| Dynamic stall is a classic nonlinear aerodynamic phenomenon occurred on the retreating blade of rotor wing in helicopter forward flight. The dynamic stall limits forward speed and creates structure fatigue through blades shaking. So aeroelastic response of blade of rotor due to dynamic stall has critical effect to design blades of rotor. People have already used CFD/CSD aeroelastic response method to finish some analyses. However, because of great amount of calculation, inaccuracy of dynamic model and lack of experiment data, it is hard to understand the mechanism of aeroelastic response due to dynamic stall. The problem has been an increasingly urgent concern.For understanding aeroelastic response of wing due to dynamic stall deeply, we focus on the following aspects:1.Research and analyze the existing research results, combined with kinetic equations and BL aerodynamic model. Established physical and mathematical models of nonlinear aeroelastic response coupling with spring constrained pitching airfoid, built tightly coupled nonlinear aeroelastic response. Through preliminary analysis, achieved complex aeroelastic response image which shows pitching airfoil due to dynamic stall with spring constraint between aerodynamic and structural deformation coupled with a very complex response. Combined research from other scholars, find out not only the system parameters(the initial motion) changes have an important impact to aeroelastic response, but also different aerodynamic models have a significantly different response prediction results which further confirmed the development of more realistic the aerodynamic model is very important. However, a more accurate understanding of the response mechanism of the real system is needed. Currently, one of the most feasible way is to study through the experimental system.2.Designed apparatus for dynamic stall of pitching airfoil with elastic restraint. The apparatus could achieve exchanging springs with different spring rate, even exchanging model to a rigid one. Solved several problems as follows:(1) Force balance embeds problem. Considering small size of research wind tunnel and blocking rate, the size of force balance has been limited which makes force balance hard to be designed. We compared several projects to solve the problem. However, interference between multiple force balances is hard to be avoided. Finally, used embedded force balance to solve large loads problem and limited space problem.(2) Problem of driving model with elastic restrain. For simulating aeroelasticity in wind tunnel, spring’s free deformation under nonlinear aerodynamic forces is needed. Aeroelasticity simulator has to be set between motor and model. The spring rate of simulator need to be changeable. By analyzing structure and force, we designed a linkage to solve the problem.3.Do experimental research on pitching airfoil aerodynamic response due to dynamic stall with spring restraint. By comparing the results to the analysis of numerical response, found out large differences existing between the results of the actual system and forecast system. Main reasons are follows:(1) Damping of the model system is not considered in the kinetic equation, and hard to predict accurately can be expected. By default certain damping, the trend of result of the numerical response move closer to the experimental results;(2) the aerodynamic model itself and the actual model have discrepancies. Such as complex unsteady flows reflection is inadequate;(3) nonlinear aeroelastic coupling response makes more complex flow around airfoils, aerodynamic model is difficult to reflect changes in such flows reality. |
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