Computational Study of Asynchronous Vibrations in a 1.5 Stage Transonic Compressor

The unsteady RANS equations are solved for the internal flow through the first one and a half stages of a transonic compressor operating in an off-design condition. To establish a steady performance prediction, the mixing-plane method is used and reasonable comparison to experimental data is obtained for the design configuration. To predict the fully unsteady flow, the sliding-mesh method is used. Examining the unsteady force on the blades, substantial subharmonic force fluctuations are shown to exist. The unsteady pressure signals from the domain also support the existence of these fluctuations. Views of the time-mean and notch filtered flow help to highlight the major features of the off-design flow field, and identify how these features relate to the subharmonic fluctuations in force and pressure.