A fluid-structure coupling method for rotor blade unrunning design

This paper reports a numerical method for the design of a unrunning blade with the consideration of both nonlinear aerodynamic and centrifugal forces. Accurate prediction of blade manufacture shape in turbomachinery is crucial for performance, efficiency and aeroelastic stability. An iterative procedure starting from a given blade running shape is developed to predict the manufacture blade shape. The model is based on a three-dimensional (3D) unsteady nonlinear Navier-Stokes Computational Fluid Dynamics (CFD) solver and the mode superposition structural dynamic theory in conjunction with a finite element structural model for the rotor blade. The manufacture profile of the blade ("Cold" blade) is estimated from the running blade shape ("Hot" blade). ANSYS finite element code is used to compute the deflection of the cold blade due to centrifugal loads . A finite volume based 3D nonlinear CFD code, coupled with a mode superposition structural dynamic modal method, is employed to determine the blade deflection due to unsteady aerodynamic loading. The difference between the computed blade profile and the targeted hot blade shape is used to predict a new cold blade for the next iteration if the convergence criterion is not met. The method is applied to predict the manufacture blade shape of a large-scale propfan and a NASA rotor 67 fan. The predicted blade profile and the twist angle of the blade at various spans are presented. The results show that improvements of the manufacture blade profile can be made by including proper nonlinear aerodynamic effect on the blade deflection in the numerical model. The results also illustrate that aerodynamic nonlinear effects on structural deformation should be included for a better cold blade design.