مجله مکانیک سیالات و آیرودینامیک
سال دوازدهم شماره 1 (بهار و تابستان 1402)

In this paper the experimental of the viscous fingering phenomena at the interfacial of the two fluids at the porous media for Newtonian and Non-Newtonian fluids investigated. The viscous fingering challenged at the industrial/academic at the recently years. In this experimental study the porous media made with the Co2 laser technology. The water/glycerol as the Newtonian and Xanthan gum polymer used as the polymeric additive. Also, the methanol with the color used as the injection fluid to porous media cell. The experimental observation recorded and processed with the MATLAB code. The results shown that the efficiency for non-Newtonian fluid increased than the Newtonian. Also, the breakthrough time properties increased for polymeric fluid. The max position and perimeter in the porous media detected and the results shown that instability intensity of viscous fingering reduced when the Non-Newtonian used as the bulk fluid.

According to the need to redesign the 4-stage compressor, dynamic analysis of the fluid in the compressor rotor is needed. Since it is very difficult to access such compressors in practice, by preparing a complete model of the compressor rotor by drawing and mapping and a three-dimensional model, simulating the behavior of the fluid on the rotor including the pressure profile between the blades and the flow rate. volume and output are obtained. The results of the simulation have been compared with the experimental results of the current compressor performance including different types of compressor performance data. Then, by simulating the redesigned compressor, its performance is investigated. According to the obtained results, the maximum Mach number occurs at the inlet of the blades and in the diffusers also at the inlet of the diffusers, therefore, to control the Mach number, it is sufficient to control the Mach number only at the inlet of the blade and the inlet of the diffuser. It is also possible to consider the last stage Impeller about 10% shorter. The obtained results are used to obtain the strength and service life of the redesigned rotor.

Conventional Wrap-Around Fins (WAF) have unique aerodynamic characteristics, such as changing the roll moment direction with increasing Mach number and the nonlinearity of the aerodynamic coefficients. The placement of Wrap-Around Fins against each other eliminates their aberrant and non-linear aerodynamic characteristics and provides the condition with a less complicated guidance system. In this research, the effects of curvature of Opposite Wrap-Around Fins (OWAF) on the aerodynamic performance of the projectile has been investigated. This investigation has been done numerically, and the results were compared with the wind-tunnel accessible test data, which have good accuracy. The simulation has been carried out at a Mach number of 1.5 and an angle of attack of  0 and 5 degrees, assuming a turbulent compressible flow; the physics of the flow around the fins has been investigated. The results showed that increasing fins curvature increases lift and drag coefficients by 7% and pitch moment up to 20%. Also, the fin curvature eliminate flow separation in junction of fin leading edge and body.

In this study, a direct numerical simulation strategy using Arakawa numerical scheme for the barotropic vorticity equation as a single-layer quasi-geostrophic ocean model assuming double-gyre wind force and dissipation has been used. DNS will be compared with the exact solution for two problems with different values of Reynolds and Rossby numbers in order to evaluate the ability of this model to calculate dynamics. The results show that DNS of BVE assuming double-gyre wind force has succeeded in predicting the creation of a turbulent circulation pattern in a short time. In this prediction, it was found that the increase in Reynolds and Rossby numbers will lead to the disappearance of some vortices due to the reduction of the required depreciation for the survival of turbulence over time.

Despite the wide use of micro-turbine engines in various aerospace fields, these engines consume a relatively high amount of fuel to provide desired thrust. The fuel consumption is a key parameter in the efficiency, endurance and range of an unmanned air vehicle. An effective approach to reduce the fuel consumption of these engines while maintaining the thrust value is to convert them into micro-turbofan engines. In this research, a mixed flow micro-turbofan engine structure derived from a micro-turbojet engine is employed. In order to analyze the performance of this structure, a thermodynamic modeling using matrix iteration method and Newton-Raphson solver is performed for a micro-turbofan engine. The findings of engine modeling are validated against a gas turbine performance simulation software. Afterwards, the required fan module is designed for the converted engine. The operation of the micro-turbofan engine in the steady-state and transient regime is investigated. Comparing the performance of the new engine with the experimental data of baseline engine indicates that despite no change in thrust value, the specific fuel consumption is reduced by 20%.

In this study, effects of dielectric barrier discharge (DBD) plasma on aerodynamic flow are investigated around NACA 0012 airfoil for plasma placement according to horizontal position close to leading edge based on 2%, 6% and 10% of the chord length with 20 mN/m plasma momentum and a Reynolds number of 106 using 2-D aerodynamic flow simulations. A user-defined function (UDF) source code is developed for application of plasma discharge in this work. Obtained results show that application of plasma actuator results in delay of stall from 15 degree to 18 degree angle of attack (AOA) and aerodynamic efficiency toward higher AOAs (from 8 degree to 10 degree); where plasma placement close to separation region (according to 10% of chord length) has more aerodynamic efficiency compared to smaller AOAs. However, aerodynamic efficiency of 10% placement plasma is decreasing compared to plasma placement closer to leading edge for operation of higher than 10 degrees AOAs. In addition, positive capability of plasma actuator is investigated for wide range of Reynolds number, where plasma actuator results in improvement of aerodynamic efficiency equal to 16%, 18.9% and 70.2% in optimal AOA for Reynolds number of 105, 106 and 107

