Transient Rotordynamic Modelling using Pseudo Spectral Method with Experimental Validation on an Overhung Rotor

A high-speed spin test rig is employed for fault detection in rotating components prior to use in cryogenic engine turbopumps. The experimental studies include dynamic testing of an overhung rotor up to 36,000 RPM in the rig. The rig is supported by a pair of hybrid angular contact ball bearings provided with a spring pre-load. The stiffness of the ball bearings as well as the pre-load springs are measured experimentally. Damping is provided by a pair of oil-filled damper seals. Two orthogonally placed displacement sensors measure the rotor displacement and aid in detecting the critical speed transition. For determining the stiffness and damping coefficients of the damper seals, Pseudo Spectral Method (PSM), a semi-analytical technique, is employed to discretize and solve the nonlinear Reynolds lubrication equation to obtain the fluid pressure profile. The method is well validated with literature and offers a faster and more accurate convergence than FEM due to the use of global basis functions. Transient rotordynamic analysis performed with Timoshenko beam elements and Newmark-beta numerical integration scheme indicated good match between the prediction and experiments.