Vortex lattice method

About: Vortex lattice method is a research topic. Over the lifetime, 779 publications have been published within this topic receiving 9242 citations.

Parametric analysis of swept-wing geometry with sheared wing tips

Abstract: A computational parameter study is presented of potential reductions in induced drag and increases in lateral-directional stability due to sheared wing tips attached to an untwisted wing of moderate sweep and aspect ratio. Sheared tips are swept and tapered wing-tip devices mounted in the plane of the wing. The induced-drag results are obtained using an inviscid, incompressible surface-panel method that models the nonlinear effects due to the deflected and rolled-up wake behind the lifting surface. The induced-drag results with planar sheared tips are compared to straight-tapered tip extensions and nonplanar winglet geometries. The lateral-directional static-stability characteristics of the wing with sheared tips are estimated using a quasi-vortex-lattice method. For certain combinations of sheared-tip sweep and taper, both the induced efficiency of the wing and the relevant static-stability derivatives are predicted to increase compared to the wing with a straight-tapered tip modification.

Aerodynamic Characteristics of Elastically Deformed 3-Dimensional Membrane Sail

Abstract: It is well known that aerodynamic forces acting on an elastic lifting surface are affected by structural deformations caused by aerodynamic forces on the surface or changes of attack angle due to these deformations. This type of problems are referred to as aeroelastic problems. Aeroelastic effects are much more significant in aerodynamic performance of yacht sails than ordinary wings of aircrafts, because the sail of yacht is formed by an elastic membrane. The pressure distribution on a membrane in a flow can be calculated if the shape of the membrane is determined. However, the shape is a result from the equilibrium of aerodynamic pressure and inner stress of the membrane, which depends on aerodynamic pressure. In order to treat this kind of mutual interaction between aerodynamic forces and elastic forces, some analytical or numerical approaches have been proposed to give reasonable solutions.In the present paper, Finite Element Method and a modified Vortex Lattice Method are adopted to solve aeroelastic problems of 3-dimensional elastic membrane sails. Made is use of large deformation incremental method to calculate stress and strain in deformed state of membranes, and to determine the sail shape in equilibrium state under loadings. One of the main advantages of the incremental method is that this method can be applied to dynamic problems more easily than the iterative method.The usefulness of this approach is confirmed by comparing numerical results obtained by the present method with existing numerical solutions of elastic membranes and experimental results of yacht sails as well. As examples of application of the solution proposed in this paper, a series of numerical calculation is carried out to clarify the effect of leech tension and sail material on the aerodynamic performance of sail.

Theoretical and experimental analysis of longitudinal and lateral aerodynamic characteristics of skewed wings at subsonic speeds to high angles of attack

Abstract: The effects of sweep and aspect ratio on the longitudinal and lateral-directional aerodynamic characteristics of low-aspect-ratio skewed (oblique) wings having separation-induced vortex flows along leading and side edges were investigated in the Langley high-speed 7- by 10-foot tunnel at a low-subsonic Mach number. The theoretical analysis used the vortex-lattice method for estimating attached-flow aerodynamic characteristics and the leading-edge suction analogy of Polhamus for estimating separation induced vortex-flow effects. Experimental results were compared with asymmetric, separated, vortex flow theory.

Experimental and Numerical Studies on Static Aeroelastic Behaviours of a Forward-Swept Wing Model

Abstract: The static aeroelastic behaviours of a flat-plate forward-swept wing model in the vicinity of static divergence are investigated by numerical simulations and wind tunnel tests. A medium fidelity model based on the vortex lattice method (VLM) and nonlinear structural analysis is proposed to calculate the displacements of the wing structure with large deformation. Follower forces effect and geometric nonlinearity are considered to calculate the deformation of the wing by finite element method (FEM). In the wind tunnel tests, the divergence dynamic pressure is predicted by the Southwell method, and the static aeroelastic displacement is measured by a photogrammetric method. The results obtained by the medium fidelity model calculations show reasonable agreement with wind tunnel test results. A high fidelity model based on coupled computational fluid dynamics (CFD) and computational structural dynamics (CSD) predicts better results of the wing tip displacement when the freestream dynamic pressure is approaching the divergence dynamic pressure.

Numerical Calculation of the Security of Deploying and Retracting Underwater Towed System

Abstract: In order to evaluate the security of an underwater towed system which is deployed or retracted from the up stabilizer of a submarine, the near wake flow field of the propeller and hull was calculated. The vortex lattice method is used for the propeller based on the lifting surface theory, and the panel method is used for the hull, and also the interaction of the two parts is taken into account. A dynamic model of the towed system was established in the non-uniform wake flow field, and the shape of the towed system was investigated by finite difference method. The results of the calculation show that the security is enough for deploying and retracting cable.