Showing papers on "Vortex lattice method published in 2002"

System Identification of a Vortex Lattice Aerodynamic Model

Abstract: The state-space presentation of an aerodynamic vortex model is considered from a classical and system identification perspective. Using an aerodynamic vortex model as a numerical simulator of a wing tunnel experiment, both full state and limited state data or measurements are considered. Two possible approaches for system identification are presented and modal controllability and observability are also considered. The theory then is applied to the system identification of a flow over an aerodynamic delta wing and typical results are presented.

Optimization of flapping wing motion

Abstract: This paper presents an application of Genetic Algorithm and Sequential Quadratic Programming in improving the performance of flapping wings. A Vortex Lattice Method was employed to model a finite-span flapping wing. The flapping wing model investigated was a rigid rectangular-planform plate with two degrees of freedom, i.e. pitching and heaving. A combination of Genetic Algorithms and Sequential Quadratic Programming was employed to find out the optimum combination of flapping frequency, flapping amplitude, pitch amplitude and phase difference between pitching and heaving that gave maximum efficiency for a given thrust. The hybrid optimization method was superior in solution search capability to that of GA or SQP alone. A function approximation of aerodynamic forces was made using Radial Basis Function to improve computational time cost. However, further refinement was necessary for a successful application of this method in high dimensional search space.

Validation of a Two-Dimensional Numerical Model for Vortex/Blade Interaction

Abstract: The numerical method developed previously to analyze two-dimensional vortex-blade interaction problems is validated using recently measured vortex-induced blade vibration data. It assumed a vortex lattice method to calculate the flow field assuming a distribution of sources and discrete vortices on the blade surfaces and a free wake model for the wake flow. A discrete vortex tracking technique in Lagrangian frame is used to track the path of the vortices. The blade is modeled as elastic structures with two-degree-of-freedom in plunging and pitching direction. The fully coupled fluid-structure interaction problem is resolved by means of a time-marching technique. The flow-field is assumed to be inviscid, incompressible and two-dimensional, with no flow separation occurring on the surfaces of the blade. Two cases were examined and they included a blade-vortex interaction and a blade vortex street interaction problem. In the blade-vortex interaction case, the blade is modeled as rigid; therefore, the response of the structure is purely aerodynamics. The calculated variation of the lift coefficient of the blade with the horizontal missed distance of the convected vortex compares well with known experimental results. In the blade vortex street interaction case, the blade is modeled as elastic and is under the unsteady excitation from a Karman vortex street. The calculated blade responses due to vortex-induced vibration are compared with some recently measured vibration characteristics of a flat plate placed behind a cylinder at different separation distance. Good agreement between calculations and measured vibration amplitudes of the plate at its mid-span is obtained, thus indicating that the numerical method gives a viable model for the analysis of the aerodynamics and structural response in vortex/blade interaction problems.Copyright © 2002 by ASME

Prediction of Hydrodynamic Performances of Ducted Controllable Pitch Propellers

Abstract: A numerical method is developed to predict the steady performance of ducted controllable pitch propllers.A vortex lattice method is used for the propeller and a surface panel method is applied for the duct.The hydrodynamic interaction between the propeller and the duct is solved by an iterative method.A modified trailing vortex wake model of propeller is introduced to describe the distortion and separation of the trailing vortex sheet.By using the present method,the effect factors on the prediction of performance are investigated systematically,and in the meantime boss effect is considered.Numerical calculations are carried out for JD simplified ducted propeller series and JD-CPP series with JD duct.The numerical results are compared with experimental data and good agreement is obtained.

Numerical Simulation of Rowing Sculls at Large Angle of Attack

Abstract: In this paper, the unsteady nonlinear vortex lattice method is used to calculate hydrodynamic performance of the thin wing. Plane quadrilateral vortex lattices are used to approximate the body surface. The vortex strengths on the body and free vortex are solved by iteration alternately. The paper establishes an iteration scheme of rapid convergence, i. e., the vortex strength and free vortex location converge at the same error order. The converged solution of small aspect radio thin wing at large attack angle is also very quickly obtained. The hydrodynamic forces acting on thin wing in some depts of water are calculated by image method. The steady and unsteady hydrodynamic forces on several rectangular flat plates and circle wings with aspect ratios as small as 0.2, at attack angles as large as 60° and in some water depths are calculated. The agreement between present numerical results of these airfoils and experimental results or other calculatons indicates that the present work is successful. The rowing scull is a kind of thin wing (0.5λ1.2). It always works at large attack angles near 90°. In this paper, the steady and unsteady hydrodynamic performance of "Big Blade", which is most used in the rowing competition, is calculated. The dependence of some energetics on the concerned physical parameters, such as the depth of water, the frequency,etc., is exhibited. Based on these calculation, the technique in rowing sports in the viewpoint of hydrodynamics is analyzed.