Results 1 - 10 of 362
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[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] 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
[en] The Genetic Algorithm (GA), coupled with the potential flow solver KTRAN, was successfully applied to redesigning the ONERA M6 wing. A 6th order B-spline curve was used to represent each section of the wing. The actual values of the (x, y) coordinates of the control nodes for the B-spline curves were designated as the design variables. The least squares difference between the actual and target pressures was used as the objective function. The NACA0012 airfoil section was taken as an initial geometry. Both pressure distributions and geometry of the redesigned wing agreed well with their target values, demonstrating the ability of this technique. (author)
[en] Shape optimization requires a proper geometric representation of the blade profile; the parameters of such a representation are usually taken as design variables in the optimization process. However, the designer is more familiar with the traditional design parameters; for turbine blades these would be the leading and trailing edge radii, wedge angles, blade angles, as well as the blades stagger angle, spacing, etc. This work is concerned with the representation of the blade profile in terms of NURBS functions that implicitly satisfy the traditional designer parameters and provide enough flexibility and accuracy to represent any turbine blade shape. This NURBS representation is then tested on two distinct turbine blade shapes to demonstrate the NURBS accuracy and flexibility in capturing a target blade profile or a target blade curvature distribution and area. (author)
[en] A novel semi-passive morphing airfoil concept based on variable bending–twist coupling induced by adaptive shear center location and torsional stiffness is presented. Numerical parametric studies and upscaling show that the concept relying on smart materials permits effective twist control while offering the potential of being lightweight and energy efficient. By means of an experimental characterization of an adaptive beam and a scaled adaptive wing structure, effectiveness and producibility of the structural concept are demonstrated. (paper)
[en] The present work successfully extended the single point aerodynamic optimization method in reference 1 to a multi-point optimization procedure. The well-known weighted-sum method was used. The drag minimization study was carried out for the ONERA M6 wing at two different free stream mach numbers M∞ = 0.75 and 0.84. As a result of the drag optimization the drag coefficients on the ONERA M6 wing were reduced by 10.7% and 10.6%, respectively, for a constant lift coefficient of CL = 0.25. (author)