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.

Development of Unified High-Fidelity Flight Dynamic Modeling Technique for Unmanned Compound Aircraft

Abstract: This study presents the unified high-fidelity flight dynamic modeling technique for compound aircraft. The existing flight dynamic modeling technique is absolutely depended on the experimental data measured by wind tunnel. It means that the existing flight dynamic model cannot be used for analyzing a new configuration aircraft. The flight dynamic modeling has to be implemented when a performance analysis has to be performed for new type aircraft. This technique is not effective for analyzing the performance of the new configuration aircraft because the shapes of compound aircraft are very various. The unified high-fidelity flight dynamic modeling technique is developed in this study to overcome the limitation of the existing modeling technique. First, the unified rotor and wing models are developed to calculate the aerodynamic forces generated by rotors and wings. The revolutions per minute (RPM) and pitch change with rotation direction are addressed by rotor models. The unified wing model calculates the induced velocity by using the vortex lattice method (VLM) and the Biot–Savart law. The aerodynamic forces and moments for wings and rotors are computed by strip theory in each model. Second, the performance analysis such as propeller performance and trim for compound aircraft is implemented to check the accuracy between the proposed modeling technique and the helicopter trim, linearization, and simulation (HETLAS) program which is validated. It is judged that this study raises the efficiency of aircraft performance analysis and the airworthiness evaluation.

Vortex lattice method for a straight hydrofoil near a free surface

Abstract: The paper presents a vortex lattice method for the calculation of lift on a straight hydrofoil of finite span near the free surface of an infinitely deep fluid. The velocity field induced by the vortex lattice satisfies the linearized free surface boundary condition and the radiation condition. Lift calculations are compared with experimental results for a 5.11 aspect ratio hydrofoil of the circular arc type. Two options regarding the path of the trailing vortices are examined, i.e. that the trailing vortices leave the hydrofoil directly from the camber surface or via the trailing edge. It is shown that for moderate effective angles of attack the results are very similar, and that the first option, which is simpler and computationally more efficient than the second, is sufficiently accurate for practical purposes. The method was also used to compute the variation of hydrodynamic characteristics with depth of submergence and Froude number for a flat plate of finite span. Results are presented for aspect ratios of 2, 5 and 10 respectively.

An unsteady vortex lattice method model of a horizontal axis wind turbine operating in an upstream rotor wake

Abstract: An unsteady formulation of the vortex lattice method, VLM, is presented that uses a force- free representation of the wake behind a horizontal axis wind turbine, HAWT, to calculate the aerodynamic loading on a turbine operating in the wake of an upstream rotor. A Cartesian velocity grid is superimposed over the computational domain to facilitate the representation of the atmospheric turbulence surrounding the turbine and wind shear. The wake of an upstream rotor is modelled using two methods: a mean velocity deficit with superimposed turbulence, based on experimental observations, and a purely numeric periodic boundary condition. Both methods are treated as frozen and propagated with the velocity grid. Measurements of the mean thrust and blade root bending moment on a three bladed horizontal axis rotor modelling a 5 MW HAWT at 1:250 scale were carried out in a wind tunnel. Comparisons are made between operation in uniform flow and in the wake of a similarly loaded rotor approximately 6.5 diameters upstream. The measurements were used to validate the output from the VLM simulations, assuming a completely rigid rotor. The trends in the simulation thrust predictions are found to compare well with the uniform flow case, except at low tip speed ratios where there are losses due to stall which are yet to be included in the model. The simple wake model predicts the mean deficit, whilst the periodic boundary condition captures more of the frequency content of the loading in an upstream wake. However, all the thrust loads are over-predicted. The simulation results severely overestimate the bending moment, which needs addressing. However, the reduction in bending due to the simple wake model is found to reflect the experimental data reasonably well.

Multidisciplinary Shape and Layup Optimization of a Bendable Composite UAV Wing

Abstract: A Unique bendable UAV wing, developed at University of Florida, shows an ability to load stiffen in positive flight load direction, still remaining compliant in the opposite direction. Performance and application conditions require multidisciplinary approach for design of a bendable UAV wing. The present paper discusses a multidisciplinary design approach to optimize the shape and the layup scheme used to manufacture a bendable wing. Aerodynamics is studied using an inviscid vortex lattice method based numerical code, while nonlinear elastic FEA routine in ABAQUS is used for determining deflection under normalized flight loads. An analytical approach is used to study the stresses developed in the composite wing during rolling process and Tsai-Hill criterion is used to predict failure of the laminate due to the rolling stresses. Multidisciplinary shape and layup optimization of bendable UAV wing is performed using an elitist non-dominated sorting genetic algorithm: NSGA-II. The optimization problem is to maximize the lift-to-drag ratio and to minimize the tip deflection of wing under normalized flight loads. The optimization work is performed on a 24 inch span and 7 inch chord bendable wing.