Results 1 - 10 of 438
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[en] The objective of this article is to formulate numerical models for two-dimensional potential flow over the NACA 4412 Airfoil using linear vortex panel methods. By satisfying the no penetration boundary condition and Kutta condition, the circulation density on each boundary points (end point of every panel) are obtained and according to which, surface pressure distribution and lift coefficients of the airfoil are predicted and validated by Xfoil, an interactive program for the design and analysis of airfoil. The sensitivity of results to the number of panels is also investigated in the end, which shows that the results are sensitive to the number of panels when panel number ranges from 10 to 160. With the increasing panel number (N>160), the results become relatively insensitive to it. (paper)
[en] The paper deals with compliant mechanisms with a variable stiffness behavior. Devices with such a behavior are getting more and more attention in recent years, especially in contact applications such as human-robotic-interactions or haptic interfaces. In the work presented here the variable stiffness behavior is achieved by the targeted application of prestressing forces. An optimization based method is presented to identify suitable force application points. Furthermore, the amount and direction of force is determined in order to cause a specific change in stiffness. The method consists of a convex optimization formulation and is based on modal parameters. The method is intended to work for any given design of a compliant mechanism. In this publication the method is tested and evaluated using two compliant mechanisms—the cartwheel hinge and a shape-adaptive airfoil profile. (paper)
[en] The novel approach to parametric topology of the 2D compressor airfoil was tested at multi-criteria optimisation problem for high speed subsonic application. Some results regarding the shape of the blade are presented. (paper)
[en] In this paper the luffing of an unstiffened, two-dimensional impervious membrane is examined. When a sail boat is close-hauled the sails are required to generate high 'lift' with minimum drag. They therefore operate, as do those on hang-wing gliders, at incidences below the stall. However, unlike solid wings they must also avoid negative incidences for then a sail begins to lose its concave shape, to become S shaped and finally, as the incidence is further reduced, to oscillate, a behaviour known as luffing
[en] A computationally efficient and adaptable design tool is constructed by coupling a flow analysis code based on Euler equations, with the well established numerical optimization algorithms. Optimization technique involving two analysis methods of Simplex and Rosenbrock have been used. The optimization study involves the minimization of wave drag for two different airfoils with geometric constraints on the airfoil maximum thickness or the cross sectional area along with aerodynamic constraint on lift coefficient. The method is applied to these airfoils transonic flow design points, and the results are compared with the original values. This study shows that the conventional low speed airfoils can be optimized to become supercritical for transonic flight speeds, while existing supercritical airfoils can still be improved further at particular design condition. (author)
[en] This paper discusses airfoil design optimization using a genetic algorithm (GA) with multi-modal distribution crossover (MMDX). The proposed crossover method creates four segments from four parents, of which two segments are bounded by selected parents and two segments are bounded by one parent and another segment. After these segments are defined, four offsprings are generated. This study applied the proposed optimization to a real-world, multi-objective airfoil design problem using class-shape function transformation parameterization, which is an airfoil representation that uses polynomial function, to investigate the effectiveness of this algorithm. The results are compared with the results of the blend crossover (BLX) and unimodal normal distribution crossover (UNDX) algorithms. The objective of these airfoil design problems is to successfully find the optimal design. The outcome of using this algorithm is superior to that of the BLX and UNDX crossover methods because the proposed method can maintain higher diversity than the BLX and UNDX methods. This advantage is desirable for real-world problems.
[en] A numerical method is described in computing a conformal map from an exterior region onto the exterior of the unit disk. The numerical method is based on a boundary integral equation which is similar to the Kerzman-Stein integral equation for interior mapping. Some examples show that numerical results of high accuracy can be obtained provided that the boundaries are smooth. This numerical method has been applied to the mapping airfoils. However, due to the fact that the parametric representation of an air foil is not known, a cubic spline interpolation method has been used. Some numerical examples with satisfying results have been obtained for the symmetrical and cambered airfoils. (Author)
[en] Structurally, corrugated airfoil for flapping wing MAV applications is more desirable due to its increased strength. Therefore, any aerodynamic (penalty) effects due to corrugation on such airfoil have found considerable attention. The objective of the paper is to computationally examine the effects of corrugation on an elliptical airfoil performing translation and pitching motion at Re = 100 by comparing it with the performance of a smooth NACA 0012 airfoil. The forces and the flow structures generated over the airfoils during their unsteady motion are solved using Navier–Stokes equations. These unsteady motions include the airfoil accelerating from the rest position and quickly pitching up in a constant free stream. The two airfoils are considered in the study with 50 and 100 equally spaced perturbations on the upper and the lower surfaces, respectively. The surface of a standard ellipse has been modified with the regular perturbations or ‘corrugation’ of the order of 1% c on the upper and the lower surfaces. The current study reveals that during the airfoil acceleration from the rest to U and, subsequently, in a constant velocity translation, the corrugated airfoils (regular surface perturbations) have similar behavior of the force and the moment coefficients (also similar vorticity plots) in comparison with the smooth airfoil. However, it is also found that for the fast and the slow pitching motion in a free stream, the corrugated airfoil (after certain angle of attack) has slightly lower values of the lift and the moment coefficients in comparison with the smooth airfoil; which is due to the small effect of corrugation on the velocity profile. It is concluded that the unsteady effect dominates the geometric differences (smooth versus corrugated airfoil); therefore, corrugated airfoil can be utilized to provide structural strength for flapping wing MAV applications. (paper)
[en] Highlights: • The Link-Wise Artificial Compressibility Method (LW-ACM) is presented and evaluated. • The method is applied to attached and separated flows around airfoils at low speed and high AOA. • Investigations of the flow around NACA 0012 and TSAGI 12% airfoils are performed by using LW-ACM. • The LW-ACM is efficient and rapidly convergent when used to solve both attached and separated flows. - Abstract: The performance of the recently developed Link-Wise Artificial Compressibility Method (LW-ACM) is evaluated for aerodynamic applications and then applied for both attached and separated flows. Numerical flow simulations are performed around NACA-0012 and TSAGI-12 shaped airfoils at low speed and high angle of attack. Results of aerodynamic characteristics of the airfoils were found in good agreements with previous investigations including LBM (PowerFLOW) and FVM (CFL3D). Results also showed that LW-ACM is efficient and rapidly convergent when used to solve both attached and separated flows.
[en] Results of experimental investigations of the effects of an upstream longitudinal triangular ribbed surface on a turbulent junction flow and downstream wake are presented. The ribbed plate was placed right upstream of the wing on the flat plate surface, covering a 10 x 38 cm2 area. The junction flow was developed using a NACA0012 airfoil mounted normal to a flat plate downstream of its leading edge. The experiments were carried out at a free stream mean velocity of 31 m/s. which corresponds to a unit Reynolds number of 1.8 x 106 and the airfoil chord length Reynolds number of 5.4 x 105. Measurements were carried out at four control planes of 50%, 100%, 133%, and 166% of the wing chord length. Results show that the riblets displace the location of the horseshoe vortex away from the corner and reduce its strength. There are significant reductions in mean streamwise circulation downstream at 133% and 166% planes