Numerical Investigation Of Unsteady Aerodynamics Of Delta Wing And Structural Buffeting

Strake and delta wing configurations are widely used by modern fighter aircraft to obtainsuper maneuverability at high angle of attack, using the detached vortices generated by theleading edge of those low aspect ratio aerodynamic components. However, the vortices willburst when the angle of attack is too high, and the swirling turbulence flow behind thebursting point would make the aircraft buffeting. The objective of this paper is to investigatethe unsteady vortex flow upon the delta wing and the characteristics of aircraft buffeting inthe turbulence flow behind vortex breakdown by numerical simulations. The main works ofthis study are listed as follows:(1) The details of a numerical method for the unsteady vortex flow upon delta wing areintroduced, and the methods of the static and dynamic grid generation are present as well.The multi-grid algorithm(MGA) is introduced here to accurate computation convergence.The numerical method is verified by the cases of Hummel76°delta wing,76°/40°doubledelta wing and AGARD CT5.(2) The effect of the delta wing configuration on the aerodynamic responses of delta wingpitching and rolling motion is investigated by computing the unsteady flow upon fourtypical delta wing configurations, including60°single delta wing,80°/60°double deltawing,80°/40°double delta wing, and wing-body configuration. The simulation results forthe motion of the four configurations are compared and analyzed in details, and the effectof the strake, swept angle and center body on the time lag effect of aerodynamic responsesare discussed as well.(3) A nonlinear aerodynamic identification method for the delta wing motion with smallamplitude is established. A nonlinear aerodynamic reduced order model(ROM) isdeveloped based on the second order Volterra Series. The wavelet multi-resolutionanalysis is employed to truncate the identification parameters. The identification of anairfoil with pitching and plunging motion are carried out individually by traditional firstorder ROM and the presented method The results of both methods are compared with theCFD results to verify the identification ability, and the identification results of a76°sharp-edged delta wing with pitching oscillations are provided subsequently.(4) The CFD/CSD coupled computation system is developed for aeroelastic simulation. Thedetails of the coupled calculation method are presented, including CFD/CSD couplingmethod, the modal superposition method for solving structural dynamic functions, and theinterpolation method between the CFD field and the CSD field. The coupling computationmethod is verified by the standard aeroelastic model AGARD445.6. Furthermore, A rigid rotation dynamic function is introduced in the above coupled system to construct aCFD/CSD/RBD coupling system.(5) The characteristics of tail buffeting induced by vortex breakdown are investigated bynumerical simulation for a76°delta wing/vertical tail configuration. The generalizeddeformations and accelerations of the flexible tail are obtained at30°and40°angle ofattack. The time-frequency characteristics of the buffeting responses are analyzed andcompared with traditional flutter/LCO problems.(6) The effect of rolling motion on the delta wing buffeting is investigated by numericalsimulation. The computation results of a60°delta wing buffeting in the viscous flow arecompared with the inviscid results at high angle of attack. It is found that the flowviscosity suppress the buffeting responses. The buffeting responses of the delta wing withrolling motion are obtain by CFD/CSD/RBD coupled simulation. The buffeting resultswith the rolling motion are compared with previous no-motion results. It is found thatwith rolling motion, the excitation of low-frequency structural mode by the flowfield ismuch enhanced together with the obvious augmentation of rms buffeting acceleration...