Numerical Simulation of Manoeuvring Aircraft by CFD Aerodynamic and Flight-Mechanic Coupling

Kurzfassung

The improvement of manoeuvrability and agility is a substantial requirement of modern fighter aircraft. Today rolling rates of 200°/s and more will be achieved especially by unstable design of the aircraft. Most of today's and probably future fighter aircraft will be Delta-Wing-Configurations. The flow field of such configurations is dominated by vortices developing by flow separation at the wings and the fuselage. The delay in time of vortex position and condition to the on flow conditions of the manoeuvring aircraft can lead to significant phase shifts in the distribution of loads. In this case reliable results for the analysis of flight properties can only be obtained by a non-linear integration of the unsteady stationary aerodynamic and real flight movement. Today this can only be realised by flight tests and not during the design period. Flight tests as well as modifications after the definition phase lead normally to a substantial increase in cost and time. To help decrease these post-definition-phase modifications, it is useful to have a numerical tool which enables aircraft designers to analyse and evaluate the dynamic behaviour of their designs during the design phase itself. To accomplish this task, a simulation tool which can simulate the dynamic behaviour of aircraft has been designed within the DLR project AeroSUM-"Aerodynamic Simulation of Unsteady Manoeuvres". The main objective of the current simulations is the coupling between the aerodynamic and flight-mechanic interactions. The software package which is used for these simulations is divided into several modules, all of which are communicating through a central computational interface. The computational interface manages both the data- and work-flow between the software modules. The numerical simulation of the flow-field is performed with an unstructured, time accurate Navier-Stokes flow solver, TAU, which has been developed by DLR. For the Simulation of configurations with moveable control panels, the chimera technique for unstructured meshes is implemented within the TAU-Code. For the coupling between the aerodynamics and flight-mechanics, the simulation tool SIMPACK is used, which contains the flight mechanic equations and is used as a GUI for the simulation environment. For the validation of the results of the numerical simulation software, comparisons to experimental data will be performed. The experimental data will be obtained from extensive wind-tunnel testing of a generic delta-wing aircraft model, see Figure 1 and 2. The AeroSUM wind-tunnel model is a cropped-delta-wing configuration consisting of a fuselage and wings with trailing edge flaps. It is specially designed for testing in the "Transonic Wind-Tunnel Göttingen (TWG)". The experimental set-up is capable of simulating both controlled and free-to-roll manoeuvres, at various angles-of-attack, as well as static flight conditions. In this paper we will present several results from the current simulations. The first results to be shown are the static aerodynamic parameters of the configuration, and the structure of the vortex-dominated flow-field, at various angles-of-attack and roll-angle settings, see Figure 3 and 4. The surface-pressure and roll-moments will be shown to compare favourably with the experimental data. The static simulation cases are the starting points for each unsteady simulation. Additionally to this, some unsteady manoeuvre simulations will be shown. The delta wing is set in guided periodic roll-motion with a given velocity respectively in an oscillating motion with a given frequency and amplitude. Comparisons with the experimental data will be shown as well. Finally we will present some coupled simulation, i.e. free-roll manoeuvres initiated by flap deflection of the delta wing trailing edge flaps. The desired manoeuvrability capabilities of fighter aircraft keep increasing, thus the design and development of such aircraft become ever more complex. It is hoped that the use of coupled simulation-packages like TAU-SIMPACK will assist in keeping the complexity of fighter aircraft development at a manageable level for years to come. Therefore, the final aim of the project is the capability to simulate a fully configured, manoeuvring fighter aircraft, i.e. an aircraft with several control-surfaces and thrust-vector devices.