Subsynchronous vibrations in rotating machinery can be detrimental, reaching amplitudes of vibration much greater than 1x. Subsynchronous vibrations are caused by many factors including fluid trapped in a hollow cavity. For trapped fluid, the system is excited when operating just above the first natural frequency, about 0.9X. A test rig was built to replicate the trapped fluid subsynchronous response. Previous testing facilities have experimentally replicated the response with exciters, but this test rig is self-excited by the rotordynamics of the system. Testing results showed that very little fluid is needed to see a sub-synchronous response, with fluid depths as low as 20 mils exciting the system. An increase in the fluid depth does not eliminate the subsynchronous vibrations but instead increases the response amplitude. During the response, waves form at the surface of the fluid, which are the cause of the excitation. This paper discusses the design of the test rig which perfectly replicates response data observed in industry.
