Subsonic unsteady aerodynamics for general configurations (original) (raw)
A finite element approach to subsonic aerodynamics
International Journal for Numerical Methods in Engineering, 1979
A study of the application of the Finite Element Method to compressible potential flows, typified by the airfoil problem, is undertaken. Some novel approaches, believed to simplify solution techniques, are presented. The solutions use two pseudo-variational integrals, appropriate to subsonic flows, and possessing a physical iterative basis. With constant-derivatives triangular elements formulated for cylindrical coordinates , accurate solutions are easily obtained for the flow over a circular cylinder. For arbitrary airfoils a simple mapping is used to transform them into near circles. An appropriate mesh is then constructed in the mapped plane. The paper then presents two solution approaches by which this non-linear problem is solved in both the near circle plane and the airfoil plane.
2004
A numerlcalprocedure has been developed for analyzlngwlngs and wingbody combinations and for designing optimum wlng camber surfaces in the presence of a body. The method is very general and applies to wings of arbltraryplanformand bodies of arbitrary cross section and camber. The procedure has been programed for automatic computation and considerable effort has been made to allow the user to analyze a great variety of conflguratlonswlth relatively simple input data. For a glvenwing or wing-body combination, five classes of problems may be solved: (1) Wing _arp required to support a given loading on the wing (2) Wing loading for a given wing warp (3) Pressures on the upper and lower surfaces of a warped wing of small but finite thickness (4) Minimum drag wing shape for a given llft constraint (9) Minimum drag wing shape for a given lift and moment constraint The validity of the method has been confirmed by comparison wlth exact solutions to the linearized flow equation for several si...
Nonlinear Aeroelastic Analysis of Complete Aircraft in Subsonic Flow
Journal of Aircraft, 2000
Aeroelastic instabilities are among the factors that may constrain the ight envelope of aircraft and, thus, must be considered during design. As future aircraft designs reduce weight and raise performance levels using directional material, thus leading to an increasingly exible aircraft, there is a need for reliable analysis that models all of the important characteristics of the uid-structure interaction problem. Such a model would be used in preliminary design and control synthesis. A theoretical basis has been established for a consistent analysisthat takes into account 1) material anisotropy, 2) geometrical nonlinearities of the structure, 3) unsteady ow behavior, and 4) dynamic stall for the complete aircraft. Such a formulation for aeroelastic analysis of a complete aircraft in subsonic ow is described. Linear results are presented and validated for the Goland wing (Goland, M., "The Flutter of a Uniform Cantilever Wing,"
Approximate Modeling of Unsteady Aerodynamics for Hypersonic Aeroelasticity
Journal of Aircraft, 2010
Various approximations to unsteady aerodynamics are examined for the aeroelastic analysis of a thin doublewedge airfoil in hypersonic flow. Flutter boundaries are obtained using classical hypersonic unsteady aerodynamic theories: piston theory, Van Dyke's second-order theory, Newtonian impact theory, and unsteady shock-expansion theory. The theories are evaluated by comparing the flutter boundaries with those predicted using computational fluid dynamics solutions to the unsteady Navier-Stokes equations. In addition, several alternative approaches to the classical approximations are also evaluated: two different viscous approximations based on effective shapes and combined approximate computational approaches that use steady-state computational-fluid-dynamics-based surrogate models in conjunction with piston theory. The results indicate that, with the exception of first-order piston theory and Newtonian impact theory, the approximate theories yield predictions between 3 and 17% of normalized root-mean-square error and between 7 and 40% of normalized maximum error of the unsteady Navier-Stokes predictions. Furthermore, the demonstrated accuracy of the combined steady-state computational fluid dynamics and piston theory approaches suggest that important nonlinearities in hypersonic flow are primarily due to steadystate effects. This implies that steady-state flow analysis may be an alternative to time-accurate Navier-Stokes solutions for capturing complex flow effects.
A Correction Method for Unsteady Transonic Aerodynamics
AIAA Scitech 2019 Forum, 2019
This paper presents a new method for transonic pitching airfoils based on a RANS CFD study and the Theodorsen model of an oscillating pitching flat plate. This study quantifies the deviation of the lift coefficient predictions using CFD from that obtained using the Theodorsen model, which is based on the incompressible potential flow assumption. The present method corrects this theoretical model by modulating the Theodorsen functions by coefficient functions that depend on the reduced frequency and the Mach number. It is demonstrated that the modified theoretical model predicts lift coefficient in good agreement with the CFD results in the Mach number range from incompressible (M =0.2) to transonic (M =0.755) flow for a range of reduced frequencies typical of transonic flutter. The simulations are first validated by comparing pitching NACA0012 airfoil results with experimental results at transonic flight conditions, which establishes the requirements for a grid converged unsteady transonic solution. The hysteresis loop, C l versus α, attains a grid independent solution that compares well with experiment. The present correction method will guide the development of a new state space model for the Variable Camber Continuous Trailing Edge Flap (VCCTEF) system and eventually a new transfer function that will be incorporated in a new aeroelastic framework leading to an appropriate transonic flutter model for use in the future aircraft systems in development under the NASA Advanced Air Transportation Technologies (AATT) project.
Unsteady supersonic aerodynamics based on BEM, including thickness effects in aeroelastic analysis
Journal of Fluids and Structures, 2004
A general three-dimensional aeroelastic solver is developed based on coupled finite element and boundary element methods and applied to investigate the flutter boundaries in supersonic flows. The boundary element method is applied to three-dimensional unsteady supersonic potential flow as the aerodynamic model and coupled with the finite element method for structural modelling, in order to construct the system of aeroelastic equations. The aeroelastic equations are solved for the flutter prediction using the frequency domain approach. Flutter boundaries for two types of wing planforms at supersonic speeds are determined and compared with the existing experimental results and previous numerical investigations which show good agreement.