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۱A Novel Strategy for Designing and Manufacturing a Fixed Wing MAV for the Purpose of Increasing Maneuverability and Stability in Longitudinal Axis
اطلاعات انتشار: Journal Of Applied Fluid Mechanics، هفتم،شماره۳، ۲۰۱۴، سال ۰
تعداد صفحات: ۱۲
In this study, a novel simple strategy is proposed to choose and accommodate an airfoil based on the effects of airfoil type and plan–form shape on the flight performance of a micro air vehicle. In this strategy, after defining flight mission, the weight of the micro air vehicle is estimated and then, aerodynamic parameters and thrust force are calculated. In the next step, some different plan–forms and airfoils are investigated to be selected for decreasing the stall region in high attack anglesby open source software named XFLR5. Having calculated the aerodynamic center, the pitching moment needed to stabilize the micro air vehicle is computed. Due to the static margin, the airfoil camber line is changed to stabilize the micro air vehicle and then, its thickness is improved to reach to a high aerodynamic characteristic. To evaluate the software results, some flight tests are performed which then compared to the software results that show a good agreement. Finally, some adjustments and improvements are made on the micro air vehicle and then, its performance is obtained by the flight tests. The flight test results show it has an excellent aerodynamic performance, stability and maneuverability.
اطلاعات انتشار: Journal Of Applied Fluid Mechanics، هشتم،شماره۴، ۲۰۱۵، سال ۰
تعداد صفحات: ۹
Recently a new inverse design algorithm has been developed for the design of ducts, called ball–spine (BS). In the BS algorithm, the duct walls are considered as a set of virtual balls that can freely move along some specified directions, called ‘spines’. Initial geometry is guessed and the flow field is analyzed by a flow solver. Comparing the computed pressure distribution (CPD) with the target pressure distribution (TPD), new balls positions for the modified geometry are determined. This procedure is repeated until the target pressure is achieved. In the present work, the ball–spine algorithm is applied to three–dimensional design of axial compressor blades. The design procedure is tested on blades based on NACA65–410 and NACA65–610 profiles and the accuracy of the method is shown to be very good. As an application, the pressure distributionof the blade with NACA65–610 profiles is modified and the pressure gradient in the aft part of the blade is decreased and selected as target pressure distribution. The corresponding geometry which satisfies the target pressure is determined using the BS design algorithm.
اطلاعات انتشار: Journal Of Applied Fluid Mechanics، نهم،شماره۵، ۲۰۱۶، سال ۰
تعداد صفحات: ۱۳
Journal bearings are widely used in different machineries. Reynolds equation is the governing equation to predict pressure distribution and load bearing capacity in journal bearings. There are many analytical and numerical methods for solving this equation. The main disadvantage of these methods is their inability to analyze complex geometries. In this paper, a comprehensive method based on dynamic mesh method is developed to solve the conservation equations of mass, momentum and energy. This method has smaller error compared to other techniques. To verify the accuracy of this method, the bearings with different length to diameter ratios are analytically and numerically analyzed under different loads and compared with each other. In continue, the turbocharger’s bearing is numerically simulated and the effects of rotational speed change are studied. Finally, the turbocharger’s bearing with four axial grooves are simulated. The simulations results show that adding grooves to the turbocharger’s bearing causes the bearing eccentricity ratio and lubricant flow rate to increase and the attitude angle, rate of temperature rise and frictional torque to decrease.
اطلاعات انتشار: دوم،شماره۳، پاييز ، سال ۱۳۹۱
تعداد صفحات: ۹
The purpose of this study is to design a three–stage axial compressor with identical pressure ratio which makes an adequate pressure ratio and efficiency in design point conditions with rotational velocity of 38000rpm and mass flow rate of 3.2kg\s. First of all, considering some restrictions such as Dehaller number more than 0.7 in all sections of the stator and the rotor, and relative Mach number less than 0.8 at the tip of the rotor blade , one dimensional design is performed. In this design, blade base diameter is considered the same in all stages, regarding shaft diameter. In order to reduce casing diameter, inlet guide vanes are utilized so that the relative Mach number at the tip of the first stage rotor blade decreases. Therefore, the design of the rotor blades and the stator are based on reaction coefficient of 0.5. According to calculated input and output angles, adequate profile for each section is selected from NACA–Mellor diagrams. The output of the one dimensional design program is calculation of all the geometric parameters including blades input and output angles, blades length and diameter, solidity coefficient, number of blades and installation angle at three different sections of hub, mid and tip in compliance with the constraints. Thus, the three–dimensional shape of the blades is created. To investigate the performance of the designed compressor at design point, an appropriate grid is selected on the three–dimensional geometry of the compressor and the three–dimensional numerical solution is obtained using a full Navier–Stokes program.
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