Fan and compressor stages of turbofan aircraft engines are subjected to dynamic excitations. Often these excitations are at frequencies equal to or multiples of the rotor speed. This form of dynamic stimulus is called per-revolution excitation or integral-order excitation. When the natural resonant frequency of a fan stage coincides with the frequency of the source, severe vibration usually results. For shrouded fan stages the natural frequency is that of a coupled dynamic system consisting of disk, blades, and shroud. A modeling technique is developed to study the vibration. Small scale models are cast of flexible silicone rubber, known as RTV. The rubber models rotate and are excited by air nozzles located at discrete circumferential positions. Visual observation of the standing-wave oscillation clearly shows the familiar relations of forced vibrations such as magnification factor, phase shift, and the effects of damping. RTV silicone rubber is easily cast into complex shapes. This allows rapid evaluation of the many resonant-response blade-disk shroud configurations including unsymmetrical designs that may be difficult to analyze with current computing techniques.
Dynamic Models of Vibrating Rotor Stages