D. Vallespin

Evaluation of Dynamic Derivatives Using Computational Fluid Dynamics

This paper focuses on the evaluation of the dynamic stability derivative formulation. The derivatives are calculated using the Euler and Reynolds-averaged Navier–Stokes equations, and a time-domain solver was used for the computation of aerodynamic loads for forced periodic motions. To validate the predictions, two test cases are used. For the standard dynamic model geometry, a database of dynamic simulations illustrates the effects of the systematic variation of motion and fluid parameters involved. A satisfactory agreement was observed with available experimental data, and the dependency of dynamic derivatives on a number of parameters, such as Mach number, mean angle of attack, frequency, and amplitude, was assessed. For the transonic cruiser wind-tunnel geometry, static and unsteady aerodynamic characteristics were validated against experimental measurements. The ability of models based on the dynamic derivatives to predict large-amplitude motion forces and moments was assessed. It was demonstrated that the dynamic derivative model does not represent all of the important effects due to aerodynamics.

Validation of Vortical Flow Predictions for a UCAV Wind Tunnel Model

A study of the aerodynamic behaviour of the Stability And Control Configuration wind tunnel model is presented. Both the sharp and round leading edge versions of the model are analysed in terms of the flow characteristics. A validation of the Reynolds Averaged NavierStokes predictions obtained using two block structured codes is made. Both static and dynamic cases are compared with wind tunnel measurements. The vortical flow features are described in detail for the range of conditions analysed. The predictions are in good agreement with the experiments at low angles of attack, whereas for higher incidences, α > 15◦, discrepancies are seen. A dual vortex structure is present in this region for both leading edge configurations resulting in a highly nonlinear aerodynamic behaviour.

Simulation of Aircraft Manoeuvres based on Computational Fluid Dynamics

The use of computational fluid dynamics to generate and test aerodynamic data tables for flight dynamics analysis is described in this paper. The test case used is the Ranger 2000 fighter trainer for which flight test data is available. The generation of the tables is done using sampling and reconstruction to allow a large number of table entries to be generated at low computational cost. The testing of the tables is done by replaying, through a time accurate CFD calculation which features the moving control surfaces, manoeuvres and comparing the forces and moments against the tabular values. The manoeuvres are generated using a time optimal prediction code with the feasible solutions based on the tabular aerodynamics. The generated maneouvres are evaluated against flight data to show that they are qualitatively representative. Then the time accurate and tabular aerodynamics are compared, and as expected are in close agreement.

Vortical flow prediction validation for an unmanned combat air vehicle model

As part of the NATO Applied Vehicle Technology 161 technical group, a study of the aerodynamic behavior of the stability and control configuration wind-tunnel model is presented. Sharp and round leading-edge versions of the model are computed. A validation of Reynolds-averaged Navier–Stokes predictions obtained using two block structured codes are made. Static cases are analyzed and compared with wind-tunnel measurements. The vortical flow features are described in detail for a range of angles of attack. The predictions are in good agreement with the experiments at low angles of attack, whereas for higher angles of incidence (alpha > 15), some discrepancies are seen. A dual vortex structure is present in this region for both leading-edge configurations, resulting in highly nonlinear aerodynamic behavior.

Computation and evaluation of dynamic derivatives using CFD

This paper focuses on the computation of dynamic derivatives for full aircraft configurations. The flow is modelled using the Euler and RANS equations and an unsteady time-domain solver is used for the computation of aerodynamic loads for forced periodic motions. The study investigates the variation of damping values through the transonic regime and for several permutations of motion parameters for the Standard Dynamics Model geometry. A benchmark against experimental data is presented for the Transonic CRuiser wind tunnel geometry. For the SDM, strake vortices and their breakdown are observed when increasing the mean angle of attack during the applied pitch sinusoidal motion. A good agreement is obtained with available experimental data. For the TCR, a validation of longitudinal aerodynamic characteristics is first considered. Numerical experiments for the estimation of damping derivatives and for large amplitude forced oscillations in pitch axis are compared to wind tunnel data. Simulations are in agreement with experimental data up to high angles of attack.

A framework for constrained control allocation using CFD based tabular data

This paper describes a framework for control allocation problem using Computational Fluid Dynamics (CFD) aerodata, which is represented by a multidimensional array of dimensionless coefficients of aerodynamic forces and moments, stored as a function of the state vector and control-surface deflections. The challenges addressed are, first, the control surface treatment for the automated generation of aerodata using CFD and, second, sampling and data fusion to allow the timely calculation of large data tables. In this framework, the generation of aerodynamic tables is described based on an efficient sampling/data fusion approach. Also, the treatment of aerodynamics of control surfaces is being addressed for three flow solvers: TORNADO, a vortex-lattice method, and two CFD codes, EDGE from the Swedis Defence Agency and PMB from the University of Liverpool. In TORNADO, the vortex points located at the trailing edge of the flaps are rotated around the hinge line to simulate the deflected surfaces. The transpiration boundary conditions approach is used for modeling moving flaps in EDGE, whereas, the surface deflection is achieved using mode shapes in PMB. The test cases used to illustrate the approaches is the Ranger 2000 fighter trainer and a reduced geometry description of Boeing 747-100. Data tables are then generated for the state vector and multiple control surface deflections. The look-up table aerodata are then used to resolve the control allocation problem under the constraint that each surface has an upper and lower limit of deflection angle.