Numerical researches on aeroelastic problem of a rotor due to IGV/Fan interaction

The commercial code CFX-10 was used For NASA Rotor 67, the blades are most likely to flutter in the second bending mode with IBPA of 60°. It is widely known that the upstream wake is a major contributor to the rotor blade forced vibration. The present research shows that the wake will also change the flutter characteristics of the rotor blade significantly. If the natural frequency of the most dangerous flutter mode of the blade is close to the IGV passing frequency, flutter may happen even it is very stable analyzed without IGV. This vibration is more like a sympathetic vibration. For a mode whose natural frequency is far away from the IGV passing frequency, the wake may also drive the vibration to be unstable. Though the IGV doesn't influence the performance of the rotor much, it does add significant nonlinear effects to the flutter behavior of the rotor blades. Designers need to increase the gap distance between IGV and rotor to avoid the significant change of the flutter boundary to solve the unsteady flow field. The code was validated by the calculation of STCF4 and NASA Rotor 67. The aeroelastic characteristics of Rotor 67 without IGV are analyzed with energy method, and then the results are compared with that of the model with IGV. The results show that Rotor 67 most likely to flutter in the second mode with an IBPA of 60°. The IGV excitation will add significant nonlinear effects to the flutter behavior of the rotor blades, and may lower the flutter boundary greatly. Unsteady calculations with a larger IGV-rotor gap show that this wake effects will not be weaken unless the IGV is far away enough.