Journal of Mechanical Engineering
Volume:7 Issue: 3, Summer 2023

In the era of rapid technological developments, the green aircraft and winglets of airplanes play a crucial role in reducing fuel consumption and its ensuing pollution. In this regard, the novelty of this paper is to focus on investigating the effect of the different geometrical parameters of winglets planforms on improving the aerodynamic performance of a wing with a supercritical airfoil (NACA 641412) at lower Reynolds numbers (take-off and landing phase). These investigations were conducted experimentally in a wind tunnel by force measurements through an external force balance. The aerodynamic coefficients of CL and CL/CD were obtained for the clean wing and nine various winglet planforms at a wide range of angles of attack from -4° to 20° and Reynolds numbers from Re=0.99×105 to Re=1.98×105. Furthermore, to get better insight into the physics of the flow, the numerical simulation of specific cases was carried out. According to the force measurement and vorticity magnitude results, among single winglets of W1, W2, W3, and W4, the W1 winglet with vertical height and linear side showed a better performance in all Reynolds numbers with a maximum lift increment of 26%; also, the W7 winglet planform represented the best performance as in double winglets with a maximum lift-todrag ratio increment of 40%.

This paper refers to retrieving the lost heat of exhaust gas and working fluid of a turbocharged Diesel engine employing a Dual-Pressure Organic Rankine Cycle. The efficiency and emission of Diesel compression ignition engines are studied by considering a one-dimensional twozone thermodynamic model. In the proposed system, exhaust gas and intercooler waste heat have been utilized in the high and low-pressure evaporators, respectively. The used cycle has the capability of reducing the irreversibility of the heat transfer process in the evaporators and increasing the turbines’ power. Furthermore, hybrid fuels are used in the turbocharged Diesel engine to decrease the level of environmental pollutants. Accordingly, an exergy-based thermodynamic approach is employed to analyze a Diesel engine’s performance and its emissions. The proposed engine includes Diesel fuel mixed with methanol and ethanol with different volume fractions of 5% and 10%. The results indicate a reduction in power and maximum brake torque of the engine as well as a remarkable decrement in the emission of pollutants such as nitrogen oxides and carbon monoxide (equal to 15%) by using the alcoholic compounds with Diesel fuel. Also, R123 is an appropriate coolant utilized in the Dual-Pressure Organic Rankine Cycle for recovering the lost heat of the Diesel engine.

In this paper, a theoretical model for simulation of a solar updraft tower power plant with the assumption of axisymmetric condition is developed to study the impact of hot gas injection at the chimney base as well as extraction of a portion of hot gas after the turbine and re-entered it at the collector inlet. A new computational code is written by Matlab software and the effects of operational parameters are studied. Results show that the maximum power output is increased by 49.9% by increasing the extraction fraction from 0% to 40% at a wind velocity of 10 m/s. Besides, the obtained results show that the power output is enhanced as the mass flow rate of hot gas increases. As a result, the maximum power output at a hot gas mass flow rate of 30 kg/s is approximately 37% higher than the one at a hot gas mass flow rate of 10 kg/s. Results reveal that the optimum performance of SUTPP takes place at the ratio of pressure drop across the turbine to driving pressure potential in the range from 0.83 to 0.87. Furthermore, the power output in the presence of wind is investigated and the positive influence of wind is illustrated. Results indicate that by increasing the wind velocity from 10 m/s to 30 m/s, the maximum power output is increased by 386.1%

The present study developed a model to deform a viscous droplet in a viscous matrix by a shear flow based on changing the normal vector. The initial cross-section was assumed to be a regular polygon with 1000 sides instead of a circle or ellipsoid, and also this model was independent of the initial polygon shape. Changing the normal vector and the length of each side of the droplet was a function of the velocity gradient. To calculate the velocity gradient over each side of the shape, the equations of tangential and normal stress, the conservation of mass equation, and the absence of mass transfer equation between two phases were solved simultaneously. By knowing the velocity gradient, normal vectors and the length of each side are calculated; therefore, the new shape can be plotted by drawing sides one after another. The results displayed that the time of the break-up, which this model predicts, coincides with the experimental results. On the other hand, the predicted shape of the droplet at the break-up has logically coincided with the experimental results in the middle range of the Capillary number ratio (1.4 -2.6 critical Capillary number). The drop’s dimensions show less than 30% deviation and its rotation less than 20%. Additionally, the dimension of the end bubble also shows a deviation of less than 40%.

This study explores the enhancement of mechanical properties in 3D-printed polylactic acid and acrylonitrile-butadiene-styrene parts through ultrasonic treatment. Tensile samples were fabricated using fused filament fabrication with varying infill percentages (60% and 100%) and layer thicknesses (0.15 mm and 0.30 mm). Post-processing involved a high-power ultrasonic treatment for 2 seconds, followed by tensile testing. The results demonstrated an average 10% increase in tensile strength for both acrylonitrile-butadiene-styrene and polylactic acid after ultrasonic treatment, with the highest tensile strengths measured at approximately 41 MPa and 38 MPa, respectively. However, strain at fracture experienced a decline, except in the samples with an infill percentage of 100 and a number of layers of 10. Scanning electron microscopy revealed dimensional changes and raster merging, more pronounced in 60% and 100% infill samples, respectively. The study employed a comprehensive full factorial design of experiments and finite element simulation for ultrasonic treatment setup design. The interaction of 3D printing and ultrasonic treatment parameters was investigated, with the infill percentage exhibiting the most substantial impact on the ultimate tensile strength. The results highlight the potential of ultrasonic treatment to enhance mechanical properties, reduce defects, and improve the structural integrity of 3D-printed components.

Planning the flight path for a fleet of fixed-wing unmanned aerial vehicles during search and rescue operations poses a significant challenge as it requires minimizing search time and optimizing the formation of the unmanned aerial vehicles. This paper proposes a novel integration of a leaderfollower formation flight technique for multiple fixed-wing unmanned aerial vehicles with a minimumtime search path planning algorithm. In the first step, the proposed algorithm, based on continuous ant colony optimization, plans a sequence of safe and feasible waypoints for the leader while determining appropriate azimuth angles for the followers. In the next step, the algorithm utilizes a nonlinear threedegree-of-freedom model, developed based on a leader-follower formation flight technique, to plan the followers’ flight paths. Applying Dubins curves based on kinematic constraints of the unmanned aerial vehicles not only reduces computational time but also ensures the feasibility of the best search paths between planned waypoints. Furthermore, in the presence of static obstacles, a developed function in the planning process addresses collision and obstacle avoidance constraints. The effectiveness and performance of the suggested method in detecting targets in minimum-time search missions and the ability of the planner to reconfigure the formation of unmanned aerial vehicles in cluttered environments are demonstrated through comprehensive simulation studies and Monte Carlo analysis .