مجله مهندسی مکانیک امیرکبیر
سال پنجاه و پنجم شماره 7 (مهر 1402)

Hypersonic glide vehicles are a novel type of hypersonic weapons that have received extensive attention. These vehicles can seriously challenge any defense system by traveling long distances of about thousands of kilometers in the atmosphere at very high speeds up to more than 20 Mach. In this research, the aerodynamic design of a hypersonic glide vehicle has been done based on the waverider theory and conical-derived waverider Method . In this study, a parametric method with three parameters, including cone shock angle β, dihedral angle φ, and compression ratio S, was introduced and used as a design code. In the design process, the HTV2 hypersonic glide vehicle was used as a reference model. To achieve configurations with operational dimensions, by changing the design parameters, four waverider configurations with identical dimensions were identified as the reference model. By analyzing these four configurations using the computational fluid dynamics method, the configuration with the best aerodynamic and volume results was selected as the preferred design configuration. Compared to the reference model, the preferred configuration has 36% more aerodynamic efficiency and 15% less volume, and indicating the efficiency of the used method.

Fluid-structural interaction is one of the most challenging phenomena observed in the surrounding environment, which can play a major role in increasing heat transfer, reducing drag and lift coefficients, energy dissipation, and reducing pressure drop. By inspiration from similar phenomena in nature, the dynamic behavior of flexible structures which interact with fluid is recognized as a novel application in industrial process such as marine equipment, heat exchangers, and fluid transports. So, this phenomenon should be considered as a way to increase efficiency, eliminate defects and also prevent possible damage in industrial issues on a smaller scale. In this study, the effect of a detached flexible plate, which are placed at specific distance from a circular cylinder, on aerodynamic and thermal parameters is investigated. This study is simulated by the finite volume method and the finite element method, simultaneously, and also kw-SST model is considered as the turbulent flow model. The fin is placed at different distances of 0.5D, 1D and 1.5D in upstream and downstream of the circular cylinder, where D is diameter of the cylinder. The results show that placing the fin at distance 1D from cylinder in downstream, increases the Nusselt up to 15%. Moreover, the maximum reduction of the drag coefficient is obtained in this situation

The nacelle cover and nose cones of most megawatt wind turbines are made of composite sheets. Due to the different shapes and geometries as well as the large dimensions of this components, this components are composed of several parts that must be connected to each other by non-permanent mechanical connections such as bolts. Therefore, it is very important to know all the effective parameters affecting composite joints. One of the most important design parameters of bolt connections is the amount of blot preload or tightening torque. Due to the composite material of the sheets on both sides of the joint, it is not possible to increase the preload without any concern. Because, this in itself can lead to damage to the composite sheets. Therefore, in this paper, first, the effect of bolt preload or bolt tightening torque on composite joints has been evaluated experimentally. For this purpose, identical specimens with bolt tightening torques of 2, 10, 20, 30, 40 and 50 Nm have been fabricated and subjected to tensile testing. Then, after determining the optimal preload force, 4 different types of arrangement were experimentally tested to find the best bolt arrangement. Finally, by examining different aspects, the best arrangement for connecting different parts of the nacelle cover and nose cone is determined.

The pH level of nanofluids plays an important role in stability and thermal conductivity. But limited studies have been done in this field. In this research, the effect of pH on the stability and thermal conductivity of ZnO-EG nanofluid at concentrations of 0.05 and 0.75% volumetric fraction and MgO-W at concentrations of 0.05 and 0.5% volumetric fraction were investigated. Experimental measurements of the thermal conductivity were performed by KD2 Pro at a constant temperature of 25 °C. The results showed that the pH strongly affected the stability of nanofluids, so that at the pH of the isoelectric point (IEP), complete aggregation and sedimentation were observed. The thermal conductivity of nanofluids have the lowest value at the pH of the isoelectric point, but as the pH moves away from the isoelectric point, the thermal conductivity has increased. The highest enhancement in the thermal conductivity of ZnO-EG nanofluid was 63%, which was obtained at a volume fraction of 0.75% and pH = 12. However, the highest enhancement in the thermal conductivity of MgO-W nanofluid was 49%, which obtained at a volume fraction of 0.5% and pH = 12. Finally, using the experimental results and with the help of curve fitting, equations with good quality were presented to predict the effective thermal conductivity of metal oxide nanofluids.

In the present study,by simulating the process of two consecutive sneezes using a real model of the upper airway of a 65-year-old non-smoking man,the dispersion pattern of droplets resulting from the process of two consecutive sneezes has been investigated.Using computational fluid dynamics,the velocity of airflow during two consecutive sneezes was checked and the k-ωSST turbulence model was used to check the flow.Assuming realistic flow rate changes in both sneezes,the maximum flow rate during sneezing according to the subject's age and gender is equal to553L/min.In the present study,the simulation has been carried out by considering a wide range of droplets with diameters of1 to1000microns, and about 2million drops have been injected into the surrounding environment during the process of two consecutive sneezes.In this study,the temperature of the air in the surrounding environment and the air jet coming out of the respiratory system are assumed to be24 and35 C,and the relative humidity of the surrounding environment and the air jet is assumed to be 65and95%.The maximum rate of penetration and spread of droplets resulting from two consecutive sneezes in 5seconds is19.9and7.5% higher than the rate of penetration and distribution of droplets resulting from a single normal sneeze at the same time.Most of the injected droplets have evaporated in the surrounding environment during the process of two consecutive sneezes,and less than40000drops are left in the environment in 5seconds.

Using biogas, rather than pure hydrogen, in a solid oxide fuel cell (SOFC) can help the green energy production chain. This research investigates the influence of operating conditions on the performance of a biogas-fueled SOFC. In this regard, a 3D numerical model is developed using finite volume approach and Fluent software. User Defined Functions are employed to introduce the steam reforming processes inside the SOFC. Second-order upwind scheme and SIMPLE algorithm are used for the discretization of governing equations and the pressure-velocity coupling. The results indicate that the power density first increases and then decreases by increasing the steam to fuel (S/C) ratio. Increasing the biogas methane content causes the performance of the SOFC to improve through enhancing the rates of reforming reactions. At a voltage of 0.5V and an operating temperature of 1073K, increasing the biogas methane percentage from 45% to 65%, causes the power to increase by 15%. Also, increasing the operating temperature enhances the SOFC performance through increasing the rates of reforming and electrochemical reactions and the electrolyte ionic conductivity. At a voltage of 0.5V, for a biogas methane percentage of 65%, increasing the operating temperature from 1073K to 1273K, leads to a 132% growth of power. It is also found that the optimal S/C ratio decreases with temperature and increases with biogas methane content and lies within the range of 0.3-1.2.