Combustion process improvement as one of the most important factors in the energy supplement for different devices has attracted great attention. Recently the concept of plasma assisted combustion as a new approach to increase efficiency and reliability of combustion based systems in the different working conditions has considered. In the present paper, two different experimental setups are used to investigate plasma system effects on the operational characteristics of combustion process. At the first setup, open and confined Bunsen burner is used to study premixed stagnated flame. In this structure flame properties are measured by optical schlieren photography method based on generation and stability of the flame cone. At the second setup, constant volume chamber is used to analyze propagating flame in combustible environment. In this structure high speed schlieren photography from propagating flame front and high frequency pressure measurement is used to study premixed propagating flame. Results indicate that, in the open stagnated flame plasma effects improve the laminar flame speed, in the confined stagnated flame plasma effects improve the flame stability and in the propagating flame plasma effects reduce the ignition delay, develop the lean flammability limit and increase laminar flame speed.

One of the new methods that are used in order to remove actuators and scanning targets in top attack bomblets is the spiral or helical method. In this method, biologically inspired by the flying concept of the single-winged seed, for instance, those of the maple and ash trees, the bomblets undergo a helical motion to scan the region and meet the target in the descent phase.  In order to perform a conical flight, the bomblets should be launched at a certain height with a certain initial speed. The parachute system has a large processional movement of the body in the descent phase and creates many problems to have a stable flight. In this article, it has been tried to use two asymmetric wings in the landing phase instead of the parachute to reduce the sensitivity of the bomblets to environmental factors such as wind. But due to the asymmetry of the body and the rotation of the body, the use of the wings can affect the quality of the scan. In order to investigate the effects of scanning quality, fluid-dynamic simulation has been used. The results show that due to the presence of rotation and the coupling of dynamic equations, the cross moments of inertia should be close to zero so that the scanning quality is within an acceptable range. This is especially difficult due to its asymmetry, which can lead to penalties such as an increase in the weight of the warhead or a decrease in the warhead.

In this research, a thermodynamic model has been developed to simulate the effects of fouling and erosion of the compressor blades of a V94.2 gas turbine. The novel approach of this study involves considering the influence of ambient temperature and humidity on the performance of a faulty turbine as well as using the turbine control system under full load conditions, referred to as Outlet Temperature Control (OTC). In this approach, maintaining a corrected turbine outlet temperature is employed to keep the turbine inlet temperature within a safe range for the blades. This model has been validated using real-world data of a gas turbine. The results demonstrate that by adjusting the OTC control setpoint and taking into account the turbine inlet temperature, a portion of the performance losses can be compensated for. The findings indicate that compressor fouling has a greater impact on parameters such as power output, turbine inlet temperature, and gas turbine efficiency compared to blade erosion. Furthermore, deviation from healthy performance varies with environmental conditions. The results also show that by increasing the control setpoint of a degraded turbine by 6 degrees, considering ambient temperature, power can be increased by 1%, and turbine inlet temperature can be increased by 0.8%.

In this research, the performance of ramjet engine combustion chamber has been evaluated by applying geometrical and physical changes such as changing the diameter of the chamber, changing the size and displacement of the secondary and dilution air holes and changing the mass flow passing through these holes. To do this, at first some typical ramjet combustion chambers were introduced and some of their features were discussed. Then using the information and guidance presented in scientific and technical references a suitable combustion chamber was designed for the defined inlet and outlet conditions. After the geometry has been determined, the simulation process has been carried out in Fluent software and while presenting the results, the performance of the chamber has been investigated. The results show that the values obtained for the geometry of the chamber and the position of the holes are reliable and changing the sizes has no global advantage and is not recommended. Furthermore, it is found that displacing air holes location could improve solution convergence.
 
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This study used the finite volume method and ANSYS software to investigate the effect of elbow air duct vane structures on its performance. Elbow air ducts are among the most widely used ducts in HVAC systems, and changes in their geometry and structure have a significant impact on their performance. The purpose of this study is to investigate changes in the structure of elbow air duct vanes from simple to several different models. These changes include zigzag, semicircular, and sinusoidal vanes with different sizes and pitches, comparing them with a simple vane. Therefore, changes in the temperature, velocity and pressure fields of the air flow in the elbow duct are evaluated. The results of this research show that using zigzag vanes, with smaller pitches, whose lateral ends are facing downwards, causes more disturbance in the air flow in the elbow duct, and increases the heat transfer with the environment. The vane edge tips also had an impact on the amount of disturbance. Also, using sinusoidal vanes has reduced the pressure on the outer radial wall of the elbow air duct. So that, respectively, the use of sinusoidal and simple straight vanes created the lowest and highest pressure levels for the outer wall of the elbow air duct

Improvement of quality and life of the working hydraulic oil is very important in preventing the subsequent defects. This improvement leads not only to the defect prevention but also to the pollution reduction. The machinery accessibility can be increased by the offline filtration. In the present work, the data of the hydraulic oil consumption of dump truck and Shovel are obtained to investigate the feasibility and requirement of the offline filtration. The results of oil analysis have been investigated for this aim. The standard codes were appropriated to the oil contamination data to be analyzed. Results showed that the oil contamination level is high during the normal working life which is an indication of improper online filtration. It requires the more efficient additional offline filtration beside the online ones. The offline filtration requirements have been evaluated according to the hydraulic system specifications.         .