Research On Static Aeroelastic Characteristis And Torsion Suppression Of Forward Swept Wing

Due to inherent aeroelastic torsion divergence problem at transonic speed forward swept configuration have been abandoned until appearances of advanced composite material and digital flight control system.For the application of forward swept configuration,research on aerodynamic,aeroelastic characteristics and torsion divergence depression technology of forward swept wing have enormous value in scientific research and engineering significance.In the paper a loosely coupled computational aeroelastic（CAE）method by integrating CFD solver based on Reynolds-averaged Navier-Stokes equations and CSD solver based on finite element method and mode method is develop as aeroelastic research tool.Study on aerodynamic characteristic,aeroelastic characteristic and aeroelastic torsion depression methods are conducted as follows:The differences of basic aerodynamic characteristic on forward swept wing between early theoretical analysis,numerical simulations,wind tunnel tests and flight tests always exist.Therefore a forward swept wing and an equivalent backward swept wing（identical aspect ratio,identical tip ratio,identical swept angle magnitude,identical structural grid distribution）is designed to verify the results.Results shows at inviscid condition forward swept wing has excellent aerodynamic performance including stalling characteristic and induced drag performance.While the turbulence viscousity evidently retard the aerodynamic effectiveness of forward swept wing which is totally different from the results based potential theory in the previous literature.Momentum transportation on forward swept wing is more severe than backward swept wing which leads to a“Elliptical distribution”on forward swept wing.One of the consequences is that smaller induced drag will be generated.Another consequence is boundary layer will be accumulated which results in early separation at wing root which tremendously reduces the aerodynamic performance of forward swept wing.Through integrating a close close canard at the front of forward swept wing,boundary layer accumulation at the wing root is mended by the vortex induced by canard.Static aeroelastic calculation on forward swept wing at different swept angle and dynamic pressure are conducted with CAE approach developed in the paper.Wingtip torsion increase with the increasing of dynamic pressure and the increase curves transform from the linear change at low dynamic pressure to exponential change at high dynamic pressure.Meanwhile with the increment of forward swept angle,wingtip deformation decrease while the wingtip torsion increase first and then decrease with the maximum torsion appears at swept angle 35°。Two strategies including structure optimization and flow control are adopted to reduce the forward swept wing torsional displacements.Structure optimization is mainly utilizing the bending-torsion coupling effect to stiffen the local strength at torsional direction and increase the torsion divergence pressure of forward swept wing with advanced composite material.Flow control usually changes the wing surface pressure to reduce the wing load and torsional torque by passive and active control methods.From the perspective of structure optimization stress strain equation of composite laminate beam is derived based on classic laminate theory.Ply parameters including ply orientation and thickness are taken into consideration to study the influence on bending-torsion coupling effect.Results show that ply orientation can change the magnitude and direction of structure’s bending-torsion coupling coefficientD₁₆,D₂₆ while ply thickness can only change the magnitude.Composite aeroelastic tailoring method based on Radial Basis Function Neural Network and Genetic Algorithm are built as a aeroelastic tailoring framework to optimize the forward swept wing layer orientation and thickness under the engineering application circumstance.The method can increase the sample training and optimal effectiveness with the guarantee of the accuracy compared with the CAE simulation.Results show that skin optimization has the most powerful influence on bending-torsion coupling of forward swept wing out of other wing structure like beam and rib.Aeroelastic tailoring of skin’s ply orientation and thickness on a typical forward swept wing is carried out.Results show ply orientation and thickness tailoring can both increase the bending and torsional stiffness of forward swept wing,reduce the wingtip displacement and torsional angle with the constrains of wing structure weight.Bending-torsion coupling effects increase with the increase of angle of attack as the depression of wing tip deformation and torsion angle increase.The aeroelastic tailoring can provide more effective torsion depression at gaver torsion condition at Ma=1.Active aeroelastic wing is introduced to suppress the forward swept wing torsion with the change of control surfaces through flow control.With the limit of wing structure weight,active aeroelastic wing can effectively expand the wing’s function to aeroelastic control by optimize the wing surface pressure distribution.By simulating the aeroelastic performance of a forward swept wing at different deflection and different dynamic pressure,we found that LE and TE downward deflections on FSW can effectively decrease the torsion angles,displacements and root bending moments at the same lift coefficient.With the increase of dynamic pressure the flexibility of FSW would enhance the depression of deformation.What’s more,better rolling performance of FSW was obtained.Unreasonable deflection of control surfaces will cause the serious wing surface separation and recession of aerodynamic and aeroelastic performance of forward swept wing.