Showing papers on "Vortex lattice method published in 2003"

A model to compare the flight control energy requirements of morphing and conventionally actuated wings

Abstract: This work presents a theoretical analysis of the actuation energy requirements of a morphing aircraft. Morphing aircraft lack discrete control surfaces and use distributed actuation of the wing surface for maneuvering. An adaptive camberline is designed that generates morphed wing shapes in response to variations in leading and trailing-edge camber. Aerodynamic energy expressions are derived from the camberline functions using a unique energy computation stemming from the vortex lattice method (VLM). Beam theory is applied to morphing airfoil sections situated along the wingspan to obtain closed-form strain energy expressions. The resulting work expressions are combined and energy optimal wing deflections are found using Lagrange multipliers. In the optimization, total energy is the cost function and constraints are placed on achieving commanded changes in lift and moment coefficients. The functions are numerically implemented to compare work expressions for a wing with morphing inputs and a conventional wing, with inboard and outboard flaps. It is shown analytically that morphing aircraft have the capability to outperform conventional vehicles in terms of required flight control energy. This work also provides a theoretically sound methodology for morphing wing energy analysis that can be applied in future trade studies of morphing vehicles. Introduction Morphing aircraft are a topic of current research interest in the aerospace community. Such aircraft allow shape optimization over the entire flight regime _________________________ * Graduate Student, Department of Aerospace and Ocean Engineering, Student Member AIAA † Graduate Student, Department of Mechanical Engineering ‡ Professor, Department of Mechanical Engineering § Professor, Department of Aerospace and Ocean Engineering, Associate Fellow AIAA ¶ George R. Goodson Professor, Department of Mechanical Engineering Copyright © 2003 by Christopher O. Johnston. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission in addition to enhanced combat performance by allowing arbitrary vehicle orientation while tracking challenging flight paths. Of recent interest is the possibility of producing minimum energy control deflections by using the distributed actuation capability of morphing vehicles. Petit’s work demonstrated an initial morphing wing analysis based on conformal mapping. His analysis included a numerical computation of the aerodynamic energy response in tracking a flight path. This work builds upon that analysis but approaches the problem in a different manner. As opposed to conformal mapping, the analysis begins at the camberline in terms of a load distribution and derives full analytical expressions for the aerodynamic energy requirements while morphing. Gern used NASTRAN to determine the energy requirements of a morphing and conventional wing in rolling maneuvers. As opposed to a numerical calculation of the energy requirements, this work presents a closed-form expression for the aerodynamic and strain energy functions allowing theoretical insight to be gained into the optimization. Other works have investigated the energy relations of morphing wings but have not presented a general method that is comprehensive enough to proceed with an in-depth analysis. The design of an adaptive camberline function facilitates the use of the VLM energy method and beam theory to derive general energy relations for the vehicle and perform a direct comparison with a conventional aircraft. The next section covers the analytical design of the morphing camberline, followed by the derivation of the closed-form strain energy expressions, and the aerodynamic energy development. We then illustrate the optimization technique via a simple example problem. The paper concludes with numerical work comparisons of a morphing and conventional wing. Adaptive Camberline Derivation The first requirement for morphing analysis is the design of a camberline that will generate morphed wing shapes in response to control inputs. A morphed wing shape is defined by a wing that exhibits changes in A MODEL TO COMPARE THE FLIGHT CONTROL ENERGY REQUIREMENTS OF MORPHING AND CONVENTIONALLY ACTUATED WINGS

Numerical modeling of rudder sheet cavitation including propeller/rudder interaction and the effects of a tunnel

Abstract: This paper presents the coupling of a vortex lattice method (MPUF-3A), a finite volume method (GBFLOW3D), and a boundary element method (PROPCAV) to allow for the prediction of rudder sheet cavitation, including the effect of propeller, as well as the effects of tunnel walls. The unsteady cavity prediction on the propeller blades is performed using MPUF-3A to satisfy both a constant pressure condition on the cavity surface and the flow tangency condition on the cavity and blade surfaces. The effects of the tunnel and a vortical inflow are modeled via GBFLOW-3D by solving the 3-D Euler equations with slip boundary conditions on the walls and by representing the effect of the propeller blades via body forces. The cavity prediction on the rudder is accomplished via PROPCAV (which can handle back and face leading edge or mid-chord cavitation) in the presence of the 3-D flow field produced by the propeller. This flow-field is determined via GBFLOW-3D, in which the propeller is represented via a non-axisymmetric distribution of body forces. The effects of the tunnel walls are also considered in this case by applying a boundary element method on the walls, in the presence of the rudder. A multi-block Euler scheme is also developed in order to determine the effect of the rudder on the propeller

