Dynamical effects of shrouds on fan blade vibration and its corresponding design method

Taking the shrouded blades in a certain turbofan engine as the investigation object, and considering the nonlinear effect of the contact stiffness and damping between neighbor blades, the effects of designable configuration parameters on constrained modes and vibration response were studied by the combination of Newton-Rapson iteration and multi-harmonic balance method. The results reveal that the shroud position is the key parameter which affects the stiffness and resonance frequency of the blade primarily, and the radial relative position is recommended to be between 55% and 75%, which is beneficial to increase the blade stiffness and to decrease the vibration deformation. The axial position is suggested to be in the middle of the blade, in order to increase the contact stiffness of the shroud and the first order resonance frequency of the blade. The shroud coupling angle and initial interference value affect the resonance stress value chiefly, but have little effects on the resonance frequency. In addition, the design flow for the vibration suppression on shrouded blades is put forward: the first step is to increase the blade stiffness by adjusting the shroud radial position, followed by optimizing the shroud axial position to increase the resonance margin of low order modes, and finally optimizing the shroud coupling angle. The initial interference value are recommended to suppress the resonance stress amplitude.