A methodology is presented for using the Volterra-Wiener theory of nonlinear systems in aeroservoelastic (ASE) analyses and design. The theory is applied to the development of nonlinear aerodynamic response models that can be defined in state-space form and are, therefore, appropriate for use in modern control theory. The Volterra-Wiener theory relies on the identification of nonlinear kernels that can be used to predict the response of a nonlinear system due to an arbitrary input. A numerical kernel identification technique, based on unit impulse responses, is presented and applied to a simple bilinear, single-input-single-output (SISO) system. The linear kernel (unit impulse response) and the nonlinear second-order kernel of the system are numerically identified and compared with the exact, analytically defined linear and second-order kernels. This kernel identification technique is then applied to the computational aeroelasticity program-transonic small disturbance (CAP-TSD) code for identification of the linear and second-order kernels of a NACA64A010 rectangular wing undergoing pitch at M = 0.5, M = 0.85 (transonic), and M = 0.93 (transonic). Results presented demonstrate the feasibility of this approach for use with nonlinear, unsteady aerodynamic responses.

Application of nonlinear systems theory to transonic unsteady aerodynamic responses

Multi-Disciplinary Design and Performance Assessment of Effective, Agile NATO Air Vehicles

This paper reports on a numerical investigation of the use of trailing-edge circulation control as a roll effector on a generic unmanned combat aerial vehicle: the DLR-F19 stability and control configuration. The Coanda effect induced by fluidic injections at the trailing edge of a wing is used to increase circulation and generate lift. Reynolds-averaged Navier–Stokes predictions are validated against wind-tunnel experiments conducted at the Georgia Institute of Technology and NASA’s basic aerodynamic research tunnel on an airfoil employing trailing-edge circulation control. Two turbulence models are used: the Wilcox k-ω model and Menter’s shear-stress transport, showing that the Wilcox k-ω model provides the best comparisons with the experimental data. Baseline data for the stability and control configuration with conventional control surfaces from wind-tunnel experiments done at the low speed wind-tunnel owned by the German- Dutch Wind Tunnels foundation (DNW-NWB) are used to ensure the correct flow fea...

Circulation Control as a Roll Effector for Unmanned Combat Aerial Vehicles

Using DC PSE operator discretization in Eulerian meshless collocation methods improves their robustness in complex geometries

In this paper, the radial basis function (RBF) is used to construct the approximating function of the reproducing kernel particle method (RKPM), which can eliminate the negative effect of different kernel functions on the calculating accuracy. The radial basis reproducing kernel particle method (RRKPM) is proposed. Furthermore, the RRKPM is applied to solve the elastic mechanical problems of the functionally graded materials (FGM), and the RRKPM for FGM is established. The corresponding formulae of the RRKPM for FGM are derived. Compared with the traditional RKPM, the RRKPM has higher calculating accuracy and stability. Finally, the numerical examples illustrate that the RRKPM is correct and effective to solve the elastic mechanical problems of the FGM.

Numerical solution of functionally graded materials based on radial basis reproducing kernel particle method

SUMMARY
An implicit meshless scheme is developed for solving the Euler equations, as well as the laminar and Reynolds-averaged Navier–Stokes equations. Spatial derivatives are approximated using a least squares method on clouds of points. The system of equations is linearised, and solved implicitly using approximate, analytical Jacobian matrices and a preconditioned Krylov subspace iterative method. The details of the spatial discretisation, linear solver and construction of the Jacobian matrix are discussed; and results that demonstrate the performance of the scheme are presented for steady and unsteady two dimensional fluid flows. Copyright © 2012 John Wiley & Sons, Ltd.

An implicit meshless method for application in computational fluid dynamics

Meshless methods are attractive for simulating moving body problems The selection of the stencils over the domain for the meshless solver is crucial for the method to be competitive with established computational fluid dynamics techniques Stencil selection is relatively straightforward if the point distributions are isotropic in nature, however, this is rarely the case in computations that solve the Navier–Stokes equations In this paper, a fully automatic method of selecting the stencils from anisotropic point distributions, which are obtained from overlapping structured grids, is outlined The original connectivity and the concept of a resolving direction are used to help construct good quality stencils with limited user input

Semi-meshless stencil selection for anisotropic point distributions

The ability of computational fluid dynamics to predict the steady and unsteady fluid flow over a generic UCAV configuration, with and without control surface deflections, at off design conditions is investigated. The complex, non-linear flow, various combinations of control surface deflection and the presence of multiple interacting vortices on the flow histories provides a challenging test for current capability. A range of static and dynamic test cases have been computed, for both low and high speed flows, for comparison with experimental data, obtained as part of the NATO STO AVT-201 Task Group. The simulations are performed using a multiblock code to solve the Reynolds-Averaged Navier-Stokes equations; and the control surfaces are modelled with a deformed mesh and blended gaps that simplify the geometry. These tests will provide an assessment of the ability of computational fluid dynamics to evaluate such flows, and will allow for deficiencies in the state of the art to be identified.

Numerical simulation of control surface deflections over a generic UCAV configuration at off-design flow conditions

A study into the prediction of the effectiveness of different trailing-edge controls on an unmanned combat aerial vehicle configuration, on which complex vortical flow develops at moderate to high angles of attack, is described Stability and control of these vehicles is demanding and requires early knowledge of the changes in forces and moments from control-surface deflections Computational results are compared with data from wind-tunnel tests over the Mach number range 0146≤M≤09 for undeflected controls The effectiveness of the controls at subsonic and transonic conditions is then discussed The influence of the mesh treatment and turbulence model on the realism of the predictions is considered The computational-fluid-dynamics predictions show good agreement with measurements and show limited sensitivity to geometry treatment and turbulence model for the flow conditions where the controls are effective Computational fluid dynamics is shown to be capable of predicting the control-surface influence,

Prediction of Control Effectiveness for a Highly Swept Unmanned Air Vehicle Configuration

Tabular aerodynamic models are frequently used for computational flight simulation. It is necessary to understand the limitations of such models to ensure adequacy for the relevant manoeuvres. The assessment is carried out for an aerofoil with a trailing edge flap for both forced and free–response manoeuvres. The limitations of the tabular model are then assessed through a comparison of loads or trajectories against a time–accurate computational fluid dynamics solution. A number of manoeuvres are used covering both linear and nonlinear aerodynamic regimes. It is seen that the assumptions in the tabular model are adequate except for neglecting history effects for certain regimes where nonlinearities are significant.

/pdf/assessment-of-tabular-models-using-cfd-1kemlvdrft.pdf

Assessment of tabular models using CFD

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