Influences of Pod on the Propeller Performance

Abstract: Based on the theoretical prediction method and experimental results for single-propeller type podded propulsors, the influences of the pod upon the propeller hydrodynamic performance were investigated. The propeller blades are calculated with a vortex lattice method, while the pod including its strut with a boundary element method for non-lifting bodies. Hydrodynamic interactions between the propeller and the pod are treated via iterative calculations. Based on the present numerical results, the influence of the pod on the radial distribution of circulation as well as the pod-induced wake characteristics were discussed.

Prediction of the steady performance of tractor-type podded propeller

Abstract: A numerical method based on the potential flow theory is proposed in this paper for predicting the steady performance of tractor-type podded propellers. The propeller blades are calculated by a vortex lattice method, while the pod including its strut by a boundary element method for non-lifting bodies. Hydrodynamic interactions between the propeller and the pod are treated via iterative calculations. To account for the influence of the pod on the trailing vortex wake of the propeller blades, an existing trailing vortex wake model is modified. With the present method, the steady performances of podded propellers are calculated, and the results agree well with experimental data obtained in a cavitation tunnel.

A Design Method of Ducted Propeller by Coupled Lifting Surface Theory/Panel Method

Abstract: This paper presents a theoretical design method of ducted propeller,in which a vortex lattice method is employed for the propeller design and calculation of interaction velocities on the duct due to propeller and a poˉtential based panel method is applied for the duct performance prediction and calculation of interaction velocities on the propeller due to duct with known duct profile.The hydrodynamic interaction between the propeller and the duct is treated in an iterative manner and thrust allocation of the propeller and duct is determined simultaneously.Two coupled schemes for panel method are adopted:(1)coupled at each step of propeller design process;(2)coupled after the whole design process of propeller.The design examples show that both can get the converged and conˉsistent results.

Modeling and Control of a Morphing Airfoil

Abstract: This paper presents aeroelastic modelling and robust control design for a morphing airfoil concept. A finite dimensional linear time invariant aeroelastic model is developed for a multi-input multi-output morphing airfoil structure. The shape of the airfoil (NACA airfoil series 2415) is controlled by actuators distributed along the top airfoil surface that produce vertical deflections of the top surface at several locations. This results in an airfoil shape change (i.e., “morphing” of the wing), which causes changes in the aerodynamic loading on the wing. The objective is to control the deformation of the airfoil in realtime so as to achieve the desirable aerodynamic forces on the wing. The structural model is developed using the finite element approach. A finite element toolbox in Matlab, namely FEMLAB, is used to obtain eigenfrequencies and mode shapes. A finite dimensional dynamic model of the structure is obtained by the assumed modes method. A static aerodynamic model is developed with a vortex lattice method and coupled with the structural dynamic model to yield a linear aeroelastic model of the morphing wing. A robust LQG design is presented for tracking the commanded lift and roll moment. Some parametric studies are also presented for the choice of different materials. Simulation results are given to demonstrate the viability of the proposed modelling and control methodology for morphing wing concept.Copyright © 2003 by ASME

A small aircraft in hazardous wake near ground using unsteady vortex lattice method

Abstract: The interaction between small aircraft and vortex system generated by another much larger aircraft is investigated. An aerodynamic model based on the modified unsteady vortex lattice method and the method of images was developed. A simple wake model can be developed using this vortex system. The large aircraft represented by a large wing, while, the small aircraft represented by a small wing, were used in this study. Investigation was done for the small aircraft, as it is entering and flying parallel to the wake left by the larger aircraft near ground, during aircraft landing operation, with all aerodynamic surfaces assumed to be of zero thickness. The lateral position of the small wing with respect to the large wing center line is assumed to be variable. Changes in lift, drag, pitching moment and rolling moment coefficients, for the small aircraft, are calculated and presented for deferent cases of study. A case study shows that, as the small aircraft enters the wake left by a large aircraft, a sudden decrease in aerodynamic forces and moments takes place. This situation is more noticeable and dangerous near ground as the small aircraft approaching the ground during landing or take off operations. The lateral position of the small aircraft with respect to the larger one has a great effect, where the lift force could become unsymmetric on both sides of the small wing. This could put the small aircraft into a rolling motion, where it could be deviated from its flight path during the landing or take off operations, an accident might be the result.