Comparative analysis of numerical methods for rotor blade unrunning design

In modern turbomachinery, accurate prediction of rotor blade shape for manufacture from its design shape is vital for performance, efficiency and aeroelastic stability. The manufacture “cold” blade shapes of a large-scale ratio transonic hollow fan and a NASA Rotor 67 fan were predicted from the design “hot” shapes utilised four kinds of numerical simulation methods, such as non-coupling, weak coupling, steady two-way coupling, and unsteady bidirectional coupling methods. The advantages and disadvantages of these methods were discussed by emphasizing on aerodynamic loading modes in the iterative procedure of blade unrunning design. The last numerical method employs a fluid-structure coupling scheme to determine blade deflections due to unsteady aerodynamic loads. The results show that there is a big difference between the “cold” blade shapes predicted using non-coupling method and the other three methods which conside aerodynamic coupling, this illustrates that the aerodynamic influence cannot be ignored. Comparison of the calculation “cold” shapes of the hollow swept and bowed fan with the conventional fan shows that improvements of the manufacture profile of the hollow fan blade can be made by including proper nonlinear aerodynamic effect on blade deflections in the numerical model. The results also illustrate that aerodynamic nonlinear effects should be included for a better blade unrunning design.