complete revolution and the 3-bladed rotor has the best aerodynamic performance, in a manner that, it reaches a maximum power coefficient of 0.21 at TSR=0.5. Although increasing the number of blades decreases the output torque oscillations, it also decreases the average power coefficient of the rotor. Results also show that, Reynolds number does not have significant effects on the average power coefficients of the rotors, in the studied range of Reynolds numbers, 7.7×104 ≤ Re ≤ 1.2×105.

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Improvement of shooting accuracy with air gun pellets is very important in sport competitions which is always questioned by shooting enthusiasts. In this study, the performance of a transonic spherical projectile as an air gun pellet with 4.5 mm-caliber under a mechanism known as Hop-up is numerically examined. The motion of this projectile is assumed in four degrees of freedom including three translational motions and one transverse rotational motion. Hop-up mechanism is resulted in a rotational motion of spherical projectile, so a Magnus Force is generated which prevents the altitude loss of the projectile. The Navier-Stokes equations are solved in compressible non-stationary turbulent conditions with equations of the pellet motion in a coupled form and in a moving computational grid by a computer program. The present numerical simulation is based on “Roe” scheme with second-order accuracy using a finite volume method and because of the importance of time dependent parameters, second-order time accurate was applied. To validate the computer program operation, the results were compared to valid experimental data. The results obtained from these studies showed that proper rotation of the projectile for a certain distance prevents its height drop when hits the target. A relation was also obtained between the target location, shooting kinetic energy and proper angular velocity which can neutralize the projectile altitude loss at arbitrary distavces. It is also demonstrated that by increasing the angular velocity, the vortex shedding onset is accelerated and the projectile momentum is decreased.

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Condensation phenomena in steam flow, can cause droplets with different sizes to form. For an exact prediction of two phase flow behavior, it is necessary to consider the effects of all droplets with different sizes on the steam. In this paper, nucleation equation in an Eulerian–Lagrangian framework has been used to analyze one–dimensional flow of wet steam in a supersonic convergent–divergent nozzle. Polydispersed and monodispersed radius methods for modeling the formed droplets are compared. In polydispersed method, all the formed droplets in the spontaneous condensation zone, are retained in the calculations, without being merged with other groups; but in monodispersed method, all groups are merged, and only one group with averaged radius is retained in the calculations. The polydispersed method has an advantage and can predict the complete droplet spectra. Results of comparing the two methods with experimental data indicates that the predicted radius in the polydispersed method, in every four investigated cases, is closer to experimental data, than that of monodispersed method.

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The circular hydraulic jump usually forms when a liquid jet impinges on a horizontal flat plate. However, under certain conditions of fluid viscosity, volume flow rate and obstacle height downstream of the jump, the flow changes from super-critical to sub-critical and hydraulic jump changes shape from circular to polygonal. Despite the phenomenon of the hydraulic polygon jump has observed about two decades, the experimental relationship has not been presented to estimate the number of sides of hydraulic polygon jumps. The size and number of sides of a polygonal hydraulic jump depend on various factors such as fluid volume flow rate, jet diameter, fluid height downstream of the jump, and fluid physical properties; in other words, they depend on the dimensionless numbers of Reynolds, Weber, and Bond. Hence, in this study Taguchi analysis, as a Design of Experiment method, was used to investigate the effect of volume flow rate, jet diameter and obstacle height downstream of the jump on the number of the sides of a polygon hydraulic jump and Linear and nonlinear relationships was proposed for estimating the number of the sides of a polygonal hydraulic jump in terms of the above mentioned parameters.

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One of the important issues in shooting by air guns is to select the appropriate projectile for different distances of the target. In this paper, the performance of four samples of air gun projectiles (pellets) is studied. The motion of these projectiles is assumed in four degrees of freedom including three translational motions and one rotational motion. The considered projectiles have three calibers of 4.5, 5.5 and 6.35 mm, and four different types, namely flat nose, sharp nose, round nose and spherical. In order to numerical simulation of the problem, after these projectiles have been modeled geometrically, the 3-D compressible turbulent Navier-Stokes equations and dynamic equations of the projectiles motion are solved in a coupled form and in a moving computational grid. The numerical simulation is based on “Roe” scheme with second-order accuracy in space and time using a finite volume method. To validate the computer program operation, the results are compared to valid experimental data. Computed results describe the trajectory, velocity variations and altitude loss of the projectiles with time and location. Comparison of the projectiles performance including the trajectory, velocity variations and altitude loss indicate that the round nose projectile has the best performance in long distances compared to the other samples and the flat nose projectile has a great performance in short distances, while it has a weak behavior in long distances. Additionally, effect of nose shape on the performance of the sharp and round nose projectiles is investigated and the optimum nose shapes are obtained.

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Applying membranes with especial geometries and fouling characteristics has been an area of research and a subject of interest in membrane science community. While a considerable part of fouling happenings are originated from chaotic roots such as Brownian motions, the remainders can be scheduled to approach on desired filtration features. Here in this study the somehow invisible features of progressive fouling which is the case for novel micro-engineered membranes was realized in some details. The problem of progressive fouling was considered as a result of dead-ended filtration of non-colloidal particles over a vertically extended pore geometry. It was shown that, in this filtration apparatus, due to a serialized activation and deactivation of flow passages, progressive fouling can change its seat with other more flow resistive classical types of surface and pore blockings and control filtration path more apparently. Results was considered for different amounts of pore extension and porosities. It was found that employing an especial set of pore extension length and porosity make it feasible to derive manageable filtration processes with high levels of purification and permeation performances.

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