Fluid-structure Interaction Study Of An Elastic Wing On Fixed Supports

Engineering often involves structures with high aspect ratios,such as oversized wind turbine blades,composite propellers for nuclear submarines,large span of suspension bridge construction,etc..They are likely to work with substantial bending and vibration in the torsional direction.It is of great practical engineering significance to understand the effects vibration of such flexible elastic thin airfoils during working.The structural response and flow field characteristics of a high-aspect-ratio wing are studied.The FBG strain sensors and six-component force balance are used to measure structural strain and aerodynamic forces of the wing.Hot wire and particle image velocimetry technique are utilized to measure the characteristics of the flow field.Note that the strain,force and the flow field is measured simultaneously during the experiments.The Reynolds number of the experiments ranges from 3.2×10~4 to 1.49×10~5 and the angle of attack is between 0° and 90°.It was found that flutter occurred in the range of angle of attack ?=6?8° with Rec=1.49×10~5.After a exceeds 8°,there is a sudden drop in the lift force curve because of stall,and the stall stage last until ?=14° at which the lift force starts to increase again.The lift force then increases with a and reaches its maximum at ?=50°.According to the variation of aerodynamic forces and the change in the flow fluctuation with the angle of attack,four regimes are proposed,that is,small angle of attack zone 0?4°,flutter zone 6?8° stall zone 10?14° and high angle of attack zone 20?90°.In this study,the influence of the wing on the flow field in different vibration regions is studied,and the angles of attack of ?=0°,8°,14°,60° are selected.By means of phase averaging,POD and other research methods,the phase averaging or mode decomposition and reconstruction of the flow in each region are analyzed and described.Flow did not separate in the small angle of attack area.Fluid was close to the surface of the wing,and no vibration occurred on the wing.During the flutter area,the wing occurred flutter,which significantly affected the structure of the flow field.And each flutter cycle will produce a large-scale vortex.Next the wing is in the stall regime,and the broken vortex with a smaller scale is distributed in the vorticity diagram.And there is no obvious flow law.At last,the flow with a large angle of attack distributes vortices with opposite vorticity values at the leading edge and the trailing edge.The positive vorticity and negative vorticity are close to symmetry at a large angle of attack.The negative vorticity generated by the leading edge has a larger influence range.The leading factor of wing vibration is the effect of vortex shedding.The added stiffness and added damping are introduced,and the equation for normalized frequencies f*is derived as a function of U_r andm*.The first-order bending frequency changes with U_r andm*.In this experiment,f*increases with increasing U_r.