Multi-state lead-lag damper development and validation

A multi-state lead-lag damper was designed and developed to reduce damper forces when damping is not required. This was achieved via a set of bypass channels that can be opened or closed in order to vary the damper forces. A first generation prototype was built and bench tested to validate the multi-state behavior of the design. Additionally, to predict the damper behavior, an analytical model and a computational fluid dynamics (CFD) model using the commercial program FLUENT® were developed and compared to the experimental data. The prototype damper was bench tested over a range of frequencies and dynamic displacements in both the open and closed configurations. Comparison between the open and closed configurations demonstrated the ability of the bypass channels to reduce damper force by more than 70%, with the capability to widely tune this value by varying the bypass channel diameter. The CFD model allows detailed investigation into the internal flow dynamics of the damper device and is able to capture the shape of the experimental force vs. displacement hysteresis loops. It over predicts damper forces in the closed configuration with an average error in peak force prediction of approximately 30% and slightly under predicts damper forces in the open configuration, though the error in peak force approximation is only around 1%. Prediction errors of the loss stiffness are close to 30%. The analytical model greatly under predicts both the open and closed configurations of the experimental damper. The initial bench testing and CFD study verify the validity of the bypass damper concept, and prove the device ready for the next stage of development and testing.